GONADOTROPIN-RELEASING-HORMONE (GNRH) NEURONS IN THE HYPOGONADAL MOUSE ELABORATE NORMAL PROJECTIONS DESPITE THEIR BIOSYNTHETIC DEFICIENCY

This study was undertaken to determine whether gonadotropin-releasing hormone (GnRH) neurons in the mutant hypogonadal (hpg) mouse can establish axonal connections with their target despite their failure to synthesize and secrete the GnRH neuropeptide. Normal and hpg males received intraperitoneal injections of the retrograde tracer Fluoro-Gold. This tracer does not cross the blood-brain-barrier and hence is taken up only by neurons in the central nervous system whose axons terminate on fenestrated capillaries, such as the capillaries of the median eminence. The brains of the injected animals were processed for in situ hybridization to visualize GnRH transcribing cells. In 3 hpg males 64.1 +/- 5.6% of GnRH transcribing cells contained Fluoro-Gold, while 55.8 +/- 6.4% of the cells in 3 normal males had Fluoro-Gold. Thus, we have demonstrated that secretory-deficient GnRH neurons can establish axonal connections with their primary secretory target, the median eminence. We conclude that the capability of GnRH neurons to recognize and interact with their target is not dependent upon their neurosecretory function.