The effect of acute ethanol on dopamine metabolism and other neurotransmitters in the hypothalamus and the corpus striatum of mice

Voluntary binge-patterned alcohol drinking and sex-specific influences on monoamine-related neurochemical signatures in the mouse gut and brain

BACKGROUND

Altered monoamine (i.e., serotonin, dopamine, and norepinephrine) activity following episodes of alcohol abuse plays key roles not only in the motivation to ingest ethanol, but also physiological dysfunction related to its misuse. Although monoamine activity is essential for physiological processes that require coordinated communication across the gut-brain axis (GBA), relatively little is known about how alcohol misuse may affect monoamine levels across the GBA. Therefore, we evaluated monoamine activity across the mouse gut and brain following episodes of binge-patterned ethanol drinking.

METHODS

Monoamine and select metabolite neurochemical concentrations were analyzed by ultra-high-performance liquid chromatography in gut and brain regions of female and male C57BL/6J mice following "Drinking in the Dark" (DID), a binge-patterned ethanol ingestion paradigm.

RESULTS

First, we found that alcohol access had an overall small effect on gut monoamine-related neurochemical concentrations, primarily influencing dopamine activity. Second, neurochemical patterns between the small intestine and the striatum were correlated, adding to recent evidence of modulatory activity between these areas. Third, although alcohol access robustly influenced activity in brain areas in the mesolimbic dopamine system, binge exposure also influenced monoaminergic activity in the hypothalamic region. Finally, sex differences were observed in the concentrations of neurochemicals within the gut, which was particularly pronounced in the small intestine.

CONCLUSION

Together, these data provide insights into the influence of alcohol abuse and biological sex on monoamine-related neurochemical changes across the GBA, which could have important implications for GBA function and dysfunction.

Common genes regulate food and ethanol intake in Drosophila

The abuse liability of alcohol (ethanol) is believed to result in part from its actions on neurobiological substrates that underlie the motivation toward food and other natural reinforcers, and a growing body of evidence indicates that these substrates are broadly conserved among animal phyla. Understanding the extent to which the substrates regulating ethanol and food intake overlap is an important step toward developing therapeutics that selectively reduce ethanol intake. In the current experiments, we measured food and ethanol intake in Recombinant Inbred (RI) lines of Drosophila melanogaster using several assays, and then calculated genetic correlations to estimate the degree to which common genes might underlie behavior in these assays. We found that food intake and ethanol intake as measured in the capillary assay are genetically correlated traits in D. melanogaster, as well as in a panel of 11 Drosophila species that we tested subsequently. RI line differences in food intake in a dyed food assay were genetically unrelated to ethanol intake in the capillary assay or to ethanol preference measured using an olfactory trap apparatus. Using publicly available gene expression data, we found that expression profiles across the RI lines of a number of genes (including the D2-like dopamine receptor, DOPA decarboxylase, and fruitless) correlated with the RI line differences in food and ethanol intake we measured, while the expression profiles of other genes, including NPF, and the NPF and 5-HT2 receptors, correlated only with ethanol intake or preference. Our results suggest that food and ethanol intake are regulated by some common genes in Drosophila, but that other genes regulate ethanol intake independently of food intake. These results have implications toward the development of therapeutics that preferentially reduce ethanol intake.

Inhibition of phosphorylated tyrosine hydroxylase attenuates ethanol-induced hyperactivity in adult zebrafish (Danio rerio)

