Postnatal changes in glutamate binding in the lower medulla of the rat.

Changes in [3H]glutamate (Glu) binding occurring in the lower medulla of the rat between birth (P0) and adulthood (P72) were investigated on cryostat sections using in vitro receptor autoradiography. Densitometric measurements were performed in both autonomic (nucleus tractus solitarii, dorsal motor nucleus of the vagus nerve, ventrolateral medulla) and non-autonomic (inferior olive, spinal trigeminal nucleus) medullary regions. In all these areas, binding densities peaked at P9 and then gradually declined. Values close to those measured in adult animals were reached by P23-P30. These data indicate that glutamatergic neurotransmission within the lower medulla undergoes developmental changes during the early postnatal period. They thereby suggest that the neural circuits essential in organizing autonomic functions are still immature at birth.