ANXIOGENIC-LIKE EFFECT OF GLYCINE AND D-SERINE MICROINJECTED INTO DORSAL PERIAQUEDUCTAL GRAY-MATTER OF RATS

The glutamatergic system of the dorsal periaqueductal gray matter (DPAG) has been implicated in anxiety. This study shows that microinjections of glycine (GLY) or D-serine (D-SER), into the DPAG of rats, dose-dependently reduced the number of entries and the time spent on open arms of an elevated plus-maze (EPM), an established animal model for measuring anxiety-related behavior. This anxiogenic-like effect was greatest following DPAG application of either 80 nmol GLY or 160 and 320 nmol D-SER. Microinjections of these same amino acid doses outside the DPAG, or of L-serine (320 nmol) inside the DPAG, produced neither of these pro-anxiety effects, The current results suggest that, in vivo, the GLY modulatory site of N-methyl-D-asparate receptors is not fully saturated, and further substantiate a role for the DPAG excitatory amino acid system in anxiety.