Modulation of defensive behavior by periaqueductal gray NMDA/glycine-B receptor

Therapeutic Potential of Myricetin in the Treatment of Neurological, Neuropsychiatric, and Neurodegenerative Disorders

Myricetin (MC), 3,5,7,3',4',5'-hexahydroxyflavone, chemically belongs to a flavonoid category known to confer antioxidant, antimicrobial, antidiabetic, and neuroprotective effects. MC is known to suppress the generation of Reactive Oxygen Species (ROS), lipid peroxidation (MDA), and inflammatory markers. It has been reported to improve insulin function in the human brain and periphery. Besides this, it modulates several neurochemicals including glutamate, GABA, serotonin, etc. MC has been shown to reduce the expression of the enzyme Mono Amine Oxidase (MAO), which is responsible for the metabolism of monoamines. MC treatment reduces levels of plasma corticosterone and restores hippocampal BDNF (full form) protein in stressed animals. Further, MC has shown its protective effect against amyloid-beta, MPTP, rotenone, 6-OHDA, etc. suggesting its potential role against neurodegenerative disorders. The aim of the present review is to highlight the therapeutic potential of MC in the treatment of several neurological, neuropsychiatric, and neurodegenerative disorders.

GABAA Receptor and Serotonin Transporter Expression Changes Dissociate Following Mild Traumatic Brain Injury: Influence of Sex and Estrus Cycle Phase in Rats

Mild traumatic brain injuries (mild TBIs) can affect both males and females, but females are more likely to report long-term psychological complications, including changes in mood and generalized anxiety. Additionally, reproductive cycle phase has been shown to affect mild TBI symptom expression within females. These variances may result from sex differences in mild TBI-induced alterations to neurotransmission in brain regions that influence mood and emotion, possibly mediated by sex steroids. The hippocampus and amygdala are implicated in stress responses and anxiety, and within these regions, gamma-aminobutyric acid (GABA) and serotonin modulate output and behavioral expression. Metabolites of progesterone can allosterically enhance GABAergic signaling, and sex steroids are suggested to regulate the expression of the serotonin transporter (SERT). To determine how mild TBI might alter GABA receptor and SERT expression in males and females, immunocytochemistry was used to quantify expression of the alpha-1 subunit of the GABA_A receptor (α1-GABA_A), SERT, and a neuronal marker (NeuN) in the brains of adult male and naturally-cycling female rats, both with and without mild TBI, 17 days after injury. Mild TBI altered the expression of α1-GABA_A in the amygdala and hippocampus in both sexes, but the direction of change observed depended on sex and reproductive cycle phase. In contrast, mild TBI had little effect on SERT expression. However, SERT expression differed between sexes and varied with the cycle phase. These findings demonstrate that regulation of neurotransmission following mild TBI differs between males and females, with implications for behavioral outcomes and the efficacy of therapeutic strategies.

Targeting GluN2B/NO Pathway Ameliorates Social Isolation-Induced Exacerbated Attack Behavior in Mice

Exacerbated attack behavior has a profound socioeconomic impact and devastating social consequences; however, there is no satisfactory clinical management available for an escalated attack behavior. Social isolation (SI) is widespread during this pandemic and may exert detrimental effects on mental health, such as causing heightened attack behavior. To explore the therapeutic approaches that alleviate the SI-induced heightened attack behavior, we utilized pharmacological methods targeting the GluN2B/NO signaling pathway during the attack behavior. Ifenprodil and TAT-9C peptide targeting GluN2B showed that the inhibition of GluN2B mitigated the SI-induced escalated attack behavior and the SI-induced aberrant nitric oxide (NO) level in the brain. Additionally, the potentiation of the NO level by L-arginine reversed the effects of the inhibition of GluN2B. Moreover, we showed that high doses of L-NAME and 7-NI and subeffective doses of L-NAME in combination with ifenprodil or TAT-9C or subeffective doses of 7-NI plus ifenprodil or TAT-9C all decreased the SI-induced escalated attack behavior and reduced the NO level, further supporting the idea that GluN2B/NO signaling is a crucial modulator of the escalated attack behavior.

The effect of 5-HT4 serotonin receptors in the CA3 hippocampal region on D-AP5-induced anxiolytic-like effects: Isobolographic analyses

Increasing evidence shows the close relationship between hippocampal glutamatergic and serotonergic systems through the modulation of behavioral responses. This study aimed to investigate the possible involvement of 5-HT₄ receptors in the CA3 hippocampal region in anxiolytic-like effects induced by D-AP5 (a competitive antagonist of the glutamate NMDA [N-Methyl-D-aspartate] receptor). Male Wistar rats were placed in the elevated plus maze (EPM) apparatus that is used to assess anxiety-related behaviors, and the percentages of open arm time (%OAT) and open arm entries (%OAE) which are associated with anxiety-related behaviors were measured. The close arm entries (CAE) which is correlated with locomotor activity was also evaluated. The results showed that, intra-CA3 injection of D-AP5 (0.4 μg/rat), RS67333 (1.2 μg/rat; a 5-HT₄ receptor agonist), and RS23597-190 (1.2 μg/rat; a 5-HT₄ receptor antagonist) increased %OAT and %OAE, indicating the anxiolytic-like effect of these drugs. Also, only RS23597-190 (1.2 μg/rat) decreased CAE. Intra-CA3 injection of sub-threshold dose of RS67333 (0.012 μg/rat) or RS23597-190 (0.012 μg/rat), 5 min before the injection of D-AP5 (0.2 μg/rat) increased %OAT, indicating potentiating the anxiolytic-like effect of D-AP5. The isobolographic analyses also showed the additive or synergistic anxiolytic-like effect of intra-CA3 co-administration of D-AP5 with RS67333 or RS23597-190, respectively. In conclusion, CA3 5-HT₄ receptors are involved in D-AP5-induced anxiolytic-like behaviors in rats.

