RESUMEN
Evidence indicates that periaqueductal gray matter (PAG) plays an important role in defensive responses and pain control. The activation of cannabinoid type-1 (CB1) or mu-opioid (MOR) receptors in the dorsal region of this structure (dPAG) inhibits fear and facilitates antinociception induced by different aversive stimuli. However, it is still unknown whether these two receptors work cooperatively in order to achieve these inhibitory actions. This study investigated the involvement and a likely interplay between CB1 and MOR receptors localized into the dPAG on the regulation of fear-like defensive responses and antinociception (evaluated in tail-flick test) evoked by dPAG chemical stimulation with N-methyl-d-aspartate (NMDA). Before the administration of NMDA, animals were first intra-dPAG injected with the CB1 agonist ACEA (0.5 pmol), or with the MOR agonist DAMGO (0.5 pmol) in combination with the respective antagonists AM251 (CB1 antagonist, 100 pmol) or CTOP (MOR antagonist, 1 nmol). To investigate the interplay between these receptors, microinjection of CTOP was combined with ACEA, or microinjection of AM251 was combined with DAMGO. Our results showed that both the intra-PAG treatments with ACEA or DAMGO inhibited NMDA-induced freezing expression, whereas only the treatment with DAMGO increased antinociception induced with NMDA, which are completely blocked by its respective antagonists. Interestingly, the inhibitory effects of ACEA or DAMGO on freezing was blocked by CTOP and AM251, respectively, indicating a functional interaction between these two receptors in the mediation of defensive behaviors. However, this cooperative interaction was not observed during the NMDA-induced antinociception. Our findings indicate that there is a cooperative action between the MOR and CB1 receptors within the dPAG and it is involved in the mediation of NMDA-induced defensive responses. Additionally, the MORs into the dPAG are involved in the modulation of the antinociceptive effects that follow a fear-like defense-reaction induced by dPAG chemical stimulation with NMDA.
Asunto(s)
Miedo/efectos de los fármacos , N-Metilaspartato/farmacología , Nocicepción/efectos de los fármacos , Sustancia Gris Periacueductal/metabolismo , Receptor Cannabinoide CB1/metabolismo , Receptores Opioides mu/metabolismo , Analgésicos Opioides/farmacología , Animales , Ácidos Araquidónicos/farmacología , Conducta Animal/efectos de los fármacos , Agonistas de Receptores de Cannabinoides/farmacología , Antagonistas de Receptores de Cannabinoides/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Agonistas de Aminoácidos Excitadores/farmacología , Reacción Cataléptica de Congelación/efectos de los fármacos , Masculino , Microinyecciones , Dolor/tratamiento farmacológico , Dolor/metabolismo , Dimensión del Dolor/efectos de los fármacos , Piperidinas/farmacología , Pirazoles/farmacología , Ratas , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inhibidores , Somatostatina/análogos & derivados , Somatostatina/farmacologíaRESUMEN
The dorsomedial hypothalamus (DMH) and the dorsal periaqueductal gray (DPAG) have been implicated in the genesis and regulation of panic-related defensive behaviors, such as escape. Previous results point to an interaction between serotonergic and opioidergic systems within the DPAG to inhibit escape, involving µ-opioid and 5-HT1A receptors (5-HT1AR). In the present study we explore this interaction in the DMH, using escape elicited by electrical stimulation of this area as a panic attack index. The obtained results show that intra-DMH administration of the non-selective opioid receptor antagonist naloxone (0.5 nmol) prevented the panicolytic-like effect of a local injection of serotonin (20 nmol). Pretreatment with the selective µ-opioid receptor (MOR) antagonist CTOP (1 nmol) blocked the panicolytic-like effect of the 5-HT1AR agonist 8-OHDPAT (8 nmol). Intra-DMH injection of the selective MOR agonist DAMGO (0.3 nmol) also inhibited escape behavior, and a previous injection of the 5-HT1AR antagonist WAY-100635 (0.37 nmol) counteracted this panicolytic-like effect. These results offer the first evidence that serotonergic and opioidergic systems work together within the DMH to inhibit panic-like behavior through an interaction between µ-opioid and 5-HT1A receptors, as previously described in the DPAG.
Asunto(s)
Hipotálamo/metabolismo , Trastorno de Pánico/metabolismo , Pánico/fisiología , Receptor de Serotonina 5-HT1A/metabolismo , Receptores Opioides mu/metabolismo , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Analgésicos Opioides/farmacología , Animales , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Reacción de Fuga/efectos de los fármacos , Reacción de Fuga/fisiología , Hipotálamo/efectos de los fármacos , Masculino , Naloxona/farmacología , Pánico/efectos de los fármacos , Sustancia Gris Periacueductal/efectos de los fármacos , Sustancia Gris Periacueductal/metabolismo , Piperazinas/farmacología , Piridinas/farmacología , Ratas , Ratas Wistar , Serotonina/farmacología , Somatostatina/análogos & derivados , Somatostatina/farmacologíaRESUMEN
A wealth of evidence indicates that the activation of 5-HT1A and 5-HT2A receptors in the dorsal periaqueductal grey matter (dPAG) inhibits escape, a panic-related defensive behaviour. Results that were previously obtained with the elevated T-maze test of anxiety/panic suggest that 5-HT1A and µ-opioid receptors in this midbrain area work together to regulate this response. To investigate the generality of this finding, we assessed whether the same cooperative mechanism is engaged when escape is evoked by a different aversive stimulus electrical stimulation of the dPAG. Administration of the µ-receptor blocker CTOP into the dPAG did not change the escape threshold, but microinjection of the µ-receptor agonist DAMGO (0.3 and 0.5 nmol) or the 5-HT1A receptor agonist 8-OHDPAT (1.6 nmol) increased this index, indicating a panicolytic-like effect. Pretreatment with CTOP antagonised the anti-escape effect of 8-OHDPAT. Additionally, combined administration of subeffective doses of DAMGO and 8-OHDPAT increased the escape threshold, indicating drug synergism. Therefore, regardless of the aversive nature of the stimulus, µ-opioid and 5-HT1A receptors cooperatively act to regulate escape behaviour. A better comprehension of this mechanism might allow for new therapeutic strategies for panic disorder.
