Perception of academic examination stress: effects on serum leptin, cortisol, appetite and performance

BACKGROUND

Examination stress is a psychological stress that activate hypothalamic-pituitary adrenocortical (HPA) axis to increase circulating levels of glucocorticoids. The fat derived hormone leptin is also released in response to stress-inducing condition. To workout the role of leptin and cortisol in response to perceived levels of examination stress and their effects on academic performance. The present study was designed to monitor the relationship of self reported perceived levels of examination stress on serum levels of cortisol and leptin in female students going to appear in university examination.

METHODS

Fifty-six female undergraduate students participated in the study. Examination stress, appetite levels were assessed by a questionnaire and blood samples were collected one hour before appearing in the examination. Performance was evaluated from the marks obtained in that particular examination.

RESULTS

Serum cortisol levels increased with an increase in the intensity of perceived examination stress. Serum leptin levels increased only in the group under moderate stress while increases in mild and severe stress group were not significant. Mild to moderate stress enhanced performance but severe stress decreased it.

CONCLUSIONS

The present study shows an inverted U-shaped relationship between self reported different levels of perceived examination stress and academic performance.

Protective effects of aqueous fruit extract from Sea Buckthorn (Hippophae rhamnoides L. Spp. Turkestanica) on haloperidol-induced orofacial dyskinesia and neuronal alterations in the striatum

BACKGROUND

Long-term treatment of haloperidol, a neuroleptic, induces neurodegeneration specifically in the striatum (caudate and putamen), which plays an important role in the development of orofacial dyskinesia, a putative model of tardive dyskinesia (TD). This study investigated the protective effects of a concomitant treatment of aqueous fruit extract of Sea buckthorn (Hippophae rhamnoides L. spp. Turkestanica) (SBT-FE) (40 mg/kg, orally) plus haloperidol (3.0 mg/kg, ip) administration on an animal model of TD and on striatal neuronal alterations.

MATERIAL/METHODS

Rats received daily haloperidol (3.0 mg/kg ip) and saline injections for 15 days. Seven-day posttreatment, aqueous SBT-FE (40 mg/kg) was administered daily via a feeding tube. Hypolocomotive effects (home cage activity, exploratory activity, catalepsy, and vacuous chewing movements) were monitored consecutively in each group. On the last day of the experiments, changes in extracellular levels of striatal dopamine (DA), dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) were determined by HPLC-EC.

RESULTS

Aqueous SBT-FE attenuated haloperidol-induced VCMs after second week of treatment and locomotor activity was greater in rats treated with SBT-FE compared with the controls. The results indicate that DA and HVA levels in the striatum were significantly (P <.01) altered in rats given SBT-FE before injections of haloperidol.

CONCLUSIONS

Hippophae rhamnoides fruit extract has a protective role against haloperidol-induced orofacial dyskinesia. Consequently, use of Hippophae rhamnoides as a possible therapeutic agent for the treatment of tardive dyskinesia should be considered.

Attenuation of somatodendritic responses to 8-hydroxy-2-di-npropylamino tetralin following long-term dietary sugar consumption in rats

OBJECTIVE

To determine changes in response to a selective serotonin-1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) following long-term consumption of sugar as part of meal in rats.

STUDY DESIGN

Experimental study.

PLACE AND DURATION OF STUDY

The Department of Biochemistry, University of Karachi, from June to August 2005.

METHODOLOGY

The study was conducted on 24 male albino Wistar rats. Sugar containing diet was prepared by mixing standard rodent diet and table sugar in the ratio of 3:1 (w/w) and rats were fed freely on this diet. Control rats were fed freely on standard rodent diet. After five weeks of treatment, control and sugar diet treated animals were injected with 8-OH-DPAT, at a dose of 0.5 mg/ml/kg, to monitor the effects of drug on food intake and brain serotonin (5-hydroxytryptamine, 5-HT) metabolism. Dissected neural tissue was analyzed electrochemically and findings were compared by Newman-Keuls test.

RESULTS

Administration of 8-OH-DPAT elicited hyperphagia and decreased 5-HT metabolism in normal diet treated rats. The neurochemical and hyperphagic responses to 8-OH-DPAT were smaller in sugar than normal diet treated animals suggesting a downregulation of somatodendritic responses in sugar diet treated animals.

CONCLUSION

A decrease in serotonin metabolism but not an increase in the responsiveness of somatodendritic 5-HT-1A receptors is involved in sugar-rich diet induced hyperphagia.

Repeated administration of Nigella sativa decreases 5-HT turnover and produces anxiolytic effects in rats

The black cumin or Nigella sativa L. seeds have many acclaimed medicinal properties. Pharmacological studies have been conducted on the aqueous and methanol extracts of N. sativa L. seeds to evaluate their effects on the central nervous system. In the present study, N. sativa oil was used to study its effect on anxiety in rats. Open field and elevated plus maze models were selected for the evaluation of anxiolytic effect of drug. After four weeks of daily administration of drug, the rats exhibited an increase in open field activity. The drug also produced anti-anxiety effect in rats when tested in elevated plus maze. Concentrations of 5-HT, 5-HIAA in brain and concentrations of plasma and brain tryptophan determined by HPLC-EC detector. Result shows that oral administration of N. sativa oil increased brain levels of 5-HT but the levels of brain 5-HIAA decreased significantly. Brain and plasma levels of tryptophan also increased significantly following oral repeated administration of N. sitiva oil. Based on this, it may be suggested that N. sativa oil is a useful choice for the treatment of anxiety.

Dietary supplementations of amino acids: evidence for enhanced serotonergic functions following haloperidol withdrawal in rat medial prefrontal cortex

OBJECTIVE

To investigate the effects of orally supplemented amino acids L-Tryptophan (Trp) and L-Valine (Val) in rats repeatedly injected with haloperidol following one week of drug withdrawal, with particular reference to extrapyramidal symptoms (EPS) and serotonin (5-hydroxytryptamine; 5-HT) metabolism in medial prefrontal cortex (mPFC).

STUDY DESIGN

Experimental study.

PLACE AND DURATION OF STUDY

Department of Biochemistry, University of Karachi from December 2007 to February 2008.

METHODOLOGY

The study was conducted on thirty six locally bred male Albino Wistar rats. Freshly prepared amino acids (Val and Trp) were added in the drinking water of rats on alternate days and haloperidol at doses of 5.0 mg/kg or saline were injected twice daily for three weeks following one week of withdrawal. Locomotor/ exploratory activities were scored in activity boxes and open field apparatuses. Catalepsy was monitored on an inclined surface. The animals tested for locomotor activity and catalepsy for two weeks follow-up post-injections plus one week of drug withdrawal were decapitated to collect mPFC regions of rat brain for neurochemical analysis by high performance liquid chromatography with electrochemical detection (HPLC-EC).

