Prenatal stress in the rat alters 5-HT1A receptor binding in the ventral hippocampus

Exposure of a pregnant woman to physical and/or psychological stress might affect her offspring by promoting the development of various learning, behavioral and/or mood disorders in later life. The 5-HT1A and 5-HT2A receptors are prominently implicated in the modulation of anxiety and mood-related behaviors. Using a semi-quantitative radiolabel immunocytochemical analysis (immunobinding), we studied the effect of prenatal stress on binding of these two receptor subtypes in the hippocampus of 4-week-old male and female Fischer 344 rats. Levels of 5-HT1A immunobinding in the ventral hippocampus, which is primarily implicated in emotional processing, were significantly decreased in male offspring after prenatal stress. A trend towards a decrease was observed in the ventral hippocampus of females. In contrast, 5-HT1A immunobinding within the dorsal hippocampus, which is mainly related to learning and memory, was not affected by prenatal stress in offspring of either gender. Likewise, no significant differences between control and prenatally stressed rats were observed for levels of 5-HT2A immunobinding in either part of the hippocampus or gender. The observed reduction in hippocampal 5-HT1A receptor binding in male offspring after prenatal stress may have important consequences for adult anxiety- and depressive-like behavior.     

Neonatal 3,4-methylenedioxymethamphetamine (MDMA) exposure alters neuronal protein kinase A activity, serotonin and dopamine content, and [35S]GTPgammaS binding in adult rats

Recreational use of methylenedioxymethamphetamine (MDMA) has dramatically increased among juveniles and young adults of child-bearing age, and the potential for fetal exposure has increased. For this reason, it is surprising that comparatively few studies have assessed the long-term impact of early MDMA exposure on serotonin (5-HT) and dopamine (DA) neurotransmitter systems. The purpose of this study was to determine whether repeated exposure to MDMA during the preweanling period would cause long-term changes in 5-HT and DA functioning. Rats were treated with saline or 20 mg/kg MDMA (two injections per day) from postnatal day (PD) 11-20. At PD 90, rats were killed, and their dorsal striatum, prefrontal cortex, and hippocampus were removed. 5-HT and DA content, as well as their metabolites, were measured using HPLC. In addition, cAMP-dependent protein kinase A (PKA) activity and agonist-stimulated [35S]GTPgammaS binding was assayed using tissue homogenates from each brain region. Results indicated that early MDMA exposure caused a decrease in PKA activity and 5-HT content in the prefrontal cortex and hippocampus while increasing the efficacy of 5-HT1A receptors as measured by agonist-stimulated [35S]GTPgammaS binding. Additionally, DA content was reduced in the dorsal striatum and prefrontal cortex. These data indicate that early MDMA exposure has long-term effects on the 5-HT and DA neurotransmitter systems that may be mediated, at least partially, by changes in 5-HT1A receptor sensitivity.     

Activation and blockade of dorsal hippocampal Serotonin6 receptors regulate anxiety-like behaviors in a unilateral 6-hydroxydopamine rat model of Parkinson’s disease

ABSTRACT

Objectives: This study aimed to investigate the effect of serotonin₆ (5-HT₆) receptors in the dorsal hippocampus (dHip) on the regulation of Parkinson’s disease (PD)-associated anxiety.

Methods: We examined whether intra-dHip injection of both 5-HT₆ receptor agonist and antagonist was involved in the regulation of anxiety-like behaviors in sham-operated rats and rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle by the open-field and elevated plus maze (EPM) tests. Four weeks after injection of 6-OHDA, the concentrations of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) in relative related brain regions were measured by reverse-phase high-performance liquid chromatography.

Results: In sham-operated rats, intra-dHip injection of both 5-HT₆ receptor agonist WAY208466 (3 and 6 µg/rat) and antagonist SB258585 (4 µg/rat) increased the percentage of time spent in the center area in the open-field test and percentages of open arm entries and open arm time in EPM test, indicating that induced anxiolytic effects. In the lesioned rats, WAY208466 (1.5, 3 and 6 µg/rat) produced anxiolytic responses, whereas SB258585 (2 and 4 µg/rat) produced anxiogenic effects. Neurochemical results showed that intra-dHip injection of WAY208466 (6 µg/rat) decreased NA level in the amygdala, and SB258585 (4 µg/rat) increased DA levels in the dHip and vHip in sham-operated rats, whereas WAY208466 increased DA levels in the dHip, vHip, and amygdala in the lesioned rats.

