Salsolinol differentially affects mice selected for sensitivity to alcohol

Salsolinol: an Unintelligible and Double-Faced Molecule-Lessons Learned from In Vivo and In Vitro Experiments

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a tetrahydroisoquinoline derivative whose presence in humans was first detected in the urine of Parkinsonian patients on l-DOPA (l-dihydroxyphenylalanine) medication. Thus far, multiple hypotheses regarding its physiological/pathophysiological roles have been proposed, especially related to Parkinson’s disease or alcohol addiction. The aim of this review was to outline studies related to salsolinol, with special focus on in vivo and in vitro experimental models. To begin with, the chemical structure of salsolinol together with its biochemical implications and the role in neurotransmission are discussed. Numerous experimental studies are summarized in tables and the most relevant ones are stressed. Finally, the ability of salsolinol to cross the blood–brain barrier and its possible double-faced neurobiological potential are reviewed.

Revisiting the controversial role of salsolinol in the neurobiological effects of ethanol: old and new vistas

The possible involvement of salsolinol (Sal), an endogenous condensation product of ACD (the first metabolite of ethanol) and dopamine, in the neurochemical basis underlying ethanol action has been repeatedly suggested although it has not been unequivocally established, still being a controversial matter of debate. The main goal of this review is to evaluate the presumed contribution of Sal to ethanol effects summarizing the reported data since the discovery in the 1970s of Sal formation in vitro during ethanol metabolism until the more recent studies characterizing its behavioral and neurochemical effects. Towards this end, we first analyze the production and detection of Sal, in different brain areas, in basal conditions and after alcohol consumption, highlighting its presence in regions especially relevant in regulating ethanol-drinking behaviour and the importance of the newly developed methods to differentiate both enantiomers of Sal which could help to explain some previous negative findings. Afterwards, we review the behavioral and neurochemical studies. Finally, we present and discuss the previous and current enunciated mechanisms of action of Sal in the CNS.

Differential effects of norepinephrine on phosphatidylinositol 4,5-bisphosphate stimulated hydrolysis in brains of mice genetically selected for differences in ethanol sensitivity

The effects of norepinephrine on phosphoinositide turnover were evaluated in five brain regions of the long sleep (LS) and short sleep (SS) mice. These mice were selectively bred for differences in central nervous system sensitivity to ethanol with the LS exhibiting much greater sensitivity to a hypnotic dose of ethanol than the SS, as determined by the ability of the mice to regain their righting reflex. Norepinephrine (10(-3) M, 10(-4) M, and 10(-5) M) significantly increased phosphoinositide turnover in the hippocampus, hypothalamus, locus ceruleus, cerebellum, and cortex within each line of mice. Basal and norepinephrine-stimulated phosphoinositide turnover were significantly higher in the SS mice as compared with the LS mice in the cerebellum and cortex but not the other brain regions. Incorporation of 3H-inositol into 3H-phosphatidylinositols was not different between SS and LS mice in the cerebellum and cortex. The greater norepinephrine-stimulated phosphoinositide turnover in the cerebellum and cortex of the SS versus the LS mice may contribute to the CNS sensitivity to ethanol in these two lines of mice. However, ethanol (500 mM) had no effect on basal or norepinephrine-stimulated phosphoinositide turnover in any of the five brain areas examined in the LS and SS mice.

Thiopental, phenobarbital, and chlordiazepoxide induce the same differences in narcotic reaction as ethanol in long-sleep and short-sleep selectively-bred mice

Hypnotic effects following administration of thiopental, phenobarbital or chlordiazepoxide were evaluated in mice selectively-bred for differential hypnotic sensitivity to ethanol. For every dose employed, except one which had no effect, all three agents induced greater sedation in the ethanol-sensitive Long-Sleep (LS) line than in the ethanol-insensitive Short-Sleep (SS) line. Such findings with regard to the LS and SS lines suggest that the differences in sedative response to ethanol, as well as some barbiturates and benzodiazepines, may be mediated, in part, by a common mechanism. The second experiment showed that age of the subjects can be an important variable influencing hypnotic-induced sleep time. For thiopental, significant line differences occurred only with 150 day old mice, whereas chlordiazepoxide produced differences in 50, 75, 100 and 150 day old mice.