RESULTS

There was significant increase (p<0.01) in locomotor activity in rats orally supplemented with Val and Trp following one week of drug withdrawal from repeated administration. Marked reduction in cataleptogenic effects of the drug was also observed. Significant (p<0.01) increases in the brain Trp and mPFC 5-HT metabolism in Val and Trp supplemented animals were also noticed.

CONCLUSION

These findings help to demonstrate the effect of dietary amino acids, in particular, Trp to potentiate mPFC serotonergic modulation of neuroleptic activity.

Tolerance in the anxiolytic profile following repeated administration of diazepam but not buspirone is associated with a decrease in the responsiveness of postsynaptic 5-HT-1A receptors

To understand the role of serotonin (5-hydroxytryptamine; 5-HT)-1A receptors in the treatment of anxiety and the development of tolerance to benzodiazepines the present study was designed to monitor the responsiveness of postsynaptic 5-HT-1A receptors following repeated administration of diazepam and buspirone. Results show that tolerance in the anxiolytic profile is produced following repeated administration (2 weeks) of diazepam (2 mg/kg) but not buspirone (0.5 mg/kg). The behavioral effects of 8-OH-DPAT at a dose of 0.25 mg/kg were monitored 3 days after repeated administration of saline or buspirone or diazepam. The results show that 8-OH-DPAT elicited forepaw treading was smaller in repeated diazepam but not repeated buspirone injected rats, while hyperlocomotive effects of 8-OH-DPAT were smaller in both repeated buspirone and repeated diazepam injected rats. The results suggest that postsynaptic 5-HT-1A receptor-dependent responses were attenuated following long-term administration of diazepam but not buspirone. Role of 5-HT-1A receptors in the development of tolerance to the anxiolytic effects of diazepam but not buspirone is discussed.

Neurochemical and behavioral effects of m-CPP in a rat model of tardive dyskinesia

Present study was designed to monitor the responsiveness of 5HT (5-Hydroxytryptamine) -2C receptors following the long-term administration of haloperidol in rats. Effects of m-CPP (meta-Chlorophenyl piperazine) were monitored 48 h after withdrawal from repeated (twice a day for 5 week) administration of haloperidol (at the dose of 1 mg/kg). Vacuous chewing movements (VCMs) were monitored on weekly basis. Two days after withdrawal, animals were injected with saline (1 ml/kg of body weight) or m-CPP (3 mg/kg of body weight). Activities in open field and light dark activity box were monitored 15 and 30 min post injection respectively. Animals were then decapitated (4 h post injection) to collect dorsal striatum (DS) samples for the neurochemical analysis by HPLC-EC (High Performance Liquid Chromatography with Electrochemical detection) method. Results from the present study showed significant hypolocomotive effect of m-CPP (p<0.05) in both repeated haloperidol as well as repeated saline injected rats. Neurochemical analysis of DS by HPLC-EC method showed that administration of m-CPP significantly (p<0.05) decreased 5-HIAA (5-Hydroxyindol acetic acid) in repeated haloperidol injected rats. In conclusion, present study provides evidence that 5HT-2C receptors become hypersensitive in a rat model of Tardive Dyskinesia (TD). These findings have potential implication in the treatment of TD and attenuation of EPS induced by typical neuroleptics.

Reversal of haloperidol-induced tardive vacuous chewing movements and supersensitive somatodendritic serotonergic response by buspirone in rats

Tardive dyskinesia (TD), a syndrome of involuntary hyperkinesias in the orofacial region that develops in patients chronically treated with neuroleptic agents is a major limitation of the therapy. Rats chronically treated with haloperidol exhibit vacuous chewing movements (VCMs) with the twitching of facial musculature and tongue protrusion. The syndrome is widely used as an animal model of TD. Evidence suggests a role of 5-hydroxytryptamine (5-HT; serotonin)-1A receptors in the pathogenesis and treatment of TD because repeated administration of haloperidol resulted in an increase in the effectiveness of 5-HT-1A receptors while drugs with agonist activity at 5-HT-1A receptors could attenuate haloperidol-induced VCMs. The present study was designed to test the hypothesis that a decrease in the responsiveness of somatodendritic 5-HT-1A receptors by the coadministration of buspirone could reverse the induction of VCMs and supersensitivity at 5-HT-1A receptors by haloperidol. Rats treated with haloperidol at a dose of 1 mg/kg twice a day for 2 weeks displayed VCMs with twitching of facial musculature that increased in a time dependent manner as the treatment continued to 5 weeks. Coadministration of buspirone attenuated haloperidol-induced VCMs after 2 weeks and completely prevented it after 5 weeks. The intensity of 8-hydroxy-2-di (n-propylamino) tetralin (8-OH-DPAT)-induced locomotion was greater in saline+haloperidol injected animals but not in buspirone+haloperidol injected animals. 8-OH-DPAT-induced decreases of 5-HT metabolism were greater in saline+haloperidol injected animals but not in buspirone+haloperidol injected animals. It is suggested that an impaired somatodendritic 5-HT-1A receptor dependent response is a major contributing factor in the pathophysiology of TD and a normalization of the somatodendritic response by drugs may help extending therapeutics in schizophrenia.

Serotonin-1A receptor responsiveness in stress and following adaptation to stress

Stress is one of the environmental factors that may predispose psychiatric illness such as, depression. Stress may come from external environment in the form of stimuli such as heat, cold, loud noise and lack of oxygen. A deficiency of serotonin (5-hydroxytryptamine; 5-HT) is described in human depression. Parallel studies on experimental animals show that exposure to an uncontrollable stress inducing situation elicits behavioral deficits and increases serotonin metabolism in the brain. Stress-induced behavioral deficits and the increases of brain serotonin did not occur when the stress was administered repeatedly for 5 days, suggesting adaptation has occurred. The present study shows that responses to 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT), a selective 5-HT 1A agonist decreased following exposure to single stress and the decreases were normalized following adaptation to stress. The drug 8-OH-DPAT was also found to attenuate stress-induced behavioral deficits. The results are discussed in the context of stress-induced psychiatric disorder such as, depression and its treatment by 5-HT 1A agonist.