Asunto(s)
Reacción de Fuga/fisiología , Pánico/fisiología , Sustancia Gris Periacueductal/fisiología , Receptor de Serotonina 5-HT1A/fisiología , Receptores Opioides mu/fisiología , 8-Hidroxi-2-(di-n-propilamino)tetralin/antagonistas & inhibidores , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Animales , Estimulación Eléctrica , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Reacción de Fuga/efectos de los fármacos , Masculino , Microinyecciones , Pánico/efectos de los fármacos , Sustancia Gris Periacueductal/efectos de los fármacos , Ratas , Receptor de Serotonina 5-HT1A/efectos de los fármacos , Receptor de Serotonina 5-HT2A , Receptores Opioides mu/antagonistas & inhibidores , Somatostatina/administración & dosificación , Somatostatina/análogos & derivados , Somatostatina/farmacologíaRESUMEN
Single nucleotide polymorphisms (SNPs) in the human OPRM1 gene result in common variants of Mu Opioid Receptors (hMORs). The A118G SNP occurs at high frequency in certain human populations and produces an aminoacidic substitution: N40D (hMOR-N to hMOR-D) at protein level. N40D is reported to alter pain thresholds and morphine efficacy. hMORs inhibit Ca(V)2.2 channels (N-type currents) at presynaptic nociceptor terminals in dorsal horn, thus reducing calcium influx, transmitter release, and transmission of noxious signals. Nociceptors express different splice isoforms of Ca(V)2.2. Isoforms distinguished by the presence of alternatively spliced exon e37a are of interest because channels containing e37a are particularly enriched in nociceptors. Recent studies showed that Ca(V)2.2e37a is more sensitive to inhibition by Mu Opioid Receptors than the ubiquitous splice variant Ca(V)2.2e37b. Here, we evaluate the effect of hMOR-N and hMOR-D on cloned Ca(V)2.2e37a channels expressed in mammalian cells. We observe that hMOR-D inhibits Ca(V)2.2e37a currents at agonist concentrations 4-fold lower than those needed to inhibit Ca(V)2.2e37a currents by the same degree via hMOR-N. We observe little difference in hMOR-D and hMOR-N inhibition of Ca(V)2.2e37b currents. Our study demonstrates that this common site of OPRM1 polymorphism affects the inhibitory actions of MORs on both major Ca(V)2.2 isoforms expressed in nociceptors.
Asunto(s)
Canales de Calcio Tipo N/metabolismo , Receptores Opioides mu/genética , Analgésicos Opioides/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Células HEK293 , Humanos , Técnicas de Placa-Clamp , Polimorfismo de Nucleótido Simple , Isoformas de Proteínas/antagonistas & inhibidores , Receptores Opioides mu/agonistasRESUMEN
The µ-opioid receptor (MOR) is a member of the G protein-coupled receptor family and the main target of endogenous opioid neuropeptides and morphine. Upon activation by ligands, MORs are rapidly internalized via clathrin-coated pits in heterologous cells and dissociated striatal neurons. After initial endocytosis, resensitized receptors recycle back to the cell surface by vesicular delivery for subsequent cycles of activation. MOR trafficking has been linked to opioid tolerance after acute exposure to agonist, but it is also involved in the resensitization process. Several studies describe the regulation and mechanism of MOR endocytosis, but little is known about the recycling of resensitized receptors to the cell surface. To study this process, we induced internalization of MOR with [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO) and morphine and imaged in real time single vesicles recycling receptors to the cell surface. We determined single vesicle recycling kinetics and the number of receptors contained in them. Then we demonstrated that rapid vesicular delivery of recycling MORs to the cell surface was mediated by the actin-microtubule cytoskeleton. Recycling was also dependent on Rab4, Rab11, and the Ca(2+)-sensitive motor protein myosin Vb. Finally, we showed that recycling is acutely modulated by the presence of agonists and the levels of cAMP. Our work identifies a novel trafficking mechanism that increases the number of cell surface MORs during acute agonist exposure, effectively reducing the development of opioid tolerance.
