Hindbrain catecholamine neurons control rapid switching of metabolic substrate use during glucoprivation in male rats

Using the retrogradely transported immunotoxin, antidopamine β-hydroxylase-saporin (DSAP), we showed previously that hindbrain catecholamine neurons innervating corticotropin-releasing hormone neurons in the paraventricular nucleus of the hypothalamus are required for glucoprivation-induced corticosterone secretion. Here, we examine the metabolic consequences of the DSAP lesion in male rats using indirect calorimetry. Rats injected into the paraventricular nucleus of the hypothalamus with DSAP or saporin (SAP) control did not differ in energy expenditure or locomotor activity under any test condition. However, DSAP rats had a persistently higher respiratory exchange ratio (RER) than SAPs under basal conditions. Systemic 2-deoxy-D-glucose did not alter RER in DSAP rats but rapidly decreased RER in SAP controls, indicating that this DSAP lesion impairs the ability to switch rapidly from carbohydrate to fat metabolism in response to glucoprivic challenge. In SAP controls, 2-deoxy-D-glucose-induced decrease in RER was abolished by adrenalectomy but not adrenal denervation. Furthermore, dexamethasone, a synthetic glucocorticoid, decreased RER in both SAP and DSAP rats. Thus, rapid switching of metabolic substrate use during glucoprivation appears to be due to impairment of the catecholamine-mediated increase in corticosterone secretion. Sustained elevation of basal RER in DSAP rats indicates that catecholamine neurons also influence metabolic functions that conserve glucose under basal conditions.