Reversal of haloperidol-induced extrapyramidal symptoms by buspirone: a time-related study

Effects of coadministration of buspirone were investigated on the time course of haloperidol-induced extrapyramidal symptoms in rats. Rats treated with haloperidol at a dose of 1 mg/kg exhibited impaired motor coordination and a decrease in exploratory activity. Coadministration of buspirone at a dose of 1 mg/kg attenuated haloperidol-induced deficits of motor coordination but no effect was produced on the deficits of exploratory activity, possibly because of a 'floor effect'. Long-term administration of haloperidol (1 mg/kg) twice a day for 5 weeks did not produce tolerance to haloperidol-induced deficits of exploratory activity. The deficits of motor coordination were attenuated after 4-5 weeks of drug administration. Coadministration of buspirone for 3-5 weeks attenuated and reversed haloperidol-induced deficits of exploratory activity. Deficits of motor coordination were smaller in rats cotreated with buspirone after 1 week but not after 2-5 weeks. Administration of haloperidol for 2 weeks elicited vacuous chewing movements with twitching of facial musculature that increased in a time-dependent manner as the treatment continued to 5 weeks. Animals cotreated with buspirone exhibited a gradual reversal of the response during 2-5 weeks of treatment. The mechanism involved in the attenuation/reversal of haloperidol-induced extrapyramidal symptoms by buspirone is discussed. Prior administration of buspirone for 2 weeks may be of help in the improvement of extrapyramidal symptoms induced by antipsychotic drugs.

Increase in the effectiveness of somatodendritic 5-HT-1A receptors in a rat model of tardive dyskinesia

The present study concerns responsiveness of pre- and postsynaptic 5-hydroxytryptamine (5-HT)-1A receptors in a rat model of tardive dyskinesia (TD). Vacuous chewing movements (VCMs) in rats are widely accepted as an animal model of TD. Results show that haloperidol injected at a dose of 1 mg/kg twice a day for 5 weeks elicited VCMs, which increased in a time dependent manner following the drug administration for 3-5 weeks. Tolerance was produced in motor coordination during the potentiation of VCMs. Exploratory activity in an open field and in an activity box decreased in haloperidol treated animals. The effects of 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT; 0.5 mg/kg) were monitored 48-h after withdrawal from repeated administration of haloperidol. 8-OH-DPAT-induced locomotion was greater in haloperidol treated rats. 5-HT synthesis increased in haloperidol treated animals, while 8-OH-DPAT-induced decreases of 5-HT synthesis were greater in repeated haloperidol than repeated saline injected animals. The results suggest that an increase in the effectiveness of somatodendritic 5-HT-1A receptors may decrease the inhibitory influence of 5-HT on the activity of dopaminergic neurons to precipitate VCMs. The 5-HT-1A agonist may help to alleviate neuroleptic-induced TD.

Serotonergic modulation of dopamine neurotransmission: a mechanism for enhancing therapeutics in schizophrenia

Although the principal mechanism by which all antipsychotic drugs act is the blockade of dopamine D-2 receptors, typical antipsychotics given in doses within the clinically effective range induce extrapyramidal symptoms (EPS). Serotonin Hydroxytryptamine, 5-HT can modulate the activity of dopaminergic neurons, while the activity of atypical antipsychotic agent towards serotonin receptors is involved in the ability of these agents to produce fewer EPS. In order to extend therapeutics in schizophrenia, it is important to examine the serotonergic modulation of neuroleptic activity. This review analyzes differences in neurochemical, behavioral and pharmacological profiles of typical and atypical antipsychotics and the role of serotonin receptors in the attenuation of EPS-induced by the typical neuroleptics. In addition to blocking dopamine receptors, the atypical antipsychotics also have affinities for serotonin receptors. Serotonergic modulation of motor activity appears primarily of inhibitory type. Stimulation of somatodendritic 5-HT-1A receptors decreases the availability of 5-HT at inhibitory 5-HT-2C receptors located on dopaminergic neurons to attenuate acute parkinsonian-like effects of typical antipsychotics. An increase in the effectiveness of pre and postsynaptic 5-HT-1A receptors following long-term administration of haloperidol raises the possibility that 5-HT agonists may also prove useful for the alleviation of late appearing tardive dyskinesias. Clinicians can now apply the knowledge of serotonergic modulation of neuroleptic action to the treatment of schizophrenic patients by using selected serotonergic anxiolytics and antidepressants as adjuvants in the treatment of schizophrenia.

5-HT-1A receptor responsiveness following subchronic administration of buspirone

Anxiety and its disorders have long been known to be familial. Anxiety levels are associated with low social connectedness and high environmental threats. Studies provide evidence that anxiety disorders may be link to malfunctioning of serotonin neurotransmission. The present study is designed to monitor serotonin-1A (5-HT-1A) receptor responsiveness following subchronic administration of a serotonergic anxiolytic buspirone. Administration of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) at a dose of 0.25 mg/kg produced comparable syndrome in repeated saline and repeated buspirone injected rats. Cage crossings were significantly lower in repeatedly buspirone injected rats. Decreases in 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels were higher in saline than buspirone injected rats. Result suggests that following long term administration of buspirone somatodendritic and postsynaptic 5-HT-1A receptors are desensitized. Role of serotonin 1A receptors in the treatment of anxiety is discussed.

Intraerythrocyte and serum electrolytes in diabetic patients with hypertension

OBJECTIVE

To determine the serum and intraerythrocyte concentrations of vasoactive ions in patients of diabetes mellitus of either gender with hypertension.

DESIGN

Cross-sectional study.

PLACE AND DURATION OF STUDY

The Department of Biochemistry, University of Karachi, from May-June 2002.

PATIENTS AND METHODS

The study was conducted on 48 volunteers. Out of 48, 24(12 men and 12 women) were hypertensive patients with diabetes mellitus. Remaining (12 men and 12 women) were normal healthy subjects. Biochemical estimations were done by flame photometry and spectrophotometry. Data were analyzed by Two-way ANOVA followed by Newman-Keuls test.

RESULTS

A decrease in serum concentrations of sodium, calcium, magnesium, phosphorus, chloride and intraerythrocyte potassium and an increase in the levels of glucose, haematocrit and intraerythrocyte sodium was observed in both male and female patients with diabetes mellitus and hypertension. No significant changes were observed in serum potassium levels.

CONCLUSION

The results suggest that dysregulations of electrolyte balance caused by hyperinsulinemia or altered glucose metabolism may lead to hypertension.

Attenuation of restraint induced behavioral deficits by buspirone and propranolol in rats

OBJECTIVE

To determine the effect of buspirone and propranolol on restraint stress-induced behavioral deficits in a learned helplessness model.

DESIGN

Experimental study.

PLACE AND DURATION OF STUDY

The experiment was performed in the Department of Biochemistry, University of Karachi and completed during a period of three months (3 June 2004 to 17 August 2004).

SUBJECTS AND METHODS

The study was conducted on 36 male albino Wistar rats. Animals injected with saline, buspirone (0.2 mg/kg) and propranolol (1 mg/kg) for 2 weeks were exposed to an episode of 2 hours restraint stress. Cumulative food intake and body weight changes were monitored over a period of 24 hours. Exploratory activity in the lit area of light dark box was monitored 24 hours after the termination of restraint period.

