Interaction between L-glutamate and ethanol on the central depressant properties of ethanol in mice

Circadian regulation of central ethanol sensitivity by the mPer2 gene

The effect of alcohol is known to vary with the time of the day. Although initially it was suggested that this phenomenon may be due to diurnal differences in ethanol metabolism, more recent studies were contradicting. In the present study, we therefore first set out in assessing the diurnal variations in ethanol sensitivity in mice analysing, concurrently, ethanol elimination rates. Ethanol-induced (3.5 g/kg; intraperitoneal) loss of righting reflex (LORR) duration was thus determined at several Zeitgeber time (ZT) points (ZT5, 11, 17 and 23) in C57BL/6N mice. In parallel, the corresponding ethanol elimination rates were also assessed. The results display the existence of a distinct diurnal rhythm in LORR duration peaking at ZT11, whereas no differences could be observed regarding the elimination rates of alcohol. Successively, we checked the involvement of the clock genes mPer1 and mPer2 in conveying this rhythm in sensitivity, testing LORR and hypothermia at the peak and trough previously observed (ZT5 and ZT11). Per1(Brdm1) mice demonstrate a similar diurnal pattern as control mice, with enhanced LORR durations at ZT11. In contrast, Per2(Brdm1) mice did not exhibit a temporal variation to the depressant effects of ethanol with respect to LORR, revealing a constant high sensitivity to ethanol. The present study reveals a central role of the mPer2 gene in inhibiting alcohol sensitivity at the beginning of the inactive phase.

Regional Influence of Cannabinoid CB1 Receptors in the Regulation of Ethanol Self-Administration by Wistar Rats

Substantial evidence suggests a facilitatory influence of cannabinoid CB1 receptors in the modulation of ethanol consumption by rodents. Studies performed in rats selectively bred for high alcohol preference point to an involvement of CB1 receptors in the nucleus accumbens (NAC), ventral tegmental area (VTA) and medial prefrontal cortex (mPFC) in the modulation ethanol self-administration. However, the neural mechanisms through which CB1 receptors regulate ethanol intake in out-bred Wistar rats have not been investigated. The present study evaluated alterations in ethanol self-administration induced by localized infusions of the CB1 receptor antagonist SR141716A (0, 1 and 3 μg/side) into the NAC, anterior and posterior VTA and mPFC. Separate groups of Wistar rats were trained to operantly respond for an oral ethanol solution and prepared with bilateral injection cannulae aimed at each brain region. Results revealed significant decreases in ethanol intake following intra-NAC SR141716A administration, consistent with our prior observation of ethanol-induced increases extracellular 2-arachidonoyl glycerol (2-AG) in this brain region. We also observed a significant dose-dependent reduction in ethanol intake following SR141716A administration into the posterior, but not anterior VTA, consistent with evidence of a specific involvement of the posterior VTA in the regulation of ethanol intake. Ethanol consumption was unaltered following intra-mPFC SR141716A administration and ethanol self-administration did not induce robust changes in anandamide or 2-AG levels in mPFC microdialysates. These findings implicate an involvement of CB1 receptors in the NAC and posterior VTA, but not anterior VTA and mPFC in the regulation of ethanol self-administration behavior by outbred Wistar rats.

Neuropharmacology of alcohol addiction

Despite the generally held view that alcohol is an unspecific pharmacological agent, recent molecular pharmacology studies demonstrated that alcohol has only a few known primary targets. These are the NMDA, GABA(A), glycine, 5-hydroxytryptamine 3 (serotonin) and nicotinic ACh receptors as well as L-type Ca(2+) channels and G-protein-activated inwardly rectifying K(+) channels. Following this first hit of alcohol on specific targets in the brain, a second wave of indirect effects on a variety of neurotransmitter/neuropeptide systems is initiated that leads subsequently to the typical acute behavioural effects of alcohol, ranging from disinhibition to sedation and even hypnosis, with increasing concentrations of alcohol. Besides these acute pharmacodynamic aspects of alcohol, we discuss the neurochemical substrates that are involved in the initiation and maintenance phase of an alcohol drinking behaviour. Finally, addictive behaviour towards alcohol as measured by alcohol-seeking and relapse behaviour is reviewed in the context of specific neurotransmitter/neuropeptide systems and their signalling pathways. The activity of the mesolimbic dopaminergic system plays a crucial role during the initiation phase of alcohol consumption. Following long-term, chronic alcohol consumption virtually all brain neurotransmission seems to be affected, making it difficult to define which of the systems contributes the most to the transition from controlled to compulsive alcohol use. However, compulsive alcohol drinking is characterized by a decrease in the function of the reward neurocircuitry and a recruitment of antireward/stress mechanisms comes into place, with a hypertrophic corticotropin-releasing factor system and a hyperfunctional glutamatergic system being the most important ones.

