RESUMO
Despite significant advances in the study of fear and fear memory formation, little is known about fear learning and expression in females. This omission has been proven surprising, as normal and pathological behaviors are highly influenced by ovarian hormones, particularly estradiol and progesterone. In the current study, we investigated the joint influence of serotonin (5-HT) neurotransmission and estrous cycle phases (low or high levels of estradiol and progesterone) on the expression of conditioned fear in a group of female rats that were previously divided according to their response to stressful stimuli into low or high anxiety-like subjects. The baseline amplitude of the unconditioned acoustic startle responses was high in high-anxiety female rats, with no effect on the estrous cycle observed. Data collected during the proestrus-estrus phase revealed that low-anxiety rats had startle amplitudes similar to those of high-anxiety rats. It is supposed that high-anxiety female rats benefit from increased estradiol and progesterone levels to achieve comparable potentiated startle amplitudes. In contrast, female rats experienced a significant decrease in hormone levels during the Diestrus phase. This decrease is believed to play a role in preventing them from displaying a heightened startle response when faced with strongly aversive stimuli. Data collected after 5-HT and 8-OH-DPAT were administered into the basolateral nuclei and dorsal periaqueductal gray suggest that 5-HT neurotransmission works with progesterone and estrogen to reduce startle potentiation, most likely by activating the serotonin-1A receptor subtype.
Assuntos
Complexo Nuclear Basolateral da Amígdala , Estradiol , Medo , Substância Cinzenta Periaquedutal , Progesterona , Receptor 5-HT1A de Serotonina , Reflexo de Sobressalto , Animais , Feminino , Ratos , Ansiedade/metabolismo , Ansiedade/fisiopatologia , Complexo Nuclear Basolateral da Amígdala/metabolismo , Complexo Nuclear Basolateral da Amígdala/efeitos dos fármacos , Condicionamento Clássico/fisiologia , Condicionamento Clássico/efeitos dos fármacos , Estradiol/farmacologia , Estradiol/metabolismo , Ciclo Estral/fisiologia , Medo/fisiologia , Medo/efeitos dos fármacos , Substância Cinzenta Periaquedutal/metabolismo , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Progesterona/farmacologia , Progesterona/metabolismo , Ratos Wistar , Receptor 5-HT1A de Serotonina/metabolismo , Reflexo de Sobressalto/fisiologia , Reflexo de Sobressalto/efeitos dos fármacos , Serotonina/metabolismoRESUMO
Popular medicine has been using oleoresin from several species of copaíba tree for the treatment of various diseases and its clinical administration potentially causes antinociception. Electrical stimulation of ventrolateral (vlPAG) and dorsolateral (dlPAG) columns of the periaqueductal gray matter also causes antinociception. The aim this study was to verify the antinociceptive effect of oleoresin extracted from Copaifera langsdorffii tree and to test the hypothesis that oleoresin-induced antinociception is mediated by µ1- and κ-opioid receptors in the vlPAG and dlPAG. Nociceptive thresholds were determined by the tail-flick test in Wistar rats. The copaíba tree oleoresin was administered at different doses (50, 100 and 200 mg/kg) through the gavage technique. After the specification of the most effective dose of copaíba tree oleoresin (200 mg/kg), rats were pretreated with either the µ1-opioid receptor selective antagonist naloxonazine (at 0.05, 0.5 and 5 µg/ 0.2 µl in vlPAG, and 5 µg/ 0.2 µl in dlPAG) or the κ-opioid receptor selective antagonist nor-binaltorphimine (at 1, 3 and 9 nmol/ 0.2 µl in vlPAG, and 9 nmol/ 0.2 µl in dlPAG). The blockade of µ1 and κ opioid receptors of vlPAG decreased the antinociception produced by copaíba tree oleoresin. However, the blockade of these receptors in dlPAG did not alter copaíba tree oleoresin-induced antinociception. These data suggest that vlPAG µ1 and κ opioid receptors are critically recruited in the antinociceptive effect produced by oleoresin extracted from Copaifera langsdorffii.
