Alcohol drinking in the rat induced by acute intra-cerebral infusion of two tetrahydroisoquinolines and a beta-carboline

Linking Ethanol-Addictive Behaviors With Brain Catecholamines: Release Pattern Matters

Using a variety of animal models that simulate key features of the alcohol use disorder (AUD), remarkable progress has been made in identifying neurochemical targets that may contribute to the development of alcohol addiction. In this search, the dopamine (DA) and norepinephrine (NE) systems have been long thought to play a leading role in comparison with other brain systems. However, just recent development and application of optogenetic approaches into the alcohol research field provided opportunity to identify neuronal circuits and specific patterns of neurotransmission that govern the key components of ethanol-addictive behaviors. This critical review summarizes earlier findings, which initially disclosed catecholamine substrates of ethanol actions in the brain and shows how the latest methodologies help us to reveal the significance of DA and NE release changes. Specifically, we focused on recent optogenetic investigations aimed to reveal cause-effect relationships between ethanol-drinking (seeking and taking) behaviors and catecholamine dynamics in distinct brain pathways. These studies gain the knowledge that is needed for the better understanding addiction mechanisms and, therefore, for development of more effective AUD treatments. Based on the reviewed findings, new messages for researches were indicated, which may have broad applications beyond the field of alcohol addiction.

Elucidating the biological basis for the reinforcing actions of alcohol in the mesolimbic dopamine system: the role of active metabolites of alcohol

The development of successful pharmacotherapeutics for the treatment of alcoholism is predicated upon understanding the biological action of alcohol. A limitation of the alcohol research field has been examining the effects of alcohol only and ignoring the multiple biological active metabolites of alcohol. The concept that alcohol is a "pro-drug" is not new. Alcohol is readily metabolized to acetaldehyde within the brain. Acetaldehyde is a highly reactive compound that forms a number of condensation products, including salsolinol and iso-salsolinol (acetaldehyde and dopamine). Recent experiments have established that numerous metabolites of alcohol have direct CNS action, and could, in part or whole, mediate the reinforcing actions of alcohol within the mesolimbic dopamine system. The mesolimbic dopamine system originates in the ventral tegmental area (VTA) and projects to forebrain regions that include the nucleus accumbens (Acb) and the medial prefrontal cortex (mPFC) and is thought to be the neurocircuitry governing the rewarding properties of drugs of abuse. Within this neurocircuitry there is convincing evidence that; (1) biologically active metabolites of alcohol can directly or indirectly increase the activity of VTA dopamine neurons, (2) alcohol and alcohol metabolites are reinforcing within the mesolimbic dopamine system, (3) inhibiting the alcohol metabolic pathway inhibits the biological consequences of alcohol exposure, (4) alcohol consumption can be reduced by inhibiting/attenuating the alcohol metabolic pathway in the mesolimbic dopamine system, (5) alcohol metabolites can alter neurochemical levels within the mesolimbic dopamine system, and (6) alcohol interacts with alcohol metabolites to enhance the actions of both compounds. The data indicate that there is a positive relationship between alcohol and alcohol metabolites in regulating the biological consequences of consuming alcohol and the potential of alcohol use escalating to alcoholism.

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.

A re-evaluation of the role of tetrahydropapaveroline in ethanol consumption in rats

The role of tetrahydropapaveroline (THP), a condensation product of a dopaldehyde with dopamine, in the regulation of alcohol consumption was investigated. In the first experiment, rats received intraventricular injections of either racemic THP hydrobromide (0.65 or 1.3 microg/microl), R-(+)-THP (0.66 or 1.4 microg/microl), or an equal volume of vehicle. The lower doses of both (+/-)-THP and (+)-THP significantly increased volitional alcohol intake. For the racemic compound, the increase was significant at 7-13% concentrations. The R-(+)-enantiomer increased consumption at 4-11 and 15-20% concentrations of ethanol. The higher doses of both compounds did not significantly alter alcohol preference. A second experiment evaluated the chronic effect of THP delivered subcutaneously via osmotic minipump. Animals receiving THP (0.1, 0.5, 1.0, 2.0, and 4.0 mg/ml) did not differ in their alcohol intake, compared to vehicle-treated controls. Whether or not endogenously formed THP participates in the etiology of alcohol addiction remains unclear. Nonetheless, there are few known compounds that induce a preference for unsweetened alcohol solutions over water in laboratory animals.

The role of opioid-dopamine interactions in the induction and maintenance of ethanol consumption

1. Alcohol is one of the most widely used recreational drugs, but also one of the most widely abused, causing vast economic, social and personal damage. 2. Several animal models are available to study the reinforcing mechanisms that are the basis of the abuse liability of ethanol. Innate differences in opioid or dopamine neurotransmission may enhance the abuse liability of ethanol, as indicated by animal and human studies. 3. Opioid antagonists have been shown to be effective, both experimentally and clinically, in decreasing ethanol consumption, presumably since ethanol induces the release of endogenous opioid peptides in vivo. However, ethanol may also stimulate the formation of opiate-like compounds, which could interact with opioid (or dopamine) receptors. Ethanol may cause changes in neurotransmission mediated via opioid receptors that determines whether alcohol abuse is more or less likely. 4. Ethanol appears to facilitate dopamine release by increasing opioidergic activity, disinhibiting dopaminergic neurons (by inhibition of GABAergic neurotransmission) via mu-opioid receptors in the ventral tegmental area (VTA) and delta-opioid receptors in the nucleus accumbens (NAcc). The effects of ethanol would be antagonised by presynaptic kappa-opioid receptors present on dopaminergic terminals in the NAcc. 5. Mesolimbic dopamine release induced by ethanol consumption seems to indicate ethanol-related stimuli are important, focussing attention on and enabling learning of the stimuli. However, studies indicate that there are redundant pathways, and neural pathways 'downstream' of the mesolimbic dopamine system, which also enable the reinforcing properties of ethanol to be mediated.

