Tempering aversive/traumatic memories with cannabinoids: a review of evidence from animal and human studies.

RATIONALE: Aversive learning and memory are essential to cope with dangerous and stressful stimuli present in an ever-changing environment. When this process is dysfunctional, however, it is associated with posttraumatic stress disorder (PTSD). The endocannabinoid (eCB) system has been implicated in synaptic plasticity associated with physiological and pathological aversive learning and memory. OBJECTIVE AND METHODS: The objective of this study was to review and discuss evidence on how and where in the brain genetic or pharmacological interventions targeting the eCB system would attenuate aversive/traumatic memories through extinction facilitation in laboratory animals and humans. The effect size of the experimental intervention under investigation was also calculated. RESULTS: Currently available data indicate that direct or indirect activation of cannabinoid type-1 (CB1) receptor facilitates the extinction of aversive/traumatic memories. Activating CB1 receptors around the formation of aversive/traumatic memories or their reminders can potentiate their subsequent extinction. In most cases, the effect size has been large (Cohen's d ≥ 1.0). The brain areas responsible for the abovementioned effects include the medial prefrontal cortex, amygdala, and/or hippocampus. The potential role of cannabinoid type-2 (CB2) receptors in extinction learning is now under investigation. CONCLUSION: Drugs augmenting the brain eCB activity can temper the impact of aversive/traumatic experiences by diverse mechanisms depending on the moment of their administration. Considering the pivotal role the extinction process plays in PTSD, the therapeutic potential of these drugs is evident. The sparse number of clinical trials testing these compounds in stress-related disorders is a gap in the literature that needs to be addressed.

Elastase-2 Knockout Mice Display Anxiogenic- and Antidepressant-Like Phenotype: Putative Role for BDNF Metabolism in Prefrontal Cortex.

Several pieces of evidence indicate that elastase-2 (ELA2; chymotrypsin-like ELA2) is an alternative pathway to the generation of angiotensin II (ANGII). Elastase-2 knockout mice (ELA2KO) exhibit alterations in the arterial blood pressure and heart rate. However, there is no data on the behavioral consequences of ELA2 deletion. In this study, we addressed this question, submitting ELA2KO and wild-type (WT) mice to several models sensitive to anxiety- and depression-like, memory, and repetitive behaviors. Our data indicates a higher incidence of barbering behavior in ELA2KO compared to WT, as well as an anxiogenic phenotype, evaluated in the elevated plus maze (EPM). While a decrease in locomotor activity was observed in ELA2KO in EPM, this feature was not the main source of variation in the other parameters analyzed. The marble-burying test (MBT) indicated increase in repetitive behavior, observed by a higher number of buried marbles. The actimeter test indicated a decrease in total activity and confirmed the increase in repetitive behavior. The spatial memory was tested by repeated exposure to the actimeter in a 24-h interval. Both ELA2KO and WT exhibited decreased activity compared to the first exposure, without any distinction between the genotypes. However, when submitted to the cued fear conditioning, ELA2KO displayed lower levels of freezing behavior in the extinction session when compared to WT, but no difference was observed during the conditioning phase. Increased levels of BDNF were found in the prefrontal cortex but not in the hippocampus of ELA2KO mice compared to WT. Finally, in silico analysis indicates that ELA2 is putatively able to cleave BDNF, and incubation of the purified enzyme with BDNF led to the degradation of the latter. Our data suggested an anxiogenic- and antidepressant-like phenotype of ELA2KO, possibly associated with increased levels of BDNF in the prefrontal cortex.

P2X7 purinergic receptors participate in the expression and extinction processes of contextual fear conditioning memory in mice.

