Footshock Research Articles

Norepinephrine and corticosterone in the medial prefrontal cortex and hippocampus predict PTSD-like symptoms in mice.

This study measured changes in brain extracellular norepinephrine (NE) and free corticosterone (CORT) levels in a mouse model of post-traumatic stress disorder and related them to hyperarousal and fear memory retention. To this end, microdialysis in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of male C57BL/6NCrl mice was performed during an acoustic startleresponse (ASR) and following an electric foot shock (FS), as well as during an ASR and recall of contextual fear (CF) 1day later. Changes in ASR-stimulated NE levels in the mPFC corresponded to ASR 34days after FS. Changes in basal and ASR-stimulated extracellular NE levels in the HPC, in contrast, were related to expression of early (day 2) and late (day 34) CF after FS. The increase in extracellular NE levels correlated in a U-shape manner with arousal levels and CF, thus suggesting a non-direct relationship. Stress of different modalities/strength (ASR, FS and CF) caused a similar relative increase in free CORT levels both in the mPFC and the HPC. One day after FS, ASR-induced increases in the CORT content in the mPFC tended to correlate with the FS-potentiated ASR in a U-shape manner. Taken together, these data show that the intracerebral increase in free CORT was likely related to an immediate response to stress, whereas NE neurotransmission in the forebrain predicted arousal and CF 1month after trauma.

Sex differences in the stress response in SD rats

Sex differences play an important role in depression, the basis of which is an excessive stress response. We aimed at revealing the neurobiological sex differences in the same study in acute- and chronically-stressed rats. Female Sprague-Dawley (SD) rats were randomly divided into 6 groups: chronic unpredictable mild stress (CUMS), acute foot shock (FS) and controls, animals in all 3 groups were sacrificed in proestrus or diestrus. Male SD rats were randomly divided into 3 groups: CUMS, FS and controls. Comparisons were made of behavioral changes in CUMS and control rats, plasma levels of corticosterone (CORT), testosterone (T) and estradiol (E2), and of the hypothalamic mRNA-expression of stress-related molecules, i.e. estrogen receptor α and β, androgen receptor, aromatase, mineralocorticoid receptor, glucocorticoid receptor, corticotropin-releasing hormone, arginine vasopressin and oxytocin. CUMS resulted in disordered estrus cycles, more behavioral and hypothalamic stress-related molecules changes and a stronger CORT response in female rats compared with male rats. Female rats also showed decreased E2 and T levels after FS and CUMS, while male FS rats showed increased E2 and male CUMS rats showed decreased T levels. Stress affects the behavioral, endocrine and the molecular response of the stress systems in the hypothalamus of SD rats in a clear sexual dimorphic way, which has parallels in human data on stress and depression.

Individual differences in gene expression of vasopressin, D2 receptor, POMC and orexin: Vulnerability to relapse to heroin-seeking in rats

Individual vulnerability to stress-induced relapse during abstinence from chronic heroin exposure is a key feature of opiate addiction, with limited studies on this topic. Arginine vasopressin (AVP) and its V1b receptor, components of the brain stress responsive systems, play a role in heroin-seeking behavior triggered by foot shock (FS) stress in rats. In this study, we tested whether individual differences in the FS-induced heroin-seeking were associated with alterations of AVP and V1b, as well as other stress responsive systems, including pro-opiomelanocortin (POMC), orexin, plasma ACTH and corticosterone, as well as dopamine D2 receptor (D2) and plasma prolactin. Sprague–Dawley rats were subjected to 3-hour intravenous heroin self-administration (SA) and then tested in extinction, and FS-induced and heroin priming-induced reinstatements. The rats that self-administered heroin were divided into high and low reinstatement responders induced by FS (H-RI; L-RI). Over SA sessions, both the H-RI and L-RI displayed similar active lever responding, heroin infusion and total heroin intake. Compared to the L-RI, however, the H-RI showed greater active lever responses during stress-induced reinstatement, with higher AVP mRNA levels in medial/basolateral amygdala and lower D2 mRNA levels in caudate putamen. However, heroin priming resulted in similar reinstatement in both groups and produced similarly low POMC and high orexin mRNA levels in hypothalamus. Our results indicate that: 1) enhanced amygdalar AVP and reduced striatal D2 expression may be related to individual vulnerability to stress-induced reinstatement of heroin- seeking; and 2) heroin abstinence-associated alterations of hypothalamic orexin and POMC expression may be involved in drug priming-induced heroin-seeking.