The quantitative determination of R- and S-salsolinol in the striatum and adrenal gland of rats selectively bred for disparate alcohol drinking

To explore the hypothesis that endogenous 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol) might be involved in the etiology of alcoholism, its concentration was determined in the striatum and adrenal gland of rats bred selectively for disparate alcohol drinking. The alcohol-naive alcohol-preferring (P) and the high-alcohol-drinking (HAD) lines of rats demonstrated significantly lower striatal and adrenal salsolinol content when compared with the alcohol-non-preferring (NP) and the low-alcohol-drinking (LAD) lines. In the P-line of rats, 4 weeks of free-choice alcohol drinking had no significant effect on striatal salsolinol levels, although adrenal levels of salsolinol were significantly higher. The salsolinol assayed in the striatum of all lines of rats occurred as a racemic mixture of enantiomers that was unchanged following 4 weeks of alcohol exposure. Unlike striatal tissue, the adrenals of alcohol naive P-rats contained significantly more S- than R-salsolinol (ratio S/R = 83/17) and alcohol consumption resulted in the formation of a nearly racemic mixture of enantiomers. These results suggest a role for genetic factors in the formation of endogenous salsolinol and its potential regulation by short-term alcohol intake.

Citalopram as an inhibitor of voluntary ethanol intake in the male rat

Psychological dependence was induced in rats by a 1-year intermittent exposure to intoxicating doses of ethanol, and recorded by the rat's ability to later take the same dose of ethanol independent of the offered concentration. Citalopram (10 or 40 mg/kg/day) was given for 3 weeks with ethanol available only the first and the last day; 10 mg/kg had no effect. On the first treatment day 40 mg/kg decreased ethanol intake. On the last treatment day 40 mg/kg had no effect. The following week the ethanol intake was higher than before the treatment in the 40 mg/kg group. During the four posttreatment weeks the ethanol intake of the 40 mg/kg group dropped significantly. Citalopram was retested 18 weeks after the first treatment during 1 week, with continuous access to ethanol; 10 mg/kg had no effect and 40 mg/kg decreased ethanol intake at day 1, reaching a minimum in day 3. A tolerance to this effect was seen at the end of the week. Thus, in this model an acute dose of citalopram can decrease ethanol intake, but tolerance to this effect develops when citalopram is given both with and without access to ethanol.

Drinking patterns in genetic low-alcohol-drinking (LAD) rats after systemic cyanamide and cerebral injections of THP or 6-OHDA

A key question related to the role of acetaldehyde and aldehyde adducts in alcoholism concerns their relationship to the genetic mechanisms underlying drinking. Experimentally, the low-alcohol-drinking (LAD) rat represents a standard rodent model having a strong aversion to alcohol. In these experiments, preferences for water vs. alcohol, offered in concentrations from 3% to 30%, were determined over 10 days in adult LAD rats (N = 6 per group). Then a saline vehicle or either 10 or 20 mg/kg of the aldehyde dehydrogenase (AIDH) inhibitor, cyanamide, was injected s.c. twice daily for 3 days. Secondly, either 0.5 or 1.0 microg of tetrahydropapaveroline (THP) was infused i.c.v. twice daily for 3 days in LAD rats (N = 8) and, as a genetic control, THP also was infused identically in Sprague-Dawley (SD) rats (N = 8). The results showed that the lower and higher doses of cyanamide augmented alcohol intakes in 33% and 50% of the LAD rats, respectively, with the patterns of drinking resembling that of genetic high-alcohol-drinking HAD or P rats. Although i.c.v. infusions of THP had little effect on alcohol preference of LAD rats, alcohol drinking was enhanced significantly in the SD rats. In a supplementary study, 200 microg of 6-hydroxydopamine (6-OHDA) also was infused i.c.v. in LAD rats (N = 7) on two consecutive days; no change occurred in the characteristic aversion to alcohol. These findings suggest that in certain individuals, a perturbation in the synthesis of AIDH can modify the genetically based aversion to alcohol, thus precipitating the liability for alcoholism. In that neither THP nor 6-OHDA lesioning exerted any effect on the genetic nondrinking LAD animal suggests that an unknown endogenous factor in the brain must underlie the cyanamide-induced shift to alcohol preference. We conclude that the genetic elements that normally prevent the progression to addictive drinking in most individuals appear to be invariant and irreversible.

N-methyl-(R)salsolinol as a dopaminergic neurotoxin: from an animal model to an early marker of Parkinson's disease

A dopamine-derived 1(R), 2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydrosioquinoline [N-methyl-(R)salsolinol] was found to occur enantioselectively in human brain. This isoquinoline induced parkinsonism in rat after injection in the striatum, and the behavioral, biochemical and pathological changes were very similar to those in Parkinson's disease. N-Methyl-(R)salsolinol depleted dopamine neurons in the rat substantia nigra without necrotic tissue reaction, which may be due to the apoptotic death process, as proved by its induction of DNA damage in dopaminergic neuroblastoma SH-SY5Y cells. N-Methyl-(R)salsolinol was found to increase significantly in the cerebrospinal fluid of parkinsonian patients. All these results suggest that N-methyl-(R)salsolinol may be an endogenous neurotoxin to cause Parkinson's disease and the enzymes involved in its biosynthesis and catabolism may be endogenous factors in the pathogenesis of this disease.

Formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines in human urine

Human urine samples were examined for the occurrence of formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines generated by condensation of the methanol oxidation product with biogenic amines. Positive results were obtained for the tryptamine condensation product 1,2,3,4-tetrahydro-beta-carboline and the serotonine condensation product 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline as well as for the condensation products with tyramine, dopamine, adrenaline and noradrenaline 1,2,3,4-tetrahydroisoquinoline, 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, 4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, and the metabolite 6-methoxy-7-hydroxy-1,2,3,4-tetrahydroisoquinoline. Negative results were obtained for N-methyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-1,2,3,4-tetrahydro-beta-carboline, 6-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in samples of chronic alcoholics as well as in the urine of healthy volunteers. No correlation between alcohol ingestion or state of alcoholization could be demonstrated.