Zebrafish have been successfully employed in the study of the behavioural and biological effects of ethanol. Like in mammals, low to moderate doses of ethanol induce motor hyperactivity in zebrafish, an effect that has been attributed to the activation of the dopaminergic system. Acute ethanol exposure increases dopamine (DA) in the zebrafish brain, and it has been suggested that tyrosine hydroxylase, the rate-limiting enzyme of DA synthesis, may be activated in response to ethanol via phosphorylation. The current study employed tetrahydropapaveroline (THP), a selective inhibitor of phosphorylated tyrosine hydroxylase, for the first time, in zebrafish. We treated zebrafish with a THP dose that did not alter baseline motor responses to examine whether it can attenuate or abolish the effects of acute exposure to alcohol (ethanol) on motor activity, on levels of DA, and on levels of dopamine's metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). We found that 60-minute exposure to 1% alcohol induced motor hyperactivity and an increase in brain DA. Both of these effects were attenuated by pre-treatment with THP. However, no differences in DOPAC levels were found among the treatment groups. These findings suggest that tyrosine hydroxylase is activated via phosphorylation to increase DA synthesis during alcohol exposure in zebrafish, and this partially mediates alcohol's locomotor stimulant effects. Future studies will investigate other potential candidates in the molecular pathway to further decipher the neurobiological mechanism that underlies the stimulatory properties of this popular psychoactive drug.

A critical evaluation of influence of ethanol and diet on salsolinol enantiomers in humans and rats

BACKGROUND

(R/S)-Salsolinol (SAL), a condensation product of dopamine (DA) with acetaldehyde, has been speculated to have a role in the etiology of alcoholism. Earlier studies have shown the presence of SAL in biological fluids and postmortem brains from both alcoholics and nonalcoholics. However, the involvement of SAL in alcoholism has been controversial over several decades, since the reported SAL levels and their changes after ethanol exposure were not consistent, possibly due to inadequate analytical procedures and confounding factors such as diet and genetic predisposition. Using a newly developed mass spectrometric method to analyze SAL stereoisomers, we evaluated the contribution of ethanol, diet, and genetic background to SAL levels as well as its enantiomeric distribution.

METHODS

Simultaneous measurement of SAL enantiomers and DA were achieved by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS). Plasma samples were collected from human subjects before and after banana (a food rich in SAL) intake, and during ethanol infusion. Rat plasma and brain samples were collected at various time points after the administration of SAL or banana by gavage. The brain parts including nucleus accumbens (NAC) and striatum (STR) were obtained from alcohol-non-preferring (NP) or alcohol-preferring (P) rats as well as P-rats which had a free access to ethanol (P-EtOH).

RESULTS

Plasma SAL levels were increased significantly after banana intake in humans. Consistently, administration of banana to rats also resulted in a drastic increase of plasma SAL levels, whereas brain SAL levels remained unaltered. Acute ethanol infusion did not change SAL levels or R/S ratio in plasma from healthy humans. The levels of both SAL isomers and DA were significantly lower in the NAC of P rats in comparison to NP rats. The SAL levels in NAC of P rats remained unchanged after chronic free-choice ethanol drinking. There were decreasing trends of SAL in STR and DA in both brain regions. No changes in enantiomeric ratio were observed after acute or chronic ethanol exposure.

CONCLUSIONS

SAL from dietary sources is the major contributor to plasma SAL levels. No significant changes of SAL plasma levels or enantiomeric distribution after acute or chronic ethanol exposure suggest that SAL may not be a biomarker for ethanol drinking. Significantly lower SAL and DA levels observed in NAC of P rats may be associated with innate alcohol preference.

Effect of acetaldehyde on behavioral and neurochemical changes induced by MK-801 in rats

Alterations in motor activity related to dopamine changes in some brain regions have been described as consequences of the modifications produced by systemic administration of MK-801 (a noncompetitive NMDA receptor antagonist) in rats. Acetaldehyde (ACH), the main metabolite of ethanol, has been implicated in different alterations in the central nervous system after ethanol ingestion. ACH might exert some control on dopaminergic transmission through the formation of other compounds with dopamine, which eventually may modify dopamine content and its metabolism. In order to evaluate such a hypothesis, we used Wistar rats in the present study to evaluate the effect of ACH on locomotor alterations and dopamine metabolism changes induced by MK-801. Our results show that the MK-801-treated group had a significant increase in locomotor activity. In contrast, we did not find significant differences in locomotion tests after ACH administration. However, the group to which both drugs were administered showed a significant decrease in locomotor activity compared with those given MK-801 alone. Neurochemical analysis showed an increase in dopamine content in the striatum and frontal cortex after MK-801 administration, however; the increase was reversed by giving 200 mg/kg of ACH. These results indicate that ACH can produce an antagonic-like effect on locomotor alterations and dopamine content changes induced by MK-801, thus modulating the MK-801-induced hyperlocomotion by interfering with dopamine metabolism.

