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

Neural substrates for regulating self-grooming behavior in rodents

Grooming, as an evolutionarily conserved repetitive behavior, is common in various animals, including humans, and serves essential functions including, but not limited to, hygiene maintenance, thermoregulation, de-arousal, stress reduction, and social behaviors. In rodents, grooming involves a patterned and sequenced structure, known as the syntactic chain with four phases that comprise repeated stereotyped movements happening in a cephalocaudal progression style, beginning from the nose to the face, to the head, and finally ending with body licking. The context-dependent occurrence of grooming behavior indicates its adaptive significance. This review briefly summarizes the neural substrates responsible for rodent grooming behavior and explores its relevance in rodent models of neuropsychiatric disorders and neurodegenerative diseases with aberrant grooming phenotypes. We further emphasize the utility of rodent grooming as a reliable measure of repetitive behavior in neuropsychiatric models, holding promise for translational psychiatry. Herein, we mainly focus on rodent self-grooming. Allogrooming (grooming being applied on one animal by its conspecifics via licking or carefully nibbling) and heterogrooming (a form of grooming behavior directing towards another animal, which occurs in other contexts, such as maternal, sexual, aggressive, or social behaviors) are not covered due to space constraints.

The Pituitary-Adrenal Response to Paradoxical Sleep Deprivation Is Similar to a Psychological Stressor, Whereas the Hypothalamic Response Is Unique

Stressors of different natures induce activation of the hypothalamic-pituitary-adrenal (HPA) axis at different magnitudes. Moreover, the HPA axis response to repeated exposure is usually distinct from that elicited by a single session. Paradoxical sleep deprivation (PSD) augments ACTH and corticosterone (CORT) levels, but the nature of this stimulus is not yet defined. The purpose of the present study was to qualitatively compare the stress response of animals submitted to PSD to that of rats exposed once or four times to cold, as a physiological stress, movement restraint (RST) as a mixed stressor and predator odour (PRED) as the psychological stressor, whilst animals were submitted for 1 or 4 days to PSD and respective control groups. None of the stressors altered corticotropin releasing factor immunoreactivity in the paraventricular nucleus of the hypothalamus (PVN), median eminence (ME) or central amygdala, compared to control groups, whereas vasopressin immunoreactivity in PSD animals was decreased in the PVN and increased in the ME, indicating augmented activity of this system. ACTH levels were higher after repeated stress or prolonged PSD than after single- or 1 day-exposure and control groups, whereas the CORT response was habituated by repeated stress, but not by 4-days PSD. This dissociation resulted in changes in the CORT : ACTH ratio, with repeated cold and RST decreasing the ratio compared to single exposure, but no change was seen in PRED and PSD groups. Comparing the magnitude and pattern of pituitary-adrenal response to the different stressors, PSD-induced responses were closer to that shown by PRED-exposed rats. In contrast, the hypothalamic response of PSD-exposed rats was unique, inasmuch as this was the only stressor which increased the activity of the vasopressin system. In conclusion, we propose that the pituitary-adrenal response to PSD is similar to that induced by a psychological stressor.

Neurochemical organization of the ventral striatum's olfactory tubercle

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

Behavioral and Biochemical Impact of Chronic Unpredictable Mild Stress on the Acquisition of Nicotine Conditioned Place Preference in Rats

Addiction is a chronic psychiatric disease which represents a global problem, and stress can increase drug addiction and relapse. Taking into account frequent concomitance of nicotine dependence and stress, the purpose of the present study was to assess behavioral and biochemical effects of chronic unpredictable mild stress (CUMS) exposure on nicotine reward in rats measured in the conditioned place preference (CPP) paradigm. Rats were submitted to the CUMS for 3 weeks and conditioned with nicotine (0.175 mg/kg) for 2 or 3 days. Our results revealed that only CUMS-exposed animals exhibited the CPP after 2 days of conditioning indicating that stressed rats were more sensitive to the rewarding properties of nicotine and that chronic stress exacerbates nicotine preference. Administration of metyrapone (50 mg/kg), a glucocorticosteroid antagonist, and imipramine (15 mg/kg), an antidepressant, abolished nicotine CPP in stressed rats after 2 days of conditioning. The biochemical experiments showed increased markers of oxidative stress after nicotine conditioning for 2 and 3 days, while the CUMS further potentiated pro-oxidative effects of nicotine. Moreover, metyrapone reversed oxidative changes caused by stress and nicotine, while imipramine was not able to overwhelm nicotine- and stress-induced oxidative damages; however, it could exert antioxidant effect if administered repeatedly. The results suggest that recent exposure to a stressor may augment the rewarding effects of nicotine through anhedonia- and stress-related mechanisms. Our study contributes to the understanding of behavioral and biochemical stress-induced modification of the rewarding effects of nicotine on the basis of the development of nicotine dependence.

