The presence of substance P-immunoreactive nerve fibres in the organum vasculosum laminae terminalis of the Mongolian gerbil (Meriones unguiculatus).

Serial frontal and sagittal sections through the organum vasculosum laminae terminalis (OVLT) of the male Mongolian gerbil (Meriones unguiculatus) were incubated with an antibody against substance P and stained by the indirect peroxidase anti-peroxidase technique. A high density of nerve fibres with large-sized terminals exhibiting substance P-immunoreactivity was observed in the OVLT in close relation to the blood vessels both in the internal and the external zone of the organ. In addition, a few fibres penetrated into the ependyma covering the organ. These results indicate that substance P is released into the bloodstream from the OVLT and in addition might influence the ependymal cells bordering the organ towards the third ventricle.