Changes in regional long-term oxidative metabolism induced by partial serotonergic denervation and chronic variable stress in rat brain

Neural underpinnings of fine motor skills under stress and anxiety: A review

This review offers a comprehensive examination of how stress and anxiety affect motor behavior, particularly focusing on fine motor skills and gait adaptability. We explore the role of several neurochemicals, including brain-derived neurotrophic factor (BDNF) and dopamine, in modulating neural plasticity and motor control under these affective states. The review highlights the importance of developing therapeutic strategies that enhance motor performance by leveraging the interactions between key neurochemicals. Additionally, we investigate the complex interplay between emotional-cognitive states and sensorimotor behaviors, showing how stress and anxiety disrupt neural integration, leading to impairments in skilled movements and negatively impacting quality of life. Synthesizing evidence from human and rodent studies, we provide a detailed understanding of the relationships among stress, anxiety, and motor behavior. Our findings reveal neurophysiological pathways, behavioral outcomes, and potential therapeutic targets, emphasizing the intricate connections between neurobiological mechanisms, environmental factors, and motor performance.

Chronic unpredictable stress negatively regulates hippocampal neurogenesis and promote anxious depression-like behavior via upregulating apoptosis and inflammatory signals in adult rats

Psychological and physical stress play a pivotal role in etiology of anxiety and depression. Chronic psychological and physical stress modify various physiological phenomena, as a consequence of which oxidative stress, decreased neurotransmitter level, elevated corticosterone level and altered NSC homeostasis is observed. However, the precise mechanism by which chronic stress induce anxious depression and modify internal milieu is still unknown. Herein, we show that exposure to CUS increase oxidative stress, microgliosis, astrogliosis while it reduces hippocampal NSC proliferation, neuronal differentiation and maturation in adult rats. CUS exposure in rats reduce dopamine and serotonin level in cortex and hippocampus, which result in increased anxiety and depression-like phenotypes. We also found elevated level of NF-κB and TNF-α while decreased anti-inflammatory cytokine IL-10 level, that led to increased expression of Bax and cleaved Caspase-3 whereas down regulation of antiapoptotic protein Bcl2. Additionally, CUS altered adult hippocampal neurogenesis, increased gliosis and neuronal apoptosis in cerebral cortex and hippocampus which might be associated with reduced AKT and increased ERK signaling, as seen in the rat brain tissue. Taken together, these results indicate that CUS induce oxidative stress and neuroinflammation which directly affects NSC dynamics, monoamines levels and behavioral functions in adult rats.

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

Oxidative metabolism alterations in the emotional brain of anxiety-prone rats

Mood disorders such as anxiety and depression are heterogeneous disorders with many sufferers unresponsive to current pharmacological treatments. Individual differences in temperament represent one factor that may underlie symptom heterogeneity, so understanding its biological underpinnings can help pave the way to personalized therapies and improved patient outcomes. The present study uses a rodent model of temperamental differences to examine whether individual differences in emotional behavior phenotypes correspond to altered limbic brain cellular metabolism, an indicator of neuronal activity. The model uses two selectively bred rat lines - high novelty responder rats (HRs) that show highly exploratory behavior in a novel environment, active coping style and resilience to chronic mild stress compared to low novelty responder rats (LRs), which are inhibited in novel environments, display passive coping style, and are susceptible to chronic stress. Utilizing transcriptome data from a prior study in adult HR/LR rats, we first show that a preponderance of genes differing in the HR vs. LR hippocampus and amygdala are involved in cellular metabolism. This led us to then ask if oxygen consumption was altered in isolated mitochondria of the hippocampus and amygdala of HR/LR rats; here we found increased oxygen consumption reserve capacity in LR amygdala. Our last experiment examined activity of cytochrome c oxidase (COX), an enzyme responsible for ATP production and correlate of metabolic activity, in several brain regions of HR/LR rats. We found that LRs displayed higher COX activity in the dentate gyrus, prefrontal cortex, and dorsal raphe compared to HRs, with no significant HR/LR difference in nuclei of the amygdala. Correlational analyses of COX activity across brain regions suggested divergent connectivity between the prefrontal cortex, amygdala, hippocampus, and dorsal raphe of HR vs. LR rats. Together these studies point to altered cellular metabolism in the limbic brain of LR/HR animals, which may reflect altered neural circuitry that drives their divergent behavioral profiles.