Examination of Concurrent Exposure to Repeated Stress and Chlorpyrifos on Cholinergic, Glutamatergic, and Monoamine Neurotransmitter Systems in Rat Forebrain Regions

Repeated stress has been reported to cause reversible impairment in the central nervous system (CNS). It was proposed that alterations in glutamatergic, cholinergic, and monoamine neurotransmitter systems after exposure to stress are initial CNS events contributing to this impairment and that exacerbation could occur with concurrent exposure to cholinesterase inhibitors. Effects of concurrent exposure to repeated stress and chlorpyrifos on activities of acetylcholinesterase (AChE), carboxylesterase, and choline acetyltransferase (ChAT); concentrations of excitatory amino acids, monoamines, and their metabolites; and maximum binding densities ( Bmax) and equilibrium dissociation rate constants ( Kd) of glutamatergic N-methyl-d-aspartate (NMDA) and total muscarinic cholinergic receptors were studied in the blood, hippocampus, cerebral cortex, or hypothalamus of adult Long-Evans rats. Stress treatments extended over 28 days included (1) control rats handled 5 days/week; (2) rats restrained 1 h/day for 5 days/week; (3) rats swum 30 min for 1 day/week; or (4) rats restrained 4 days/week and swum for 1 day/week. On day 24, each stress treatment group was randomly divided and injected either with corn oil or chlorpyrifos, 160 mg/kg subcutaneously (sc) (60% of the maximum tolerated dose), 4 h after restraint. Blood and brain tisssues were collected on day 28. Rats restrained and swum had a statistical trend toward increasing concentrations of glutamate in the hippocampus when compared to rats only swum ( p = .064). Chlorpyrifos administration decreased restraint-induced elevated aspartate in the hippocampus, and decreased Bmax of total muscarinic receptors in the cerebral cortex. In addition, chlorpyrifos decreased Bmax and Kd of total muscarinic receptors in the cerebral cortex of swum rats. Results demonstrated that chlorpyrifos inhibited AChE activity in blood, cerebral cortex, and hippocampus, but stress did not affect AChE activity. Carboxylesterase activity was inhibited by chlorpyrifos and by repeated restraint with swim. Swim stress decreased concentrations of norepinephrine in the hippocampus and hypothalamus, and increased concentrations of dopamine and its metabolite, DOPAC, in the hypothalamus. Both stress and chlorpyrifos altered serotonin concentrations, and the interactions of repeated stress and chlorpyrifos on serotonin approached significance in the hippocampus ( p = .06) and hypothalamus ( p = .08). Therefore, stress models were demonstrated to alter glutamatergic and monoamine responses, whereas chlorpyrifos alone had effects on cholinergic and monoamine systems in the rat CNS. However, the interactions between stress and chlorpyrifos significant at p < 0.05 were restricted to attenuation of elevated aspartate in the hippocampus of restrained with swim rats and decreased Kd of acetylcholine receptors in the cerebral cortex of swum rats and restrained rats.

Corticosterone in drinking water: altered kinetics of a single oral dose of corticosterone and concentrations of plasma sodium, albumin, globulin, and total protein

Effects of chronic exposure to corticosterone in drinking water on corticosterone kinetics, blood chemistry, and concentrations of catecholamines in parts of brain were studied in Long-Evans rats. Rats were randomly grouped into 3-2 treatments (n-4), with three treatments of drinking water (tap water, or 2.5% ethanol, or 400 mg/mL of corticosterone in 2.5% ethanol) for 28 days and two treatments of gavage with a single dose of either corn oil or corticosterone 20 mg/kg on day 28. Blood samples were collected at 0, 15, 30, 60, 120, 240, 480, and 720 min after dosing to determine plasma corticosterone concentrations. Blood samples were collected for clinical pathology on day 42. Hippocampus, cerebral cortex, caudate-putamen, and pons were examined to determine concentrations of catecholamines and activities of esterases. Concentrations of plasma corticosterone before gavage of the corticosterone-drinking rats (47.619 ± 1.13 ng/mL) were lower than the water (418.479 ± 1.13 ng/mL) or the ethanol rats (383.719 ± 1.13 ng/mL, P <0.0001). Plasma corticosterone rose to peak concentrations by 15 min after gavage in all three groups of drinking rats. Corticosterone- drinking rats had concentrations of plasma corticosterone that returned to basal levels slower than water- and ethanol-drinking rats. Plasma sodium and chloride concentrations were lower in the corticosterone-drinking rats than the water-drinking rats P <0.01). Plasma albumin, globulin, and total protein were highest in the corticosterone-drinking rats when compared to the other groups of drinking rats P <0.001, P <0.05, and P <0.001, respectively). Corticosterone in drinking water did not affect activities of brain neurotoxic esterase, carboxylesterase, acetylcholinesterase, or concentrations of monoamines and their metabolites. A single oral dose of corticosterone reduced neurotoxic esterase activity in the cerebral cortex P <0.05) and increased norepinephrine concentrations in the hippocampus P <0.05).