The purinergic system consists of two large receptor families - P2X and P2Y. Both are activated by adenosine triphosphate (ATP), although presenting different functions. These receptors are present in several brain regions, including those involved in emotion and stress-related behaviors. Hence, they seem to participate in fear- and anxiety-related responses. However, few studies have investigated the purinergic system in threatening situations, as observed in contextual fear conditioning (CFC). Therefore, this study investigated the involvement of purinergic receptors in the expression and extinction of aversive memories. C57Bl/6 background mice were submitted to the CFC protocol. Wildtype (WT) mice received i.p. injection of either a nonselective P2 receptor (P2R) antagonist, P178 (10 or 30 mg/kg); a selective P2X7 receptor (P2X7R) antagonist, A438079 (10 mg/kg); a selective P2Y1 receptor (P2Y1R) antagonist, MRS2179 (10 mg/kg); or vehicle 10 min prior to or immediately after the extinction session. Additionally, P2X7R KO mice were tested in the CFC protocol. After P2R antagonist treatment, contextual fear recall increased, while acquisition of extinction was impaired. Similar results were observed with the selective P2X7R antagonist, but not with the selective P2Y1R antagonist. Interestingly, P2X7R KO mice showed increased contextual fear recall, associated with impaired acquisition of extinction, in accordance with pharmacologic P2X7R antagonism. Our results suggest that specific pharmacological or genetic blockade of P2X7R promotes anxiogenic-like effects, along with deficits in extinction learning. Thus, these receptors could present an alternative treatment of stress-related psychiatric disorders.

A single episode of high intensity sound inhibits long-term potentiation in the hippocampus of rats.

Exposure to loud sounds has become increasingly common. The most common consequences of loud sound exposure are deafness and tinnitus, but emotional and cognitive problems are also associated with loud sound exposure. Loud sounds can activate the hipothalamic-pituitary-adrenal axis resulting in the secretion of corticosterone, which affects hippocampal synaptic plasticity. Previously we have shown that long-term exposure to short episodes of high intensity sound inhibited hippocampal long-term potentiation (LTP) without affecting spatial learning and memory. Here we aimed to study the impact of short term loud sound exposure on hippocampal synaptic plasticity and function. We found that a single minute of 110 dB sound inhibits hippocampal Schaffer-CA1 LTP for 24 hours. This effect did not occur with an 80-dB sound exposure, was not correlated with corticosterone secretion and was also observed in the perforant-dentate gyrus synapse. We found that despite the deficit in the LTP these animals presented normal spatial learning and memory and fear conditioning. We conclude that a single episode of high-intensity sound impairs hippocampal LTP, without impairing memory and learning. Our results show that the hippocampus is very responsive to loud sounds which can have a potential, but not yet identified, impact on its function.

The Endocannabinoid System and Anxiety.

The medical properties of Cannabis sativa is known for centuries. Since the discovery and characterization of the endogenous cannabinoid system, several studies have evaluated how cannabinoid compounds and, particularly, how the modulation of the endocannabinoid (eCB) system influences a wide range of functions, from metabolic to mental disorders. Cannabinoids and eCB system often exert opposite effects on several functions, such as anxiety. Although the mechanisms are not completely understood, evidence points to different factors influencing those effects. In this chapter, the recent advances in research about the relationship between eCB system and anxiety disorders in humans, as well as in animal models, will be discussed. The recent data addressing modulation of the eCBs in specific brain areas, such as the medial prefrontal cortex, amygdaloid complex, bed nucleus of stria terminalis, hippocampus, and dorsal periaqueductal gray, will be summarized. Finally, data from animal models addressing the mechanisms through which the eCB system modulates anxiety-related behavior dependent on stressful situations, such as the involvement of different receptors, distinct eCBs, modulation of neurotransmitters release, HPA axis and immune system activation, and plastic mechanisms, will also be discussed.

NMDA and non-NMDA glutamate receptors in the paraventricular nucleus of the hypothalamus modulate different stages of hemorrhage-evoked cardiovascular responses in rats.

