Activation of dorsal periaqueductal gray by glycine produces long lasting hyponociception in rats without overt defensive behaviors

• Published in: Life sciences (1973) 2008-07, Vol.83 (3), p.118-121
• Main Authors: Martins, M.A., Carobrez, A.P., Tonussi, C.R.
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal - drug effects; Dose-Response Relationship, Drug; Glycine; Glycine - pharmacology; HA966; Hyponociception; Ligands; Male; Maze Learning - drug effects; Microinjections; NMDA; Pain Measurement; Pain Threshold - drug effects; Periaqueductal Gray - metabolism; Periaqueductal Gray - physiology; Periaqueductal gray matter; Rats; Rats, Sprague-Dawley; Receptors, Glycine - metabolism; Receptors, N-Methyl-D-Aspartate - metabolism; Time Factors
• ISSN: 0024-3205; 1879-0631
• DOI: 10.1016/j.lfs.2008.05.012

Electrical or glutamate stimulation of the dorsal periaqueductal gray matter (DPAG) of rats induces overt defensive behavior, such as freezing or flight, and hyponociception, while glycine and d-serine, a specific NMDA/GLY B-site ligand, produced only subtle defensive behavior related to risk assessment and avoidance from the open arms in the elevated plus-maze test. In order to verify whether the GLY B site in the DPAG could also be involved in hyponociception, glycine (GLY; 10, 20, 50, and 80 nmol/0.3 µl) and (+/−)-3-amino-1-hydroxy-2-pyrrolidone (HA966; 10 nmol/0.3 µl), a GLY B-site antagonist, were microinjected in rats submitted to the radiant heat-induced tail-flick test. GLY increased tail-flick latencies in a dose-dependent way. This hyponociceptive effect was completely reversed by co-administration with HA966. GLY given in the deep layer of superior colliculus did not produce changes in tail-flick latencies. Therefore, the results suggest that the activation of GLY B receptors in the DPAG is also involved in the hyponociception elicited by this brain area.