Behavioral and Biochemical Interaction Between Nicotine and Chronic Unpredictable Mild Stress in Mice

Nicotine, the main component of tobacco smoke, exerts influence on mood, and contributes to physical and psychological dependence. Taking into account frequent concomitance of nicotine abuse and stress, we aimed to research behavioral and biochemical effects associated with nicotine administration in combination with chronic unpredictable mild stress (CUMS). Mice were submitted to the procedure of CUMS for 4 weeks, 2 h per day. Our results revealed that CUMS-exposed animals exhibited behavioral alteration like anxiety disorders in the elevated plus maze (EPM) test, the disturbances in memory in the passive avoidance (PA) test and depressive effects in the forced swim test (FST). Moreover, nicotine (0.05–0.5 mg/kg), after an acute or subchronic administration decreased stress-induced depression- and anxiety-like effect as well as memory deficit. Administration of metyrapone (50 mg/kg), a glucocorticosteroid antagonist, alleviated the depressive effect induced by the CUMS. The biochemical experiments showed decreased values of the total antioxidant status (TAS), activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) with simultaneously increased in malondialdehyde (MDA) concentration in mice submitted to the CUMS. The same effects were observed after an acute and subchronic nicotine administration within all examined brain structures (i.e., hippocampus, cortex, and cerebellum) and in the whole brain in non-stressed and stressed mice confirming pro-oxidative effect of nicotine. Our study contributes to the understanding of behavioral and biochemical mechanisms involved in stress-induced disorders such as depression, anxiety and memory disturbances as well as dual nicotine-stress interactions on the basis of the development of nicotine dependence.

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.

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.

Protective effects of luteolin on cognitive impairments induced by psychological stress in mice

In the present study, the protective effects of luteolin were investigated against psychological stress-induced cognitive impairment. To emulate the psychological stress, mice received restraint stress for six hours daily, between 9:00 and 15:00 hours, for 21 consecutive days. The results of step-through test, open-field test and Morris Water Maze test demonstrated that psychological stress treatment could result in cognitive impairments in mice. This cognition dysfunction was improved by treatment with low- and medium-dose luteolin. In addition, psychological stress induced an increased serum corticosterone concentration with a decreased serum norepinephrine and dopamine concentration. These alterations were attenuated by treatment with luteolin. Also, psychological stress significantly decreased the glutathione (GSH) concentrations and superoxide dismutase (SOD) activities in prefrontal cortex and hippocampus, while the malondialdehyde (MDA) concentrations were enhanced. However, these oxidative alterations in prefrontal cortex and hippocampus induced by psychological stress were significantly reversed by treatment of luteolin. Further, the current study indicated a decline of catalase (CAT) activities in the hippocampus of the ST group, which was significantly prevented by low, medium and high dose of luteolin. On the other hand, there was no significance in CAT activities of the prefrontal cortex among the six groups. Collectively, the present results suggest that luteolin treatment serves as a key role in improving the psychological stress-induced cognitive impairments.

Brain region specific monoamine and oxidative changes during restraint stress

BACKGROUND AND PURPOSE

Stress-induced central effects are regulated by brain neurotransmitters, glucocorticoids and oxidative processes. Therefore, we aimed to evaluate the simultaneous alterations in the monoamine and antioxidant systems in selected brain regions (frontal cortex, striatum and hippocampus) at 1 hour (h) and 24h following the exposure of restraint stress (RS), to understand their initial response and possible crosstalk.

METHODS AND RESULTS

RS (150 min immobilization) significantly increased the dopamine levels in the frontal cortex and decreased them in the striatum and hippocampus, with selective increase of dopamine metabolites both in the 1h and 24h RS groups compared to control values. The serotonin and its metabolite levels were significantly increased in both time intervals, while noradrenaline levels were decreased in the frontal cortex and striatum only. The activities of superoxide dismutase, glutathione peroxidase and the levels of lipid peroxidation were significantly increased with significant decrease of glutathione levels in the frontal cortex and striatum both in the 1h and 24h RS groups. There was no significant change in the catalase activity in any group. In the hippocampus, the glutathione levels were significantly decreased only in the 1h RS group.

CONCLUSIONS

Our study implies that the frontal cortex and striatum are more sensitive to oxidative burden which could be related to the parallel monoamine perturbations. This provides a rational look into the simultaneous compensatory central mechanisms operating during acute stress responses which are particular to precise brain regions and may have long lasting effects on various neuropathological alterations.