Assuntos
Substância Cinzenta Periaquedutal , Extratos Vegetais , Receptores Opioides kappa , Ratos , Animais , Ratos Wistar , Árvores , Antagonistas de Entorpecentes/farmacologia , Analgésicos/farmacologia , Receptores Opioides muRESUMO
BACKGROUND: Periaqueductal gray matter (PAG) is a brain region rich in kappa-opioid receptors (KOR). KOR in PAG mediates behavioral responses related to pain integration, and panic response, among others. Its participation in the addiction phenomena has been poorly studied. Hence, this preliminary study explored the pharmacological effects of KOR stimulation/blockade in dorsal-PAG (D-PAG) during alcohol withdrawal on anxiety-type behaviors and alcohol intake/preference. METHODS: Juvenile male Wistar rats were unexposed (A-naïve group) or exposed to alcohol for 5 weeks and then restricted (A-withdrawal group). Posteriorly, animals received intra D-PAG injections of vehicle (10% DMSO), salvinorin A (SAL-A; a selective KOR agonist), or 2-Methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine (PF-04455242; a highly selective KOR-antagonist). Subsequently, the defensive burying behavior (DBB) and alcohol intake/preference paradigms were evaluated. RESULTS: SAL-A markedly increased burying time, the height of bedding, and alcohol consumption/preference in A-withdrawal, while slightly increased the height of bedding in A-näive rats. PF-04455242 decreased both burying and immobility duration, whereas increases latency to burying, frequency of rearing, and the number of stretches attempts with no action on alcohol intake/preference in A-withdrawal rats. CONCLUSIONS: In general, stimulation/blockade of KOR in A-withdrawal animals exert higher responses compared to A-naïve ones. SAL-A produced anxiety-like behaviors and increased alcohol consumption/preference, especially/solely in the alcohol-withdrawal condition, while PF-04455242 augmented exploration with no effects on alcohol intake/preference. Our findings suggest a possible pharmacologic hyperreactivity of the KOR in PAG during alcohol withdrawal.
Assuntos
Alcoolismo , Síndrome de Abstinência a Substâncias , Ratos , Masculino , Animais , Receptores Opioides kappa/agonistas , Receptores Opioides kappa/metabolismo , Substância Cinzenta Periaquedutal , Ratos WistarRESUMO
The central nucleus of the amygdala (CeA) is involved in the expression of fear and anxiety disorders. Anatomically, it is divided into medial (CeM), lateral (CeL), and capsular (CeC) divisions. The CeA is densely innervated by dopaminergic projections that originate in the ventral periaqueductal gray/dorsal raphe (vPAG/DR) and the ventral tegmental area (VTA). However, whether dopamine (DA) exerts a homogenous control over the CeA or differentially regulates the various CeA subdivisions is still unknown. Here, we performed a neuroanatomical analysis of the mouse CeA and found that DAergic innervations from the PAG/DR and VTA constitute distinct, non-overlapping, pathways differing also in the relative expression of the dopamine transporter. By quantifying the distribution of DAergic fibers and the origin of DA inputs we identified two distinct regions in the CeL: a frontal region innervated by the VTA and vPAG/DR, a caudal region innervated only by the vPAG/DR, and three distinct regions in the CeC: fronto-dorsal innervated only by the VTA, fronto-ventral with sparse DAergic innervation, and a caudal region with low innervation from the vPAG/DR. In addition, we found that each region displays a distinct pattern of c-Fos activation following the administration of various DAeric drugs such as cocaine, SKF 38,393, quinpirole or haloperidol. In summary, we revealed unique properties of the DAergic pathways innervating the CeA, distinguishing six topographically segregated and functionally distinct regions. This unanticipated level of heterogeneity calls for more precise neuroanatomical specificity in future functional studies of the CeA.
