Expression of peripherin, NADPH-diaphorase and NOS in the adult rat neocortex

Peripherin is mainly expressed in peripheral neurones and in CNS neurones which extend axons into peripheral nerves. However, this intermediate filament protein has also been detected in a few other neurones entirely located within the CNS. The present study focuses on the adult rat neocortex. Peripherin immunoreactive (P+) neuronal somata and their neuritic extensions were observed in cortical layers II, III, V and VI, while a few P+ nerve fibres could be seen in layer I. All the P+ neurones could be selectively stained using reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry, a typical feature of aspiny neurones. Some of the P+ neurones could also be immunostained with an antibody raised against nitric oxide synthase (NOS). These results provide evidence that peripherin is present in a discrete population of aspiny interneurones of the adult rat neocortex. The functional significance of the co-expression of peripherin and NOS needs further investigation.