Metabolic effects obtained from excitatory amino acid stimulation of the sulcal prefrontal cortex

Indirect calorimetry was used to assess metabolic changes in rats following injections of the excitatory amino acid D,L-homocysteic acid (DLH) into the sulcal or medial prefrontal cortex. Injection of 7 nmol of DLH into the sulcal prefrontal cortex (SPC) increased respiratory quotient (RQ), indicating increased utilization of carbohydrate as an energy substrate. This treatment also decreased energy expenditure in the absence of related changes in motor activity, suggesting an inhibition of thermogenesis. A larger dose of DLH (50 nmol) injected into the SPC caused opposite effects, with a significant decrease in RQ and increased energy expenditure and motor activity. Rectal temperature was also increased by 20 or 50 nmol DLH but decreased with 7 nmol DLH. The anatomical specificity of these effects was indicated in that equivalent injections DLH into the medial prefrontal cortex did not affect energy balance. From this and related evidence it is concluded that SPC neurons exert a potent influence upon thermogenesis and metabolic substrate utilization that is bidirectional according to the magnitude of the excitatory stimulation that is applied.