Effects of the Estrous Cycle and Ovarian Hormones on Central Expression of Interleukin-1 Evoked by Stress in Female Rats

Exposure to stressors such as foot shock (FS) leads to increased expression of multiple inflammatory factors, including the proinflammatory cytokine interleukin-1 (IL-1) in the brain. Studies have indicated that there are sex differences in stress reactivity, suggesting that the fluctuations in gonadal steroid levels across the estrous cycle may play a regulatory role in the stress-induced cytokine expression. The present studies were designed to investigate the role of 17-β-estradiol (E₂) and progesterone (Pg) in regulating the cytokine response within the paraventricular nucleus (PVN) of the hypothalamus through analysis of gene expression with real-time RT-PCR. Regularly cycling female rats showed a stress-induced increase in PVN IL-1 levels during the diestrous, proestrous, and estrous stages. During the metestrous stage, no change in IL-1 levels was seen following FS; however, estrogen receptor (ER)-β levels did increase. Ovariectomy resulted in an increase in PVN IL-1 levels, which was attenuated by treatment with estradiol benzoate (10 or 50 µg), indicating an E₂-mediated anti-inflammatory effect. Ovariectomized rats treated with Pg (500 or 1,250 µg) showed no alteration in IL-1 levels, but Pg did up-regulate ER-β gene expression. The results from the current study implicate a potential mechanism through which high availability of endogenous Pg during the metestrous stage increases ER-β sensitivity, which in turn attenuates the PVN IL-1 response to stress. Thus, the interaction between gonadal steroid hormones and their central receptors may exert a powerful inhibitory effect on neuroimmune consequences of stress throughout the estrous cycle.

Effects of stressors on the reinforcing efficacy of nicotine in adolescent and adult rats

Stress increases drug intake. This depends on the stressor, drug, and aspect of drug seeking assessed. The objectives of these experiments done in adolescent and adult male rats were to (1) examine social defeat effects on acquisition of nicotine self-administration (SA) and the reinforcing efficacy of nicotine and (2) determine the effects of acute exposure to intermittent footshock (FS) or yohimbine on the reinforcing efficacy of nicotine. In experiment 1, rats received four defeat exposures prior to nicotine SA acquisition and progressive ratio (PR) SA sessions (30 μg/kg nicotine/infusion). Exposure to an olfactory cue previously paired with defeat was also tested on responding maintained by nicotine on the PR schedule. In experiments 2 and 3, the effects of FS (5 and 10 min) or yohimbine (0.625 and 1.25 mg/kg, i.p.) on PR responding for nicotine (15, 30, or 60 μg/kg/infusion) were assessed. Adolescents were aged PD34-36 and adults PD81-85 at the beginning of nicotine SA training. Defeat did not affect nicotine SA acquisition. Prior exposure to defeat or a defeat-paired olfactory cue did not affect PR responding for nicotine. FS modestly decreased PR responding in adolescents at the middle nicotine infusion dose. Yohimbine increased PR responding independent of nicotine infusion dose and age. Together with previous work with other drugs, our data indicate that the effects of stress on the reinforcing efficacy of nicotine are stressor- and drug-dependent. This suggests that there is heterogeneity among stressors on how they affect neuronal systems underlying drug intake.

Early Life Stress Affects the Serotonergic System Underlying Emotional Regulation

Traumatic events in early life are implicated in an increased risk of psychiatric diseases, such as depression and anxiety disorders. Serotonin is thought to play a central role in stress-induced psychiatric diseases. Serotonergic systems, including neural organization and receptor function, could dramatically change with each developmental stage. Here, we reviewed the persistent influence of early life stress on emotional regulation, focusing on the serotonergic system in rats. An aversive stimulus, foot shock (FS), during the early postnatal period (2-3 weeks after birth) produced behavioral, neuroanatomical and electrophysiological changes accompanied by serotonergic dysfunction, especially functional impairment of the serotonin (5-hydroxytryptamine; 5-HT)1A receptor in the cortico-limbic area. These findings suggest that normalization of the cortico-limbic serotonergic function has therapeutic potential for early stress-induced emotional disturbance.

