NEUROCHEMICAL DIFFERENTIATION OF RAT ENTERIC NEURONS DURING PRENATAL AND POSTNATAL LIFE

The presence of nitric oxide synthase (the enzyme which synthesizes ni tric oxide), vasoactive intestinal peptide (VIP) and pituitary adenyly l-cyclase-activating peptide (PACAP) in the rat enteric nervous system between term (E18) and 90 days postpartum (P90) was investigated by i mmunohistochemistry. Neuronal maturity was ascertained by emanining fo r the presence of two novel neuron intermediate filament proteins: alp ha-internexin in, which is transiently expressed in developing neurons , and peripherin, which is expressed in differentiating as well as in mature neurons. The alimentary canal of the foetus at E18, unfed newbo rn, suckling, weaning and adult rats was studied. Throughout the rat g ut the myenteric neurons were recognized by the time the foetal stage was reached and the submucous neurons by the suckling period, alpha-In ternexin was present at E18; its levels increased during ageing and we re markedly reduced at P30. Peripherin was first detected at birth; it s levels increased with ageing and pratically almost all of the neuron s and nerve fibres were labelled from P30. Nitric oxide synthase was p resent at E18 and the number of labelled neurons gradually increased w ith ageing, while both VIP and PACAP could be detected by the end of t he suckling period in an equal number of neurons to that in adulthood, These data indicate that in the rat gut the onset of the mature neuro nal phenotype is not yet achieved at birth and that the neurochemical differentiation is accomplished during the first month of postnatal li fe.