Datumetine exposure alters hippocampal neurotransmitters system in C57BL/6 mice

Our previous study showed that datumetine modulates NMDAR activity with long term exposure leading to memory deficit and altered NMDAR signaling. We aim to explore the neurotransmitters perturbations of acute datumetine-NMDAR interaction. Fifteen C57/BL6 mice were used for the study, they are divided into three groups of 5 animals each. Animals were administered DMSO (DMSO/Control), 0.25 mg/kg body weight of datumetine (0.25 Datumetine) and 1 mg/kg bodyweight of datumetine (1.0 Datumetine) intraperitoneally for 14 days. At the end of treatment, animals were euthanized in isofluorane chamber, perfused transcardially with 1XPBS followed by PFA. Immunofluorescence procedure was done to check the distribution of neurons, astrocytes, microglia and major neuronal subtypes in the hippocampus. Expansion and electron microscopy techniques were used to assess the condition of the synapses. Quantitative data were expressed as mean ± SEM and analyzed using ANOVA with Tukey post hoc using p < 0.05 as significant. Datumetine increased the expression of CD11b, GFAP, vGlut1, GABA, CHRNA7 and TH while expression of TrPH and NeuN were reduced in the hippocampus compared to control animals. Synaptic loss was evident in datumetine exposed animals with reduced synaptic vesicles accompanied by a thickness of postsynaptic density than that of control animals. This study concludes that acute datumetine exposure alters hippocampal neurotransmitter systems.

The effects of trauma on brain and body: A unifying role for the midbrain periaqueductal gray

Post-traumatic stress disorder (PTSD), a diagnosis that may follow the experience of trauma, has multiple symptomatic phenotypes. Generally, individuals with PTSD display symptoms of hyperarousal and of hyperemotionality in the presence of fearful stimuli. A subset of individuals with PTSD; however, elicit dissociative symptomatology (i.e., depersonalization, derealization) in the wake of a perceived threat. This pattern of response characterizes the dissociative subtype of the disorder, which is often associated with emotional numbing and hypoarousal. Both symptomatic phenotypes exhibit attentional threat biases, where threat stimuli are processed preferentially leading to a hypervigilant state that is thought to promote defensive behaviors during threat processing. Accordingly, PTSD and its dissociative subtype are thought to differ in their proclivity to elicit active (i.e., fight, flight) versus passive (i.e., tonic immobility, emotional shutdown) defensive responses, which are characterized by the increased and the decreased expression of the sympathetic nervous system, respectively. Moreover, active and passive defenses are accompanied by primarily endocannabinoid- and opioid-mediated analgesics, respectively. Through critical review of the literature, we apply the defense cascade model to better understand the pathological presentation of defensive responses in PTSD with a focus on the functioning of lower-level midbrain and extended brainstem systems.

NO in the dPAG modulates panic-like responses and ASIC1a expression in the prefrontal cortex and hippocampus in mice

Panic disorder (PD) is a multifactorial neuropsychiatric disorder. Our previous study has demonstrated that the nitric oxide (NO) pathway and the acid-sensing ion channel 1a (ASIC1a) level in the dorsal midbrain periaqueductal gray (dPAG) are involved in the modulation of panic-like responses. In addition, the prefrontal cortex (PFC) and the hippocampus also play a role in panic-like responses. However, no studies have investigated the protein level of ASIC1a in the PFC and hippocampus in a mouse model of panic-like disorders after alteration of the NO pathway in the dPAG. We investigated the production of a panic attack with intra-dPAG injections of SNAP, an NO donor, and 7-NI, an nNOS inhibitor. Moreover, we measured ASIC1a protein levels in the PFC and hippocampus. The rat exposure test (RET) is frequently used as an animal model of panic. In our study, C57BL/6 mice received an intra-dPAG injection of SNAP or 7-NI before RET; neurobehavioral tests were then conducted, followed by mechanistic evaluation through western blot analysis in the PFC and hippocampus. An intra-dPAG infusion of SNAP significantly increased the panic-like effect, whereas treatment with 7-NI decreased fear behavior. Mice treated with SNAP/7-NI showed significantly increased/decreased ASIC1a expression in the PFC, and a decreasing/increasing trend in the hippocampus. The present study suggests that the NO pathway in the dPAG plays a key role in panic-like responses in mice confronted by a rat, further, NO intra-dPAG injection also modulates the ASIC1a expression levels in the PFC and hippocampus.

What we imagine is what we do? A critical overview about mental imagery as a strategy to study human defensive responses

There is not a single and perfect instinctive behavior to react to threatening situations. However, the study of particular features of these situations suggests the existence of prototypical emotional reactions and associated defensive behaviors. Since all living beings are subjected to common evolutionary pressures, such as predation and conspecific competition, it is plausible that there is conservation of some basic defensive responses in their behavioral repertoire. The choice for approaching or withdrawing from a given situation depends, among others things, on environmental features, including the threat intensity and the distance from the source of the threat. If these basic responses were conserved in humans, they should be expressed in ways similar to those observed in non-human animals. Due to ethical reasons and easy application, mental imagery has been used to test this hypothesis. The studies included in this review point to the validity of this method, with both self-report and neurophysiological findings corroborating the hypothesis under scrutiny. Despite the need for additional investigation to deal with some limitations, the information obtained with this method can help to a better understanding of the conditions that provoke specific defensive behaviors and related emotions. This knowledge may also contribute to identify vulnerability factors for fear/anxiety-related disorders.

Intercollicular nucleus electric stimulation encoded “walk forward” commands in pigeons

The bio-robot research field is growing. Robo-pigeons have been successfully programmed to turn left or right; however, a satisfactory method of commanding a robo-pigeon to walk forward is still lacking. This problem has become a roadblock to progress in bio-robot research and applications. In mammals, the midbrain periaqueductal gray region (PAG) plays a key role in mediating defensive reactions in response to fear and anxiety. The avian intercollicular nucleus (ICo) is thought to correspond to the PAG. In this study, we found that microstimulating the ICo could successfully induce a robo-pigeon to walk forward. Compared with stimulation of the previously used archistriatum, the response time was considerably shorter and the behavior accuracy significantly higher. This paper describes in detail the process of controlling a robo-pigeon such that it walks forward and backward along a prescribed straight line. From the results, we draw the conclusion that the ICo is suitable for prompting the “walk forward” order in robo-pigeons.

Neuroanatomical Substrates of Rodent Social Behavior: The Medial Prefrontal Cortex and Its Projection Patterns

Social behavior encompasses a number of distinctive and complex constructs that form the core elements of human imitative culture, mainly represented as either affiliative or antagonistic interactions with conspecifics. Traditionally considered in the realm of psychology, social behavior research has benefited from recent advancements in neuroscience that have accelerated identification of the neural systems, circuits, causative genes and molecular mechanisms that underlie distinct social cognitive traits. In this review article, I summarize recent findings regarding the neuroanatomical substrates of key social behaviors, focusing on results from experiments conducted in rodent models. In particular, I will review the role of the medial prefrontal cortex (mPFC) and downstream subcortical structures in controlling social behavior, and discuss pertinent future research perspectives.