Dopamine-derived endogenous 1(R),2(N)-dimethyl-6,7-dihydroxy- 1,2,3,4-tetrahydroisoquinoline, N-methyl-(R)-salsolinol, induced parkinsonism in rat: biochemical, pathological and behavioral studies

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal) and related compounds were examined for their selective neurotoxicity to dopamine neurons by injection into the rat striatum. Among salsolinol analogs examined, only N-methyl-(R)- salsolinol (NM(R)Sal) induced behavioral changes very similar to those in Parkinson's disease: hypokinesia, stiff tail, limb twitching at rest and postural abnormality. Biochemical analysis showed that after NM(R)Sal injection, NM(R)Sal itself and its oxidation product, 1-2-dimethyl-6,7-dihydroxyisoquinolinium ion (DMDHIQ+) accumulated in the striatum, and also in the substantia nigra definite amount of DMDHIQ+ was detected. Dopamine and noradrenaline were reduced in the striatum and more markedly in the substantia nigra, whereas serotonin and its metabolite were not affected. Morphological analysis revealed selective reduction of tyrosine hydroxylase (TH)-containing neurons in the substantia nigra after continuous NM(R)Sal administration in the striatum. These results demonstrate the selective cytotoxicity of NM(R)Sal to the dopamine neurons in the substantia nigra, and the possible involvement of this 6,7-dihydroxy-isoquinoline in the pathogenesis of Parkinson's disease is discussed.

Determination of (R)- and (S)-salsolinol sulfate and dopamine sulfate levels in plasma of nonalcoholics and alcoholics

We have developed a new method to determine free as well as sulfoconjugated salsolinol (SAL), separated into both enantiomers, and free and sulfoconjugated dopamine in human blood plasma. Among the group of nonalcoholics (R)-SAL (mean +/- SEM: 0.24 +/- 0.07 ng/ml) was found in all blood samples and (S)-SAL in 1 out of 20 (0.08 ng/ml). Ethanol loading induced a rise of both enantiomers as well as of dopamine whereby (S)-SAL was detected in the plasma of 13 subjects only [(R)-SAL: 0.79 +/- 0.24 ng/ml; (S)-SAL: 0.49 +/- 0.15 ng/ml; DA: 8.84 +/- 0.75 ng/ml]. The later finding favors the notion of an enzymatic formation of (S)-SAL. In alcoholics, (R)-SAL and (S)-SAL were elevated at the day of admission for detoxification [(R)-SAL: 0.65 +/- 0.82 ng/ml; (S)-SAL: 0.35 +/- 0.05 ng/ml] and normalized after several months, suggesting intoxication marker characteristics [month 6: (R)-SAL: 0.24 +/- 0.14 ng/ml; (S)-SAL: 0.20 +/- 0.05 ng/ml]. Patients with alcoholic parents had lowered (R)-SAL and (S)-SAL levels compared with family history negative alcoholics, suggesting genetic association of disturbance of the SAL biosynthesis and alcoholism. Among the personality traits, suicidality was linked with low (R)-SAL and (S)-SAL concentrations in contrast to novelty seeking, impulsivity, and harm avoidance scores. The scores on the self-rating anxiety scale correlated positive with (R)-SAL. These findings suggest trait marker characteristics of salsolinol.

Increased alcohol intake in low alcohol drinking rats after chronic infusion of the beta-carboline harman into the hippocampus

Harman (1-methyl-beta-carboline) has been shown to induce volitional drinking of ethyl alcohol in the rat. The purpose of this study was to examine the long-term effect of sustained delivery of harman into the dorsal hippocampus on the subsequent preference for alcohol in the genetically bred low alcohol drinking (LAD) rat. The individual pattern of preference for alcohol was first determined following a standard 3-30% alcohol self-selection test for 10 days. Thereafter, a cerebral cannula for constant infusion was implanted stereotaxically into the dorsal hippocampus. The cannula was attached to an osmotic minipump implanted subcutaneously, which was filled with either an artificial cerebrospinal fluid (CSF) vehicle or harman. Harman was delivered at a rate of 1.0 or 3.0 micrograms/h (i.e., 5.5 or 16.5 nmol/h, respectively) for a period of 14 days. Four days after surgery, the rats underwent a second 3-30% alcohol preference test for 10 days. Both doses of harman induced a threefold increase in the voluntary consumption of alcohol, expressed as g/kg per day. This effect of the beta-carboline seems to be specific for ethanol because its intake by the LAD rats was increased significantly only when concentrations from 11% to 30% were presented. Harman also enhanced the daily intake of food in a dose-dependent manner, but did not affect body weights or the volumes of water and total fluid consumed. These results, thus, demonstrate that the long-term exposure of hippocampal neurons to harman induces a preference for high concentrations of alcohol even in a line of rats lacking such a genetic predisposition.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydroisoquinolines in human urine

A gas chromatographic-mass spectrometric method has been developed for the identification of 1,2,3,4-tetrahydroisoquinoline and six metabolites extracted from urine in the picogram range. The derivatization procedure for the substances, formed by reaction of formaldehyde with biogenic amines, employs propionic anhydride and can take place in aqueous medium. In this way artificial formation of these compounds via condensation of biogenic amines with aldehydes or alpha-keto acids during the work-up procedure is eliminated. The procedure results in hydrophobic compounds, which are quantitatively extractable by liquid-liquid extraction with organic solvents. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydro-beta-carbolines in human urine

A gas chromatographic-mass spectrometric method for the identification of 1,2,3,4-tetrahydro-beta-carboline and four metabolites extracted from urine is described. In a first step the substances, formed by reaction of formaldehyde with biogenic amines, were derivatized in aqueous solution with methyl chloroformate to eliminate an artificial formation of these compounds via condensation of endogenous indole ethylamines with aldehydes or alpha-keto acids during the work-up procedure. This initial derivatization formed stable hydrophobic compounds and improved the extractability for a liquid-liquid extraction. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns. The method can identify these compounds in the picogram range.

Age dependent development of ethanol drinking in rats after inhibition of aldehyde dehydrogenase

The purpose of this experiment was to determine the temporal characteristics associated with the age-related development of volitional consumption of ethanol induced by the pharmacological inhibition of aldehyde dehydrogenase (AlDH). To induce preference for ethanol, the AlDH inhibitor, cyanamide, was administered to male Sprague-Dawley rats which were 30 days of age. Cyanamide (n = 8) was injected subcutaneously twice daily in a dose of 10 mg/kg over a period of 3 days while the control group (n = 6) received the saline vehicle solution according to the same schedule. Then at 50, 70, 90, and 110 days of age, both groups of rats were given a standard 11-day test of preference for water versus ethanol offered in concentrations ranging from 3% through 30%. The results showed that at 70 days of age the preference for ethanol increased above the level of the 50-day test in terms of absolute g/kg intakes and proportion of ethanol to water consumed over the lower range of 3% through 15% concentrations. During the tests at 90 and 110 days of age, the cyanamide-treated rats further increased their preference for ethanol significantly over the levels at the 70-day test in terms of both g/kg and proportional intakes. The pattern of drinking of ethanol offered in the higher concentrations of 25% and 30% was unrelated to the age of the rats and the overall intakes were significantly higher than those of the lower concentrations. These findings demonstrate that the enzymatic inhibition of AlDH systematically acts in a delayed fashion to shift the pattern of preference for ethanol which is contingent on the maturation of the animal. In this instance, the volitional intake of ethanol in the cyanamide-treated rats reached its maximal level by 90-110 days of age. It is proposed that an endocrine mechanism involved in gonadal maturation may function in the intense shift in alcohol drinking.

