Effects of pretreatment with Luteinizing Hormone Releasing Hormone (LHRH) on behaviors induced by apomorphine in rats

Abstract

The influence of LHRH on the behavioral effects induced by apomorphine (APO) was studied in male rats. Several doses of apomorphine (31.25, 62.5, 125, 250 and 500 μg/kg) were administered subcutaneously (SC) after LHRH 100 μg/kg or solvent. Low doses of apomorphine induced hypomotility and impaired acquisition of a conditioned avoidance response (CAR). High doses produced hypermotility, stereotyped sniffing and a short lasting increase, followed by a decrease in the acquisition of CARs. Pretreatment with LHRH potentiated the hypomotility induced by low doses of apomorphine (62.5 and 125 μg/kg) and the hypermotility, stereotyped sniffing and the enhancement in acquisition of CARs produced by higher doses of apomorphine (250 and 500 μg/kg). These findings suggest that LHRH could indirectly regulate dopamine activity through an increase in sensitivity of dopamine receptors (pre- and postsynaptic), which mediate the behavioral effects of APO. It is postulated that this hypersensitivity of DA receptors could be the consequence of an inhibition of presynaptic dopaminergic transmission, induced by LHRH.