Assuntos
Núcleo Central da Amígdala , Dopamina , Camundongos , Animais , Dopamina/metabolismo , Núcleo Central da Amígdala/metabolismo , Substância Cinzenta Periaquedutal/metabolismo , Núcleo Dorsal da Rafe , Área Tegmentar Ventral/metabolismoRESUMO
The cuneiform nucleus (CUN) is a midbrain structure located lateral to the caudal part of the periaqueductal gray. In the present investigation, we first performed a systematic analysis of the afferent and efferent projections of the CUN using FluoroGold and Phaseolus vulgaris leucoagglutinin as retrograde and anterograde neuronal tracers, respectively. Next, we examined the behavioral responses to optogenetic activation of the CUN and evaluated the impact of pharmacological inactivation of the CUN in both innate and contextual fear responses to a predatory threat (i.e., a live cat). The present hodologic evidence indicates that the CUN might be viewed as a caudal component of the periaqueductal gray. The CUN has strong bidirectional links with the dorsolateral periaqueductal gray (PAGdl). Our hodological findings revealed that the CUN and PAGdl share a similar source of inputs involved in integrating information related to life-threatening events and that the CUN provides particularly strong projections to brain sites influencing antipredatory defensive behaviors. Our functional studies revealed that the CUN mediates innate freezing and flight antipredatory responses but does not seem to influence the acquisition and expression of learned fear responses.
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Formação Reticular Mesencefálica , Substância Cinzenta Periaquedutal , Substância Cinzenta Periaquedutal/fisiologia , NeurôniosRESUMO
Background: Resting-state functional connectivity (rs-FC) may aid in understanding the link between pain-modulating brain regions and the descending pain modulatory system (DPMS) in fibromyalgia (FM). This study investigated whether the differences in rs-FC of the primary somatosensory cortex in responders and non-responders to the conditioned pain modulation test (CPM-test) are related to pain, sleep quality, central sensitization, and the impact of FM on quality of life. Methods: This cross-sectional study included 33 females with FM. rs-FC was assessed by functional magnetic resonance imaging. Change in the numerical pain scale during the CPM-test assessed the DPMS function. Subjects were classified either as non-responders (i.e., DPMS dysfunction, n = 13) or responders (n = 20) to CPM-test. A generalized linear model (GLM) and a receiver operating characteristic (ROC) curve analysis were performed to check the accuracy of the rs-FC to differentiate each group. Results: Non-responders showed a decreased rs-FC between the left somatosensory cortex (S1) and the periaqueductal gray (PAG) (P < 0.001). The GLM analysis revealed that the S1-PAG rs-FC in the left-brain hemisphere was positively correlated with a central sensitization symptom and negatively correlated with sleep quality and pain scores. ROC curve analysis showed that left S1-PAG rs-FC offers a sensitivity and specificity of 85% or higher (area under the curve, 0.78, 95% confidence interval, 0.63-0.94) to discriminate who does/does not respond to the CPM-test. Conclusions: These results support using the rs-FC patterns in the left S1-PAG as a marker for predicting CPM-test response, which may aid in treatment individualization in FM patients.
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Serotonin 5-hydroxytryptamine (5-HT) is a key neurotransmitter for the modulation and/or regulation of numerous physiological processes and psychiatric disorders (e.g., behaviors related to anxiety, pain, aggressiveness, etc.). The periaqueductal gray matter (PAG) is considered an integrating center for active and passive defensive behaviors, and electrical stimulation of this area has been shown to evoke behavioral responses of panic, fight-flight, freezing, among others. The serotonergic activity in PAG is influenced by the activation of other brain areas such as the medial hypothalamus, paraventricular nucleus of the hypothalamus, amygdala, dorsal raphe nucleus, and ventrolateral orbital cortex. In addition, activation of other receptors within PAG (i.e., CB1, Oxytocin, µ-opioid receptor (MOR), and γ-aminobutyric acid (GABAA)) promotes serotonin release. Therefore, this review aims to document evidence suggesting that the PAG-evoked behavioral responses of anxiety, panic, fear, analgesia, and aggression are influenced by the activation of 5-HT1A and 5-HT2A/C receptors and their participation in the treatment of various mental disorders.