Facilitation of fear extinction by the 5‐HT1A receptor agonist tandospirone: Possible involvement of dopaminergic modulation

Fear extinction-based exposure treatment is an important component of psychotherapy for anxiety disorders such as posttraumatic stress disorder (PTSD). Recent studies have focused on pharmacological approaches combined with exposure therapy to augment extinction. In this study, we elucidated the therapeutic potential of the serotonin 1A (5-HT(1A) ) receptor agonist tandospirone compared with the effects of the N-methyl-D-aspartate partial agonist D-cycloserine (DCS), focusing on the possible involvement of dopaminergic mechanisms. We used a rat model of juvenile stress [aversive footshock (FS)] exposure during the third postnatal week (3wFS). The 3wFS group exhibited extinction deficit reflected in sustained fear-related behavior and synaptic dysfunction in the hippocampal CA1 field and medial prefrontal cortex (mPFC), which are responsible for extinction processes. Tandospirone administration (5 mg/kg, i.p.) before and after the extinction trials ameliorated both the behavioral deficit and synaptic dysfunction, i.e., synaptic efficacy in the CA1 field and mPFC associated with extinction training and retrieval, respectively, was potentiated in the tandospirone-treated 3wFS group. Extracellular dopamine release in the mPFC was increased by extinction retrieval in the non-FS control group. This facilitation was not observed in the 3wFS group; however, tandospirone treatment increased cortical dopamine levels after extinction retrieval. DCS (15 mg/kg, i.p.) also ameliorated the extinction deficit in the 3wFS group, but impaired extinction in the non-FS control group. These results suggest that tandospirone has therapeutic potential for enhancing synaptic efficacy associated with extinction processes by involving dopaminergic mechanisms. Pharmacological agents that target cortical dopaminergic systems may provide new insights into the development of therapeutic treatments of anxiety disorders, including PTSD.

Not all stressors are equal: behavioral and endocrine evidence for development of contextual fear conditioning after a single session of footshocks but not of immobilization.

Exposure of animals to footshocks (FS) in absence of any specific cue results in the development of fear to the compartment where shocks were given (contextual fear conditioning), and this is usually evaluated by time spent freezing. However, the extent to which contextual fear conditioning always develops when animals are exposed to other stressors is not known. In the present work we firstly demonstrated, using freezing, that exposure of adult rats to a single session of FS resulted in short-term and long-term contextual fear conditioning (freezing) that was paralleled by increased hypothalamic-pituitary-adrenal (HPA) activation. In contrast, using a similar design, no HPA or behavioral evidence for such conditioning was found after exposure to immobilization on boards (IMO), despite this stressor being of similar severity as FS on the basis of standard physiological measures of stress, including HPA activation. In a final experiment we directly compared the exposure to the two stressors in the same type of context and tested for the development of conditioning to the context and to a specific cue for IMO (the board). We observed the expected high levels of freezing and the conditioned HPA activation after FS, but not after IMO, regardless of the presence of the board during testing. Therefore, it can be concluded that development of fear conditioning to context or particular cues, as evaluated by either behavioral or endocrine measures, appears to be dependent on the nature of the aversive stimuli, likely to be related to biologically preparedness to establish specific associations.

Possible Modulation of the Amygdala on Metaplasticity Deficits in the Hippocampal CA1 Field in Early Postnatally Stressed Rats

Several lines of evidence have shown that early life experiences have a profound impact on fear-related behavior, but the detailed mechanisms are unknown. The present study examined the possible involvement of the amygdala in behavioral deficits associated with fear memory in a juvenile stress model, with a focus on hippocampal synaptic function. Adult rats exposed to footshock (FS) stress during the second postnatal period (2wFS group) exhibited low levels of freezing in response to contextual fear conditioning (CFC). The CFC-induced suppression of long-term potentiation (LTP) in the CA1 field was not found in the 2wFS group. Additionally, synaptic metaplasticity, that is, low-frequency stimulation-induced suppression of subsequent LTP, did not occur in the 2wFS group; instead, LTP was induced. These synaptic changes mimicked the impairment in metaplasticity induced by reversible inactivation of the basolateral amygdala (BLA). Inactivation of the BLA markedly decreased freezing behavior in non-FS controls, similar to the 2wFS group. Furthermore, extracellular signal-regulated kinase activation in the BLA in response to CFC did not occur in the 2wFS group. These findings suggest that early postnatal stress may cause long-term dysfunction of the modulatory effect of the amygdala on hippocampal function associated with fear memory.

