THE PHARMACOONTOGENY OF THE PERIFORNICAL LATERAL HYPOTHALAMIC BETA-2-ADRENERGIC AND DOPAMINERGIC RECEPTOR SYSTEMS MEDIATING EPINEPHRINE-INDUCED AND DOPAMINE-INDUCED SUPPRESSION OF FEEDING IN THE RAT

The functional ontogeny of beta2-adrenergic and dopaminergic receptors in the perifornical lateral hypothalamus (PLH) that mediate adrenergic and dopaminergic suppression of feeding in rats was investigated. Rat pups, ranging in age from 2 to 15 days, were removed from their mothers and implanted with a brain cannula directed unilaterally at the PLH or a more rostral site lateral to the anterior nucleus of the hypothalamus. On the next day, following a 22-h period of food and water deprivation, each pup was implanted with an intra-oral cannula for oral infusion of milk that could be swallowed or rejected. Subsequently, each pup received an intracerebral injection of saline, or a single dose of epinephrine (EPI, 0.1-30.0 nmol), the beta2-adrenergic receptor agonist salbutamol (1.0-30.0 nmol) or the dopaminergic receptor agonist apomorphine (1.0-30.0 nmol). Milk intake was then assessed following a 1-h period of infusion. The results showed significant dose-dependent suppression of milk intake in pups as young as 2 days of age in response to PLH injection of EPI, salbutamol and apomorphine. In contrast to its effectiveness in the PLH at 2 days of age, EPI failed to suppress milk intake at this age following injection into a more rostral site lateral to the anterior nucleus of the hypothalamus. Together, these findings suggest that both beta2-adrenergic and dopaminergic receptors, mediating adrenergic and dopaminergic suppression of feeding, are functionally mature very early in the postnatal development of the rat. Moreover, consistent with evidence in adult rats, these catecholaminergic receptors in young pups appear to be located in the region of the PLH.