ROLE OF OPIOIDERGIC AND MONOAMINERGIC NEUROTRANSMISSION IN THE GNRH RELEASE MECHANISM OF EBP-PRIMED OVX RATS

We examined the effect of intracerebroventricular (i.c.v.) administrat ion of mu-opioid agonist, morphine, and its antagonist naloxone follow ed by morphine on the activities of monoamine-metabolizing enzymes, na mely tyrosine hydroxylase (TH) and monoamine oxidase (MAO) along with adenosinetriphosphatase (Na+, K+ -ATPase), the enzyme responsible for the maintenance of ionic gradients across the membrane, in seven discr ete regions of brain from estrogen- and progesterone-primed ovariectom ized rats. TH activity decreased after morphine treatment in some area s such as the median eminence-arcuate region (ME-ARC), the amygdala, a nd the thalamus, showing statistically significant change. MAO activit y increased in all the areas studied, but more appreciable change was observed in medial preoptic area (mPOA), the ME-ARC region, and the co rtex. Pronounced increase in Na+, K+ -ATPase enzyme activity was obser ved after the drug treatment. Naloxone given prior to morphine injecti on resulted in recovery of the enzyme activities in most of the areas studied. Our study may provide insights into the precise opioidergic m odulation of gonadotropin releasing hormone (GnRH) release mechanisms through the involvement of monoaminergic system, elucidating the basis of various neuronal dysfunctions and their management in opioid addic ts. (C) 1998 Elsevier Science Inc.