Reduced evoked fos expression in activity-related brain regions in animal models of behavioral depression

Social Defeat Stress in Adolescent Mice Induces Depressive-like Behaviors with Reduced Oligodendrogenesis

Strong stress related to adverse experiences during adolescence can cause mental disorders, as well as affecting brain structure and function. However, the underlying neurobiological mechanisms remain largely unknown. To investigate whether stress induced by adverse experience during adolescence affects oligodendrocyte (OL) remodeling, social defeat stress was applied to 6-week-old adolescent mice for 10 days, followed by behavioral tests and assessments of oligodendrogenesis. Socially defeated mice showed depressive-like behaviors in behavioral experiments. Stress led to a decrease in the number of newly born OLs in the anterior cortical region and the number of proteolipid protein-positive mature OLs in the corpus callosum and posterior cerebral cortex. Fewer bromodeoxyuridine-incorporated CC1-positive mature OLs were observed in these regions in socially defeated mice. To assess whether decreased oligodendrogenesis caused by social defeat stress is related to depressive-like symptoms under stress, clemastine, a drug that induces OL generation, was administered to socially defeated adolescent mice, resulting in the rescue of the behavioral abnormalities accompanied by increased oligodendrogenesis. These findings suggest that oligodendrogenesis in adverse environments during adolescence plays a role in psychiatric disorders, and clemastine may provide a potential therapeutic drug for adolescent mental disorders, targeting OLs.

Effects of neuromedin U-8 on stress responsiveness and hypothalamus-pituitary-adrenal axis activity in male C57BL/6J mice

Neuromedin U (NMU) is a highly conserved neuropeptide that has been implicated in the stress response. To better understand how it influences various aspects of the stress response, we studied the effects of intracerebroventricular NMU-8 administration on stress-related behavior and activity of the hypothalamus-pituitary-adrenal (HPA) axis in male C57BL/6J mice. We investigated these NMU-8 effects when mice remained in their home cage and when they were challenged by exposure to forced swim stress. NMU-8 administration resulted in increased grooming behavior in mice that remained in their home cage and in a significant increase in c-Fos immunoreactivity in the paraventricular hypothalamus (PVH) and arcuate nucleus (ARC). Surprisingly, NMU-8 administration significantly decreased plasma corticosterone concentrations. Furthermore, NMU-8 administration increased immobility in the forced swim test in both naïve mice and mice that were previously exposed to swim stress. The effect of NMU-8 on c-Fos immunoreactivity in the PVH was dependent on previous exposure to swim stress given that we observed no significant changes in mice exposed for the first time to swim stress. In contrast, in the ARC we observed a significant increase in c-Fos immunoreactivity regardless of previous stress exposure. Interestingly, NMU-8 administration also significantly decreased plasma corticosterone concentrations in mice that were exposed to single forced swim stress, while this effect was no longer observed when mice were exposed to forced swim stress for a second time. Taken together, our data indicate that NMU-8 regulates stress responsiveness and suggests that its effects depend on previous stress exposure.

Chronic social stress induces peripheral and central immune activation, blunted mesolimbic dopamine function, and reduced reward-directed behaviour in mice

Psychosocial stress is a major risk factor for depression, stress leads to peripheral and central immune activation, immune activation is associated with blunted dopamine (DA) neural function, DA function underlies reward interest, and reduced reward interest is a core symptom of depression. These states might be inter-independent in a complex causal pathway. Whilst animal-model evidence exists for some specific steps in the pathway, there is currently no animal model in which it has been demonstrated that social stress leads to each of these immune, neural and behavioural states. Such a model would provide important existential evidence for the complex pathway and would enable the study of causality and mediating mechanisms at specific steps in the pathway. Therefore, in the present mouse study we investigated for effects of 15-day resident-intruder chronic social stress (CSS) on each of these states. Relative to controls, CSS mice exhibited higher spleen levels of granulocytes, inflammatory monocytes and T helper 17 cells; plasma levels of inducible nitric oxide synthase; and liver expression of genes encoding kynurenine pathway enzymes. CSS led in the ventral tegmental area to higher levels of kynurenine and the microglia markers Iba1 and Cd11b and higher binding activity of DA D1 receptor; and in the nucleus accumbens (NAcc) to higher kynurenine, lower DA turnover and lower c-fos expression. Pharmacological challenge with DA reuptake inhibitor identified attenuation of DA stimulatory effects on locomotor activity and NAcc c-fos expression in CSS mice. In behavioural tests of operant responding for sucrose reward validated as sensitive assays for NAcc DA function, CSS mice exhibited less reward-directed behaviour. Therefore, this mouse study demonstrates that a chronic social stressor leads to changes in each of the immune, neural and behavioural states proposed to mediate between stress and disruption of DA-dependent reward processing. The model can now be applied to investigate causality and, if demonstrated, underlying mechanisms in specific steps of this immune-neural-behavioural pathway, and thereby to identify potential therapeutic targets.