Acquisition and expression of fear memories are distinctly modulated along the dorsolateral periaqueductal gray axis of rats exposed to predator odor

The dorsolateral region of the midbrain periaqueductal gray (dlPAG) modulates both innate and conditioned fear responses. However, the contribution of the rostrocaudal portions of the dlPAG to defense reactions and aversive memories remains unclear. Here, we sought to investigate the effects of N-methyl-d-aspartate (NMDA) receptor blockade within rostral or caudal dlPAG of rats exposed to innate and learned fear to cat odor. For this, adult male Wistar rats were microinjected with the NMDA antagonist D-2-amino-5-phosphono-pentanoate (AP5; 3 or 6nmol/0.2μl) into the rostral or caudal dlPAG before and after the exposure to the cat odor or to the context paired with the predator odor. The results demonstrated that cat odor exposure induced unconditioned defensive behaviors as well as contextual fear. AP5 microinjected in the rostral dlPAG reduced the defensive responses to cat odor and impaired the acquisition, but not consolidation of contextual fear. On the other hand, AP5 infused within the caudal dlPAG promoted long-lasting reduction of contextual fear expression. Altogether, our data suggest that NMDA receptors mediate a functional dichotomy in the rostrocaudal axis of dlPAG regulating unconditioned and conditioned defensive reactions to predatory cues.

Anxiety-like responses induced by nitric oxide within the BNST in mice: Role of CRF1 and NMDA receptors

It has been shown that the bed nucleus of the stria terminalis (BNST) of rats contains nitrergic neurons, which are activated during animal exposure to aversive stimuli. The BNST is also populated by glutamatergic and corticotrophin releasing factor (CRFergic) neurons, which in turn are activated under stressful situations. Here we investigated the anxiogenic-like effects of intra-BNST injections of a nitric oxide (NO) donor, NOC-9 in mice. The role of CRFergic and glutamatergic systems on defensive behavior induced by NOC-9 was investigated with previous intra-BNST infusion of different doses of CP376395, a CRF type 1 receptor antagonist (CRF1), or AP-7, an NMDA (N-methyl-D-aspartate) receptor antagonist. Anxiety-like behavior was assessed immediately and 5 min after intra-BNST drug injection, exposing mice to a novel arena and to the elevated plus-maze (EPM; an anxiogenic situation). Results showed that NOC-9 provoked a short period (≈ 150 s) of freezing behavior in the novel arena and increased anxiety in the EPM. Both CP and AP-7 attenuated the anxiogenic-like effects of NOC-9 in the EPM without changing freezing behavior in the novel arena. When given alone (i.e. without prior intra-BNST injection of NOC-9), AP-7 (0.20 nmol), but not CP (0.75, 1.50, or 3.00 nmol), attenuated anxiety in mice exposed to the EPM. These results suggest that CRF1 and NMDA receptors located within the BNST differentially modulate aversive effects induced by NO production in this limbic forebrain structure.

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.

The levels of the GluN2A NMDA receptor subunit are modified in both the neonatal and adult rat brain by an early experience involving denial of maternal contact

The composition of the N-methyl-d-aspartate receptor receptor in GluN2A/GluN2B subunits is important in determining its characteristics and its role in plasticity, a property of the brain which is known to be critically affected by early experiences. In the present work we employed an early experience model involving either receipt (RER) or denial (DER) of the expected reward of maternal contact within the context of learning by the pups of a T-maze on postnatal days (PND) 10-13. We investigated the effects of the RER and DER early experiences on GluN1, GluN2A and GluN2B levels in the prefrontal cortex (PFC), hippocampus and amygdala of the rat. We show that on PND13 the DER animals had lower GluN2A levels in the PFC. In adulthood DER males had higher GluN2A levels in the hippocampus, both under basal conditions and after exposure to a novel environment. The early experiences did not affect the response to the novelty. After exposure to a novel environment animals of all three groups (DER, RER, Control) responded with an increase in GluN2A levels in the brain areas examined. We did not detect any effects on GluN1 or GluN2B levels. The alterations in GluN2A levels observed in the DER animals could in part be responsible for their behavioral phenotype, described previously, which includes an increased susceptibility for the expression of depressive-like behavior.

D-cycloserine injected into the dorsolateral periaqueductal gray induces anxiolytic-like effects in rats

D-cycloserine (DCS) is a partial agonist of the glycine site coupled to the NMDA receptor (NMDAR). As a consequence, depending on the doses used it can function as an agonist or antagonist at this site. In rodents, anxiolytic-like effects have been observed after the systemic administration of high doses of DCS. The brain sites of these effects have not been investigated. Direct brain injection of glycine site antagonists or agonists into the dorsolateral periaqueductal gray (dlPAG), a brain structure involved in the modulation of defensive-related behaviors, produces anxiolytic- or anxiogenic-like effects, respectively. The present study investigated if the dlPAG could be a brain site of the anxiolytic effects observed after DCS systemic administration. Male Wistar rats received intra-dlPAG injections of DCS (25, 50, 100 or 200 nmol) and were exposed to the elevated plus-maze (EPM) or to the light-dark box. DCS, at the dose of 200 nmol, increased open arm exploration and the time spent in the light compartment, respectively. Based on this result we tested the effects of intra-dlPAG DCS (200 nmol) administration in animals submitted to the Vogel conflict tests. Anxiolytic-like effect was also observed in this test indicated by the increase of punished responses. The drug did not change locomotor activity, discarding potential confounding factors. These results indicated that administration of DCS, a partial agonist of the NMDAR-associated glycine site, into the dlPAG induces anxiolytic-like effects in different models, pointing to a possible site of action of this compound.

