GLYCINE AT THE NMDA RECEPTOR IN CAT VISUAL CORTEX: SATURATION AND CHANGES
WITH AGE.
Czepita, D., N.W. Daw and S.N.M. Reid.
From.
APStracts 2:0252N, 1995.
SUMMARY AND CONCLUSIONS
1. Saturation of the glycine site at the N-methyl-D-aspartate (NMDA) receptor
in cat visual cortex was tested by iontophoresing D-serine, and the
contribution of this site to the visual response was tested by iontophoresing
7-Chlorokynurenic acid (7-Cl-KYNA). Animals were tested at ages 3 weeks, 6
weeks, 5 months and adult. 2. In at least 40% of cells (24/57), D-serine
increased the response significantly, showing that the glycine site was not
saturated. However the increase was rarely more than 100%. 3. The amount by
which D-serine increased the response did not vary significantly with age. 4.
In five cases there was positive evidence for saturation of the glycine site.
D-serine did not increase the response significantly; however, when D-serine
was applied on top of 7-Cl-KYNA, it did increase the response compared to that
seen with 7-Cl-KYNA alone. These cases were all in 3-week old animals. In
other cases (28/57), D-serine did not increase the response significantly, but
we could not be absolutely certain that the D-serine had reached the site of
action. 5. The effect of 7-Cl-KYNA was largest in 3-week animals, in agreement
with previous findings that the effect of D-2-amino-5-phosphonovalerate (APV)
is largest at this age. 6. These results may provide a small part of the
explanation for the finding that the NMDA receptor-mediated component of the
visual response decreases between 3 and 6 weeks of age, while the number of
NMDA receptors is increasing. However, the magnitude of the results make it
likely that other factors are more important.
Received 2 September 1995; accepted in final form 14 August 1995.
APS Manuscript Number J555-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.