Sex-Related Predisposition to Post-Traumatic Stress Disorder Development-The Role of Neuropeptides.

Post-traumatic stress disorder (PTSD) is characterized by re-experiencing a traumatic event, avoidance, negative alterations in cognitions and mood, hyperarousal, and severe functional impairment. Women have a two times higher risk of developing PTSD than men. The neurobiological basis for the sex-specific predisposition to PTSD might be related to differences in the functions of stress-responsive systems due to the interaction between gonadal hormones and stress peptides such as corticotropin-releasing factor (CRF), orexin, oxytocin, and neuropeptide Y. Additionally, in phases where estrogens levels are low, the risk of developing or exacerbating PTSD is higher. Most studies have revealed several essential sex differences in CRF function. They include genetic factors, e.g., the CRF promoter contains estrogen response elements. Importantly, sex-related differences are responsible for different predispositions to PTSD and diverse treatment responses. Fear extinction (the process responsible for the effectiveness of behavioral therapy for PTSD) in women during periods of high endogenous estradiol levels (the primary form of estrogens) is reportedly more effective than in periods of low endogenous estradiol. In this review, we present the roles of selected neuropeptides in the sex-related predisposition to PTSD development.

Individual susceptibility or resistance to posttraumatic stress disorder-like behaviours.

The aim of this study was to explore the neurobiological background of individual susceptibility and resistance to the development of posttraumatic stress disorder (PTSD)-like behaviours. Rats were divided into susceptible, PTSD(+), and resistant, PTSD(-), groups based on freezing duration during exposure to aversive context and the time spent in the central area in open field test one week after threefold stress experience (modified single prolonged stress). PTSD(-) rats showed increased concentrations of corticosterone in plasma and changes in GAD67 expression: decreased in the infralimbic cortex (IL) and increased in the lateral amygdala (LA), dentate gyrus (DG), and CA1 area of the hippocampus. Moreover, in this group, we found an increase in the number of CRF-positive nuclei in the parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN). The PTSD(+) group, compared to PTSD(-) rats, had decreased concentrations of corticosterone in plasma and reduced CRF expression in the pPVN, higher CRF expression in the CA1, increased expression of CRF-positive nuclei and GR receptors in the CA3 area of the hippocampus, and increased expression of GR receptors in the DG and the central amygdala (CeA). Biochemical analysis showed higher concentrations of noradrenaline, glutamic acid in the dorsal hippocampus and amygdala and lower levels of dopamine and its metabolites in the amygdala of the PTSD(+) group than in the PTSD(-) group. The study revealed different behavioural and biochemical profiles of PTSD(+) and PTSD(-) rats and suggested that individual differences in hypothalamic-pituitary-adrenal (HPA) axis activity may determine hippocampal- and amygdala-dependent memory and fear processing.

Low-anxiety rats are more sensitive to amphetamine in comparison to high-anxiety rats.

This study utilised the two injection protocol of sensitisation (TIPS) and the conditioned place preference test to validate and extend previous findings on the effects of amphetamine on positive reinforcement-related 50 kHz ultrasonic vocalisation (USV) in rats. We also examined changes in the expression of c-Fos and the NMDA receptor 2B (GluN2B) subunit, markers of neuronal activity and plasticity, in brain regions of rats in response to TIPS. We used low anxiety-responsive (LR) and high anxiety-responsive (HR) rats, which are known to exhibit different fear-conditioned response strengths, different susceptibilities to amphetamine in the TIPS procedure and different amphetamine-dependent 50 kHz USV responses. The LR rats, compared to the HR rats, not only vocalised much more intensely but also spent significantly more time in the amphetamine-paired compartment. After the second dose of amphetamine, the LR rats exhibited more c-Fos and GluN2B activation in layers II and III of the M1/M2 motor cortex area and prefrontal cortex (PRE, PRL, IL) and also presented with more GluN2B activation in the basal amygdala. These data reveal that HR and LR rats exhibit different levels of reactivity in the cortical-limbic pathway, which controls reward-related motivational processes. These findings contribute to the general hypothesis that heterogeneity in emotional processes is one of the causes of sensitisation to amphetamine and drug addiction.