Early postnatal stress alters extracellular signal‐regulated kinase signaling in the corticolimbic system modulating emotional circuitry in adult rats

The present study elucidated whether early life stress alters the extracellular signal-regulated kinase (ERK) pathway that underlies fear retrieval and fear extinction based on a contextual fear conditioning paradigm, using a juvenile stress model. Levels of phospho-ERK (pERK), the active form of ERK, increased after fear retrieval in the hippocampal CA1 region but not in the medial prefrontal cortex (mPFC). ERK activation in the CA1 following fear retrieval was not observed in adult rats who received aversive footshock (FS) stimuli during the second postnatal period (2wFS), which exhibited low levels of freezing. In fear extinction, pERK levels in the CA1 were increased by repeated extinction trials, but they were not altered after extinction retrieval. In contrast, pERK levels in the mPFC did not change during extinction training, but were enhanced after extinction retrieval. These findings were compatible in part with electrophysiological data showing that synaptic transmission in the CA1 field and mPFC was enhanced during extinction training and extinction retrieval, respectively. ERK activation in the CA1 and mPFC associated with extinction processes did not occur in rats that received FS stimuli during the third postnatal period (3wFS), which exhibited sustained freezing behavior. The repressed ERK signaling and extinction deficit observed in the 3wFS group were ameliorated by treatment with the partial N-methyl-D-aspartate receptor agonist D-cycloserine. These findings suggest that early postnatal stress induced the downregulation of ERK signaling in distinct brain regions through region-specific regulation, which may lead to increased behavioral abnormalities or emotional vulnerabilities in adulthood.

Mixture of cis-3-hexenol and trans-2-hexenal attenuates behavioral and stress responses induced by 2,5-dihydro-2,4,5-trimethylthiazoline and electric footshock stress in rats

Green odor (GO), a mixture of cis-3-hexenol and trans-2-hexenal, attenuates stress responses and anxiety to psychological stressors in rodents; however, it remains unknown whether GO affects behavioral and stress responses to risk-related olfactory stimuli and actual noxious stimuli. The present study investigated the effects of green odor on behavioral and plasma adrenocorticotropic hormone (ACTH) responses to 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), a component of fox feces, and electric footshock (FS) stress. When rats were simultaneously exposed to TMT and GO, they showed decreases in immobility and plasma ACTH levels compared with TMT alone. GO exposure after TMT increased immobility, but blocked the elevation of plasma ACTH levels compared with rats exposed to distilled water after TMT. This means that GO presentation during TMT attenuated the TMT-induced behavioral response and GO presentation during and after TMT inhibited TMT-induced elevation of plasma ACTH levels. Furthermore, electric FS-induced plasma ACTH elevations were attenuated by simultaneous GO and FS exposure. GO presentation after FS attenuated plasma ACTH elevations and fecal responses. These findings reveal that GO has alleviating effects on olfactory stimulus- and noxious stimulus-induced behavioral and endocrinal responses.

Exogenous oxytocin (OT) ameliorates pulmonary damage caused by Escherichia coli (E. coli) infection in chronically stressed rats

This study examines the hypothesis that exogenous OT will reduce pulmonary damage caused by E. coli infection in stressed rats. Four groups of male albino rats were used as follows: 1) rats received an intratracheal (i.t.) injection of 0.2 mL E. coli suspension containing 1·109 bacteria/mL in saline; 2) rats were subjected to footshock (FS) stress for 1–11 days; 3) rats were subjected to FS stress for 7 days and then received an i.t. injection of E. coli; 4) rats subjected to FS stress had concurrently received i.m. injections of OT (0,02 IU/mL) for 7 days and then were injected with E. coli. The lungs, hypothalamus, and neurohypophysis were analyzed by light and electron microscopy, immunohistochemistry on days 1 to 11 (groups: 1–2) and days 8 to 11 (groups: 3–4). We found that an E. coli infection in chronically stressed rats caused a greater inflammatory response, cell death and fibrosis than were seen in non‐FS animals. The detrimental changes in the former coincided with increased inhibition of OT release from neurohypophysial terminals. The injections of OT reduced the number of apoptotic cells (~40%) and production of MMP‐9 (~75%), while it stimulated the expression of Bcl‐2, Clara cell protein (CC‐16), and lactoferrin in the lungs. Thus, we concluded that exogenous OT shows a therapeutic effect against E. coli‐induced lung injury under condition of chronic stress, when the release of endogenous neuropeptide is impaired.

