RESUMEN
Obesity, associated with the intake of a high-fat diet (HFD), and anxiety are common among those living in modern urban societies. Recent studies suggest a role of microbiome-gut-brain axis signaling, including a role for brain serotonergic systems in the relationship between HFD and anxiety. Evidence suggests the gut microbiome and the serotonergic brain system together may play an important role in this response. Here we conducted a nine-week HFD protocol in male rats, followed by an analysis of the gut microbiome diversity and community composition, brainstem serotonergic gene expression (tph2, htr1a, and slc6a4), and anxiety-related defensive behavioral responses. We show that HFD intake decreased alpha diversity and altered the community composition of the gut microbiome in association with obesity, increased brainstem tph2, htr1a and slc6a4 mRNA expression, including in the caudal part of the dorsomedial dorsal raphe nucleus (cDRD), a subregion previously associated with stress- and anxiety-related behavioral responses, and, finally, increased anxiety-related defensive behavioral responses. The HFD increased the Firmicutes/Bacteroidetes ratio relative to control diet, as well as higher relative abundances of Blautia, and decreases in Prevotella. We found that tph2, htr1a and slc6a4 mRNA expression were increased in subregions of the dorsal raphe nucleus in the HFD, relative to control diet. Specific bacterial taxa were associated with increased serotonergic gene expression in the cDRD. Thus, we propose that HFD-induced obesity is associated with altered microbiome-gut-serotonergic brain axis signaling, leading to increased anxiety-related defensive behavioral responses in rats.
Asunto(s)
Ansiedad , Eje Cerebro-Intestino , Dieta Alta en Grasa , Microbioma Gastrointestinal , Animales , Masculino , Dieta Alta en Grasa/efectos adversos , Microbioma Gastrointestinal/fisiología , Ansiedad/microbiología , Eje Cerebro-Intestino/fisiología , Ratas , Ratas Sprague-Dawley , Obesidad/microbiología , Obesidad/psicología , Obesidad/metabolismo , Transducción de Señal/fisiología , Conducta Animal/fisiologíaRESUMEN
Disruption of the brain serotoninergic (5-HT) system during development induces long-lasting changes in molecular profile, cytoarchitecture, and function of neurons, impacting behavioral regulation throughout life. In male and female rats, we investigate the effect of neonatal tryptophan hydroxylase (TPH) inhibition by using para-chlorophenylalanine (pCPA) on the expression of 5-HTergic system components and neuropeptides related to adolescent social play behavior regulation. We observed sex-dependent 5-HT levels decrease after pCPA-treatment in the dorsal raphe nucleus (DRN) at 17 and 35 days. Neonatal pCPA-treatment increased playing, social and locomotory behaviors assessed in adolescent rats of both sexes. The pCPA-treated rats demonstrated decreased Crh (17 days) and increased Trh (35 days) expression in the hypothalamic paraventricular nucleus (PVN). There was sex dimorphism in Htr2c (17 days) and VGF (35 days) in the prefrontal cortex, with the females expressing higher levels of it than males. Our results indicate that neonatal pCPA-treatment results in a long-lasting and sex-dependent DRN 5-HT synthesis changes, decreased Crh, and increased Trh expression in the PVN, resulting in a hyperactivity-like phenotype during adolescence. The present work demonstrates that the impairment of TPH function leads to neurobehavioral disorders related to hyperactivity and impulsivity, such as attention deficit hyperactivity disorder (ADHD).
Asunto(s)
Núcleo Hipotalámico Paraventricular , Serotonina , Ratas , Femenino , Masculino , Animales , Fenclonina/farmacología , Núcleo Hipotalámico Paraventricular/metabolismo , Serotonina/metabolismo , Núcleo Dorsal del Rafe/metabolismo , Triptófano Hidroxilasa/metabolismoRESUMEN
Obesity, associated with the intake of a high-fat diet (HFD), and anxiety are common among those living in modern urban societies. Recent studies suggest a role of microbiome-gut-brain axis signaling, including a role for brain serotonergic systems in the relationship between HFD and anxiety. Evidence suggests the gut microbiome and the serotonergic brain system together may play an important role in this response. Here we conducted a nine-week HFD protocol in male rats, followed by an analysis of the gut microbiome diversity and community composition, brainstem serotonergic gene expression (tph2, htr1a, and slc6a4), and anxiety-related defensive behavioral responses. We show that HFD intake decreased alpha diversity and altered the community composition of the gut microbiome in association with obesity, increased brainstem tph2, htr1a and slc6a4 mRNA expression, including in the caudal part of the dorsomedial dorsal raphe nucleus (cDRD), a subregion previously associated with stress- and anxiety-related behavioral responses, and, finally, increased anxiety-related defensive behavioral responses. The HFD increased the Firmicutes/Bacteroidetes ratio relative to control diet, as well as higher relative abundances of Blautia, and decreases in Prevotella. We found that tph2, htr1a and slc6a4 mRNA expression were increased in subregions of the dorsal raphe nucleus in the HFD, relative to control diet. Specific bacterial taxa were associated with increased serotonergic gene expression in the cDRD. Thus, we propose that HFD-induced obesity is associated with altered microbiome-gut-serotonergic brain axis signaling, leading to increased anxiety-related defensive behavioral responses in rats.
