Because
glucose is the primary substrate for oxidative metabolism of the adult brain, measurements of
glucose utilization provide information on cerebral energy metabolism, which ultimately is linked to neuronal activity. Early studies utilized in vitro techniques to measure
carbohydrate oxidation as well as glycolytic and citric acid cycle enzymatic activities as a function of age. Although the results of these studies are somewhat equivocal, they generally indicate a decline in cerebral carbohydrate metabolism in senescent rodents. More recently, local cerebral
glucose utilization (LCGU) has been measured in awake, resting rats with the 2-deoxy-D[1-14C]
glucose metabolic mapping technique. Using this technique, decrements in LCGU have been observed in rats by midlife.
Co-dergocrine, an ergot
alkaloid used extensively in geriatric psychopharmacology, reversed subcortical LCGU decrements in brain areas associated with motor function, motivation, and learning. In contrast, the
drug decreased frontal cortical LCGU in middle-aged rats. Stimulatory effects of
co-dergocrine on LCGU in brain areas associated with motivation and learning support the view that the
drug may be useful against age-associated disorders of cognition. Furthermore, the
co-dergocrine-induced decrease in cortical
glucose utilization coupled with the
drug's cerebral vasoconstrictive action may render cortical cells less susceptible to the sequelae of
ischemia.