Regional rat brain noradrenaline turnover in response to restraint stress

Isometric exercise facilitates attention to salient events in women via the noradrenergic system

The locus coeruleus (LC) regulates attention via the release of norepinephrine (NE), with levels of tonic LC activity constraining the intensity of phasic LC responses. In the current fMRI study, we used isometric handgrip to modulate tonic LC-NE activity in older women and in young women with different hormone statuses during the time period immediately after the handgrip. During this post-handgrip time, an oddball detection task was used to probe how changes in tonic arousal influenced functional coordination between the LC and a right frontoparietal network that supports attentional selectivity. As expected, the frontoparietal network responded more to infrequent target and novel sounds than to frequent sounds. Across participants, greater LC-frontoparietal functional connectivity, pupil dilation, and faster oddball detection were all positively associated with LC MRI structural contrast from a neuromelanin-sensitive scan. Thus, LC structure was related to LC functional dynamics and attentional performance during the oddball task. We also found that handgrip influenced pupil and attentional processing during a subsequent oddball task. Handgrip decreased subsequent tonic pupil size, increased phasic pupil responses to oddball sounds, speeded oddball detection speed, and increased frontoparietal network activation, suggesting that inducing strong LC activity benefits attentional performance in the next few minutes, potentially due to reduced tonic LC activity. In addition, older women showed a similar benefit of handgrip on frontoparietal network activation as younger women, despite showing lower frontoparietal network activation overall. Together these findings suggest that a simple exercise may improve selective attention in healthy aging, at least for several minutes afterwards.

Effects of acute handling stress on cerebral monoaminergic neurotransmitters in juvenile Senegalese sole Solea senegalensis

Juvenile Senegalese sole Solea senegalensis were subjected for short periods to two different types of handling-related stress: air exposure stress and net handling stress. The S. senegalensis were sacrificed 2 and 24 h after the stress events and the levels of serotonin (5-HT), noradrenaline (NA), dopamine (DA) and their respective major metabolites, 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC), were measured in three brain regions (telencephalon, hypothalamus and optic tectum) and compared with those in control, non-stressed S. senegalensis. Neither type of stress caused any significant alteration of serotoninergic activity (5-HIAA:5-HT ratio) or NA levels. Dopaminergic activity (DOPAC:DA ratio) was lower in stressed fish in all of the brain regions studied. For both air exposure stress and net handling stress, DA levels were significantly higher (P < 0.05) than in the control S. senegalensis. In addition, the higher DA levels after net handling stress were always significantly higher (P < 0.05) than those observed after acute air exposure stress, except in the telencephalon after 24 h. The significantly lower DOPAC:DA ratio (P < 0.05) in all of the brain regions studied was only observed in response to net handling stress.

Odor cues released by Ehrlich tumor-bearing mice are aversive and induce psychological stress

BACKGROUND/AIMS

This study aimed to verify if odor cues released by Ehrlich tumor-bearing mice are aversive and stressful.

METHODS

Female mice were divided into a control group and an experimental group. One animal of each experimental pair of mice was inoculated with 5 × 10(6) Ehrlich tumor cells intraperitoneally; the other animal was kept undisturbed and was referred to as a CSP (companion of sick partner). One mouse of each control pair was treated intraperitoneally with 0.9% NaCl (1 mg/kg); the other animal (CHP, companion of healthy partner) was kept undisturbed.

RESULTS

It was shown that, in relation to CHP, CSP mice (1) spent less time within the companion zone in a T-maze place preference test, (2) had increased levels of social interaction, (3) had increased levels of plasmatic adrenaline and noradrenaline and (4) displayed no changes in serum corticosterone levels before and after an immobilization stress challenge. It was also shown that (5) cohabitation with 2 tumor-bearing mice was more effective in decreasing neutrophil oxidative burst than cohabitation with 1 sick partner and (6) the presence of a healthy conspecific within the cage of the tumor-injected/CSP pair abrogated the effects of cohabitation on neutrophil activity. These results show that odor cues released by Ehrlich tumor-injected mice are aversive and induce psychological stress.

CONCLUSION

We postulate that the aversive response induced by the chemosignals released by Ehrlich tumor-injected animals activates the sympathetic nervous system and causes the neuroimmunal changes that occur in the mice cohabiting with the sick mice.

Noradrenergic α2A-receptor stimulation in the ventral hippocampus reduces impulsive decision-making

RATIONALE

Guanfacine, an α2A-adrenergic receptor agonist, is currently in use for treatment of a variety of psychiatric disorders that are associated with impulsive decision-making (e.g., attention-deficit hyperactivity disorder; ADHD). In animals and humans, the behavioral effects of adrenergic agents are presumed to involve neuromodulation of the prefrontal cortex, consistent with the demonstrated actions of dopaminergic agents. However, recent experimental work has shown that the ventral hippocampus (vHC) contributes to decision-making and impulse control, raising the possibility that the hippocampus may be an important site of action for these drugs.

OBJECTIVE

The purpose of this study was to examine the effect of local vHC infusions of guanfacine and other neuropharmacological agents on behavioral decisions that involve a trade-off between reward size and delay.

METHODS

Different cohorts of rats were implanted with bilateral guide cannulae targeting the vHC. We examined the animals' behavior in a touchscreen version of a delay discounting task following intra-vHC infusions of: (a) guanfacine (α2A-adrenergic receptor agonist), (b) SCH 23390 (dopamine D1 receptor antagonist), and (c) muscimol/baclofen (GABAA/B agonists).

RESULTS

Guanfacine led to a dose-dependent reduction in impulsive decision-making, increasing the animals' tolerance for delay in exchange for a larger reward. By contrast, infusion of SCH 23390 had no behavioral effects. Consistent with previous lesion studies, reversible pharmacological inactivation with muscimol/baclofen increased impulsive decision-making.

CONCLUSIONS

These data provide the first evidence that guanfacine, a commonly used treatment for ADHD, may derive its clinical benefits through hippocampal stimulation, via α2A-adrenergic receptors.

Psychiatric symptoms of noradrenergic dysfunction: a pathophysiological view

What psychiatric symptoms are caused by central noradrenergic dysfunction? The hypothesis considered in this review is that noradrenergic dysfunction causes the abnormalities in arousal level observed in functional psychoses. In this review, the psychiatric symptoms of noradrenergic dysfunction were inferred pathophysiologically from the neuroscience literature. This inference was examined based on the literature on the biology of psychiatric disorders and psychotropics. Additionally, hypotheses were generated as to the cause of the noradrenergic dysfunction. The central noradrenaline system, like the peripheral system, mediates the alarm reaction during stress. Overactivity of the system increases the arousal level and amplifies the emotional reaction to stress, which could manifest as a cluster of symptoms, such as insomnia, anxiety, irritability, emotional instability and exaggerated fear or aggressiveness (hyperarousal symptoms). Underactivity of the system lowers the arousal level and attenuates the alarm reaction, which could result in hypersomnia and insensitivity to stress (hypoarousal symptoms). Clinical data support the hypothesis that, in functional psychoses, the noradrenergic dysfunction is in fact associated with the arousal symptoms described above. The anti-noradrenergic action of anxiolytics and antipsychotics can explain their sedative effects on the hyperarousal symptoms of these disorders. The results of animal experiments suggest that excessive stress can be a cause of long-term noradrenergic dysfunction.

