Distribution of alpha(2)-adrenergic receptor binding in the developing human brain stem

Rapid and dramatic changes occur in cardiorespiratory function during early human life. Catecholamines within select brain stem nuclei are implicated in the control of autonomic and respiratory function, including in the nucl eus of the solitary tract and the dorsal motor nucleus of X. Animal and adu lt human studies have shown high binding to alpha (2)-adrenergic receptors in these regions. To determine the developmental profile of brainstem alpha (2)-adrenergic binding across early human life, we studied brain stems fro m five fetuses at midgestation, three newborns (37-38 postconceptional week s), and six infants (44-61 postconceptional weeks). We used quantitative ti ssue receptor autoradiography with [H-3]para-aminoclonidine as the radiolig and and phentolamine as the displacer. In the fetal group, binding was high (63-93 fmol/mg tissue) in the nucleus of the solitary tract. dorsal motor nucleus of X, locus coeruleus, and reticular formation, it was low (< 32 fm ol/mg tissue) in the principal inferior olive and basis pontis. Binding dec reased in all regions with age: in infancy, the highest binding was in the intermediate range (32-62 fmol/mg tissue) and was localized to the nucleus of the solitary tract and dorsal motor nucleus of X. The most substantial d ecrease in binding (75%-85%) between the fetal and infant periods occurred in the pontine and medullary reticular formation and hypoglossal nucleus. B inding remained lour in the principal inferior olive and basis pontis. The decreases in binding with age remained significant after quench correction. These data suggest that rapid and dramatic changes occur in early human li fe in the brain stem catecholaminergic system in regions related to cardior espiratory control.