RESUMEN
The perinatal environment interacts with the genotype of the developing organism resulting in a unique phenotype through a developmental or perinatal programming phenomenon. However, it remains unclear how this phenomenon differentially affects particular targets expressing specific drinking responses depending on the perinatal conditions. The main goal of the present study was to compare the dipsogenic responses induced by different thirst models as a function of two perinatal manipulation models, defined by the maternal free access to hypertonic sodium solution and a partial aortic ligation (PAL-W/Na) or a sham-ligation (Sham-W/Na). The programmed adult offspring of both perinatal manipulated models responded similarly when was challenged by overnight water dehydration or after a sodium depletion showing a reduced water intake in comparison to the non-programmed animals. However, when animals were evaluated after a body sodium overload, only adult Sham-W/Na offspring showed drinking differences compared to PAL and control offspring. By analyzing the central neurobiological substrates involved, a significant increase in the number of Fos + cells was found after sodium depletion in the subfornical organ of both programmed groups and an increase in the number of Fos + cells in the dorsal raphe nucleus was only observed in adult depleted PAL-W/Na. Our results suggest that perinatal programming is a phenomenon that differentially affects particular targets which induce specific dipsogenic responses depending on matching between perinatal programming conditions and the osmotic challenge in the latter environment. Probably, each programmed-drinking phenotype has a particular set point to elicit specific repertoires of mechanisms to reestablish fluid balance.
Asunto(s)
Ingestión de Líquidos , Sed , Animales , Femenino , Embarazo , Ratas , Sodio , Sed/fisiología , Equilibrio Hidroelectrolítico/fisiologíaRESUMEN
BACKGROUND: Acute hypoxia, which is panicogenic in humans, also evokes panic-like behavior in male rats. Panic disorder is more common in women and susceptibility increases during the premenstrual phase of the cycle. AIMS: We here investigated for the first time the impact of hypoxia on the expression of panic-like escape behavior by female rats and its relationship with the estrous cycle. We also evaluated functional activation of the midbrain panic circuitry in response to this panicogenic stimulus and whether short-term, low-dose fluoxetine treatment inhibits the hyper-responsiveness of females in late diestrus. METHODS: Male and female Sprague Dawley rats were exposed to 7% O2. Females in late diestrus were also tested after short-term treatment with fluoxetine (1.75 or 10 mg/kg, i.p.). Brains were harvested and processed for c-Fos and tryptophan hydroxylase immunoreactivity in the periaqueductal gray matter (PAG) and dorsal raphe nucleus (DR). RESULTS: Acute hypoxia evoked escape in both sexes. Overall, females were more responsive than males and this is clearer in late diestrus phase. In both sexes, hypoxia induced functional activation (c-Fos expression) in non-serotonergic cells in the lateral wings of the DR and dorsomedial PAG, which was greater in late diestrus than proestrus (lowest behavioral response to hypoxia). Increased responding in late diestrus (behavioral and cellular levels) was prevented by 1.75, but not 10 mg/kg fluoxetine. DISCUSSION: The response of female rats to acute hypoxia models panic behavior in women. Low-dose fluoxetine administered in the premenstrual phase deserves further attention for management of panic disorders in women.
Asunto(s)
Conducta Animal/efectos de los fármacos , Diestro/efectos de los fármacos , Núcleo Dorsal del Rafe/efectos de los fármacos , Fluoxetina/farmacología , Hipoxia/complicaciones , Pánico/efectos de los fármacos , Sustancia Gris Periacueductal/efectos de los fármacos , Inhibidores Selectivos de la Recaptación de Serotonina/farmacología , Caracteres Sexuales , Animales , Modelos Animales de Enfermedad , Femenino , Masculino , Ciclo Menstrual/efectos de los fármacos , Trastorno de Pánico/tratamiento farmacológico , Ratas , Ratas Sprague-Dawley , Inhibidores Selectivos de la Recaptación de Serotonina/administración & dosificaciónRESUMEN
Mygalin, a diacylspermidine that is naturally found in the hemolymph of the spider Acanthoscurria gomesiana, is of interest for development as a potential analgesic. Previous studies have shown that acylpolyamines modulate glutamatergic receptors with the potential to alter pain pathways. This study aimed to evaluate the effects of mygalin on acute and chronic pain in rodents. For evaluation of acute pain, Wistar rats were subjected to tail-flick and hot-plate nociceptive tests. For the evaluation of chronic neuropathic pain, a partial ligation of the sciatic nerve was performed and, 21 days later, animals were examined in hot-plate, tail-flick, acetone, and von Frey tests. Either Mygalin or vehicle was microinjected in the dorsal raphe nucleus (DRN) before the tests. Another group was pretreated with selective antagonists of glutamate receptors (LY 235959, MK-801, CNQX, and NBQX). Mygalin decreases nociceptive thresholds on both acute and chronic neuropathic pain models in all the tests performed. The lowest dose of mygalin yielded the most effective nociception, showing an increase of 63% of the nociceptive threshold of animals with neuropathic chronic pain. In conclusion, mygalin microinjection in the DRN results in antinociceptive effect in models of neuropathic pain, suggesting that acylpolyamines and their derivatives, such as this diacylspermidine, could be pursued for the treatment of neuropathic pain and development of selective analgesics.
