Potentiation of ethanol narcosis by dopamine- and l-DOPA-based isoquinolines

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

The route and significance of endogenous synthesis of alkaloids in animals

There is now substantial evidence that several TIQs and beta-carbolines are present in vivo and increase during certain pathological conditions. It still remains to be determined, however, precisely what roles they play in endogenous functions and whether or not they are critical for the expression of these pathological conditions. Accumulating biochemical information continues to support the notion that these compounds can act as false transmitters. The exciting new findings, which will certainly receive a great deal more attention, concern the interaction of some of the beta-carbolines with the benzodiazepine receptor. Determining if a beta-carboline is an endogenous receptor ligand will attract further research interest on the theoretical and specifically clinically-directed levels. Biochemical, morphological, and behavioral data indicate that some of the condensation products can act as neurotoxins. Very few experiments have included an examination of long-term effects of exposure to one of these alkaloids, so the amount of information on this issue is limited. Chronic rather than acute administration of an alkaloid is more likely to mimic the pathological states in which these compounds are hypothesized to play a role. Biochemically, both the dopaminergic and serotonergic systems have been shown to be affected by chronic treatments with certain alkaloids. Progressive and long-term behavioral alterations also have been reported. Such changes may reflect an adaptation to an increase or decrease in activity of particular systems or a neurotoxic action.

Ability of 3-carboxysalsolinol to produce ethanol-like discrimination in rats

The purpose of the present study was to investigate the possible generalization to 3-carboxysalsolinol (3C-SAL) in a group of rats trained to discriminate a low dose of ethanol (200 mg/kg IP) from the nondrug condition and in antoher group trained to discriminate 0.16 mg/kg IP apomorphine (AP) from the nondrug condition using a drug discrimination paradigm. In test sessions, ED50 for ethanol was 52.0 mg/kg and ED50 for AP was 0.01 mg/kg. In the ethanol-trained rats, 1.8 mg/kg 3C-SAL produced drug responses. In the AP-trained rats, 200 mg/kg ethanol produced drug responses whereas 1.8 mg/kg 3C-SAL produced only a partial drug response. The results are in harmony with the hypothesis that salsolinol in the central nervous system of the rat may be responsible for the discriminability of ethanol. The possible involvement of dopaminergic systems is discussed.

Interaction of salsolinol and tetrahydropapaveroline with catecholamines

Formation of aberrant amine metabolites, tetrahydroisoquinolines (TIQs) has been hypothesized to account for some of the effects of ethanol. These compounds have been shown to interact with catecholamine neurons in a variety of ways by in vitro techniques. The most interesting facet of these alkaloids, however, is the fact that they cause an increase in preference for and voluntary consumption of ethanol when administered into the ventricle of the rat in exceedingly low amounts. Investigation of the neurochemical effects in vivo of two of the TIQs tetrahydropapaveroline (THP) and salsolinol, indicates that they influence several aspects of presynaptic catecholamine function when examined acutely. The mechanism of action responsible for the radical long-lasting behavioral effects of these substances has yet to be defined.

Putative role of isoquinoline alkaloids in alcoholism: a link to opiates

Although the isoquinoline hypothesis has stimulated and even tantalized the scientific inquiry of a small number of investigators, it has been an area of widespread controversy. For the most part, until recently, alcohol researchers would ascribe very little importance to the role played by insoquinolines in alcohol actions or in the disease state known as alcoholism. To most, there was adequate evidence that these condensation amines had potent pharmacologic properties but little was known about their biochemical and behavioral interaction with ethanol or opiates. As pointed out here, there is an increasing amount of evidence that indicates the putative role of isoquinolines as regulators of alcohol dependence. There is even evidence that suggests a possible "link" to opiates. If this turns out to be the case, then it is rational to consider the possibility that when one imbibes alcohol a central opiate-like substance is, in essence, produced. It would appear that the sum total of evidence to date supports the notion that there are common territories between the two highly addictive classes of drugs--alcohol and opiates. Although still not definite, future studies may well confirm the intermediacy of the TIQ compounds.

The synaptic properties of some tetrahydroisoquinoline alkaloids

The ability of TIQs to alter the synaptic properties of catecholamines by interacting with receptor, transport, or metabolic mechanisms has been demonstrated.

Analgesic effects of 3-carboxysalsolinol alone and in combination with morphine

A biphasic dose-response pattern is generated by the isoquinoline, 3-carboxysalsolinol, in analgesia tests conducted in mice. Carbidopa pretreatment enhances this effect, as well as the morphine-induced analgesic increase by 3-carboxysalsolinol. Naloxone blockade of all of these responses suggests an interaction of the alcohol-based isoquinoline with central opiate receptors.

Peyote, a potential ethnopharmacologic agent for alcoholism and other drug dependencies: possible biochemical rationale

The authors examine folk psychiatry among Native American Church members from an enthnopharmacologic viewpoint. Alcohol and opiate abuse among Indian and non-Indian are presented in case histories proving to be asymptomatic under Indian guidance and through participation in the peyote ritual. The biochemical alkaloids common in the peyote cactus, rather than just the psychoactive substances (mescaline), are purported to be pharmacologically similar to the neuroamine-derived alkaloids found in the brain during alcohol intoxification. Evidence is reviewed that points out possible common features of alcohol and opiate dependence leading to the speculation for a common mode of treatment may reside in plants rich in isoquinoline alkaloids.

Effects of salsolinol on smooth muscle responses to various biogenic amines

Isolated smooth muscle tissues from rats, guinea pigs and rabbits were used to investigate pharmacological effects of salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline). By itself, salsolinol did not produce any profound or sustained sympathomimetic or 5-hydroxytryptamine-like activity in the concentrations used in these experiments (7.7 and 77 muM). Salsolinol was found to antagonize the contraction of the rabbit aorta induced by noradrenaline but did not affect the adrenaline-induced relaxation of the guinea pig tracheal chain. On both the rat fundus and oestrus rat uterus, salsolinol exhibited significant anti-5-hydroxytryptamine activity but responses of these tissues to acetylcholine and histamine remained unaffected, indicating that the action was not non-specific. These results suggest that in vivo formation of salsolinol after ethanol ingestion could produce significant pharmacological effects.