Ionotropic glutamate receptor subunit expression in the rat hippocampus: lack of an effect of a long-term ethanol exposure paradigm.
BACKGROUND
Studies have shown that acute ethanol exposure inhibits ionotropic glutamate receptor function and that long-term ethanol exposure results in maladaptive increases in the expression of some of these receptors in neurons. It has been postulated that these changes, when unopposed by ethanol, contribute, in part, to the hyperexcitability associated with ethanol withdrawal. In this study, we compared the effect of long-term ethanol exposure on the hippocampal expression levels of subunits belonging to the three families of ionotropic glutamate receptors.


METHODS
Adult male Sprague-Dawley rats were fed an ethanol-containing diet for 16 days. This diet contained 0% ethanol on days 1 and 2, 3% on days 3 and 4, 5% on days 5 to 7, and 6.7% on days 8 to 16. Control rats received an equivalent amount of an isocaloric diet without ethanol. Rats were killed on day 16 at the peak of ethanol consumption. Hippocampal homogenates were prepared by sonication and analyzed by Western immunoblotting techniques. On a separate group of rats, we measured withdrawal scores and audiogenic seizures on day 17.


RESULTS
Ethanol-exposed rats had significantly higher withdrawal scores, and a significantly higher percentage of them developed audiogenic seizures; this indicates that the 16-day ethanol diet induces ethanol dependence. Unexpectedly, we found that expression of NR1 (including the expression of NR1 subunits containing the N1, C1, and C2 inserts), NR2A, NR2B, NR2C, GluR1, GluR2/3, GluR5, GluR6/7, and KA2 subunits was not altered in hippocampal homogenates from ethanol-exposed rats.


CONCLUSIONS
These results indicate that maladaptive changes in the hippocampal expression levels of ionotropic glutamate receptor subunits do not always occur in ethanol-dependent rats. Consequently, other mechanisms must mediate the hyperexcitability state associated with ethanol withdrawal in these animals.
Ferreira
V M
VM
Department of Neurosciences, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131-5223, USA.
Frausto
S
S
Browning
M D
MD
Savage
D D
DD
Morato And
G S
GS
Valenzuela
C F
CF
D000437:Alcoholism / Q000209:etiology; D000818:Animals; D000431:Ethanol / Q000009:adverse effects / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000378:metabolism; D018092:Kainic Acid Receptors / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012640:Seizures / Q000139:chemically induced / Q000503:physiopathology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology; D013997:Time Factors
D000431:Ethanol; D020033:Protein Isoforms; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate