Environment-dependent effects of ethanol on DOPAC and HVA in various brain regions of ethanol-tolerant rats

Effects of post-ethanol administration of NMDA and non-NMDA receptor antagonists on the development of ethanol tolerance in C57B1 mice

The effect of post-ethanol administration of NMDA and non-NMDA receptor antagonists on the development of environment-dependent ethanol tolerance was studied in C57B1 mice. Ethanol tolerance was produced by daily injections of ethanol (3.5 g/kg, IP) in the same experimental environment and measured as ethanol-produced "sleep-time" during 5 consecutive days. The non-competitive NMDA receptor antagonist, dizocilpine (MK-801; 0.1 mg/kg, IP), and the competitive NMDA receptor antagonist, CGP 39551 (5 mg/kg, IP), both given 120 min after the administration of ethanol, inhibited the development of tolerance to the hypnotic actions of ethanol. In contrast, the development of ethanol tolerance was not altered by administration of the specific AMPA/KA receptor blocking agents, NBQX (10 mg/kg, IP), and LY326325 (2.5 mg/kg, IP), respectively. Modulation of NMDA receptor activity by drugs like NMDA, d-cycloserine, and milacemide, which are known to enhance learning and memory in rodents, had no significant effect on the development of ethanol tolerance. Our present data confirm and extend previous findings which indicate that NMDA, but not non-NMDA, glutamate receptors may play an important role in the neuroadaptive processes associated with the development of ethanol tolerance.

Alcohol withdrawal reaction as a result of adaptive changes of excitatory amino acid receptors

Recent electrophysiological and biochemical studies suggest that ethanol interferes with excitatory amino acid (EAA) neurotransmission. Here, we present electrophysiological evidence that, following cessation of a chronic ethanol treatment, noradrenergic locus coeruleus (LC) neurons display hyperactivity at the same time as a specifically enhanced sensitivity to microiontophoretically applied NMDA or quisqualate. Furthermore, after chronic ethanol treatment, but not before, the NMDA receptor antagonist MK 801 (0.3-2.4 mg/kg, i.v.) dose-dependently inhibited the firing of the LC neurons. Our data indicate that an up-regulation of EAA receptors located on LC neurons accounts for the changes in LC firing in ethanol-treated rats. We propose that activation of the LC contributes to the clinical signs of the ethanol abstinence reaction and that EAA antagonists may be beneficial therapeutically for its treatment.

Evidence that genetic differences in habituation and GABAergic mechanisms may be related to sensitivity to ethanol and development of ethanol tolerance in mice

Habituation to a test environment following daily exposure for 5 days was examined in three genetically different strains of mice. C57 animals showed significant habituation to the new environment already on the second day. The habituation of NMRI mice was significant on the third day, whereas CBA mice showed no habituation at all during the experimental period. There was no difference between the animal strains in learning capacity in a passive avoidance test, but CBA mice displayed a significant increase in latency in their performance. When tested for sensitivity to the convulsant actions of GABAergic antagonists, picrotoxin produced seizures at lower doses in CBA as compared to NMRI and C57 mice, whereas there was no difference between the strains in the seizure activity produced by the specific GABA receptor antagonist bicuculline. When the animals were tested for sensitivity to ethanol in a horizontal wire test, ethanol (2 g/kg, IP) produced muscle relaxation in CBA mice whereas the performance of NMRI and C57 was not affected. A large dose of ethanol (4 g/kg, IP) produced a significantly longer sleeping time in CBA mice as compared to NMRI and C57 animals. Ethanol-produced hypothermia was, however, similar in all animals. Environment-dependent development of tolerance to ethanol following daily injections of ethanol for 4 days was examined. C57 mice showed the most rapid development of tolerance towards ethanol's hypnotic actions, whereas CBA mice showed no tolerance to this effect of ethanol. No difference between the strains to the development of tolerance to ethanol's hypothermic effects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)