THE EFFECT OF REPEATED AMPHETAMINE ADMINISTRATION ON THE PROOPIOMELANOCORTIN MESSENGER-RNA LEVEL IN THE RAT PITUITARY - AN IN-SITU HYBRIDIZATION STUDY

The effect of single and repeated administration of amphetamine (5 mg/ kg i.p., twice daily, 14 days) on the proopiomelanocortin (POMC) mRNA level was investigated in the rat pituitary. In situ hybridization his tochemistry, using a S-35-d-ATP-labelled deoxyoligonucleotide probe an d densitometric analysis of autoradiograms, showed that repeated admin istration of amphetamine moderately increased the POMC mRNA level (by similar to 16%) in the anterior and the intermediate lobes of the pitu itary at 72, but not 2, hr after the last injection. Adrenalectomy (48 h after the last drug injection) increased the POMC mRNA level only i n the anterior lobe of repeated saline- and amphetamine-treated rats b y 59 and 67%, respectively. No significant changes in POMC mRNA level in either lobe were found following single administration of amphetami ne. These results suggest that repeated amphetamine administration lea ds to a delayed arid moderate increase in POMC biosynthesis in the rat pituitary. On the other hand, the responsiveness of the POMC pituitar y system to adrenalectomy was not significantly altered in rats treate d repeatedly with amphetamine.