The dorsolateral periaqueductal grey N-methyl-D-aspartate/nitric oxide/cyclic guanosine monophosphate pathway modulates the expression of contextual fear conditioning in rats

The dorsolateral periaqueductal grey (dlPAG) plays an essential role in unconditioned fear responses and could also be involved in the expression of contextual fear responses. Activation of glutamate N-methyl-D-aspartate (NMDA) receptors and the nitric oxide (NO) pathway in this region facilitates anxiety-like responses. In the present study we investigated if antagonism of NMDA receptors or inhibition of the NO pathway in the dlPAG would attenuate behavioral and cardiovascular responses of rats submitted to a contextual fear-conditioning paradigm. Male Wistar rats with unilateral cannulae aimed at the dlPAG were re-exposed to a chamber where they had received footshocks 48 h before. Ten min before the test the animals received an intra-dlPAG injection of vehicle, AP7 (NMDA receptor antagonist), N-propyl-L-arginine (neuronal NO synthase inhibitor), carboxy-PTIO (NO scavenger) or 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ) (guanylate cyclase inhibitor). Freezing and cardiovascular responses were recorded continuously for 10 min. Intra-dlPAG administration of AP7 before re-exposure to the aversively conditioned context attenuated these responses. Similar effects were observed after the NO synthase inhibitor, NO scavenger or guanylate cyclase inhibitor. Our findings suggest that activity of dlPAG NMDA/NO/cyclic guanosine monophosphate (cGMP) pathway facilitates the expression of contextual fear responses.

Gestational and lactational exposure to bisphenol-A affects anxiety- and depression-like behaviors in mice

Bisphenol-A (BPA), an environmental endocrine disruptor, has attracted attention because of its adverse effects on the brain and behavioral development. Previous evidence indicates that perinatal exposure to low levels of BPA affects anxiety-like and cognitive behaviors in adult rodents. The present study aims to investigate the changes of anxiety- and depression-like behaviors of perinatally exposed mice in adulthood following the gestational (gestation days 7 to 20) or lactational (postnatal days 1 to 14) exposure to BPA (0.4 or 4 mg/kg/d). The results indicated that both gestational and lactational exposures to BPA increased anxiety and depression-like behavior in mice of both sexes. The females with gestational exposure exhibited an increased anxiety-like state in the four models tested, including the open field, dark-light transition task, mirrored maze, and elevated plus maze tasks. Furthermore, the females with lactational exposure and the males with gestational exposure exhibited an anxiogenic-like behavior in two models, whereas the males with lactational exposure exhibited an anxiogenic-like behavior only in the elevated plus maze test. The results of the forced swim task showed that gestational exposure markedly increased the immobile time in both sexes, and the same effect was induced by lactational exposure only with 4 mg/kg/d BPA. Furthermore, western blot analyses showed that both gestational and lactational exposures inhibited the expression of the AMPA receptor subunit GluR1 in the hippocampus and amygdala in mice of both sexes, whereas the level of the NMDA receptor subunit NR1 was increased in the amygdala following gestational exposure but was reduced in the hippocampus of the females with lactational exposure. These results suggest that both gestational and lactational exposures to BPA increased anxiety- and depression-like behaviors of adult mice of both sexes. In addition gestational exposure exhibited a stronger effect on anxiety-like state in females. The altered levels of AMPA and NMDA receptors in the hippocampus and amygdala may be associated with BPA-induced behavioral changes.

NMDARs mediate the role of monoamine oxidase A in pathological aggression

Converging evidence shows that monoamine oxidase A (MAO A), the key enzyme catalyzing serotonin (5-hydroxytryptamine; 5-HT) and norepinephrine (NE) degradation, is a primary factor in the pathophysiology of antisocial and aggressive behavior. Accordingly, male MAO A-deficient humans and mice exhibit an extreme predisposition to aggressive outbursts in response to stress. As NMDARs regulate the emotional reactivity to social and environmental stimuli, we hypothesized their involvement in the modulation of aggression mediated by MAO A. In comparison with WT male mice, MAO A KO counterparts exhibited increases in 5-HT and NE levels across all brain regions, but no difference in glutamate concentrations and NMDAR binding. Notably, the prefrontal cortex (PFC) of MAO A KO mice exhibited higher expression of NR2A and NR2B, as well as lower levels of glycosylated NR1 subunits. In line with these changes, the current amplitude and decay time of NMDARs in PFC was significantly reduced. Furthermore, the currents of these receptors were hypersensitive to the action of the antagonists of the NMDAR complex (dizocilpine), as well as NR2A (PEAQX) and NR2B (Ro 25-6981) subunits. Notably, systemic administration of these agents selectively countered the enhanced aggression in MAO A KO mice, at doses that did not inherently affect motor activity. Our findings suggest that the role of MAO A in pathological aggression may be mediated by changes in NMDAR subunit composition in the PFC, and point to a critical function of this receptor in the molecular bases of antisocial personality.

Nicotine-induced anxiogenic-like behaviours of rats in the elevated plus-maze: possible role of NMDA receptors of the central amygdala

The objective of the present study was to investigate the possible role of the N-methyl-D-aspartate (NMDA) receptor system of the central amygdala (CeA) in the anxiogenic-like effect of nicotine. Male Wistar rats with cannulas aimed to the CeA were submitted to the elevated plus-maze (EPM). Intraperitoneal (i.p.) injections of nicotine (0.6 and 0.8 mg/kg) decreased percentage open arm time spent (%OAT) and percentage open arm entries (%OAE), but not locomotor activity, indicating an anxiogenic-like response. Bilateral intra-CeA microinjection of NMDA (0.005-0.1 μ g/rat) decreased %OAT, but not %OAE and locomotor activity. Moreover, intra-CeA microinjection of NMDA (0.05 μ g) with an ineffective dose of nicotine (0.4 mg/kg, i.p.) reduced %OAT and %OAE without effect on locomotor activity. On the other hand, intra-CeA microinjection of the NMDA receptor antagonist D-AP5 (0.05-0.5 μ g/rat) increased both %OAT and %OAE, showing an anxiolytic-like effect of the drug. Co-administration of the same doses of D-AP5 with nicotine (0.6 mg/kg, i.p.) increased %OAT and %OAE, but not locomotor activity. Intra-CeA microinjection of D-AP5 reversed the response induced by NMDA (0.1 μ g/rat) in the EPM. The results may support the possible involvement of glutamate transmission, through NMDA receptors of central amygdala in the anxiogenic-like effect of nicotine in the EPM task.

