ACCESS OF LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS TO THE VASCULATURE IN THE RAT

Luteinizing hormone-releasing hormone is secreted into the hypophysial portal vasculature through which it controls the release of the gonadotropins. The peptide also acts as a neurotransmitter in various loci within the central nervous system. It is not known whether these roles are performed by separate populations of luteinizing hormone-releasing hormone neurons. Some recent tracing experiments suggest that this is the case (Silverman et al., J. Neurosci. 7, 2312, 1987; Jennes and Stumpf, Neuroscience 18, 403, 1986). One aspect of this question was addressed in the current study by intraperitoneal introduction of Fluoro-Gold (a retrograde tracer) into male and female rats under various age and hormonal conditions. Brain sections from the anterior olfactory nuclei to the median eminence were treated for the immunocytochemical demonstration of luteinizing hormone-releasing hormone. In all cases, regardless of the age, sex or hormonal condition of the animal, the Fluoro-Gold tracer was found in more than 90% of the luteinizing hormone-releasing hormone neurons. We conclude that virtually all luteinizing hormone-releasing hormone neurons in the rat secrete outside the blood-brain barrier, including those which project to sites within the central nervous system. © 1990.