Administration of AP5, a glutamate antagonist, unmasks glycine analgesic actions in the rat.
The effect of intrathecal (IT) injection of glycine alone or in combination with 2-amino-5-phosphonopentanoate (AP5) on two nociceptive tests--the vocalization threshold to tail-shock (VTTS) and the tail-flick latency (TFL)--was studied in ovariectomized Sprague-Dawley rats. IT injection of 400 micrograms glycine induced a nonsignificant decrease, that is, in comparison with saline, in both nociceptive thresholds. IT AP5 (10 micrograms) provoked a slight but significant increase in both nociceptive thresholds within the first 15 min postinjection. Combination of both glycine (400 micrograms) and AP5 (10 micrograms) produced marked and prolonged analgesia in both tests, which was significantly different from that obtained with AP5 alone. The results suggest that IT glycine acting through the strychnine-sensitive Gly1 receptor produces analgesia provided its effect on the Gly2 receptor linked to the NMDA receptor is prevented by an antagonist.
Beyer
C
C
Centro de Investigaciòn en Reproducciòn Animal, CINVESTAV, Universidad Autònoma de Tlaxcala, Mèxico.
Komisaruk
B R
BR
Lòpez-Colomè
A M
AM
Caba
M
M
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology*; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004597:Electroshock; D018691:Excitatory Amino Acid Antagonists; D005260:Female; D018698:Glutamic Acid; D005998:Glycine / Q000494:pharmacology*; D007278:Injections, Spinal; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000187:drug effects; D014828:Vocalization, Animal / Q000187:drug effects
D000700:Analgesics; D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D015763:2-Amino-5-phosphonovalerate; D005998:Glycine