Novel Ocimumoside A and B as anti-stress agents: modulation of brain monoamines and antioxidant systems in chronic unpredictable stress model in rats

Therapies targeting central stress mechanisms are fundamental for the development of successful treatment strategies. Ocimum sanctum (OS) is an Indian medicinal plant traditionally used for the treatment of various stress-related conditions. Previously, we have isolated and characterized three OS compounds; Ocimarin, Ocimumoside A and Ocimumoside B. However, their role in modulating chronic stress-induced central changes is unexplored. Thus, in the present study the efficacy of these OS compounds have been evaluated on the chronic unpredictable stress (CUS)-induced alterations in the monoaminergic and antioxidant systems in the frontal cortex, striatum and hippocampus, along with the changes in the plasma corticosterone levels. CUS (two different types of stressors daily for seven days) resulted in a significant elevation of plasma corticosterone level, which was reversed to control levels by pretreatment with Ocimumoside A and B (40 mg/kg p.o.), while Ocimarin showed no effect. The levels of NA, DA and 5-HT were significantly decreased in all the three brain regions by CUS, with a selective increase of DA metabolites. A significant decrease in the glutathione (GSH) content, the activities of superoxide dismutase and catalase with a significant increase in the glutathione peroxidase activity and lipid peroxidation was observed in all the three regions of the brain by CUS. The OS compounds alone did not cause any significant change in the baseline values of these parameters. However, Ocimumoside A and B (40 mg/kg body p.o.) attenuated these CUS-induced alterations with an efficacy similar to that of standard anti-stress (Panax quinquefolium; 100 mg/kg p.o.) and antioxidant (Melatonin; 20 mg/kg i.p.) drugs. While, Ocimarin failed to modulate these CUS-induced alterations. Therefore, this is the first report which identified the anti-stress activity of novel Ocimumoside A and B at the level of central monoamines and antioxidant properties, implicating their therapeutic importance in the prevention of stress-related disorders.

Effects of epigallocatechin-3-gallate on behavioral impairments induced by psychological stress in rats

This study was conducted to explore the effects of epigallocatechin-3-gallate (EGCG) on cognitive performances in psychological stress rats. An animal model of psychological stress was developed by restraint stress for three weeks. Male Wistar rats were randomly assigned to four groups as follows: normal control group, stress control group and two stress groups with green tea polyphenols (GTPs) and EGCG modulation, respectively. The changes of behavioral performances of rats were examined by the open-field test and step-through test. Results showed that behavioral performances of stress control group were changed abnormally, and they were improved in GTPs and EGCG modulation groups. In addition, plasma levels of cortisol, dopamine, norepinephrine, 5-hydroxytryptamine, interleukin-6 and interleukin-2 were detected. Stress control group had increased contents of cortisol, interleukin-6 and interleukin-2, and meanwhile had declined levels of 5-hydroxytryptamine and catecholamines. These changes in GTPs and EGCG modulation groups were similar to that of the normal control group. The expressions of metallothioneins in the hippocampus were detected by reverse transcription polymerase chain reaction. In contrast with the normal control group, their expressions in all the three stress groups were enhanced clearly. The results suggested that GTPs and EGCG modulation could improve the cognitive impairments induced by psychological stress. The related mechanisms may be involved with the changes of catecholamines, 5-hydroxytryptamine, cytokines and expressions of metallothioneins.

Dietary l-tyrosine alleviates the behavioral alterations induced by social isolation stress in mice

Chronic stress induces abnormal mental state and behavior, and can be a risk factor for mental disorders. Although it is reported that l-tyrosine, an amino acid that is a precursor of catecholamine synthesis, alleviated the change of cognition and behavior induced by acute stress, knowledge about its effects on chronic stress is limited. In the present study, the effects of dietary l-tyrosine on behavioral alteration induced by chronic stress were investigated by employing a social isolation stress model in mice. Social isolation stress increased locomotor activity in both the home cage and open field. These increases of locomotor activity were suppressed by dietary l-tyrosine. Moreover, l-tyrosine increased both the concentration and turnover rate of norepinephrine metabolites. These findings partly suggest the availability of dietary l-tyrosine for psychic dysfunctions induced by chronic stress.

Effect of Bacopa monniera on stress induced changes in plasma corticosterone and brain monoamines in rats

Bacopa monniera (BM) is well known for its neuropharmacological effects. Our previous studies indicated the adaptogenic effect of standardized extract of BM in various stress models. In the present study, effect of BM was evaluated on acute stress (AS) and chronic unpredictable stress (CUS) induced changes in plasma corticosterone and monoamines-noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in cortex and hippocampus regions of brain in rats. Panax root powder (Panax quinquefolium) was taken as standard. Subjecting animals to AS (immobilization for 150 min once only) and CUS (different stressors for 7 days) resulted in significant elevation in plasma corticosterone levels, which was significantly countered by treatment with BM at a dose of 40 and 80 mg/kg p.o. similar to the effects of Panax quinquefolium (PQ) at 100 mg/kg p.o. AS exposure significantly increased the levels of 5-HT and decreased NA content in both the brain regions while DA content was significantly increased in cortex and decreased in hippocampus regions. In CUS regimen, levels of NA, DA and 5-HT were significantly depleted in cortex and hippocampus regions of brain. Treatment with BM (40 and 80 mg/kg) attenuated the stress induced changes in levels of 5-HT and DA in cortex and hippocampus regions but was ineffective in normalizing the NA levels in AS model, whereas PQ treatment significantly reverted back the effects of stress. In CUS model, pretreatment with BM and PQ significantly elevated the levels of NA, DA and 5-HT levels in cortex and levels of NA and 5-HT in hippocampus regions. Hence, our study indicates that the adaptogenic activity of BM might be due to the normalization of stress induced alteration in plasma corticosterone and levels of monoamines like NA, 5-HT and DA in cortex and hippocampus regions of the brain, which are more vulnerable to stressful conditions analogous to the effects of PQ.