In vivo study of salsolinol produced by a high concentration of acetaldehyde in the striatum and nucleus accumbens of free-moving rats

BACKGROUND

Salsolinol, a neuropharmacologically active compound, is formed by the condensation of acetaldehyde (AcH) with dopamine (DA) in the brain. The aim of our study was to examine the effect of a high concentration of AcH on salsolinol formation and to compare the release of DA, serotonin (5-HT), and salsolinol in the striatum and nucleus accumbens (NAc) in free-moving rats.

METHODS

After the insertion of a microdialysis probe, male Wistar rats (250-300 g) were treated with cyanamide (CY, a potent aldehyde dehydrogenase inhibitor) + ethanol (EtOH), CY + 4-methylpyrazole (4-MP, a strong alcohol dehydrogenase inhibitor) + EtOH, 4-MP + EtOH, CY, and 4-MP. Simultaneous quantitation of DA, 5-HT, and salsolinol in dialysates was performed by using in vivo microdialysis coupled with high-performance liquid chromatography with an electrochemical detector and blood EtOH and AcH by using a head-space gas chromatographic method.

RESULTS

Salsolinol was detected only in the CY + EtOH groups in both the striatum and NAc, and we also detected a high AcH concentration in the blood in those groups. A correlation was found between the dialysate levels of salsolinol and blood concentrations of AcH. The striatal levels of DA and 5-HT were approximately two times higher, whereas salsolinol levels were approximately three times higher compared with the usual level in the NAc. No significant difference of DA and 5-HT levels in the dialysates was observed in either the control or the other study groups.

CONCLUSION

Our observation suggested that the brain salsolinol formation may depend on the concentrations of DA and AcH in freely moving rats, and there is no effect of a high concentration of AcH on DA and 5-HT levels in the striatum and NAc.

Drosophila melanogaster, a genetic model system for alcohol research

In its natural environment, which consists of fermenting plant materials, the fruit fly Drosophila melanogaster encounters high levels of ethanol. Flies are well equipped to deal with the toxic effects of ethanol; they use it as an energy source and for lipid biosynthesis. The primary ethanol-metabolizing pathway in flies involves the enzymes alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH); their role in adaptation to ethanol-rich environments has been studied extensively. The similarity between Drosophila and mammals is not restricted to the manner in which they metabolize ethanol; behaviors elicited by ethanol exposure are also remarkably similar in these organisms. Flies show signs of acute intoxication, which range from locomotor stimulation at low doses to complete sedation at higher doses, they develop tolerance upon intermittent ethanol exposure, and they appear to like ethanol, showing preference for ethanol-containing media. Molecular genetic analysis of ethanol-induced behaviors in Drosophila, while still in its early stages, has already revealed some surprising parallels with mammals. The availability of powerful tools for genetic manipulation in Drosophila, together with the high degree of conservation at the genomic level, make Drosophila a promising model organism to study the mechanism by which ethanol regulates behavior and the mechanisms underlying the organism's adaptation to long-term ethanol exposure.

Invertebrate models of drug abuse

Susceptibility to drug addiction depends on genetic and environmental factors and their complex interactions. Studies with mammalian models have identified molecular targets, neurochemical systems, and brain regions that mediate some of the addictive properties of abused drugs. Yet, our understanding of how the primary effects of drugs lead to addiction remains incomplete. Recently, researchers have turned to the invertebrate model systems Drosophila melanogaster and Caenorhabditis elegans to dissect the mechanisms by which abused drugs modulate behavior. Due to their sophisticated genetics, relatively simple anatomy, and their remarkable molecular similarity to mammals, these invertebrate models should provide useful insights into the mechanisms of drug action. Here we review recent behavioral and genetic studies in flies and worms on the effects of ethanol, cocaine, and nicotine, three of the most widely abused drugs in the world.