Here we report the involvement of N-Methyl-d-Aspartate (NMDA) and non-NMDA glutamate receptors from the paraventricular nucleus of the hypothalamus (PVN) in the mediation of cardiovascular changes observed during hemorrhage and post-bleeding periods. In addition, the present study provides further evidence of the involvement of circulating vasopressin and cardiac sympathetic activity in cardiovascular responses to hemorrhage. Systemic treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP (50 µg/kg, i.v.) increased the latency to the onset of hypotension during hemorrhage and slowed post-bleeding recovery of blood pressure. Systemic treatment with the ß1-adrenergic receptor antagonist atenolol (1 mg/kg, i.v.) also increased the latency to the onset of hypotension during hemorrhage. Moreover, atenolol reversed the hemorrhage-induced tachycardia into bradycardia. Bilateral microinjection of the selective NMDA glutamate receptor antagonist LY235959 (2 nmol/100 nL) into the PVN blocked the hypotensive response to hemorrhage and reduced the tachycardia during the post-hemorrhage period. Systemic treatment with dTyr(CH2)5(Me)AVP inhibited the effect of LY235959 on hemorrhage-induced hypotension, without affecting the post-bleeding tachycardia. PVN treatment with the selective non-NMDA receptor antagonist NBQX (2 nmol/100 nL) reduced the recovery of blood pressure to normal levels in the post-bleeding phase and reduced hemorrhage-induced tachycardia. Combined blockade of both NMDA and non-NMDA glutamate receptors in the PVN completely abolished the hypotensive response in the hemorrhage period and reduced the tachycardiac response in the post-hemorrhage period. These results indicate that local PVN glutamate neurotransmission is involved in the neural pathway mediating cardiovascular responses to hemorrhage, via an integrated control involving autonomic nervous system activity and vasopressin release into the circulation.

Involvement of M1 and CB1 receptors in the anxiogenic-like effects induced by neostigmine injected into the rat prelimbic medial prefrontal cortex.

The prelimbic (PL) medial prefrontal cortex is a brain region highly involved in the control of emotional responses, being modulated by several neurotransmitter systems, including the cholinergic and endocannabinoid. Activation of muscarinic type 1 (M1) receptors in the brain induces retrograde suppression of inhibition through the induction of endocannabinoid release, which, in turn, activates cannabinoid type 1 (CB1) receptors. No study so far, however, has been conducted to investigate if the cholinergic and endocannabinoid systems interact in the PL to modulate anxiety-related behaviors. Thus, the present work aimed at verifying if intra-PL administration of neostigmine, an acetylcholinesterase inhibitor, would produce changes in anxiety-like behavior and if these effects are mediated by M1 and CB1 receptor activation. Independent groups of animals received bilateral injections of vehicle, the M1 receptor antagonist pirenzepine (0.06, 0.6, and 6 nmol), the CB1 receptor antagonist AM251 (0.1 nmol), or the fatty acid amide hydrolase (FAAH) enzyme inhibitor URB597 (1, 3, and 10 pmol), followed by vehicle or neostigmine (0.01, 0.1, and 1 nmol), and were submitted to the elevated plus-maze (EPM) test. Neostigmine (1 nmol) decreased open arm exploration of the maze. This anxiogenic-like effect was reproduced in another anxiety-related animal model, the light-dark box. Previous injection of pirenzepine or AM251 abolished this response in the EPM, whereas URB597 had no effect. These results suggest that CB1 and M1 receptors interact in the PL to control anxiety-like behaviors.

Dorsolateral periaqueductal gray matter CB1 and TRPV1 receptors exert opposite modulation on expression of contextual fear conditioning.