Discussion: dHip 5-HT₆ receptors are involved in the regulation of anxiety-like behaviors, which may be mediated through different neurochemical mechanisms, and the dHip is an important site involved in these effects.

Abbreviation: PD: Parkinson’s disease;6-OHDA: 6-hydroxydopamine; dHip: dorsal hippocampus; vHip: ventral hippocampus; 5-HT: serotonin; MFB: medial forebrain bundle; DA: dopamine; NA: noradrenaline; EPM: elevated plus-maze; GABA: gamma-aminobutyric acid; BLA: basolateral amygdala     

In utero ethanol exposure decreased the density of serotonin neurons. Maternal ipsapirone treatment exerted a protective effect.

Prior studies from this laboratory showed that in utero ethanol exposure severely retards the development of the serotonin (5-HT) system; we demonstrated a reduced concentration of 5-HT and 5-HT reuptake sites and alterations in the concentration of 5-HT(1A) receptors in ethanol-exposed offspring. These investigations also found that maternal treatment with a 5-HT(1A) agonist, buspirone, prevented most of the ethanol-associated damage to the developing 5-HT system. In the present investigation, we investigated whether the ethanol-associated changes in the 5-HT system are due to a reduction of 5-HT neurons and whether any changes in the density of 5-HT neurons can be prevented by maternal treatment with another 5-HT(1A) agonist, ipsapirone. Using immunocytochemistry, we found that in utero ethanol exposure reduced the density of 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons of postnatal day 5 (PN5) rats. In all three brain areas, the offspring of ethanol-fed, saline-treated dams exhibited a 28%-40% reduction in 5-HT neurons. Ipsapirone prevented the ethanol-induced reduction in 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons. In the dorsal and median raphe of control offspring, ipsapirone did not alter the concentration of 5-HT neurons. However, this drug did reduce 5-HT neurons in the B9 region of the offspring of control-fed rats.     

Perinatal exposure to low-dose of bisphenol A causes anxiety-like alteration in adrenal axis regulation and behaviors of rat offspring: A potential role for metabotropic glutamate 2/3 receptors

AimsThe present study focuses on detecting anxiety-like behavior and associated neurochemical alterations in adolescent rats exposed perinatally to bisphenol A (BPA), an estrogen-mimicking endocrine disrupter and investigating the possible involvement of metabotropic glutamate 2/3 receptors (mGlu2/3 receptors) in BPA-induced anxiogenic effects.Methods and resultsWhen female breeders were administered orally with BPA (40 μg/kg/d) during pregnancy and lactation, their pups (here named ‘BPA-exposed offspring’) developed an anxiety-like phenotype, characterized by the hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, impaired glucocorticoid receptor (GR)-mediated negative feedback regulation of the HPA axis, altered hippocampal synaptic plasticity and increased anxiety-like behaviors. BPA-exposed offspring also showed a reduced expression of mGlu2/3 receptors in the hippocampus. BPA-exposed offspring further subjected to systemic administration of mGlu2/3 receptor agonist (LY379268, 0.5 mg/kg, i.p.) or antagonist (LY341495, 1.5 mg/kg, i.p.) twice per day for 6 days. The results indicated that chronic LY379268 treatment corrected the anxiety-like behaviors and associated neurochemical and endocrinological alterations in BPA-exposed offspring.ConclusionOur data demonstrate for the first time that the perinatal BPA exposure induces an anxiety-like phenotype in behaviors and -related neuroendocrinology, and suggest that the changes in mGlu2/3 receptor might lie at the core of the pathological reprogramming triggered by early-life adversity. mGlu2/3 receptor may serve as a novel biomarker and potential therapeutic target for anxiety disorders associated with adverse early-life agents including perinatal BPA exposure.     

Behavioural and neurochemical responses evoked by repeated exposure to an elevated open platform