Menkes disease: Oral administration of glyoxal-bis(N(4)-methylthiosemicarbazonato)-copper(II) rescues the macular mouse

BACKGROUND

Menkes disease is a copper metabolism disorder caused by mutations in ATP7A, a copper-transporting P-type ATPase. In this study, oral copper supplementation via glyoxal-bis(N(4)-methylthiosemicarbazonato)-copper(II) (CuGTSM), a lipophilic copper complex, was investigated in male hemizygous macular (Mo^Ml/y) mice, a mouse model of Menkes disease.

METHODS

CuGTSM was administered by oral gavage on postnatal days 5, 8, 11, 17, 23, and 32. The copper levels in the organs and serum, copper-dependent enzyme activities in the brain, and ceruloplasmin (Cp) activity in the serum were measured at 15 days and 3 and 8 months of age. Histological analysis of the intestines and the rotarod test were also performed.

RESULTS

CuGTSM treatment extended the lifespan of Mo^Ml/y mice and partly restored the copper concentrations and cytochrome oxidase and DBH activities in the brain; however, the rotarod test showed impaired motor performance. The treatment also increased copper concentrations and Cp activity in the serum. In suckling Mo^Ml/y mice, CuGTSM treatment transiently induced diarrhea accompanied by copper accumulation and altered villus morphology in the ileum.

CONCLUSION

Oral administration of CuGTSM extended the lifespan of Mo^Ml/y mice. Oral administration is attractive, but pharmaceutical studies are needed to reduce the adverse enteral effects.

The effect of 12-wk ω-3 fatty acid supplementation on in vivo thalamus glutathione concentration in patients "at risk" for major depression

OBJECTIVES

As life expectancy increases, the need to prevent major health disorders is clear. Depressive symptoms are common in older adults and are associated with cognitive decline and greater risk for transitioning to major depression. Oxidative stress may be implicated in the pathophysiology of major depression and can be measured in vivo using proton magnetic resonance spectroscopy via the neurometabolite glutathione (GSH). Evidence suggests ω-3 fatty acid (FA) supplementation may prevent depression and directly affect GSH concentration. The aim of this study was to examine the effect of ω-3 FA supplementation on in vivo GSH concentration in older adults at risk for depression.

METHODS

Fifty-one older adults at risk for depression were randomized to receive either four 1000-mg ω-3 FA supplements daily (containing eicosapentaenoic acid 1200 mg plus docosahexaenoic acid 800 mg) or placebo (four 1000-mg paraffin oil placebo capsules daily) for 12 wk. Participants underwent magnetic resonance spectroscopy, as well as medical, neuropsychological, and self-report assessments at baseline and after 12 wk of supplementation. GSH was measured in the thalamus and calculated as a ratio to creatine. Depressive symptoms were measured using the Patient Health Questionnaire.

RESULTS

Compared with the group given the ω-3 FA supplements, the placebo group had greater change in the GSH-to-creatine ratio in the thalamus (t = 2.00; P = 0.049) after the 12 wk intervention. This increase was in turn associated with a worsening of depressive symptoms (r = 0.43; P = 0.043).

CONCLUSIONS

Depressive symptom severity in older adults appears to be associated with increased brain levels of GSH, a key marker of oxidative stress. Importantly, ω-3 FA supplementation may attenuate oxidative stress mechanisms, thereby offering benefits for depression prevention.

Brain glucose metabolism in an animal model of depression

An increasing number of data support the involvement of disturbances in glucose metabolism in the pathogenesis of depression. We previously reported that glucose and glycogen concentrations in brain structures important for depression are higher in a prenatal stress model of depression when compared with control animals. A marked rise in the concentrations of these carbohydrates and glucose transporters were evident in prenatally stressed animals subjected to acute stress and glucose loading in adulthood. To determine whether elevated levels of brain glucose are associated with a change in its metabolism in this model, we assessed key glycolytic enzymes (hexokinase, phosphofructokinase and pyruvate kinase), products of glycolysis, i.e., pyruvate and lactate, and two selected enzymes of the tricarboxylic acid cycle (pyruvate dehydrogenase and α-ketoglutarate dehydrogenase) in the hippocampus and frontal cortex. Additionally, we assessed glucose-6-phosphate dehydrogenase activity, a key enzyme in the pentose phosphate pathway (PPP). Prenatal stress increased the levels of phosphofructokinase, an important glycolytic enzyme, in the hippocampus and frontal cortex. However, prenatal stress had no effect on hexokinase or pyruvate kinase levels. The lactate concentration was elevated in prenatally stressed rats in the frontal cortex, and pyruvate levels remained unchanged. Among the tricarboxylic acid cycle enzymes, prenatal stress decreased the level of pyruvate dehydrogenase in the hippocampus, but it had no effect on α-ketoglutarate dehydrogenase. Like in the case of glucose and its transporters, also in the present study, differences in markers of glucose metabolism between control animals and those subjected to prenatal stress were not observed under basal conditions but in rats subjected to acute stress and glucose load in adulthood. Glucose-6-phosphate dehydrogenase activity was not reduced by prenatal stress but was found to be even higher in animals exposed to all experimental conditions, i.e., prenatal stress, acute stress, and glucose administration. Our data indicate that glycolysis is increased and the Krebs cycle is decreased in the brain of a prenatal stress animal model of depression.

