DIFFERENTIAL INHIBITION OF NMDA-INDUCED AND NALOXONE-INDUCED LH-RELEASE BY NMDA RECEPTOR ANTAGONIST AND CRH IN OVARIECTOMIZED ESTROGEN-PRIMED RATS

A possible functional relationship between endogenous opioid peptides (EOPs), corticotropin-releasing hormone (CRH) and excitatory amino aci ds (EAAs) in the control of LH secretion was investigated in ovariecto mized estrogen-primed rats. An intraventricular (icy) injection of an EAA agonist, N-methyl-D-aspartate (NMDA), or an EOP antagonist, naloxo ne, produced an abrupt increase in the serum LH level. While icy pretr eatment of the animals with 2-amino-5-phosphonovaleric acid, a specifi c NMDA receptor antagonist, did not affect by itself basal LH levels, it significantly suppressed the NMDA-induced and also the naloxone-ind uced LH release. An icy injection of CRH also interfered with the nalo xone-induced LH release. However, the NMDA-induced LH release was not affected by an icy injection of CRH or of beta-endorphin. These result s suggest that the sites of EOP and CRH inhibition may be located upst ream of the site of NMDA stimulation on the GnRH neuronal pathway, and that CRH can inhibit LH secretion without mediation by EOP neurons.