The involvement of cholinergic and noradrenergic systems in behavioral recovery following oxotremorine treatment to chronically stressed rats

Chronic stress in rats has been shown to impair learning and memory, and precipitate several affective disorders like depression and anxiety. The mechanisms involved in these stress-induced disorders and the possible reversal are poorly understood, thus limiting the number of drugs available for their treatment. Our earlier studies suggest cholinergic dysfunction as the underlying cause in the behavioral deficits following stress. Muscarinic cholinergic agonist, oxotremorine is demonstrated to have a beneficial effect in reversing brain injury-induced behavioral dysfunction. In this study, we have evaluated the effect of oxotremorine treatment on chronic restraint stress-induced cognitive deficits. Rats were subjected to restraint stress (6 h/day) for 21 days followed by oxotremorine treatment for 10 days. Spatial learning and memory was assessed in a partially baited eight-arm radial maze task. Stressed rats exhibited impairment in performance, with decreased percentage of correct choices and an increase in the number of reference memory errors (RMEs). Oxotremorine treatment (0.1 or 0.2 mg/kg, i.p.) to stressed rats resulted in a significant increase in the percent correct choices and a decrease in the number of RMEs compared with stress as well as the stress+vehicle-treated groups. In the retention test, oxotremorine treated rats committed less RMEs compared with the stress group. Chronic restraint stress decreased acetylcholinesterase (AChE) activity in the hippocampus, frontal cortex and septum, which was reversed by both the doses of oxotremorine. Further, oxotremorine treatment also restored the norepinephrine levels in the hippocampus and frontal cortex. Thus, this study demonstrates the potential of cholinergic muscarinic agonists and the involvement of both cholinergic and noradrenergic systems in the reversal of stress-induced learning and memory deficits.

Novel stressors affected catecholamine stores in socially isolated normotensive and spontaneously hypertensive rats

Catecholamines in some central (hypothalamus and hippocampus) and peripheral tissues (adrenal glands and heart auricles) of long-term socially isolated normotensive and spontaneously hypertensive rats exposed to novel immobilization stress were determined by a simultaneous single isotope radioenzymatic assay. Long-term isolation (21 days) produced depletion of hypothalamic norepinephrine (NE) stores and hippocampal dopamine (DA) stores in both normotensive and spontaneously hypertensive rats. Acute immobilization stress (2 h) significantly decreased NE and DA stores in hypothalamus and hippocampus of naive normotensive and spontaneously hypertensive rats controls. However, novel immobilization stress applied to normotensive rats previously subjected to long-term isolation produced no changes in catecholamine levels in hypothalamus, while resulting in somewhat higher depletion of NE stores in hypothalamus of spontaneously hypertensive rats treated in the same way. Novel immobilization stress decreased NE and DA stores in hippocampus of normotensive but was without effect on NE and DA stores of spontaneously hypertensive rats. Social isolation did not affect catecholamine stores in peripheral tissues but novel immobilization stress produced a significant decrease in catecholamine content. The results suggest that some central and peripherals tissues of spontaneously hypertensive rats and normotensive rats differ with regard to catecholamine content and that there are certain differences in their responsiveness to stress.

Different Effects of Novel Stressors on Sympathoadrenal System Activation in Rats Exposed to Long-Term Immobilization

Activation of the sympathoadrenal system, evaluated by plasma levels of epinephrine (E) and norepinephrine (NE) after exposure of rats to various stressors, is well documented. However, response of rats exposed long-term to a homotypic stressor and then exposed once to a heterotypic novel stressor is poorly understood. In the present study, we examined changes in plasma levels of catecholamines (CA) and corticosterone (COR) of rats after a single (2-h) or long-term repeated immobilization (41 times, 2 h daily) and in rats adapted to long-term immobilization exposed once to the novel stress of cold exposure or insulin or 2-deoxy-D-glucose (2DG) administration. Long-term immobilization produced a significant elevation of basal plasma COR but not NE and E levels. Long-term immobilized rats exposed to insulin or 2DG showed significant elevation of plasma CA and COR levels in comparison to the administration to control rats. Exposure of long-term immobilized and control rats to cold stress increased plasma NE and COR, whereas plasma E was not significantly changed. The exposure of long-term immobilized rats to a further single immobilization (2 h) increased plasma CA levels, but, in naive control rats, the single immobilization produced more pronounced increases. These data suggest that rats exposed to homotypic long-term immobilization are able to respond to heterotypic stressors by higher activation of the sympathoadrenal system as compared with the control, previously unstressed rats. Reduced plasma CA levels in long-term immobilized rats exposed to homotypic stressor are most probably due to an adaptation at the level of brain regulatory centers.

