Alterations in peripheral and central dopamine receptor sensitivity after subchronic treatment with fluphenazine and sulpiride

Behavioural subsensitivity induced by long-term administration of a low dose of haloperidol to rats

This study examines the effects on open-field and stereotyped behaviour of rats of abrupt withdrawal from repeated treatment with a low (0.03 mg kg-1) dose of haloperidol. Single administration of this low dose of haloperidol significantly increased open-field locomotion without modifying apomorphine (0.5 or 2.0 mg kg-1)-induced stereotyped behaviour. Forty-eight hours after abrupt withdrawal from 0.03 mg kg-1 haloperidol (twice daily for 15 days) a significant decrease in locomotion frequency was observed, but no change was observed in apomorphine-induced stereotypy. Our results suggest that dopamine autoreceptor supersensitivity might be evaluated in a behavioural situation of absence of postsynaptic dopamine receptor supersensitivity.

Effects of chronic SCH 23390 treatment on dopamine autoreceptor function in rat brain

The effects of chronic treatment with SCH 23390 (0.5 mg/kg per day, 18 days), a selective (DA) D-1 receptor antagonist, on dopamine autoreceptor function in rats were investigated. The decrease of DA metabolism in mesolimbic and nigrostriatal systems and inhibition of spontaneous explorative locomotor activity by low doses of the selective D-2 receptor agonist, quinpirole, were used as behavioral and biochemical indices of DA autoreceptor function. The DA metabolism decreasing effect of quinpirole (20 and 50 micrograms/kg) in mesolimbic or nigrostriatal DA systems was similar in SCH 23390- and vehicle-treated rats. Two-way analysis of variance showed that rats treated chronically with SCH 23390 were significantly more active than vehicle-treated rats. However, there were no statistically significant differences in the quinpirole-induced hypomotility response between these groups. These results indicate that chronic D-1 blockade, unlike classical antipsychotic drugs, does not modulate the biochemical and behavioral indices of DA autoreceptor activation, suggesting a lack of interaction between DA autoreceptors and D-1 receptors in the central nervous system.

Dopamine D2 and muscarinic receptor binding characteristics in rat brain after withdrawal of subchronic fluphenazine and sulpiride treatment

1. The effects of subchronic (10 days) treatment with two antischizophrenic drugs, fluphenazine and sulpiride, on rat brain dopamine and muscarinic receptor sites were studied at various time points after withdrawal from the drug treatments. Striatal D-2 dopamine receptors and cortical muscarinic receptors were characterized with the radioligands 3H-spiperone and 3H-quinuclidinyl benzilate (3H-QNB), respectively. 2. Neither drug treatment affected significantly the number or affinity of cortical muscarinic receptors during the withdrawal time of 18 days. 3. The number of D-2 receptors in striatum was not altered after 4 or 8 fluphenazine-free days, but after 18 days fluphenazine caused an increase of 55% in the density of D-2 receptors. Sulpiride caused a slight increase in Bmax of striatal D-2 receptors after 4 and 8 withdrawal days but the maximum increase of 29% was observed after 18 withdrawal days. 4. Fluphenazine treatment caused an increase in the apparent dissociation constant 4 days after the termination of the treatment suggesting that residual neuroleptic levels may have been retained after this dose regimen, since the Kd returned near control levels as the withdrawal time passed. Sulpiride, however, caused a moderate increase in Kd throughout the withdrawal time. 5. In conclusion, these results suggest that even a rather short treatment with fluphenazine or sulpiride, a classical and an atypical neuroleptic, respectively, can induce pronounced changes in striatal dopamine receptor characteristics after a drug washout period of almost three weeks. Thus, possible delayed actions of classical as well as novel neuroleptic drugs on neurotransmitter function should be considered in studies examining the neuroleptic withdrawal effects.