Ethanol potentiates dopamine release during acute hypoxia in rat striatum

We, and others, have previously demonstrated that N-methyl-D-aspartate (NMDA) receptor is involved in hypoxia or ischemia-mediated responses. We found that the NMDA antagonist ketamine attenuates cortical nitric oxide release during cerebroischemia. It has been reported that ethanol (EtOH) antagonizes NMDA-induced responses in various systems. In the present study, the interaction of EtOH and KCl-evoked striatal dopamine release in vivo during acute hypoxia was examined. High-speed chronoamperometric recording techniques, using Nafion-coated carbon fiber electrodes, were used to evaluate extracellular dopamine (DA) concentration in the striatum of urethane-anesthetized Sprague-Dawley rats. KCl was directly applied to the striatum to evoke release of DA. These anesthetized animals were paralyzed with d-tubocurarine and connected to a respirator to allow controlled respiration. Systemic concentrations of oxygen were altered by changing the rate of the respirator. We previously reported that lowering the respiratory rates from 90 to 20 times/min for 5 min decreased arterial PO(2) and facilitated KCl-induced DA release in the striatum. In this study, we found that application of NMDA antagonist MK801 attenuates hypoxic DA release, suggesting that NMDA receptor is involved in this hypoxic reaction. In contrast, EtOH dose dependently enhanced KCl-evoked DA release during hypoxia. To further examine the interactions of excitatory amino acid and EtOH on DA release, glutamate was locally applied to the striatum. Glutamate-induced DA release was not affected by the systemic application of EtOH. Taken together, these data suggest that EtOH enhances DA release in vivo during short-term hypoxia, possibly through mechanisms other than excitatory amino acid pathways.

Investigations into pharmacological antagonism of general anaesthesia

The effects of convulsant drugs, and of thyrotropin releasing hormone (TRH), were examined on the general anaesthetic actions of ketamine, ethanol, pentobarbitone and propofol in mice. The aim was to investigate the possibility of selective antagonism, which, if seen, would provide information about the mechanism of the anaesthesia. The general anaesthetic effects of ketamine were unaffected by bicuculline; antagonism was seen with 4-aminopyridine and significant potentiation with 300 mg kg(-1) NMDLA (N-methyl-DL-aspartate). The calcium agonist, Bay K 8644, potentiated the anaesthesia produced by ketamine and antagonism of such anaesthesia was seen with TRH. A small, but significant, antagonism of the general anaesthesia produced by ethanol was seen with bicuculline, and a small, significant, potentiation with 4-aminopyridine. There was an antagonist effect of TRH, but no effect of NMDLA. Potentiation of the anaesthetic effects of pentobarbitone was seen with NMDLA and with 4-aminopyridine and the lower dose of bicuculline (2.7 mg kg(-1)) also caused potentiation. There was no significant change in the ED(50) value for pentobarbitone anaesthesia with TRH. Bicuculline did not alter the anaesthetic actions of propofol, while potentiation was seen with NMDLA and 4-aminopyridine. TRH had no significant effect on propofol anaesthetic, but Bay K 8644 at 1 mg kg(-1) significantly potentiated the anaesthesia. These results suggest that potentiation of GABA(A) transmission or inhibition of NMDA receptor-mediated transmission do not appear to play a major role in the production of general anaesthesia by the agents used.