Immunohistochemical investigation of the vomeronasal organ. Nitric oxide synthase expression in the mouse during postnatal development

The expression of nitric oxide synthase type I (NOS-I), the key enzyme for the synthesis of the gaseous neurotransmitter nitric oxide, was investigate d by means of immunohistochemistry in the vomeronasal organ (VNO) of mice f rom postnatal day 1 for 2 months. The results show that NOS is expressed in extrinsic nerve supplying the developing erectile tissue of VNO (the so-ca lled VNO pump) as well as blood vessels in the connective tissue laying und er the receptor epithelium at postnatal day 1. At 8, 15 and 21 postnatal da ys, and at 2 months the density of NOS-l-immunoreactive nerves goes along w ith the development of the erectile tissue. From postnatal day 8 onwards, N OS-l-immunoreactive fibers are found also in the vicinity of the VNO glands . These data suggest that nitric oxide (NO) modulates VNO activity early af ter birth in the mouse. (C) 1999 Elsevier Science Ireland Ltd. All rights r eserved.