Asunto(s)
Dolor Agudo/tratamiento farmacológico , Analgésicos/administración & dosificación , Dolor Crónico/tratamiento farmacológico , Núcleo Dorsal del Rafe/efectos de los fármacos , Neuralgia/tratamiento farmacológico , Espermidina/análogos & derivados , Arañas/metabolismo , Drogas Sintéticas/administración & dosificación , Animales , Modelos Animales de Enfermedad , Hemolinfa/química , Masculino , Microinyecciones/métodos , Ratas , Ratas Wistar , Espermidina/administración & dosificación , Resultado del TratamientoRESUMEN
Previous studies showed that mecamylamine a noncompetitive and nonspecific blocker of nicotinic acetylcholine receptors (nAChRs), stimulates the activity of the dorsal raphe nucleus (DRN) serotonergic neurons and DRN serotonin (5-HT) release. In the present study, the mechanisms involved in these mecamylamine-induced effects were examined using electrophysiology and calcium-imaging studies, both performed in Wistar rat midbrain slices. Mecamylamine (0.5-9 µM), bath administered, increased the firing frequency of identified 5-HT DRN neurons by a maximum of 5% at 3 µM. This effect was accompanied by a 112 % increase in the frequency of spontaneous excitatory postsynaptic currents of 5-HT DRN neurons. It was blocked by the AMPA/kainate receptor blocker CNQX (10 µM) and by the specific α4ß2 nAChRs blocker dihydro-ß-erythroidine (100 nM) but was not affected by tetrodotoxin (TTX, 500 nM). Simultaneously, mecamylamine produced a 58 % decrease in the frequency of GABAergic spontaneous inhibitory postsynaptic currents, an effect that was not influenced by TTX. Calcium-imaging studies support the results obtained with the electrophysiological studies by showing that mecamylamine (3 µM) increases the activity of a cell population located in the midline of the DRN, which was sensitive to the inhibitory effects of 8-OH-DPAT, an agonist at 5-HT1A receptors. It is assumed that mecamylamine, in low concentrations, acts as an agonist of α4ß2 nAChRs present on the glutamatergic DRN terminals, thus increasing intra-raphe glutamate release. This stimulatory effect is reinforced by the decrease in DRN GABA release, which is dependent on the mecamylamine-induced blockade of α7 nAChRs located on DRN GABAergic terminals. We hypothesize that at least a part of mecamylamine antidepressant effects described in animal models of depression are mediated by an increase in DRN 5-HT release.
Asunto(s)
Potenciales de Acción/efectos de los fármacos , Núcleo Dorsal del Rafe/efectos de los fármacos , Bloqueadores Ganglionares/farmacología , Mecamilamina/farmacología , Neuronas Serotoninérgicas/efectos de los fármacos , Animales , Calcio/metabolismo , Núcleo Dorsal del Rafe/metabolismo , Masculino , Técnicas de Placa-Clamp , Ratas , Ratas Wistar , Neuronas Serotoninérgicas/metabolismoRESUMEN
BACKGROUND: Stimulation of serotonergic neurons within the dorsal raphe dorsomedial subnucleus facilitates inhibitory avoidance acquisition in the elevated T-maze. It has been hypothesized that such anxiogenic effect is due to serotonin release in the basolateral nucleus of the amygdala, where facilitation of serotonin 2C receptor-mediated neurotransmission increases anxiety. Besides the dorsal raphe dorsomedial subnucleus, the dorsal raphe caudal subnucleus is recruited by anxiogenic stimulus/situations. However, the behavioral consequences of pharmacological manipulation of this subnucleus are still unknown. AIMS: Investigate whether blockade of serotonin 2C receptors in the basolateral nucleus of the amygdala counteracts the anxiogenic effect caused by the stimulation of dorsal raphe dorsomedial subnucleus serotonergic neurons. Evaluate the effects caused by the excitatory amino acid kainic acid or serotonin 1A receptor-modulating drugs in the dorsal raphe caudal subnucleus. METHODS: Male Wistar rats were tested in the elevated T-maze and light-dark transition tests after intra-basolateral nucleus of the amygdala injection of the serotonin 2C receptor antagonist SB-242084 (6-chloro-2,3-dihydro-5-methyl-N-[6-[(2-methyl-3-pyridinyl)oxy]-3-pyridinyl]-1H-indole-1-carboxyamide dihydrochloride) followed by intra-dorsal raphe dorsomedial subnucleus administration of the serotonin 1A receptor antagonist WAY-100635 (N-[2-[4-2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinil-cyclohexanecarboxamide maleate). In the dorsal raphe caudal subnucleus, animals were injected with kainic acid, WAY-100635 or the serotonin 1A receptor agonist 8-OH-DPAT ((±)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide) and tested in the elevated T-maze. RESULTS: SB-242084 in the basolateral nucleus of the amygdala blocked the anxiogenic effect caused by the injection of WAY-100635 in the dorsal raphe dorsomedial subnucleus. Kainic acid in the dorsal raphe caudal subnucleus increased anxiety, but also impaired escape expression in the elevated T-maze. Neither WAY-100635 nor 8-OH-DPAT in the dorsal raphe caudal subnucleus affected rat's behavior in the elevated T-maze. CONCLUSION: Serotonin 2C receptors in the basolateral nucleus of the amygdala mediate the anxiogenic effect caused by the stimulation of serotonergic neurons in the dorsal raphe dorsomedial subnucleus. The dorsal raphe caudal subnucleus regulates anxiety- and panic-like behaviors, presumably by a serotonin 1A receptor-independent mechanism.
