Responses in the hypothalamic monoaminergic system activity in ewes to beta-endorphin, CRF and their antagonists.

This article reviews data concerning the action of opioidergic and monoaminergic system on LHRH secretion. Generally, in anestrous ewes beta-endorphin and/or corticoliberin significantly change extracellular concentrations of monoamine metabolites in the MBH-ME, but in estrous ewes both beta-endorphin and CRF alters also dopamine, noradrenaline and serotonin levels. Responses of catecholaminergic and serotoninergic system in the MBH-ME to naloxone or CRF-antagonist depend, to a large degree, on the phase of reproduction. In anestrous ewes subjected to stressful stimuli an opiate receptor blocker, naloxone, and CRF-antagonist attenuate the stress - induced activity of catecholaminergic and serotoninergic system in the MBH-ME; in non-stressed animals they suppress only serotoninergic system activity in this structure. No clear explanation can be offered now for either differences in response of catecholaminergic and serotoninergic system in the MBH to beta-endorphin and CRF in various periods of reproduction or for differences in the responses of these systems to CRF antagonist and naloxone in non-stressed and stressed ewes. It has been suggested that the responses in monoaminergic system activity are highly dependent upon the physiological state of the animal and that beta-endorphin and corticoliberin may indirectly modulate LHRH and other hypothalamic hormone secretion by monoaminergic systems.