Alpha-methyl-para-tyrosine effects in mice selectively bred for differences in sensitivity to ethanol

The responses of catecholamine systems in long sleep (LS) and short sleep (SS) mice to alpha-methyl-p-tyrosine (AMPT) have been examined. Marked differences were found between LS and SS mice in the dose necessary for maximal brain catecholamine depletion and in the time-course of the catecholamine depletion. Brain catecholamines in the LS mice were depleted by lower doses of AMPT and the levels remained depressed for longer periods of time in this line of mice. These differences may be explained only partially by an increased susceptibility of the LS mice to the hypothermia and toxic effects caused by AMPT administration, as they persist with non-toxic AMPT dosage regimens and under conditions where the degree of hypothermia is comparable in both lines of mice. In addition, there were no differences between the Ki values for the effect of AMPT on the tyrosine hydroxylase from striata of these mouse lines. The primary cause of the heightened response to AMPT in LS mice would appear to be pharmacokinetic in nature, as brain and plasma peak levels of AMPT in LS mice were greater and the levels remained higher for a longer time. The depletion of brain tyrosine by AMPT combined with the lower affinity of the LS striatal tyrosine hydroxylase for the substrate tyrosine may also contribute to the heightened response in LS mice.

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.

Reinterpretation of the literature indicates differential sensitivities of long-sleep and short-sleep mice are not specific to alcohol

This paper reviews the findings and conclusions of the literature pertinent to the Long-Sleep and Short-Sleep selectively-bred lines of mice and challenges the widely-held notion that the selective breeding program was successful in separating alleles for specific sensitivities to just alcohol. Rather, it is argued that these lines of mice were selected for differing activity of a more general process. Recent evidence, as well as reevaluated previous evidence, indicates that Long-Sleep mice are more sensitive to the soporific effects of three major classes of CNS depressants (alcohols, barbiturates, and benzodiazepines), as well as many other anesthesia-inducing compounds (adenosine, chloral hydrate, trichloroethanol, paraldehyde, nitrous oxide, enflurane, and isoflurane). Further, much evidence also supports the conclusion that most of these hypnotic-depressants and anesthetics could exert their soporific influence by a potentiation of GABA activity. The other characteristic of interest in this regard is susceptibility to convulsions. Short-Sleep mice have significantly lower thresholds to both flurothyl-induced and bicuculline-induced convulsions, as well as being more likely to suffer from paroxysms during ethanol withdrawal.

Effect of ethanol on tyrosine hydroxylation in brain regions of long and short sleep mice

The effect of ethanol on the in vivo rate of tyrosine hydroxylation in 6 brain regions was examined in two lines of mice selectively bred for a differential sensitivity to ethanol. The mice are designated long-sleep (LS) and short-sleep (SS) and lose their righting reflex for a duration of 100 minutes (LS) and 13 minutes (SS) following an intraperitoneal dose of ethanol of 4.0 g/kg. DOPA accumulation after NSD-1015 administration was measured in the absence and presence of ethanol (4.0 g/kg, IP) in the periods 5-35 minutes and 85-115 minutes after saline or ethanol. There were no differences between the lines in either basal catecholamine levels or basal tyrosine hydroxylation rates (as measured by DOPA accumulation) in any brain region except the cerebellum, where the norepinephrine content in the SS mice is 33% greater and the tyrosine hydroxylation rate is 25% higher than that in the LS mice. In the presence of ethanol, there was a differential effect on the in vivo tyrosine hydroxylation rate. In the cerebellum of both LS and SS mice there was a decreased rate of tyrosine hydroxylation in the early period after ethanol, but the rate in the cerebellum of SS mice returned to the control value at 85-115 min. At that time, the rate in LS mice is still decreased. In the locus ceruleus, hypothalamus and frontal cortex, ethanol has no effect on the rate of tyrosine hydroxylation in either LS or SS mice during the early period, but ethanol decreases the rate during the later period in the LS mice only.(ABSTRACT TRUNCATED AT 250 WORDS)