Cannabinoid type 1 (CB1) and Transient Potential Vanilloid type 1 (TRPV1) receptors in the dorsolateral periaqueductal gray (dlPAG) matter are involved in the modulation of conditioned response. Both CB1 and TRPV1 receptors are related to glutamate release and nitric oxide (NO) synthesis. It was previously demonstrated that both NMDA glutamate receptors and NO are involved in the conditioned emotional response. Therefore, one aim of this work was to verify whether dlPAG CB1 and TRPV1 receptors modulate the expression of contextual conditioned emotional response. Moreover, we also investigated the involvement of NMDA receptors and the NO pathway in this response. Male Wistar rats with local dlPAG guide cannula were submitted to contextual fear conditioning. Following 24 h, a polyethylene catheter was implanted in the femoral artery for cardiovascular recordings. After an additional 24 h, drugs were administered in the dlPAG and freezing behavior and autonomic responses were recorded during chamber re-exposure. Both a CB1 antagonist (AM251) and a TRPV1 agonist (Capsaicin; CPS) increased the expression of a conditioned emotional response. This response was prevented by an NMDA antagonist, a preferential neuronal NO synthase inhibitor, an NO scavenger and a soluble guanylate cyclase inhibitor (sGC). Furthermore, pretreatment with a TRPV1 antagonist also prevented the increased conditioned emotional response induced by AM251. Considering that GABA can counterbalance glutamate effects, we also investigated whether GABAA receptors were involved in the effect of a higher dose of AM251. Pretreatment with a GABAA receptor antagonist caused an increased conditioned emotional response by AM251. Our results support the possibility that dlPAG CB1 and TRPV1 receptors are involved in the expression of conditioned emotional response through the NMDA/NO/sGC pathway. Moreover, the opposite effects exerted by GABA and glutamate could produce different outcomes of drugs modulating eCBs.

M3 muscarinic receptor in the ventral medial prefrontal cortex modulating the expression of contextual fear conditioning in rats.

RATIONALE: Basal forebrain cholinergic neurons modulate the activation of cortical neurons by several stimuli such as fear and anxiety. However, the role of the muscarinic receptor in the medial prefrontal cortex (MPFC) in the modulation of the conditioned emotional response (CER) evoked in the model contextual conditioned fear remains unclear. OBJECTIVES: The objective of this study is to test the hypothesis that inhibition of the muscarinic receptor in ventral MPFC modulates CER observed during animal's re-exposure to the aversive context. METHODS: Rats implanted with cannulae aimed at the prelimbic (PL) or the infralimbic (IL) were submitted to a high-intensity contextual fear conditioning protocol. Before the test session, they received microinjections of the hemicholinium (choline reuptake blocker), atropine (muscarinic antagonist), J104129 fumarate (M1-M3 muscarinic antagonists), pirenzepine (M1 muscarinic antagonist), neostigmine (inhibitor acetylcholinesterase enzyme), or the systemic administration of the FG7142 (inverse benzodiazepine agonist). Additional independent groups received the neostigmine or FG7142 before the ineffective doses of J104129 fumarate in the low-intensity protocol of contextual fear conditioning. RESULTS: In the high-intensity protocol, the administration of hemicholinium (1 nmol), atropine (0.06-6 nmol), J104129 fumarate (6 nmol), or pirenzepine (6 nmol) attenuated the expression of CER in rats. However, in the low-intensity protocol, only J10129 fumarate (0.06 nmol) reduced the expression of the CER. Finally, neostigmine (0.1-1 nmol) or FG7142 (8 mg/Kg) increased CER expression, an effect inhibited by the low dose of the J10129 fumarate. CONCLUSIONS: These results indicated that the blockade of M3 muscarinic receptor in the vMPFC attenuates the CER expression.

Medial prefrontal cortex TRPV1 channels modulate the baroreflex cardiac activity in rats.