RESULTS

Single (2 hours) restraint stress decreased 24 hours cumulative food intake and growth rate. Exploratory activity in the lit compartment of a light-dark box also decreased. Prior administration of buspirone as well as propranolol attenuated restraint-induced deficits of food intake and growth rate. Administration of buspirone and propranolol increased lit area exploration in unrestrained animals and attenuated restraint-induced deficits of exploration.

CONCLUSION

The results show that anorexiogenic and anxiogenic effects of restraint stress were smaller in animals injected with buspirone or propranolol. Buspirone and propranolol could attenuate stress-induced behavioral deficits.

Long-term tryptophan administration enhances cognitive performance and increases 5HT metabolism in the hippocampus of female rats

It has been shown in various studies that increase in serotonergic neurotransmission is associated with increased memory consolidation whereas low brain 5HT impairs memory performance. In the first phase of our study we found that tryptophan (TRP) administration for 6 weeks increased plasma TRP and whole brain TRP, 5HT and 5HIAA levels. Many brain regions are involved in the learning process but particularly the hippocampus is known to have key role in learning and memory. The present study was therefore designed to investigate the effects of TRP loading particularly on hippocampal 5HT metabolism and cognitive performance in rats. TRP-treated rats demonstrated spatial enhancement as evidenced by a significant decrease in time to find the hidden food reward in radial arm maze test (RAM). The important finding of the present study was the greater increase in the 5HT metabolism in hippocampus than in any other brain region of the TRP-treated rats. This increased 5HT metabolism in the hippocampus emphasizes the involvement of this region in memory process.

Effects of long term consumption of sugar as part of meal on serotonin 1-a receptor dependent responses

In view of an effect of high intake of sugar on brain serotonin (5-hydroxytryptamine, 5-HT) and a role of serotonin in the regulation of appetite, the present study concerns pre and postsynaptic responses to a selective 5-HT-1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) following long term consumption of sugar as part of meal in rats. Sugar diet was prepared by mixing standard rodent diet and table sugar in ratio of 3:1 (w/w) and rats were fed freely on this diet for five weeks. Control rats were fed freely on standard rodent diet. After five weeks 8-OH-DPAT at a dose of 0.5mg/kg/ml was injected to both the groups to compare effectiveness of the drug to elicit hyperphagia (presynaptic response) and elicited hyperactivity syndrome (postsynaptic response). Results showed that 8-OH-DPAT-induced forepaw treading and flatbody posture were smaller in sugar than normal diet treated rats. Conversely 8-OH-DPAT-induced hyperlocomotion was greater in sugar than normal diet treated rats. 4h Food consumption was greater in sugar than normal diet treated rats while 8-OH-DPAT-induced hyperphagia significant in normal diet treated rats was not observed in sugar diet treated rats. The results show a decrease in the effectiveness of pre as well as postsynaptic 5-HT-1A receptor dependent responses following long term consumption of sugar diet. Role of serotonin receptor responsiveness on mood and impaired adaptation to stress is discussed.

Dopamine and serotonin neurotransmission in the reinforcing effects of alcohol and apomorphine

OBJECTIVE

To determine the role of dopamine and 5-hydroxytryptamine (5-HT; serotonin) in the reinforcing effects of alcohol and apomorphine.

DESIGN

Experimental study.

PLACE AND DURATION OF STUDY

Department of Biochemistry, University of Karachi from September to November 2004.

SUBJECTS AND METHODS

The study was conducted on 24 male albino Wistar rats. Reinforcing effects were monitored in a conditioned place preference (CPP) paradigm using a light-dark activity box. Slicing and punching method was used to collect dorsal and ventral striatum. Neurochemical estimations were done by HPLC-EC.

RESULTS

Withdrawal from repeated administration of ethanol (1g/kg/day) as well as apomorphine (1 mg/kg/day) elicited reinforcement that could be monitored in a CPP paradigm. CNS depressant effects of ethanol were not altered on repeated administration but CNS stimulatory effects of apomorphine increased. Reinforcing effects of ethanol but not apomorphine were associated with a decrease in dopamine metabolism in the ventral striatum.

CONCLUSION

A decrease in the activity of dopaminergic neurons following withdrawal from repeated administration is involved in the compulsive use of abused drugs.

Somatodendritic and postsynaptic serotonin-1A receptors in the attenuation of haloperidol-induced catalepsy

The mechanism by which stimulation of somatodendritic and/or postsynaptic 5-hydroxytryptamine (5-HT, serotonin)-1A receptor could attenuate acute Parkinsonian-like effects of typical antipsychotics is investigated by comparing the anticataleptic and neurochemical effects of 8-hydroxy-2-di-n-propylaminotetralin (8-OH-DPAT) and buspirone in rats injected with haloperidol. Cataleptic effects of a submaximal dose (1 mg/kg) of haloperidol were attenuated more by prior administration of 8-OH-DPAT (0.25 mg/kg) than buspirone (1 mg/kg). Striatal 5-HT metabolism decreased more in buspirone- than 8-OH-DPAT-injected animals. Administration of haloperidol did not alter 5-HT metabolism in saline-, 8-OH-DPAT- or buspirone-injected animals. Dopamine decreased and its metabolite homovanillic acid (HVA) increased in the striatum of rats injected with buspirone. Effects of 8-OH-DPAT on dopamine metabolism were not significant. Haloperidol-induced increases of dopamine metabolites were attenuated by prior administration of 8-OH-DPAT, but not buspirone. The mechanism by which stimulation of somatodendritic as well as postsynaptic 5-HT-1A receptors could attenuate haloperidol-induced catalepsy is discussed. The findings have potential implications in the treatment of schizophrenia and motor behavior.

Enhancement of serotonin-1A receptor dependent responses following withdrawal of haloperidol in rats

Although haloperidol is widely prescribed for the treatment of schizophrenia, its beneficial effects are accompanied by extrapyramidal side effects (EPS). In view of a role of 5-hydroxytryptamine (5-HT; serotonin)-1A receptors in the elicitation of EPS, the present study concerns pre- and postsynaptic responses to a selective 5-HT-1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) following acute and chronic administration of haloperidol in rats. In the acute administration study, effects of 8-OH-DPAT (0.5 mg/kg) were monitored 30 min after single injection of haloperidol (5 mg/kg). In the chronic administration study, effects of 8-OH-DPAT (0.5 mg/kg) were monitored 48 h after withdrawal from repeated (two times a day for 2 weeks) administration of haloperidol (5 mg/kg). The intensity of 5-HT syndrome elicited by 8-OH-DPAT was taken as measure of postsynaptic response. 8-OH-DPAT-induced decreases of 5-HT synthesis were taken as measure of presynaptic response. Results showed that 8-OH-DPAT-induced locomotion was smaller in acute haloperidol-treated rats. Conversely, these effects of 8-OH-DPAT were greater in chronic haloperidol-treated rats. Animals injected acutely or chronically with haloperidol exhibited greater 5-HT synthesis in the striatum. Administration of 8-OH-DPAT did not decrease 5-HT synthesis in the striatum of acute haloperidol-treated rats but decreased it in the striatum of chronic haloperidol-treated rats. The results show an increase in the effectiveness of pre- and postsynaptic 5-HT-1A receptor dependent responses following chronic administration of haloperidol. A causal role of 5-HT-1A receptor responsiveness in the greater incidences of EPS in patients treated with typical neuroleptics such as haloperidol is discussed.