Anatomical "circuitry" in the brain mediating alcohol drinking revealed by THP-reactive sites in the limbic system

The involvement of aldehyde adducts in the etiology of alcoholism continues to be supported by a number of experimental findings. These metabolites are synthesized endogenously from a condensation reaction of a biogenic aldehyde with a catechol- or indole-amine and act in the brain to augment or suppress the drinking of ethyl alcohol. When given by the intracerebroventricular route in an animal which does not prefer alcohol, certain tetrahydro-isoquinolines and beta-carbolines can augment significantly the voluntary intake of alcohol even in aversive concentrations. This paper describes the historical background and current status of the "Multiple Metabolite" theory of alcoholism. The recent identification of anatomical structures in the limbic-midbrain, limbic-forebrain of the Sprague-Dawley rat, which mediate changes in the intake of alcohol induced by tetrahydropapaveroline (THP) is also described. When injected in a low dose of 25 ng in a specific site, over a 3-day period, THP induces persistent increases in the intake of alcohol even in aversive concentrations. These THP-reactive sites comprise the substantia nigra, reticular formation, medial lemniscus, zona incerta, medial forebrain bundle, nucleus accumbens, olfactory tubercle, lateral septal nucleus, preoptic area, stria terminalis, and rostral hippocampus. A higher dose of 250 ng THP microinjected at homologous loci tends to inhibit the rat's self-selection of alcohol or exert no effect on drinking. Morphological mapping of histologically identified sites sensitive to THP revealed a distinct "circuitry" of neuronal structures overlapping both dopaminergic and enkephalinergic pathways. This "circuit" extends from the tegmental-nigral area of the midbrain rostrally to structures within the limbic-forebrain. When a THP-reactive structure, the N. accumbens, was lesioned by either of two neurotoxins, 6-hydroxydopamine or 5.7-dihydroxytryptamine, the rats' preference for alcohol increased sharply. This suggests that impairment of transmitter release, denervation supersensitivity or other perturbation of receptor function within this and other structures play a part in the aberrant drinking of alcohol. It is envisaged that a dopamine-enkephalin link underlies the mechanism for the onset, maintenance and permanency of alcohol preference generated by an aldehyde adduct. Finally, the "Two-Channel, Brain Metabolite" theory of alcoholism proposes that the transitory presence of an endogenously formed aldehyde adduct within cells of the brain causes a permanent perturbation of normal receptor processes and transmitter activity within synapses of specific structures of the limbic system. This theory thus explains the nature of the rewarding properties of alcohol as well as its complex addictive liability which is physiologically irreversible.

Anatomical mapping of tetrahydropapaveroline-reactive sites in brain mediating suppression of alcohol drinking in the rat

In a previous study, anatomically circumscribed sites were identified within limbic-midbrain and limbic-forebrain structures of the rat in which injections of tetrahydropapaveroline (THP) evoked the drinking of alcohol even at aversive concentrations. The purpose of the second part of this study was to identify specific sites in the same limbic structures which also were reactive to THP but which mediated the suppression of alcohol consumption. Cannulae for repeated microinjection of THP were implanted stereotaxically in male Sprague-Dawley rats at sites extending from the ventral tegmental-substantia nigra complex rostrally to the region of the olfactory tubercle. Postoperatively, the rats were tested for their self-selection of water versus alcohol offered in solutions increased over 10 consecutive days in 10 concentrations from 3 to 30%. THP was dissolved in a CSF vehicle containing Na2S2O5 or ascorbate and microinjected in a dose of 25, 50 or 250 ng contained in a volume of 1.5-2.0 microliters. Following a sequence of 5 microinjections of THP, given over 3 days, the same 10-day alcohol drinking test was repeated. Ordinarily, sites at three depths 1.0-1.5 mm beneath the tip of the guide tube were tested for their reactivity to the amine-aldehyde adduct. When injected at 21 sites within coronal planes 1.0-10.5, THP attenuated the intake of alcohol significantly. Structures sensitive to the inhibitory action of the aldehyde adduct included the substantia nigra, reticular formation, medial lemniscus, preoptic area, nucleus accumbens, olfactory tubercle, cingulate gyrus and rostral hippocampus. Within 65 loci contained within the same AP planes, little or no effect of alcohol intake was exerted by THP independent of the dose microinjected. Nonreactive loci were identified within fiber pathways including the corpus callosum and optic tract, motor systems of the caudate nucleus, and both sensory and motor relay nuclei of the thalamus. An analysis of the critical part played by the dose of THP revealed that 81% of reactive sites given the 25 ng dose mediated enhanced drinking of alcohol, as demonstrated in the first study. Conversely, the 50 and 250 ng doses injected at THP-sensitive loci reduced alcohol consumption three to seven times more often than they augmented drinking. Anatomical sites mediating an attenuation of alcohol consumption in response to the higher doses of THP overlapped with both enkephalinergic and dopaminergic systems which project from the ventral tegmentum and substantia nigra to the rostral limbic-forebrain.(ABSTRACT TRUNCATED AT 400 WORDS)

Isoquinolines, beta-carbolines and alcohol drinking: involvement of opioid and dopaminergic mechanisms

Two classes of amine-aldehyde adducts, the tetrahydroisoquinoline (TIQ) and beta-carboline (THBC) compounds, have been implicated in the mechanism in the brain underlying the addictive drinking of alcohol. One part of this review focuses on the large amount of evidence unequivocally demonstrating not only the corporeal synthesis of the TIQs and THBCs but their sequestration in brain tissue as well. Experimental studies published recently have revealed that exposure to alcohol enhances markedly the endogenous formation of condensation products. Apart from their multiple neuropharmacological actions, certain adducts when delivered directly into the brain of either the rat or monkey, to circumvent the brain's blood-barrier system, can evoke an intense and dose-dependent increase in the voluntary drinking of solutions of alcohol even in noxious concentrations. That the abnormal intake of alcohol is related functionally to opioid receptors in the brain is likely on the basis of several distinct lines of evidence which include: the attenuation of alcohol drinking by opioid receptor antagonists; binding of a TIQ to opiate receptors in the brain; and marked differences in enkephalin values in animals genetically predisposed to the ingestion of alcohol. Finally, it is proposed that the dopaminergic reward pathways which traverse the meso-limbic-forebrain systems of the brain more than likely constitute an integrative anatomical substrate for the adduct-opioid cascade of neuronal events which promote and sustain the aberrant drinking of alcohol.