BACKGROUND AND PURPOSE: The ventral portion of the medial prefrontal cortex (vMPFC) comprises the infralimbic (IL), prelimbic (PL) and dorsopenducular (DP) cortices. The IL and PL regions facilitate the baroreceptor reflex arc. This facilitatory effect on the baroreflex is thought to be mediated by vMPFC glutamatergic transmission, through NMDA receptors. The glutamatergic transmission can be modulated by other neurotransmitters, such as the endocannabinoids, which are agonists of the TRPV1 receptor. TRPV1 channels facilitate glutamatergic transmission in the brain. Thus, we hypothesized that TRPV1 receptors in the vMPFC enhance the cardiac baroreflex response. EXPERIMENTAL APPROACH: Stainless steel guide cannulae were bilaterally implanted into the vMPFC of male Wistar rats. Afterwards, a catheter was inserted into the femoral artery, for recording MAP and HR, and into the femoral vein for assessing baroreflex activation. KEY RESULTS: Microinjections of the TRPV1 receptor antagonists capsazepine and 6-iodo-nordihydrocapsaicin (6-IODO) into the vMPFC reduced the cardiac baroreflex activity in unanaesthetized rats. Capsaicin microinjected into the vMPFC increased the cardiac baroreflex activity in unanaesthetized rats. When an ineffective dose of the TRPV1 receptor antagonist 6-IODO was used, the capsaicin-induced increase in the cardiac baroreflex response was abolished. The higher doses of capsaicin administered into the vMPFC after the ineffective dose of 6-IODO displaced the dose-response curve of the baroreflex parameters to the right, with no alteration in the maximum effect of capsaicin. CONCLUSIONS AND IMPLICATIONS: The results of the present study show that stimulation of the TRPV1 receptors in the vMPFC increases the cardiac baroreceptor reflex response.

Cannabinoid modulation of predator fear: involvement of the dorsolateral periaqueductal gray.

The present study investigated the effects of systemic or intra-dorsolateral periaqueductal gray (dlPAG) administration of CB1 agonists on behavioural changes induced in rats by predator (a live cat) exposure, a model of panic responses. Since nitric oxide (NO) and cannabinoid neurotransmission are proposed to interact in the dlPAG to modulate defensive responses, we also investigated if NO is involved in the biphasic effects of anandamide (AEA) injected into the dlPAG. The results showed that systemic administration of WIN55,212-2 or intra-dlPAG AEA attenuated the defensive behaviours caused by cat exposure. Both compounds produced biphasic curves. The cannabinoid receptor type 1 (CB1) antagonist AM251 prevented the panicolytic effect of AEA whereas a neuronal NOS inhibitor turned the ineffective high dose of AEA into an effective one. These results suggest that modulation of the cannabinoid system could be a target in the treatment of panic disorders. However, the biphasic effects of these compounds could limit their therapeutic potential.

Involvement of dorsal hippocampus glutamatergic and nitrergic neurotransmission in autonomic responses evoked by acute restraint stress in rats.

The dorsal hippocampus (DH) is a structure of the limbic system that is involved in emotional, learning and memory processes. There is evidence indicating that the DH modulates cardiovascular correlates of behavioral responses to stressful stimuli. Acute restraint stress (RS) is an unavoidable stress situation that evokes marked and sustained autonomic changes, which are characterized by elevated blood pressure (BP), intense heart rate (HR) increase and a decrease in cutaneous temperature. In the present study, we investigated the involvement of an N-methyl-D-aspartate (NMDA) glutamate receptor/nitric oxide (NO) pathway of the DH in the modulation of autonomic (arterial BP, HR and tail skin temperature) responses evoked by RS in rats. Bilateral microinjection of the NMDA receptor antagonist AP-7 (10 nmol/500 nL) into the DH attenuated RS-evoked autonomic responses. Moreover, RS evoked an increase in the content of NO2/NO3 in the DH, which are products of the spontaneous oxidation of NO under physiological conditions that can provide an indirect measurement of NO production. Bilateral microinjection of N-propyl-L-arginine (0.1 nmol/500 nL; N-propyl, a neuronal NO synthase (nNOS) inhibitor) or carboxy-PTIO (2 nmol/500 nL; c-PTIO, an NO scavenger) into the DH also attenuated autonomic responses evoked by RS. Therefore, our findings suggest that a glutamatergic system present in the DH is involved in the autonomic modulation during RS, acting via NMDA receptors and nNOS activation. Furthermore, the present results suggest that NMDA receptor/nNO activation has a facilitatory influence on RS-evoked autonomic responses.