Asunto(s)
Ansiedad/inducido químicamente , Complejo Nuclear Basolateral/efectos de los fármacos , Núcleo Dorsal del Rafe/efectos de los fármacos , Receptor de Serotonina 5-HT2C/efectos de los fármacos , Serotonina/metabolismo , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Aminopiridinas/farmacología , Animales , Ansiedad/psicología , Estimulación Eléctrica , Indoles/farmacología , Ácido Kaínico , Masculino , Piperazinas/farmacología , Piridinas/farmacología , Ratas , Ratas Wistar , Neuronas Serotoninérgicas/efectos de los fármacos , Antagonistas de la Serotonina/farmacología , Agonistas de Receptores de Serotonina/farmacologíaRESUMEN
Pathophysiological mechanisms involved in orofacial pain and their relationship with emotional disorders have emerged as an important research area for multidisciplinary studies. In particular, temporomandibular disorders (TMD) have been evaluated clinically from both physiological and psychological perspectives. We hypothesized that an altered neuronal activity occurs in the amygdala and the dorsal raphe nucleus (DR), encephalic regions involved in the modulation of painful and emotional information. Adult male Wistar rats were used in an experimental complete Freund's adjuvant (CFA)-induced temporomandibular joint (TMJ) inflammation model. CFA was applied for 1 or 10 days, and the animals were euthanized for brain samples dissection for FosB/ΔFosB and parvalbumin (PV) immunostaining. Our results were consistent in showing that the amygdala and DR were activated in the persistent inflammatory phase (10 days) and that the expression of PV+ interneurons in the amygdala was decreased. In contrast, in the DR, the expression of PV+ interneurons was increased in persistent states of CFA-induced TMJ inflammation. Moreover, at 10 days of inflammation, there was an increased co-localization of PV+ and FosB/ΔFosB+ neurons in the basolateral and central nucleus of the amygdala. Different nuclei of the amygdala, as well as portions of the DR, were activated in the persistent phase (10 days) of TMJ inflammation. In conclusion, altered activity of the amygdala and DR was detected during persistent inflammatory nociception in the temporomandibular joint. These regions may be essential for both sensory and affective dimensions of orofacial pain.
Asunto(s)
Animales , Masculino , Ratas , Parvalbúminas/metabolismo , Articulación Temporomandibular/fisiología , Núcleo Dorsal del Rafe/metabolismo , Amígdala del Cerebelo/metabolismo , Ratas Wistar , Ratas Sprague-Dawley , Inflamación , NeuronasRESUMEN
Ghrelin is a recently discovered peptide, mainly produced in the stomach and involved in body's energy-maintenance processes. Ghrelin exerts its actions by activating the growth hormone secretagogue receptor (GHS-R). Recent analyses indicate that ghrelin targets the brain to regulate a wealth of functions, including behavioral responses that have been associated with stress and anxiety mechanisms. In this context, evidence shows the presence of GHS-R receptors in the dorsal raphe nucleus (DRN), the main source of serotonergic neurons that innervate encephalic structures involved in emotional control. Our study aims to evaluate the effects of the pharmacological manipulation of ghrelin receptors located in the DRN on the expression of the behavioral responses of Wistar rats. Such responses were assessed in the elevated T maze (ETM), an experimental model that allows the measurement, in the same animal, of two defensive tasks, inhibitory avoidance and escape. Our results showed that the intra-DRN infusion of ghrelin impaired the acquisition of inhibitory avoidance, an anxiolytic-like effect, and facilitated the expression of escape response in the ETM, indicating a panicogenic-like effect. The intra-DRN administration of the ghrelin receptor (GHS-R1a) antagonist PF-04628935 did not alter the behavioral tasks assessed in the ETM. Finally, our results revealed that intra-DRN infusions of PF-04628935 prior to the administration of ghrelin into this area neutralized the behavioral effects obtained in the ETM. Taken together, our data reveal the involvement of DRN GHS-R1a receptors in the regulation of defensive tasks that have been associated with generalized anxiety and panic disorders.
Asunto(s)
Reacción de Prevención/fisiología , Núcleo Dorsal del Rafe/metabolismo , Reacción de Fuga/fisiología , Receptores de Ghrelina/metabolismo , Animales , Ansiolíticos/metabolismo , Ansiolíticos/farmacología , Ansiedad/metabolismo , Trastornos de Ansiedad/metabolismo , Reacción de Prevención/efectos de los fármacos , Núcleo Dorsal del Rafe/efectos de los fármacos , Reacción de Fuga/efectos de los fármacos , Ghrelina/metabolismo , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Ratas , Ratas Wistar , Neuronas Serotoninérgicas/metabolismoRESUMEN
Angiotensin II (Ang II) acts on Ang II type 1 (AT1) receptors located in the organum vasculosum and subfornical organ (SFO) of the lamina terminalis as a main facilitatory mechanism of sodium appetite. The brain serotonin (5-HT) system with soma located in the dorsal raphe nucleus (DRN) provides a main inhibitory mechanism. In the present study, we first investigated the existence of Ang II AT1 receptors in serotonergic DRN neurones. Then, we examined whether whole body sodium depletion affects the gene expression of the AT1a receptor subtype and the presumed functional significance of AT1 receptors. Using confocal microscopy, we found that tryptophan hydroxylase-2 and serotonin neurones express AT1 receptors in the DRN. Immunofluorescence quantification showed a significant reduction in 5-HT content but no change in AT1 receptor expression or AT1/5-HT colocalisation in the DRN after sodium depletion. Whole body sodium depletion also significantly increased Agtr1a mRNA expression in the SFO and DRN. Oral treatment with the AT1 receptor antagonist losartan reversed the changes in Agtr1a expression in the SFO but not the DRN. Losartan injection into either the DRN or the mesencephalic aqueduct had no influence on sodium depletion-induced 0.3 mol L-1 NaCl intake. The results indicate the expression of Agtr1a mRNA in the DRN and SFO as a marker of sodium depletion. They also suggest that serotonergic DRN neurones are targets for Ang II. However, the function of their AT1 receptors remains elusive.