A neuroanatomical substrate for alcohol drinking: identification of tetrahydropapaveroline (THP)-reactive sites in the rat brain

Certain endogenously synthesized adducts, derived from a condensation reaction of a catechol- or indole-amine with a biogenic aldehyde, act in the brain to augment or suppress the drinking of ethyl alcohol. When infused directly into the cerebral ventricles, a tetrahydro-isoquinoline such as tetrahydropapaveroline (THP) can enhance markedly the consumption of alcohol even in noxious concentrations. The present study was undertaken to isolate and identify specific anatomical structures in the limbic-midbrain, limbic-forebrain which mediate the changes in the ingestion of alcohol induced by THP. In adult male Sprague-Dawley rats, a 23 ga guide tube was implanted stereotaxically either unilaterally or bilaterally in cerebral regions extending from coronal planes AP 1.0-10.0. Following recovery, each animal was tested by a standard screen for its self-selection of water versus an alcohol solution offered in 10 concentrations increased on each of 10 days from 3 to 30%. THP was dissolved in an artificial CSF vehicle containing Na2S2O5 or ascorbate and then microinjected in a volume of 1.5-2.0 microliters at a depth 1.0-1.5 mm beneath the tip of the guide. After a set of 5 microinjections of THP in a dose of 25, 50 or 250 ng was given over 3 days, the same 10-day alcohol preference sequence was repeated. In nearly all rats, the microinjection series was repeated at either one or two depths 1.0-1.5 mm ventral to the first, after which the same alcohol test was repeated. The results showed that THP induces or sustains significant increases in alcohol intake when the adduct was injected at 16 sites within caudal AP planes 1.0-5.0. Structures sensitive to THP included the substantia nigra, reticular formation, medial lemniscus, zona incerta and medial forebrain bundle. When injected at 21 sites located more rostrally within AP planes 6.5-10.0, THP also evoked significant increments in alcohol intake of a similar magnitude. The reactive loci included the N. accumbens, olfactory tubercle, lateral septum, preoptic area, stria terminalis, medial forebrain bundle and rostral hippocampus. In terms of the efficacy of the dose of THP microinjected, 25, 50 and 250 ng induced alcohol self-selection in 81%, 5% and 14% of the sites, respectively. Repeated microinjections following identical procedures of two control solutions at 46 homologous sites within corresponding coronal planes from AP 1.5-10.0 produced no significant alterations in g/kg or proportional intakes of alcohol. Composite anatomical maps of the THP-reactive sites revealed their integral overlap with dopaminergic pathways which originate in the ventral tegmentum and substantia nigra and project rostrally to s

Indole derivatization procedures for electron capture negative chemical ionization mass spectrometry: identification of 1-methyl-1,2,3,4-tetrahydro-beta-carboline in rat brain and lung

Procedures have been developed for the isolation of pharmacologically active indole compounds from biological samples and for the introduction of electron-capturing groups, pentafluorobenzyl and trifluoroacetyl, onto the indole nitrogen atom. The resulting derivatives have good gas chromatographic properties and strong electron affinities which make them highly suitable for detection by electron capture negative chemical ionization mass spectrometry. These procedures were used to identify 1-methyl-1,2,3,4-tetrahydro-beta-carboline as a component of rat brain and lung.

Interaction of tetrahydropapaveroline with inhibition of dopa-decarboxylase by Ro 4-4602 in brain: effects on alcohol drinking in the rat

The effects of the 1-aromatic amino acid decarboxylase inhibitor, Ro 4-4602 (benserazide), was determined on alcohol drinking induced in the rat by tetrahydropapaveroline (THP) injected by the intracerebroventricular (ICV) route. After ICV guide cannulae were implanted stereotaxically in 19 Sprague-Dawley rats, an artificial CSF solution containing 5.0 ng/micrograms THP was infused twice daily for 3 days in a volume of 5.0 microliters. Following a standard self-selection procedure, concentrations of alcohol which ranged from 3-30% were presented to the rats. A single maximally preferred solution, which in these rats ranged from 9-12% alcohol, was then offered in the presence of water. After a 4-day pretest in which alcohol intakes had stabilized, either 50 or 100 micrograms Ro 4-4602 plus THP were infused ICV to the animal during a 3-day period. Both doses of Ro 4-4602 significantly antagonized the g amount and proportional intakes of alcohol, but the higher dose was nearly twice as potent as the lower. During the 4-day postdrug test period, alcohol drinking continued to be suppressed. When THP was infused ICV over a 3-day period following the injections of Ro 4-4602, the predrug alcohol intake was partially reinstated, suggesting that this TIQ, when delivered directly into the brain, partly reversed the potent central action of Ro 4-4602. These results show that interference with the functional activity of central catecholamine pathways in the rat, by means of the inhibition of dopamine synthesis, serves to modify markedly the mechanisms underlying alcohol drinking in this species.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of ethanol and tetrahydro-beta-carboline (THBC) in a discriminative task

Rats (n = 10) were trained to discriminate between ethanol (600 mg/kg, IP) and its vehicle, or between THBC (20 mg/kg) and its vehicle in a two-lever food-motivated operant task. Once the discriminative training criterion was attained, rats in each group were administered different doses of both ethanol and THBC. The ED50 of ethanol in the ethanol-trained rats was 298.0 mg/kg and 15 mg/kg THBC produced ethanol-like responding. The ED50 of THBC in the THBC-trained rats was 3.63 mg/kg and 1200 mg/kg ethanol produced THBC-like responding. The cross-generalization between ethanol and THBC is, thus, indicated and relates to previous evidence in which both ethanol- and THBC-trained rats generalize to a common agent, TFMPP, a putatively specific 5HT1B receptor agonist. Taken together, these observations suggest that beta-carbolines may play a role in the discriminative stimulus properties of ethanol.