Revealing the cerebral regions and networks mediating vulnerability to depression: oxidative metabolism mapping of rat brain

The large variety of available animal models has revealed much on the neurobiology of depression, but each model appears as specific to a significant extent, and distinction between stress response, pathogenesis of depression and underlying vulnerability is difficult to make. Evidence from epidemiological studies suggests that depression occurs in biologically predisposed subjects under impact of adverse life events. We applied the diathesis-stress concept to reveal brain regions and functional networks that mediate vulnerability to depression and response to chronic stress by collapsing data on cerebral long term neuronal activity as measured by cytochrome c oxidase histochemistry in distinct animal models. Rats were rendered vulnerable to depression either by partial serotonergic lesion or by maternal deprivation, or selected for a vulnerable phenotype (low positive affect, low novelty-related activity or high hedonic response). Environmental adversity was brought about by applying chronic variable stress or chronic social defeat. Several brain regions, most significantly median raphe, habenula, retrosplenial cortex and reticular thalamus, were universally implicated in long-term metabolic stress response, vulnerability to depression, or both. Vulnerability was associated with higher oxidative metabolism levels as compared to resilience to chronic stress. Chronic stress, in contrast, had three distinct patterns of effect on oxidative metabolism in vulnerable vs. resilient animals. In general, associations between regional activities in several brain circuits were strongest in vulnerable animals, and chronic stress disrupted this interrelatedness. These findings highlight networks that underlie resilience to stress, and the distinct response to stress that occurs in vulnerable subjects.

Differential effects of escitalopram administration on metabolic parameters of cortical and subcortical brain regions of Wistar rats

OBJECTIVE

Considering that mitochondria may be drug targets and some characteristics of drug-mitochondria interactions may still be misjudged because of the difficulty in foreseeing and understanding all possible implications of the complex pathophysiology of mitochondria, our study aimed to investigate the effect of escitalopram on the activity of enzymes of mitochondrial energy metabolism.

METHODS

Animals received daily administration of escitalopram dissolved in saline [10 mg/kg, intraperitoneal (IP)] at 1.0 ml/kg volume for 14 days. Control rats received an equivalent volume of saline, 1.0 ml/kg (IP), for the same treatment period. Twelve hours after last injection, rats were killed by decapitation and brain areas were rapidly isolated. The samples were homogenised and the activities of mitochondrial respiratory chain complexes, some enzymes of Krebs cycle (citrate synthase, malate dehydrogenase and succinate dehydrogenase) and creatine kinase were measured.

RESULTS

We verified that chronic administration of escitalopram decreased the activities of complexes I and II-III in cerebellum, hippocampus, striatum and posterior cortex whereas prefrontal cortex was not affected. Complex II activity was decreased only in striatum without affecting prefrontal cortex, hippocampus, cerebellum and posterior cortex. However, chronic administration of escitalopram did not affect complex IV and enzymes of Krebs cycle activities as well as creatine kinase.

CONCLUSION

In this study we showed a decrease in the activities of complexes I and II-III in most of the brain structures analysed and complex II activity was decreased only in striatum. However, it remains to be determined if mitochondrial dysfunction is rather a causal or a consequential event of abnormal signalling.

Brain energy metabolism is increased by chronic administration of bupropion

OBJECTIVES

Based on the hypothesis that energy impairment may be involved in the pathophysiology of depression, we evaluated the activities of citrate synthase, malate dehydrogenase, succinate dehydrogenase (SDH), mitochondrial respiratory chain complexes I, II, II-III, IV and creatine kinase (CK) in the brain of rats submitted to chronic administration of bupropion.