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Mouse chronic social stress (CSS) leads to spleen and liver immune activation.

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Mouse CSS leads to mesolimbic immune activation and blunted dopamine function.

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Mouse CSS leads to reduced reward-directed behaviour in operant tests.

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This constitutes an important model for the study of pathophysiological mechanisms.

Apocynin Prevents Abnormal Megakaryopoiesis and Platelet Activation Induced by Chronic Stress

Environmental chronic stress (ECS) has been identified as a trigger of acute coronary syndromes (ACS). Changes in redox balance, enhanced reactive oxygen species (ROS) production, and platelet hyperreactivity were detected in both ECS and ACS. However, the mechanisms by which ECS predisposes to thrombosis are not fully understood. Here, we investigated the impact of ECS on platelet activation and megakaryopoiesis in mice and the effect of Apocynin in this experimental setting. ECS induced by 4 days of forced swimming stress (FSS) treatment predisposed to arterial thrombosis and increased oxidative stress (e.g., plasma malondialdehyde levels). Interestingly, Apocynin treatment prevented these alterations. In addition, FSS induced abnormal megakaryopoiesis increasing the number and the maturation state of bone marrow megakaryocytes (MKs) and affecting circulating platelets. In particular, a higher number of large and reticulated platelets with marked functional activation were detected after FSS. Apocynin decreased the total MK number and prevented their ability to generate ROS without affecting the percentage of CD42d⁺ cells, and it reduced the platelet hyperactivation in stressed mice. In conclusion, Apocynin restores the physiological megakaryopoiesis and platelet behavior, preventing the detrimental effect of chronic stress on thrombosis, suggesting its potential use in the occurrence of thrombosis associated with ECS.

Chronic social defeat reduces myelination in the mouse medial prefrontal cortex

The medial prefrontal cortex (mPFC) plays a key role in top-down control of the brain’s stress axis, and its structure and function are particularly vulnerable to stress effects, which can lead to depression in humans and depressive-like states in animals. We tested whether chronic social defeat produces structural alterations in the mPFC in mice. We first performed a microarray analysis of mPFC gene expression changes induced by defeat, and biological pathway analysis revealed a dominant pattern of down-regulation of myelin-associated genes. Indeed, 69% of the most significantly down-regulated genes were myelin-related. The down regulation was confirmed by in situ hybridization histochemistry for two strongly down-regulated genes, myelin oligodendrocyte glycoprotein (Mog) and ermin (Ermn), and by immunohistochemistry for myelin basic protein. To test for stress-induced changes in myelin integrity, aurophosphate (Black Gold) myelin staining was performed on mPFC sections. Quantitative stereologic analysis showed reduced myelinated fiber length and density. Behavioral analysis confirmed that the 14-day social defeat sessions resulted in induction of depressive-like states measured in social interaction and light/dark tests. The combined data suggest that chronic social defeat induces molecular changes that reduce myelination of the prefrontal cortex, which may be an underlying basis for stress-induced depressive states.

Putative Epigenetic Involvement of the Endocannabinoid System in Anxiety- and Depression-Related Behaviors Caused by Nicotine as a Stressor

Like various stressors, the addictive use of nicotine (NC) is associated with emotional symptoms such as anxiety and depression, although the underlying mechanisms have not yet been fully elucidated due to the complicated involvement of target neurotransmitter systems. In the elicitation of these emotional symptoms, the fundamental involvement of epigenetic mechanisms such as histone acetylation has recently been suggested. Furthermore, among the interacting neurotransmitter systems implicated in the effects of NC and stressors, the endocannabinoid (ECB) system is considered to contribute indispensably to anxiety and depression. In the present study, the epigenetic involvement of histone acetylation induced by histone deacetylase (HDAC) inhibitors was investigated in anxiety- and depression-related behavioral alterations caused by NC and/or immobilization stress (IM). Moreover, based on the contributing roles of the ECB system, the interacting influence of ECB ligands on the effects of HDAC inhibitors was evaluated in order to examine epigenetic therapeutic interventions. Anxiety-like (elevated plus-maze test) and depression-like (forced swimming test) behaviors, which were observed in mice treated with repeated (4 days) NC (subcutaneous 0.8 mg/kg) and/or IM (10 min), were blocked by the HDAC inhibitors sodium butyrate (SB) and valproic acid (VA). The cannabinoid type 1 (CB1) agonist ACPA (arachidonylcyclopropylamide; AC) also antagonized these behaviors. Conversely, the CB1 antagonist SR 141716A (SR), which counteracted the effects of AC, attenuated the anxiolytic-like effects of the HDAC inhibitors commonly in the NC and/or IM groups. SR also attenuated the antidepressant-like effects of the HDAC inhibitors, most notably in the IM group. From these results, the combined involvement of histone acetylation and ECB system was shown in anxiety- and depression-related behaviors. In the NC treatment groups, the limited influence of SR against the HDAC inhibitor-induced antidepressant-like effects may reflect the characteristic involvement of histone acetylation within the NC-related neurotransmitter systems other than the ECB system.