Effects of acute, repeated and chronic variable stress on in vivo tyrosine hydroxylase activity and on alpha(2)-adrenoceptor sensitivity in the rat brain

We assessed the effects of a single tail pinch and two chronic stress regimes, repeated and variable, on in vivo tyrosine hydroxylase activity and on alpha2-adrenoceptor sensitivity in two brain regions. After administering a 3,4-dihydroxyphenylalanine (DOPA) decarboxylase inhibitor, tyrosine hydroxylase activity, measured as the accumulation of DOPA, and noradrenaline (NA) content were determined by using high-performance liquid chromatography. A single tail pinch for 5 min induced an enhancement of DOPA content in hippocampus (28%) and hypothalamus (67%) which was still present 24 h later. This increase could account for the lack of changes in NA content in both regions after the application of this stressor. However, tyrosine hydroxylase activity was unmodified 24 h after exposure to both repeated (5 min of tail pinch, twice daily, for 14 days) and chronic variable stress (one of 5 different stressors, once daily, for 14 days) although there was an enhancement of NA levels in hippocampus (45 and 54%, respectively) and hypothalamus (24.5 and 36%, respectively). The sensitivity of the alpha2-adrenoceptors which regulate [3H]-NA release in hippocampal and hypothalamic synaptosomes was not modified by the acute or chronic stress protocols assayed. The results show that both paradigms of chronic stress had similar effects on the noradrenergic indices evaluated.

Selective chronic stress-induced in vivo ERK1/2 hyperphosphorylation in medial prefrontocortical dendrites: implications for stress-related cortical pathology?

Stress has been shown to affect brain structural plasticity, promote long-term changes in multiple neurotransmitter systems and cause neuronal atrophy. However, the mechanisms involved in these stress-related neural alterations are still poorly understood. Mitogen-activated protein kinase (MAPK) cascades play a crucial role in the transduction of neurotrophic signal from the cell surface to the nucleus and are implicated in the modulation of synaptic plasticity and neuronal survival. An intriguing possibility is that stress might influence brain plasticity through its effects on selective members of such intracellular signalling cascades responsible for the transduction of neurotrophin signals. Here, we have investigated the effects of stress on the expression of three members of the MAPK/extracellular-regulated kinase (ERK) pathway such as phospho-ERK1, phospho-ERK2 and phospho-cAMP/calcium-responsive element-binding protein (CREB) in the adult rat brain. Male rats were subjected to mild footshocks and the patterns of protein expression were analysed after 21 consecutive days of stress. We found that chronic stress induced a pronounced and persistent ERK1/2 hyperphosphorylation in dendrites of the higher prefrontocortical layers (II and III) and a reduction of phospho-CREB expression in several cortical and subcortical regions. We hypothesized that defects in ERK signalling regulation combined with a reduced phospho-CREB activity may be a crucial mechanism by which sustained stress may induce atrophy of selective subpopulations of vulnerable cortical neurons and/or distal dendrites. Thus, ERK-mediated cortical abnormalities may represent a specific path by which chronic stress affects the functioning of cortical structures and causes selective neural network defects.

Chronic psychosocial stress impairs learning and memory and increases sensitivity to yohimbine in adult rats

BACKGROUND

It is well known that intense and prolonged stress can produce cognitive impairments and hippocampal damage and increase noradrenergic activity in humans. This study investigated the hypothesis that chronic psychosocial stress would affect behavior, drug sensitivity, and hippocampal-dependent learning and memory in rats. The work provides a novel connection between animal and human studies by evaluating the effects of stress on a rat's response to yohimbine, an alpha(2) adrenergic receptor antagonist.

METHODS

Rats were exposed to a cat for 5 weeks and randomly housed with a different group of cohorts each day (psychosocial stress). The effects of the stress manipulations were then assessed on open field behavior, spatial learning and memory in the radial arm water maze and the behavioral response to a low dose of yohimbine (1.5 mg/kg).

RESULTS

Stressed rats displayed impaired habituation to a novel environment, heightened anxiety, and increased sensitivity to yohimbine. In addition, the stressed rats exhibited impaired learning and memory.

CONCLUSIONS

There are commonalities between the current findings on stressed rats and from studies on traumatized people. Thus, psychosocial stress manipulations in rats may yield insight into the basis of cognitive and neuroendocrine disturbances that commonly occur in people with anxiety disorders.