GABAergic control of the activity of the central nucleus of the amygdala in low- and high-anxiety rats.

The aim of this study was to examine the role of GABAergic neurotransmission in amygdala nuclei in low- (LR) and high-anxiety (HR) rats after repeated corticosterone administration and acute injection of the benzodiazepine midazolam. The animals were divided into LR and HR groups based on the duration of their conditioned freezing in a contextual fear test (CFT). Repeated daily administration of corticosterone (20 mg/kg s.c.) for 21 injections increased anxiety-like behavior in the open field and reduced body weight in both the LR and HR groups. These effects of corticosterone administration were more pronounced in the HR group. Moreover, in the HR group, chronic corticosterone administration increased the duration of freezing in the CFT test compared with the appropriate control group and treated LR rats. The behavioral effects in HR rats were accompanied by an increase in the expression of c-Fos in the lateral (LA) and central (CeA) nuclei of the amygdala and by a decrease in GABA-A alpha-2 subunit density in the CeA. Acute midazolam administration significantly attenuated the neophobia and conditioned fear responses, decreased c-Fos expression in the LA and CeA, and increased alpha-2 subunit density in the CeA only in the HR group. These studies have shown that HR rats are more susceptible to the anxiogenic effects of chronic corticosterone administration, which are associated with the attenuation of GABAergic control over the amygdala output that controls emotional responses. The current data may increase understanding of the neurobiological mechanisms responsible for individual differences in the psychopathological processes induced by repeated administration of high doses of glucocorticoids or by elevated levels of these hormones, which are associated with chronic stress and affective pathology.

Mapping of c-Fos expression in the rat brain during the evolution of pentylenetetrazol-kindled seizures.

c-Fos protein immunocytochemistry was used to map the brain structures recruited during the evolution of seizures that follows repeated administration of a subconvulsive dose (35mg/kg, ip) of pentylenetetrazol in rats. c-Fos appeared earliest in nucleus accumbens shell, piriform cortex, prefrontal cortex, and striatum (stages 1 and 2 of kindling in comparison to control, saline-treated animals). At the third stage of kindling, central amygdala nuclei, entorhinal cortex, and lateral septal nuclei had enhanced concentrations of c-Fos. At the fourth stage of kindling, c-Fos expression was increased in basolateral amygdala and CA1 area of the hippocampus. Finally, c-Fos labeling was enhanced in the dentate gyrus of the hippocampus only when tonic-clonic convulsions were fully developed. The most potent changes in c-Fos were observed in dentate gyrus, piriform cortex, CA1, lateral septal nuclei, basolateral amygdala, central amygdala nuclei, and prefrontal cortex. Piriform cortex, entorhinal cortex, prefrontal cortex, lateral septal nuclei, and CA3 area of the hippocampus appeared to be the brain structures selectively involved in the process of chemically induced kindling of seizures.

The expression of c-Fos and colocalisation of c-Fos and glucocorticoid receptors in brain structures of low and high anxiety rats subjected to extinction trials and re-learning of a conditioned fear response.

We designed an animal model to examine the mechanisms of differences in individual responses to aversive stimuli. We used the rat freezing response in the context fear test as a discriminating variable: low responders (LR) were defined as rats with a duration of freezing response one standard error or more below the mean value, and high responders (HR) were defined as rats with a duration of freezing response one standard error or more above the mean value. We sought to determine the colocalisation of c-Fos and glucocorticoid receptors-immunoreactivity (GR-ir) in HR and LR rats subjected to conditioned fear training, two extinction sessions and re-learning of a conditioned fear. We found that HR animals showed a marked decrease in conditioned fear in the course of two extinction sessions (16 days) in comparison with the control and LR groups. The LR group exhibited higher activity in the cortical M2 and prelimbic areas (c-Fos) and had an increased number of cells co-expressing c-Fos and GR-ir in the M2 and medial orbital cortex after re-learning a contextual fear. HR rats showed increased expression of c-Fos, GR-ir and c-Fos/GR-ir colocalised neurons in the basolateral amygdala and enhanced c-Fos and GR-ir in the dentate gyrus (DG) in comparison with LR animals. Our data indicate that recovery of a context-related behaviour upon re-learning of contextual fear is accompanied in HR animals by a selective increase in c-Fos expression and GRs-ir in the DG area of the hippocampus.