Asunto(s)
Analgésicos Opioides/farmacología , Cuerpo Estriado/metabolismo , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Neuronas/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/metabolismo , Animales , Vesículas Cubiertas por Clatrina/genética , Vesículas Cubiertas por Clatrina/metabolismo , Cuerpo Estriado/citología , Endocitosis/efectos de los fármacos , Endocitosis/fisiología , Humanos , Cadenas Pesadas de Miosina/genética , Cadenas Pesadas de Miosina/metabolismo , Miosina Tipo V/genética , Miosina Tipo V/metabolismo , Miosinas/genética , Miosinas/metabolismo , Neuronas/citología , Ratas , Ratas Sprague-Dawley , Receptores Opioides mu/genética , Proteínas de Unión al GTP rab/genética , Proteínas de Unión al GTP rab/metabolismo , Proteínas de Unión al GTP rab4/genética , Proteínas de Unión al GTP rab4/metabolismoRESUMEN
The experimental question is whether hypothalamic opioids, known to stimulate consummatory behavior, control a link to the nucleus accumbens (NAc). It was hypothesized that opioids injected in the hypothalamic paraventricular nucleus (PVN) alter the balance of dopamine (DA) and acetylcholine (ACh) in the NAc in a manner that fosters appetite for food or ethanol. Rats were implanted with two guide shafts, one in the NAc to measure extracellular DA and ACh by microdialysis and the other in the PVN for microinjection of opioid mu- and delta-agonists, an antagonist, or saline vehicle. The compounds tested were morphine, the mu-receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin (DAMGO), the delta-receptor agonist D-Ala-Gly-Phe-Met-NH2 (DALA), and the opioid antagonist naloxone methiodide (m-naloxone). Morphine in the PVN increased the release of accumbens DA (+41%) and decreased ACh (-35%). Consistent with this, the opioid antagonist m-naloxone decreased DA (-24%) and increased ACh (+19%). In terms of receptor involvement, DAMGO dose-dependently increased DA to up to 209% of baseline. Simultaneously, ACh levels were markedly decreased to 55% of baseline. The agonist DALA produced a smaller but significant, 34% increase in DA, without affecting ACh. In contrast, control injections of saline had no significant effect. These results demonstrate that mu- and delta-opioids in the PVN contribute to the control of accumbens DA and ACh release and suggest that this circuit from the PVN to the NAc may be one of the mechanisms underlying opiate-induced ingestive behavior as well as naltrexone therapy for overeating and alcoholism.
Asunto(s)
Acetilcolina/metabolismo , Analgésicos Opioides/farmacología , Dopamina/metabolismo , Núcleo Accumbens/metabolismo , Núcleo Hipotalámico Paraventricular/efectos de los fármacos , Ácido 3,4-Dihidroxifenilacético/metabolismo , Animales , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Encefalina Metionina/análogos & derivados , Encefalina Metionina/farmacología , Ácido Homovanílico/metabolismo , Masculino , Microdiálisis/métodos , Microinyecciones/métodos , Morfina/farmacología , Naloxona/farmacología , Antagonistas de Narcóticos/farmacología , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/fisiología , Ratas , Ratas Sprague-DawleyRESUMEN
We have recently shown that morphine withdrawal sensitizes the neural substrates of fear in the midbrain tectum structures--the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC). In the present study, we investigated the role of mu- and kappa-opioid receptors in the mediation of these effects. Periadolescent rats chronically treated with morphine (10 mg/kg; s.c.) twice daily for 10 days were implanted with an electrode glued to a guide-cannula into the dPAG or the IC. Forty-eight hours after the interruption of this treatment, the effects of intra-dPAG or intra-IC microinjections of [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO; 0.6 and 1 nmol/0.2 microl)--a selective mu-receptor agonist--or nor-binaltorphimine (BNI; 2.5 and 5 microg/0.2 microl)--a selective kappa-receptor antagonist with tardive action--on the freezing and escape thresholds determined by electrical stimulation of the dPAG and the IC were examined. For both structures, morphine withdrawal produced pro-aversive effects. DAMGO and BNI had antiaversive effects when injected into the dPAG and IC of non-dependent rats. In morphine-withdrawn rats, only BNI continued to promote antiaversive effects in both structures. Whereas DAMGO lost its antiaversive efficacy when injected into the dPAG, only its highest dose promoted antiaversive effects in the IC of morphine-withdrawn rats, suggesting the development of an apparent tolerance. Thus, the enhanced reactivity of the midbrain tectum in morphine-withdrawn periadolescent rats may be due, at least partially, to an impairment of the inhibitory influence of mechanisms mediated by mu-receptors on the neural substrates of fear in this region.