Effects of chronic social defeat on expression of dopamine β-hydroxylase in rat brains

It is documented that stress activates the locus coeruleus-norepinephrine system. However, there are far few reports regarding effects of stress on the expression of dopamine β-hydroxylase, a hallmark enzyme of the noradrenergic neuron. In the present study, adult Fischer 344 rats were subjected to chronic social defeat for 4 weeks. Dopamine β-hydroxylase expressional levels in the locus coeruleus and its terminal regions were measured by in situ hybridization and western blotting. The results showed that immediately following chronic social defeat there are significantly increased mRNA and protein levels of dopamine β-hydroxylase in the locus coeruleus, and dopamine β-hydroxylase protein levels in the hippocampus, frontal cortex and amygdala, compared with those in the control. This chronic social defeat-induced upregulation of dopamine β-hydroxylase was completely abolished by adrenalectomy, and/or by treatment with corticosteroid receptor antagonists, mifepristone and spironolactone, either alone or in combination. Furthermore, treatment with desipramine, an antidepressant with specific inhibitory effects on norepinephrine transport, prevented an increased dopamine β-hydroxylase expression by chronic social defeat in the locus coeruleus and its main terminal regions such as the hippocampus, frontal cortex and amygdala. However, treatment with fluoxetine, an antidepressant with specific inhibition for serotonin transport, only selectively blocked increased dopamine β-hydroxylase protein levels in the hippocampus caused by CSD. The present findings indicate that chronic social defeat activates the locus coeruleus-norepinephrine system by upregulating the expression of dopamine β-hydroxylase, which may increase norepinephrine synthesis. This chronic social defeat induced upregulation of DBH expression was mediated through corticosterone and corticosteroid receptors, with possible interference from antidepressants.

Serotonin transporter in lymphocytes of rats exposed to physical restraint stress

OBJECTIVES

Glucocorticoids and stress cause transcriptional and functional changes on the serotonin transporter (SERT) in the central nervous system. Stress can produce specific modifications of SERT in lymphocytes, which could be associated with alterations in immune response. The aim of this study was to evaluate the effect of a physical restraint stress protocol on (1) rat lymphocyte proliferation in the presence of the selective serotonin reuptake inhibitor fluoxetine and (2) SERT kinetic parameters, i.e. binding capacity (Bmax), affinity (Kd) and Hill coefficient (nH).

METHODS

Male adult Sprague-Dawley rats were placed in Plexiglass boxes (5 h daily for 5 days), and blood was obtained by cardiac puncture on day 6. Serum corticosterone was quantitated by an immunoenzymatic assay. Lymphocytes were isolated by density gradients and adhesion to plastic, of which there was sufficient material for further experiments, then cultured with or without the mitogen concanavalin A (Con A, 2 μg/ml) and fluoxetine (1-50 μM). Cell proliferation was measured with tetrazolium salts, and [(3)H]paroxetine was used as a SERT-specific ligand for binding assays.

RESULTS

Restraint produced a significant increase in serum corticosterone of stressed rats. The proliferative response to Con A was similar in the controls and stressed animals. Fluoxetine reduced cell proliferation with and without Con A. Restraint diminished the inhibitory effect of fluoxetine on proliferation. Restraint also increased Bmax and Kd, but decreased nH. Treatment of rats with actinomycin D, a transcription inhibitor, reduced Bmax in stressed animals.

CONCLUSIONS

Restraint stress modulated the effect of fluoxetine on cell proliferation, probably through the modification of the presence and the function of SERT.

Stressor-like effects of c-Jun N-terminal kinase (JNK) inhibition

There is an urgent need for novel treatment strategies for stressor related disorders, particularly depression and anxiety disorders. Indeed, existing drug treatments are only clinically successful in a subset of patients and relapse is common. This likely stems from the fact that stressor disorders are heterogeneous with multiple biological pathways being affected. To this end, the present investigation sought to assess in mice the contribution of the c-Jun N terminal kinase (JNK) pathway to the behavioral, hormonal and neurochemical effects of an acute stressor. Indeed, although JNK has been shown to modulate glucocorticoid receptors in vitro, virtually nothing is known of the role for JNK in affecting stressor induced pathology. We presently found that the JNK antagonist, SP600125, (but not the p38 antagonist, SB203580) increased plasma corticosterone levels under resting conditions and in the context of an acute stressor (wet bedding + restraint). SP600125 also reduced exploration in an open field arena, but prevented the stressor induced increase in open arm exploration in an elevated plus maze. Finally, SP600125 affected noradrenergic activity in the central amygdala and locus coruleus under resting condition, but prevented the noradrenergic effects within the paraventricular nucleus of the hypothalamus that were induced by the acute stressor exposure. These data suggest inhibiting endogenous JNK can have stressor-like corticoid, behavioral and central monoamine effects under basal conditions, but can actually reverse some behavioral and neurochemical effects of an acute stressor. Thus, endogenous JNK appears to affect stress relevant processes in a context-dependent manner.

Chronic social defeat up-regulates expression of norepinephrine transporter in rat brains

Stress has been reported to activate the locus coeruleus (LC)-noradrenergic system. However, the molecular link between chronic stress and noradrenergic neurons remains to be elucidated. In the present study adult Fischer 344 rats were subjected to a regimen of chronic social defeat (CSD) for 4weeks. Measurements by in situ hybridization and Western blotting showed that CSD significantly increased mRNA and protein levels of the norepinephrine transporter (NET) in the LC region and NET protein levels in the hippocampus, frontal cortex and amygdala. CSD-induced increases in NET expression were abolished by adrenalectomy or treatment with corticosteroid receptor antagonists, suggesting the involvement of corticosterone and corticosteroid receptors in this upregulation. Furthermore, protein levels of protein kinase A (PKA), protein kinase C (PKC), and phosphorylated cAMP-response element binding (pCREB) protein were significantly reduced in the LC and its terminal regions by the CSD paradigm. Similarly, these reduced protein levels caused by CSD were prevented by adrenalectomy. However, effects of corticosteroid receptor antagonists on CSD-induced down-regulation of PKA, PKC, and pCREB proteins were not consistent. While mifeprestone and spironolactone, either alone or in combination, totally abrogate CSD effects on these protein levels of PKA, PKC and pCREB in the LC and those in the hippocampus, frontal cortex and amygdala, their effects on PKA and PKC in the hippocampus, frontal cortex and amygdala were region-dependent. The present findings indicate a correlation between chronic stress and activation of the noradrenergic system. This correlation and CSD-induced alteration in signal transduction molecules may account for their critical effects on the development of symptoms of major depression.

