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Receptors for 5-HT(1A) are widely distributed throughout the basal ganglia, and their activation results in an inhibition of dopamine (DA) release. This study aimed to investigate the effect of buspirone, as a partial agonist of 5-HT(1A) receptors, on 6-hydroxydopamine (6-OHDA)-induced catalepsy in male Wistar rats. Catalepsy was induced by unilateral infusion of 6-OH-DA (6 microg/2 microl/rat) into the central region of the substantia nigra pars compacta (SNc) and assayed by the bar-test method 60, 120 and 180 min after drug administration. The results demonstrated that intraperitoneal (ip) injection of buspirone at doses of 5, 7.5 and 10 mg/kg decreased catalepsy compared with the control group. In addition, intra-SNc injection of 8-hydroxy-2-[di-n-propylamino]tetralin (8-OH-DPAT; 10 microg/rat), a 5-HT(1A) receptor agonist, decreased 6-OHDA-induced catalepsy. The effects of buspirone (7.5 mg/kg, ip) and 8-OH-DPAT (10 microg/rat, intra-SNc) were abolished by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido) butyl]piperazine hydrobromide (NAN-190; 10 microg/rat, intra-SNc), a 5-HT(1A) receptor antagonist. Our study indicates that buspirone improves catalepsy in a 6-OHDA-induced animal model of Parkinson's disease through activation of nigral 5-HT(1A) receptors. However, further investigations should be undertaken to clarify the exact mechanism of interaction between 5-HT(1A) and DA receptors.

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In the present study, the effects of chronic lithium pre-treatment (30 days) on penile erection (PE) induced by bromocriptine were investigated in rats. Intraperitoneal administration of the dopamine receptor agonist, bromocriptine (4-32 mg/kg) induced PE in a biphasic manner. The maximum response was obtained with 8 mg/kg of bromocriptine and the effect was decreased with increasing doses of the drug from 8 to 32 mg/kg. When animals were pre-treated with different doses of the D-1 dopamine receptor antagonist, SCH 23390, or the D-2 dopamine receptor antagonist, sulpiride, the PE response was decreased. The response induced by bromocriptine (4-32mg/kg) was reduced in animals pre-treated with chronic lithium. SCH 23390 did not produce a larger inhibitory effect on the bromocriptine response in animals pre-treated with chronic lithium, but the inhibitory effect of sulpiride was increased in this condition. It is concluded that chronic lithium treatment may alter the D-1/D-2 receptor activity and inhibit bromocriptine-induced PE.

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