Behavioral effects of 8-OH-DPAT in single and repeated haloperidol injected rats

Haloperidol is an antipsychotic drug and shown to be antagonist at D2 receptors and found to cause severe impairment of locomotor performance. The serotonin (5HT1A) receptor agonist 8-OH-DPAT has been reported to attenuate extrapyramidal side effects of haloperidol. The present study was designed to examine the modulatory effect of serotonergic activities on haloperidol induced up-regulation of dopamine D2 receptors. In the acute phase of study, 8-OH-DPAT (0.5 mg/kg/ml) elicited behavioral syndrome was monitored in rats preinjected with haloperidol(5 mg/kg/ml). Results of single haloperidol administration revealed that 8-OH-DPAT induced forepaw treading (p < 0.05) and hyperlocomotion (p < 0.01) were smaller in haloperidol than saline preinjected rats. In repeated phase of study, 8-OH-DPAT (0.5 mg/kg/ml) induced behavioral syndrome was monitored in rats injected with haloperidol for 10 days (x2). The result of repeated haloperidol administration showed that 8-OH-DPAT elicited flat body posture (p < 0.01) was greater in repeated haloperidol injected rats than repeatedly saline injected rats. Relationship between 5HT1A receptors and D2 receptors has been discussed. It is suggested that combining neuroleptics with 5HT1A ligands is thought to improve the preclinical profile of neuroleptics and may be of interest in the development of new compounds that have greater therapeutic potential and/or better tolerated.

Decreases of brain serotonin following a food restriction schedule of 4 weeks in male and female rats

Male and female rats fed on a restricted feeding (RF) schedule of 4 weeks to produce 20-25% reduction in body weight, were killed before (starved) and after (fed) the presentation of food to compare 5-hydroxytryptamine (5-HT) metabolism in the hypothalamus with respective freely feeding (FF) controls and to monitor sex differences in RF-induced changes of 5-HT. RF decreased plasma tryptophan concentration in RF starved and RF fed females and also in RF starved males. In the hypothalamus tryptophan levels decreased in RF starved and RF fed female rats and RF fed males. 5-HT decreased in both RF starved and RF fed male and female rats and the decreases were comparable in the two sexes. 5-hydroxyindoleacetic acid (5-HIAA), a major metabolite of 5-HT was not affected. Food restriction decreased 5-HT concentration in the rest of the brain of male but not female rats. Possible implications of the findings in the pathogenesis of food restriction/starvation related disease anorexia nervosa and its greater occurrence in women than men is discussed.

Neurochemical and extra pyramidal effects of atypical neuroleptic clozapine in rats

In view of a possible role of serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) in neuroleptic-induced muscle rigidity and catalepsy, the present study is designed to investigate the neurochemical and extrapyramidal effects of atypical antipsychotic/neuroleptic drug i.e., Clozapine (CZP) on the metabolism of serotonin and dopamine particularly in the caudate (a region of the brain involved in the control of movement), accumbens and rest of the rat brain. Interaperitoneal (i.p) injections of CZP at doses of 5.0 & 10 mg/kg decreased significantly (p<0.01) locomotor activity in familiar (home cage) environment. CZP produced a significant (P<0.01) cataleptic response only at doses of 10 mg/kg used. Maximal cataleptic effects in rats occurred at high doses of CZP. Acute administration of CZP significantly (p<0.01) decreased levels of NA in accumbens at all the doses used. Significant increases (p<0.01) in the levels of NA observed in rest of the brain only at moderate dose (5 mg/kg) of CZP. Results showed significant (p<0.01) increases in the levels of caudate DA following the administration of CZP at 10 mg/kg. However administration of CZP at all the doses produced similar significant (p<0.01) increases in the levels of HVA in all the regions of the rat brain. Overall insignificant effects of CZP occurred on brain regional TRP. However, plasma TRP significantly (p<0.01) increased at 2.5 mg/kg dose of CZP. Administration of CZP at doses of 2.5 and 10 mg/kg significantly (p<0.01) decreased 5-HT levels in the rest of the brain. Administration of CZP produced insignificant (p>0.05) effects on 5-HIAA levels in the caudate and accumbens regions but CZP at doses of 2.5 and 5 mg/kg significantly (p<0.01) decreased 5-HIAA levels in the rest of the brain. Neurochemical and extrapyramidal effects of atypical antipsychotic (clozapine) are discussed in relation to a potential therapeutic profile in rats.

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

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.

A study on the effects of some new derivatives of piperidine on neurotransmitters

Four chemically synthesized derivatives of piperidine were subjected to evaluate their pharmacological actions on Nervous System in male albino mice. The effects on neuro-transmitters such as catecholamine and indolamine assuming that these derivatives might alter them differently, studied by HPLC-EC method. The result revealed that brain dopamine and catecholamine were altered by most of these derivatives at the doses of 100 mg/kg body weight.

Increased precursor availability did not increase food intake and 5-HT turnover rate in the hypothalamus of diazepam injected rats

In view of a possible role of serotonin (5-hydroxytryptamine; 5- HT) in regulation of appetite and anxiety, the effects of 1, 3 and 5 mg/kg doses of diazepam on brain serotonin precursor and effects of single and repeated diazepam (1 mg/kg 2* daily for 4 days) administration on hypothalamic 5-HT, 5-hydroxyindoleacetic acid (5-HIAA and 5-HIAA/5-HT ratio are investigated in rats. Daily diazepam treatment decreased food intakes. Diazepam injected rats exhibited a dose-dependent increase of tryptophan in the hypothalamus. Administration of diazepam (1 mg/kg) to 4 day saline injected rats on the 5th day increased 5-HT and decreased 5-HIAA levels in the hypothalamus. 5-HIAA/5-HT level also decreased. 4-day diazepam injected rats injected with saline on the 5th day also exhibited similar changes of 5-HT. 5-HIAA and 5-HIAA/5-HT ratio. Administration of diazepam to 4 day diazepam injected rats again decreased 5-HIAA concentrations but did not increase 5-HT levels in the hypothalami of rats. Possible mechanism involved in the anorectic effects of diazepam-induced changes of hypothalamic 5-HT turnover rate is discussed.

