Attenuation of 8-OH-DPAT-induced decreases in 5-Ht synthesis in brain regions of rats adapted to a repeated stress schedule.

Department of Biochemistry, Neurochemistry and Biochemical Neuropharmacology Research Unit, University of Karachi, Karachi 75270, Pakistan.
Stress (Impact Factor: 3.46). 01/2000; 3(2):123-9. DOI: 10.3109/10253899909001117
Source: PubMed

ABSTRACT Previously it has been shown that single episode of 2 h restraint produced behavioral deficits in rats which were not observed following daily restraint period of 2h/day for 5 days. It was suggested that adaptation to a stress schedule develops when the similar stress is administered repeatedly. In view of a role of 5-hydroxytryptamine (5-HT) in adaptation to stress the present study concerns effects of a 5-HT-1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) on the synthesis of 5-HT in brain regions of rats adapted to a repeated restraint stress schedule of 2h/day for 5 days. The drug injected systemically at a dose of 1 mg/kg decreased 5-HT synthesis in the hypothalamus, cortex, hippocampus, striatum and raphe regions of previously unrestrained rats. These decreases were either smaller (raphe) or not observed (hypothalamus, cortex and hippocampus) in most brain regions of rats adapted to the repeated restraint stress schedule of 2h/day for 5 days. These results suggest that a subsensitive negative feedback effect on the synthesis of 5-HT leading to an increase in synaptic 5-HT concentration might help coping with stress demand to produce adaptation to stress.

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    ABSTRACT: Stress increases vulnerability to addiction while drugs of abuse impair coping responses to predispose to depression. Preclinical research shows that stress exposure augments locomotor sensitization effects of drugs of abuse and impairs behavioral tolerance to repeated stress. The present study investigates relationship between behavioral tolerance to repeated immobilization stress and apomorphine-induced sensitization. Apomorphine was injected either before exposure or after the termination of immobilization, daily for 5days, to monitor drug-induced behavioral sensitization and tolerance in immobilization stress-induced anorexia. We find that apomorphine-induced sensitization is enhanced and tolerance to repeated immobilization impaired if the drug is administered before exposure to stress episode. Conversely, apomorphine-induced sensitization is inhibited and adaptation to stress facilitated if the drug is administered after the termination of stress episode. It shows that apomorphine if experienced during stress produces greater sensitization and impairs stress tolerance. Conversely, sensitization effects of apomorphine are blocked and tolerance to stress facilitated in animals receiving drug after the termination of stress episode. It is suggested that additive effects of stress and apomorphine on mesocorticolimbic dopamine neurotransmission and 5-HT-1A influences on dopamine neurotransmission may have a role in the modulation of apomorphine sensitization and tolerance to repeated immobilization stress. The results may help develop potential pharmacotherapies when substance abuse/ dependence disorder and depression occur together.
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    ABSTRACT: Stress produces behavioral and neurochemical deficits. To study the relationship between adaptation to stress and macronutrient intake, the present study was designed to monitor the effects of different diets on feed intake, growth rate and serotonin (5-Hydroxytryptamine, 5-HT) metabolism following exposure to restraint stress in rats. Rats were divided into four groups (n=12) as control, sugar, protein and fat rich diet fed rats. After 5 weeks of treatment animals of each group were divided into unrestrained and restrained animals (n=6). Rats of restrained group were given immobilization stress for 2 hours/day for 5 days. Food intake and growth rates of unrestrained and restrained rats were monitored daily. Rats were decapitated on 6 th day to collect brain samples for neurochemical estimation. Results show that sugar diet fed rats produced adaptation to stress early as compared to normal diet fed rats. Food intake and growth rates of unrestrained and restrained rats were comparable on 3 rd day in sugar diet fed rats and on 4 th day in normal diet fed rats. Stress decreased food intake and growth rates of protein and fat treated rats. Repeated stress did not alter brain 5-HT and 5-HIAA levels of normal diet fed rats and sugar diet fed rats. Protein diet fed restrained rats showed elevated brain 5-HT levels. Fat diet fed restrained rats significantly decreased brain TRP and 5-HIAA levels. Finding suggested that carbohydrate diet might protect against stressful conditions. Study also showed that nutritional status could alter different behaviors in response to a stressful environment. ©2011 PVJ. All rights reserved To Cite This Article: Moin S, S Haider, S Khaliq, S Tabassum and DJ Haleem, 2012. Behavioral and neurochemical studies in stressed and unstressed rats fed on protein, carbohydrate and fat rich diet. Pak Vet J, xx(x): xxx.