Interleukin-1β-immunoreactive neurons in the hippocampus and paraventricular nucleus of the hypothalamus after stress stimulation in aged versus adult rats

It is believed that the impact of stress on interleukin-1β (IL-1β) depends on the ontogenetic age. This study examines the influence of acute or chronic exposure to forced-swim (FS) stress or high-light open-field (HL-OF) stimulation on the expression of IL-1β. Double immunofluorescence staining was used to reveal the density of IL-1β/NeuN (NeuN is a neuronal nuclear marker)-immunoreactive (-ir) cells in the hippocampal subfields CA1 and CA3, dentate gyrus (DG), and paraventricular nucleus (PVN) of the hypothalamus. Adult postnatal day 90 (P90) and aged (P720) rats were used in this experiment. The data showed a significant increase in the density of IL-1β/NeuN-ir cells in the CA1, CA3, DG, and PVN in P720 nonstressed rats in relation to P90 control animals. Neither FS nor HL-OF acute stimulation caused alteration in the density of IL-1β-ir neurons in any of the investigated structures in P90 and P720 rats in comparison with control groups. However, chronic FS caused a significant increase in CA3 and DG of P720 rats, and chronic HL-OF led to a significant increase in the density of IL-1β-ir neurons in the PVN of P90 rats and in all hippocampal subfields of P720 animals. These results indicate that chronic HL-OF stimulation is a factor that induces changes in the number of IL-1β-ir neurons in the PVN of adult rats, whereas both chronic FS and HL-OF are aggravating factors for the hippocampus of aged (P720) animals.

PACAP-deficient mice show attenuated corticosterone secretion and fail to develop depressive behavior during chronic social defeat stress

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) regulates activation of the hypothalamic-pituitary-adrenal (HPA) axis and the adrenal gland in response to various stressors. We previously found that in response to acute psychological stress (restraint), elevated corticotrophin-releasing hormone (CRH) mRNA levels in the hypothalamic paraventricular nucleus (PVN) as well as elevated plasma corticosterone (CORT) were profoundly attenuated in PACAP-deficient mice. To determine whether HPA axis responses and stress-induced depressive-like behaviors in a chronic stress paradigm are affected by PACAP deficiency, we subjected mice to 14 days of social defeat stress. Defeat-exposed PACAP-/- mice showed a marked attenuation of stress-induced increases in serum CORT levels, cellular PVN ΔFosB immunostaining, and depressive-like behaviors (social interaction and forced swim tests) compared to wild-type control mice. The PACAP-/- mice showed reduced PVN FosB-positive cell numbers, but relatively elevated cell counts in several forebrain areas including the medial prefrontal cortex, after social stress. PACAP appears to be specific for mediating HPA activation only in psychological stress because marked elevations in plasma CORT after a systemic stressor (lipopolysaccharide administration) occurred regardless of genotype. We conclude that chronically elevated CORT is a key component of depressive effects of social defeat, and that attenuation of the CORT response at the level of the PVN, as well as extrahypothalamic forebrain regions, in PACAP-deficient mice protects from development of depressive behavior.

Effects of lurasidone in behavioral models of depression. Role of the 5-HT₇ receptor subtype

Major depression is a common psychiatric disorder associated with high symptomatic and functional burdens. Pharmacological treatment is often effective, but there remain substantial unmet needs in the form of non-responders, delayed onset of clinical effect, and side effects. Recent studies have positioned the serotonin 5-HT₇ receptor as a new target for the treatment of depression. Preclinical studies have shown that antagonists induce an antidepressant-like response, a phenotype that can also be observed in mice lacking the receptor. Lurasidone is a new atypical antipsychotic agent with very high affinity for the 5-HT₇ receptor. Patients in clinical trials have reported improved scores in depression ratings. We have tested lurasidone in both acute and chronic mouse models of depression. In the tail suspension and forced swim tests lurasidone decreased immobility, an antidepressant-like response. The effect required functional 5-HT₇ receptors as it was absent in mice lacking the receptor. In the repeated open-space swim test lurasidone was able to reverse the despair induced by repeated swims in a manner similar to the commonly used antidepressant citalopram. The results provide evidence that lurasidone can act as a 5-HT₇ receptor antagonist and provide a possible explanation for the antidepressant effect data currently emerging from lurasidone clinical trials. Additionally, the results give further support for targeting the 5-HT₇ receptor in the treatment of depression. It will be of interest to clinically evaluate lurasidone as an antidepressant either as monotherapy or as an adjunctive therapy to available drugs.