Apomorphine effects on behavioral response to ethanol in mice selectively bred for differential sensitivity to ethanol

Two lines of mice selectively bred for differences in response to a hypnotic dose of ethanol were administered apomorphine alone or in combination with ethanol. When administered by itself, apomorphine produced similar dose-dependent depression of locomotor activity and increases in stereotypy in the two lines. Doses of apomorphine (0.5 microM/kg and 2 microM/kg) thought to bind only presynaptic dopamine receptors blocked the slight locomotor activation to 1.5 g/kg ethanol in the ethanol-sensitive Long-Sleep (LS) mice; in the ethanol-insensitive Short-Sleep (SS) mice which show marked activation to all subhypnotic doses of ethanol, these doses of apomorphine only attenuated the activation. A higher apomorphine dose (8 microM/kg) antagonized the locomotor depressant effects of 2.0 and 2.5 g/kg of ethanol in LS mice but did not alter the shape of the SS ethanol dose response curve for locomotor activity. Apomorphine (2 and 8 microM/kg) potentiated ethanol-induced loss of the righting reflex in LS mice in a dose dependent fashion, but did not alter this soporific effect of ethanol in SS mice. These findings extend the data base suggesting a role for dopamine both in the mechanism(s) differentiating the LS and SS mice and the stimulant and intoxicating properties of ethanol.

Effects of ethanol and salsolinol on catecholamine function in LS and SS mice

Long Sleep (LS) and Short Sleep (SS) mice differ in duration of ethanol-induced sleep time because of differences in brain sensitivity to the depressant effects of alcohols. These lines of mice also differ in their sensitivity to salsolinol, the condensation product of acetaldehyde with dopamine. Some of ethanol's acute effects may be due to salsolinol interactions with catecholamine systems. In the present study, the half-lives of salsolinol were found to be 12.8 min (LS) and 12.3 min (SS). Salsolinol administration resulted in a decrease in brain norepinephrine content in LS but not SS mice. Dopamine levels were not altered by salsolinol. Ethanol or salsolinol, in vitro, inhibited dopamine uptake by striatal synaptosomes. The IC50 values for ethanol were 491 mM (LS) and 514 mM (SS), and for salsolinol, 300 microM (SS). Thus, the mouse line which is most sensitive to the behavioral effects of salsolinol is also most sensitive to salsolinol's effects on norepinephrine levels and inhibition of dopamine uptake. However, much higher concentrations are required to alter dopamine uptake in vitro than are required to alter behavior in vivo.

Alcohol and morphine induced hypothermia in mice selected for sensitivity in ethanol

We have used changes in body temperature as an index of responsiveness to alcohol and morphine in mice selectively bred for differential sensitivity to ethanol. In agreement with other laboratories, we found that mice which show longer duration of loss of righting reflex following hypnotic doses of ethanol (long sleep; LS) also showed greater loss in body temperature following subhypnotic doses of ethanol than did the less sensitive short sleep (SS) mice. This effect was dose dependent in both lines. In contrast, SS mice were more sensitive than LS mice to the hypothermic effects of morphine, although the difference was only evident 30 min after morphine administration. Naloxone attenuated morphine induced hypothermia in mice of both genotypes, but attenuated alcohol induced hypothermia only in SS mice. Thus, SS mice may be more sensitive to an opiate agonist and an antagonist, at least as indexed by changes in body temperature, and may prove to be a useful population for evaluating both alcohol-opiate interactions and genetic differences in opiate responsiveness.

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.