TMEM132D, a new candidate for anxiety phenotypes: evidence from human and mouse studies

The lifetime prevalence of panic disorder (PD) is up to 4% worldwide and there is substantial evidence that genetic factors contribute to the development of PD. Single-nucleotide polymorphisms (SNPs) in TMEM132D, identified in a whole-genome association study (GWAS), were found to be associated with PD in three independent samples, with a two-SNP haplotype associated in each of three samples in the same direction, and with a P-value of 1.2e-7 in the combined sample (909 cases and 915 controls). Independent SNPs in this gene were also associated with the severity of anxiety symptoms in patients affected by PD or panic attacks as well as in patients suffering from unipolar depression. Risk genotypes for PD were associated with higher TMEM132D mRNA expression levels in the frontal cortex. In parallel, using a mouse model of extremes in trait anxiety, we could further show that anxiety-related behavior was positively correlated with Tmem132d mRNA expression in the anterior cingulate cortex, central to the processing of anxiety/fear-related stimuli, and that in this animal model a Tmem132d SNP is associated with anxiety-related behavior in an F2 panel. TMEM132D may thus be an important new candidate gene for PD as well as more generally for anxiety-related behavior.

GABAA receptor signaling in caudal periaqueductal gray regulates maternal aggression and maternal care in mice

Maternal aggression (maternal defense) is exhibited by lactating females towards intruders and contributes to the protection of offspring. Enhancement of Gamma-Aminobutyric acid (GABA)(A) receptor signaling by benzodiazepines elevates maternal aggression, and we previously found indirect evidence (via c-Fos immunohistochemistry) that caudal periaqueductal gray (cPAG) and lateral septum (LS) could be sites where benzodiazepines increase aggression. We recently found that GABA(A) receptor signaling in LS modulates maternal aggression, and in this study, we tested the hypothesis that GABA(A) receptor signaling in cPAG also regulates this behavior. Site-directed injections to cPAG were made in lactating mice using the GABA(A) receptor antagonist, bicuculline (3-9 ng) or the GABA(A) receptor positive modulator, chlordiazepoxide (CDP), a benzodiazepine (2.5-20 microg). Maternal aggression, other maternal behaviors, and anxiety-like measures (using the light-dark box) were then examined. GABA(A) receptor positive modulator did not increase aggression, which could have resulted from a ceiling effect. However, 8 ng and 9 ng of bicuculline in cPAG significantly decreased maternal aggression without altering other maternal behaviors or light-dark box performance, suggesting some GABA(A) receptor signaling in cPAG is required for full maternal aggression expression. Additionally, 7 ng of bicuculline significantly increased licking/grooming of pups, and decreased the number of transitions between the light and dark compartments of the light-dark box without affecting aggression. Given these results indicating that antagonizing GABA(A) receptor in cPAG dose-dependently promotes offspring grooming behavior while impairing aggression, it is possible that the cPAG represents a key site for decision making (aggression versus other behaviors) in the lactating female.

Transcriptome profiling analysis reveals region-distinctive changes of gene expression in the CNS in response to different moderate restraint stress

It is generally believed that temporary moderate stress to a living organism has protective and adaptive effects, but little is known about the responses of CNS to the moderate stresses at molecular level. This study aims to investigate the gene expression changes induced by moderate stress in CNS stress- and nociception-related regions of rats. Moderate restraint was applied to rats for 50 min and cDNA microarrays were used to detect the differential gene expression in different CNS regions. Transcriptome profiling analysis showed that at acute stage stress-related genes were up-regulated in arcuate nucleus; fight-or-flight behavior-related genes were up-regulated in periaqueductal gray, while nitric oxide and GABA signal transmission-related genes were up-regulated in spinal dorsal horn. In addition, immune-related genes were broadly regulated, especially at the late stage. These results suggested that specific genes of certain gene ontology categories were spatiotemporally regulated in specific CNS regions related to relevant functions under moderate external stimuli at acute stage, while immune response was broadly regulated at the late stage. The co-regulated genes among the three different CNS regions may play general roles in CNS when exposed to moderate stress. Furthermore, these results will help to elucidate the physiological processes involved in moderate stress in CNS.

Role of glutamate NMDA receptors and nitric oxide located within the periaqueductal gray on defensive behaviors in mice confronted by predator

RATIONALE

The midbrain periaqueductal gray (PAG) is part of the brain system involved in active defense reactions to threatening stimuli. Glutamate N-methyl-D: -aspartate (NMDA) receptor activation within the dorsal column of the PAG (dPAG) leads to autonomic and behavioral responses characterized as the fear reaction. Nitric oxide (NO) has been proposed to be a mediator of the aversive action of glutamate, since the activation of NMDA receptors in the brain increases NO synthesis.

OBJECTIVES

We investigated the effects of intra-dPAG infusions of NMDA on defensive behaviors in mice pretreated with a neuronal nitric oxide synthase (nNOS) inhibitor [Nomega-propyl-L: -arginine (NPLA)], in the same midbrain site, during a confrontation with a predator in the rat exposure test (RET).

MATERIALS AND METHODS

Male Swiss mice received intra-dPAG injections of NPLA (0.1 or 0.4 nmol/0.1 microl), and 10 min later, they were infused with NMDA (0.04 nmol/0.1 microl) into the dPAG. After 10 min, each mouse was placed in the RET.

RESULTS

NMDA treatment enhanced avoidance behavior from the predator and markedly increased freezing behavior. These proaversive effects of NMDA were prevented by prior injection of NPLA. Furthermore, defensive behaviors (e.g., avoidance, risk assessment, freezing) were consistently reduced by the highest dose of NPLA alone, suggesting an intrinsic effect of nitric oxide on defensive behavior in mice exposed to the RET.

CONCLUSIONS

These findings suggest a potential role of glutamate NMDA receptors and NO in the dPAG in the regulation of defensive behaviors in mice during a confrontation with a predator in the RET.

Progesterone withdrawal-evoked plasticity of neural function in the female periaqueductal grey matter

Cyclical changes in production of neuroactive steroids during the oestrous cycle induce significant changes in GABA_A receptor expression in female rats. In the periaqueductal grey (PAG) matter, upregulation of α4β1δ GABA_A receptors occurs as progesterone levels fall during late dioestrus (LD) or during withdrawal from an exogenous progesterone dosing regime. The new receptors are likely to be extrasynaptically located on the GABAergic interneurone population and to mediate tonic currents. Electrophysiological studies showed that when α4β1δ GABA_A receptor expression was increased, the excitability of the output neurones in the PAG increased, due to a decrease in the level of ongoing inhibitory tone from the GABAergic interneurones. The functional consequences in terms of nociceptive processing were investigated in conscious rats. Baseline tail flick latencies were similar in all rats. However, acute exposure to mild vibration stress evoked hyperalgesia in rats in LD and after progesterone withdrawal, in line with the upregulation of α4β1δ GABA_A receptor expression.