The effect of restraint stress on prepulse inhibition and on corticotropin-releasing factor (CRF) and CRF receptor gene expression in Wistar-Kyoto and Brown Norway rats

Stress plays a role in many psychiatric disorders that are characterized by deficits in prepulse inhibition (PPI), a form of sensorimotor gating. Corticotropin-releasing factor (CRF) is one of the most important neurotransmitters involved in behavioral components of the stress response, and central infusion of CRF decreases PPI in rodents. We recently demonstrated that restraint stress decreases PPI and attenuates the increase in PPI caused by repeated testing. To broaden our investigation into how restraint affects PPI, we subjected Wistar-Kyoto (WKY) and Brown Norway (BN) rats to 10 consecutive days of 2-hour restraint, or to brief handling, prior to assessing PPI. We next examined the effects of 1 or 10days of 2-hour restraint on plasma corticosterone levels in order to determine whether the endocrine response to stress parallels the behavioral effect of stress. Finally, we examined the effects of 1 or 10days of 2-hour restraint on CRF and CRF receptor gene expression in the amygdala, hippocampus, frontal cortex, and hypothalamus in order to determine whether a temporal pattern of gene expression parallels the change in the behavioral response to stress. The major findings of the present study are that 1) restraint stress attenuates the increase in PPI caused by repeated testing in both WKY and BN rats, and BN rats are more sensitive to the effects of restraint on PPI than WKY rats, 2) restraint-induced increases in corticosterone levels mirror the effect of restraint on PPI in WKY rats but not in BN rats, 3) laterality effects on gene expression were observed for the amygdala, whereby restraint increases CRF gene expression in the left, but not right, amygdala, and 4) some restraint-induced changes in CRF and CRF receptor gene expression precede changes in PPI while other changes coincide with altered PPI in a rat strain- and brain region-dependent manner.

Major depression as a disorder of serotonin resistance: inference from diabetes mellitus type II

The multifactorial nature of depression resembles that of other complex disorders such as diabetes mellitus or coronary artery disease. However, while for the latter disorders predisposing and risk factors have been identified, such knowledge is still scarce in depression. In this review we propose to use diabetes mellitus, for which characteristic milestones have been condensed to obesity-hyperinsulinaemia-insulin resistance-diabetes mellitus, as a conceptual analogical model. Based on this model we hypothesize that depression develops according to a similar pattern: prolonged psychological stress-hyperserotonism-serotonin resistance-major depression. We review extensive supporting evidence from human studies and animal models of depression, including stress involvement in the aetiology of depression, evidence for increased synaptic serotonin and decreased 5-HT1A receptor activity. Conceptualizing the pathogenesis of depression as a multi-step process may inspire new concepts, which will eventually lead to delineation of additional preventive and therapeutic interventions similar to those currently practised in diabetes.

Neuroendocrine, behavioral and macrophage activity changes induced by picrotoxin effects in mice

The relevance and property of studies related to stress effects on immune function are undisputable. All studies conducted on stress-immune relationships, however, provide from physical and/or psychological stressors. Indeed, as far as it is of our knowledge brain-innate immune responses were not analyzed after anxiogenic-like drugs use. The present experiment was then undertaken to analyze the effects of picrotoxin (0.3, 0.6 and 1.0mg/kg doses) on behavior, macrophage activity, serum corticosterone and noradrenaline (NE) levels and turnover in the brain of adult mice. Results showed that picrotoxin treatment in mice: (1) decreased motor and rearing activities in an open-field; (2) decreased the number of entries into the plus-maze open-arms and decreased the time spent in the exploration of the plus-maze open-arms; (3) decreased both motor activity and the level of holes exploration in the hole-board; (4) increased the levels of serum corticosterone in dose-dependent way; (5) increased noradrenaline (NE) and MHPG levels and NE turnover in the hypothalamus; and (6) increased Staphylococcus aureus and PMA-induced macrophage oxidative burst. However, and contrary to that reported after physical or psychological stress, this drug induced no effects on macrophage phagocytosis and NE levels and turnover in the frontal cortex. The present results are thus showing that picrotoxin induces some but not all neuro-innate immunity changes previously reported for inescapable foot-shock and psychological stressors in mice. These facts suggest that this chemical stressor triggers CNS pathways that might be somehow different from those fired by inescapable foot-shock and psychological stressors, leading to different neuro-innate immune responses.

Opioid modulation of reflex versus operant responses following stress in the rat

In pre-clinical models intended to evaluate nociceptive processing, acute stress suppresses reflex responses to thermal stimulation, an effect previously described as stress-induced "analgesia." Suggestions that endogenous opioids mediate this effect are based on demonstrations that stress-induced hyporeflexia is enhanced by high dose morphine (>5 mg/kg) and is reversed by naloxone. However, reflexes and pain sensations can be modulated differentially. Therefore, in the present study direct comparisons were made of opioid agonist and antagonist actions, independently and in combination with acute restraint stress in Long Evans rats, on reflex lick-guard (L/G) and operant escape responses to nociceptive thermal stimulation (44.5 degrees C). A high dose of morphine (>8 mg/kg) was required to reduce reflex responding, but a moderate dose of morphine (1 mg/kg) significantly reduced escape responding. The same moderate dose (and also 5 mg/kg) of morphine significantly enhanced reflex responding. Naloxone (3 mg/kg) significantly enhanced escape responding but did not affect L/G responding. Restraint stress significantly suppressed L/G reflexes (hyporeflexia) but enhanced escape responses (hyperalgesia). Stress-induced hyperalgesia was significantly reduced by morphine and enhanced by naloxone. In contrast, stress-induced hyporeflexia was blocked by both naloxone and 1 mg/kg of morphine. Thus, stress-induced hyperalgesia was opposed by endogenous opioid release and by administration of morphine. Stress-induced hyporeflexia was dependent upon endogenous opioid release but was counteracted by a moderate dose of morphine. These data demonstrate a differential modulation of reflex and operant outcome measures by stress and by separate or combined opioid antagonism or administration of morphine.

Cohabitation with a sick cage mate: Effects on noradrenaline turnover and neutrophil activity

The present study was designed to evaluate the effects of cohabitation for 11 days with a sick conspecific on hypothalamic levels and turnover of noradrenaline NA (experiment 1) and on neutrophil oxidative burst and phagocytosis in mice (experiment 2). Female mice were divided into two groups: control and experimental. One mouse of each control pair was kept undisturbed and called "companion of health partner" (CHP). One animal of each experimental pair of mice was inoculated with 5 x 10(6) Ehrlich tumor cells i.p., and the other, the subject of this study, was called "companion of sick partner" (CSP). In experiment 3, CHP and CSP mice were treated with diazepam (1.0 mg/kg) or with control solution (vehicle of diazepam, 1.0 mL/kg) 1h before evaluation of neutrophil activity. The CSP mice presented (1) decreased levels and increased turnover of hypothalamic NA; (2) decreased neutrophil oxidative burst after PMA or Staphylococcus aureus induction; (3) decreased percentage and intensity of neutrophil phagocytosis. In CSP mice, diazepam induced no changes in neutrophil oxidative burst or intensity of phagocytosis, but abolished almost completely the percentage of neutrophils performing phagocytosis. These data were discussed in the light of possible neuroimmune interactions.

