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 investigated by means of immunohistochemistry in the vomeronasal organ (VNO) of mice from 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-called VNO pump) as well as blood vessels in the connective tissue laying under the receptor epithelium at postnatal day 1. At 8, 15 and 21 postnatal days, and at 2 months the density of NOS-1-immunoreactive nerves goes along with the development of the erectile tissue. From postnatal day 8 onwards, NOS-1-immunoreactive fibers are found also in the vicinity of the VNO glands. These data suggest that nitric oxide (NO) modulates VNO activity early after birth in the mouse.