Taking the Perspective that a Depressive State Reflects Inflammation: Implications for the Use of Antidepressants

This paper reviews both the evidence that supports the characterization of depression as an inflammatory disorder and the different biochemical mechanisms that have been postulated for the connection between inflammation and depression. This association offers credible explanation for the short term efficacy of antidepressants, which have short term anti-inflammatory effects. Evidence for those anti-inflammatory effects is discussed. Evidence of the contrary long-term effects of antidepressants, which increase rather than decrease inflammation, is also reviewed. It is argued that this increase in inflammation would predict an increase in chronicity among depressed patients that have been treated with antidepressants drugs, which has been noted in the literature. A brief discussion of alternatives for decreasing inflammation, some of which have demonstrated efficacy in ameliorating depression, is presented.

Blood natural killer cell cytotoxicity enhancement correlates with an increased activity in brain motor structures following chronic stimulation of the bed nucleus of the stria terminalis in rats

The present study indicates that a chronic 14 day electrical stimulation of the bed nucleus of the stria terminalis (BST) increased blood but not spleen natural killer cell (NK) cytotoxicity and a large granular lymphocyte (LGL) number. These immune changes positively correlated with the increased activity in brain cortical and subcortical motor structures that influence the BST stimulation-induced behavioral response. No significant changes in blood and spleen leukocyte population numbers and plasma corticosterone concentration after the stimulation were found. The obtained results suggest that this immunoenhancing effect on blood NK cell function and number is dependent on the behavioral outcome of the BST stimulation rather than endocrine response.

The behavioral phenotype of pituitary adenylate-cyclase activating polypeptide-deficient mice in anxiety and depression tests is accompanied by blunted c-Fos expression in the bed nucleus of the stria terminalis, central projecting Edinger-Westphal nucleus, ventral lateral septum, and dorsal raphe nucleus

Pituitary adenylate-cyclase activating polypeptide (PACAP) has been implicated in the (patho)physiology of stress-adaptation. PACAP deficient (PACAP(-/-)) mice show altered anxiety levels and depression-like behavior, but little is known about the underlying mechanisms in stress-related brain areas. Therefore, we aimed at investigating PACAP(-/-) mice in light-dark box, marble burying, open field, and forced swim paradigms. We also analyzed whether the forced swim test-induced c-Fos expression would be affected by PACAP deficiency in the following stress-related brain areas: magno- and parvocellular paraventricular nucleus of the hypothalamus (PVN); basolateral (BLA), medial (MeA), and central (CeA) amygdaloid nuclei; ventral (BSTv), dorsolateral (BSTdl), dorsomedial (BSTdm), and oval (BSTov) nuclei of the bed nucleus of stria terminalis; dorsal (dLS) and ventral parts (vLS) of lateral septal nucleus, central projecting Edinger-Westphal nucleus (EWcp), dorsal (dPAG) and lateral (lPAG) periaqueductal gray matter, dorsal raphe nucleus (DR). Our results revealed that PACAP(-/-) mice showed greatly reduced anxiety and increased locomotor activity compared with wildtypes. In forced swim test PACAP(-/-) mice showed increased depression-like behavior. Forced swim exposure increased c-Fos expression in all examined brain areas in wildtypes, whereas this was markedly blunted in the DR, EWcp, BSTov, BSTdl, BSTv, PVN, vLS, dPAG, and in the lPAG of PACAP(-/-) mice vs. wildtypes, strongly suggesting their involvement in the behavioral phenotype of PACAP(-/-) mice. PACAP deficiency did not influence the c-Fos response in the CeA, MeA, BSTdm, and dLS. Therefore, we propose that PACAP exerts a brain area-specific effect on stress-induced neuronal activation and it might contribute to stress-related mood disorders.

Nerve growth factor (NGF) immunoreactive neurons in the juvenile rat hippocampus: response to acute and long-term high-light open-field (HL-OF) or forced swim (FS) stress stimulation

This study aimed at examining and comparing the influence of two different stress stimuli on the density (number of cells/mm²) of nerve growth factor (NGF) containing neurons in the hippocampal CA1 and CA3 pyramidal cell layers and the dentate gyrus (DG) granule cell layer in juvenile rats (P28; P-postnatal day). The high-light open-field (HL-OF) test and forced swim (FS) test were employed to investigate the effects of a single, 15-min acute exposure and repeated (15 min daily for 21 days) long-term exposure to stress. In order to detect NGF-ir neurons, immunohistochemical (-ir) techniques were used. In comparison with nonstressed animals, acute and long-term HL-OF or FS stimulation resulted in a marked increase (P<0.001) in the density of NGF-ir containing cells in all the hippocampal structures. The frequency of stress application (acute vs. long-term), however, did not have a substantial impact on the studied parameter, with the exception of the CA3 sector, where a decreased density (P<0.001) of NGF-ir neurons was observed after long-term exposure to FS. It may be concluded that a rise in the density of NGF-ir neurons in the juvenile rat hippocampus after exposure to HL-OF or FS stressors could have affected the activity of the hypothalamic-pituitary-adrenocortical (HPA) stress axis. Prolonged HL-OF or FS stress was probably aggravating enough not to trigger the habituation process. The type of stressor applied (HL-OF vs. FS) was not essentially a factor determining the density of NGF-ir cells in the hippocampus.

