The molecular and cellular actions of three classes of abused drugs--opiates, psychostimulants, and ethanol--are reviewed in the context of behavioral studies of drug dependence. The immediate effects of drugs are compared to those observed after long-term exposure. A neurobiological basis for drug dependence is proposed from the linkage between the cellular and behavioral effects of these drugs.

https://science.sciencemag.org/content/sci/242/4879/715.full.pdf

Cellular and molecular mechanisms of drug dependence.

General anaesthetics are much more selective than is usually appreciated and may act by binding to only a small number of targets in the central nervous system. At surgical concentrations their principal effects are on ligand-gated (rather than voltage-gated) ion channels, with potentiation of postsynaptic inhibitory channel activity best fitting the pharmacological profile observed in general anaesthesia. Although the role of second messengers remains uncertain, it is now clear that anaesthetics act directly on proteins rather than on lipids.

Molecular and cellular mechanisms of general anaesthesia

The ion current induced by the glutamate receptor agonist N-methyl-D-aspartate (NMDA) in voltage-clamped hippocampal neurons was inhibited by ethanol (EtOH). Inhibition increased in a concentration-dependent manner over the range 5 to 50 mM, a range that also produces intoxication. The amplitude of the NMDA-activated current was reduced 61 percent by 50 mM EtOH; in contrast, this concentration of EtOH reduced the amplitude of current activated by the glutamate receptor agonists kainate and quisqualate by only 18 and 15 percent, respectively. The potency for inhibition of the NMDA-activated current by several alcohols is linearly related to their intoxicating potency, suggesting that alcohol-induced inhibition of responses to NMDA receptor activation may contribute to the neural and cognitive impairments associated with intoxication.

/pdf/ethanol-inhibits-nmda-activated-ion-current-in-hippocampal-1mj68i2bgf.pdf

Ethanol inhibits NMDA-activated ion current in hippocampal neurons

Volatile anaesthetics have historically been considered to act in a nonspecific manner on the central nervous system. More recent studies, however, have revealed that the receptors for inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are sensitive to clinically relevant concentrations of inhaled anaesthetics. The function of GABA(A) and glycine receptors is enhanced by a number of anaesthetics and alcohols, whereas activity of the related GABA rho1 receptor is reduced. We have used this difference in pharmacology to investigate the molecular basis for modulation of these receptors by anaesthetics and alcohols. By using chimaeric receptor constructs, we have identified a region of 45 amino-acid residues that is both necessary and sufficient for the enhancement of receptor function. Within this region, two specific amino-acid residues in transmembrane domains 2 and 3 are critical for allosteric modulation of both GABA(A) and glycine receptors by alcohols and two volatile anaesthetics. These observations support the idea that anaesthetics exert a specific effect on these ion-channel proteins, and allow for the future testing of specific hypotheses of the action of anaesthetics.

Sites of alcohol and volatile anaesthetic action on GABA(A) and glycine receptors.

Ethosomes — novel vesicular carriers for enhanced delivery: characterization and skin penetration properties

Ethanol in vitro increased the fluidity of spin-labeled membranes from normal mice. Membranes from mice that had been subjected to long-term ethanol treatment were relatively resistant to this fluidizing effect. The data suggest that the membranes themselves had adapted to the drug, a novel form of drug tolerance.

https://science.sciencemag.org/content/sci/196/4290/684.full.pdf

Drug tolerance in biomembranes: a spin label study of the effects of ethanol

The effects of ethanol on membrane fluidity at 37° have been assessed by a sensitive electron paramagnetic resonance technique. Erythrocyte and brain membranes from DBA/2J mice were spin-labeled with 5-doxylstearic acid ( N -oxyl-49,49-dimethyloxazolidine derivative of 5-ketostearic acid). The molecular motion of the spin label was measured from the EPR spectrum by determining the order parameter S , an index of membrane fluidity. The fluidity of both erythrocyte and synaptosomal membranes was greater than that of myelin but less than that of mitochondrial membranes. The addition of low concentrations (0.02 or 0.04 M) of ethanol in vitro increased fluidity in erythrocyte, mitochondrial, and synaptosomal membranes. This fluidizing effect of ethanol was dose-related up to 0.35 M in all the membranes except myelin. These data suggest that nonlethal concentrations of ethanol may increase membrane fluidity in vivo .

Effects of low concentrations of ethanol on the fluidity of spin-labeled erythrocyte and brain membranes.

Intoxicating blood levels of ethanol are maintained for several days in mice housed in an atmosphere of ethanol vapor. On removal from the alcohol, all the mice develop withdrawal signs. The signs can be graded to indicate the time course and intensity of the withdrawal reaction.

https://science.sciencemag.org/content/sci/172/3980/288.full.pdf

Alcohol Dependence Produced in Mice by Inhalation of Ethanol: Grading the Withdrawal Reaction

Alcohol was administered to mice by inhalation, over periods of 1 to 13 days. Daily injections of pyrazole stabilized blood alcohol levels and thus maintained a continuous state of intoxication. The empirical relationship between alcohol concentration in the inspired air and that in the blood was determined. A syndrome of withdrawal signs developed when the mice were removed from the vapor chamber. It could be graded by scoring a characteristic convulsion elicited by handling the animals. This score presumably represents the extent of physical dependence. The intensity of withdrawal convulsions increased with duration of exposure to alcohol vapor and with blood alcohol levels. Single episodes of intoxication produced degrees of physical dependence that varied with the total dose of alcohol (blood alcohol level X days). Mild withdrawal signs appeared after a single injection of alcohol, with or without pyrazole treatment. The signs began to appear when the mice were still intoxicated. A dose of alcohol sufficient to produce a moderate degree of physical dependence did not affect the total activity of liver alcohol dehydrogenase. Liver catalase activity was depressed by pyrazole in vivo , but not in vitro .

Dora B. Goldstein

Papers

Drug tolerance in biomembranes: a spin label study of the effects of ethanol

Effects of low concentrations of ethanol on the fluidity of spin-labeled erythrocyte and brain membranes.

Alcohol Dependence Produced in Mice by Inhalation of Ethanol: Grading the Withdrawal Reaction

Relationship of alcohol dose to intensity of withdrawal signs in mice

Increased cholesterol content of erythrocyte and brain membranes in ethanol-tolerant mice