Glycine enhances glutamate-induced excitation in ventromedial hypothalamic neurons in awake rats.

The finding that glycine potentiates N-methyl-D-aspartate (NMDA) receptor-mediated responses, has tremendously changed our understanding of glutamatergic synaptic transmission in the brain. Although the phenomenon has been confirmed in number of preparations, it is yet to be demonstrated in awake animals. Further, the controversy that glycine binding sites of NMDA receptor are saturated in vivo or not, can be best verified in awake animals. Here, we have demonstrated that glycine enhanced glutamate-induced neuronal discharges in the ventromedial nucleus of the hypothalamus of awake behaving rats using microiontophoresis technique, suggesting that the glycine binding sites of NMDA receptor are not saturated under physiological conditions.