Participation of brainstem monoaminergic nuclei in behavioral depression

Several lines of research have now suggested the controversial hypothesis that the central noradrenergic system acts to exacerbate depression as opposed to having an antidepressant function. If correct, lesions of this system should increase resistance to depression, which has been partially but weakly supported by previous studies. The present study reexamined this question using two more recent methods to lesion noradrenergic neurons in mice: intraventricular (ivt) administration of either the noradrenergic neurotoxin, DSP4, or of a dopamine-β-hydroxylase-saporin immunotoxin (DBH-SAP ITX) prepared for mice. Both agents given 2 weeks prior were found to significantly increase resistance to depressive behavior in several tests including acute and repeated forced swims, tail suspension and endotoxin-induced anhedonia. Both agents also increased locomotor activity in the open field. Cell counts of brainstem monoaminergic neurons, however, showed that both methods produced only partial lesions of the locus coeruleus and also affected the dorsal raphe or ventral tegmental area. Both the cell damage and the antidepressant and hyperactive effects of ivt DSP4 were prevented by a prior i.p. injection of the NE uptake blocker, reboxetine. The results are seen to be consistent with recent pharmacological experiments showing that noradrenergic and serotonergic systems function to inhibit active behavior. Comparison with previous studies utilizing more complete and selective LC lesions suggest that mouse strain, lesion size or involvement of multiple neuronal systems are critical variables in the behavioral and affective effects of monoaminergic lesions and that antidepressant effects and hyperactivity may be more likely to occur if lesions are partial and/or involve multiple monoaminergic systems.

Environmental enrichment confers stress resiliency to social defeat through an infralimbic cortex-dependent neuroanatomical pathway

Enriched environmental (EE) housing dampens stress-induced alterations in neurobiological systems, promotes adaptability, and extinguishes submissive behavioral traits developed during social defeat stress (SD). In the present study, we hypothesized that enrichment before SD can confer stress resiliency and, furthermore, that neuronal activity in the prefrontal cortex (PFC) is requisite for this resiliency. To test these hypotheses, mice were housed in EE, standard (SE), or impoverished (IE) housing and then exposed to SD. EE conferred resilience to SD as measured in several behavioral tasks. EE-housed mice expressed elevated FosB/ΔFosB immunostaining in areas associated with emotional regulation and reward processing, i.e., infralimbic, prelimbic, and anterior cingulate cortices, amygdala, and nucleus accumbens, and this expression was mostly preserved in mice receiving EE followed by SD. In contrast, in SE- or IE-housed animals, SD increased maladaptive behaviors and greatly reduced FosB/ΔFosB staining in the forebrain. We tested the putative involvement of the PFC in mediating resilience by lesioning individual regions of the PFC either before or after EE housing and then exposing the mice to SD. We found that discrete lesions of the infralimbic but not prelimbic or cingulate cortex made before but not after EE abolished the behavioral resiliency to stress afforded by EE and attenuated FosB/ΔFosB expression in the accumbens and amygdala while increasing it in the paraventricular hypothalamic nucleus. These data suggest that pathological ventromedial PFC outputs to downstream limbic targets could predispose an individual to anxiety disorders in stressful situations, whereas enhanced ventromedial PFC outputs could convey stress resilience.

Further evidence for an immediate antidepressant action of intracerebral drug administration in a model of chronic depression

This study was designed to replicate an earlier finding of a rapid acute therapeutic action of intracerebrally administered antidepressant in chronically depressed rodents. The effects of acute fourth ventricular (ivt.) injections were compared to those of acute peripheral (i.p.) injections of desipramine (DMI) in mice subjected to repeated open-space forced swim. In confirmation, it was found that a single ivt. injection of a low (3 nmol) but not high (30 nmol) dose immediately reversed the immobility and inactivity of the model whereas acute i.p. administration was without effect up to 30 mg/kg. The repeated forced swim stress was also found to significantly reduce the net accumulation of DMI in the brain but not liver after a single i.p. injection of a moderate dose (10 mg/kg). The results suggest that stress-induced alterations of regional drug uptake or metabolism in the CNS may contribute to the therapeutic lag for antidepressants and other compounds in disorders with high distress.

Open-space forced swim model of depression for mice

This protocol describes a simplified method for inducing a chronic depression-like state in mice that is based on the repeated open-space forced swim method originally developed for rats. The method consists of mice swimming daily in lukewarm water in rat tub cages, for 15 min/day for 4 days, and thereafter once per week. This procedure produces a progressive decrease in distance swum and a concomitant increase in immobility (floating) in ∼70% of the mice, both of which persist unaltered for weeks. The model has predictive, face, and construct validity and has a number of advantages over previous methods in that it utilizes very mild stress, is short in duration, and is easily standardized. Moreover, since it utilizes a greater swimming area than the traditional (Porsolt) method it can be used to study interactions of depressive behavior with behavioral flexibility and perseveration.