Increased psychophysiological resistance to chronic stress has been related to increased 5-HT release in the dorsal hippocampus. This study investigated the changes in 5-HT release and turnover in the hippocampus evoked by acute and repeated exposure to an inescapable stressor, an elevated open platform, and compared them to the changes evoked in the frontal cortex. Repeated exposure to this stressor results in habituation of the plasma corticosterone response to the test, with full habituation being observed after 20 trials. Repeated exposure to the stressor for 5 or 10 occasions increased 5-HT turnover in the hippocampus. By contrast, 5-HT turnover in frontal cortex was increased by acute exposure to the stressor. Microdialysis studies showed that acute stress increased 5-HT overflow in prefrontal cortex but not dorsal hippocampus whereas repeated daily (10 days) exposure to the stressor increased basal extracellular 5-HT in the dorsal hippocampus, but not the prefrontal cortex. Prior exposure to the stressor on up to 10 occasions enhanced the plasma corticosterone response to a challenge in an elevated plus-maze performed 24h later whereas repeated, but not acute, exposure to the stressor, elicited anxiolytic-like behavioural responses in this test. It is concluded that acute exposure to this form of inescapable stress selectively stimulates the 5-HT projections to the frontal cortex; repeated stress elicits a sustained increase in 5-HT release and turnover in the hippocampus. The data are consistent with the hypothesis that increased 5-HT release in the hippocampus may be implicated in the mechanisms underlying habituation to inescapable stress.     

Transgenerational transmission of anxiety induced by neonatal exposure to lipopolysaccharide: implications for male and female germ lines

Neonatal lipopolysaccharide (LPS) exposure increases anxiety-like behaviour and alters neuroendocrine responses to stress in adult rats. The current study assessed whether this anxiety-related phenotype observed in rats neonatally exposed to LPS is transferable to subsequent generations. Wistar rats were exposed to LPS (0.05 mg/kg, Salmonella enteritidis) or non-pyrogenic saline (equivolume) on postnatal days 3 and 5. In adulthood, animals were subjected to restraint and isolation stress or no stress, and subsequently evaluated for anxiety-like behaviours on the elevated plus maze, acoustic startle response, and holeboard apparatus. Blood was collected to examine corticosterone responses to stress and behavioural testing in adulthood. Animals from both treatment groups which exhibited the anxiety-like phenotype were bred with untreated partners. Maternal care of the second generation (F2) was monitored over the first week of life. In adulthood, the F2 generation underwent identical testing procedures as the parental (F1) generation. The F2 offspring of females exposed to LPS as neonates exhibited an anxiety-like phenotype in adulthood and a potentiated corticosterone response to stress (p<.05). F2 offspring of males exposed to LPS as neonates also exhibited an anxiety-like phenotype (p<.05), however, no differences in corticosterone responses were observed. To determine the impact of maternal care on the anxiety-like phenotype, a cross-fostering study was conducted in which offspring of LPS-treated females were fostered to saline-treated mothers and vice versa, which was found to reverse the behavioural and endocrine phenotypes of the F2 generation. These data indicate that a neonatally bacterially induced anxiety phenotype is transferable across generations in both sexes. Maternal care is the mediating mechanism along the maternal line. We suggest that transmission may be dependent upon heritable epigenetic phenomena for the paternal line. The implications of this study apply to potential neuroimmune pathways through which psychopathology may be transmitted along filial lines.     

Prolactin and glucocorticoid receptors in the prefrontal cortex are associated with anxiety-like behavior in prenatally stressed adolescent offspring rats

Prenatal stress (PS) causes anxiety in mothers and their offspring and chewing is a commonly observed behavior during maternal stress. Prolactin (PRL) is an anti-anxiety factor that suppresses the hypothalamic–pituitary–adrenal axis. Here, we studied the roles of PRL, corticosterone (CORT), and their receptors in PS-induced anxiety-like behavior in dams and their offspring. We further investigated whether chewing during maternal stress could prevent PS-induced harmful consequences. Pregnant rats were randomly divided into PS, PS + chewing, and control groups. Anxiety-like behaviors of dams and their adolescent offspring were assessed using the open field test and elevated plus maze. Serum levels of PRL and CORT were measured by ELISA. Expression of mRNA and protein of PRLR and glucocorticoid receptor (GR) in the prefrontal cortex (PFC) were evaluated by qRT-PCR and western blotting, respectively. Compared to the control rats, dams and their female offspring, but not male offspring, in the PS group showed increased anxiety-like behaviors. The PS-affected rats had a lower serum PRL level and increased PRLR expression in the PFC. In contrast, these rats had a higher serum CORT level and decreased GR expression in the PFC. Chewing ameliorated anxiety-like behaviors and counteracted stress-induced changes in serum PRL and CORT, as well as the expression of their receptors in the PFC. Conclusion: PS-induced anxiety-like behavior is associated with changes in the serum levels of PRL and CORT and expression of their receptors in the PFC. Moreover, chewing blunts the hormonal and receptor changes and may serve as an effective stress-coping method for preventing PS-induced anxiety-like behavior.     