Model mice for mild-form glycine encephalopathy: behavioral and biochemical characterizations and efficacy of antagonists for the glycine binding site of N-methyl D-aspartate receptor

Glycine encephalopathy (GE) is caused by an inherited deficiency of the glycine cleavage system (GCS) and characterized by accumulation of glycine in body fluids and various neurologic symptoms. Coma and convulsions develop in neonates in typical GE while psychomotor retardation and behavioral abnormalities in infancy and childhood are observed in mild GE. Recently, we have established a transgenic mouse line (low-GCS) with reduced GCS activity (29% of wild-type (WT) C57BL/6) and accumulation of glycine in the brain (Stroke, 2007; 38:2157). The purpose of the present study is to characterize behavioral features of the low-GCS mouse as a model of mild GE. Two other transgenic mouse lines were also analyzed: high-GCS mice with elevated GCS activity and low-GCS-2 mice with reduced GCS activity. As compared with controls, low-GCS mice manifested increased seizure susceptibility, aggressiveness and anxiety-like activity, which resembled abnormal behaviors reported in mild GE, whereas high-GCS mice were less sensitive to seizures, hypoactive and less anxious. Antagonists for the glycine-binding site of the N-methyl-D-aspartate receptor significantly ameliorated elevated locomotor activity and seizure susceptibility in the low-GCS mice. Our results suggest the usefulness of low-GCS mice as a mouse model for mild GE and a novel therapeutic strategy.

Effects of perinatal exposure to delta-9-tetrahydrocannabinol on the emotional reactivity of the offspring: a longitudinal behavioral study in Wistar rats

RATIONALE

The endocannabinoid system plays a crucial role in the control of emotionality and recent clinical findings have shown that heavy prenatal exposure to cannabis is significantly associated with self-reported anxiety symptoms in exposed children. However, the long-term neurobehavioral consequences of in utero exposure to low-moderate doses of cannabinoid compounds have never been investigated.

OBJECTIVE

The objective of this study was to investigate whether perinatal exposure to moderate doses of the active constituent of cannabis, the CB(1) cannabinoid receptor agonist delta-9-tetrahydrocannabinol (THC), influences the emotional reactivity of rat offspring.

METHODS

Primiparous Wistar rats were treated during pregnancy and lactation with doses of THC equivalent to the current estimates of moderate cannabis consumption in humans (2.5-5 mg kg(-1), per os, from gestational day 15 to postnatal day 9). The emotional reactivity of infant, adolescent, and adult offspring was investigated using the isolation-induced ultrasonic vocalization, social interaction, and elevated plus-maze tests, respectively.

RESULTS

Perinatal THC treatment did not affect parameters of reproduction; however, at the dose of 5 mg kg(-1), it increased the number of ultrasounds emitted by rat pups removed from the nest, inhibited social interaction and play behavior in the adolescent offspring, and induced an anxiogenic-like profile in the adult offspring tested in the elevated plus-maze test.

CONCLUSION

These results suggest that the endocannabinoid system is involved in the control of emotionality since early developmental stages. Thus, even moderate doses of cannabinoid compounds, when administered during the perinatal period, can have profound consequences for brain maturation, leading to long-lasting neurodevelopmental alterations.

Distinct ventral and dorsal hippocampus AP5 anxiolytic effects revealed in the elevated plus-maze task in rats

The hippocampal formation (HPC) mediates processes associated with learning, memory, anxiety and fear. The glutamate N-methyl-d-aspartate (NMDA)-receptor subtype is involved in many HPC functional processes related to learning and memory. Although not tested for the HPC, NMDA-receptor antagonists reduced fear and anxiety related responses when applied to other brain regions mediating defensive behaviour. Consequently, this study evaluated the effects of ventral or dorsal HPC application of the NMDA-receptor antagonist, AP5, in rats submitted to the Trial 1/Trial 2 elevated plus-maze (EPM) task. Ventral, but not dorsal, infusions of AP5 (6 and 24 nmol) before EPM Trial 1 increased open arms exploration and reduced risk assessment behavior, suggesting an anxiolytic-like effect. Furthermore, no interference in the avoidance responses was detected during EPM Trial 2 after AP5 infusion into the ventral or dorsal HPC before Trial 1, post-trial 1, or before Trial 2. These data support the notion of differential involvement of ventral HPC, but not dorsal, in mechanisms associated with anxiety and suggest the participation of the glutamatergic transmission, through NMDA receptor, into the ventral HPC in the mediation of defensive behavior.

Exposure to urine of canids and felids, but not of herbivores, induces defensive behavior in laboratory rats

Predator odors induce defensive behavior in many prey species. For various reasons, studies carried out up to now have been unable to establish whether predator odor recognition is innate or not. Mostly, only particular odors or wild-living (i.e., experienced) test animals have been used in these studies, restricting the conclusiveness of the observations. In the present study, the behavioral effects of exposure to different predator odors on predator odor-naive laboratory male rats were compared with the effects of different nonpredator odors and of a no-odor control stimulus. Results show that exposure to urine of canids and felids, but not of herbivores or conspecifics, induce defensive behaviors. Taken together, the study provides support for the hypothesis that there is an innate recognition of predator odors in laboratory rats.

Elevated pCREB in the PAG after exposure to the elevated plus maze in rats previously exposed to a cat

The elevated plus maze (EPM) is an ethologically based test of anxiety-like behavior. In addition, exposure to the maze itself is stressful and anxiogenic. One of the goals of this study was to examine if the stress of EPM exposure increased pCREB-like-immunoreactivity (lir). The second goal of this study was to determine if prior stress impacted expression of pCREB-lir in animals exposed to the EPM. Toward this end, pCREB-lir was examined after exposure to the EPM in young adult male rats that had been exposed to a cat 7 days earlier. Brain areas investigated included the amygdala, periaqueductal gray (PAG), and bed nucleus of the stria terminalis (BNST), all areas considered to be part of the "fear circuit". Results show that there were no pCREB-lir differences between control rats and rats exposed to the EPM only. However, exposure to the EPM in predator stressed rats showed elevated pCREB-lir in the right lateral column of the PAG and bilaterally in the dorsal column of the PAG. In contrast, EPM exposure did not elevate pCREB-lir in the amygdala or BNST in predator stressed rats. Findings suggest mechanisms associated with neuroplasticity may be engaged by relatively mild stresses in animals with a history of severe stress exposure. This may be clinically relevant, as a key feature of posttraumatic stress disorder (PTSD) is the exaggerated reaction to a mild stressor in which the response is more appropriate to the original traumatic situation than the current conditions. If what happens in animals also occurs in humans, the findings of this study suggest that neural mechanisms of prior traumatic stress may interact with subsequent stress to reinforce psychopathology.