Stress-opioid interactions: a comparison of morphine and methadone.

The utility of methadone and morphine for analgesia and of methadone for substitution therapy for heroin addiction is a consequence of these drugs acting as opioid receptor agonists.We compared the cataleptogenic and antinociceptive effects of single subcutaneous doses of methadone hydrochloride (1-4 mg/kg) and morphine sulfate (2.5-10 mg/kg) using catalepsy and hot-plate tests, and examined the effects of the highest doses of the drugs on Fos protein expression in selected brain regions in male Sprague-Dawley rats. Methadone had greater cataleptogenic and analgesic potency than morphine. Fos immunohistochemistry revealed substantial effects on the Fos response of both the stress induced by the experimental procedures and of the drug exposure itself. There were three response patterns identified: 1) drug exposure, but not stress, significantly elevated Fos-positive cell counts in the caudate-putamen; 2) stress alone and stress combined with drug exposure similarly elevated Fos-positive cell counts in the nucleus accumbens and cingulate cortex; and 3) methadone and morphine (to a lesser extent) counteracted the stimulatory effect of nonpharmacological stressors on Fos protein expression in the somatosensory cortex barrel field, and Fos-positive cell counts in this region correlated negatively with both the duration of catalepsy and the latency time in the hot-plate test. The overlap between brain regions reacting to nonpharmacological stressors and those responding to exogenous opioids suggests that stress contributes to opioid-induced neuronal activation.

Methadone is substantially less effective than morphine in modifying locomotor and brain Fos responses to subsequent methadone challenge in rats.

Heroin addicts can benefit from methadone substitution therapy. However, little is known about the significance of pre-exposure to opioids for psychoactive effects of methadone. We modeled some behavioral and neurobiological aspects of the opioid abuse-related phenomena in Sprague-Dawley rats, using morphine (10 mg/kg/day) or methadone (1 or 2 mg/kg/day) treatment (14 doses over a 16-day period) followed by 2-week withdrawal and methadone challenge; control rats were given 0.9% NaCl treatment and methadone challenge by the same schedule. Locomotor response to the challenge showed substantial enhancement only after the morphine treatment. Fos immunohistochemistry in selected brain regions including cortex, nucleus accumbens, striatum and some parts of the hippocampus, thalamus and amygdala also revealed marked differences between the effects of the tested treatments. Sensitization of Fos response was found in a few regions of the morphine-treated rats. The rats given the higher methadone dose treatment showed a fairly weak tendency for sensitization that reached significance only in somatosensory cortex layer IV. The rats given the lower methadone dose treatment showed a weak while widespread tendency for an opposite change, which reached significance in cingulate cortex layer II/III and resulted in significant differences in Fos response between these rats and the morphine-treated rats in most regions studied. These results indicate that lasting neuroplastic changes associated with the sensitization caused by (sub)chronic exposure to opioids are relatively mild for methadone as compared to those caused by morphine, and suggest that psychoactive effects of methadone can be notably enhanced by past opiate use.

Colocalisation of c-Fos and glucocorticoid receptor as well as of 5-HT(1A) and glucocorticoid receptor immunoreactivity-expressing cells in the brain structures of low and high anxiety rats.