Activation of post-synaptic 5-HT(1A) receptors in the dorsal hippocampus prevents learned helplessness development

Activation of post-synaptic 5-HT(1A) receptors in the dorsal hippocampus is proposed to mediate stress adaptation. Chronic social stress and high corticosteroid levels would impair this coping mechanism, predisposing animals to learned helplessness. To test the hypothesis that increasing serotonin levels in the dorsal hippocampus would attenuate the development of learned helplessness, rats received inescapable foot-shock (pre-test session) and were tested in a shuttle box 24-h later. Pre-stressed animals showed impairment of escape responses. This effect was prevented by chronic (21 days) treatment with imipramine (15 mg/kg). Similar results were obtained when the animals received bilateral intra-hippocampal injections, immediately after pre-test, of zimelidine (100 nmol/0.5 microl), a serotonin reuptake blocker, or 8-OH-DPAT (10 nmol), a 5-HT(1A) receptor agonist. The zimelidine effect was prevented by pre-treatment with WAY-100635 (30 nmol), a 5-HT(1A) receptor antagonist. These data suggest that facilitation of serotonergic neurotransmission in the dorsal hippocampus mediates adaptation to severe inescapable stress, probably through the activation of post-synaptic 5-HT(1A) receptors.     

Neurochemical changes in brain serotonin neurons in immature and adult offspring prenatally exposed to cocaine

The present study investigates the age-dependent effects of prenatal cocaine exposure on changes in the neurochemical and functional status of brain serotonin neurons. Pregnant rats were administered either saline or (−)cocaine HCl (15 mg/kg, subcutaneously), twice daily from gestational days 13 through 20. Neurochemical changes in frontal cortex, hypothalamus, hippocampus, striatum and midbrain of prepubescent and adult offspring were determined by measuring: (1) the content of serotonin (5-HT) and its major metabolite 5-hydroxyindolacetic acid (5-HIAA), and (2) the ability of the serotonin releasing drug p-chloroamphetamine (PCA) to reduce brain serotonin levels. Brain catecholamine content was determined in progeny for comparative purposes. Prior to maturation, prenatal exposure to cocaine did not alter basal levels of brain 5-HT or 5-HIAA in any brain region examined. However, in adult progeny prenatally exposed to cocaine, basal 5-HT content was significantly reduced in the frontal cortex (−32%) and hippocampus (−40%), suggesting maturation-dependent effects of prenatal cocaine exposure on brain 5-HT neurons. Consistent with the maturational onset of changes in 5-HT, striatal dopamine was significantly reduced (−10%) by prenatal exposure to cocaine only in adult offspring. Reductions in 5-HT in most brain regions, produced by pharmacological challenge with p-chloroamphetamine (PCA), were comparable in prenatal saline versus cocaine offspring. One notable exception was the markedly greater reduction (−40%) in 5-HT in the midbrain of immature offspring prenatally exposed to cocaine, suggesting alterations in midbrain 5-HT neurons prior to maturation. Overall, these data demonstrate prenatal cocaine exposure produces region-specific changes in 5-HT neurons in offspring with some deficits occurring only following maturation.     

Effects of neonatal rat Borna disease virus (BDV) infection on the postnatal development of the brain monoaminergic systems

Effects of neonatal Borna disease virus infection (BDV) on the postnatal development of brain monoaminergic systems in rats were studied. Tissue content of norepinephrine (NE), dopamine (DA) and its metabolite, 3,4-dihydroxyphenol acetic acid (DOPAC), and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed by means of HPLC-EC in frontal cortex, cerebellum, hippocampus, hypothalamus and striatum of neonatally BDV-infected and sham-inoculated male Lewis rats of 8, 14, 21, 60 and 90 days of age. Both NE and 5-HT concentrations were significantly affected by neonatal BDV infection. The cortical and cerebellar levels of NE and 5-HT were significantly greater in BDV-infected rats than control animals at postnatal days (PND) 60 and 90. Tissue content of NE in hippocampus was unaffected. In hippocampus, neonatally BDV-infected rats had lower 5-HT levels at PND 8 and significantly elevated levels at PND 21 and onwards. Neither striatal levels of 5-HT nor hypothalamic levels of 5-HT and NE were affected by neonatal BDV infection, suggesting that the monoamine systems in the prenatally maturing brain regions are less sensitive to effects of neonatal viral infection. 5-HIAA/5-HT ratio was not altered in BDV-infected rats indicating no changes in the 5-HT turnover in the brain regions damaged by the virus. Neither DA nor DOPAC/DA ratio was affected by neonatal BDV infection in any of the brain regions examined. The present data demonstrate significant and specific alterations in monoaminergic systems in neonatally BDV-infected rats. This pattern of changes is consistent with the previously reported behavioral abnormalities resulting from neonatal BDV infection.     