Repeated exposure to immobilization or two different footshock intensities reveals differential adaptation of the hypothalamic–pituitary–adrenal axis

Factors involved in adaptation to repeated stress are not well-characterized. For instance, acute footshock (FS) of high intensity appears to be less severe than immobilization (IMO) in light of the speed of post-stress recovery of the hypothalamic-pituitary-adrenal (HPA) axis and other physiological variables. However, repeated exposure to IMO consistently resulted in reduction of the HPA response to the same stressor (adaptation), whereas failure to adapt has been usually reported after FS. Thus, in the present work we directly compared the activation of HPA axis and other physiological changes in response to both acute and repeated exposure to IMO and two intensities of FS (medium and high) in adult male rats. Control rats were exposed to the FS boxes but they did not receive shocks. Daily repeated exposure to IMO resulted in significant adaptation of the overall ACTH and corticosterone responses to the stressor. Such a reduction was also observed with repeated exposure to FS boxes and FS-medium, whereas repeated exposure to FS-high only resulted in a small reduction of the corticosterone response during the post-stress period. This suggests that some properties of FS-high make adaptation to it difficult. Interestingly, overall changes in food intake and body weight gain throughout the week of exposure to the stressors reveal a greater impact of IMO than FS-high, indicating that factors other than the intensity of a stressor, at least when evaluated in function of the above physiological variables, can influence HPA adaptation. Since FS exposure is likely to cause more pain than IMO, activation of nociceptive signals above a certain level may negatively affect HPA adaptation to repeated stressors.

MRNA expression of corticotropin-releasing factor and urocortin 1 after restraint and foot shock together with alprazolam administration

Corticotropin-releasing factor (CRF) is expressed in the paraventricular nucleus of the hypothalamus (PVN), and act centrally to provoke stress-like autonomic and behavioral responses. Urocortins 1–3 are additional ligands to the CRF receptors 1 and 2. Ucn 1 neurons are primarily concentrated in the Edinger–Westphal (EW) nucleus and also have been associated with stress responses. It is also known that UCN 1 respond in different ways depending on the stressor presented. Benzodiazepines can act via the CRF peptidergic system and chronic administration of alprazolam does not interfere with CRF mRNA expression in the PVN, but significantly increase Ucn 1 mRNA expression in the EW. The aim of our study was to investigate the relationship between different stressor stimuli, foot shock (FS) and restraint (R), and the mRNA expression of CRF and Ucn 1 in the PVN and EW using alprazolam (A). We employed fos activation and in situ hybridization. Restraint group presented increased fos-ir and CRF mRNA expression in the PVN compared to FS group. The stress responses of R group were prevented by A. In the EW, fos-ir was higher in the FS group than in the R group, whereas Ucn 1 mRNA expression was higher in the R group than in the FS group. Alprazolam significantly increased fos-ir and Ucn 1 mRNA expression in both groups. Our results show that PVN and EW respond in different ways to the same stressors. Furthermore, EW of stressed animals replies in a complementary way comparing to PVN with the use of Alprazolam.

Juvenile stress attenuates the dorsal hippocampal postsynaptic 5-HT1A receptor function in adult rats