Cyanamide given ICV or systemically to the rat alters subsequent alcohol drinking

Cyanamide or disulfiram serves to suppress volitional intake of alcohol presumably because of the toxic build-up of acetaldehyde dehydrogenase (AIDH). However, the presence of acetaldehyde systemically favors the in vivo synthesis of addictive-like metabolites in the brain which in turn enhance alcohol drinking. The purpose of this investigation, therefore, was to determine whether cyanamide administered to the rat, which did not have access to alcohol during treatment, would nevertheless affect the subsequent preference for alcohol. In the first experiment, cannulae were implanted bilaterally above the cerebral ventricle of 33 adult male Sprague-Dawley rats so that an artificial CSF or a solution of cyanamide could be infused intracerebroventricularly (ICV). Following post-operative recovery, each rat was tested for its alcohol preference by offering it water and a solution of ethyl alcohol which was increased over 8 days from 3-20%. After a single test concentration of alcohol (range of 5-9%) was selected for each individual animal presented with water over a 5-day interval, cyanamide was infused in a volume of 2.5 microliters per side three times daily for 4 days in one of the following total doses: 0.03, 0.1, 0.3, 0.5 or 1.0 mg. A second five-day preference test was run, and 6 weeks following cyanamide infusions a final 3-20% alcohol preference screen was run over 8 days. The results showed that a long-term, dose-dependent increase or decrease in alcohol intake occurred in those rats reactive to the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomical localization in hippocampus of tetrahydro-beta-carboline-induced alcohol drinking in the rat

Guide cannulae for unilateral or bilateral micro-injection were implanted stereotaxically into the dorsal hippocampus of the male adult Sprague-Dawley rat. Following post-operative recovery, the animal's individual preference for ethyl alcohol in concentrations from 3-30% (v/v) was tested over a 9-day period by a three-bottle, two-choice technique. Following this pre-screen, 3.0 microliter of 1,2,3,4-tetrahydro-beta-carboline (TH beta C) hydrochloride, a benzodiazepine receptor antagonist, was infused in a concentration of 25-200 ng into the hippocampus of each unrestrained rat twice a day for three to six days. After the first two days of infusion, the 9-day preference test for alcohol drinking was begun and continued identically as in the earlier test. A third alcohol preference test during which no injections were given was conducted at an interval of two weeks following the second. The micro-injection of TH beta C into certain sites in the hippocampus enhanced alcohol consumption from 0.5-2.0 g/kg during the 9-day test interval. The magnitude of this elevated intake was dependent on the site of infusion and was more pronounced when intermediate concentrations of 7-12% alcohol were offered to the rat. At sites in coronal planes encompassing AP 3.0 and AP 3.5, the micro-injection of TH beta C enhanced alcohol drinking significantly in 75% of the animals; however, when delivered at sites in coronal planes AP 1.0 through AP 2.5, TH beta C augmented alcohol drinking significantly in 15% of the rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Buspirone attenuates volitional alcohol intake in the chronically drinking monkey

Four macaque monkeys which showed excessive preference for ethyl alcohol solutions in a self-selection paradigm were used as subjects. Earlier these animals had been given intracerebroventricular (ICV) injections of human cerebrospinal fluid, which produced pharmacologically significant effects on the animals' alcohol consumption. The purpose of the present investigation was to determine whether the parenteral administration of a new anxiolytic compound, buspirone, would alter the pattern of alcohol drinking already established in the monkey. Initially the maximally selected concentration of alcohol of 12% was determined on the basis of a standard ad lib alcohol-water preference screen. Each monkey was offered 12% alcohol and water for a basal pre-injection period of 4 days. Then, on each of the next three days, either the saline control vehicle or buspirone, 1.25, 5.0 or 20.0 mg/kg, was injected intramuscularly at 930 and 1630 hours. On these days, behavioral observations were recorded before and after buspirone's administration in order to evaluate the latency as well as recovery from the drug's effect. Subsequently, a four-day post-injection, 12% alcohol-water test was conducted. Although the saline control and 1.25 mg/kg dose of buspirone were without effect on alcohol intake, both the 5.0 and 20.0 mg/kg doses of buspirone attenuated significantly the consumption of alcohol by the monkeys. This reduction in terms of absolute g/kg as well as the proportion of alcohol to water ingested was approximately 30-60% of baseline intakes. Following buspirone treatment, the amount of alcohol consumed returned essentially to previously high levels.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Cyanamide injections during alcohol deprivation increase alcohol drinking

Long-Evans male rats were given 7 weeks of choice between 10% ethanol and water and then were divided into 6 matched groups, 3 of which were then deprived of alcohol for 6 days. Subcutaneous cyanamide injections (10 mg/kg, 3 times daily, for 4 days) during alcohol deprivation produced a long lasting, significant increase in subsequent alcohol selection, over and above the increase produced by alcohol deprivation alone. The same injections given to a group not deprived of alcohol caused a significant suppression of alcohol drinking during the treatment and had disappeared 4 days after the last injection. Thereafter the drinking remained at the control level and did not rise to that of the group given the injections during deprivation. The groups did not differ in their subsequent selection of saline solutions.

Derivatization in aqueous solution, isolation and separation of tetrahydro-beta-carbolines and their precursors by liquid chromatography

Derivatization of indole ethylamines and 1,2,3,4-tetrahydro-beta-carbolines in aqueous solution with methyl chloroformate has been used to facilitate the isolation of these compounds. The initial derivatization eliminated the potential for the artifactual formation of these compounds via the condensation of the indole ethylamine with an aldehyde or alpha-keto acid during the work-up procedure. The derivatized compounds possessed improved chromatographic properties which allowed for their facile separation by reversed-phase liquid chromatography and their fluorescent detection at the nanogram level.