Effects of intra-PAG infusion of ovine CRF on defensive behaviors in Swiss-Webster mice

The midbrain dorsal periaqueductal gray (DPAG) is part of the brain defensive system involved in active defense reactions to threatening stimuli. Corticotrophin releasing factor (CRF) is a peptidergic neurotransmitter that has been strongly implicated in the control of both behavioral and endocrine responses to threat and stress. We investigated the effect of the nonspecific CRF receptor agonist, ovine CRF (oCRF), injected into the DPAG of mice, in two predator-stress situations, the mouse defense test battery (MDTB), and the rat exposure test (RET). In the MDTB, oCRF weakly modified defensive behaviors in mice confronted by the predator (rat); e.g. it increased avoidance distance when the rat was approached and escape attempts (jump escapes) in forced contact. In the RET, drug infusion enhanced duration in the chamber while reduced tunnel and surface time, and reduced contact with the screen which divides the subject and the predator. oCRF also reduced both frequency and duration of risk assessment (stretch attend posture: SAP) in the tunnel and tended to increase freezing. These findings suggest that patterns of defensiveness in response to low intensity threat (RET) are more sensitive to intra-DPAG oCRF than those triggered by high intensity threats (MDTB). Our data indicate that CRF systems may be functionally involved in unconditioned defenses to a predator, consonant with a role for DPAG CRF systems in the regulation of emotionality.

Involvement of dorsolateral periaqueductal gray N-methyl-D-aspartic acid glutamate receptors in the regulation of risk assessment and inhibitory avoidance behaviors in the rat elevated T-maze

The involvement of the dorsolateral periaqueductal gray in the regulation of fear-related behaviors such as escape and freezing is well established. It is still a matter of investigation, however, whether this midbrain area may have a relevant role in the modulation of more subtle defensive responses associated with anxiety such as risk assessment and inhibitory avoidance. By stimulating N-methyl-D-aspartic acid glutamate receptors located in the dorsolateral periaqueductal gray with its prototypical agonist N-methyl-D-aspartic acid (50 pmol), we report here an increase in both risk assessment and inhibitory avoidance behaviors of male Wistar rats tested in the elevated T-maze. These results are indicative of an anxiogenic-like effect. The selective N-methyl-D-aspartic acid receptor antagonist DL-2-amino-7-phosphonoheptanoic acid (2.0 and 4.0 nmol) had the opposite effect on both defensive tasks. Pretreatment with an ineffective dose of DL-2-amino-7-phosphonoheptanoic acid (1.0 nmol) prevented the N-methyl-D-aspartic acid anxiogenic-like effect. At the dose range of DL-2-amino-7-phosphonoheptanoic acid and/or N-methyl-D-aspartic acid tested, neither the escape response from one of the elevated T-maze open arms nor the general exploratory activity as assessed in the open-field test was affected. The present results suggest that the dorsolateral periaqueductal gray column is also involved in the regulation of defensive behaviors related to anxiety, and N-methyl-D-aspartic acid glutamate receptors are recruited for this action.

Antidepressant treatment reduces Fos-like immunoreactivity induced by swim stress in different columns of the periaqueductal gray matter

Antidepressant treatment attenuates behavioral changes induced by uncontrollable stress. The periaqueductal gray matter (PAG) is proposed to be a brain site involved in the behavioral responses to uncontrollable stress and antidepressant effects. The main goal of the present study was to investigate the effect of antidepressant treatment on the pattern of neural activation of the PAG along its mediolateral and rostrocaudal subregions after a forced swim stress episode. Male Wistar rats were sub-acutely treated with desipramine (a selective noradrenaline re-uptake blocker, three injections of 10 mg/kg in 24 h) or clomipramine (a non-selective serotonin and noradrenaline re-uptake blocker, three injections of 10 mg/kg in 24 h) and submitted to the forced swimming test (FST). Two hours after the test their brain were removed for Fos immunohistochemistry. Fos-like immunoreactivity (FLI) in rostral, intermediate and caudal portions of dorsomedial (dmPAG), dorsolateral (dlPAG), lateral (lPAG) and ventrolateral (vlPAG) PAG were quantified by a computerized system. The FST session increased FLI in most parts of the PAG. Previous treatment with desipramine or clomipramine reduced FLI in all columns of the PAG. FLI in the PAG correlated positively with to the immobility time and negatively with to climbing behavior scored during the test. These results indicate that neurons in the PAG are activated by uncontrollable stress. Moreover, inhibitory action of antidepressants on this activity may be associated with the anti-immobility effects of these drugs in the FST.

Elevated T-maze evaluation of anxiety and memory effects of NMDA/glycine-B site ligands injected into the dorsal periaqueductal gray matter and the superior colliculus of rats

Rat behaviors in the elevated T-maze (ETM) were evaluated following tectum microinjections of either glycine (GLY, 1, 10, 80 and 120 nmol) or d-serine (D-SER, 160 and 320 nmol), the putative endogenous agonists of GLY-B site at NMDA receptor, or the respective antagonist 7-chloro-kynurenic acid (7CK, 8 nmol). ETM performance was appraised by two validated scores of anxiety, i.e., the inhibitory avoidance duration (AD) and risk assessment behavior, and two scores derived from a newly developed approach to inhibitory avoidance learning curves, i.e., the learning median number of trials (T50) and avoidance variability (standard deviation of learning curve). Effects on aversive memory consolidation were assessed through changes in the AD measured 48 h after the full-acquisition of inhibitory avoidance. Drug effects were compared to those of vehicle. In most cases, microinjection of GLY-B site agonists into the dorsal periaqueductal gray (dPAG) produced increases in AD, which were compatible with an increase in anxiety. However, neither the intra-periaqueductal injection of 80 nmol GLY, nor that of 160 nmol D-SER, increased the AD. On the other hand, these microinjections invariably produced a parallel left shift in avoidance learning curves, thereby reducing the T50 but not the variability. Effects of 120 nmol GLY on AD and T50 were both antagonized by a previous microinjection of 7CK into the dPAG. The inverse relationship of AD and T50 suggests that increases in the anxiety level reduce the number of trials required for the acquisition of inhibitory avoidance. The above data also suggest the higher consistency and drug sensitivity of T50 as compared to the AD. In turn, whereas the microinjection of 120 nmol GLY into the superior colliculus (SC) did not affect the T50, it increased the AD. On the other hand, there was an increase in avoidance variability following the microinjection of either 120 nmol GLY into the SC or 8 nmol 7CK into the dPAG. Therefore, the GLY-B receptors within these structures seem to play opposite roles on avoidance variability. In contrast, neither of these treatments changed T50. Finally, whereas the risk assessment was solely decreased by the microinjection of GLY into the SC, the aversive memory was only impaired by the microinjection of 7CK into the dPAG. Overall, these data suggest that NMDA/GLY-B receptors of dPAG mediate both anxiety and aversive memory, while those in the SC are most likely involved with attention and visuomotor components of risk assessment behavior.