Assuntos
Substância Cinzenta Periaquedutal , Serotonina , Humanos , Substância Cinzenta Periaquedutal/fisiologia , Emoções , Ansiedade , Núcleo Dorsal da RafeRESUMO
Connectomics is an important field of neuroscience that examines how neurons are connected and form functional circuits that underly the brain's functions. Conventional tracers based on dye have led to great advances in mapping these connections, and now, neurotropic viruses are contributing to connectomics. In this work, two retrograde adeno-associated virus failed to transduce in projections from hypothalamic neurons to periaqueductal gray matter (PAG) but worked well in cortical connections to PAG. One of this virus also marked a substantial amount of PAG efferent projections, therefore working as an anterograde tracer. We also used hydroxystilbamidine (FluoroGold™) as a gold standard in retrograde tracing for comparison with the projections shown by the retrograde virus. As determined in past works, FluoroGold™ shows connections from the hypothalamus and cortex to the PAG. Also, an anterograde AAV was compared with one of the retrograde AAV, which showed a similar pattern of axonal projections and terminal fields. Hence, although neurotropic viruses are revolutionizing connectomics and other areas, their mechanism, neurotropism, and cell invasion need to be addressed. Their use is a great challenge and requires further studies to clarify their interaction with the nervous system's cells.
RESUMO
Defensive responses are neurophysiological processes crucial for survival during threatening situations. Defensive immobility is a common adaptive response, in rodents, elaborated by ventrolateral periaqueductal gray matter (vlPAG) when threat is unavoidable. It is associated with somatosensory and autonomic reactions such as alteration in the sensation of pain and rate of respiration. In this study, defensive immobility was assessed by chemical stimulation of vlPAG with different doses of NMDA (0.1, 0.3, and 0.6 nmol). After elicitation of defensive immobility, antinociceptive and respiratory response tests were also performed. Results revealed that defensive immobility was followed by a decrease in the nociceptive perception. Furthermore, the lowest dose of NMDA induced antinociceptive response without eliciting defensive immobility. During defensive immobility, respiratory responses were also disturbed. Interestingly, respiratory rate was increased and interspersed with prolonged expiratory phase of breathing. These findings suggest that vlPAG integrates three different defensive behavioral responses, contributing to the most effective defensive strategies during threatening situations.
Assuntos
Dor , Substância Cinzenta Periaquedutal , HumanosRESUMO
We examined the behavioral responses and Fos expression pattern of rats that were exposed to snake threats from shed snakeskin and a live snake. We differentiated the behavioral responses and the pattern of Fos expression in response to the odor cues and mild threat from a live snake. Animals exposed to the snake odor alone or to the confined snake showed a great deal of risk assessment. Conversely, the intensification of odor during exposure to the live snake decreased the threat ambiguity, and the animals froze for a significantly longer period. Our Fos analysis showed that a pathway formed by the posteroventral part of the medial amygdalar nucleus to the central part of the ventromedial hypothalamic nucleus appeared to be solely responsive to odor cues. In addition, we showed increased Fos expression in a parallel circuit comprising the lateral amygdalar nucleus, ventral subiculum, lateral septum and juxtadorsomedial region of the lateral hypothalamic area that is responsive to both the odor and mild threat from a live snake. This path is likely to process the environmental boundaries of the threat to be avoided. Both paths merge into the dorsal premammillary nucleus and periaqueductal gray sites, which all increase Fos expression in response to the snake threats and are likely to organize the defensive responses. Moreover, we found that the snake threat mobilized the Edinger-Westphal and supraoculomotor nuclei, which are involved in stress adaptation and attentional mechanisms.
RESUMO
The periaqueductal gray matter (PAG) is an essential structure involved in the elaboration of defensive responses, such as when facing predators and conspecific aggressors. Using a prey vs predator paradigm, we aimed to evaluate the PAG activation pattern evoked by unconditioned and conditioned fear situations. Adult male guinea pigs were confronted either by a Boa constrictor constrictor wild snake or by the aversive experimental context. After the behavioral test, the rodents were euthanized and the brain prepared for immunohistochemistry for Fos protein identification in different PAG columns. Although Fos-protein-labeled neurons were found in different PAG columns after both unconditioned and conditioned fear situations at the caudal level of the PAG, we found greater activation of the lateral column compared to the ventrolateral and dorsomedial columns after predator exposure. Moreover, the lateral column of the PAG showed higher Fos-labeled cells at the caudal level compared to the same area at the rostral level. The present results suggested that there are different activation patterns of PAG columns during unconditioned and conditioned fear in guinea pigs. It is possible to hypothesize that the recruitment of specific PAG columns depended on the nature of the threatening stimulus.
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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.
