Aims: 

The mediodorsal prefrontal cortex (mdPFC), a major constituent of the forebrain limbic circuitry, is known to be involved in the regulation of food intake behaviors. The major aim of our research project was to elucidate feeding associated chemical sensitivities of mdPFC neurons.

Methods: 

In the present study, extracellular single neuron activity of the mdPFC of anesthetized rats was recorded by means of multibarreled glass microelectrodes during 1) microelectrophoretic administration of D-glucose and dopamine (DA), 2) intraoral gustatory stimulations with various taste solutions, and 3) intragastric infusion of monosodium L-glutamate (MSG), D-glucose and NaCl.

Results: 

One fourth of the mdPFC cells, the glucose-monitoring (GM) neurons, displayed firing rate changes to microelectrophoretic administration of D-glucose. The predominant response to glucose was inhibition (glucose-sensitive cells), however, facilitatory responses were detected in the glucose-receptor cells. Appx. 25% of all neurons tested exhibited DA responsiveness, the inhibitory and excitatory firing rate changes were recorded in similar proportions. DA responsiveness of the GM cells was significantly higher than that of the glucose-insensitive units (p<0.001). DA exhibited only excitatory response in the glucose-receptor cells, whereas both inhibitory and excitatory firing rate changes were observed in the glucose-sensitive cells (with a predominance of inhibition). Intraoral gustatory stimulations elicited activity changes of one third of the mdPFC neurons. In case of the intragastric infusions, half of the neurons tested exhibited MSG, glucose or NaCl responsiveness too.

Conclusion: 

The GM neurons in the mdPFC, by utilizing differential DA sensitivities and integrating endogenous as well as exogenous chemical information, are suggested to play significant role in adaptive mechanisms of the central feeding control.

Support: 

Ajinomoto 51064/2009, OTKA K 68431, and HAS