Sex differences in mesolimbic dopamine responses to ethanol and relationship to ethanol intake in rats

Sex differences in ethanol intake in rats suggest that there may be sex differences in brain dopamine systems believed to mediate ethanol's reinforcing properties. To test this hypothesis, we used in vivo microdialysis to examine changes in nucleus accumbens and striatal dopamine, DOPAC and HVA following acute administration of several doses of ethanol in male and female Long-Evans rats. Following dialysis, rats were trained to bar press for oral ethanol reinforcement. In nucleus accumbens, females showed greater increases in dopamine than males at low to intermediate doses. In striatum, both sexes showed increased dopamine at the low to intermediate doses. In addition to showing increased responsiveness to ethanol-induced mesolimbic dopamine stimulation, females consumed more ethanol than males during behavioral testing. Correlations between neurochemical measures and subsequent ethanol consumption indicated that among males, both basal and peak ethanol-induced nucleus accumbens dopamine levels were inversely related to later ethanol intake. No such relationship was observed for females. Striatal neurochemical measures were not significantly related to ethanol intake. These findings supported the hypothesis of sex differences in mesolimbic responses to ethanol and suggested that the relationship of those responses to subsequent ethanol intake may differ for males and females.

Dopamine modulates acute responses to cocaine, nicotine and ethanol in Drosophila

BACKGROUND

Drugs of abuse have a common property in mammals, which is their ability to facilitate the release of the neurotransmitter and neuromodulator dopamine in specific brain regions involved in reward and motivation. This increase in synaptic dopamine levels is believed to act as a positive reinforcer and to mediate some of the acute responses to drugs. The mechanisms by which dopamine regulates acute drug responses and addiction remain unknown.

RESULTS

We present evidence that dopamine plays a role in the responses of Drosophila to cocaine, nicotine or ethanol. We used a startle-induced negative geotaxis assay and a locomotor tracking system to measure the effect of psychostimulants on fly behavior. Using these assays, we show that acute responses to cocaine and nicotine are blunted by pharmacologically induced reductions in dopamine levels. Cocaine and nicotine showed a high degree of synergy in their effects, which is consistent with an action through convergent pathways. In addition, we found that dopamine is involved in the acute locomotor-activating effect, but not the sedating effect, of ethanol.

CONCLUSIONS

We show that in Drosophila, as in mammals, dopaminergic pathways play a role in modulating specific behavioral responses to cocaine, nicotine or ethanol. We therefore suggest that Drosophila can be used as a genetically tractable model system in which to study the mechanisms underlying behavioral responses to multiple drugs of abuse.

Effects of red ginseng saponins and nootropic drugs on impaired acquisition of ethanol-treated rats in passive avoidance performance

Effects of single and repeated administration of red ginseng total saponins (ROTS) and nootropic drugs were examined on impairment of acquisition induced by single oral administration of 3 g/kg ethanol (EtOH) in a step through test. The inhibitory effect of EtOH on acquisition was significantly reduced following single or repeated RGTS administration. The nootropic drugs, piracetam and N-methyl-D-glucamine, given orally significantly reduced impairment of acquisition induced by EtOH. On the other hand, the inhibitory effect of repeated RGTS on the EtOH-induced amnesia was blocked by the pretreatment of alpha-methyl-p-tyrosine (alpha-MT), an inhibitor of catecholamine synthesis, in a dose-dependent manner but not p-chlorophenylalanine (PCPA), an inhibitor of serotonin synthesis, whereas the inhibitory effect of repeated N-methyl-D-glucamine on the EtOH-induced amnesia was blocked neither by alpha-MT nor PCPA. These results suggest that repeated RGTS and N-methyl-D-glucamine ameliorate the impairing effect of EtOH on acquisition, and the effect of RGTS on EtOH-induced amnesia is dependent on the catecholaminergic but not serotonergic neuronal activity, while RGTS and N-methyl-D-glucamine seem to have a different mechanism on EtOH-induced amnesia.