Asunto(s)
Núcleo Dorsal del Rafe/metabolismo , Expresión Génica , Receptor de Angiotensina Tipo 1/genética , Serotonina/análisis , Sodio/deficiencia , Bloqueadores del Receptor Tipo 1 de Angiotensina II/farmacología , Animales , Apetito/fisiología , Núcleo Dorsal del Rafe/química , Técnica del Anticuerpo Fluorescente , Expresión Génica/fisiología , Losartán/farmacología , Masculino , Neuronas/química , ARN Mensajero/análisis , Ratas , Ratas Wistar , Receptor de Angiotensina Tipo 1/análisis , Receptor de Angiotensina Tipo 1/fisiología , Sodio/sangre , Órgano Subfornical/química , Órgano Subfornical/metabolismo , Triptófano Hidroxilasa/análisisRESUMEN
Severe food restriction (FR), as observed in disorders like anorexia nervosa, has been associated to the reduction of estrogen levels, which in turn could lead to anxiety development. Estrogen receptors, mainly ERß type, are commonly found in the dorsal raphe nucleus (DRN) neurons, an important nucleus related to anxiety modulation and the primary source of serotonin (5-HT) in the brain. Taking together, these findings suggest an involvement of estrogen in anxiety modulation during food restriction, possibly mediated by ERß activation in serotonergic DRN neurons. Thus, the present study investigated the relationship between food restriction and anxiety-like behavior, and the involvement of DRN and ERß on the modulation of anxiety-like behaviors in animals subjected to FR. For that, female Fischer rats were grouped in control group, with free access to food, or a FR group, which received 40% of control intake during 14 days. Animals were randomly treated with 17ß-estradiol (E2), DPN (ERß selective agonist), or their respective vehicles, PBS and DMSO. Behavioral tests were performed on Elevated T-Maze (ETM) and Open Field (OF). Our results suggest that FR probably reduced the estrogen levels, since the remained in the non-ovulatory cycle phases, and their uterine weight was lower when compared to control group. The FR rats showed increased inhibitory avoidance latency in theETM indicating that FR is associated with the development of an anxiety-like state. The injections of both E2 and DPN into DRN of FR animals had an anxiolytic effect. Those data suggest thatanxiety-like behavior induced by FR could be mediated by a reduction of ERß activation in the DRN neurons, probably due to decreased estrogen levels.
Asunto(s)
Ansiedad/etiología , Receptor beta de Estrógeno/metabolismo , Privación de Alimentos , Núcleos del Rafe/metabolismo , Tejido Adiposo/efectos de los fármacos , Tejido Adiposo/patología , Animales , Ansiedad/tratamiento farmacológico , Modelos Animales de Enfermedad , Estradiol/farmacología , Ciclo Estral/efectos de los fármacos , Femenino , Locomoción/efectos de los fármacos , Locomoción/fisiología , Aprendizaje por Laberinto/efectos de los fármacos , Microinyecciones , NAD/farmacología , Núcleos del Rafe/efectos de los fármacos , Ratas , Ratas Endogámicas F344 , Útero/efectos de los fármacos , Útero/patologíaRESUMEN
It has been established that chemical stimulation of the inferior colliculus (IC) of laboratory animals evokes fear-related defensive responses, which are considered panic attack-like behaviours. In addition, there is evidence that defensive reactions provoked by chemical stimulation of midbrain tectum neurons may induce an antinociceptive response. Morphologically, the IC receives projections from other mesencephalic structures, such as the dorsal raphe nucleus (DRN), a region rich in serotonergic neurons that play a critical role in the control of defensive behaviours. Moreover, this monoaminergic brainstem reticular nucleus is suggested to comprise the endogenous pain modulatory system. The aim of the present study was to investigate the role of DRN 5-hydroxytryptamine 2A (5-HT2A) receptors in Wistar rats by local microinjection of R-96544 (a selective antagonist of the 5-HT2A receptor) at doses of 5, 10 or 15â¯nM on defensive reactions and fear-induced antinociception evoked by chemical stimulation of the central nucleus of the IC with NMDA (6, 9 or 12 nmol). Behavioural responses were analysed for 10â¯min, and then the nociceptive threshold was measured at 10â¯min intervals for 70â¯min. The dose of 12â¯nmol of NMDA was the most effective in causing panic attack-like defensive behaviours and much higher hypoalgesia. In addition, both effects were attenuated by pretreatment of the DRN with R-96544. These findings suggest the critical participation of DRN 5-HT2A receptors in the modulation of panic attack-like defensive behaviour and unconditioned fear-induced antinociception organised by neurons in the central nucleus of the IC.
