Potential sites of interaction between catecholamines and LHRH in the sheep brain

A combined immunoperoxidase/immunofluorescence procedure was used to examine potential sites of overlap between catecholamine and LHRH systems in the brains of ewes sacrificed during either anestrous or the breeding season. Cells and fibers immunoreactive for either tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH) were visualized in the same sections as immunopositive LHRH perikarya and fibers. TH- and DBH-positive varicosities in the preoptic area and anterior hypothalamus appeared to contact both LHRH cell bodies and their dendrites. Clusters of TH-positive cells and fibers were found in the organum vasculosum of the lamina terminalis, and partially overlapped the location of immunoreactive LHRH fibers in that structure. Immunoreactive TH and LHRH fibers were densely interspersed within the zona externa of the median eminence, particularly within its lateral portion. No obvious qualitative differences were apparent in either the distribution of catecholamine cells and fibers or their overlap with LHRH elements between the brains of anestrous and breeding season ewes. These observations suggest the possibility of catecholaminergic synaptic inputs onto LHRH neurons in the ewe, as well as the potential for interaction between catecholamines and LHRH at the level of the median eminence.