HALOPERIDOL INCREASES PPE MESSENGER-RNA LEVELS IN THE CAUDAL PART OF THE NUCLEUS-ACCUMBENS IN THE RAT

DOPAMINE exerts a tonic inhibitory control in the regulation of mRNA e ncoding preproenkephalin (PPE), the precursor of enkephalin, in the do rsal part of the rat striatum. Less is known about the role of this am ine in the regulation of PPE mRNA in the ventral part of the striatum which corresponds to the nucleus accumbens. In this study, the effects of an interruption of dopamine transmission by haloperidol (a dopamin ergic receptor antagonist) were examined in the rat nucleus accumbens. The levels of PPE mRNA were analysed by in situ hybridization histoch emistry by taking into account the complexity of the nucleus accumbens , i.e. by differentiating the rostro-caudal extension of the structure . It was found that PPE mRNA content was increased significantly only in the caudal part of the nucleus, indicating rostro-caudal difference s in the haloperidol effects. The differential reactivity of PPE mRNA to dopaminergic receptor blockade and to a lesion of dopaminergic neur ones along the rostro-caudal axis of the ventral striatum is discussed .