Traumatic events in early life are associated with an increased risk of psychiatric diseases in adulthood. 5-hydroxytryptamine (5-HT)(1A) receptors play a pivotal role in the 5-HTergic mechanisms associated with the etiology of stress-related disorders. The goal of the present study was to investigate whether juvenile stress influences emotional control via postsynaptic 5-HT(1A) receptor in the hippocampus and amygdala using contextual fear conditioning test in adult rats. The rats were subjected to aversive footshock (FS) during the third week of the postnatal period (3wFS group). During the postadolescent period (10-14 weeks postnatal), experiments were performed. The systemic administration of the 5-HT(1A) receptor agonist R-(+)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (0.2 mg/kg, i.p.) attenuated the freezing behavior in the non-FS group, but not in the 3wFS group. The bilateral local injection of 8-OH-DPAT (1 μg/side) into the amygdala decreased the freezing behavior in the non-FS group and the 3wFS group. However, the local injection of 8-OH-DPAT (1 μg/side) into the hippocampus decreased the freezing behavior in the non-FS group, but not in the 3wFS group. In a 5-HT(1A) receptor binding study, the Bmax of the 3wFS group decreased in the dorsal hippocampus, but not the amygdala in comparison with the non-FS group. The juvenile stress attenuated the hippocampal postsynaptic 5-HT(1A) receptor function in context-dependent conditioned fear.

Increased spontaneous activity and reduced inotropic response to catecholamines in ventricular myocytes from footshock-stressed rats

Exposure to stressors has been shown to change atrial responsiveness to catecholamines, but it is not clear yet how it affects the ventricular myocardium, which plays a major role in the catecholamine-stimulated increase in cardiac output. Adult male rats were submitted to restraint (RST) or footshock (FS) sessions for 3 days. Reactivity to agonists of the β-adrenergic pathway was analyzed in left ventricular myocytes isolated from stressed and control rats (CTR). Whereas no significant changes were detected after RST, enhancement of catecholamine-induced spontaneous activity, accompanied by decrease in inotropic maximal response, was observed in myocytes from FS rats. Changes were reversed by β1-, but not by α1- or β2-adrenoceptor (AR) blockade. Similar alterations were seen in response to forskolin. However, responsiveness to 3-isobutyl-1-methylxanthine and CaCl2 was comparable in control and FS groups. A significant negative correlation was observed between the maximally stimulated spontaneous activity rate and contraction amplitude. Results indicate that: (a) enhanced automatism during adrenergic stimulation of myocytes from FS rats is mediated by β1-ARs and seems to involve post-receptor mechanisms, probably decreased cAMP degradation; (b) the exaggerated spontaneous activity, which may contribute to generation of catecholaminergic arrhythmias, might limit the development of the inotropic response.

Inhibitory effects of antipsychotic and anxiolytic agents on stress-induced degranulation of mouse dermal mast cells

Various psychological stresses induce degranulation of mast cells. It has been confirmed by animal experiments that stress induced by restraint promotes mast-cell degranulation in various organs, and that the degranulation is inhibited by pretreatment with corticotropin-releasing factor (CRF)-neutralizing antibodies, CRF receptor antagonists, and neurotensin (NT) antagonists. Previous studies have suggested that anxiety and fear induced in animals by psychological stressors promote the production and release of various neuropeptides and neurotransmitters, and induce degranulation of mast cells in several organs. To evaluate the effect of prior treatment with antipsychotic and anxiolytic agents to inhibit foot-shock (FS) stress-induced degranulation of mouse dermal mast cells. Using a communication box system, FS was administered to mice and the degranulated dermal mast cells were counted. Chlorpromazine (2 or 4 mg/kg body weight), tandospirone (10 mg/kg body weight) or CRA1000, a selective non-peptidic CRF receptor type 1 antagonist (10 or 100 mg/kg body weight) was injected intraperitoneally 1 h before exposure to FS. After FS was administered, the number of dermal mast cells did not change. However, FS significantly increased the proportion of degranulated mast cells. Pretreatment of mice with chlorpromazine hydrochloride, an antipsychotic agent (2 or 4 mg/kg), or the anxiolytic agents tandospirone citrate (10 mg/kg) or CRA1000 (10 or 100 mg/kg), significantly inhibited the FS-induced mast-cell degranulation (P < 0.05, P < 0.01, P < 0.05, P < 0.05, and P < 0.05, respectively). Antipsychotic and anxiolytic agents may be effective treatments for stress-aggravated inflammatory skin diseases by inhibition of mast-cell degranulation.