Lack of interaction between NMDA and cholecystokinin-2 receptor-mediated neurotransmission in the dorsolateral periaqueductal gray in the regulation of rat defensive behaviors

Several neurotransmitters, including GABA, serotonin, glutamate, and cholecystokinin, modulate defensive behaviors in the dorsolateral periaqueductal gray (dlPAG). Although both glutamate and cholecystokinin have been shown to facilitate these behaviors, a possible interaction between them remains to be examined. The present study investigates whether activation or antagonism of N-methyl-D-aspartic acid (NMDA) glutamate and cholecystokinin 2 (CCK(2)) receptors located in the dlPAG would interact in animals tested in the elevated T-maze. The effect of the NMDA (50 pmol) was evaluated in rats pretreated with the CCK(2) receptor antagonist LY225910 (0.05 nmol). In addition, the effect of the CCK(2) receptor agonist CCK-4 (0.08 nmol) was evaluated in rats pretreated with the NMDA receptor antagonist AP-7 (1.0 nmol). Intra-dlPAG injection of NMDA increased risk assessment and inhibitory avoidance behaviors. This NMDA anxiogenic-like effect was unaltered by the pretreatment with LY225910. Similarly, the shortening of escape latencies induced by CCK-4 was unaffected by AP-7. No drug changed the general exploratory activity as assessed in the open-field. These results, showing that the activation of dlPAG NMDA or CCK(2) receptors facilitate anxiety- and fear-related behaviors, further implicate glutamate and cholecystokinin-mediated neurotransmission in this midbrain area on modulation of defensive behaviors. However, the regulatory action of these two excitatory neurotransmitters seems to be exerted through independent mechanisms.

Activation of neurons containing the enzyme nitric oxide synthase following exposure to an elevated plus maze

The elevated plus-maze (EPM) is one of the most used animal models of anxiety. Exposure to the EPM activates brain regions related to anxiety/fear. Systemic or intra-dorsolateral periaqueductal gray (dlPAG) inhibition of nitric oxide synthase (NOS) induces anxiolytic effect in animals submitted to an EPM. Additionally, exposure to an innate fear stimulus, such as a live predator, activates neurons containing NOS in regions related to defensive behavior. Considering these pieces of evidence, the present study investigated if neurons containing NOS localized in regions related to anxiety/fear are also activated after exposure to an EPM. Male Wistar rats were exposed to the EPM for 15 min and 2 h later their brains were removed and processed for c-Fos immunohistochemistry (a marker of neuronal functional activation) and NADPH-diaphorase histochemistry (NADPH-d; used to detect the presence of NOS neurons). Exposure to the EPM significantly increased double-stained cells (c-Fos + NADPHd positive neurons) in the parvocellular paraventricular (pPVN) and lateral (LH) hypothalamic nuclei, dlPAG and dorsal raphe nucleus (DRN), but not in the amygdaloid complex, bed nucleus of stria terminallis, dorsal premammillary nucleus of hypothalamus and inferior colicullus. These results suggest that exposure to an EPM activates NOS containing neurons in brain areas related to fear/anxiety.

Prior electrical stimulation of dorsal periaqueductal grey matter or deep layers of the superior colliculus sensitizes rats to anxiety-like behaviors in the elevated T-maze test

Electrical stimulation of the dorsal periaqueductal grey matter (DPAG) and deep layers of the superior colliculus (DLSC) of the rat elicits anxiety-like reactions such as freezing and flight. The temporal course of the effects of the aversive electrical stimulation of the DPAG (5, 15 and 30 min afterward) and DLSC (5, 10 and 15 min afterward) on the defensive response of rats exposed to elevated T-maze were determined. The elevated T-maze generates two defensive behaviors, inhibitory avoidance and one-way escape, which have been related, respectively, to generalized anxiety and panic disorders. Prior electrical stimulation of the DPAG (15 min) and DLSC (5 min) enhanced inhibitory avoidance when compared to no-operated and sham animals, although not affecting escape. Therefore, stimulation of the DPAG and DLSC causes a heightened responsivity to anxiogenic stimulus, but not to panicogenic stimulus, inherent to elevated T-maze. These findings support the participation of the DPAG and DLSC in the elaboration of adaptive responses to stressful situations. Besides, the data supports the view that prior electrical stimulation of DPAG and DLSC is selective in sensitizing rats to anxiety-like behaviors, but not to panic-like behaviors in the elevated T-maze test.

Brain mechanisms of aggressive behavior: An updated review

During the 25 years since a motivational systems model was proposed to explain the brain mechanisms of aggressive behavior (D.B. Adams. Brain mechanisms for offense, defense, and submission. Behav. Brain. Sci. 2, (1979a) 200-241) considerable research has been carried out. Updating the model in the light of this research requires several changes. A previous distinction between submission and defense systems is abandoned and, instead, it is proposed that two distinct subsets of the defense motivational mechanism may be recognized, one for anti-predator defense and the other for consociate defense. Similarly, the offense motivational mechanism is now considered to have at least two subsets, one mediating territorial and the other competitive fighting. Data continue to indicate that the defense motivational mechanism is located in the midbrain central gray and adjoining tissue. Also data tend to support the hypothesis that the offense motivational mechanism is located in the hypothalamus at the level of the anterior hypothalamus. Consideration is also given to a motivational system for patrol/marking which is related to aggressive behavior. Research is reviewed that bears on the neural structure of motivating and releasing/directing stimuli and motor patterning mechanisms of offense, defense and patrol/marking, as well as the location of learning and hormonal effects, and attention is given to how the model can be tested.

Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action

Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.