Mice lacking dopamine D4 receptors are supersensitive to ethanol, cocaine, and methamphetamine

The human dopamine D4 receptor (D4R) has received considerable attention because of its high affinity for the atypical antipsychotic clozapine and the unusually polymorphic nature of its gene. To clarify the in vivo role of the D4R, we produced and analyzed mutant mice (D4R-/-) lacking this protein. Although less active in open field tests, D4R-/- mice outperformed wild-type mice on the rotarod and displayed locomotor supersensitivity to ethanol, cocaine, and methamphetamine. Biochemical analyses revealed that dopamine synthesis and its conversion to DOPAC were elevated in the dorsal striatum from D4R-/- mice. Based on these findings, we propose that the D4R modulates normal, coordinated and drug-stimulated motor behaviors as well as the activity of nigrostriatal dopamine neurons.

The effects of ethanol in combination with the alpha 2-adrenoceptor agonist dexmedetomidine and the alpha 2-adrenoceptor antagonist atipamezole on brain monoamine metabolites and motor performance of mice

The time course of the effects of ethanol alone and in combination with the selective alpha 2-adrenoceptor agonist dexmedetomidine and the alpha-adrenoceptor antagonist atipamezole was studied in NIH-Swiss mice. Core body temperature, rotarod performance, motility and changes in the noradrenaline, dopamine, and 5-hydroxytryptamine (5-HT) metabolite contents of different brain parts (limbic forebrain, striatum, lower brainstem, the rest of the forebrain + midbrain and hypothalamus) were measured. Atipamezole (3 mg/kg) attenuated the hypothermia induced by either ethanol (3 g/kg) alone or ethanol in combination with dexmedetomidine (0.3 mg/kg). Atipamezole shortened the duration of the ethanol-impaired and ethanol + dexmedetomidine-impaired rotarod performance. Further, atipamezole prevented the decreased motility due to the combined treatment with ethanol and dexmedetomidine. Ethanol increased 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) values. Dexmedetomidine alone decreased MHPG and 5-hydroxyindoleacetic acid (5-HIAA) concentrations and increased DOPAC and HVA values. Dexmedetomidine combined with ethanol resulted in a further increase in DOPAC and HVA values. Pharmacokinetic parameters did not contribute to this antagonism of ethanol's effects by atipamezole, nor did the antagonism observed in rotarod performance or hypothermia seem to correlate with the changes seen in the brain noradrenaline and dopamine or 5-HT metabolism. In conclusion, these findings suggest that several ethanol effects are not mediated via direct activation of alpha 2-adrenoceptors, even though some of ethanol's behavioral and physiological effects may be antagonized by coadministration of alpha 2-adrenoceptor antagonists.

Fetal alcohol syndrome: the vulnerability of the developing brain and possible mechanisms of damage

Fetal alcohol exposure has multiple deleterious effects on brain development, and represents a leading known cause of mental retardation. This review of the effects of alcohol exposure on the developing brain evaluates results from human, animal and in vitro studies, but focuses on key research issues, including possible mechanisms of damage. Factors that affect the risk and severity of fetal alcohol damage also are considered.

Sex differences in ethanol-induced dopamine release in nucleus accumbens and in ethanol consumption in rats

In vivo microdialysis was used to examine changes in nucleus accumbens and striatal dopamine, dihydrophenylacetic acid (DOPAC), and homovanillic acid (HVA) following acute administration of ethanol (0.0, 0.25, 0.5, 1.0, or 2.0 g/kg) in male and female Long-Evans rats. Following dialysis, rats were trained to bar-press for oral ethanol reinforcement. In nucleus accumbens, females showed significant increases in extracellular dopamine following 0.25 or 0.5 g/kg ethanol, but did not show significant increases over baseline at the higher doses. Males showed slight increases in dopamine at the lower doses and decreased dopamine at 2.0 g/kg. In striatum, both sexes showed increased dopamine at the lower doses and decreased dopamine at 2.0 g/kg. There were slight increases in nucleus accumbens DOPAC and HVA at some doses in both sexes, but no changes in striatal metabolite levels. In addition to showing increased responsiveness to ethanol-induced mesolimbic dopamine stimulation, females consumed more ethanol than males during behavioral testing. The pattern of both greater ethanol-induced nucleus accumbens dopamine release and greater ethanol consumption in females supports the hypothesis that ethanol reward is mediated, at least in part, by the mesolimbic dopamine system.