Inhibition of restraint-induced anorexia by injected tryptophan

Tryptophan injected at doses of 50mg/kg did not alter 24 h cumulative food intake and growth rate in rats. A single episode of 2 h restraint stress decreased food intake and growth rate of saline and tryptophan injected rats. The decreases of both food intake and growth rate were smaller in tryptophan injected (food intake 23.9% p<0.05; growth rate 2.9% p<0.05) than saline injected (food intake 78.5% p<0.01; growth rate 6.1% p<0.01) rats suggesting that tryptophan administration inhibits restraint-induced anorexia. Following an acute challenge with 2h restraint increases of 5-hydroxytryptamine (5-HT; serotonin) and 5-hydroxyindoleacetic acid (5-HIAA) but not tryptophan were greater in tryptophan injected than saline injected rats. The findings imply that tryptophan-induced increases of brain 5-HT and 5-HIAA have little effect on functional serotoninergic activity under basal conditions but a facilitatory effect on functional response occurs in conditions of increased serotoninergic neuronal activity such as during stress.

Neurochemical and behavioural effects of long term intake of tea

Tea consumption in many cases is the main source of caffeine intake in humans. In the present study neurochemical and behavioural effects of long-term tea intake are monitored in rats. Long-term tea administration did not alter plasma tryptophan (TRP) but significantly attenuated brain TRP and 5-hydroxytryptamine (5-HT, serotonin) levels. Brain 5-hydroxyindole acetic acid (5-HIAA) was comparable in both tea-treated and control rats. An increase in home cage activity was observed after one week in rats taking tea as sole source of liquid, whereas no change on the activity was observed in an open field. Caffeinism has been associated with depression. The decreases of brain monoamine metabolism observed in present study are discussed as lowering of mood observed in tea or coffee consumers.

Effect of chlorpromazine on brain biogenic amines in normal and hyperglycemic state

In present study the effects of chlorpromazine (CPZ) were studied on NA, DA and its metabolities i.e. DOPAC and HVA as well as on 5-HT and its metabolite 5-HIAA in normal and hyperglycemic rats. Significant differences were noted in brain biogenic amines of normal and diabetic control animals. In case of CPZ treated normal and hyperglycemic rats significant differences were observed only in case DOPAC and 5-HIAA. NA and 5-HIAA levels were significantly affected by CPZ and diabetes interaction.

The neurochemical profile of long term oral administration of moclobemide

Moclobemide, a benzamide derivative, predominantly inhibits the A form of monoamine oxidase (MAO) and its MAO binding is reversible. Acute administration of moclobemide has been shown to induce an increase in brain levels of monoamines and a concomitant decrease in their respective metabolite. In the present study, the drug was administered to rats orally in drinking water at doses of 0.5-1.0 mg/day/rat of an average weight of 250 g for three weeks. This was equivalent to the recommended human dose of 150-300 mg/day. The drug administration did not alter food intake, growth rate and activity of rats. Brain levels of 5-hydroxytryptamine (5-HT) and dopamine (DA) increased. However, increases in 5-hydroxyindoleacetic acid (5-HIAA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) as reported in acute studies were not observed following chronic drug administration in the present study in addition, an increase in brain levels of tryptophan also occurred. Neurochemical profile of long-term moclobemide administration is explainable in terms of an inhibition of MAO activity, increased availability of 5-HT precursor tryptophan and decreased egress of monoamine metabolites.

Effects of diazepam and cinchocaine on biogenic amines

Neurochemical and behavioural research show that benzodiazepines are well know anxiolytic drugs, which are also used for the treatment of epilepsy, hypnosis and insomnia. Administration of benzodiazepine to experimental animals produces anxiolytic-like effects in various animal and decreases exploratory activity. Psychomotor stimulants such as cinchocaine also showed potent effect on brain biogenic amines and their metabolite. The present studies indicate the changes in dopamine and 5-HT and their metabolites levels after acute administration of cinchocaine and diazepam.

Effects of cinchocaine cocaine analogs on brain mono amines and their metabolites in male mice

Cinchocaine analogs were studied to determine the effects of acute administration of cocaine analogs on dopamine, 5- hydroxytryptamine (5-HT) and their metabolites. Psychomotor stimulants, (such as cinchocaine), potently influencing dopamine transport carrier were used to characterize in-vivo DA transmission. DA, DOPAC, HVA level and indoleamine were measured in brain after drug administration. Significant changes in levels of DA, DOPAC, 5-HT, 5HIAA and HVA were noted. The present findings suggests that acute administration of cinchocaine increases the level of Dopamine, 5-HT and their metabolites and alter the level of amines as compare to control group. These studies also indicate that difference in structure do not affect the binding sites and inhibition of amine uptake.

Neurochemical and behavioural effects of diazepam: evidences from animal models

Neurochemical and behavioural research show that benzodiazepines (BZs) are the well-known anxiolytic drugs which are also used for the treatment of epilepsy, hypnosis and insomnia. Administration of BZs to experimental animals produces anxiolytic-like effects in various animal models and decreases exploratory activity. A role of serotonin (5-HT; 5-hydroxytryptamine) in both anxiolytic and anti-exploratory effects of BZs have been suggested. Drugs which mimic 5-HT function at the post synaptic sites have been shown to decrease anxiety in experimental animals. The present study analyses regionally specific effects of BZs on brain serotonin metabolism in relation to the reported behavioural and therapeutic profiles of the drugs.

Adaptation to repeated restraint stress in rats: failure of ethanol-treated rats to adapt in the stress schedule

Adaptation to a repeated restraint stress schedule was monitored in ethanol-treated and control rats. A single episode of 2 h restraint decreased food intake in both control and ethanol-treated rats. The decreases in control rats were not observed following the 5th daily restraint of 2 h/day, suggesting that adaptation has occurred. Ethanol-treated rats, however, exhibited decreased food intake even after 5th daily restraint of 2 h/day. Ethanol administration decreased weekly but not daily cumulative food intake in unrestrained rats. Food intakes of ethanol-treated and control restrained rats were comparable following 1st-3rd daily restraints, but were smaller in ethanol-treated rats following the 4th and 5th daily restraints. Open-field ambulatory activities monitored 24 h after the 5th daily restraint on the 6th day were comparable in control restrained and unrestrained rats. Ethanol-treated and control unrestrained rats also exhibited comparable ambulation, but ethanol-treated rats exhibited smaller activity than control restrained or ethanol-treated unrestrained rats. Fluid intakes of ethanol and control rats were comparable during the 2 weeks of ethanol administration, but daily restraint schedule decreased ethanol intake. The findings show adaptation to repeated restraint in control rats and inability of ethanol-treated rats to adapt in the stress schedule. These findings imply that excessive alcohol consumption may impair adaptation to stress and thus conceivably precipitate depression.