Complex interaction between anandamide and the nitrergic system in the dorsolateral periaqueductal gray to modulate anxiety-like behavior in rats.

Stimulation of cannabinoid CB1 receptors or inhibition of nitric oxide synthase (NOS) in the dorsolateral periaqueductal gray (dlPAG) decreases anxiety-like behavior. Moreover, activation of CB1 receptors attenuates flight responses induced by nitric oxide (NO) donors in the dlPAG, suggesting that endocannabinoids and NO could interact to control defensive responses such as anxiety-like behavior. To test this hypothesis male Wistar rats received intra-dlPAG microinjections of anandamide (AEA) or NO inhibitors and were tested in the elevated plus maze (EPM). Combined administration of low and ineffective doses of AEA and the NO scavenger (c-Ptio), the nNOS inhibitor (NPA) or the soluble guanylate cyclase inhibitor (ODQ) induced anxiolytic-like effects. The CB1 receptor antagonist AM251, but not the GABAA receptor antagonist bicuculline, attenuated the effect induced by AEA+c-Ptio combination. No effect, however, was found when anxiolytic doses of these same drugs were administered together. Combination of higher, ineffective doses of AEA and c-Ptio, NPA or ODQ was again anxiolytic. The effect of the former combination was prevented by low and ineffective doses of the GABAA receptor antagonist bicuculline or the GABA synthesis inhibitor L-allilglycine, suggesting that they depend on GABAA-mediated neurotransmission. AM251 was also able to attenuate this effect, indicating that in the presence of NO inhibition, the resultant anxiolytic-like effect could be due to AEA action on CB1 receptors. The present results suggest that the AEA and nitrergic systems exert a complex functional interaction in the dlPAG to modulate anxiety behavior, probably interfering, in addition to glutamate, also with GABAergic mechanisms.

Medial amygdaloid nucleus 5-HT2c receptors are involved in the hypophagic effect caused by zimelidine in rats.

The medial amygdaloid nucleus (MeA) is a sub-region of the amygdaloid complex that has been described as participating in food intake regulation. Serotonin has been known to play an important role in appetite and food intake regulation. Moreover, serotonin 5-HT(2C) and 5-HT(1A) receptors appear to be critical in food intake regulation. We investigated the role of the serotoninergic system in the MeA on feeding behavior regulation in rats. The current study examined the effects on feeding behavior regulation of the serotonin reuptake inhibitor, zimelidine, administered directly into the MeA or given systemically, and the serotoninergic receptors mediating its effect. Our results showed that microinjection of zimelidine (0.2, 2 and 20 nmol/100 nL) into the MeA evoked dose dependent hypophagic effects in fasted rats. The selective 5-HT(1A) receptor antagonist WAY-100635 (18.5 nmol/100 nL) or the 5-HT(1B) receptor antagonist SB-216641 microinjected bilaterally into the MeA did not change the hypophagic effect evoked by local MeA zimelidine treatment. However, microinjection of the selective 5-HT(2C) receptor antagonist SB-242084 (10 nmol/100 nL) was able to block the hypophagic effect of zimelidine. Moreover, microinjection of the 5-HT(2C) receptor antagonist SB-242084 into the MeA also blocked the hypophagic effect caused by zimelidine administered systemically. These results suggest that MeA 5-HT(2C) receptors modulate the hypophagic effect caused by local MeA administration as well as by systemic zimelidine administration. Furthermore, 5-HT(2C) into the MeA could be a potential target for systemic administration of zimelidine.

Neuroanatomical substrates involved in cannabinoid modulation of defensive responses.