Asunto(s)
Miedo/psicología , Colículos Inferiores/citología , Neuronas/fisiología , Nocicepción/fisiología , Dolor/psicología , Receptor de Serotonina 5-HT2A/metabolismo , Animales , Condicionamiento Psicológico/fisiología , Modelos Animales de Enfermedad , Núcleo Dorsal del Rafe , Relación Dosis-Respuesta a Droga , Agonistas de Aminoácidos Excitadores/farmacología , Reacción Cataléptica de Congelación/efectos de los fármacos , Masculino , N-Metilaspartato/farmacología , Neuronas/efectos de los fármacos , Nocicepción/efectos de los fármacos , Dolor/tratamiento farmacológico , Umbral del Dolor/efectos de los fármacos , Umbral del Dolor/fisiología , Pirrolidinas/farmacología , Ratas , Ratas Wistar , Estadísticas no ParamétricasRESUMEN
Galanin is a neuropeptide distributed in human and rat brain regions that are involved with emotional regulation, such as the dorsal raphe nucleus (DRN). Galanin effects in the DRN are mediated by GAL1 and GAL2 receptors. Intracerebral infusion of a GAL2 (AR-M1896) or a GAL1 (M617) agonist induced either antidepressant or depressive-like effect, respectively, in rats exposed to the forced swimming test (FST). However, it is not clear if GAL1 and/or GAL2 receptors present in the DRN would be involved in such effects. Therefore, we investigated the effects induced by intra-DRN infusion of galanin (0.3â¯nmol), AR-M1896 (1â¯nmol, GAL2 agonist), or M617 (GAL1 agonist) in rats exposed to the FST. Galanin and AR-M1896 intra-DRN administration induced antidepressant-like effect in the FST. However, M617 did not induce any change in the FST. Neither M617 nor AR-M1896 changed the locomotor activity of rats in the open field test. Intra-DRN pre-treatment with M871 (1â¯nmol), a selective GAL2 antagonist, counteracted the antidepressant-like effect induced by galanin. These results suggest that galanin signaling through GAL2 receptors in the DRN produces triggers antidepressant-like effect.
Asunto(s)
Antidepresivos/administración & dosificación , Depresión/tratamiento farmacológico , Núcleo Dorsal del Rafe/fisiología , Galanina/administración & dosificación , Precursores de Proteínas/administración & dosificación , Receptor de Galanina Tipo 2/fisiología , Animales , Depresión/psicología , Núcleo Dorsal del Rafe/efectos de los fármacos , Inyecciones Intraventriculares , Masculino , Fragmentos de Péptidos/administración & dosificación , Péptidos/administración & dosificación , Ratas , Ratas Wistar , Receptor de Galanina Tipo 2/agonistas , Receptor de Galanina Tipo 2/antagonistas & inhibidores , Natación/fisiología , Natación/psicología , Resultado del TratamientoRESUMEN
Chronic exposure to 4-vinylcycloxene diepoxide (VCD) in rodents accelerates the natural process of ovarian follicular atresia modelling perimenopause in women. We investigated why estrogen therapy is beneficial for symptomatic women despite normal or high estrogen levels during perimenopause. Female rats (28 d) were injected daily with VCD or oil for 15 d; 55-65 d after the first injection, pellets of 17ß-estradiol or oil were inserted subcutaneously. Around 20 d after, the rats were euthanized (control rats on diestrus and estradiol-treated 21 d after pellets implants). Blood was collected for hormone measurement, the brains were removed and dorsal raphe nucleus (DRN), hippocampus (HPC), and amygdala (AMY) punched out for serotonin (5-HT), estrogen receptor ß (ERß), and progesterone receptor (PR) mRNA level measurements. Another set of rats was perfused for tryptophan hydroxylase (TPH) immunohistochemistry in the DRN. Periestropausal rats exhibited estradiol levels similar to controls and a lower progesterone level, which was restored by estradiol. The DRN of periestropausal rats exhibited lower expression of PR and ERß mRNA and a lower number of TPH cells. Estradiol restored the ERß mRNA levels and number of serotonergic cells in the DRN caudal subregion. The 5-HT levels were lower in the AMY and HPC in peristropausal rats, and estradiol treatment increased the 5-HT levels in the HPC and also increased ERß expression in this area. In conclusion, estradiol may improve perimenopause symptoms by increasing progesterone and boosting serotonin pathway from the caudal DRN to the dorsal HPC potentially through an increment in ERß expression in the DRN.