Behavioral and neurochemical consequences of lipopolysaccharide in mice: anxiogenic-like effects

Systemic administration of lipopolysaccharide (LPS) induces sickness behaviors, as well as alterations of hypothalamic-pituitary-adrenal functioning commonly associated with stressors. In the present investigation, it was demonstrated that systemic LPS treatment induced a sickness-like behavioral profile (reduced active behaviors, soporific effects, piloerection, ptosis), which appeared to be dependent upon the novelty of the environmental context in which animals were tested. As well, LPS induced anxiogenic-like responses, including decreased time spent in the illuminated portion of a light-dark box, reduced open-arm entries in a plus-maze test, and decreased contact with a novel stimulus object in an open-field situation. The behavioral changes were accompanied by increased plasma ACTH and corticosterone levels. As well, LPS induced increased turnover of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the paraventricular nucleus (PVN), median eminence plus arcuate nucleus, hippocampus, as well as NE turnover within the locus coeruleus and DA turnover within the nucleus accumbens. Although these neurochemical variations were reminiscent of those elicited by stressors, LPS was not particularly effective in modifying DA activity within the prefrontal cortex or NE within the amygdala, variations readily induced by stressors. Whether the LPS-induced anxiogenic-like responses were secondary to the illness engendered by the endotoxin remains to be determined. Nevertheless, it ought to be considered that bacterial endotoxin challenge, and the ensuing cytokine changes, may contribute to emotionality and perhaps even anxiety-related behavioral disturbances.     

Attenuating effects of the isolated rearing condition on increased brain serotonin and dopamine turnover elicited by novelty stress

Isolation and acute environmental change are risk factors in human depression. In the present study, we investigated the differences in the brain monoamine activity of rats between two rearing conditions, isolated and group. Moreover, we examined the responses to novelty stress. Male F344 rats aged 11 weeks were divided into the above two groups. Four weeks later they were further divided into non-stress and stress groups. The latter received 20 min exposure to novelty stress. Isolation significantly changed brain monoamine levels, with the levels of dopamine (DA) in the nucleus accumbens and midbrain, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the midbrain, and 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus increasing. Serotonin (5-HT) levels also increased in all brain areas except the raphe nuclei. HVA levels in the raphe nuclei decreased. Novelty stress significantly altered brain monoamine levels. DA, DOPAC, and HVA levels in the prefrontal cortex decreased, as did those of 5-HT in the prefrontal cortex and hippocampus. DA levels in the nucleus accumbens increased. Isolation attenuated the enhanced brain monoamine turnover elicited by novelty stress. The enhanced DA turnover ratio in the prefrontal cortex of the group-reared group was attenuated in the isolated-reared group, and the unchanged DA turnover ratio in the nucleus accumbens of the group-reared group declined in the isolated-reared group. The enhanced 5-HT turnover ratio in the prefrontal cortex, nucleus accumbens, and hippocampus of the group-reared group was attenuated in the isolated-reared group. Isolation may exacerbate adaptation to stress, and be related to the etiology of human depression.     

Reduced anxiety-related behaviour in transgenic mice overexpressing serotonin 1A receptors

Serotonergic neurons play a major role in the modulation of emotion and behaviour. Especially knockout studies have revealed a role for the serotonin(1A) (5-HT(1A)) receptor in anxiety related behaviour. Mutant animals exhibit enhanced anxiety-like responses, possibly resulting from impaired autoinhibitory control of midbrain serotonergic neurons. To further elucidate the role of the 5-HT(1A) receptors in affective behaviour, a complementary approach has been used and transgenic mice overexpressing this receptor subtype have been generated. The expression of the active 5-HT(1A) receptor protein as indicated by autoradiography was transiently increased during early postnatal development (P1.5) as compared to wild-type mice. Within the next 2 weeks, the increase in receptor binding vanished and was also not apparent in adult animals indicating adaptive changes in the regulation of 5-HT(1A) receptor expression. Although no evidence for increased receptor binding in the brains of adult homozygous mice was found by autoradiography, typical phenotypic changes indicative of 5-HT(1A) receptor overactivity were apparent. Transgenic mice revealed a reduced molar ratio of 5-hydroxyindoleacetic acid to serotonin in several brain areas and elevated serotonin values in the hippocampus and striatum. Moreover, anxiety-like behaviour was decreased in male and female transgenic mice and body temperature was lowered in male transgenic mice in comparison with heterozygous and wild-type mice. These findings further underline the pivotal role of 5-HT(1A) receptors in the homeostasis of anxiety-like behaviour and the crucial importance of stimulation of the 5-HT(1A) receptor during the early postnatal development for normal anxiety-like behaviour throughout life.     