Single and repeated immobilization stress differentially trigger induction and phosphorylation of several transcription factors and mitogen-activated protein kinases in the rat locus coeruleus

The locus coeruleus (LC) is a critical stress-responsive location that mediates many of the responses to stress. We used immunoblotting and immunohistochemistry to investigate changes in induction and phosphorylation of several transcription factors and kinases in the LC that may mediate the stress-triggered induction of tyrosine hydroxylase (TH) transcription. Rats were exposed to single or repeated immobilization stress (IMO) for brief (5 min), intermediate (30 min) or sustained (2 h) duration. Single IMO elicited rapid induction of c-Fos and phosphorylation of cyclic AMP response element-binding protein (CREB) without changing the expression of early growth response (Egr)1, Fos-related antigen (Fra)-2 or phosphorylated activating transcription factor-2. Repeated IMO triggered increased phosphorylation and levels of CREB along with transient induction of c-Fos and increased Fra-2 expression. Several mitogen-activated protein kinases were activated by repeated IMO, shown by increased phosphorylation of p38, c-Jun N-terminal kinase (JNK)1/2/3 and extracellular signal-regulated kinase (ERK1/2). ERK1 was the major isoform expressed, and ERK2 the predominant isoform phosphorylated. Repeated IMO elicited hyperphosphorylation of ERK1/2 selectively in TH immunoreactive neurons, with substantial nuclear localization. These distinct alterations in transcriptional pathways following repeated compared with single stress may be involved in mediating long-lasting neuronal remodeling and are implicated in the mechanisms by which acute beneficial responses to stress are converted into prolonged adaptive or maladaptive responses.

In vivo neurochemical monitoring and the study of behaviour

In vivo neurochemical monitoring techniques measure changes in the extracellular compartment of selected brain regions. These changes reflect the release of chemical messengers and intermediates of brain energy metabolism resulting from the activity of neuronal assemblies. The two principal techniques used in neurochemical monitoring are microdialysis and voltammetry. The presence of glutamate in the extracellular compartment and its pharmacological characteristics suggest that it is released from astrocytes and acts as neuromodulator rather than a neurotransmitter. The changes in extracellular noradrenaline and dopamine reflect their role in the control of behaviour. Changes in glucose and oxygen, the latter a measure of local cerebral blood flow, reflect synaptic processing in the underlying neuronal networks rather than a measure of efferent output from the brain region. In vivo neurochemical monitoring provides information about the intermediate processing that intervenes between the application of the stimulus and the resulting behaviour but does not reflect the final efferent output that leads to behaviour.

Effect of novel stressors on gene expression of tyrosine hydroxylase and monoamine transporters in brainstem noradrenergic neurons of long-term repeatedly immobilized rats

Responses of central noradrenergic (NE) neurons to stressors like immobilization (IMO), cold exposure, insulin-induced hypoglycemia, and cellular glucoprivation caused by 2-deoxy-D-glucose (2-DG) were investigated in intact and long-term repeatedly immobilized (LTR, 2 h daily IMO for 41 days) rats. Expression of tyrosine hydroxylase (TH), norepinephrine transporter (NET) and vesicular monoamine transporter (VMAT2) genes were determined by using in situ hybridization histochemistry in brainstem A1, A2, A5 and locus coeruleus (LC) neurons. TH mRNA levels were increased by single IMO or 2-DG administration in all areas studied. Cold was effective only in LC and A2 neurons while insulin had no effect. LTR immobilization elevated TH mRNA levels in all investigated cell groups. These elevations were equally high to those elicited by a single IMO in each noradrenergic group, except the LC where LTR IMO was less effective than the single IMO. The levels of NET and VMAT2 mRNAs were elevated only in the A1 and A2 cell groups of LTR IMO rats. A newly applied IMO in LTR rats did not alter TH, NET, and VMAT2 mRNA levels in any NE cell group investigated. Novel stressors like cold and 2-DG exaggerated the increased TH mRNA levels only in the LC of LTR IMO rats, unlike in the other NE cell groups. The present data indicate that repeated exposure of rats to homotypic stressor induces an adaptation of NE neurons, whereas single exposure of such animals to heterotypic novel stressor produces an exaggerated response of the system at the level of TH (in LC) and NET (in A1, A2) gene expression.

Effects of 8-OHDPAT administration into the dorsal raphe nucleus and dorsal hippocampus on fear behavior and regional brain monoamines distribution in rats

The effects of R(+)-8-hydroxy-dipropylaminotetralin (8-OHDPAT) administration into the dorsal raphe nucleus (DRN) or bilaterally into the dorsal hippocampus (HIP) on fear behavior in a modified version of the light-dark transitions test and regional brain monoamines (NA, DA, 5-HT) and their metabolites (MHPG, DOPAC, 5-HIAA) in the hypothalamus, midbrain central gray matter, amygdala, hippocampus and pons were examined. The experiments were performed on 36 male, 3-month old Wistar rats. Administration of 8-OHDPAT (200 ng) into the DRN reduced time out from the illuminated part of the chamber and time of motionless behavior in the illuminated part, increased the number of returns from the dark to illuminated part and number of head dipping from the dark to illuminated part without effect on time of motionless behavior in the dark part and on time of locomotor activity in the illuminated as well as in dark part of the chamber. HPLC analysis showed reduction of 5-HT content in the midbrain and amygdala, reduction of 5-HIAA content in pons, increased 5-HIAA/5-HT ratio in the hippocampus and increased DOPAC/DA ratio in the hypothalamus, midbrain, hippocampus and pons without affecting the MHPG/NA ratio and NA content. The administration of 8-OHDPAT (100 ng per site) into the HIP reduced time out from the illuminated part of chamber, time of locomotor activity in the illuminated part and head dipping from the dark to illuminated part without effect on the number of returns from the dark to illuminated part, time of locomotor activity in the dark part and time of motionless in the illuminated as well as in the dark part of chamber. HPLC analysis showed reduction of NA content in the hypothalamus, amygdala and pons, increased the MHPG content in all the investigated structures, increased MHPG/NA ratio in all the investigated structures except the hypothalamus. Dopamine content decreased in the hypothalamus and amygdala, and DOPAC/DA ratio increased in the amygdala and hippocampus. Concentrations of 5-HT, 5-HIAA and 5-HIAA/5-HT ratio were unchanged. The results obtained indicate that 8-OHDPAT acting on the pre-synaptic 5-HT1A receptors decreases fear behavior and acting on 5-HT1A post-synaptic receptors increases fear behavior in the light-dark transitions test. The neurochemical base of anxiolytic and anxiogenic effects evoked by 8-OHDPAT is being discussed.