Localization of nesfatin-1 neurons in the mouse brain and functional implication

Nesfatin-1 reduces food intake when injected centrally in rodents. We recently described wide distribution of nucleobindin2 (NUCB2)/nesfatin-1 immunoreactivity in rat brain autonomic nuclei activated by various stressors. We used C57BL/6 mice to localize brain NUCB2/nesfatin-1 immunoreactivity and assessed activation of NUCB2/nesfatin 1 neurons after water avoidance stress (WAS). Gastric emptying of a non-nutrient liquid was also determined. NUCB2/nesfatin-1 immunoreactivity was detected in cortical areas including piriform, insular, cingulate and somatomotor cortices, the limbic system including amygdaloid nuclei, hippocampus and septum, the basal ganglia, bed nucleus of the stria terminalis, the thalamus including paraventricular and parafascicular nuclei, the hypothalamus including supraoptic, periventricular, paraventricular (PVN), arcuate nuclei and ventromedial and lateral hypothalamic areas. Intensely labeled NUCB2/nesfatin-1 neurons were detected in a previously undefined region which we named intermediate dorsomedial hypothalamus. In the brainstem, NUCB2/nesfatin-1 immunoreactivity was detected in the raphe nuclei, Edinger-Westphal nucleus, locus coeruleus (LC), lateral parabrachial nucleus, ventrolateral medulla (VLM) and dorsal vagal complex. WAS induced Fos expression in 35% of NUCB2/nesfatin-1-immunoreactive neurons in the PVN, 50% in the LC, 54% in the rostral raphe pallidus, 58% in the VLM, 39% in the middle part of the nucleus of the solitary tract (NTS) and 33% in the caudal NTS. Nesfatin-1 injected intracerebroventricularly significantly decreased gastric emptying. These data showed that NUCB2/nesfatin-1 immunoreactivity is distributed in mouse brain areas involved in the regulation of stress response and visceral functions activated by an acute psychological stressor suggesting that nesfatin-1 might play a role in the efferent component of the stress response.

Antidepressant-like action of intracerebral 6-fluoronorepinephrine, a selective full α-adrenoceptor agonist

The present study examined the ability of 6-fluoronorepinephrine (6FNE), a full selective α-adrenoceptor agonist, to produce antidepressant-like effects in mice. The drug, administered in the 4th ventricle, produced marked anti-immobility effects at mid-dose range in the acute forced swim, tail suspension and repeated open-space forced swim tests with minimal effect on open-field motor activity and also reversed anhedonia following lipopolysaccharide administration. Its antidepressant effects were equal to or greater than that of an established systemic antidepressant, desmethylimipramine, given subacutely. Experiments with α-adrenoceptor antagonists indicated that the drug acts primarily via the α2-receptor in contrast to endogenous catecholamines which appear to control depressive behaviour primarily via the α1-receptor. Antidepressant activity declined at higher doses signifying a possible pro-depressant effect of one of the α-adrenoceptor subtypes. Compared to the selective α2-agonist, dexmedetomidine, 6FNE showed equivalent antidepressant action in the tail suspension test but appeared to have a greater efficacy or speed of action in the repeated open-space forced swim test which produces a more sustained depression. Studies of regional brain Fos expression induced during the antidepressant tests showed that 6FNE tended to inhibit neural activity in two stress-responsive regions (locus coeruleus and paraventricular hypothalamus) but to enhance activity in two areas involved in motivated behaviour (nucleus accumbens shell and lateral septal nucleus) producing a neural pattern consistent with antidepressant action. It is concluded that 6FNE elicits a rapid and effective antidepressant and anti-stress response that may compare favourably with available antidepressants.

The role of the central noradrenergic system in behavioral inhibition

Although the central noradrenergic system has been shown to be involved in a number of behavioral and neurophysiological processes, the relation of these to its role in depressive illness has been difficult to define. The present review discusses the hypothesis that one of its chief functions that may be related to affective illness is the inhibition of behavioral activation, a prominent symptom of the disorder. This hypothesis is found to be consistent with most previous neuropsychopharmacological and immunohistochemical experiments on active behavior in rodents in a variety of experimental conditions using manipulation of neurotransmission at both locus coeruleus and forebrain adrenergic receptors. The findings support a mechanism in which high rates of noradrenergic neural activity suppress the neural activity of principal neurons in forebrain regions mediating active behavior. The suppression may be mediated through postsynaptic galaninergic and adrenergic receptors, and via the release of corticotrophin-releasing hormone. The hypothesis is consistent with clinical evidence for central noradrenergic system hyperactivity in depressives and with the view that this hyperactivity is a contributing etiological factor in the disorder. A similar mechanism may underlie the ability of the noradrenergic system to suppress seizure activity suggesting that inhibition of the spread of neural activation may be a unifying function.