Modulation of the stress response by ethanol in the rat frontal cortex

Microdialysis was used to characterize the effects of two doses of ethanol, stress, and their interaction on the dopaminergic system. Saline-treated animals showed no changes in levels of dopamine (DA) or dihydroxyphenylacetic acid (DOPAC). Neither a 0.5- nor a 2-g/kg IP injection of ethanol had an effect on DA or DOPAC in resting animals. Immobilization caused marked increases in DA levels and smaller increases in DOPAC. Pretreatment with 0.5 g/kg ethanol did not reduce the stress-induced increase in DA or DOPAC. However, pretreatment with 2 g/kg ethanol strongly reduced and antagonized the stress-induced increases in DA and potentiated the stress-induced increase in extracellular DOPAC. Our data show that ethanol can have different, dose-dependent effects in resting vs. stressed animals, that it has different effects on DA and DOPAC, and that the high dose antagonized stress-induced increases in DA. The latter adds biochemical evidence to the tension-reduction hypothesis of ethanol by perhaps implicating a reduction in the DA stress response by ethanol as a contributing factor in the development of alcoholism.

Ethanol alters monoamines in specific mouse brain regions

Ethanol (3.5 g/kg 60 min post-IP injection) produced the following changes in regional brain monoamine levels and in the respective metabolite/neurotransmitter ratios: for the noradrenergic system, MHPG was decreased in the amygdala and increased in the hypothalamus, while the MHPG/NE ratio was increased in the prefrontal cortex and the hypothalamus. For the dopaminergic system, DA was decreased in the olfactory tubercle, DOPAC was increased in the prefrontal cortex and septum, and DOPAC/DA was increased in the prefrontal cortex, septum, striatum, and hypothalamus. HVA was increased in the prefrontal cortex and septum, while HVA/DA was increased in the same regions plus the olfactory bulb. 3MT was decreased in the olfactory tubercle and striatum. The serotonergic system was not altered. The results demonstrate that ETOH produces selective regional changes in the concentration and utilization of monoamines in mouse brain with a predominant influence on dopaminergic systems and a lesser effect on noradrenergic activity.

The influence of acute ethanol exposure on growth hormone release in female rats

This study investigates the site (hypothalamic or pituitary) at which ethanol (ETOH) alters GH release in female rats. Both the hypothalamic response to clonidine (CLON), an alpha 2-adrenergic agonist, and the pituitary response to growth-hormone releasing hormone (GRH) were tested. Jugular cannulae were inserted for drug administration and undisturbed blood sampling. ETOH was injected IP 24 and 1 h before experimentation. In animals receiving saline or ETOH (1, 2, or 3 g/kg), there was no response to CLON and no difference in GH levels between groups. On the other hand, there was a significant surge in GH release in response to a high dose of GRH (1000 ng/kg) in both saline controls and in ETOH (3 g/kg) animals. Although there was no difference in the height of the surge between groups, baseline GH levels were higher in animals that received ETOH. In response to a low dose of GRH (250 ng/kg) the GH surge was only significant in the ETOH animals. In animals receiving somatostatin antiserum (anti-SRIF; 0.5 ml) in combination with the low GRH dose, the surge in GH levels was significant in both saline and ETOH animals, however, the surge was higher in saline compared to ETOH animals. The results of this study suggest that: 1) ETOH alters the SRIF system (release of reception) in female rats and that this interaction is evident when GRH concentration is low, and 2) ETOH may also inhibit GH release by interfering with the GRH system, however, the site of this influence most likely does not involve an alpha 2-GRH component.