Asunto(s)
Analgésicos Opioides/efectos adversos , Miedo/efectos de los fármacos , Miedo/fisiología , Morfina/efectos adversos , Síndrome de Abstinencia a Sustancias/fisiopatología , Techo del Mesencéfalo/fisiopatología , Analgésicos Opioides/administración & dosificación , Analgésicos Opioides/farmacología , Animales , Cateterismo , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Encefalina Ala(2)-MeFe(4)-Gli(5)/administración & dosificación , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Reacción de Fuga/efectos de los fármacos , Reacción de Fuga/fisiología , Reacción Cataléptica de Congelación/efectos de los fármacos , Reacción Cataléptica de Congelación/fisiología , Masculino , Microinyecciones , Naltrexona/administración & dosificación , Naltrexona/análogos & derivados , Naltrexona/farmacología , Antagonistas de Narcóticos/administración & dosificación , Antagonistas de Narcóticos/farmacología , Ratas , Ratas Wistar , Receptores Opioides kappa/antagonistas & inhibidores , Receptores Opioides kappa/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/metabolismo , Techo del Mesencéfalo/efectos de los fármacosRESUMEN
Anxiety is an affective symptom common to withdrawal from acute or chronic opiate treatment. Although the potentiation of the acoustic startle reflex has been proposed as an index of increased anxiety, there are variable effects of the opiate withdrawal on the startle reflex in chronic dependence models. On the other hand, withdrawal from acute morphine treatment consistently potentiates the acoustic startle reflex, a response that seems to be mediated by the central nucleus of the amygdala (CeA). However, the underlying neurochemical mechanisms have not been elucidated yet. In the present study, we firstly made a comparison between the effects of the withdrawal from both acute and chronic treatments with morphine on the motor activity and the anxiety-like behavior of rats tested in two experimental models, the acoustic startle reflex and the open-field tests. Our second objective was to investigate the role of GABAergic and opioid mechanisms of the CeA in the modulation of the withdrawal-potentiated startle as a measure of anxiety induced by morphine withdrawal. For the production of chronic dependence, rats received morphine injections (10 mg/kg; s.c.) twice daily during 10 days. Forty-eight hours after the interruption of this treatment, independent groups were probed in the startle reflex and open-field tests. For the acute dependence model, groups of rats were tested in the open field and startle tests under control conditions and under withdrawal from a single injection of morphine (10 mg/kg; s.c.) precipitated by naltrexone injections (0.1 mg/kg; s.c.). The results obtained showed that withdrawal from chronic and acute morphine treatments produced anxiety-like behavior in the open field test, although the anxiogenic-like effects could not be dissociated from the motor effects in the acute dependence model. On the other hand, only the withdrawal from acute morphine treatment significantly potentiated the startle response. Next, we examined the effects of intra-CeA microinjections of muscimol-a GABA(A) receptors agonist-and DAMGO-a mu-opioid receptors agonist-on the potentiated startle induced by acute morphine withdrawal. The results obtained showed that intra-CeA injections of muscimol (1 nmol) and DAMGO (0.5 and 1 nmol) significantly inhibited this response. These findings suggest that the acute dependence model is more suitable to study the aversive effects of morphine withdrawal on the acoustic startle response than the chronic opiate dependence model. Besides, mechanisms mediated by mu- and GABA(A)-receptors in the CeA appear to exert an inhibitory influence on the anxiety-like behavior induced by withdrawal from acute morphine treatment.
Asunto(s)
Amígdala del Cerebelo/fisiología , Morfina/farmacología , Narcóticos/farmacología , Receptores Opioides/fisiología , Reflejo de Sobresalto/efectos de los fármacos , Síndrome de Abstinencia a Sustancias/psicología , Ácido gamma-Aminobutírico/fisiología , Analgésicos Opioides/administración & dosificación , Analgésicos Opioides/farmacología , Animales , Encefalina Ala(2)-MeFe(4)-Gli(5)/administración & dosificación , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Agonistas del GABA/administración & dosificación , Agonistas del GABA/farmacología , Agonistas de Receptores de GABA-A , Microinyecciones , Morfina/administración & dosificación , Actividad Motora/efectos de los fármacos , Muscimol/administración & dosificación , Muscimol/farmacología , Narcóticos/administración & dosificación , Ratas , Ratas Wistar , Receptores Opioides mu/agonistasRESUMEN
Opioid mechanisms are involved in the control of water and NaCl intake and opioid receptors are present in the lateral parabrachial nucleus (LPBN), a site of important inhibitory mechanisms related to the control of sodium appetite. Therefore, in the present study we investigated the effects of opioid receptor activation in the LPBN on 0.3 M NaCl and water intake in rats. Male Holtzman rats with stainless steel cannulas implanted bilaterally in the LPBN were used. In normohydrated and satiated rats, bilateral injections of the opioid receptor agonist beta-endorphin (2 nmol/0.2 microl) into the LPBN induced 0.3 M NaCl (17.8+/-5.9 vs. saline: 0.9+/-0.5 ml/240 min) and water intake (11.4+/-3.0 vs. saline: 1.0+/-0.4 ml/240 min) in a two-bottle test. Bilateral injections of the opioid antagonist naloxone (100 nmol/0.2 microl) into the LPBN abolished sodium and water intake induced by beta-endorphin into the LPBN and also reduced 0.3 M NaCl intake (12.8+/-1.5 vs. vehicle: 22.4+/-3.1 ml/180 min) induced by 24 h of sodium depletion (produced by the treatment with the diuretic furosemide s.c.+sodium deficient food for 24 h). Bilateral injections of beta-endorphin into the LPBN in satiated rats produced no effect on water or 2% sucrose intake when water alone or simultaneously with 2% sucrose was offered to the animals. The results show that opioid receptor activation in the LPBN induces hypertonic sodium intake in satiated and normohydrated rats, an effect not due to general ingestive behavior facilitation. In addition, sodium depletion induced 0.3 M NaCl intake also partially depends on opioid receptor activation in the LPBN. The results suggest that deactivation of inhibitory mechanisms by opioid receptor activation in the LPBN releases sodium intake if excitatory signals were activated (sodium depletion) or not.