Asunto(s)
Encéfalo/efectos de los fármacos , Estradiol/farmacología , Estrógenos/farmacología , Terapia de Reemplazo de Hormonas , Perimenopausia/efectos de los fármacos , Serotonina/metabolismo , Animales , Encéfalo/citología , Encéfalo/metabolismo , Ciclohexenos , Estradiol/metabolismo , Receptor beta de Estrógeno/metabolismo , Estrógenos/metabolismo , Femenino , Modelos Animales , Perimenopausia/metabolismo , ARN Mensajero/metabolismo , Ratas Wistar , Receptores de Progesterona/metabolismo , Triptófano Hidroxilasa/metabolismo , Compuestos de ViniloRESUMEN
Several studies have shown that serotonin plays a dual role in the modulation of defensive behaviors related to anxiety and panic. A major source of serotonergic projections to limbic structures responsible for this modulation is the dorsal raphe nucleus (DR). Anatomical studies indicate that the prelimbic (PL) cortex sends dense glutamatergic projections to the DR, leading to stimulation or inhibition of serotonin release in structures innervated by the DR. The objective of the present study was to investigate if GABAergic disinhibition of the PL by means of local administration of picrotoxin (PIC), a chloride channel blocker, can affect serotonergic tone and the expression of defensive behaviors related to anxiety and panic. We used the elevated T-maze model and Vogel conflict test to evaluate defensive responses associated with anxiety or panic. The results showed that intra-PL PIC caused an increase in c-Fos activation in serotonergic cells in DR subregions. Furthermore, the intra-PL injection of PIC induced a panicolytic-like effect without affecting behaviors associated with anxiety. Our findings suggest that the PL-DR pathway, through DR serotonergic stimulation, is involved in the control of panic-related behaviors by control of serotonin release in structures that modulate panic responses, such as the dorsal periaqueductal gray.
Asunto(s)
Trastornos de Ansiedad/metabolismo , Conducta Animal/fisiología , Núcleo Dorsal del Rafe/metabolismo , Trastorno de Pánico/metabolismo , Serotonina/metabolismo , Animales , Ansiedad/metabolismo , Núcleo Dorsal del Rafe/efectos de los fármacos , Reacción de Fuga/efectos de los fármacos , Reacción de Fuga/fisiología , Masculino , Pánico/fisiología , Sustancia Gris Periacueductal/efectos de los fármacos , Sustancia Gris Periacueductal/metabolismo , Picrotoxina/farmacología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas , Ratas Wistar , Ácido gamma-Aminobutírico/metabolismoRESUMEN
About 40% of the dorsal raphe nucleus (DRN) neurons co-express serotonin (5-HT) and galanin. Serotonergic pathways from the DRN to the amygdala facilitate learned anxiety, while those from the DRN to the dorsal periaqueductal grey matter (DPAG) impair innate anxiety. Previously, we showed that galanin infusion in the DRN of rats induces anxiolytic effect by impairing inhibitory avoidance without changing escape behaviour in the elevated T-maze (ETM). Here, we evaluated: (1) which galanin receptors would be involved in the anxiolytic effect of galanin in the DRN of rats tested in the ETM; (2) the effects of galanin intra-DRN on panic-like behaviours evoked by electrical stimulation of the DPAG. The activation of DRN GAL1 receptors by M617 (1.0 and 3.0nmol) facilitated inhibitory avoidance, whereas the activation of GAL2 receptors by AR-M1896 (3.0nmol) impaired the inhibitory avoidance in the ETM, suggesting an anxiogenic and an anxiolytic-like effect respectively. Both agonists did not change escape behaviour in the ETM or locomotor activity in the open field. The anxiolytic effect of AR-M1896 was attenuated by the prior administration of WAY100635 (0.18nmol), a 5-HT1A antagonist. Galanin (0.3nmol) administered in the DRN increased discreetly flight behaviours induced by electrical stimulation of the DPAG, suggesting a panicolytic effect. Together, our results showed that galanin mediates opposite anxiety responses in the DRN by activation of GAL1 and GAL2 receptors. The anxiolytic effect induced by activation of Gal2 receptors may depend on serotonergic tone. Finally, the role of galanin in panic related behaviours remains uncertain.
Asunto(s)
Ansiedad/tratamiento farmacológico , Núcleo Dorsal del Rafe/efectos de los fármacos , Galanina/farmacología , Receptor de Galanina Tipo 1/efectos de los fármacos , Receptor de Galanina Tipo 2/efectos de los fármacos , Animales , Ansiolíticos/farmacología , Ansiedad/metabolismo , Trastornos de Ansiedad/tratamiento farmacológico , Núcleo Dorsal del Rafe/metabolismo , Galanina/metabolismo , Masculino , Sustancia Gris Periacueductal/efectos de los fármacos , Ratas Wistar , Receptor de Galanina Tipo 1/metabolismo , Receptor de Galanina Tipo 2/metabolismo , Antagonistas del Receptor de Serotonina 5-HT1/farmacologíaRESUMEN
The dorsal raphe nucleus (DRN) is a key structure of the endogenous pain inhibitory system. Although the DRN is rich in serotoninergic neurons, cholinergic neurons are also found in that nucleus. Both ictal and inter-ictal states are followed by post-ictal analgesia. The present study investigated the role of cholinergic mechanisms in postictal antinociceptive processes using microinjections of atropine and mecamylamine, muscarinic and nicotinic cholinergic receptor antagonists, respectively, in the DRN of rats. Intraperitoneal injection of pentylenetetrazole (PTZ) (at 64mg/kg) caused tonic and tonic-clonic seizures. The convulsive motor reactions were followed by an increase in pain thresholds, a phenomenon known as post-ictal analgesia. Pre-treatment of the DRN with atropine or mecamylamine at 1µg, 3µg and 5µg/0.2µL decreased the post-ictal antinociceptive phenomenon. The present results showed that the post-ictal analgesia was mediated by muscarinic and nicotinic cholinergic receptors in the DRN, a structure crucially involved in the neural network that organises post-ictal hypoalgesia.
