Ontogenesis of prostaglandin E2 binding sites in the brainstem of the sheep.

Perinatal changes in plasma prostaglandin E2 (PGE2) act at the level of the fetal brainstem to modulate respiratory activity. In-vitro receptor autoradiography was used to determine whether PGE2 binding sites (putative receptors) are located in brainstem regions responsible for respiratory control. Frozen brainstem sections were obtained from fetal sheep at 140 d of gestation, lambs at 5 h and 10 d after birth, and adults (n = 3 at each age). In the perinatal brainstem, high density binding was localized near the following nuclei: hypoglossal, tractus solitarius, parabrachial and spinal trigeminal-oral. Moderate levels of binding were localized near the nuclei of the spinal trigeminal tract, ambiguus, inferior olivary, cuneate, gracilis, facial, medial vestibular, superior vestibular, and abducens. Binding density did not change with age within the perinatal period. However, binding in three high density regions (hypoglossal, spinal trigeminal and parabrachial nuclei) decreased significantly in adulthood, whereas the binding in the nucleus of the solitary tract remained high. We hypothesize that the PGE2 binding sites that we identified near respiratory regions of the brainstem may mediate the central respiratory effects of PGE2.