Administration of Cannabis sativa derivatives causes anxiolytic or anxiogenic effects in humans and laboratory animals, depending on the specific compound and dosage used. In agreement with these findings, several studies in the last decade have indicated that the endocannabinoid system modulates neuronal activity in areas involved in defensive responses. The mechanisms of these effects, however, are still not clear. The present review summarizes recent data suggesting that they involve modulation of glutamate and GABA-mediated neurotransmission in brain sites such as the medial prefrontal cortex, amygdaloid complex, bed nucleus of the stria terminalis, hippocampus and dorsal periaqueductal gray. Moreover, we also discuss results indicating that, in these regions, the endocannabinoid system could be particularly engaged by highly stressful situations.

Bed nucleus of the stria terminalis α1- and α2-adrenoceptors differentially modulate the cardiovascular responses to exercise in rats.

Dynamic exercise evokes sustained blood pressure and heart rate (HR) increases. Although it is well accepted that there is a CNS mediation of cardiovascular adjustments during dynamic exercise, information on the role of specific CNS structures is still limited. The bed nucleus of the stria terminalis (BST) is involved in exercise-evoked cardiovascular responses in rats. However, the specific neurotransmitter involved in BST-related modulation of cardiovascular responses to dynamic exercise is still unclear. In the present study, we investigated the role of local BST adrenoceptors in the cardiovascular responses evoked when rats are submitted to an acute bout of exercise on a rodent treadmill. We observed that bilateral microinjection of the selective α1-adrenoceptor antagonist WB4101 into the BST enhanced the HR increase evoked by dynamic exercise without affecting the mean arterial pressure (MAP) increase. Bilateral microinjection of the selective α2-adrenoceptor antagonist RX821002 reduced exercise-evoked pressor response without changing the tachycardiac response. BST pretreatment with the nonselective ß-adrenoceptor antagonist propranolol did not affect exercise-related cardiovascular responses. BST treatment with either WB4101 or RX821002 did not affect motor performance in the open-field test, which indicates that effects of BST adrenoceptor antagonism in exercise-evoked cardiovascular responses were not due to changes in motor activity. The present findings are the first evidence showing the involvement of CNS adrenoceptors in cardiovascular responses during dynamic exercise. Our results indicate an inhibitory influence of BST α1-adrenoceptor on the exercise-evoked HR response. Data also point to a facilitatory role played by the activation of BST α2-adrenoceptor on the pressor response to dynamic exercise.

Different role of the ventral medial prefrontal cortex on modulation of innate and associative learned fear.

Reversible inactivation of the ventral portion of medial prefrontal cortex (vMPFC) of the rat brain has been shown to induce anxiolytic-like effects in animal models based on associative learning. The role of this brain region in situations involving innate fear, however, is still poorly understood, with several contradictory results in the literature. The objective of the present work was to verify in male Wistar rats the effects of vMPFC administration of cobalt chloride (CoCl(2)), a selective inhibitor of synaptic activity, in rats submitted to two models based on innate fear, the elevated plus-maze (EPM) and light-dark box (LDB), comparing the results with those obtained in two models involving associative learning, the contextual fear conditioning (CFC) and Vogel conflict (VCT) tests. The results showed that, whereas CoCl(2) induced anxiolytic-like effects in the CFC and VCT tests, it enhanced anxiety in rats submitted to the EPM and LDB. Together these results indicate that the vMPFC plays an important but complex role in the modulation of defensive-related behaviors, which seems to depend on the nature of the anxiety/fear inducing stimuli.

Opposite role of infralimbic and prelimbic cortex in the tachycardiac response evoked by acute restraint stress in rats.