Asunto(s)
Puente/efectos de los fármacos , Puente/fisiología , Receptores Opioides delta/metabolismo , Receptores Opioides mu/metabolismo , Cloruro de Sodio/farmacocinética , betaendorfina/farmacología , Animales , Ingestión de Líquidos/efectos de los fármacos , Ingestión de Líquidos/fisiología , Interacciones Farmacológicas , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Masculino , Microinyecciones , Naloxona/farmacología , Antagonistas de Narcóticos/farmacología , Ratas , Ratas Sprague-Dawley , Receptores Opioides delta/antagonistas & inhibidores , Receptores Opioides mu/antagonistas & inhibidores , Respuesta de Saciedad/efectos de los fármacos , Respuesta de Saciedad/fisiología , Sacarosa/farmacología , Agua/metabolismo , betaendorfina/metabolismoRESUMEN
Previous studies have established a relationship between sleep disruption and pain, and it has been suggested that hyperalgesia induced by paradoxical sleep deprivation (PSD) could be due to a reduction of opioidergic neurotransmission in the brain. In the present study rats deprived of sleep for 96 h as well as rats allowed to recover for 24h after PSD and normal controls received vehicle or morphine (2.5, 5 and 10 mg/kg, i.p.) and were tested on a hot plate 1h later. Quantitative receptor autoradiography was used to map alterations in binding to brain mu-opioid receptors in separate groups. Results demonstrated that PSD induced a significant reduction in thermal pain threshold, as measured by paw withdrawal latencies. This effect did not return to baseline control values after 24h of sleep recovery. The usual analgesic effect of morphine was observed in the control group but not in PSD or rebound groups except at the highest dose (10 mg/kg). Binding of [3H]DAMGO to mu sites did not differ significantly among the three groups in any of the 33 brain regions examined. These results do not exclude the participation of the opioid system in PSD-induced pain hypersensitivity since sleep-deprived rats were clearly resistant to morphine. However, the fact no changes were seen in [3H]DAMGO binding indicates that mechanisms other than altered mu-opioid binding must be sought to explain the phenomenon.
Asunto(s)
Encéfalo/metabolismo , Hiperalgesia/metabolismo , Umbral del Dolor/fisiología , Receptores Opioides mu/metabolismo , Privación de Sueño/complicaciones , Analgésicos Opioides/metabolismo , Analgésicos Opioides/farmacología , Análisis de Varianza , Animales , Encéfalo/efectos de los fármacos , Encefalina Ala(2)-MeFe(4)-Gli(5)/metabolismo , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Calor , Hiperalgesia/tratamiento farmacológico , Hiperalgesia/etiología , Masculino , Morfina/metabolismo , Morfina/farmacología , Umbral del Dolor/efectos de los fármacos , Ratas , Ratas Wistar , Receptores Opioides mu/efectos de los fármacos , Estadísticas no ParamétricasRESUMEN
Although the expression of the morphine (MOR) withdrawal syndrome is more marked in male mice than in females, we have demonstrated that the GABAB agonist baclofen (BAC) is able to attenuate MOR withdrawal signs in either sex. In order to extend these previous observations, the aim of the present study was to evaluate the mu-opioid receptor labeling in various brain areas in mice of either sex, during MOR withdrawal and its prevention with BAC. Prepubertal Swiss-Webster mice were rendered dependent by intraperitonial (i.p.) injection of MOR (2 mg/kg) twice daily for 9 days. On the 10th day, dependent animals received naloxone (NAL; 6 mg/kg, i.p.) 60 min after MOR, and another pool of dependent mice received BAC (2 mg/kg, i.p.) previous to NAL. Thirty minutes after NAL, mice were sacrificed and autoradiography with [3H]-[D-Ala2, N-Me-Phe4, -glycol5] enkephalin (DAMGO) was carried out on mice brains at five different anatomical levels. Autoradiographic mapping showed a significant increase of mu-opioid receptor labeling during MOR withdrawal in nucleus accumbens core (NAcC), caudate putamen (CPu), mediodorsal thalamic nucleus (MDTh), basolateral and basomedial amygdala, and ventral tegmental area vs. respective control groups in male mice. In contrast, opiate receptor labeling was not significantly modified in any of the brain areas studied in withdrawn females. BAC reestablished mu-opioid receptor binding sites during MOR withdrawal only in NAcC of males, and a similar tendency was observed in CPu and MDTh, even when it was not statistically significant. The sexual dimorphism observed in the present study confirms previous reports indicating a greater sensitivity of males in response to MOR pharmacological properties. The present results suggest that the effect of BAC in preventing the expression of MOR withdrawal signs could be related with the ability of BAC to reestablish the mu-opioid receptor labeling in certain brain areas.