We sought to determine the colocalisation of c-Fos (a marker of neuronal activation) and glucocorticoid receptors (GRs) as well as of 5-HT(1A) and glucocorticoid receptor immunoreactivity-expressing cells (ir) in the dorsomedial prefrontal cortex (M2), dentate gyrus of the hippocampus (DG), and basolateral nucleus of the amygdala (BLA) in low and high anxiety rats (i.e., rats with duration of a freezing response in the conditioned fear test one standard error or more below or above the mean value: low responders (LR) and high responders (HR), respectively). It was found that 1.5 h after a testing session of the conditioned fear test, the LR animals had a higher activity of the cortical M2 area and DG (c-Fos), a higher expression of GRs-ir, as well as an increased number of cells co-expressing c-Fos and GRs-ir in the same brain areas. In the case of HR rats, they had similar expression of c-Fos in the BLA, but a significantly higher concentration of GRs-ir and c-Fos/GR colocalised neurons in the same amygdala nucleus. The pattern of distribution of 5-HT(1A) and GR receptor-ir in LR and HR animals was similar to the c-Fos and GRs-ir expression. LR animals showed a higher density of 5-HT(1A) and GRs-ir in the cortical M2 area and DG as well as an increased number of cells co-expressing 5-HT(1A) and GR-ir in the same brain areas. HR rats had a significantly higher concentration of 5-HT(1A) and GR-ir as well as a greater number of c-Fos/GR protein colocalised neurons in the BLA. The present data add to the arguments for the neurobiological background of differences in individual responses to aversive conditioned stimuli.

The influence of CRF and alpha-helical CRF(9-41) on rat fear responses, c-Fos and CRF expression, and concentration of amino acids in brain structures.

In the present study we have examined the influence of intracerebroventricullary administered CRF, and a non-selective CRF receptor antagonist, alpha-helical CRF((9-41)), on rat conditioned fear response, serum corticosterone, c-Fos and CRF expression, and concentration of amino acids (in vitro), in several brain structures. Pretreatment of rats with CRF in a dose of 1 microg/rat, enhanced rat-freezing response, and further increased conditioned fear-elevated concentration of serum corticosterone. Moreover, exogenous CRF increased aversive context-induced expression of c-Fos in the parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN), CA1 area of the hippocampus, and M1 area of the frontal cortex. A different pattern of behavioral and biochemical changes was present after pre-test administration of alpha-helical CRF((9-41)) (10 microg/rat): a decrease in rat fear response and serum corticosterone concentration; an attenuation of fear-induced c-Fos expression in the dentate gyrus, CA1, Cg1, Cg2, and M1 areas of the frontal cortex; a complete reversal of the rise in the number of CRF immunoreactive complexes in the M2 cortical area, induced by conditioned fear. Moreover, alpha-helical CRF((9-41)) increased the concentration of GABA in the amygdala of fear-conditioned rats. Altogether, the present data confirm and extend previous data on the integrative role of CRF in the central, anxiety-related, behavioral and biochemical processes. The obtained results underline also the role of frontal cortex and amygdala in mediating the effects of CRF on the conditioned fear response.

The role of the dorsomedial part of the prefrontal cortex serotonergic innervation in rat responses to the aversively conditioned context: behavioral, biochemical and immunocytochemical studies.

In this study we have explored differences in animal reactivity to conditioned aversive stimuli using the conditioned fear test (a contextual fear-freezing response), in rats subjected to the selective lesion of the prefrontal cortex serotonergic innervation, and differing in their response to the acute painful stimulation, a footshock (HS--high sensitivity rats, and LS--low sensitivity rats, selected arbitrarily according to their behavior in the 'flinch-jump' pre-test). Local administration of serotonergic neurotoxin (5,7-dihydroxytryptamine) to the dorsomedial part of the prefrontal cortex caused a very strong, structure and neurotransmitter selective depletion of serotonin concentration. In HS rats, the serotonergic lesion significantly disinhibited rat behavior controlled by fear, enhanced c-Fos expression in the dorsomedial prefrontal area, and increased the concentration of GABA in the basolateral amygdala, measured in vivo after the testing session of the conditioned fear test. The LS animals revealed an opposite pattern of behavioral and biochemical changes after serotonergic lesion: an increase in the duration of a freezing response, and expression of c-Fos in the basolateral and central nuclei of amygdala, and a lower GABA concentration in the basolateral amygdala. In control conditions, c-Fos expression did not differ in LS and HS, naïve, not conditioned and not exposed to the test cage animals. The present study adds more arguments for the controlling role of serotonergic innervation of the dorsomedial part of the prefrontal cortex in processing emotional input by other brain centers. Moreover, it provides experimental data, which may help to better explain the anatomical and biochemical basis of differences in individual reactivity to stressful stimulation, and, possibly, to anxiolytic drugs with serotonergic or GABAergic profiles of action.