Assuntos
Comportamento Animal/efeitos dos fármacos , Diestro/efeitos dos fármacos , Núcleo Dorsal da Rafe/efeitos dos fármacos , Fluoxetina/farmacologia , Hipóxia/complicações , Pânico/efeitos dos fármacos , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Inibidores Seletivos de Recaptação de Serotonina/farmacologia , Caracteres Sexuais , Animais , Modelos Animais de Doenças , Feminino , Masculino , Ciclo Menstrual/efeitos dos fármacos , Transtorno de Pânico/tratamento farmacológico , Ratos , Ratos Sprague-Dawley , Inibidores Seletivos de Recaptação de Serotonina/administração & dosagemRESUMO
GPR55 is a receptor expressed in several central nervous system areas, including the periaqueductal gray (PAG). Current knowledge of GPR55 physiology in PAG only covers pain integration, but it is involved in other actions such as anxiety, panic, motivated behaviors, and alcohol intake. In the present study, juvenile male Wistar rats were unexposed (alcohol-naïve group; A-naïve) or exposed to alcohol for 5 weeks (alcohol-pre-exposed group; A-pre-exposed). Posteriorly, animals received intra dorsal-PAG (D-PAG) injections of vehicle (10% DMSO), LPI (1 nmol/0.5 µl) and ML-193 (1 nmol/0.5 µl, a selective GPR55 antagonist). Finally, defensive burying behavior (DBB) paradigm and alcohol preference were evaluated. Compared to the A-naïve group, the A-pre-exposed vehicle group had higher (p < 0.05): (i) time of immobility; (ii) latency to and duration of burying; and (iii) alcohol consumption. In both groups (i.e., A-naïve and A-pre-exposed) treatment with LPI: (i) decreased duration of burying (p < 0.05); (ii) suppressed time of immobility; and (iii) increased alcohol intake (p < 0.05). On the other hand, treatment with ML-193: (i) decreased duration of immobility in A-pre-exposed (but not in A-naïve rats); (ii) promoted an aggressive response against the shock-probe in A-pre-exposed rats (p < 0.05); and (iii) increased alcohol intake (p < 0.05). Our results suggest that blockade of GPR55 in D-PAG is associated with anxiety-like behaviors, defensive aggressive behaviors, and higher alcohol intake, whereas LPI in D-PAG produced anxiolytic-like effects (probably GPR55-mediated), but not prevention of alcohol intake.
Assuntos
Agressão/efeitos dos fármacos , Consumo de Bebidas Alcoólicas/fisiopatologia , Ansiedade/induzido quimicamente , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Receptores Acoplados a Proteínas G/antagonistas & inibidores , Agressão/fisiologia , Animais , Ansiedade/fisiopatologia , Comportamento Animal , Lisofosfolipídeos/administração & dosagem , Masculino , Modelos Animais , Substância Cinzenta Periaquedutal/metabolismo , Substância Cinzenta Periaquedutal/fisiopatologia , Ratos , Receptores de Canabinoides/metabolismo , Receptores Acoplados a Proteínas G/metabolismoRESUMO
The periaqueductal gray (PAG) is a complex mesencephalic structure involved in the integration and execution of active and passive self-protective behaviors against imminent threats, such as immobility or flight from a predator. PAG activity is also associated with the integration of responses against physical discomfort (e.g., anxiety, fear, pain, and disgust) which occurs prior an imminent attack, but also during withdrawal from drugs such as morphine and cocaine. The PAG sends and receives projections to and from other well-documented nuclei linked to the phenomenon of drug addiction including: (i) the ventral tegmental area; (ii) extended amygdala; (iii) medial prefrontal cortex; (iv) pontine nucleus; (v) bed nucleus of the stria terminalis; and (vi) hypothalamus. Preclinical models have suggested that the PAG contributes to the modulation of anxiety, fear, and nociception (all of which may produce physical discomfort) linked with chronic exposure to drugs of abuse. Withdrawal produced by the major pharmacological classes of drugs of abuse is mediated through actions that include participation of the PAG. In support of this, there is evidence of functional, pharmacological, molecular. And/or genetic alterations in the PAG during the impulsive/compulsive intake or withdrawal from a drug. Due to its small size, it is difficult to assess the anatomical participation of the PAG when using classical neuroimaging techniques, so its physiopathology in drug addiction has been underestimated and poorly documented. In this theoretical review, we discuss the involvement of the PAG in drug addiction mainly via its role as an integrator of responses to the physical discomfort associated with drug withdrawal.