Stressor specificity of central neuroendocrine responses: implications for stress-related disorders

Despite the fact that many research articles have been written about stress and stress-related diseases, no scientifically accepted definition of stress exists. Selye introduced and popularized stress as a medical and scientific idea. He did not deny the existence of stressor-specific response patterns; however, he emphasized that such responses did not constitute stress, only the shared nonspecific component. In this review we focus mainly on the similarities and differences between the neuroendocrine responses (especially the sympathoadrenal and the sympathoneuronal systems and the hypothalamo-pituitary-adrenocortical axis) among various stressors and a strategy for testing Selye's doctrine of nonspecificity. In our experiments, we used five different stressors: immobilization, hemorrhage, cold exposure, pain, or hypoglycemia. With the exception of immobilization stress, these stressors also differed in their intensities. Our results showed marked heterogeneity of neuroendocrine responses to various stressors and that each stressor has a neurochemical "signature." By examining changes of Fos immunoreactivity in various brain regions upon exposure to different stressors, we also attempted to map central stressor-specific neuroendocrine pathways. We believe the existence of stressor-specific pathways and circuits is a clear step forward in the study of the pathogenesis of stress-related disorders and their proper treatment. Finally, we define stress as a state of threatened homeostasis (physical or perceived treat to homeostasis). During stress, an adaptive compensatory specific response of the organism is activated to sustain homeostasis. The adaptive response reflects the activation of specific central circuits and is genetically and constitutionally programmed and constantly modulated by environmental factors.

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.

Role of locus coeruleus in foot shock-evoked Fos expression in rat brain

The robust activation of locus coeruleus neurons in response to a variety of stressors, in conjunction with the widespread outputs of the locus coeruleus, suggest that the locus coeruleus may be important in mediating responses to stress. Previous studies in rats have demonstrated that exposure to foot shock elicits Fos expression, a marker of neuronal activation, in the locus coeruleus and other brain sites. In order to evaluate the involvement of the locus coeruleus in foot shock-induced activation of other brain sites, shock-induced Fos expression was examined in the locus coeruleus and other brain areas known to be activated by foot shock, following direct inhibition of the locus coeruleus by local infusion of muscimol, a GABA agonist, prior to foot shock. Control rats received infusions of artificial cerebrospinal fluid into the locus coeruleus or muscimol into areas outside of locus coeruleus. Rats infused with artificial cerebrospinal fluid and then exposed to foot shock had significant increases in Fos expression in several brain areas, including locus coeruleus, nucleus O, several subdivisions of the hypothalamus, subnuclei of amygdala, bed nucleus of the stria terminalis and cingulate cortex. Inhibition of the locus coeruleus prior to foot shock significantly inhibited Fos expression in the locus coeruleus, nucleus O, some subdivisions of the hypothalamus including the magnocellular and medial parvicellular paraventricular hypothalamic nucleus, subnuclei of amygdala, and cingulate cortex. In contrast, inhibition of the locus coeruleus did not affect shock-induced Fos expression in other areas, including certain subdivisions of the hypothalamus and bed nucleus of the stria terminalis. We suggest that foot shock may activate multiple pathways, with activation of certain discrete nuclei requiring input from the locus coeruleus and activation of others occurring independently of locus coeruleus input.

Separation-induced body weight loss, impairment in alternation behavior, and autonomic tone: effects of tyrosine

We have investigated the effects of tyrosine on alternation behavior and hippocampal adrenergic and cholinergic tone in a model of self-induced weight loss caused by separation stress. Separation decreased body weight in mice (P < .001) and spontaneous alternations in the T-maze (P < .001). This impairment was associated with depletion of both norepinephrine (NE, P < .001) and dopamine (P < .01) while increasing MHPG (P < .05) and the ratio of MHPG/NE (P < .05). Increasing tyrosine availability restored performance to control levels (P < .001) and repleted dopamine (P < .05) and presumably also NE (indicated by increases in both MHPG, P < .001, and MHPG/NE, P < .05). Stress increased adrenergic alpha(2)-receptor density (P < .001) without changing its K(d) and the B(max) and K(d) of beta-receptors, suggesting that it decreased NE transmission through action on alpha(2)-receptors. The balance between beta- and alpha(2)-receptors appeared to be related to alternation behavior as shown by the decrease (P < .01) and increase (P < .05) in their ratios induced by stress and tyrosine, respectively. With regard to cholinergic tone, separation stress increased M1 receptor density (P < .05) and its mRNA signal (P < .001). Tyrosine further increased M1 receptor density of stressed mice (P < .05). Tyrosine might be a potential therapy for cognitive and mood problems associated with the maintenance of a reduced body weight in the treatment of obesity and in the extreme case of anorexia nervosa.