Morphine and methadone pre-exposures differently modify brain regional Fos protein expression and locomotor activity responses to morphine challenge in the rat.

Methadone is commonly used in substitution therapy of heroin addicts; hence, its potential for modifying reactions to opiates is of clinical importance. We compared the effects of repeated daily and every-other-day pre-exposure of rats to s.c. morphine and methadone on locomotor activity and CNS neuronal activation (as assessed by Fos immunohistochemistry) responses to s.c. morphine challenge given 2 weeks after the completion of the pretreatment. The challenge revealed behavioral sensitization after daily morphine pretreatment only. Dorsomedial striatum and basolateral amygdaloid nucleus showed robust morphine-induced Fos protein induction that was unaffected by the pretreatments tested. Centrolateral striatum, shell and core of the nucleus accumbens, paraventricular thalamic nucleus and some layers of motor and somatosensory cortices showed but negligible Fos protein induction in drug-naive rats; this response was markedly enhanced by morphine pretreatment only, which effect might be related to the emergence of opiate addiction. Minor Fos responses to morphine were also found in layers IV and VI of the somatosensory cortex and layer VI of the insular cortex of the drug-naïve rats; these responses were significantly enhanced both by morphine and methadone pretreatment. The similarity of methadone and morphine pretreatments' effects in the latter cortical regions might be relevant to the ability of methadone to alleviate signs of abstinence syndrome and craving in heroin addicts. In summary, this study revealed differing and relatively long-lasting effects of prolonged administration of morphine and methadone on the profile of behavioral and CNS neuronal activation responses to morphine challenge in the rat.

Expression of c-Fos and CRF in the brains of rats differing in the strength of a fear response.

The aim of the study was to examine the neurochemical background of differences in the individual responses to conditioned aversive stimuli, using the strength of a rat conditioned freezing response (the contextual fear test), as a discriminating variable. It was shown that low responders (LR), i.e. rats with duration of a freezing response one standard error, or more, below the mean value, had a higher activity of the M2 cortical area, and the median raphe nucleus (c-Fox expression), in comparison to the high responders (HR), i.e. rats with the duration of a freezing response one standard error, or more, above the mean value. These animals had also stronger 5-HT- and CRF-related immunostaining in the M2 area, and increased concentration of GABA in the basolateral nucleus of amygdala (in vivo microdialysis). The LR group vocalized more during test session in the aversive band, and had higher serum levels of corticosterone, examined 10 min after test session. It was shown that different natural patterns of responding to conditioned aversive stimuli are associated with different involvement of brain structures and with dissimilar neurochemical mechanisms.

Inhibition of neophobia-stimulated c-Fos expression in the dorsomedial part of the prefrontal cortex in rats pretreated with midazolam.

The effect of an anxiolytic drug, midazolam, on the expression of c-Fos protein (the product of the immediate early gene, c-fos) in the rat brain was studied in animals that were exposed to the stress of neophobia using the open field test. Midazolam (0.5 mg/kg, ip) selectively and significantly attenuated the neophobia-induced increase in the number of Fos-like immunoreactive neurons in the dorsomedial part of the prefrontal cortex, but not in the primary motor cortex, the piriform cortex or the amygdalar nuclei. Overall, the effects of midazolam indicate that the prefrontal cortex is a likely candidate region in which drugs exert their anxiolytic action, and that the dorsomedial part of the prefrontal cortex may participate in the formation and expression of acute innate fear responses.