Asunto(s)
Baclofeno/farmacología , Dependencia de Morfina/tratamiento farmacológico , Morfina/efectos adversos , Receptores Opioides mu/efectos de los fármacos , Síndrome de Abstinencia a Sustancias/tratamiento farmacológico , Envejecimiento/metabolismo , Animales , Autorradiografía , Baclofeno/uso terapéutico , Sitios de Unión/efectos de los fármacos , Sitios de Unión/fisiología , Encéfalo/anatomía & histología , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Modelos Animales de Enfermedad , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Femenino , Agonistas del GABA/farmacología , Agonistas del GABA/uso terapéutico , Masculino , Ratones , Dependencia de Morfina/metabolismo , Dependencia de Morfina/fisiopatología , Antagonistas de Narcóticos/farmacología , Narcóticos/efectos adversos , Receptores Opioides mu/metabolismo , Caracteres Sexuales , Síndrome de Abstinencia a Sustancias/metabolismo , Síndrome de Abstinencia a Sustancias/fisiopatologíaRESUMEN
Adenylyl cyclase is activated by prostaglandin E and inhibited by mu-opioids. Since cAMP-related events influence the activity of the Na Pump and its biochemical correlate Na,K-ATPase in many systems, we tested the hypothesis that prostaglandin E1 and [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), a mu-opioid agonist, have opposing actions on Na,K-ATPase activity. Studies were conducted with alamethicin-permeabilized SH-SY5Y human neuroblastoma cells. Prostaglandin E1 (1 microM) transiently inhibited Na,K-ATPase activity for 10-15 min. A direct activator of protein kinase A, 8-Br-cAMP (150 and 500 microM), also inhibited, but more rapidly and for a shorter duration. Both DAMGO (1 microM) and Rp-adenosine 3',5'-cyclic monophosphorothioate (500 microM), a protein kinase A-inhibitor, reversed the inhibitory effect of prostaglandin E1. DAMGO alone (1 microM) stimulated Na,K-ATPase activity up to nearly three-fold control activity. The stimulatory action of DAMGO was blocked by cyclosporine A (2 microM), an inhibitor of calcineurin, and was dependent on Ca2+ entry through nifedipine-sensitive Ca2+ channels. In the presence of 1 mM EGTA, DAMGO inhibited Na,K-ATPase activity. DAMGO-induced inhibition was blocked by the inositol 1,4,5-trisphosphate receptor antagonist xestospongin C (1 microM). Na,K-ATPase is poised to modulate neuronal excitability through its roles in maintaining the membrane potential and transmembrane ion gradients. The differential effects of prostaglandin E1 and opioids on Na,K-ATPase activity may be related to their actions in hyperalgesia.
Asunto(s)
Alprostadil/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Inhibidores Enzimáticos/farmacología , Receptores Opioides mu/agonistas , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Canales de Calcio Tipo L/metabolismo , Línea Celular Tumoral , AMP Cíclico/metabolismo , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Activación Enzimática/efectos de los fármacos , Humanos , Transducción de Señal/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/antagonistas & inhibidoresRESUMEN
1. We have previously demonstrated the existence of a dual neuromodulatory regulation of prolactin secretion by the opioid system. In the present work, we evaluated the opioid receptor subtypes involved in both the stimulatory and the inhibitory regulation of prolactin secretion in pregnant rats. 2. Specific opioid agonists and antagonists were administered intracerebro ventricular (i.c.v.) to rats on day 3 and on day 19 pregnancy in rats of pretreated with mifepristone. Blood samples were obtained after decapitation at 12.00 and 18.00 h. Serum prolactin levels were measured by RIA. 3. The mu-selective agonist DAMGO and beta-endorphin caused a significant increase in serum prolactin secretion on day 3 of pregnancy, during the diurnal surge and intersurge period. Pretreatment with naloxone prevented the increase on prolactin levels induced by DAMGO. The administration of U-50,488, a kappa-selective agonist or DPDPE, a delta-selective agonist, did not modify serum prolactin concentration while the mu1-antagonist naloxonazine reduced significantly serum prolactin levels. On day 19 of pregnancy, the release of prolactin induced by mifepristone was significantly increase by naloxonazine, while the kappa-antagonist nor-binaltorfimine induced only a small but significant increase. No effect was observed after administration of the delta-antagonist naltrindole. 4. We conclude that the mu-opioid receptor seems to be more specifically involved in both the stimulatory and inhibitory regulation by the opioid system on prolactin secretion during pregnancy. The increase on serum prolactin levels on day 3 after administration of DAMGO and beta-endorphin may suggest the participation of other regulatory mechanisms as the dopaminergic and serotoninergic systems. On day 19, only the endogenous ligands delta did not participate in the regulation of prolactin secretion, while the participation of the kappa-opioid receptor was significantly less effective than the endogenous ligand mu. Our results provide evidences of an important role of the opioid system through specific receptors on the regulation of prolactin secretion during early and late pregnancy.