Focal application of alcohols elevates extracellular dopamine in rat brain: a microdialysis study

Dopaminergic systems are thought to play a major role in the stimulant and reinforcing properties of drugs of abuse, including ethanol. The present study describes the effects of local perfusion with ethanol (and other alcohols) on extracellular dopamine in the striatum and nucleus accumbens. Following the establishment of basal dopamine levels (2-3 h), various concentrations of ethanol in artificial CSF (0.01-10% v/v) were slowly perfused through a microdialysis probe. Each dose of ethanol was found to increase dopamine concentrations in both the striatum and nucleus accumbens. This increase was dose-related in the striatum. The exclusion of calcium and inclusion of 12.5 mM magnesium in the perfusion medium prevented, or greatly attenuated the ethanol-induced dopamine (DA) release. Thus, the release of DA by ethanol is exocytotic in nature and involves calcium-dependent processes. The other alcohols tested, namely methanol and butanol, demonstrated a structure-activity relationship together with ethanol, in their ability to increase extracellular DA. The relative potency was butanol greater than ethanol greater than methanol. The diffusion of ethanol into the brain tissue was investigated following perfusion through the probe. Relatively low concentrations of ethanol were found in striatal tissue during perfusion and they declined rapidly with time, following the removal of ethanol from the perfusate. The concentrations of ethanol achieved in brain tissue following focal application through the microdialysis probe were relevant to human intoxication.

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.

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.

Inhibition of brain dopa-decarboxylase by RO 4-4602 infused ICV blocks alcohol drinking induced in rats by cyanamide

Following the stereotaxic implantation of chronic cannulae for intracerebroventricular (ICV) infusion, rats were given an alcohol preference test to establish their preferred concentration in comparison with water. After alcohol was removed, 15 mg/kg cyanamide was then injected subcutaneously for 4 days in order to maximize volitional intake of single solutions of alcohol, which in these animals ranged from 7 to 15%. The L-dopa-decarboxylase inhibitor benserazide (Ro 4-4602) injected subcutaneously twice daily in doses of 50-100 mg/kg failed to alter the rats' alcohol consumption either in terms of g/kg or proportional values. However, when given ICV twice daily in concentrations of 10 ng-2.0 micrograms per 5.0 microliters volume, benserazide attenuated the rats' alcohol drinking significantly. This reduction occurred in a dose-dependent manner in terms of both absolute and proportional intakes of alcohol. Pre-treatment of the animals with 1.0 microgram benserazide given ICV, when alcohol was removed from the test situation, did not abolish the subsequent ingestion of alcohol but its peripheral administration (50 mg/kg) enhanced drinking. These results suggest that the interference with the metabolic pathway of dopamine or serotonin synthesis, possibly through the mechanism of reduced formation of aldehyde adducts in the brain, markedly alters the pattern of voluntary drinking in the rat. Alternatively, benserazide could act by its central inhibition of aldehyde dehydrogenase, which in turn would concomitantly elevate levels of acetaldehyde and thereby reduce alcohol drinking.

Involvement of noradrenergic system in a remarkably rapid tongue clonus produced by acute hypnotic doses of ethanol in Fischer F344 rats

Ethanol (2.95 g/kg, IP) eliminated the righting reflex and induced vigorous tongue clonus spontaneously or following tactile tongue stimulation in Fischer F344 rats. Responses normally lasted 30-60 min, and was reinstated by tactile stimulation in those cases where it subsided quickly. Sub-hypnotic (1.95 g/kg) or high (3.95 g/kg) doses failed to elicit clonus, even after tactile stimulation. A lipophilic alpha 1-adrenergic agonist (St 587) promptly initiated tongue clonus in rats treated with a 3.95 g/kg dose of ethanol. Prazosin, a selective alpha 1-adrenergic antagonist, blocked clonus, while the dopamine selective antagonist pimozide failed to modify this response. We infer an alpha 1-adrenergic effect in which norepinephrine is released by ethanol.

Ethanol withdrawal alters apomorphine-induced motility

Acute administration of ethanol is accompanied by alterations in dopamine turnover and release, and chronic ethanol exposure is associated with changes in biochemical measures of dopamine receptor function. This paper presents data examining the effects of chronic ethanol exposure on behavioral responses to the dopamine receptor agonist apomorphine. Measurements of behavior were obtained through the use of an electronic motility monitor which permitted the quantification of movements in terms of their characteristic frequency components. Results are presented which indicate that apomorphine-induced movements with modal frequencies of 2 Hz and of 8-9 Hz are significantly increased during the 12 to 24 hr following ethanol withdrawal, suggesting an increase in the functional responsiveness of central dopaminergic systems.