Early postnatal stress affects 5-HT 1A receptor function in the medial prefrontal cortex in adult rats

Traumatic events in early life are associated with an increased risk of psychiatric diseases in adulthood. 5-hydroxytryptamine (5-HT) 1A receptors are known to play a pivotal role in the 5-HTergic mechanisms associated with the etiology of stress-related disorders. The goal of the present study was to investigate whether early postnatal stress influences 5-HT 1A receptor function in the medial prefrontal cortex in adult rats. Rats were subjected to aversive foot shock (FS) during the third week of the postnatal period (3wFS group). During the postadolescent period (10–14 weeks postnatal), immunohistochemical experiments were carried out to investigate c-Fos expression following the administration of R-(+)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a 5-HT 1A receptor agonist. In the 3wFS group, the 8-OH-DPAT-induced c-Fos expression in the medial prefrontal cortex was significantly attenuated compared to that in the non-FS control group. A dual immunofluorescence study revealed that a small proportion of c-Fos positive cells co-express parvalbumin, and a relatively large proportion of c-Fos positive cells co-express glutaminase, suggesting that most c-Fos positive cells are glutamatergic neurons. We found that local perfusion of 8-OH-DPAT via a dialysis probe decreased extracellular 5-HT levels in the medial prefrontal cortex of the non-FS group, but not in the 3wFS group. However, the levels of 8-OH-DPAT-induced 5-HT syndrome were not significantly different between the non-FS and 3wFS groups. Therefore, aversive stress in the third week of the postnatal period attenuates 5-HT 1A receptor function in the medial prefrontal cortex in adulthood and produces feedback inhibition of the raphe nuclei via postsynaptic 5-HT 1A receptors.

Neonatal administration of fluoxetine did not alter the anxiety indicators, but decreased the locomotor activity in adult rats in the elevated plus-maze

The objective of this study was evaluate the anxiety and locomotor activity (LA) in 52 Wistar adult male rats, being 26 treated with fluoxetine (10 mg/Kg - sc) in the neonatal period. These same rats received foot shock (FS) (1.6-mA - 2-s) in the 90th day. The anxiety and LA were appraised by plus-maze. The time spent in the open arms was used as anxiety index and the LA was measured by number of entries in closed arms (NECA) and the total of entries (TE). T-test was used with p<0.05 and expresses data in mean+/-SEM. There were reductions with the fluoxetine group in the NECA (2.35+/-0.33) and in the TE (3.96+/-0.61) compared to the controls (4.65+/-0.52) and (6.96+/-0.94). The neonatal administration of fluoxetine did not alter the anxiety, but reduced the LA in the animals that received FS.

Gender differences in corticotropin and corticosterone secretion and corticotropin-releasing factor mRNA expression in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala in response to footshock stress or psychological stress in rats

Anorexia nervosa is mostly seen in adolescent females, although the gender-differentiation mechanism is unclear. Corticotropin-releasing factor (CRF), a key peptide for stress responses such as inhibition of food intake, increases in arousal and locomotor activity, and gonadal dysfunction, is thought to be involved in the pathophysiology of anorexia nervosa. CRF in the paraventricular nucleus of the hypothalamus (PVN) and CRF in the central nucleus of the amygdala (CeA) are involved in the regulation of stress responses, and gender differences in CRF mRNA expression in these regions in response to various stressors are controversial. We therefore examined CRF gene expression in the PVN and CeA as well as corticotropin (ACTH) and corticosterone secretion in response to a 60-min period of electric footshock (FS) or psychological stress (PS) induced by a communication box in both male and female rats in proestrus or diestrus in an effort to elucidate the mechanism underlying the gender difference in the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the mechanism underlying the remarkable prevalence of anorexia nervosa in females. Female rats in proestrus showed higher basal plasma ACTH and CRF mRNA expression levels in the PVN and CeA than males. Females more rapidly showed higher plasma ACTH and corticosterone levels and a higher CRF mRNA expression level in the PVN in response to FS than males. Although females in both proestrus and diestrus showed significant increases in plasma ACTH and corticosterone and CRF mRNA expression in the PVN in response to PS, no significant responses of the HPA axis to PS were found in males. FS significantly increased CRF mRNA expression in the CeA in both females and males, with significantly higher peaks in females in proestrus than in males, while PS significantly increased CRF mRNA expression in the CeA only in males. These results suggest that gender affects differentially the function of the stress-related regions such as the PVN and CeA. The finding that CRF gene expression in the PVN responds to PS only in females may be a clue to elucidation of the neurobiological mechanism underlying the gender-differential prevalence of anorexia nervosa.