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Substância Cinzenta Periaquedutal , Transtornos Relacionados ao Uso de Substâncias , Tonsila do Cerebelo , Humanos , Morfina , NociceptividadeRESUMO
Antidepressant drugs are first-line treatment for panic disorder. Facilitation of 5-HT1A receptor-mediated neurotransmission in the dorsal periaqueductal gray (dPAG), a key panic-associated area, has been implicated in the panicolytic effect of the selective serotonin reuptake inhibitor fluoxetine. However, it is still unknown whether this mechanism accounts for the antipanic effect of other classes of antidepressants drugs (ADs) and whether the 5-HT interaction with 5-HT2C receptors in this midbrain area (which increases anxiety) is implicated in the anxiogenic effect caused by short-term treatment with ADs. The results showed that previous injection of the 5-HT1A receptor antagonist WAY-100635 in the dPAG blocked the panicolytic-like effect caused by chronic systemic administration of the tricyclic AD imipramine in male Wistar rats tested in the elevated T-maze. Neither chronic treatment with imipramine nor fluoxetine changed the expression of 5-HT1A receptors in the dPAG. Treatment with these ADs also failed to significantly change ERK1/2 (extracellular-signal regulated kinase) phosphorylation level in this midbrain area. Blockade of 5-HT2C receptors in the dPAG with the 5-HT2C receptor antagonist SB-242084 did not change the anxiogenic effect caused by a single acute injection of fluoxetine or imipramine in the Vogel conflict test. These results reinforce the view that the facilitation of 5-HT1A receptor-mediated neurotransmission in the dPAG is a common mechanism involved in the panicolytic effect caused by chronic administration of ADs. On the other hand, the anxiogenic effect observed after short-term treatment with these drugs does not depend on 5-HT2C receptors located in the dPAG.
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Antidepressivos/farmacologia , Ansiedade/tratamento farmacológico , Pânico/efeitos dos fármacos , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Receptor 5-HT1A de Serotonina/fisiologia , Receptor 5-HT2C de Serotonina/fisiologia , Aminopiridinas/farmacologia , Animais , Western Blotting , Teste de Labirinto em Cruz Elevado , Fluoxetina/farmacologia , Imipramina/farmacologia , Indóis/farmacologia , Masculino , Teste de Campo Aberto/efeitos dos fármacos , Substância Cinzenta Periaquedutal/metabolismo , Substância Cinzenta Periaquedutal/fisiologia , Piperazinas/farmacologia , Piridinas/farmacologia , Ratos , Ratos Wistar , Receptor 5-HT1A de Serotonina/efeitos dos fármacos , Receptor 5-HT1A de Serotonina/metabolismo , Receptor 5-HT2C de Serotonina/efeitos dos fármacos , Receptor 5-HT2C de Serotonina/metabolismo , Antagonistas do Receptor 5-HT1 de Serotonina/farmacologiaRESUMO
Periaqueductal gray (PAG) is a midbrain region that projects to areas controlling behavioral and autonomic outputs and is involved in the behavioral and physiological components of defense reactions. Since Raphe Pallidus (RPa) is a medial medullary region comprising sympathetic premotor neurons governing heart function, it is worth considering the PAG-RPa path. We assessed: i) whether PAG projects to RPa; ii) the amplitude of cardiac responses evoked from PAG; iii) whether cardiovascular responses evoked from PAG rely on RPa. Experiments conducted in Wistar rats (±300 g) were approved by Ethics Committee CEUA-UFG (092/18). Firstly, (n = 3), monosynaptic retrograde tracer Retrobeads was injected into RPa; PAG slices were analyzed. Other two groups (n = 6 each) were anesthetized with urethane (1.4 g/kg) and chloralose (120 mg/kg) and underwent craniotomy, tracheostomy, catheterization of femoral artery and vein and of cardiac left ventricle. In one group, we injected the GABAA receptor antagonist, bicuculline methiodide (BMI - 40 pmol/100 nL) into lateral/dorsolateral PAG. Another group was injected (100 nL) with the GABAA receptor agonist muscimol (20 mM) into RPa, 20 min before BMI into PAG. The results were: i) retrogradely labelled neurons were found in PAG; ii) PAG activation by BMI caused positive chronotropism and inotropism, which were accompanied by afterload increases; iii) RPa inhibition with Muscimol reduced heart rate, arterial and ventricular pressures; iv) the subsequent PAG activation still increased arterial pressure, cardiac chronotropy and inotropy, but these responses were significantly attenuated. In conclusion, PAG activation increases cardiac chronotropy and inotropy, and these responses seem to rely on a direct pathway reaching ventromedial medullary RPa neurons.
