• Energy Research

AbstractEthanol, 0.65 gm per kilogram of body weight, was administered orally to 6 normal subjects. The mean blood ethanol levels ranged from 0.74 to 0.99 gm per liter over a subsequent 40‐minute testing period. The proportion of the soleus motoneuron pool activated by the Achilles tendon reflex was reduced. Vibratory inhibition of the monosynaptic reflex was used as an estimate of spinal presynaptic inhibition. It was unaffected by ethanol.

The structure and function of the blood-brain barrier (BBB) is determined mainly by the characteristics of brain capillary endothelial membranes. Lipophilic drugs that modify the cell membrane might be anticipated to alter the BBB. We investigated the effect of acute ethanol in combination with either a barbiturate or a non-barbiturate anesthetic on the ability of the rat BBB to exclude circulating horseradish peroxidase (HRP). Rats were injected into the peritoneal cavity with ethanol plus either a barbiturate (pentobarbital) or a non-barbiturate (ketamine hydrochloride) anesthetic. HRP was subsequently injected transcardially 30 s prior to decapitation. In the ethanol plus barbiturate-treated rats focal leakage of HRP caused peroxidase levels in the cerebral cortex to be about 8-fold higher than in ethanol plus ketamine hydrochloride-treated rats. Ultrastructurally endothelial cells in leaking vascular segments were infiltrated with HRP and, in some cases, they were lysed so that the structural integrity of the blood-brain interface was lost. Lysed segments were accompanied by staining of the adjacent basal lamina with HRP, and edematous astrocytic endfeet. These results show that ethanol plus a barbiturate anesthetic causes breakdown in the BBB by structurally damaging brain capillary endothelial cells. Whether the damage is caused by the expansion and lysing of the cell membrane by these two lipophilic drugs, or by increased intracellular calcium to toxic levels is not yet known.

The effects of an acute intoxicating concentration of ethanol (50 mM) on the electrotonic membrane properties of hippocampal dentate granule neurons were studied using a system model incorporating electrotonic coupling between neurons. Uncoupling of cells by other alcohols has been shown in several tissues. The system model allows a quantitative estimation of the changes in coupling and other neuronal electrotonic properties. The input impedance of a neuron was measured from the voltage decay of a short hyperpolarizing current pulse. An analytic expression of the input impedance has been written incorporating somatic, dendritic, and electrical coupling parameters. Using this particular current stimulation, the modelling results showed that ethanol selectively increased the junctional resistance by more than 2.5 times, hence uncoupling the neurons. A 30% increase in the final time-constant, tau 0, was also obtained from the voltage transient. Other parameters were not significantly affected. A neuronal model without electrotonic coupling to other neurons gave rise to physiologically impossible values for the membrane resistance and capacitance. With resistive and capacitive coupling in the model, uncoupling did not occur with ethanol. It is concluded that ethanol uncouples neurons by increasing the effective gap junctional resistance in dentate granule neurons.

The electrophysiologically measured effects of perfused ethanol were examined in neuromuscular junctions and hippocampal slices removed concurrently from naive and ethanol-tolerant rats. At the neuromuscular junction, ethanol augmented the frequency height, and half-width of spontaneous miniature endplate potentials (Mepp). No tolerance was noted to these effects in junctions from ethanol-fed animals. Ethanol depressed the stratum radiatum evoked hippocampal CA1 population spike. Clearcut tolerance to this effect was noted in slices from chronically ethanol-fed animals.

The effect of low dose (20 mM) ethanol superfusion on the membrane and synaptic properties of dentate granule neurons was studied in hippocampal slices from young-mature (6-8 months) and old (25-29 months) Fischer-344 rats. In young neurons, ethanol hyperpolarized the resting membrane potential (RMP) and prolonged the post-spike train afterhyperpolarization (AHP). By contrast, ethanol depolarized old neurons and decreased their AHPs, in addition to reducing IPSP amplitudes and spike frequency adaptation. These effects can be explained by ethanol-enhancing potassium conductance (gK) in young neurons and diminishing gK in old neurons.

The electrophysiological effects of ethanol in low doses (5 to 20 millimoles per liter or 23 to 92 milligrams per 100 milliliters) were examined intracellularly in CA1 cells of rat hippocampus in vitro. Inhibitory and excitatory postsynaptic potentials were increased when ethanol was applied to the respective synaptic terminal regions. Postsynaptically, ethanol caused a moderate hyperpolarization with increased membrane conductance, even when synaptic transmission was blocked. Ethanol augmented the hyperpolarization that followed repetitive firing or that followed the eliciting of calcium spikes in the presence of tetrodotoxin, but not the rapid afterhyperpolarization in calcium-free medium. Ethanol appears to augment calcium-mediated mechanisms both pre- and postsynaptically.

The ubiquitous role of calcium in ethanol actions measured electrophysiologically in central neurons is discussed. Acute ethanol administration to rat hippocampal neurons in vitro causes a hyperpolarization, increased AHPs, increased EPSPs and IPSPs, decreased modelled electronic interneuronal coupling, decreased high threshold Ca2+ currents, increased Ik, and increased synaptic GABAA currents. Alcohol withdrawal reverses some of these actions. Ca2+ is implicated in all of the above ethanol mediated effects.

Recent studies have demonstrated that ethanol potentiation of GABAA receptor function can be regulated by second-messenger-dependent processes. As a preliminary step to further characterize this interaction, we used the whole-cell patch-clamp technique to study the effects of guanosine phosphate analogs on ethanol potentiation of GABAA-mediated synaptic transmission in rat hippocampal CA1 neurons. Intracellular dialysis with 400 microM GDP beta S, an analog that inhibits G-protein coupled events, significantly reduced ethanol, but not pentobarbital, potentiation of IPSCs. In contrast, dialysing neurons with 100 microM GTP gamma S, an irreversible G-protein activator, selectively facilitated ethanol potentiation of GABAA IPSCs. These results suggest that one or more G-protein coupled events regulate the ethanol sensitivity of synaptic GABAA receptors.

The N1-P2 wave of the auditory evoked potential was studied in 19 alcoholics, six of whom had withdrawal seizures on previous admissions. The recordings were made at 1 and 5 days after cessation of drinking. Eight nonalcoholic volunteers were used as controls. The latencies of N1 and P2 were slightly prolonged in alcoholics, but during the detoxification period they frequently shortened (p less than 0.05), occasionally attaining the values of the controls. One day after withdrawal, the amplitude of N1-P2 was consistently reduced in the alcoholics compared to the controls (p less than 0.05 and p less than 0.01), but higher in alcoholics with a seizure history compared to alcoholics without seizures (p less than 0.05 and p less than 0.001). Five days after cessation of drinking, the amplitude in the alcoholic groups always increased from the admission values (p less than 0.05 and p less than 0.01). By that time, the alcoholics with a history of withdrawal seizures had significantly (p less than 0.05 and p less than 0.01) higher amplitudes than those of the controls or the alcoholics without seizures. Large N1-P2 amplitude during alcohol withdrawal may reflect increased cerebral excitability and contribute to the identification of alcoholics with high risk for withdrawal seizures.