Effects of Fluoxetine on Tyrosine Hydroxylase Expression in Schedule-Induced Polydipsia Rats / 신경정신의학

OBJECTIVE: It has been suggested that fluoxetine inhibits the dopaminergic neurotransmission by serotonergic mediation. And also, it has been shown to inhibit synthesis of DOPA in dopamine-rich areas of the rat forebrain. These dopamine-antagonistic capacity of fluoxetine is only supported by anecdotal report that the increased amount of motor disability in patients with idiopathic Parkinson's disease after exposure to fluoxetine. However, there is still no evidence of the direct effect of fluoxetine on dopaminergic neuronal cell body in the substantia nigra, VTA, caudate & putamen. This study was designed to evaluate the effects of fluoxetine in rat brain which showed decreased numbers of dopaminergic neuronal cell body induced by schedule-induced polydipsia(SIP). METHODS: We incidentally found that 4 weeks of schedule-induced polydipsic rats revealed the suppression of tyrosine hydroxylase expression in the substantia nigra, VTA, caudate & putamen with the immunohistochemistric measures. After 3 weeks of intraperitoneal injection of 10mg/kg of fluoxetine to the schedule induced polydipsic rats, the tyrosine hydroxylase expression was also measured with immunohistochemistry. We compared the tyrosine hydroxylase expression among the normal control, the polydipsic rats, and the rats with fluoxetine treatment. RESULTS: 1) By contrast with the control, the polydipsic rats revealed the evidence of decreased tyrosine hydroxylase expression in the substantia nigra, VTA, caudate & putamen. 2) After daily injection of fluoxetine for 3 weeks, the polydipsic rats showed increment of tyrosine hydroxylase expression in those areas. CONCLULSION: In previous studies, a great deal of results suggest that fluoxetine negatively influence the dopaminergic systems indirectly via serotonergic activation such as inhibition of dopamine synthesis or transport system. Although our results are obtained from rodents, we suggest that fluoxetine directly and positively enhance the dopamine system in the substantia nigra, VTA, caudate & putamen. The chronic adminstration of fluoxetine may be helpful to dopamine-depleted condition in clinical situations. We anticipate the replication studies of our findings and well-controlled clinical trial.

Effects of Risperidone on the Schedule-Induced Polydipsia in Rats / 신경정신의학

OBJECTIVES: This study was designed to evaluate the effects of risperidone on the schedule-induced polydipsia (SIP) which is one of animal model of obsessive-compulsive disorder in rats. We administered risperidone as a serotonin and dopamine blocking agent, fluoxetine as a selective serotonin reuptake inhibitor, and haloperidol as a dopamine antagonist to rats which showed schedule-induced polydipsic behaviour. METHODS: Sprage-Dawley rats weighing 200 - 250gm were individually housed and main-tained and allowed free access to water. The rats were placed on a restricted diet. To induce polydipsia, rats were placed in the cage where a pellet dispenser automatically dispensed 90mg pellets on a fixed-time 60 seconds (FT 60s) feeding schedule over 150 minute test session per day. Water was available at all times in the cage. After 4 weeks of daily exposure to the FT 60s feeding schedule, experimental rats met a predetermined criterion for polydipsic behavior (greater than 3 times of water per session on average). 5 groups of rats were administered risperidone (0.1mg/kg, i.p), risperidone (0.5mg/kg, i.p), fluoxetine (5mg/kg, i.p.), haloperidol (0.1mg/kg, i.p.), and vehicle (1cc/kg, i.p. ) for 3 weeks. The rats were tested once a week to access schedule induced polydipsic behavior. Water bottles were weighed before and after the 150-minute test session. The chronic effects of administration of experimental drugs on schedule induced polydipsic behavior were analyzed with ANOVA and Scheffe test as a posthoc comparison. In order to measure water consumption in non-polydipsic food-deprived rats, a separate group of rats (N=8) was individually housed and given a single bolus (14.5gm) of food per day which maintained them at their average body weight. RESULTS: The results were as follows; 1) After 4 weeks of scheduled feeding procedure, the experimental group showed significant differences than the bolus control in the amount of water consumption as compared with their average water intakes for 4 weeks. At the same periods, there were no differences between the experimental group and the bolus control in the body weight. 2) The fluoxetine group showed significant decrease in the amount of water intake at 1st, 2nd, and 3rd weeks of drug treatment as compared with their average amount of polydipsic water intakes. The risperidone 0.1mg group and the risperidone 0.5mg group showed significant decrease in the amount of water intake at the 3rd weeks of drug treatment as compared with their baseline of polydipsic water intakes. However, the haloperidol group and the vehicle control group showed no changes of amounts of water intake for 3 weeks of treatment as compared with their baseline of polydipsic water intakes. 3) The fluoxetine group (22.5+/-10.4ml) showed significantly lower amounts of water intake than haloperidol group (41.3+/-7.1ml) at 2nd weeks of drug treatment. And also the fluoxetine group (18.8+/-3.5ml) showed significantly lower amounts of water intake than the haloperidol group (35.0+/-11.7ml) and the vehicle control (34.4+/-6.8ml) at 3rd weeks of drug treatment. The risperidone 0.1mg group and the risperidone 0.5mg group showed significantly lower amounts of water intake than the haloperidol group (35.0+/-11.7ml) at 2nd weeks and the vehicle control (37.5+/-12.5 , 34.4+/-6.8ml) at 2nd and 3rd weeks of drug treatment. CONCLUSIONS: Above findings suggest that the fixed time feeding procedure for schedule induced polydipsia could be applied as an effective animal model of obsessive compulsive disorder for the evaluation of pharmacological challenge study. We confirmed that chronic treatment with risperidone revealed antipolydipsic effect as effective as fluoxetine on the schedule-induced polydipsic behaviour but the onset of effect was later than fluoxetine.