Prefrontal cortex alpha 2 adrenoceptors and energy balance.

The sulcal prefrontal cortex (SPC) influences thermogenesis, energy substrate utilization and feeding behaviour. The present study examined the role of SPC alpha noradrenergic receptors in these effects. Fifty nmol norepinephrine (NE) injected into the SPC produced a large and long-lasting increase in respiratory quotient (RQ), indicating enhanced carbohydrate utilization and fat synthesis. This dose also reduced energy expenditure without corresponding decreases in locomotor activity, suggesting an inhibition of thermogenesis. Neither a lower dose of NE (25 nmol) injected into the SPC, nor injections of NE (50 nmol) into a variety of sites adjacent to the SPC affected energy balance. The alpha 2 agonist clonidine (20 nmol) injected into the SPC produced similar effects to 50 nmol NE, with a large increase in RQ and a decrease in thermogenesis. Forty nmol clonidine, however, decreased RQ and reduced both energy expenditure and activity. The alpha 1 agonist L-phenylephrine (20 and 40 nmol) injected into the SPC had no clear effect on energy balance. Finally, it was shown that clonidine or NE injected into the SPC promotes food intake. These results implicate alpha 2 adrenoceptors in the sulcal prefrontal cortex in the control of food intake, thermogenesis and metabolic substrate utilization.