Release and synthesis rates of catecholamines in hypothalamic, limbic and midbrain structures following intraventricular injection of beta-endorphin in male rats.

Serum hormone levels and turnover rates of dopamine (DA), norepinephrine (NE) and epinephrine (E) in tissue of pontine midbrain, limbic caudate, and hypothalamic structures were measured following intraventricular injection of 20 microgram beta-endorphin. Turnover of DA was increased in the locus coeruleus and in structures innervated by the nigrostriatal and mesolimbic DA systems while it decreased in the posterior hypothalamus. The NE turnover was reduced in the locus coeruleus and posterior mediobasal hypothalamus. In all tissues examined, beta-endorphin treatment had no significant effect on E turnover. Serum levels of prolactin and corticosterone increased following beta-endorphin treatment whereas LH, FSH and TSH levels decreased. The observed effects of beta-endorphin on preoptic and hypothalamic DA and NE turnover rates may explain these hormonal changes. The reduced NE turnover in the locus coeruleus may be induced by increased DA turnover. The observation, that NE turnover in structures innervated by locus coeruleus neurons may go in different direction suggest that NE turnover is regulated independently from the activity of locus coeruleus neurons, hence that the regulation must occur at the terminals by a direct or indirect interaction with endorphinergic neurons.