Do two models of acute and chronic stress stimulation influence the amount of nerve growth factor (NGF) and its receptor TrkA in the hippocampal neurons of middle aged rats?

Our study aimed to explore the influence of two different stressors: acute (once for 15 min) and chronic (15 min daily for 21 days) exposure to high light open field (HL-OF) or forced swim (FS) on the density of nerve growth factor (NGF) and tyrosine kinase A (TrkA) immunoreactive neurons in the hippocampal CA1 and CA3 pyramidal cell layers and dentate gyrus (DG) granule cell layer in middle aged (360 days old; P360; P, postnatal day) rats. In contrast to non-stressed animals, acute HL-OF stimulation resulted in an increase (p<0.001) in the density of NGF-ir cells in CA1, CA3, DG, whereas chronic HL-OF produced no changes in all hippocampal regions. The rats which underwent acute and chronic FS tests showed no statistically significant differences in the density of NGF-ir containing cells in the CA1, CA3, and DG subfields compared with control rats. Except for DG, where after 21 days of FS the density of TrkA-ir neurons was found to increase (p<0.05) in comparison to unstressed rats, no changes were noted in the density of TrkA-ir in the studied hippocampal structures as a result of acute and chronic HL-OF or FS exposure. These results indicate that acute HL-OF stress stimulation was the only factor inducing changes in the density of NGF-ir containing neurons in the hippocampal CA1, CA3, and DG of middle aged rats. In respect of the density of NGF-ir and TrkA-ir cells in the hippocampal structures, prolonged exposure to HL-OF or FS stressors did not constitute an aggravating factor for rats in the studied ontogenetic period.

Is subcortical-cortical midline activity in depression mediated by glutamate and GABA? A cross-species translational approach

Major depressive disorder has recently been characterized by abnormal resting state hyperactivity in anterior midline regions. The neurochemical mechanisms underlying resting state hyperactivity remain unclear. Since animal studies provide an opportunity to investigate subcortical regions and neurochemical mechanisms in more detail, we used a cross-species translational approach comparing a meta-analysis of human data to animal data on the functional anatomy and neurochemical modulation of resting state activity in depression. Animal and human data converged in showing resting state hyperactivity in various ventral midline regions. These were also characterized by abnormal concentrations of glutamate and gamma-aminobutyric acid (GABA) as well as by NMDA receptor up-regulation and AMPA and GABA receptor down-regulation. This cross-species translational investigation suggests that resting state hyperactivity in depression occurs in subcortical and cortical midline regions and is mediated by glutamate and GABA metabolism. This provides insight into the biochemical underpinnings of resting state activity in both depressed and healthy subjects.

Bidirectional regulation of stress responses by galanin in mice: involvement of galanin receptor subtype 1

The neuropeptide galanin has been shown to play a role in psychiatric disorders as well as in other biological processes including regulation of pain threshold through interactions with three G-protein coupled receptors, galanin receptor subtypes 1-3 (GalR1-3). While most of the pharmacological studies on galanin in stress-related disorders have been done with rats, the continuous development of genetically engineered mice involving galanin or its receptor subtype(s) validates the importance of mouse pharmacological studies. The present study on mice examined the homeostatic, endocrinological and neuroanatomical effects of the galanin, injected intracerebroventricularly (i.c.v.), in regulation of stress responses after restraint stress. Furthermore, the roles of GalR1 on these effects were studied using GalR1 knockout (KO) mice. The core body temperature and the locomotor activity were monitored with radio telemetry devices. Galanin (i.c.v.) decreased locomotor activity and exerted a bidirectional effect on the restraint stress-induced hyperthermia; a high dose of galanin significantly attenuated the stress-induced hyperthermic response, while a low dose of galanin moderately enhanced this response. The bidirectional effect of galanin was correlated with changes in stress hormone levels (adrenocorticotropic hormone and corticosterone). To neuroanatomically localize the effects of galanin on stress response, cFos immunoreactivity was assessed in galanin receptor rich areas; paraventricular nucleus (PVN) of the hypothalamus and the locus coeruleus (LC), respectively. A high dose of galanin significantly induced cFos activity in the LC but not in the PVN. In GalR1KO mice, a high dose of galanin failed to induce any of the above effects, suggesting the pivotal role of GalR1 in decreased locomotor activity and stress-resistant effects caused by galanin i.c.v. injection studied here.

