Distribution of gonadrotropin releasing hormone agonist binding sites in the rat central nervous system

Abstract

Specific binding sites for gonadotropin releasing hormone (GnRH) in the central nervous system of the rat were studied with in vitro autoradiography and with radioligand assays. The results show that GnRH bindings sites are present in the lamina glomerulosa and plexiformis externa, the nucleus olfactorius anterior pars externa, and the frontal cortex at the sulcus rhinalis. In the septum, only a few GnRH binding sites are detected in the lateral and dorsal portions of the nucleus septi lateralis. In addition, a small number of GnRH receptors are seen in the mediobasal hypothalamus and amygdala while substantial binding is apparent in the interpeduncular nucleus, central gray and superior collicle. In the hippocampal formation the GnRH agonists bind to the dorsal and ventral subiculum as well as to receptors in the areas CA 1 through CA 4. The highest concentration of GnRH receptors is found in the parasubiculum. Competitive binding assays with membrane preparations from the hippocampus and interpeduncular nucleus indicate that the binding of the GnRH agonists is reversible and has a binding affinity of 1× 10 0M −1. Injections of radioactive GnRH agonist Buserelin into the lateral ventricle results in selective and reversible labeling of the hippocampal areas CA 1 through CA 4 as well as the interpeduncular nucleus, central gray and the prasubiculum. The results of the present study indicate that GnRH binds to specific receptors in select areas of the central nervous system of the rat where the peptide may regulate sensory, behavioral and endocrine events. It is suggested that endogenous GnRH reaches its sites of action in the central nervous system either after synaptic/asynaptic release from nerve terminals which are located next to their target cells or after release into the cerebrospinal fluid which can transport the peptide to, for example, the hippocampus.