Asunto(s)
Sistema Hipotálamo-Hipofisario/metabolismo , Péptidos Opioides/farmacología , Preñez/metabolismo , Prolactina/metabolismo , Receptores Opioides/metabolismo , 3,4-Dicloro-N-metil-N-(2-(1-pirrolidinil)-ciclohexil)-bencenacetamida, (trans)-Isómero/farmacología , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Ritmo Circadiano/efectos de los fármacos , Ritmo Circadiano/fisiología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Encefalina D-Penicilamina (2,5)/farmacología , Estro/efectos de los fármacos , Estro/fisiología , Femenino , Sistema Hipotálamo-Hipofisario/efectos de los fármacos , Inyecciones Intraventriculares , Masculino , Mifepristona/farmacología , Antagonistas de Narcóticos/farmacología , Embarazo , Preñez/sangre , Prolactina/sangre , Ratas , Ratas Wistar , Receptores Opioides/agonistas , Receptores Opioides kappa/agonistas , Receptores Opioides kappa/antagonistas & inhibidores , Receptores Opioides kappa/metabolismo , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inhibidores , Receptores Opioides mu/metabolismo , betaendorfinaRESUMEN
Population spikes associated with the paired pulse ratio protocol were used to measure the presynaptic inhibition of corticostriatal transmission caused by mu-opioid receptor activation. A 1 microM of [D-Ala(2), N-MePhe(4), Gly-ol(5)]-enkephalin (DAMGO), a selective mu-opioid receptor agonist, enhanced paired pulse facilitation by 44+/-8%. This effect was completely blocked by 2 nM of the selective mu-receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-NH (CTOP). Antagonists of N- and P/Q-type Ca(2+) channels inhibited, whereas antagonists of potassium channels enhanced, synaptic transmission. A 1 microM of omega-conotoxin GVIA, a blocker of N-type Ca(2+) channels, had no effect on the action of DAMGO, but 400 nM omega-agatoxin TK, a blocker of P/Q-type Ca(2+)-channels, partially blocked the action of this opioid. However, 5 mM Cs(2+) and 400 microM Ba(2+), unselective antagonists of potassium conductances, completely prevented the action of DAMGO on corticostriatal transmission. These data suggest that presynaptic inhibition of corticostriatal afferents by mu-opioids is mediated by the modulation of K(+) conductances in corticostriatal afferents.
Asunto(s)
Analgésicos Opioides/farmacología , Corteza Cerebral/efectos de los fármacos , Cuerpo Estriado/efectos de los fármacos , Canales de Potasio/fisiología , Somatostatina/análogos & derivados , Transmisión Sináptica/efectos de los fármacos , Vías Aferentes/efectos de los fármacos , Agatoxinas , Animales , Bario/farmacología , Canales de Calcio/efectos de los fármacos , Corteza Cerebral/fisiología , Cesio/farmacología , Cuerpo Estriado/fisiología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Técnicas In Vitro , Masculino , Canales de Potasio/efectos de los fármacos , Ratas , Ratas Wistar , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inhibidores , Somatostatina/farmacología , Venenos de Araña/farmacologíaRESUMEN
The effect of a 25-day restricted diet (50% of the normal food intake) on uterine glucose metabolism of ovariectomized (25 days) and non-ovariectomized rats, was studied. Underfeeding reduces (14)CO(2) production from U(14)C-glucose in intact animal. However, in spayed rats, results are the opposite. In intact rats receiving a low food intake, the effect of the addition to the KRB medium of various agonist opioids, was studied. Dinorphin A did not bring about any change. On the other hand, beta endorphin increased glucose metabolism. Also, the addition of Dago and Dadle increased (14)CO(2) production, while their corresponding specific blockers, beta-FNA and Naltrindole, reversed it. Ovariectomized rats subjected to food restriction are not affected by opioid agonists. In vitro morphine, like endogenous opioids, increased (14)CO(2) in intact restricted diet rats. Arachidonic acid metabolism in these rats show that underfeeding brings about a decrease in PGF(2 alpha) and PGE(2), but the addition of morphine does not alter this situation, for which eicosanoids metabolites are not related to the effect of morphine. The morphine effect was not altered by naloxone. The subcutaneous injection of morphine increased glucose metabolism in intact underfed animals, while naloxone reduced (14)CO(2) in spayed rats subjected to underfeeding. It can be concluded that uteri from ovariectomized rats receiving a restricted diet are influenced by a mechanism of upregulation related to endogenous opioids. These likely originate in other tissues, and so prevent us from seeing the morphine effect.
Asunto(s)
Eicosanoides/biosíntesis , Glucosa/metabolismo , Morfina/farmacología , Narcóticos/farmacología , Péptidos Opioides/farmacología , Útero/efectos de los fármacos , Animales , Técnicas de Cultivo , Dinorfinas/farmacología , Ingestión de Alimentos , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Leucina Encefalina-2-Alanina/farmacología , Femenino , Naloxona/farmacología , Antagonistas de Narcóticos/farmacología , Ovariectomía , Ratas , Ratas Wistar , Útero/metabolismo , betaendorfina/farmacologíaRESUMEN
Biochemical and pharmacological evidence suggest that the dopaminergic mesolimbic system plays a key role in mediating the reinforcing properties of alcohol and other drugs of abuse. Alcohol reinforcement and high alcohol drinking behavior have been postulated to be partially mediated by a neurobiological mechanism involving the alcohol-induced activation of the endogenous opioid system. The aim of this work was to study the effect of the in vivo acute administration of ethanol on mu (mu) opioid receptors in the rat dopaminergic meso-accumbens and mesocortical pathways by quantitative receptor autoradiography. [(3)H]DAMGO binding was significantly decreased in the ventral tegmental area (VTA) 30 min after ethanol administration. A small ethanol-induced reduction was observed in the shell region of the nucleus accumbens 1 h after exposure. In contrast, 2 h after ethanol administration, [(3)H]DAMGO binding was significantly increased in the frontal and prefrontal cortices. The observed changes correlated well with high ethanol plasma levels. Our results suggest that the reinforcing properties of ethanol may be partially mediated by mechanisms involving the ethanol-induced down- and up-regulation of mu receptors in the dopaminergic mesolimbic system. Mu receptors in the VTA and the frontal and prefrontal cortices may be involved in the in vivo acute responses to ethanol and could play a key role in modulating the dopaminergic activity of the mesocortical pathway in response to the drug. In contrast, the contribution of both mu and delta receptors in the nucleus accumbens might be relevant in these processes.