Regionally specific effects of diazepam on brain serotonin metabolism in rats: sustained effects following repeated administration

The effects of single (1mg/kg) and repeated (1mg/kg 2* daily for 4 days) diazepam administration are investigated on brain regional 5-hydroxytryptamine (5-HT; serotonin) and 5-hydroxy indoleacetic acid (5-HIAA) concentration in rats. Daily treatment decreased food intakes but body weights did not decrease. Administration of diazepam (1mg/kg) to 4 day saline injected rats on the 5th day decreased 5-HT levels in the hippocampus and increased it in the hypothalamus. 5-HIAA levels were increased in the striatum and decreased in the hypothalamus 4 day diazepam injected rats injected with saline on the 5th day also exhibited similar changes of 5-HT and 5-HIAA. Cortical levels of 5-HIAA were also smaller in these rats. Administration of diazepam to 4 day diazepam injected rats again decreased 5-HT in the hippocampus and 5-HIAA in the hypothalamus. 5-HT and 5-HIAA were both decreased in the striatum. Regionally specific effects of diazepam on brain serotonin metabolism are discussed in relation to their possible functions.

Food restriction decreases serotonin and its synthesis rate in the hypothalamus

Rats fed on a restricted feeding (RF) schedule of 4 h day-1 to produce a 15-20% reduction in body weight were killed before (starved) and after (fed) the presentation of food on the sixth day to compare 5-hydroxytryptamine (5-HT; serotonin) metabolism and synthesis rate in the hypothalamus with freely feeding (FF) controls. The RF rats showed lower 5-HT concentration and synthesis rate than FF controls. Restricted feeding did not decrease tryptophan concentration in the hypothalamus. However, RF-fed rats had lower tryptophan concentration than RF starved rats. 5-HIAA concentration was comparable in RF fed rats and FF controls but higher in RF starved rats. Possible implications of the findings in the pathogenesis of the food deprivation/starvation-related disease anorexia nervosa are discussed.

Stress and hypertension: role of serum, red cell and tissue electrolytes

The role of stress in the precipitation of hypertension is often described in clinical studies, although the underlying mechanism remains unknown. The present study concerns the role of electrolytes in stress induced hypertension in rats. Acute immobilization stress of one hour elevated systolic blood pressure (SBP) in rats. Restraint induced blood pressure elevation was associated with increased sodium concentration in the red cells, heart and kidney, and decreased potassium in the red cells. Magnesium concentration increased and calcium concentration decreased in the serum. Increases of calcium and decreases of magnesium were also observed in the heart and kidney tissues. The results may help toward an understanding of the relationship between hypertension and electrolyte homeostasis. A possible role of Na(+)-K(+)-ATPase activity leading to observed changes of electrolytes or vice versa is discussed.

24h withdrawal following repeated administration of caffeine attenuates brain serotonin but not tryptophan in rat brain: implications for caffeine-induced depression

Caffeine injected at doses of 20, 40 and 80 mg/kg increased brain levels of tryptophan, 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in rat brain. In view of a possible role of 5-HT in caffeine-induced depression the effects of repeated administration of high doses of caffeine on brain 5-HT metabolism are investigated in rats. Caffeine was injected at doses of 80 mg/kg daily for five days. Control animals were injected with saline daily for five days. On the 6th day caffeine (80 mg/kg) injected to 5 day saline injected rats increased brain levels of tryptophan, 5-HT and 5-HIAA. Plasma total tryptophan levels were not affected and free tryptophan increased. Brain levels of 5-HT and 5-HIAA but not tryptophan decreased in 5 day caffeine injected rats injected with saline on the 6th day. Plasma total and free tryptophan were not altered in these rats. Caffeine-induced increases of brain tryptophan but not 5-HT and 5-HIAA were greater in 5 day caffeine than 5 day saline injected rats. The findings are discussed as repeated caffeine administration producing adaptive changes in the serotonergic neurons to decrease the conversion of tryptophan to 5-HT and this may precipitate depression particularly in conditions of caffeine withdrawal.

Brain regional serotonin synthesis following adaptation to repeated restraint

A single 2 h episode of restraint stress decreased food intake and growth rate of rats. These deficits were not observed after five restraint periods of 2 h a day, suggesting that adaptation occurred. An acute challenge with 2 h restraint increased 5-hydroxytryptamine (5-HT) synthesis rate in the cortex, hypothalamus, midbrain and hindbrain of previously unrestrained rats, but not those adapted to 5 days of 2 h daily restraint. Hippocampal and striatal 5-HT synthesis was not increased significantly by 2 h restraint in previously unrestrained rats but was increased and decreased, respectively, in rats exposed to five 2 h daily restraints, when they were restrained on the sixth day. The findings suggest an important role of 5-HT particularly in the hippocampus, in adaptation to stress.

Tolerance to diacetyl morphine antinociception: effects on brain serotonin

The effects of 5 mg kg-1 diacetyl morphine (DAM) on brain serotonin metabolism of rats were investigated following tolerance to the antinociceptive effects of 2.5 mg kg-1 DAM. Brain levels of tryptophan and 5-hydroxy indoleacetic acid (5-HIAA) were higher in the DAM-tolerant rats killed 24 h after last daily administration of 2.5 mg kg-1 DAM. Administration of 5 mg kg-1 DAM produced less antinociception in DAM-tolerant than DAM-naive rats and increased brain tryptophan concentration in both tolerant and naive rats. 5-HIAA concentrations increased only in naive rats. Combined use of drugs interfering with brain 5-HT turnover along with opiates may be of future benefit for the treatment of chronic pain.

Enhancement of hepatic tryptophan pyrrolase activity and decreases of open field locomotion following single and repeated administration of high doses of caffeine in rats

In view of a possible role of kynurenine in caffeine-induced anxiety syndrome, the effects of single and repeated administration of caffeine on hepatic tryptophan (T)-pyrrolase activity are investigated. Single administration of caffeine at doses of 80 mg/kg decreased open field locomotion and increased hepatic T-pyrrolase activity. Locomotor stimulating effects of 80 mg/kg caffeine, monitored in the home cages of rats, were attenuated following daily administration of caffeine for 5 days. Open field locomotor activity of rats and its caffeine-induced decrement were also attenuated following 5 daily administrations of caffeine on the 6th day. Basal levels of hepatic T-pyrrolase activity increased after 5 daily administrations of caffeine on the 6th day. Acute administration of caffeine did not further elevate hepatic T-pyrrolase activity in 5 day caffeine injected rats. Drug adjuvants decreasing hepatic T-pyrrolase activity may prove valuable for extending the clinical utility of caffeine.

