INDUCTION AND VARIANTS OF NEURONAL NITRIC-OXIDE SYNTHASE TYPE-I DURING SYNAPTOGENESIS

In the adult central nervous system, nitric oxide (NO) is formed from L-arginine by the so-called constitutive or type I NO synthase (NOS-I-155) However, expression of NOS-I-155 immunoreactivity and activity was low or not detectable in developing mouse and rat brain. NOS-I-155 was sharply induced coincident with the onset of synaptogenesis in specific brain regions, This was followed by a second phase in which total NOS-I-155 expression decreased both in specific cell populations and in the total synaptosomal subcellular fraction, Furthermore, two putative variants of NOS-I were transiently observed: an NOS-I-immunoreactive protein with increased electrophoretic mobility (NOS-I-144) and a transient hypersensitivity of NOS-I-155 to the competitive substrate inhibitor N-omega-nitro-L-arginine. It is concluded that NOS-I expression is not constitutive but locally induced. In the central nervous system, this regionally specific, biphasic pattern of postnatal NOS-I induction is consistent with a role for NO in synaptogenesis and synaptic plasticity.