Stress-triggered activation of gene expression in catecholaminergic systems: dynamics of transcriptional events

Stress triggers important adaptive responses that enable an organism to cope with a changing environment. However, when prolonged or repeated, stress can be extremely harmful. The release of catecholamines is a key initial event in responses to stressors and is followed by an increase in the expression of genes that encode catecholamine-synthesizing enzymes. This process is mediated by transcriptional mechanisms in the adrenal medulla and the locus coeruleus. The persistence of transcriptional activation depends on the duration and repetition of the stress. Recent work has begun to identify the various transcription factors that are associated with brief or intermediate duration of a single or repeated stress. These studies suggest that dynamic interplay is involved in converting the transient increases in the rate of transcription into prolonged (potentially adaptive or maladaptive) changes in gene expression.

Expression of aggression attenuates both stress-induced gastric ulcer formation and increases in noradrenaline release in the rat amygdala assessed by intracerebral microdialysis

The effects of an aggressive biting response on stress-induced noradrenaline (NA) release in the rat amygdala and gastric ulcer formation were studied with an intracerebral microdialysis technique. Rats were exposed to a 60-min period of cold restraint stress with or without being allowed to bite a wooden stick. They were sacrificed 100 min after release from stress to investigate gastric ulcer formation. Cold-restraint stress increased NA release to 304 +/- 22.3 and 206 +/- 23.8% of basal levels (mean +/- SEM) in the nonbiting and biting groups, respectively. The stress-induced increases in NA release in the nonbiting group were significantly higher than those in the biting group. In the nonbiting group, significant increases in NA release continued for 80 min after release from stress; however, NA levels in the biting group recovered to basal levels immediately after the cessation of stress. Although many severe gastric lesions with bleeding were found in the nonbiting group, fewer gastric lesions without bleeding were found in the biting group. The cumulative length of gastric lesions in the nonbiting group and in the biting group was 26.2 +/- 7.4 and 6.8 +/- 3.9 mm (mean +/- SEM), respectively. The mean number of ulcers in the nonbiting group and the biting group was 11.8 +/- 1.3 and 1.8 +/- 0.7 (mean +/- SEM), respectively. Both the cumulative length of ulcers and the number of ulcers were significantly lower than those seen in the nonbiting group. These findings strongly suggest that expression of aggression during stress exposure attenuates not only stress-induced increases in NA release in the rat amygdala but also gastric ulcer formation consequent to stress.

Corticosterone levels during extinction of runway response in rats

This investigation examined whether the hypothalamic-pituitary-adrenocortical axis would activate during extinction of a straight runway response. Four groups of rats were trained to run in a straight runway for 3 (for 3S and 3L groups) or 10 (for 10S and 10L groups) food pellets as a reward for either 15 (for 3S and 10S groups) or 25 (for 3L and 10L groups) acquisition days followed by 3 extinction days. Blood samples for determination of serum corticosterone concentration were taken from all animals under 5 different situations: 10 min after entering the experimental room, after the 24th acquisition day, after the first and third extinction days and under the deprivation control. Running speed of 10S and 10L groups in extinction days were reduced more quickly than that of 3S and 3L groups. After the third extinction day, serum corticosterone concentrations were significantly elevated in 10S and 10L, but not in 3S and 3L groups. These results indicate that the amount of reward in the acquisition phase influences not only the running speed, but also the corticosterone concentration in the extinction phase.

The effect of acute, chronic and chronic intermittent stress on the central noradrenergic system

The objective of this investigation was to examine the immediate and long term effects of acute, chronic and chronic intermittent stress on the central noradrenergic system of rats. Male Sprague-Dawley rats were subjected to one hour of physical immobilization stress either as a single exposure, or as 14 exposures applied either on consecutive days, or randomly over 60 days. Animals were sacrificed immediately, 6 h and 24 h following the last stressor. Levels of norepinephrine (NE) and 3-methoxy-4-hydroxyphenylethylene-glycol sulfate (MHPG-sulfate) were measured in the hypothalamus, hippocampus, cerebral cortex and locus coeruleus region and beta-adrenergic receptor (BAR) density was determined in the cortex. Immediately after acute stress, a significant reduction in hypothalamic NE levels and marked increases in MHPG-sulfate levels in all four brain regions were observed. In contrast immediately after the last stressor of a chronic or chronic intermittent stress regimen, no change in NE concentration was observed while levels of MHPG-sulfate in the four brain regions showed a smaller increase than that observed after an acute stressor. Acute stress induced changes normalized within 6 h while chronic and chronic intermittently stressed animals had altered NE or MHPG-sulfate levels in certain brain regions for up to 6-24 h. Cortical BAR binding parameters remained unchanged after all stress paradigms.

Activation of the mesocortical dopamine system by feeding: lack of a selective response to stress

There is wide agreement that catecholamine systems in the prefrontal cortex are activated by stressful stimuli. To date, however, the extent to which other stimuli can increase the activity of these systems has received little attention. In the present study, the effects of tail pinch stress and feeding on dopamine and noradrenaline release in the prefrontal cortex of rats were examined using in vivo brain microdialysis. Both stimuli increased dopamine release, with peak effects reaching 212% above baseline for tail pinch and 165% above baseline for feeding. The effects of the two stimuli on peak dopamine release were not significantly different. Both stimuli also significantly increased noradrenaline release, with peak effects reaching 128% above baseline for tail pinch and 98% above baseline for feeding. The effects of the two stimuli on peak noradrenaline release were not significantly different. These results indicate that activation of catecholaminergic afferents to the prefrontal cortex is not specific to stress, but also occurs in response to non-stressors with positive motivational valence.

Noradrenergic mechanisms in stress and anxiety: I. Preclinical studies

There is considerable preclinical evidence for a relationship between noradrenergic brain systems and behaviors associated with stress and anxiety. The majority of noradrenergic neurons are located in the locus coeruleus (pons), with projections throughout the cerebral cortex and multiple subcortical areas, including hippocampus, amygdala, thalamus, and hypothalamus. This neuroanatomical formation of the noradrenergic system makes it well suited to rapidly and globally modulate brain function in response to changes in the environment, as occurs during the presentation of stressors. Stress exposure is associated with an increase in firing of the locus coeruleus and with associated increased release and turnover of norepinephrine in brain regions which receive noradrenergic innervation. Increased firing of the locus coeruleus is also associated with behavioral manifestations of fear, such as arched back and piloerection in the cat. Exposure to chronic stress results in long-term alterations in locus coeruleus firing and norepinephrine release in target brain regions of the locus coeruleus. Norepinephrine is also involved in neural mechanisms such as sensitization and fear conditioning, which are associated with stress. These findings are relevant to an understanding of psychiatric disorders, such as panic disorder and post-traumatic stress disorder (PTSD), the symptoms of which have been hypothesized to be related to alterations in noradrenergic function.