The effects of acute corticosterone administration on anxiety, endogenous corticosterone, and c-Fos expression in the rat brain.

The effects of acute pretreatment of rats with corticosterone (5 and 20 mg/kg, s.c.) on emotional behavior, expression of c-Fos protein in brain structures, and serum concentration of corticosterone were studied to model the short-term glucocorticoid-dependent changes in brain functions. Corticosterone was administered 90 min before training of a conditioned fear reaction (a freezing response), and behavioral, hormonal and immunocytochemical effects were examined 1 day later, on the test day. Pretreatment of rats with corticosterone significantly attenuated the freezing reaction in the conditioned fear test. The effect of the corticosterone was accompanied by a selective enhancement of the aversive context-induced c-Fos expression in some brain structures: the parvocellular and magnocellular neurons of the paraventricular hypothalamic nucleus (pPVN and mPVN), the medial amygdala nucleus (MeA), and the cingulate cortex, area 1 (Cg1), as well as an increase in the concentration of aversive context-induced endogenous serum glucocorticoid, 1.5 h and 10 min after the test session, respectively. It is suggested that the behavioral effects of acute pretreatment of rats with corticosterone could be due to changes in the mnemonic processes in the brain, inhibition of brain corticotropin releasing factor (CRF) synthesis, or stimulation of GABA-A receptor modulating neurosteroids synthesis. It is hypothesized that the enhanced activity of Cg1, MeA, pPVN, and mPVN, and the hypothalamic-pituitary-adrenal axis with concomitant increased serum glucocorticoid concentration, might serve to facilitate active coping behavior in a threatening situation.

Fluoxetine attenuates the effects of pentylenetetrazol on rat freezing behavior and c-Fos expression in the dorsomedial periaqueductal gray.

The aim of the study was to investigate the role of the periaqueductal gray (PAG) in anxiolytic-like actions of fluoxetine in animals treated with an anxiogenic drug, pentylenetetrazol (PTZ), and subjected to fear conditioning procedure. The data showed that PTZ given at the dose of 30 mg/kg 15 min before a retention trial significantly decreased freezing reaction (p<0.01), and potently enhanced rat locomotor activity (p<0.01), in comparison to the control group. These effects were reversed by prior (60 min) administration of fluoxetine (20 mg/kg). Simultaneously, PTZ significantly increased c-Fos expression in the dorsomedial periaqueductal gray (DMPAG), examined 2h after the retention trial, in comparison to the control group (p<0.01). Fluoxetine (20 mg/kg) administered 60 min before PTZ reversed this effect. PTZ given at the same dose and time interval in the open field test did not affect rat locomotor behavior. Importantly, fluoxetine pretreatment did not change PTZ concentration in brain tissue. Our experiment based on PTZ-enhanced aversive conditioning revealed that acutely administered fluoxetine antagonized PTZ-induced panic-like behavior, and this phenomenon was accompanied by inhibition of activity of DMPAG.

The effects of acute and chronic administration of corticosterone on rat behavior in two models of fear responses, plasma corticosterone concentration, and c-Fos expression in the brain structures.