METHODS

Animals received daily administration of bupropion dissolved in saline (10 mg/kg, intraperitoneal) at 1.0 ml/kg body weight. The rats received injections once a day for 14 days; control rats received an equivalent volume of saline. Twelve hours after the last administration, the rats were killed by decapitation and brain was rapidly removed and kept on an ice plate. The activities of the enzymes were measured in different brain areas.

RESULTS

We observed that the activities of citrate synthase and malate dehydrogenase, mithocondrial respiratory chain complexes I, II-III and IV and CK were not altered after chronic administration of bupropion. However, SDH activity was increased in the prefrontal cortex and cerebellum. In the hippocampus, cerebellum and striatum the activity of complex II was increased after chronic administration of bupropion.

CONCLUSIONS

Our results demonstrated that bupropion increased some enzymes of brain energy metabolism. These findings are in accordance with other studies which showed that some antidepressants may improve energy metabolism. The present results reinforce the hypothesis that antidepressants modulate brain energy metabolism.

Activating effects of chronic variable stress in rats with different exploratory activity: association with dopamine d(1) receptor function in nucleus accumbens

BACKGROUND/AIMS

Rats display persistent behavioural phenotypes of low (LE) versus high (HE) exploratory activity in the exploration box paradigm. LE rats that prefer passive coping strategies show differential dopaminergic activity in the striatum. The main hypothesis of this study was that chronic variable stress (CVS) would have a higher impact on LE rats.

METHODS

Animals were submitted to a CVS regimen lasting 32 days that was followed by a behavioural test battery. The functional states of their dopamine D(1) and D(2) receptors were measured in the striatum and nucleus accumbens (NAcc). Cerebral oxidative metabolism was assessed via cytochrome c oxidase histochemistry in 65 brain regions.

RESULTS

CVS decreased weight gain, to a higher extent in LE rats, and lowered the sucrose preference after the first week, but habituation to the anhedonic effect had developed by the end of the experiment. CVS did not change the behavioural phenotypes initially assigned. No effect of stress on D(2) receptor function was found. Chronically stressed animals exhibited higher levels of social interaction and D(1) receptor-mediated cAMP accumulation in the NAcc, but not in the striatum. CVS was associated with higher oxidative metabolism levels in the anteroventral thalamus, median raphe nuclei and central periaqueductal grey matter. These changes after stress did not depend upon the exploratory phenotype.

CONCLUSION

This study revealed changes in brain biochemistry after habituation to CVS that might be implicated in successful adaptation to chronic stress.

Activity of mitochondrial respiratory chain is increased by chronic administration of antidepressants

OBJECTIVE

Depressive disorders, including major depression, are serious and disabling for affected patients. Although the neurobiological understanding of major depressive disorder focuses mainly on the monoamine hypothesis, the exact pathophysiology of depression is not fully understood.

METHODS

Animals received daily intra-peritoneal injections of paroxetine (10 mg/kg), nortriptyline (15 mg/kg) or venlafaxine (10 mg/kg) in 1.0 ml/kg volume for 15 days. Twelve hours after the last injection, the rats were killed by decapitation, where the brain was removed and homogenised. The activities of mitochondrial respiratory chain complexes in different brain structures were measured.

RESULTS

We first verified that chronic administration of paroxetine increased complex I activity in prefrontal cortex, hippocampus, striatum and cerebral cortex. In addition, complex II activity was increased by the same drug in hippocampus, striatum and cerebral cortex and complex IV activity in prefrontal cortex. Furthermore, chronic administration of nortriptyline increased complex II activity in hippocampus and striatum and complex IV activity in prefrontal cortex, striatum and cerebral cortex. Finally, chronic administration of venlafaxine increased complex II activity in hippocampus, striatum and cerebral cortex and complex IV activity in prefrontal cortex.

CONCLUSION

On the basis of the present findings, it is tempting to speculate that an increase in brain energy metabolism by the antidepressant paroxetine, nortriptyline and venlafaxine could play a role in the mechanism of action of these drugs. These data corroborate with other studies suggesting that some antidepressants modulate brain energy metabolism.