The area postrema is involved in paraquat-induced conditioned aversion behavior and neuroendocrine activation of the hypothalamic-pituitary-adrenal axis

Paraquat is a herbicide capable of eliciting conditioned taste aversion (CTA), a behavioral response characteristic of toxicosis. The area postrema (AP) is a hindbrain circumventricular organ previously shown to be important in mediating signs of paraquat-induced toxicity, namely CTA and weight loss. The relationship between neural substrates for paraquat-induced CTA and activation of the hypothalamic-pituitary-adrenal (HPA) axis was investigated in Sprague-Dawley rats with lesions centered on the AP (APX) and sham-operated (SHM) rats administered paraquat (25 mumol/kg) or saline (1 ml/kg). Injection of paraquat at a dose sufficient to condition taste aversion, but produce no other signs of overt toxicity, significantly increased plasma corticosterone concentrations in SHM rats up to 4 h after administration. Paraquat-induced activation of the HPA axis was significantly attenuated in AP-lesioned rats as compared to sham-operated controls. These findings suggest the area postrema is a common neural substrate for the behavioral and neuroendocrine responses to paraquat.

The effects of two chronic intermittent stressors on brain monoamines

The effects of chronic exposure (27 days) to two different stressors on brain monoaminergic activity was studied in adult male rats. The stressors used were restraint in tubes (RES) and immobilization in wooden boards (IMO). Both chronically stressed and stress naive (control) rats were subjected to 0, 15, and 60 min of the same stressor to which they were chronically exposed. Previous chronic exposure to either RES or IMO significantly reduced ACTH response to the same stressor. Monoaminergic response to these stressors was studied by measuring the levels of noradrenaline (NA), serotonin (5-HT) and their metabolites: 3-methoxy,4-hydroxyphenyletileneglycol sulfate (MHPG-SO4) and 5-hydroxyindoleacetic acid (5-HIAA), respectively. The regions studied were: pons plus medulla, midbrain, hypothalamus, hippocampus, and frontal cortex. Previous chronic exposure to the stressors induced only few changes in the resting levels of the monoamines and their metabolites. In addition, monoaminergic response to the same stressor to which they were chronically exposed was always similar in control and chronically stressed rats. These data indicate that brain NA and 5-HT metabolism is less sensitive than ACTH to the process of habituation to a repeated stressor, at least in the gross areas of the brain analyzed in the present study.

Fear induced by the blockade of GABAA-ergic transmission in the hypothalamus of the cat: behavioral and neurochemical study

Intrahypothalamic injections of d-Tubocurarine (DT) and bicuculline (BM) in the cat produced a fear reaction characterized by terrific mewing, increased locomotor activity, jumps and attempt to escape from the chamber, pupillary dilatation, increased respiratory rate, and sometimes urination and defecation. HPLC analysis showed a significant increase in the noradrenergic system activity in the emotional brain areas (hypothalamus, midbrain, amygdala) and frontal cortex at the time of the fear drive. No changes in the cat's behavior and in the monoaminergic systems activity occurred after muscimol+d-Tubocurarine injections into the hypothalamus. Similar behavioral and neurochemical effects evoked by DT and BM suggest that the fear response evoked by DT does not result from the blockade of N-cholinergic transmission but rather from their action on GABAA receptor complex. The results obtained indicate that the central triggering mechanism for fear drive depends on the blockade of GABAA-ergic transmission.

Inhibition of catecholamine synthesis with alpha-methyl-p-tyrosine apparently increases brain serotoninergic activity in the rat: no influence of previous chronic immobilization stress

The functional relationship between brain catecholamines and serotoninergic function was studied in stress-naive and chronically immobilized rats after blockade of catecholamine synthesis with alpha-methyl-p-tyrosine (alpha MpT). The levels of noradrenaline (NA), serotonin, and 5-hydroxyindole acetic acid (5-HIAA) in pons plus medulla, brainstem, hypothalamus, hippocampus, and frontal cortex, and those of 3-methoxy, 4-hydroxyphenile-tileneglicol sulphate (MHPG-SO4) in the hypothalamus were measured by HPLC. Chronic immobilization (IMO) resulted in higher NA levels in pons plus medulla and hypothalamus, the latter area (the only one in which the NA metabolite was determined) also showing slightly elevated MHPG-SO4 levels as compared to stress-naive rats. Chronic IMO did not alter either serotonin or 5-HIAA levels, but acute stress consistently increased 5-HIAA levels in all areas, independently of previous chronic stress. Administration of alpha-MpT drastically reduced NA and increased 5-HIAA levels in all brain regions excepting the frontal cortex. The effect of the drug on serotoninergic function was not altered by previous chronic exposure to IMO. These data suggest that the noradrenergic system appears to exert a tonic inhibitory effect on serotoninergic activity in the brain, with the intensity of the effect depending on the brain area studied. In addition, chronic stress does not appear to alter the functional relationship between noradrenergic and serotoninergic activities, although interactions might exist in more restricted brain areas; this deserves further study.

Alpha-adrenergic receptors mediate imipramine/alarm substance-induced reaction in rats

The mechanism of adverse imipramine-induced reactions (jitteriness, convulsions) was investigated by precipitating such reactions in rats with three injections (IP) of imipramine (5-40 mg/kg) at 24, 5, and 1 h before testing, and comparing their occurrence with comparable treatments using specific noradrenergic and serotonergic reuptake inhibitors [nortriptyline (10 or 30 mg/kg, IP), citalopram (0.5-5.0 mg/kg, IP)]. This initial study indicated that these reactions were mediated by imipramine's noradrenergic effects. Subsequent combinations of imipramine and an alpha 2 agonist (clonidine, 5 mg/kg) and antagonist (yohimbine, 2 mg/kg), and a beta-adrenergic antagonist (propranolol, 2 or 5 mg/kg) (all administered IP 0.5 h after the last injection of imipramine) suggested imipramine's adverse effects were mediated by alpha 2 receptors. The possible involvement of the locus ceruleus in these effects was considered.

Stress, antidepressant drugs, and the locus coeruleus

This review presents a synthesis of a large body of seemingly inconsistent literature on the role of the locus coeruleus-norepinephrine (LC-NE) system and the corticotropin-releasing hormone (CRH)-median eminence system in mediating the CNS effects of stress and the therapeutic effects of antidepressant drugs. The clinical implications of these findings for the etiology and treatment of stress-related psychiatric disorders such as depression will be discussed.

Hemodynamic stress activates locus coeruleus neurons of unanesthetized rats

The effects of hypotensive stress elicited by nitroprusside infusion on discharge activity of noradrenergic locus coeruleus (LC) neurons of unanesthetized rats were characterized. Nitroprusside (75 micrograms/30 microliters/min, 15 min IV infusion) decreased mean arterial pressure of unanesthetized rats by 50 +/- 2 mmHg (n = 5). Simultaneous recordings of LC spontaneous discharge revealed an increase in discharge rate (197 +/- 87%) that was associated with hypotension. A lower concentration of nitroprusside (10 micrograms/30 microliters/min) that decreased blood pressure of halothane-anesthetized rats by 55 +/- 2 mmHg was much less effective in producing hypotension and did not increase LC discharge when administered to unanesthetized rats. Prior administration of the CRF antagonist, alpha helical CRF9-41 (50 micrograms, ICV) greatly attenuated LC activation by nitroprusside. These findings demonstrate that LC activation elicited by nitroprusside is dependent on the magnitude of hypotension. The present results also demonstrate that nitroprusside is a less potent hemodynamic challenge in unanesthetized rats. Finally, LC activation associated with nitroprusside administration to unanesthetized rats is mediated to a large extent by CRF, confirming findings in anesthetized rats.