Serotonin and learned helplessness: a regional study of 5-HT1A, 5-HT2A receptors and the serotonin transport site in rat brain

Serotonin (5-HT) plays a central role in the neurochemistry of the learned helplessness animal model of depression. Using quantitative autoradiography, we measured the density of 5-HT1A and 5-HT2A receptors and of 5-HT transport sites in medial prefrontal cortex, dorsal hippocampus, septum, hypothalamus, and amygdala in learned helpless rats, and in rats that were nonhelpless after inescapable stress, as well as in shuttlebox-tested and nonhandled controls. We found no changes in 5-HT1A receptor density among the groups in any region studied. In dorsal hippocampus, 5-HT2A receptor density was decreased in nonhelpless rats, while in amygdala 5-HT2A receptor density was decreased in both groups of stressed rats, whether helpless or nonhelpless. In the hypothalamus 5-HT2A receptor density, was decreased in helpless rats as compared to controls. In medial prefrontal cortex, the serotonin transport sites showed decreased density in helpless rats as compared to controls but not to nonhelpless rats. These findings further highlight the complexity of regional 5-HT effects in the learned helplessness animal model.     

Anxiety-like behaviour and associated neurochemical and endocrinological alterations in male pups exposed to prenatal stress

Epidemiological studies suggest that emotional liability in infancy could be a predictor of anxiety-related disorders in the adulthood. Rats exposed to prenatal restraint stress ("PRS rats") represent a valuable model for the study of the interplay between environmental triggers and neurodevelopment in the pathogenesis of anxious/depressive like behaviours. Repeated episodes of restraint stress were delivered to female Sprague-Dawley rats during pregnancy and male offspring were studied. Ultrasonic vocalization (USV) was assessed in pups under different behavioural paradigms. After weaning, anxiety was measured by conventional tests. Expression of GABA(A) receptor subunits and metabotropic glutamate (mGlu) receptors was assessed by immunoblotting. Plasma leptin levels were measured using a LINCOplex bead assay kit. The offspring of stressed dams emitted more USVs in response to isolation from their mothers and showed a later suppression of USV production when exposed to an unfamiliar male odour, indicating a pronounced anxiety-like profile. Anxiety like behaviour in PRS pups persisted one day after weaning. PRS pups did not show the plasma peak in leptin levels that is otherwise seen at PND14. In addition, PRS pups showed a reduced expression of the γ2 subunit of GABA(A) receptors in the amygdala at PND14 and PND22, an increased expression of mGlu5 receptors in the amygdala at PND22, a reduced expression of mGlu5 receptors in the hippocampus at PND14 and PND22, and a reduced expression of mGlu2/3 receptors in the hippocampus at PND22. These data offer a clear-cut demonstration that the early programming triggered by PRS could be already translated into anxiety-like behaviour during early postnatal life.     

Effects of lesions to the dorsal and ventral hippocampus on defensive behaviors in rats

This study investigated the role of the hippocampus in both unconditioned and conditioned defensive behaviors by examining the effects of pretraining ibotenic acid lesions to the dorsal and ventral hippocampus in male Long-Evans hooded rats exposed to three types of threat stimuli: cat-odor, a live cat and footshock. Defensive behaviors were assessed during exposure to cat-odor and a live cat, and immediately following the presentation of footshock. Conditioned defensive behaviors were also assessed in each context 24 h after initial threat exposure. During both unconditioned and conditioned trials, dorsal hippocampal lesions failed to significantly alter any behavioral measure in each test of defense. In contrast, ventral hippocampal lesions significantly reduced unconditioned defensive behaviors during exposure to cat-odor without producing any observable effects during cat exposure. Furthermore, ventral lesions significantly attenuated conditioned defensive behaviors following the administration of footshock and during re-exposure to each context. These results suggest a specific role for the ventral, not dorsal, hippocampus in modulating anxiety-like behaviors in certain animal models of defense.     

