A. Resink et al., CHARACTERIZATION OF AGONIST-INDUCED DOWN-REGULATION OF NMDA RECEPTORSIN CEREBELLAR GRANULE CELL-CULTURES, Journal of neurochemistry, 66(1), 1996, pp. 369-377
Exposure of cerebellar granule cells to NMDA in culture at 5 days in v
itro, when cells are not yet vulnerable to NMDA, evoked a pronounced r
eduction in NMDA receptor activity, measured by NMDA-induced Ca-45(2+)
influx, and counteracted the normal developmental increase in NMDA re
ceptors. The effect was concentration and time dependent, the half-max
imal effect being reached at about 45 mu M and by 4-5 h. The decrease
in NMDA receptor function was accompanied by a significant reduction i
n the protein level of the obligatory NMDA receptor subunit (NR) NR1.
Both parameters remained at a low level as long as the agonist was pre
sent. However, receptor down-regulation was reversible, as receptor pr
otein levels and NMDA responses were restored to control values upon N
MDA removal, this process requiring protein synthesis. NMDA treatment
also elicited a decrease in NR1, NR2A, and NR2B subunit messenger RNA
(mRNA) levels. However, in comparison with NMDA receptor proteins, the
decrease was faster, and NMDA receptor mRNA content recovered to cont
rol levels within 24 h in spite of the presence of NMDA. Concerning th
e mechanisms of agonist-induced regulation of NMDA receptor expression
, it seems that protein kinase C-mediated protein phosphorylation is n
ot involved, whereas inhibition of Ca2+/calmodulin-dependent kinase II
/IV by KN-62 does depress NMDA receptor expression even in the absence
of NMDA.