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Pressão Sanguínea/fisiologia , Coração/fisiologia , Núcleo Pálido da Rafe/fisiologia , Substância Cinzenta Periaquedutal/fisiologia , Sistema Nervoso Simpático/fisiologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Agonistas de Receptores de GABA-A/farmacologia , Antagonistas de Receptores de GABA-A/farmacologia , Coração/efeitos dos fármacos , Masculino , Vias Neurais/efeitos dos fármacos , Vias Neurais/fisiologia , Núcleo Pálido da Rafe/efeitos dos fármacos , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Ratos Wistar , Sistema Nervoso Simpático/efeitos dos fármacosRESUMO
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.
Assuntos
Medo/efeitos dos fármacos , N-Metilaspartato/farmacologia , Nociceptividade/efeitos dos fármacos , Substância Cinzenta Periaquedutal/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Receptores Opioides mu/metabolismo , Analgésicos Opioides/farmacologia , Animais , Ácidos Araquidônicos/farmacologia , Comportamento Animal/efeitos dos fármacos , Agonistas de Receptores de Canabinoides/farmacologia , Antagonistas de Receptores de Canabinoides/farmacologia , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , Agonistas de Aminoácidos Excitatórios/farmacologia , Reação de Congelamento Cataléptica/efeitos dos fármacos , Masculino , Microinjeções , Dor/tratamento farmacológico , Dor/metabolismo , Medição da Dor/efeitos dos fármacos , Piperidinas/farmacologia , Pirazóis/farmacologia , Ratos , Receptores Opioides mu/agonistas , Receptores Opioides mu/antagonistas & inibidores , Somatostatina/análogos & derivados , Somatostatina/farmacologiaRESUMO
Growing evidence suggests an important role of fluoxetine with serotonin 5-HT1A and 5-HT2C receptors in the modulation of emotion and nociception in brain areas such as the amygdala and periaqueductal gray (PAG). Acute fluoxetine impairs 5-HT2C (but not 5-HT1A) receptor activation in the amygdaloid complex. Given that fluoxetine produces its clinical therapeutic effects only when given chronically, this study investigated the effects of chronic treatment with fluoxetine on the effects produced by 5-HT1A or 5-HT2C receptors activation in the amygdala or PAG on fear-induced antinociception. We recorded the effects of chronic fluoxetine on serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) levels as well as serotonin turnover; 5-HT1A and 5-HT2C receptor protein levels in the amygdala and PAG. Also, we evaluated the effects of chronic fluoxetine combined with intra-amygdala or intra-PAG injection of MK-212 (a 5-HT2C agonist; 0.63 nmol) or 8-OH-DPAT (a 5-HT1A agonist; 10 nmol) on the antinociceptive response in mice confined in the open arm of the elevated plus-maze (EPM). Nociception was assessed with the writhing test induced by intraperitoneal injection of 0.6% acetic acid. Results showed that fluoxetine (20 mg/kg, s.c.) enhanced the open-arm induced antinociception (OAA) and reduced the number of writhes in mice confined in the enclosed arm, featuring an analgesic effect. In addition, fluoxetine increased the expression of 5-HT2C receptors and 5-HT levels whereas reduced its turnover in the amygdala. While fluoxetine did not change 5-HT and 5-HIAA levels, and its turnover in the PAG, it up-regulated 5HT1A and 5-HT2C receptors in this midbrain area. Chronic fluoxetine (5.0 mg/Kg, an intrinsically inactive dose on nociception) antagonized the enhancement of OAA produced by intra-amygdala or intra-PAG injection of MK-212. Fluoxetine also impaired the attenuation of OAA induced by intra-amygdala injection of 8-OH-DPAT and totally prevented OAA in mice that received intra-PAG 8-OH-DPAT. These results suggest that (i) 5-HT may facilitate nociception and intensify OAA, acting at amygdala 5-HT1A and 5-HT2C receptors, respectively, and (ii) fluoxetine modulates the OAA through activation of 5-HT2C receptors within the PAG. These findings indicate that chronic fluoxetine impairs the effects of 5-HT1A and 5-HT2C receptors activation in the amygdala and PAG on fear-induced antinociception in mice.