The influences of ethanol and other factors on the excretion of urinary salsolinol in social drinkers

Salsolinol, a substance that may participate in the development of alcoholism, has been identified in urine and other biological samples from alcoholics. Differentials have been observed between alcoholics and controls. Salsolinol forms when dopamine reacts with acetaldehyde, which may exist in higher concentrations in the blood of alcoholics after alcohol ingestion. Hence, it was postulated that there is a relationship between level of social drinking and the elaboration of salsolinol. Salsolinol is also found in certain food and beverage products. Eighty volunteers, balanced for gender, social drinking level, ethanol dose administered and experimental diet provided urine samples 90 minutes and three hours after ethanol was consumed. Salsolinol levels were analysed in urine using high performance liquid chromatography. A 24 hour carryover effect was observed. Diet, ethanol dose and social drinking level had main and interactive effects on excreted quantities of salsolinol. Gender, situational stress and cigarette smoking had minor if any influence on salsolinol excretion. While there was no evident difference in amounts of salsolinol excreted by light and heavy drinkers in the absence of external sources of salsolinol, heavy social drinkers excreted less salsolinol than did light drinkers after consuming a "salsolinol-enriched" diet, suggesting that they differ in some aspect of absorption, distribution, or metabolism of salsolinol after drinking ethanol. Accordingly, studies that attempt to determine whether salsolinol has any relationship to drinking behaviour in humans should be particularly concerned with salsolinol that occurs in exogenous sources.

Binding of beta-carbolines and tetrahydroisoquinolines by opiate receptors of the delta-type

Effects of various beta-carbolines (BC's) and two tetrahydroisoquinolines (TIQ's) on the specific binding of a natural opiate delta-receptor ligand, leucine enkephalin, have been studied in rat synaptosomal membranes, and compared with the effects on the binding of mu-receptor ligands dihydromorphine and naloxone. Harmaline (7-MeO-1-Me-dihydro-BC) was the most potent compound studied (Ki value 3.5 microM), while the two TIQ's (salsolinol and salsolidine) were less potent than BC's (Ki greater than 100 microM) in inhibiting the binding of delta-receptors. In general, BC's showed more affinity for delta-receptors than for mu-receptors; salsolinol was more potent against the binding of mu-receptors. Inhibition of binding was generally of the competitive type: Kd values increased and Bmax values were not altered. The Na dependence suggests that BC's and salsolinol are antagonists or partial agonists of opioids. Since the binding affinity of BC's and TIQ's was on the micromolar level only, the opiate receptors do not appear to be the major sites of action for BC's or TIQ's.

The neurotoxicity of ethanol

Alterations in nervous system functioning following acute and chronic ethanol exposure have been studied in a great number of experimental investigations. Results from many of these investigations can be difficult to interpret, particularly since a variety of techniques and exposure models are employed. This review emphasizes those studies which, in the opinion of the author, fit into a pattern where results from studying one function of the nervous system is in accordance with results from studying another. Thus, the fluidizing effect of ethanol on the neuronal membrane - an effect which ethanol shares with anaesthetics - leads to a change in protein function which in turn affects ion transport such as Na+ and Ca++ across the membrane due to changes in the ion channels. Cation influx is probably directly coupled to neurotransmitter release which is in agreement with the finding that ethanol exposure results in inhibition of Na+ and Ca++ current as well as acetylcholine release. The sensitization of the dopaminergic system after ethanol exposure may also be related to the changes in cation flux, and the changes in this system probably play a crucial rôle in the development of tolerance and withdrawal symptoms. Other aspects such as impairment of protein synthesis, altered GABA function of impairment of neuron excitability and conduction are more difficult to place in proper perspective. The rôle of acetaldehyde in acute as well as chronic ethanol intoxication also remains a controversy. These may, however, be secondary phenomena to primary changes in different part of the nervous system not necessarily important in the clinical situation. Behavioural and anatomical studies particularly from recent years have shown that experimental animals develop memory disturbances following chronic exposure even when kept on sufficient diet. These findings argue strongly for a direct toxic effect of ethanol, and are furthermore compatible with behavioural changes in chronic alcoholics, dominated by memory impairment. Since it has been argued that the cholinergic system plays a significant rôle for memory function, a possible explanation for some of the psychological and anatomical deficits caused by ethanol is thus the changes in the function of the cholinergic system particularly in the hippocampal regions.

Effect of hippocampal lesions produced by intracerebroventricular kainic acid on alcohol drinking in the rat

An alcohol self-selection test was first given to adult male rats of either the Sprague-Dawley or Long-Evans strain in which the concentrations available with water were increased from 3% to 30% over an eight-day period. Subsequently, the animals were anesthetized and, using stereotaxic procedures, a 1.2 or 2.4 nmole dose of kainic acid was infused bilaterally into the cerebral ventricle (ICV) over a 30-sec interval and in a total volume of 10 microliters. When the same alcohol self-selection test was repeated two weeks post-operatively, alcohol intake was significantly suppressed in terms of both g/kg intake per day as well as proportion of alcohol to water selected. Alcohol intake of the control rats infused with the CSF carrier vehicle was unchanged. When a much longer interval of 7-10 min was used to infuse the 2.4 nmole dose of kainic acid ICV, the intake of alcohol of this group also was not significantly changed. Post-mortem histological analysis of forebrain tissue of the kainic acid infused rats confirmed cytological damage to the hippocampus, particularly in cell fields CA3 and CA4, which has been reported previously. Since the hippocampus has been implicated recently in the mechanisms underlying alcohol drinking, our results suggest that a pathological lesion of this limbic-forebrain structure could influence the degree to which alcohol is self-administered in a free-choice situation.

Presence of formaldehyde in biological media and organic solvents: artifactual formation of tetrahydro-beta-carbolines

A gas chromatography-mass spectrometry method is described for the identification and quantitation of 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (6OHTHBC). During the analysis of 6OHTHBC in human platelets, the artifactual formation of 6OHTHBC was observed and shown to be due to the presence of formaldehyde in both organic solvents and in platelet homogenates. Formaldehyde was facilely removed from the organic solvent via a Pictet-Spengler reaction; however, removal from tissue homogenates was not possible by using conventional aldehyde-trapping agents. The solution of these problems and their consequences for persons attempting to establish the in vivo presence of tetrahydro-beta-carbolines or biochemically study tissue preparations are discussed.