Decreases of plasma tryptophan concentrations following restricted feeding do not decrease serotonin and its metabolite in rat brain

Rats trained on a restricted feeding (RF) schedule of 4 h/day were killed before (starved) and after (fed) the presentation of food to compare hepatic and brain tryptophan metabolism with feeding (FF) controls. The RF rats exhibited greater holo-tryptophan pyrrolase activity in the liver than FF controls. Holoenzyme activity of starved rats was greater than fed animals. Plasma levels of tryptophan higher in the FF rats were comparable in the starved and fed groups of RF rats. Plasma levels of glucose comparable in the FF and RF fed rats were smaller in the starved animals. Brain levels of tryptophan comparable in the RF fed rats and FF controls were smaller in RF starved rats. Brain concentrations of serotonin (5-hydroxytryptamine) and its metabolite 5-hydroxyindoleacetic acid comparable in the RF starved rats and FF controls were higher in the RF fed rats. Possible implication of the findings in the pathogenesis of food deprivation/starvation related disease, anorexia nervosa is discussed.

Function specific supersensitivity of m-chlorophenyl piperazine-induced serotonergic neurotransmission in female compared to male rats

Administration of various doses of m-chlorophenylpiperazine (m-CPP), a 5-hydroxytryptamine (5-HT) agonist, to rats increased plasma levels of corticosterone and decreased locomotor activity in a dose dependent manner. The increases of plasma corticosterone but not the decreases of locomotor activity were greater in female than male rats. Hypophagic effects of m-CPP not different in freely feeding male and female rats were greater in females when food deprived animals used. The findings along with our previous report show a functional supersensitivity of 5-HT neurotransmission involved in the regulation of hypothalamo-pituitary adrenocortical axis and appetite suppression in female sex, and suggest a possible basis for the greater occurrence of depression and anorexia in women than men.

Serotonergic neurotransmission in the regulation of appetite: a receptor approach

Neurochemical research on brain 5-hydroxytryptamine (5-HT; serotonin) and feeding shows that rat brain serotonin metabolism is increased following ingestion of a carbohydrate rich diet to generate a neurochemical signal for the termination of meal. Increased metabolism may not necessarily enhance postsynaptic function; neuropharmacological studies therefore gained attention. Drugs which mimick 5-HT function at the post synaptic sites have been shown to decrease feeding in experimental animals. Moreover some 5-HTergic drugs are potent anorectic agents. Multiple receptors for 5-HT exist in the central nervous system. Drugs with selectivity towards 5-HT-1B/ 5-HT-1C sites produced hypophagia, while 5-HT-1A selective drugs increased food intake. Studies designed to investigate sensitivity of these receptors following starvation or satiety may prove useful to develop drugs for therapeutic purposes.

Sex differences in neurochemical and behavioural effects of 8-hydroxy-2-(di-n-propylamino) tetralin

A number of neurochemical investigations have shown that 5-hydroxytryptamine (5-HT) metabolism and turnover is greater in females than male rats. However increased 5-HT metabolism does not necessarily imply greater 5-HT release at the functional post-synaptic sites. Pharmacological research based on 5-HT receptor stimulation therefore gained attention. Studies of this type are complicated because of the multiplicity of 5-HT receptors in the central nervous system. Chemical ligands may not have sufficient selectivity, to specifically bind to a single receptor population. Moreover, both the density and distribution of 5-HT receptors may follow a different pattern in male and female rats. 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) is a centrally acting 5-HT agonist with a ligand binding profile showing selectivity towards 5-HT-1A receptor sites. The present article integrates research on neurochemical and behavioural effects of 8-OH-DPAT in male and female rats, in order to investigate sex-related differences in 5-HT-1A receptor dependent functions.

Repeated corticosterone treatment attenuates behavioural and neuroendocrine responses to 8-hydroxy-2-(di-n-propylamino) tetralin in rats

The effects of 5 day corticosterone treatment (50 mg/kg s.c.; 2 x daily) are investigated on the behavioural and neuroendocrine responses to a 5-HT-1A selective agonist, 8-hydroxy -2-(di-n-propylamino) tetralin (8-OH-DPAT) in rats. Daily corticosterone treatment decreased body weight and food intake. After 5 day treatment a drug challenge of 0.25 and 0.5 mg/kg 8-OH-DPAT given on the sixth day produced smaller forepaw treading but comparable head waeving, flat body posture and also hypothermia in 5 day corticosterone than 5 day saline injected rats. Hyperphagic effects of only 0.25 mg/kg 8-OH-DPAT were attenuated in 5 day corticosterone injected animals. The effects of 8-OH-DPAT on the increases of plasma corticosterone were markedly attenuated in the 5 day corticosterone injected animals. The findings may help towards an understanding of steroid-induced affective changes and psychosis.

Hippocampal 5-hydroxytryptamine synthesis is greater in female rats than in males and more decreased by the 5-HT1A agonist 8-OH-DPAT

Brain regional 5-hydroxytryptamine (5-HT) and/or 5-hydroxyindoleacetic acid (5-HIAA) concentrations tended to be slightly higher in female rats than in males but differences were substantial only in the hippocampus where female values were 34% and 36% higher respectively. These findings were consistent with the synthesis rates of 5-HT as this was 53% greater in the female than in the male hippocampi. Other regions did not show significant sex differences. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 1 mg/kg sc) caused comparable decreases of 5-HT synthesis rate in both sexes and in all regions studied except the hippocampus where the percentage decrease was twice as large in the females (-64%) as in the males (-32%) so that the sex difference in 5-HT synthesis in this region largely disappeared. The results are discussed in relation to sex differences in behaviour and hippocampal function.

Injected tryptophan increases brain but not plasma tryptophan levels more in ethanol treated rats

In previous studies, long term treatment with ethanol has been shown to enhance brain 5-hydroxytryptamine 5-(HT) metabolism by increasing the activity of the regulatory enzyme tryptophan hydroxylase and or availability of circulating tryptophan secondarily to an inhibition of hepatic tryptophan pyrrolase. In the present study ethanol treatment given for two weeks decreased hepatic apo-tryptophan pyrrolase but not total tryptophan pyrrolase activity in rats. Tryptophan levels in plasma and brain did not increase significantly. But there was a marked increase of 5-HT but not 5-hydroxyindoleacetic acid (5-HIAA) concentration in brain, suggesting a possible increase in the activity of tryptophan hydroxylase. The effect of a tryptophan load on brain 5-HT metabolism was therefore compared in controls and ethanol treated rats. One hour after tryptophan injection (50 mg/kg i.p.) plasma concentrations of total and free tryptophan were identical in controls and ethanol treated rats, but the increases of brain tryptophan 5-HT and 5-HIAA were considerably greater in the latter group. The results are consistent with long term ethanol treatment enhancing brain serotonin metabolism and show that brain uptake/utilization of exogenous tryptophan is increased in ethanol treated rats and may be useful to understand the role and possible mechanism of tryptophan/serotonin involvement in mood regulation.