Sexual behavior triggers the appearance of non-neuronal cells containing gonadotropin-releasing hormone-like immunoreactivity.

Gonadotropin-releasing hormone (GnRH) regulates the secretion of pituitary gonadotropins and facilitates the display of sexual behavior. We report that in doves, following a brief period of courtship, non-neuronal cells containing GnRH-like immunoreactivity (ir) are seen in the habenula of both male and female doves. These cells appear to be translocated from either the cerebrospinal fluid or from capillaries in the pia or choroid plexus into the parenchyma of the brain. Immunoreactive cells are virtually absent in the habenula in control animals housed alone. The identity of the ir cells that enter the habenula is unknown but they would appear to be of either the macrophage or the mast cell lineage. Both of these blood-derived cells have heterochromatic nuclei and irregular cell surfaces with many filamentous processes, as do the GnRH-ir cells. The vacuolated granules of the ir cells could be indicative of mast cell degranulation or of endocytic vesicles of a phagocytosing cell. These data suggest that there is a population of cells within the habenula that are of similar size and morphology to the GnRH-ir ceils and are metachromatic when stained with toluidine blue. The latter is a property of heparin-containing mast cells. Lineage specific markers that permit a double-label study will be required to determine the exact nature of the GnRH-ir cells. Whatever their lineage, the translocation of non-neuronal cells into the undamaged adult central nervous system has not been described previously, and may provide a means of delivering biologically active substances into specific brain regions.