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

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Abstract
The occurrence of nonpineal mediated effects of superior cervical ganglionectomy (SCGx) on neuroendocrine function prompted a study of SCGx effects on medial basal hypothalamic (MBH) norepinephrine (NE) content and uptake, and on MBH .alpha.- and .beta.-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 .alpha.-adrenoceptor sites occurred in MBH; the .beta.-adrenoceptors remained unchanged. To correlate the increase of binding sites with adrenoceptor-mediated supersensitive responses in MBH, the effects on NE, isoproterenol or 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 [pinealectomy]. SCGx increased both .alpha.- and .beta.-adrenoceptor sensitivity of MBH tubulin. Px, while leaving the .alpha.-adrenoceptor supersensitive response unmodified, removed the .beta.-adrenoceptor-mediated effect on tubulin because: isoproterenol injection did not affect MBH tubulin in SCGx-Px rats; NE or L-dopa induced a depression of MBH tubulin which was partially impaired by propranolol in SCGx rats and was refractory to .beta.-adrenergic blockade in SCGx-Px animals; the .alpha.-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. Evidently, SCGx depresses NE uptake and incrases .alpha.-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.