Noradrenergic regulation of α₁-receptor during the postnatal development of the guinea pig

In guinea pig brain, α₁-noradrenergic receptor concentrations undergo region-specific fluctuations during the first weeks of postnatal life. However, the factors involved in the regulation of these receptors have yet to be identified. In this study, the ontogeny of one possible regulatory factor, norepinephrine, was examined in relation to postnatal changes in α₁-receptor levels in several different regions of guinea pig brain. Results from these studies showed that while the activity of the noradrenergic system increased throughout the first weeks of postnatal development in each brain area examined, the concentration of α₁-receptors decreased in preoptic area and hypothalamus and increased in cortex. In subsequent experiments, the effects of noradrenergic lesions with 6-hydroxydopamine on α₁-receptor levels were assessed to examine the possibility that α₁-receptors are differently sensitive to noradrenergic stimulation in cortex and preoptic area/hypothalamus in immature guinea pigs. Noradrenergic lesions which reduced norepinephrine levels by 87-94% resulted in significant elevations in α₁-receptors in all regions examined. These results are discussed with reference to the anatomical distribution of α₁-receptors and their regulation by norepinephrine.