Behavioral and neurochemical changes in response to acute stressors: influence of previous chronic exposure to immobilization

The effect of daily (2 h) exposure to immobilization (IMO) for 15 days on the behavioral and neurochemical responses of adult male rats to acute stress caused by 2-h IMO or 2-h tail-shock was studied. The brain areas studied were frontal cortex, hippocampus, hypothalamus, midbrain, and pons plus medulla. Chronic exposure to IMO did not alter noradrenaline (NA), 3-methoxy,4-hydroxyphenyletileneglycol-SO4 (MHPG-SO4), serotonin, or 5-hydroxindoleacetic acid (5-HIAA) concentrations in any brain area as measured approximately 20 h after the last exposure to IMO. Exposure to behavioral tests did not modify neurochemical variables except NA levels in the hypothalamus of nonchronically stressed (control) rats. Both exposure to 2-h IMO or 2-h shock significantly decreased NA levels in hypothalamus and midbrain of nonchronically stressed rats. These decreases in response to the two acute stressors were not observed in chronically stressed rats. However, MHPG-SO4 levels increased to the same extent in control and chronically stressed rats after exposure to the acute stressors. Likewise, increased 5-HIAA concentrations observed in response to acute stressors were similar in control and chronically stressed rats. The inhibition of activity (areas crossed and rearing) in the holeboard caused by acute IMO was less marked in rats previously exposed to the same stressor than in control rats, but the response to shock was similar. In the forced swim test, acute IMO decreased struggling in control rats but tended to increase it in chronically stressed rats. The response to shock followed the same pattern as that to IMO, although it was slight.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced Tyrosine Hydroxylation in Hippocampus of Chronically Stressed Rats upon Exposure to a Novel Stressor

We have used microdialysis to measure the in vivo level of tyrosine hydroxylation in hippocampus of the freely moving rat. An inhibitor of aromatic amino acid decarboxylase, NSD-1015, was administered through the dialysis probe and the resulting accumulation of 3,4-dihydroxyphenylalanine (DOPA) in extracellular fluid of hippocampus was quantified. Administration of the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine, decreased extracellular DOPA to undetectable level. In addition, both systemic and local application of clonidine, an alpha 2-adrenergic agonist, produced a decrease in extracellular DOPA. In response to acute tail shock, a significant increase in extracellular DOPA was observed. Thus, it appears that in vivo accumulation of DOPA after local administration of NSD-1015 provides a reliable index of hippocampal tyrosine hydroxylation. We have used this technique to investigate whether prior exposure to chronic stress alters the in vivo level of tyrosine hydroxylation in hippocampus under basal conditions as well as in response to a novel stressor. In rats previously exposed to chronic cold stress, the basal accumulation of extracellular DOPA did not differ from naive controls. Acute tail shock, however, produced a significantly greater and more prolonged elevation in extracellular DOPA of chronically stressed rats. These data suggest that enhanced biosynthetic capacity of noradrenergic terminals may be one mechanism underlying adaptation to chronic stress.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Effects of stress and adrenalectomy on tyrosine hydroxylase mRNA levels in the locus ceruleus by in situ hybridization

The locus ceruleus-norepinephrine system is one of the principal effectors of the stress response. Acute stress induces norepinephrine synthesis and release, and noradrenergic cells compensate by increasing the activity of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. Here we use in situ hybridization histochemistry to show the effects of acute and chronic intermittent stress on the expression of tyrosine hydroxylase mRNA in the rat locus ceruleus. Restraint stress increased tyrosine hydroxylase mRNA in the locus ceruleus but not in dopaminergic nuclei such as the substantia nigra or ventral tegmental area. One hour of footshock or restraint caused a rapid increase in locus ceruleus tyrosine hydroxylase mRNA which returned to basal levels within 24 h. Chronic intermittent stress (1 hour of restraint or footshock per day for 14 days) produced no change in tyrosine hydroxylase mRNA. Neither adrenalectomy nor dexamethasone replacement significantly affected mRNA expression. These findings indicate that acute stress can increase the expression of tyrosine hydroxylase mRNA in the locus ceruleus but that adaptation occurs to repeated stress, and that the expression of tyrosine hydroxylase mRNA in the locus ceruleus is independent of direct glucocorticoid modulation.

Noradrenergic mechanisms in the central amygdalar nucleus and gastric stress ulcer formation in rats

Microinjections of noradrenaline (NA, 0.3, 3.0 and 30.0 micrograms) into the central amygdalar nucleus (CEA) produced dose-related attenuations of cold restraint (3 h at 4 degrees C) induced gastric ulcer formation in rats. On the other hand, stress ulcer aggravating effects were seen with beta-adrenoceptor antagonist, propranolol (10 micrograms) but not with the alpha-adrenoceptor antagonist, prazosin (1 and 10 micrograms). Moderate enhancements of gastric stress lesions were also seen with the NA release inhibitor clonidine (1 microgram) and the neurotoxin DSP-4 (25 micrograms). Further, pretreatment of rats with intra-amygdalar (i.am.) propranolol but not prazosin, antagonized and reversed the gastric cytoprotective effects of NA. The results indicate that beta-adrenoceptor-mediated NAergic mechanisms at the level of the CEA are important for the maintenance of gastric mucosal integrity during immobilization stress.

Effect of ethanol on plasma amino acids and related compounds of stressed male rats

Plasma amino acid levels in rats are known to be affected by ethanol or by immobilization stress. This paper investigated the effect of ethanol on plasma amino acid levels of stressed rats. Rats received ethanol (2 g/kg, IP) 15 minutes prior to a 30-min immobilization period. Blood samples were obtained from individual rats before, during and after stress. Ethanol lowered the concentration of most plasma amino acids (AA) or related compounds in stressed rats (e.g., aspartic acid, threonine, serine, glycine, alanine, valine, tyrosine, phenylalanine, tryptophan). Some compounds remained unaffected (e.g., taurine, cystine, ethanolamine and methylhistidines) and one (phosphoethanolamine) increased initially. A comparison of the effects of ethanol on plasma AA and related compounds in resting and stressed rats shows similarities and differences. In general, ethanol tends to change the concentrations of these compounds away from normal levels in nonstressed rats, whereas in stressed rats, ethanol tends to antagonize stress-induced changes. This study shows that ethanol can affect individual AA and related compounds differently in nonstressed and stressed rats and that ethanol reduces stress-induced changes. The latter finding supports the "tension-reduction hypothesis" of ethanol.

