Identification and distribution of nitric oxide synthase in the brain of adult zebrafish

Nitric oxide (NO) is proposed to be involved in developmental and plastic processes. We investigated the presence and distribution of nitric oxide synthase (NOS) in the zebrafish (Danio rerio) using molecular and histochemical techniques. A partial gene sequence corresponding to the neuronal NOS isoform (nNOS) was identified, and in situ hybridization revealed cellular nNOS mRNA expression throughout the brain of adult zebrafish, distributed in distinct central nuclei and in proliferation zones. NOS immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase activity partly coincided with the nNOS mRNA expression, however was present also in additional neuronal and non-neuronal cell types. The results indicate the occurrence of different NOS isoforms in the adult brain, of which nNOS may participate in neurotransmission, and in mechanisms related to the continuous growth and neuronal plasticity of the teleost brain.