Brain responses to chronic social defeat stress: effects on regional oxidative metabolism as a function of a hedonic trait, and gene expression in susceptible and resilient rats

Chronic social defeat stress, a depression model in rats, reduced struggling in the forced swimming test dependent on a hedonic trait-stressed rats with high sucrose intake struggled less. Social defeat reduced brain regional energy metabolism, and this effect was also more pronounced in rats with high sucrose intake. A number of changes in gene expression were identified after social defeat stress, most notably the down-regulation of Gsk3b and Map1b. The majority of differences were between stress-susceptible and resilient rats. Conclusively, correlates of inter-individual differences in stress resilience can be identified both at gene expression and oxidative metabolism levels.

Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress

Rezin GT, Gonçalves CL, Daufenbach JF, Carvalho-Silva M, Borges LS, Vieira JS, Hermani FV, Comim CM, Quevedo J, Streck EL. Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress.

OBJECTIVE

Recently, we reported that mitochondrial respiratory chain complexes I, III and IV were inhibited in the cerebral cortex and cerebellum of rats submitted to chronic mild stress (CMS) and that acute ketamine administration reversed this effect. Therefore, we investigated whether the inhibition of these enzymes may be reversed by chronic administration of ketamine.

METHODS

Adult male Wistar rats were submitted to CMS and chronically treated with ketamine. After 40 days of CMS, consumption of sweet food, adrenal gland weight, body weight and enzymatic activity of the complexes were measured.

RESULTS

We verified that CMS decreased the intake of sweet food, increased the adrenal gland weight and the control group gained weight after 40 days but the stressed group did not; ketamine administration reversed these effects. We also verified that chronic administration of ketamine reversed the inhibition of complexes I, III and IV in cerebral cortex. However, in cerebellum, only complex IV inhibition was reversed. The chronic ketamine administration partially reverses the inhibition caused by CMS.

CONCLUSION

We hypothesise that CMS inhibits complexes I, III and IV activities and that chronic administration of ketamine administration partially reverses such an effect. Therefore, it seems reasonable to propose that ketamine administration might be a useful therapy for patients affected by major depression.

Alterations in monoamine levels and oxidative systems in frontal cortex, striatum, and hippocampus of the rat brain during chronic unpredictable stress

Stress plays a key role in the induction of various clinical disorders by altering monoaminergic response and antioxidant defenses. In the present study, alterations in the concentrations of dopamine (DA), serotonin (5-HT) and their metabolites, and simultaneous changes in the antioxidant defense system and lipid peroxidation in different brain regions (frontal cortex, striatum, and hippocampus) were investigated immediately and 24 h after exposure to chronic unpredictable stress (CUS). CUS involved subjecting Sprague-Dawley rats to two different types of stressors varying from mild to severe intensity every day in an unpredictable manner, over a period of 7 days. CUS significantly decreased DA and 5-HT concentrations, with increased DA turnover ratios in the selected brain regions. In the frontal cortex and striatum, DA metabolite concentrations were increased; however, in the hippocampus they remained unaltered. Further, a decrease of 5-hydroxyindoleacetic acid content was observed in the frontal cortex and striatum, with no significant alteration in the hippocampus. CUS also reduced the activities of superoxide dismutase and catalase, with increased lipid peroxidation and decreased glutathione levels in the selected brain regions. Glutathione peroxidase activity was increased in the frontal cortex and hippocampus only. The pattern of CUS-induced monoamine and oxidative changes immediately after the last stressor and 24 h later were similar when compared with the control group, indicating that the observed changes were due to the chronic exposure to the various stressors and were not merely acute effects of the last stressor. The altered redox state in the striatum and frontal cortex might be related to the perturbed DA and/or 5HT levels, while the hippocampus seems to be less influenced by CUS in terms of monoamine metabolite changes. These results suggest that the perturbed monoamine levels could interact with the oxidative load during CUS. Hence, the current study has implications for pharmacological interventions targeting both central monoamines and cellular antioxidants as a potential stress management strategy for protecting against central stress-induced disorders.

Brain creatine kinase activity is increased by chronic administration of paroxetine

