Postnatal development of protein P-38 ('synaptophysin') immunoreactivity in pontine and medullary gustatory zones of rat.

Neurons located in gustatory zones of the nucleus of the solitary tract (NST) and parabrachial nucleus (PBN) exhibit extensive morphological development during the first 5-7 weeks of rat's postnatal life. The present study examined the time course for development of protein P-38 ('synaptophysin'), a specific integral membrane glycoprotien of clear synaptic vesicles, in the rostral NST and PBN. Results show that volumetric fractions of P-38 immunoreactions increase in the NST from P1 to P10, and are adult-like in the NST after approximately P11. In contrast, volumetric fractions of P-38 immunoreactivity increase in the PBN between approximately P11 and P30. Because we have previously demonstrated that dendritic growth in the rostral gustatory NST precedes dendritic growth in the PBN, these results confirm that maturation of both presynaptic and postsynaptic constituents of brainstem gustatory relays develop in a temporally sequential manner. Relationships between neurological development of brainstem gustatory relays and the ontogeny of taste-guided responses are discussed.