Tetrahydro-beta-carbolines: effect on alcohol intake in rats

Some beta-carbolines, such as tetrahydro-beta-carboline (THBC) and 6-methoxy-THBC, occur normally in mammalian tissues, and 1-methyl-THBC has been found in human blood after alcohol intake. Continuous intraventricular (ICV) infusion of THBC and 1-methyl-THBC for 14 days was shown to increase voluntary alcohol intake in rats during the second week of infusion. In this study the experimental arrangement was slightly modified. Alcohol was offered for 7 days before the start of the 14 days of ICV infusion with Alzet minipumps and alcohol concentration (3-30% v/v) was increased every second day. The rats consumed less alcohol in the second day with the same concentration. Also, the dose of 47 nmoles/hr of 1-Me-THBC increased the voluntary alcohol intake over the controls, but only during the last 7 days. The same dose of 6-MeO-THBC, a serotonergic beta-carboline, was ineffective. Neither drug changed the total fluid intake. This study suggests that the increased voluntary alcohol intake by THBC's is not due to their serotonergic effect. A hypothesis concerning a possible involvement of opiate receptors is presented.

Alcohol drinking in the rat: increases following intracerebroventricular treatment with tetrahydro-beta-carbolines

Voluntary alcohol intake has been reported to increase in rats after the repeated intracerebroventricular (ICV) administration of 1,2,3,4-tetrahydro-beta-carboline (THBC) and some tetrahydroisoquinolines, although negative results have also been reported. THBC is a normal constituent in human plasma and platelets; 1-methyl-1,2,3,4-tetrahydro-beta-carboline (1-Me-THBC), however, occurs in the blood after a person drinks alcohol. We have evaluated the effects of two doses of THBC and 1-Me-THBC on voluntary alcohol consumption in rats. ICV infusions were given with Alzet minipumps for 14 days rather than giving repeated ICV injections. Stability of the drugs in the pump was verified using mass spectrometry. On each day the rats chose between water, alcohol (increasing concentrations from 3 to 30%) and an empty bottle. Alcohol intake increased by about 100% (p less than 0.05) during the last six days when 47 nmoles/hr of either THBC or 1-Me-THBC was infused. At the end of the experiment elevated blood concentrations of alcohol (0.02-0.78(0)/00) were found in rats belonging to the THBC or 1-Me-THBC groups and drinking 30% alcohol. The infusion of 0.47 nmoles/hr of either drug did not increase alcohol intake as compared to control.

Alcohol drinking induced in the monkey by tetrahydropapaveroline (THP) infused into the cerebral ventricle

In the female macaque monkey acclimated to a primate chair, Collison cannulae were stereotaxically implanted bilaterally in the lateral cerebral ventricle. The voluntary self-selection of ethyl alcohol versus water was determined repeatedly during a series of 12-day test sequences in which the concentration of the alcohol solution offered to the primate was increased systematically over 12 successive days from 3% to 30%. Following control preference sequences, the dopamine-dopaldehyde condensation product, tetrahydropapaveroline (THP), was infused daily in each monkey's cerebral ventricle (ICV) in a volume of 200-400 microliter. THP was dissolved in an artificial CSF, with pH adjusted to 3.8 with 0.1 mg/ml ascorbate, and infused in one of ten doses varying from 0.125-400 microgram. EAch monkey was administered one low and one high dose of the condensation product throughout each of two successive alcohol preference tests. When THP was infused in doses of less than 2.0 microgram, the monkeys' alcohol preference failed to change. However, a marked increase in alcohol intake, in terms of both g/kg/day as well as the proportion of alcohol to water selected, was produced by THP infused ICV in doses of 5.0 to 20.0 microgram. Although average intakes in the latter animals were between 4.0 and 5.0 g/kg/day, the monkeys selected certain concentrations of alcohol in amounts of up to 7.0 g/kg/day. The two highest doses of THP, 40.0 and 400.0 microgram, inhibited the self-selection of alcohol even when presented in low, non-aversive concentrations in the 3% to 6% range. Overall, these results with the primate corroborate earlier findings in the rat of abnormal alcohol intake produced by centrally infused THP. They further support the theory that amine-aldehyde metabolites, if present in certain concentrations in the brain, may constitute a causal neurochemical factor in the addictive or otherwise immoderate drinking of alcohol.

Naloxone alters alcohol drinking induced in the rat by tetrahydropapaveroline (THP) infused ICV

In male rats of the Sprague-Dawley or Long-Evans strain, intracerebroventricular (ICV) cannulae were implanted permanently using stereotaxic techniques. Tetrahydropapaveroline (THP) was infused ICV for up to 14 days either chronically around the clock or acutely once per day in doses previously found to induce an abnormally high intake of alcohol. During these periods, alcohol preference for individual rats was determined by a self-selection procedure in which the concentration of alcohol was increased from 3 to 30% on each day of a 12-day interval. Those rats which displayed a substantial increase in their intake of alcohol were selected for naloxone treatment and subsequently assigned a fixed concentration of alcohol at which maximum consumption occurred. Naloxone was administered subcutaneously two to six times per day for three consecutive days in total daily doses ranging from 1.5 to 3.0 mg/kg. Each rat served as its own control and was given 0.9% saline isovolumetrically according to the same temporal schedule. Naloxone generally suppressed alcohol intake in animals by 20% to 45%, but the reduction in drinking depended upon the injection regimen as well as the prior level of alcohol consumption. In "high drinking" rats, the mean alcohol intake of 6.2 g/kg/day was reduced to 3.7 g/kg/day by naloxone whereas in "low drinkers" the mean intake of 3.5 g/kg/day was suppressed to 2.8 g/kg/day by the opiate antagonist. These results further support the suggestion of a possible opiate receptor link in the pathogenesis and maintenance of aberrant drinking of alcohol, the mechanism of which may involve the endogenous action of an amine-aldehyde condensation product in the brain.

Acute treatment with trimethyltin alters alcohol self-selection

Male rats of the Long-Evans strain were divided into two equal groups of nine each and given either 7.0 mg/kg trimethyltin (TMT) or 0.9% saline by intragastric gavage. The pattern of self-selection of alcohol in concentrations of 3%--30% was examined in both groups at 21 and 150 days following the gavage. The TMT-treated rat consistently drank less alcohol than did the controls at every concentration of alcohol. This difference in alcohol intake was equally significant when the rats were tested in a food-contingent, schedule-induced polydipsia situation. Further, although the TMT-lesioned animal consumed fewer calories per day in the form of alcohol, their overall daily caloric intakes were slightly higher than those of the controls. These results are interpreted as a consequence of damage to structures of the forebrain and as part of a syndrome of behavioral and neurological pathology.

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.