Major depression is a serious and recurrent disorder often manifested with symptoms at the psychological, behavioral, and physiological levels. In addition, several works also suggest brain metabolism impairment as a mechanism underlying depression. Creatine kinase (CK) plays a central role in the metabolism of high-energy consuming tissues such as brain, where it functions as an effective buffering system of cellular ATP levels. Considering that CK plays an important role in brain energy homeostasis and that some antidepressants may modulate energy metabolism, we decided to investigate CK activity from rat brain after chronic administration of paroxetine (selective serotonin reuptake inhibitor), nortriptiline (tricyclic antidepressant) and venlafaxine (selective serotonin-norepinephrine reuptake inhibitor). Adult male Wistar rats received daily injections of paroxetine (10 mg/kg), nortriptiline (15 mg/kg), venlafaxine (10 mg/kg) or saline in 1.0 mL/kg volume for 15 days. Twelve hours after the last administration, the rats were killed by decapitation, the hippocampus, striatum and prefrontal cortex were immediately removed, and activity of CK was measured. Our results demonstrated that chronic administration of paroxetine increased CK activity in the prefrontal cortex, hippocampus and striatum of adult rats. On the other hand, nortriptiline and venlafaxine chronic administration did not affect CK activity in these brain areas. In order to verify whether the effect of paroxetine on CK is direct or indirect, we also measured the in vitro effect of this drug on the activity of the enzyme. We verified that paroxetine did not affect CK activity in vitro. Considering that metabolism impairment is probably involved in the pathophysiology of depressive disorders, an increase in CK activity by antidepressants may be an important mechanism of action of these drugs.

Increased vulnerability to depressive-like behavior of mice with decreased expression of VGLUT1

BACKGROUND

Many studies link depression to an increase in the excitatory-inhibitory ratio in the forebrain. Presynaptic alterations in a shared pathway of the glutamate/gamma-aminobutyric acid (GABA) cycle may account for this imbalance. Evidence suggests that decreased vesicular glutamate transporter 1 (VGLUT1) levels in the forebrain affect the glutamate/GABA cycle and induce helpless behavior. We studied decreased VGLUT1 as a potential factor enhancing a depressive-like phenotype in an animal model.

METHODS

Glutamate and GABA synthesis as well as oxidative metabolism were studied in heterozygous mice for the VGLUT1+/- and wildtype. The regulation of neurotransmitter levels, proteins involved in the glutamate/GABA cycle, and behavior by both genotype and chronic mild stress (CMS) were studied. Finally, the effect of chronic imipramine on VGLUT1 control and CMS mice was studied.

RESULTS

VGLUT1+/- mice showed increased neuronal synthesis of glutamate; decreased cortical and hippocampal GABA, VGLUT1, and excitatory amino acid transporter 1 (EAAT1) as well as helplessness and anhedonia. CMS induced an increase of glutamate and a decrease of GABA, the vesicular GABA transporter (VGAT), and glutamic acid decarboxylase 65 (GAD65) in both areas and led to upregulation of EAAT1 in the hippocampus. Moreover, CMS induced anhedonia, helplessness, anxiety, and impaired recognition memory. VGLUT1+/- CMS mice showed a combined phenotype (genotype plus stress) and specific alterations, such as an upregulation of VGLUT2 and hyperlocomotion. Moreover, an increased vulnerability to anhedonia and helplessness reversible by chronic imipramine was shown.

CONCLUSIONS

These studies highlight a crucial role for decreased VGLUT1 in the forebrain as a biological mediator of increased vulnerability to chronic mild stress.

Modulation of basal and stress-induced amygdaloid substance P release by the potent and selective NK1 receptor antagonist L-822429

It has been shown that anxiety and stress responses are modulated by substance P (SP) released within the amygdala. However, there is an important gap in our knowledge concerning the mechanisms regulating extracellular SP in this brain region. To study a possible self-regulating role of SP, we used a selective neurokinin-1 (NK1) receptor antagonist to investigate whether blockade of NK1 receptors results in altered basal and/or stress-evoked SP release in the medial amygdala (MeA), a critical brain area for a functional involvement of SP transmission in enhanced anxiety responses induced by stressor exposure. In vitro binding and functional receptor assays revealed that L-822429 represents a potent and selective rat NK1 receptor antagonist. Intra-amygdaloid administration of L-822429 via inverse microdialysis enhanced basal, but attenuated swim stress-induced SP release, while the low-affinity enantiomer of L-822429 had no effect. Using light and electron microscopy, synaptic contacts between SP-containing fibres and dendrites expressing NK1 receptors was demonstrated in the medial amygdala. Our findings suggest self-regulatory capacity of SP-mediated neurotransmission that differs in the effect on basal and stress-induced release of SP. Under basal conditions endogenous SP can serve as a signal that tonically inhibits its own release via a NK1 receptor-mediated negative feedback action, while under stress conditions SP release is further facilitated by activation of NK1 receptors, likely leading to high local levels of SP and activation of receptors to which SP binds with lower affinity.