Selective changes in the contents of noradrenaline, dopamine and serotonin in rat brain areas during aging

This study examines the age-associated changes in noradrenaline (NA), dopamine (DA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), serotonin (5-HT) and 5-hydroxy-3-indoleacetic acid (5-HIAA) in different brain areas of rats. DA and DOPAC concentrations in striatum increased at third month of age, remaining without significant variations until 12th month of age, and decreasing in 24-month-old rats. DA concentration dropped in hippocampus, amygdala and brainstem of 24-month-old-rats, whereas DOPAC levels decreased only in hippocampus. These changes suggest an age-dependent deficit of the dopaminergic system, presumably related to a reduced number/activity of DA nigrostriatal and mesolimbic neurons. An age-induced decline in NA content was found in the pons-medulla, the area containing NA neuronal bodies. Concentrations of 5-HT were reduced with aging in frontal cortex, showing a tendency to decrease in all brain areas examined. The increased 5-HIAA/5-HT ratio found in frontal cortex, amygdala and striatum suggests an age-related decreased synthesis and an accelerated 5-HT metabolism. The 5-HIAA content decreased in brainstem of the oldest rats. These findings point to a selective impairment of nigrostriatal and mesolimbic DA in aging rats, whereas reductions in NA were restricted to cell bodies region and 5-HT showed changes of different extent in areas of terminals and neuronal cell bodies.     

Effect of corticotropin releasing factor receptor 1 antagonist on extracellular norepinephrine, dopamine and serotonin in hippocampus and prefrontal cortex of rats in vivo

Corticotropin releasing factor (CRF) is a major mediator of adaptive responsiveness to stress. We measured changes in extracellular concentrations of catecholamine and indoleamines in freely moving rats in response to administration of CRF1 antagonist CP-154,526 by using in vivo microdialysis. Dialysis probes were placed stereotaxically in either the hippocampus or the prefrontal cortex. We examined the response in the hippocampus or the prefrontal cortex to 32.0 mg/kg i.p. administration of CP-154,526. CP-154,526 reduced the extracellular concentration of norepinephrine (NE) from 30 min to 180 min and 5-hydroxytryptamine (5-HT) from 30 min to 60 min after injection in the hippocampus. CP-154,526 did not remarkably change dopamine (DA). There were no significant differences between CP-154,526 and vehicle in NE, 5-HT and DA in the prefrontal cortex. The present results indicate that CRF1 receptor antagonist produced a decrease in dialysate concentration of NE and 5-HT, but not DA, in the hippocampus. These results suggest that the CRH-1 receptor antagonist suppresses the release of NE and 5-HT in the hippocampus.     

Aniracetam enhances cortical dopamine and serotonin release via cholinergic and glutamatergic mechanisms in SHRSP

Aniracetam, a cognition enhancer, has been recently found to preferentially increase extracellular levels of dopamine (DA) and serotonin (5-HT) in the prefrontal cortex (PFC), basolateral amygdala and dorsal hippocampus of the mesocorticolimbic system in stroke-prone spontaneously hypertensive rats. In the present study, we aimed to identify actually active substances among aniracetam and its major metabolites and to clarify the mode of action in DA and 5-HT release in the PFC. Local perfusion of mecamylamine, a nicotinic acetylcholine (nACh) and N-methyl-D-aspartate (NMDA) receptor antagonist, into the ventral tegmental area (VTA) and dorsal raphe nucleus (DRN) completely blocked DA and 5-HT release, respectively, in the PFC elicited by orally administered aniracetam. The effects of aniracetam were mimicked by local perfusion of N-anisoyl-gamma-aminobutyric acid [corrected] (N-anisoyl-GABA), one of the major metabolites of aniracetam, into the VTA and DRN. The cortical DA release induced by N-anisoyl-GABA applied to the VTA was also completely abolished by co-perfusion of mecamylamine. Additionally, when p-anisic acid, another metabolite of aniracetam, and N-anisoyl-GABA were locally perfused into the PFC, they induced DA and 5-HT release in the same region, respectively. These results indicate that aniracetam enhances DA and 5-HT release by mainly mediating the action of N-anisoyl-GABA that targets not only somatodendritic nACh and NMDA receptors but also presynaptic nACh receptors.