Asunto(s)
Núcleo Dorsal del Rafe/fisiopatología , Umbral del Dolor/efectos de los fármacos , Receptores Muscarínicos/fisiología , Receptores Nicotínicos/fisiología , Transmisión Sináptica/fisiología , Acetilcolina/farmacología , Analgésicos/farmacología , Animales , Atropina/farmacología , Núcleo Dorsal del Rafe/efectos de los fármacos , Epilepsia Tónico-Clónica/metabolismo , Epilepsia Tónico-Clónica/fisiopatología , Neuronas GABAérgicas/metabolismo , Masculino , Mecamilamina/farmacología , Antagonistas Muscarínicos/farmacología , Antagonistas Nicotínicos/farmacología , Dimensión del Dolor/métodos , Umbral del Dolor/fisiología , Ratas , Ratas Wistar , Neuronas Serotoninérgicas/fisiología , Accidente Cerebrovascular/metabolismo , Accidente Cerebrovascular/fisiopatología , Transmisión Sináptica/efectos de los fármacosRESUMEN
The dorsal raphe nucleus (DRN) contains large populations of serotonergic (5-HT) neurons. This nucleus receives GABAergic inhibitory afferents from many brain areas and from DRN interneurons. Both GABAergic and 5-HT DRN neurons express functional nicotinic acetylcholine receptors (nAChRs). Previous studies have demonstrated that nicotine increases 5-HT release and 5-HT DRN neuron discharge rate by stimulating postsynaptic nAChRs and by increasing glutamate and norepinephrine release inside DRN. However, the influence of nicotine on the GABAergic input to 5-HT DRN neurons was poorly investigated. Therefore, the aim of this work was to determine the effect of nicotine on GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs) of 5-HT DRN neurons and the subtype of nAChR(s) involved in this response. Experiments were performed in coronal slices obtained from young Wistar rats. GABAergic sIPSCs were recorded from post hoc-identified 5-HT DRN neurons with the whole cell voltage patch-clamp technique. Administration of nicotine (1 µM) increased sIPSC frequency in 72% of identified 5-HT DRN neurons. This effect was not reproduced by the α4ß2 nAChR agonist RJR-2403 and was not influenced by TTX (1 µM). It was mimicked by the selective agonist for α7 nAChR, PNU-282987, and exacerbated by the positive allosteric modulator of the same receptor, PNU-120596. The nicotine-induced increase in sIPSC frequency was independent on voltage-gated calcium channels and dependent on Ca(2+)-induced Ca(2+) release (CICR). These results demonstrate that nicotine increases the GABAergic input to most 5-HT DRN neurons, by activating α7 nAChRs and producing CICR in DRN GABAergic terminals.
Asunto(s)
Núcleo Dorsal del Rafe/fisiología , Potenciales Postsinápticos Inhibidores/efectos de los fármacos , Nicotina/farmacología , Agonistas Nicotínicos/farmacología , Neuronas Serotoninérgicas/fisiología , Receptor Nicotínico de Acetilcolina alfa 7/fisiología , Ácido gamma-Aminobutírico/fisiología , Animales , Señalización del Calcio , Núcleo Dorsal del Rafe/citología , Núcleo Dorsal del Rafe/efectos de los fármacos , Modelos Neurológicos , Ratas , Ratas Wistar , Neuronas Serotoninérgicas/efectos de los fármacos , Serotonina/metabolismoRESUMEN
The dorsal raphe nucleus (DRN) is involved in the control of several physiological functions, including nociceptive modulation. This nucleus is one of the main sources of serotonin to the CNS and neuromodulators such as opioids and GABA may be are important for its release. This study evaluated the influence of serotonergic, GABAergic and opioidergic stimulation, as well as their interactions in the DRN, on vocalization nociceptive response during a peripheral noxious stimulus application in guinea pigs. Morphine (1.1 nmol), bicuculline (0.50 nmol) and alpha-methyl-5-HT (1.6 nmol) microinjection on the DRN produces antinociception. The antinociception produced by morphine (1.1 nmol) and alpha-methyl-5-HT (1.6 nmol) into the DRN was blocked by prior microinjection of naloxone (0.7 nmol). The alpha-methyl-5-HT effect blocked by naloxone may indicate the existence of 5-HT2A receptors on enkephalinergic interneurons within the dorsal raphe. Pretreatment with muscimol (0.26 nmol) also prevented the antinociceptive effect caused by morphine (1.1 nmol) when administered alone at the same site, indicating an interaction between GABAergic and opioidergic interneurons. The antinociception produced by bicuculline (0.5 nmol) in the DRN was blocked by prior administration of 8-OH-DPAT (0.5 nmol), a 5-HT1A agonist. This may indicate that the 5-HT autoreceptor activation by 8-OH-DPAT at DRN effector neurons can oppose the bicuculline disinhibition effect applied to the same effectors. Thus, we suggest that 5-HT2 receptor activation in the DRN promotes endorphin/enkephalin release that may disinhibit efferent serotonergic neurons of this present structure by inhibiting GABAergic interneurons, resulting in antinociception.