RESUMO
OBJECTIVE Motor cortex stimulation (MCS) is a neurosurgical technique used to treat patients with refractory neuropathic pain syndromes. MCS activates the periaqueductal gray (PAG) matter, which is one of the major centers of the descending pain inhibitory system. However, the neurochemical mechanisms in the PAG that underlie the analgesic effect of MCS have not yet been described. The main goal of this study was to investigate the neurochemical mechanisms involved in the analgesic effect induced by MCS in neuropathic pain. Specifically, we investigated the release of g-aminobutyric acid (GABA), glycine, and glutamate in the PAG and performed pharmacological antagonism experiments to validate of our findings. METHODS Male Wistar rats with surgically induced chronic constriction of the sciatic nerve, along with sham-operated rats and naive rats, were implanted with both unilateral transdural electrodes in the motor cortex and a microdialysis guide cannula in the PAG and subjected to MCS. The MCS was delivered in single 15-minute sessions. Neurotransmitter release was evaluated in the PAG before, during, and after MCS. Quantification of the neurotransmitters GABA, glycine, and glutamate was performed using a high-performance liquid chromatography system. The mechanical nociceptive threshold was evaluated initially, on the 14th day following the surgery, and during the MCS. In another group of neuropathic rats, once the analgesic effect after MCS was confirmed by the mechanical nociceptive test, rats were microinjected with saline or a glycine antagonist (strychnine), a GABA antagonist (bicuculline), or a combination of glycine and GABA antagonists (strychnine+bicuculline) and reevaluated for the mechanical nociceptive threshold during MCS. RESULTS MCS reversed the hyperalgesia induced by peripheral neuropathy in the rats with chronic sciatic nerve constriction and induced a significant increase in the glycine and GABA levels in the PAG in comparison with the naive and sham-treated rats. The glutamate levels remained stable under all conditions. The antagonism of glycine, GABA, and the combination of glycine and GABA reversed the MCS-induced analgesia. CONCLUSIONS These results suggest that the neurotransmitters glycine and GABA released in the PAG may be involved in the analgesia induced by cortical stimulation in animals with neuropathic pain. Further investigation of the mechanisms involved in MCS-induced analgesia may contribute to clinical improvements for the treatment of persistent neuropathic pain syndromes
RESUMO
Exposure to stressful conditions induces long-lasting neurobiological changes in selected brain areas, which could be associated with the emergence of negative emotional responses. Moreover, the interaction of a stressful experience and the retrieval of an established fear memory trace enhance both fear expression and fear retention. Related to this, the stimulation of the dorsolateral part of the mesencephalic periaqueductal gray matter (dlPAG) prior to retrieval potentiates a fear memory trace previously acquired. Therefore, the question that arises is whether the dlPAG mediates the increased fear expression and fear retention after retrieval. Rats were subjected to a contextual fear conditioning paradigm using a single footshock, and 1 day later, rats were subjected to a stressful situation. As previously reported, there was an increase of freezing response only in those rodents that were re-exposed to the associated context at 1 and 5 days after stress exposure. Muscimol intra-dlPAG prior to the restraint event prevented such increase. Conversely, Muscimol intra-dlPAG infusion immediately after the stress experience had no effect on the resulting fear memory. When the neuroendocrine response to stress was explored, intra-dlPAG infusion of muscimol prior to stress decreased Fos expression in the paraventricular nucleus and serum corticosterone levels. Moreover, this treatment prevented the enhancement of the density of hippocampal "mature" spines associated with fear memory. In conclusion, the present results suggest that the dlPAG is a key neural site for the negative valence instruction necessary to modulate the promoting influence of stress on fear memory.