Possible dopaminergic stimulation of locus coeruleus alpha1-adrenoceptors involved in behavioral activation

alpha(1)-Adrenoceptors of the locus coeruleus (LC) have been implicated in behavioral activation in novel surroundings, but the endogenous agonist that activates these receptors has not been established. In addition to the canonical activation of alpha(1)-receptors by norepinephrine (NE), there is evidence that dopamine (DA) may also activate certain brain alpha(1)-receptors. This study examined the contribution of DA to exploratory activity in a novel cage by determining the effect of infusion of various dopaminergic and adrenergic drugs into the mouse LC. It was found that the D2/D3 agonist, quinpirole, which selectively blocks the release of CNS DA, produced a dose-dependent and virtually complete abolition of exploration and all movement in the novel cage test. The quinpirole-induced inactivity was significantly attenuated by coinfusion of DA but not by the D1 agonist, SKF38390. Furthermore, the DA attenuation of quinpirole inactivity was blocked by coinfusion of the alpha(1)-adrenergic receptor antagonist, terazosin, but not by the D1 receptor antagonist, SCH23390. LC infusions of either quinpirole or terazosin also produced profound inactivity in DA-beta-hydroxylase knockout (Dbh -/-) mice that lack NE, indicating that their behavioral effects were not due to an alteration of the release or action of LC NE. Measurement of endogenous DA, NE, and 5HT and their metabolites in the LC during exposure to the novel cage indicated an increase in the turnover of DA and NE but not 5HT. These results indicate that DA is a candidate as an endogenous agonist for behaviorally activating LC alpha(1)-receptors and may play a role in the activation of this nucleus by novel surroundings.

Evaluation of the repeated open-space swim model of depression in the mouse

The present study evaluated the extension of a new rat model of depression, repeated open-space swimming, which overcomes drawbacks of existing models, to mice. Mice were swum for 15 min daily in a large tank of tepid water for 4 days and thereafter at 4 day intervals for a period of 3 weeks. Some of the animals were provided with an active coping (escape) response. Variables measured included time floating, distance swum, immobility on a subsequent tail-suspension test, sucrose preference and brain cell proliferation (Ki67 immunohistochemistry) as well as responses to 2 antidepressant drugs, desmethylimipramine and fluoxetine, and 2 non-antidepressant drugs, haloperidol and diazepam. The repeated swims were found to increase time floating and tail-suspension immobility and to decrease distance swum, sucrose preference and brain cell proliferation. Both chronic antidepressant drugs as well as the active coping response attenuated the increased time floating while neither of the non-antidepressant drugs had this effect. The distance swum measure was found to be more variable. Chronic fluoxetine also reversed the increased tail-suspension immobility, reduced sucrose preference and reduced brain cell proliferation caused by the model. It is concluded that repeated open-space swim represents a useful new model of depression in the mouse.

An anti-immobility effect of exogenous corticosterone in mice

Although traditionally considered to be etiological factors in depression, corticosteroids have been shown to exert an acute antidepressant action under some conditions. To investigate the mechanism of this effect, the present experiment sought to develop an animal model of it in mice using the repeated forced swim procedure. Corticosterone or desmethylimipramine was administered in the drinking water before, during or after repeated daily forced swims or a tail suspension test. Glucocorticoid and mineralocorticoid receptor involvement were assessed by coadministration of RU486 or spironolactone. Plasma corticosterone and fos expression in the paraventricular nucleus of the hypothalamus and piriform cortex were also measured in the treated animals. Corticosterone, given either before/during or after repeated swim, was found to produce a rapid reduction of immobility that was greater than that produced by desmethylimipramine given by the same route and dose and for the same duration. There was a nonsignificant tendency toward this effect in the tail suspension test. RU486 failed to block the effect but results with spironolactone were ambiguous. Plasma corticosterone was elevated in an inverted U-shaped fashion by the hormone treatment. Fos expression in response to the last swim was blunted in the paraventricular hypothalamus but enhanced in the piriform cortex. It is concluded that short-term treatment with corticosterone has a marked antidepressant effect in the mouse repeated forced swim test and merits further consideration as a short-term therapeutic agent in low doses. The hormone may act by suppression of neural activity in central stress circuits leading to a disinhibition of regions involved in active behavioral coping.

A final common pathway for depression? Progress toward a general conceptual framework

Functional neuroimaging studies of depressed patients have converged with functional brain mapping studies of depressed animals in showing that depression is accompanied by a hypoactivity of brain regions involved in positively motivated behavior together with a hyperactivity in regions involved in stress responses. Both sets of changes are reversed by diverse antidepressant treatments. It has been proposed that this neural pattern underlies the symptoms common to most forms of the depression, which are the loss of positively motivated behavior and increased stress. The paper discusses how this framework can organize diverse findings ranging from effects of monoamine neurotransmitters, cytokines, corticosteroids and neurotrophins on depression. The hypothesis leads to new insights concerning the relationship between the prolonged inactivity of the positive motivational network during a depressive episode and the loss of neurotrophic support, the potential antidepressant action of corticosteroid treatment, and to the key question of whether antidepressants act by inhibiting the activity of the stress network or by enhancing the activity of the positive motivational system.