The aim of this paper was to examine changes in rat emotional behavior, and to find the brain structures, which are involved in the mediation of behavioral effects, related to the repeated administration of glucocorticoids. The effects of acute and chronic pretreatment of rats with two doses of corticosterone (5 and 20 mg/kg) were analyzed in two models of fear responses: neophobia-like behavior in the open field test, and freezing reaction in the conditioned fear test. Behavioral effects of repeated glucocorticoid administration were compared to changes in blood total corticosterone concentration, and expression of immediate early gene (c-Fos) in brain structures. It was found that acute administration of corticosterone (90 min before tests) enhanced rat exploratory behavior, and decreased freezing reaction. On the other hand, repeated administration of corticosterone (for 25 days, the final injection 90 min before contextual fear conditioning training) decreased plasma corticosterone concentration, inhibited exploratory behavior, enhanced freezing responses on retest and produced a complex pattern of changes in c-Fos expression, stimulated by exposure of rats to the aversively conditioned context. Aversive context induced c-Fos in the magnocellular neurons of the hypothalamic paraventricular nucleus (mPVN), dentate gyrus (DG), cingulate cortex area 1 (Cg1), and primary motor cortex (M1). In rats chronically treated with corticosterone this effect was attenuated in the mPVN and DG, enhanced in the M1, and additionally observed in the CA1, CA2 layers of the hippocampus, and in the central nucleus of amygdala (CeA), in comparison to control animals not subjected to contextual fear test. In sum, the present data suggest that chronic corticosterone treatment enhances the activity of primary motor cortex and CeA with subsequent improvement of memory of aversive events, and simultaneously stimulates a negative feedback mechanism operating in PVN with ensuing decrease in blood corticosterone concentration.

Behavioral, immunocytochemical and biochemical studies in rats differing in their sensitivity to pain.

The aim of the study was to further explore the anatomical and neurochemical background of differences in response to the conditioned aversive stimuli. The different patterns of behavioral coping strategies (a conditioned freezing response and ultrasonic vocalization) were analyzed in animals differing in their response to the acute painful stimulation, a foot-shock (HS: high sensitivity rats, LS: low sensitivity rats, and MS: medium sensitivity rats, according to their behavior in the flinch-jump pre-test), and correlated with plasma corticosterone levels, expression of c-Fos protein, and distribution of 5-HT innervation, in different brain structures. It was found that HS rats showed significantly more freezing behavior, whereas LS animals vocalized much more intensively. The behavior of LS group (less freezing response and stronger vocalization) was related to activation of prefrontal cortex (PFCX), increased activity of adrenal glands and stronger serotonin immunostaining in the PFCX, in comparison with HS animals. The more passive strategy of coping with the aversive event of HS group was related to increased activity of amygdalar nuclei and some areas of the hippocampus, and stronger 5-HT immunostaining in the baso-lateral nucleus of the amygdala, in comparison with LS rats. The present findings suggest that animals more vulnerable to stress might have innate deficits in the activity of brain systems controlling the hypothalamic-pituitary-adrenal axis that would normally allow them to cope with stressful situations. It appears also that response to pain may determine other patterns of emotional behavior, probably reflecting different activation thresholds of some brain structures controlling anxiety, e.g. prefrontal and secondary motor cortex.

Effects of methadone and morphine on c-Fos expression in the rat brain: similarities and differences.

This is the first study designed to compare the pattern of stimulation of c-Fos in selected brain structures after an acute administration of morphine and methadone. Methadone and morphine induced activation of c-Fos protein in the terminal forebrain projecting areas of the brain dopaminergic system, i.e. the striatum and nucleus accumbens. Taking into account generally accepted differences in the potency of pharmacological effects of the two drugs, it is surprising that this effect was most evident after the dose of 5 mg/kg of either drug.

Buspirone attenuates conditioned fear-induced c-Fos expression in the rat hippocampus.

The role of hippocampus in the anxiolytic-like effect of buspirone in the conditioned emotional response test (CER, a freezing response), was examined by immunocytochemical detection of the c-Fos protein. It was shown that buspirone at the dose of 0.5 and 1.5 mg/kg i.p. given before test session, which was 24 h after the aversive training, significantly decreased freezing response within a limited dose range of the U-shaped dose-response relationship. Exposure of animals to aversively conditioned context (a contextual fear) induced the production of c-Fos protein in the dentate gyrus, CA-1 and CA-3 layers of the hippocampus. Pretreatment with buspirone (1.5 mg/kg) significantly attenuated the effects of aversive memory on c-Fos protein expression in the CA-1 and CA-3 layers of the hippocampus. These immunocytochemical results support previous data obtained in our laboratory with the help of selective neurotoxic lesions and intrahippocampal drug injections suggesting an important role of hippocampus in the anxiolytic effects of buspirone.