Nicotine attenuates stress-induced changes in plasma amino acid concentrations and locomotor activity in rats

It is known that stressor stimuli (both systemic and processive) and nicotine activate central nervous system. Surprisingly, numerous studies have demonstrated an increase in nicotine self-administration among smokers when exposed to stress in order to reduce the stress-related tension. Therefore, in the present study, we decided to investigate the influence of nicotine on both behavioral (i.e., on locomotor activity) and metabolic (i.e., on the level of amino acids in the plasma) changes following water immersion restraint stress in rats. As expected, the stress produced evident decline in locomotor activity of the rats (p < 0.001) and in the levels of all plasma amino acids studied (p < 0.05). Nicotine alone also significantly reduced locomotor activity (p < 0.05) and the levels of some plasma amino acids. However, when administered to rats subjected to water immersion and restraint, nicotine attenuated both stress-induced decrease in locomotor activity (p < 0.05) and in some plasma amino acids. Thus, this study demonstrated that the mode of action of nicotine is strongly dependent on the level of initial brain activity, which provide new evidence for arousal-modulation model of nicotine action.

Effect of a 14-day hindlimb suspension on beta-adrenoreceptors in rats

Exposure to long-term simulated microgravity exhibits reduced sympathetic nervous system activity. This study tested the hypothesis that the hypersensitivity of adrenoreceptors would explain partly many other features of the hemodynamic consequences of return from space. The biochemical properties of the beta adrenoreceptors (betaAR) were determined using 125I-cyanopindolol (125I-CYP) binding in three rat groups: (1) The first experimental group consisted of 24 h-restrained orthostatic rats in the horizontal position, to test the early effect of the attachment to the suspension device; (2) the second experimental group consisted of 24 h-restrained antiorthostatic rats, to test the early effect of the suspension; (3) the third experimental group consisted of 14 day-restrained antiorthostatic rats, to test the long term effect of the suspension. The study was performed in two organs involved in blood pressure regulation, i.e. the heart (atria and ventricles were separated) and kidneys. The Scatchard analysis of 125I-cyanopindolol binding in both organs indicated no significant alterations in the dissociation constant (Kd) and the maximum binding capacity (Bmax) in the three experimental groups. These results do not allow the conclusion about the SNS adaptation pattern to simulated microgravity. Thus, the hypothesis that betaAR are involved in the cardiovascular adaptation to simulated microgravity is not verified in this model where, as a matter of fact, cardiovascular deconditioning is not verified even if this model is widely used.

Stress-induced changes of norepinephrine uptake sites in the locus coeruleus of C57BL/6J and DBA/2J mice: a quantitative autoradiographic study using [3H]-tomoxetine

Inbred C57BL/6J (C57) and DBA/2J (DBA) mice were subjected to open-field evaluation and Porsolt swim test after restraint stress. Norepinephrine (NE) uptake sites in the locus coeruleus (LC) of these inbred mice were studied by using [3H]-tomoxetine. Results showed that naive C57 mice were more active in the open field and possessed more NE uptake sites in the LC than naive DBA mice. Previous work has shown that restraint decreases open field activity in C57 mice, but not DBA mice, whereas the present study has demonstrated that, after restraint stress, C57 mice spent more time immobile than DBA mice did in the forced swim test. Furthermore, in these stressed animals, NE uptake sites in the LC were greatly increased with consistently more uptake sites in C57 mice. Collectively, results of this study and the literature suggest that enhanced NE function in the LC of C57 mice is associated with their susceptibility to stress-induced behavioral depression.

Chronic variable stress induces supersensitivity of central alpha2-adrenoceptors which modulate the jaw-opening reflex in the rat

In a previous study, we found that the sensitivity of central postsynaptic alpha2-adrenoceptors which modulate, in an inhibitory way, the activity of the jaw-opening reflex (JOR) is reduced after chronic repeated stress (tail pinch) in the rat. The aim of this study was to assess the effects of exposure to a chronic variable stress regime on these adrenoceptors. To do this, the digastric electromyographic responses elicited by orofacial electrical stimulation after the intravenous administration of cumulative doses (x3.3) of the alpha2-adrenoceptor agonist, clonidine (0.1-10000 microgram/kg), were recorded. As expected, in unmanipulated control rats, clonidine inhibited the reflex, in a dose-dependent manner, until abolition (ED50 = 17.3 +/- 2.2 microgram/kg). Single tail pinch did not significantly alter the ability of clonidine to abolish the reflex. However, chronic variable stress led to an enhancement of the inhibitory effect of clonidine on the amplitude of JOR, resulting in a shift to the left of the dose-response curve in comparison with that of the control group (ED50 was reduced by 37%, P = 0.032), without affecting either the estimated maximum effect for the agonist or the slope of the inhibitory function. This in vivo result indicates that chronic variable stress leads to an increased sensitivity of central alpha2-adrenoceptors which modulate JOR, in contrast to the desensitization of these adrenoceptors found after repeated exposure to the same stressor.