The ventral medial prefrontal cortex (vMPFC) comprises the prelimbic cortex (PL) and the infralimbic cortex (IL). Conflicting results have been reported from studies aiming to investigate the role played by the vMPFC in behavioral and autonomic responses evoked in rodents exposed to experimental protocols that promote defense responses. Acute restraint is an unavoidable stress situation that evokes marked and sustained cardiovascular changes, which are characterized by elevated blood pressure (BP) and intense heart rate (HR) increases. We report here a comparison between the effects of pharmacological inhibition of IL and PL neurotransmission on BP and HR responses evoked by acute restraint in rats. Bilateral microinjection of 200 nl of the unspecific synaptic blocker CoCl(2) (1 mM) into the PL increased HR response associated with restraint, without affecting the restraint-induced BP response. However, when local synapses in the IL were inhibited by bilateral injection of CoCl(2) into that area, the restraint-induced HR increases were significantly reduced, without a significant effect on the concomitant BP response. No responses were observed when CoCl(2) was microinjected into structures surrounding the vMPFC, such as the cingulate cortex area 1, the corpus callosum, or the tenia tecta. The present results confirm the involvement of the vMPFC in modulation of the tachycardiac response evoked by acute restraint but not of the restraint-evoked blood pressure response. They also indicate that the IL and PL areas have opposite roles in the cardiac response, facilitating and reducing, respectively, restraint-evoked tachycardiac responses.

Antiaversive effects of cannabinoids: is the periaqueductal gray involved?

Cannabinoids play an important role in activity-dependent changes in synaptic activity and can interfere in several brain functions, including responses to aversive stimuli. The regions responsible for their effects, however, are still unclear. Cannabinoid type 1 (CB1) receptors are widely distributed in the central nervous system and are present in the periaqueductal gray (PAG), a midbrain structure closely involved in responses related to aversive states. Accordingly, exposure to stressful stimuli increases endocannabinoid (eCB) levels in the PAG, and local administration of CB1 agonists or drugs that facilitate eCB-mediated neurotransmission produces antinociceptive and antiaversive effects. To investigate if these drugs would also interfere in animal models that are sensitive to anxiolytic drugs, we verified the responses to intra-PAG injection of CB1 agonists in rats submitted to the elevated plus-maze, the Vogel punished licking test, or contextual aversive conditioning model. The drugs induced anxiolytic-like effects in all tests. The same was observed with the transient receptor potential vanilloid type 1 (TRPV1) antagonist capsazepine and with cannabidiol, a nonpsychotomimetic phytocannabinoid that produces anxiolytic-like effects after systemic administration in humans and laboratory animals. These results, therefore, suggest that the PAG could be an important site for the antiaversive effects of cannabinoids.

alpha(1)-Adrenoceptors in the lateral septal area modulate food intake behaviour in rats.

BACKGROUND AND PURPOSE: Control of food intake is a complex behaviour which involves many interconnected brain structures. The present work assessed if the noradrenergic system in the lateral septum (LS) was involved in the feeding behaviour of rats. EXPERIMENTAL APPROACH: In the first protocol, the food intake of rats was measured. Then non-food-deprived animals received either 100 nL of 21 nmol of noradrenaline or vehicle unilaterally in the LS 10 min after local 10 nmol of WB4101, an alpha(1)-adrenoceptor antagonist, or vehicle. In the second protocol, different doses of WB4101 (1, 10 or 20 nmol in 100 nL) were microinjected bilaterally into the LS of rats, deprived of food for 18 h and food intake was compared to that of satiated animals. KEY RESULTS: One-sided microinjection of noradrenaline into the LS of normal-fed rats evoked food intake, compared with vehicle-injected control animals, which was significantly reduced by alpha(1)-adrenoceptor antagonism. In a further investigation, food intake was significantly higher in food-deprived animals, compared to satiated controls. Pretreatment of the LS with WB4101 reduced food intake in only food-deprived animals in a dose-related manner, suggesting that the LS noradrenergic system was involved in the control of food intake. CONCLUSION AND IMPLICATIONS: Activation by local microinjection of noradrenaline of alpha(1)-adrenoceptors in the LS evoked food intake behaviour in rats. In addition, blockade of the LS alpha(1)-adrenoceptors inhibited food intake in food-deprived animals, suggesting that the LS noradrenergic system modulated food intake behaviour and satiation.