Superior Cervical Ganglionectomy Depresses Norepinephrine Uptake, Increases the Density of α-Adrenoceptor Sites, and Induces Supersensitivity to Adrenergic Drugs in Rat Medial Basal Hypothalamus

Abstract

The occurrence of nonpineal mediated effects of superior cervical ganglionectomy (SCGx) on neuroendocrine function prompted us to study SCGx effects on medial basal hypothalamic (MBH) norepinephrine (NE) content and uptake, and on MBH α- and β-adrenoceptor sites assessed by ³H-dihydroergocryptine and ³H-dihydroalprenolol binding. SCGx depressed MBH NE uptake but did not affect NE content in MBH homogenates. After SCGx, a significant 35% increase of α-adrenoceptor sites occurred in MBH whereas the β-adrenoceptors remained unchanged. In order to correlate the increase of binding sites with adrenoceptor-mediated supersensitive responses in MBH, the effects on NE, isoprotere-nol or L-dihydroxyphenylalanine (L-dopa) on MBH tubulin concentration were assessed. Each drug brought about a greater depression of MBH tubulin in SCGx than in control rats. A dose-response study of the MBH tubulin decrease after L-dopa treatment indicated that SCGx augmented the potency of L-dopa by 2.5-fold, shifting the dose-response curve to the left in a parallel manner. Such increase in potency was only 1.6-fold when SCGx was associated with Px. SCGx increased both α- and β-adrenoceptor sensitivity of MBH tubulin. Px, while leaving the α-adrenoceptor supersensitive response unmodified, removed the β-adrenoceptor-mediated effect on tubulin because: (i) isoproterenol injection did not affect MBH tubulin in SCGx-Px rats; (ii) NE or L-dopa induced a depression of MBH tubulin which was partially impaired by propranolol in SCGx rats and was refractory to β-adrenergic blockade in SCGx-Px animals; (iii) the α-adrenergic blocker phentolamine abolished effectively NE or L-dopa effect on MBH tubulin in SCGx-Px rats but not in SCGx rats. Dose-related decreases of cerebral cortex tubulin after L-dopa treatment were essentially similar in SCGx, SCGx-Px or sham-operated rats. These results indicate that SCGx depresses NE uptake and increases α-adrenoceptor sites in MBH as well as the adrenoceptor-mediated response of MBH tubulin. A functionally relevant link between superior cervical ganglia and MBH appears to occur in the rat.