Asunto(s)
Depresores del Sistema Nervioso Central/farmacología , Corteza Cerebral/efectos de los fármacos , Etanol/farmacología , Núcleo Accumbens/efectos de los fármacos , Receptores Opioides mu/metabolismo , Área Tegmental Ventral/efectos de los fármacos , Alcoholismo/fisiopatología , Analgésicos Opioides/metabolismo , Analgésicos Opioides/farmacología , Animales , Autorradiografía , Depresores del Sistema Nervioso Central/sangre , Corteza Cerebral/citología , Corteza Cerebral/metabolismo , Dopamina/metabolismo , Encefalina Ala(2)-MeFe(4)-Gli(5)/metabolismo , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Etanol/sangre , Sistema Límbico/citología , Sistema Límbico/efectos de los fármacos , Sistema Límbico/metabolismo , Masculino , Vías Nerviosas , Núcleo Accumbens/citología , Núcleo Accumbens/metabolismo , Péptidos Opioides/metabolismo , Ensayo de Unión Radioligante , Ratas , Ratas Wistar , Tritio , Área Tegmental Ventral/citología , Área Tegmental Ventral/metabolismoRESUMEN
The effects of intrathecal administration of nimodipine or omega-conotoxin GVIA (L- and N-type calcium channel blockers, respectively) alone or followed by DAMGO, DADLE or bremazocine (mu-, delta- and kappa-opioid agonists, respectively) were studied on the rat tail flick test. The N- (16 to 64 pmoles), but not the L-type blocker (60 to 240 pmoles) produced a dose and time-dependent increase in the latency for the tail-flick reflex. DAMGO (30 to 120 pmoles) or bremazocine (190 to 560 pmoles), but not DADLE (50 to 200 pmoles), produced a dose-dependent increase in the latency for the tail-flick reflex. The effect of the highest dose of DAMGO was smaller, while the effects of DADLE and bremazocine were not changed after nimodipine (60 pmoles). The effects of DADLE were significantly potentiated, while the effects of DAMGO and bremazocine were not changed after omega-conotoxin GVIA (16 pmoles). The intrathecal administration of an N-type calcium channel blocker with a delta-opioid agonist seems to be the most effective combination to produce antinociception in the rat tail flick test.
Asunto(s)
Analgésicos Opioides/agonistas , Analgésicos/metabolismo , Bloqueadores de los Canales de Calcio/farmacología , Nimodipina/farmacología , Dimensión del Dolor , omega-Conotoxinas/farmacología , Animales , Benzomorfanos/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Inyecciones Espinales , Masculino , Ratas , Ratas Wistar , Cola (estructura animal)/efectos de los fármacosRESUMEN
The effects of intrathecal administration of nimodipine or omega-conotoxin GVIA(L- and N-type calcium channel blockers, respectively) alone or followed by DAMGO, DADLE or bremazocine (mu-, delta- and kappa- opioid agonists, respectively) were studied on the rat tail flick test. The N- (16 to 64 pmoles), but not the L-type blocker (60 to 240 pmoles) produced a dose and time-dependent increase in the latency for the tail-flick reflex. DAMGO (30 to 120 pmoles) or bremazocine (190 to 560 pmoles), but not DADLE (50 to 200 pmoles), produced a dose-dependent increase in the latency for the tail-flick reflex. The effect of the highest dose of DAMGO was smaller, while the effects of DADLE and bremazocine were not changed after nimodipine (60 pmoles). The effects of DADLE were significantly potentiated, while the effects of DAMGO and bremazocine were not changed after omega-conotoxin GVIA (16 pmoles). The intrathecal administration of an N-type calcium channel blocker with a delta-opioid agonist seems to be the most effective combination to produce antinociception in the rat tail flick test.
Asunto(s)
Animales , Ratas , Masculino , Analgésicos Opioides/agonistas , Analgésicos/metabolismo , Benzomorfanos/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Nimodipina/farmacología , omega-Conotoxinas/farmacología , Cola (estructura animal)/efectos de los fármacos , Inyecciones Espinales , Ratas WistarRESUMEN
The effects of intrathecal administration of nimodipine or omega-conotoxin GVIA(L- and N-type calcium channel blockers, respectively) alone or followed by DAMGO, DADLE or bremazocine (mu-, delta- and kappa- opioid agonists, respectively) were studied on the rat tail flick test. The N- (16 to 64 pmoles), but not the L-type blocker (60 to 240 pmoles) produced a dose and time-dependent increase in the latency for the tail-flick reflex. DAMGO (30 to 120 pmoles) or bremazocine (190 to 560 pmoles), but not DADLE (50 to 200 pmoles), produced a dose-dependent increase in the latency for the tail-flick reflex. The effect of the highest dose of DAMGO was smaller, while the effects of DADLE and bremazocine were not changed after nimodipine (60 pmoles). The effects of DADLE were significantly potentiated, while the effects of DAMGO and bremazocine were not changed after omega-conotoxin GVIA (16 pmoles). The intrathecal administration of an N-type calcium channel blocker with a delta-opioid agonist seems to be the most effective combination to produce antinociception in the rat tail flick test. (AU)