Ethanol-induced changes in tyrosine hydroxylase activity in brains of mice selectively bred for differences in sensitivity to ethanol

The effects of ethanol on tyrosine hydroxylase (TH) activity in five brain areas were analyzed in two lines of mice selectively bred for their differences in sensitivity to ethanol. Following a 4.1 g/kg dose of ethanol, intraperitoneally, short sleep (SS) mice lose their righting reflex for a duration of 20 minutes and long sleep (LS) mice fail to regain their righting reflex until 120 minutes. A significant increase in TH activity occurred in the striatum, locus coeruleus and frontal cortex in both lines of mice approximately 25 minutes following ethanol administration. A decrease in TH activity occurred in the substantia nigra of SS mice at 5 minutes following ethanol administration. However, there was no significant differences in TH activity in any of these four brain regions between LS and SS mice at any time following ethanol administration. In contrast, hypothalamic TH activity was significantly increased at 25 minutes in the SS mice and at 125 minutes in the LS mice following the administration of ethanol, times which coincided with the regaining of the righting reflex. These data suggest that activation of TH in the hypothalamus of LS and SS mice in response to ethanol is associated with arousal from ethanol induced narcosis.

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.

Withdrawal-like signs induced by a single administration of ethanol in mice that differ in ethanol sensitivity

These experiments studied changes produced by a hypnotic dose of ethanol in the LS and SS lines of mice, which differ in ethanol sensitivity. In the first experiment, animals were injected either with ethanol or saline, and activity and seizure susceptibility measured 7-9 h later when blood levels of ethanol would have reached zero. Ethanol-treated mice of both genetic lines were less active in an open field test and more susceptible to clonic convulsions induced by flurothyl than saline-injected controls. There was no difference in the magnitude of these changes in the two lines. In the control condition SS (short-sleep) mice were more active than LS (long-sleep) mice, and more susceptible than LS mice to myoclonic but not to clonic seizures. The effect of the ethanol injection on body temperature was evaluated in separate groups of animals. LS mice showed a more pronounced hypothermia than SS mice when temperature was measured 2 h after injection. Six hours after injection, SS mice exhibited a small but statistically significant overshoot in temperature, after which they again became hypothermic with respect to controls; hyperthermia was not observed in LS animals.

Effects of gamma-butyrolactone, amphetamine, and haloperidol in mice differing in sensitivity to alcohol

Gamma-butyrolactone (GBL) induced longer loss of righting reflex in mice (LS-line) selectively bred for greater sensitivity to ethanol than in less sensitive SS-line mice. GBL also induced a three-fold greater increase of brain dopamine levels in LS than in SS mice. Among three inbred strains, GBL-induced loss of righting reflex was greater in BALB/c, and greater in DBA/2 than in C57BL/6 mice. A low dose of GBL produced biphasic effects on locomotor activity. Both an initial depressant action and a later increase in activity were greater in LS than in SS mice. These GBL effects on activity were modified in a genotype-dependent fashion by amphetamine. Results of these experiments as well as greater catalepsy-inducing properties of haloperidol in SS mice suggest that genotypic influences on motor reactivity to ethanol may be modeled by GBL effects on brain dopamine systems.

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.

Genetics and alcoholism simulacra

The author explores the role of genetic techniques in developing simulacra for eventual use as models in alcoholism research.

Genetics and ethanol tolerance

This paper reviews some of the research on genetic bases of individual differences in ethanol tolerance of mice conducted at the Institute for Behavioral Genetics and at its predecessor laboratory at the University of California, Berkeley. Tolerance is, of course, a complex concept. Theoretical distinctions are made between tachyphylaxis and more slowly acquired tolerance and between dispositional and tissue tolerance. Pragmatically, a variety of measures (such as locomotor activity, sleep time, hypothermia) can be used to define these processes, and the different indices may yield quite different results even when they presumably indicate the same process. It is clear that an understanding of genetic influence in "ethanol tolerance" will require wide sampling of this complex domain. The work described here represents only a beginning, but it may illustrate the general approaches that are available for addressing the issue.

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.

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.