Audiogenic stress response: behavioral characteristics and underlying monoamine mechanisms

Behavioral characterization of the audiogenic stress response in rats revealed an intensity related multiphasic pattern including an initial, transient activation followed by prolonged periods of response suppression during the remainder of the noise exposure and excitation after noise offset. These observations emphasize the need to consider the temporal proximity between exposure to a stressor and either behavioral characterization and/or determinations of neurochemical changes relevant to the stress response. In a second series of studies, the effect of the NE alpha 2 agonist clonidine and the NE alpha 2 antagonist yohimbine were evaluated on the different components of the audiogenic stress response. The effects of intracerebroventricular xylamine-induced depletion of NE were also examined. The results seem to indicate that CNS noradrenergic systems may not be specifically implicated in regulating the responsiveness to noise stimulation but instead may subserve a more general role in adjusting baseline levels of motoric output in response to environmental conditions.

Expression of aggression attenuates stress-induced increases in rat brain noradrenaline turnover

This experiment determined whether or not an aggressive biting response could attenuate stress-induced increases in brain noradrenaline (NA) turnover, by measuring contents of NA and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in discrete brain regions of male Wistar rats. Rats were exposed to a 10 min supine restraint stress with or without being allowed to bite a wooden stick. In each group, the animals were sacrificed by decapitation either 0 min or 50 min after release from stress. NA and MHPG-SO4 levels were unaffected in both biting and non-biting groups immediately after stress, as compared to controls. Fifty min after release from stress, increases in plasma corticosterone levels induced by stress recovered in the biting group but remained high in the non-biting group. MHPG-SO4 levels significantly increased in the hypothalamus, amygdala, thalamus, midbrain, basal ganglia, hippocampus and cerebral cortex in both stressed groups, however the increases in the non-biting group were significantly higher than those in the biting group in the first 5 of these regions. These findings clearly show that giving rats an opportunity to express aggression during stress exposure results in a significant attenuation of stress-induced increases in NA turnover in specific brain regions, such as the hypothalamus and limbic areas. The present experiment provides a possible neurochemical basis for clinical studies showing that suppression of anger in a stressful, frustrating situation leads to pathological consequences in humans.

Effect of acute ethanol administration on noradrenaline metabolism in brain regions of stressed and nonstressed rats

The effects of ethanol on noradrenaline (NA) metabolism of brain regions in stressed and nonstressed rats were investigated. Male Wistar rats were injected IP with either saline, or ethanol at 0.5 g/kg or 2 g/kg, 5 min before exposure to 1-hr immobilization stress. Levels of NA and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) in various brain regions and plasma corticosterone levels were fluorometrically determined. Immobilization stress caused significant increases in MHPG-SO4 levels in all brain regions examined, i.e., the hypothalamus, amygdala, hippocampus, cerebral cortex and locus coeruleus (LC) region. In nonstressed rats, ethanol significantly increased MHPG-SO4 levels in the hypothalamus, hippocampus and cerebral cortex, but not in the amygdala or in the LC region. In stressed rats, ethanol attenuated stress-induced increases in MHPG-SO4 levels preferentially in the amygdala and LC region, but not in the remaining three regions. Although ethanol per se dose-dependently elevated plasma corticosterone levels in nonstressed rats, ethanol at 2 g/kg attenuated the stress-induced elevation of corticosterone. These results suggest that the attenuating effect of ethanol on stress-induced increases in NA turnover in the amygdala and LC region might be related to the stress-relieving properties of this drug.

Immobilization and restraint effects on pain reactions in animals

Acute physical restraint represents a potent stressor in several animal species and is accompanied by a complex pattern of hormonal responses and functional changes in the central nervous system. Repeated immobilization leads to partial blunting of the behavioral and hormonal responses, with transient modifications of neurotransmitter systems in the brain. Pain reactions, as investigated by different kinds of nociceptive tests, are usually attenuated both during and immediately following acute immobilization and the analgesic effect of opiate compounds potentiated; these behavioral alterations may be attributed at least in part to activation of an endogenous opioid system. In some species, restraint may induce a reflex immobility (animal hypnosis or tonic immobility) which is also characterized by suppression of pain reactions in rabbits, probably subserved by different mechanisms. Analysis of available data suggests that pain testing in unanesthetized, restrained animals may involve alterations of the animal's reactivity to noxious stimuli.

Changes in central GABAergic function following acute and repeated stress

1. The function of gamma-aminobutyric acid (GABA)ergic systems in response to acute and repeated stressful manipulations was evaluated in both the corpus striatum and frontal cerebral cortex of the rat. 2. In the corpus striatum the activity of the synthetic enzyme for GABA (glutamic acid decarboxylase, GAD) and the levels of GABA were reduced by acute immobilization stress (1 h). GABA turnover was reduced only by acute cold stress (3 h, 4 degrees C). 3. In the frontal cerebral cortex no changes were observed after acute stressful manipulations, but repeated stress (0.5 h immobilization per day for 14 days) enhanced both GAD activity and GABA turnover, and reduced GABA levels. 4. In conclusion, it would appear that the GABAergic system in the corpus striatum of the rat is most sensitive to acute stress and that the system in the frontal cerebral cortex area is preferentially responsive to chronic stress. It is speculated that the cortical GABAergic system is responsible for adaptive responses to the adverse conditions prevailing during chronic stress.

Dietary protein and carbohydrate effects on blood parameters related to stress in cat

Adult cats were adapted to hypoglucidic semi-purified diets containing casein or soya as the protein source to study the effects of a 2 hr immobilization period. Body weight of cats fed hypoglucidic diets was significantly decreased. The control casein group showed higher plasma dopamine-beta-hydroxylase activity but lower pyridoxal 5'-phosphate level than control soya group. Cats fed hypoglucidic casein diet, plasma glucose, insulin and pyridoxal 5'-phosphate levels were increased whereas cats fed hypoglucidic soya diet, pyridoxal 5'-phosphate levels were decreased and dopamine-beta-hydroxylase activity increased when data were compared to their respective control groups. A 2 hr immobilization period induced hyperglycemia in all groups whereas cats fed soya diets, plasma insulin level and dopamine-beta-hydroxylase activity were significantly increased and pyridoxal 5'-phosphate content significantly decreased. These results demonstrate that dietary casein and soya protein might be differentiated on a physiological basis and immobilization emphasized the biochemical disturbances observed between the groups thus suggesting a greater resistance to stress in casein groups than in soya groups.

A benzodiazepine receptor inverse agonist inhibits stress-induced ulcer formation

The effects of a benzodiazepine receptor inverse agonist (FG 7142) on gastric ulcer formation were studied in restrained rats. FG 7142 (10-50 mg/kg) reduced in a dose-dependent fashion both the number and cumulative length of gastric ulcers elicited by restraint for 2 hr at 4 degrees C, but did not affect ulcer formation in unrestrained animals maintained in this environment. FG 7142 also reduced gastric ulcer formation in restrained rats maintained at 22 degrees C for 5 hr. The ability of FG 7142 to reduce restraint-stress induced gastric ulcer formation was blocked by the benzodiazepine receptor antagonist ZK 93426 and the beta-adrenoceptor antagonist propranolol. These findings suggest that FG 7142 produces a benzodiazepine-receptor mediated reduction in gastric ulcer formation, which may result from its ability to increase activity of the sympathetic nervous system.