Biochemical evidence for activation of specific monoamine pathways by ethanol

The effects of an acute intraperitoneal (IP) low (0.5 g/kg) or high (2.5 g/kg) dose of ethanol on the contents of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in 7 selected CNS regions of the rat were examined after 15, 30 and 60 minutes. The IP administration of 0.5 g/kg ethanol produced blood alcohol concentrations (BACs) of 41 +/- 4, 40 +/- 4 and 15 +/- 1 mg% (N = 8 each) after 15, 30 and 60 minutes, respectively. This low dose of ethanol did not alter the levels of DA, DOPAC, HVA, 5-HT and 5-HIAA in any of the 7 CNS regions at any of the time points examined. The dose of 2.5 g/kg ethanol produced BACs of 254 +/- 26, 268 +/- 20 and 282 +/- 10 mg% (N = 8 each) after 15, 30 and 60 minutes, respectively. This high dose of ethanol did not alter the contents of DA and 5-HT in any of the regions examined at any of the times, except for a 30% increase in the content of DA in the posterior striatum after 60 minutes. The administration of 2.5 g ethanol/kg elevated the levels of DOPAC and/or HVA 25 to 70% over saline control values in the (a) nucleus accumbens (ACC) and hypothalamus (HYPO) after 15, 30 and 60 minutes, and (b) posterior striatum (PSTR), lateral septal nucleus (LSN) and frontal cortex (FCTX) after 60 minutes. The contents of DOPAC and/or HVA were not altered by the high dose of ethanol in either the thalamus or olfactory bulbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Apomorphine-induced hypothermia increases during ethanol withdrawal

Changes in several measures of dopamine function have been observed following acute or chronic ethanol exposure. The present study examined the effects of chronic ethanol exposure on the hypothermia following acute administration of the dopamine agonist apomorphine. Animals withdrawn from chronic ethanol exposure showed a significantly greater decrease in body temperature following apomorphine than did ethanol-naive controls, suggesting an increase in sensitivity to dopaminergic stimulation during ethanol withdrawal.

The role of dopamine in the facilitatory effect of angiotensin II on impaired learning in rats chronically treated with ethanol

Rats with impaired active avoidance induced by chronic (9 weeks) administration of ethanol were studied. Angiotensin II (ANG II) administered (ICV, 2.0 micrograms) 12 h after the withdrawal of the alcohol not only neutralized the toxic effect of ethanol but also improved learning. When administered on the 5th day after ethanol withdrawal, the effect of ANG II was weaker. Tests of stereotypy and catalepsy were used to study the possible role of the dopaminergic system in this action of ANG II. It was shown that both chronic alcohol treatment and ANG II alone increased apomorphine (1 mg/kg) and amphetamine (7.5 mg/kg) stereotypy but the effects of ANG II were greater. ANG II did not change the stereotypy induced by amphetamine but increased the stereotypy induced by apomorphine in the group of animals chronically treated with alcohol. Haloperidol-induced catalepsy was reduced in these rats. ANG II alone intensified catalepsy and eliminated the effect of ethanol. Both ANG II and alcohol increased striatal dopamine (DA) concentration. This effect of ANG II was significantly greater in the animals chronically treated with alcohol. The above changes were not observed after the DA level had been reduced by alpha-methyl-p-tyrosine (250 mg/kg), nor were changes observed in the striatal DOPAC. The results suggest involvement of the central dopaminergic system in the effect of ANG II on the ethanol-induced impairment of acquisition of active avoidance but, however, the results of the biochemical determinations of DA turnover do not provide an explanation of these changes.

Ethanol-induced hypothermia and biogenic amine metabolites

Ethanol is known to cause hypothermia. The rectal temperature of rats receiving ethanol, 4 g/kg i.p., at an ambient temperature of 23 degrees C decreased by 2 degrees C. This body temperature decrease could be prevented by keeping the animals at an ambient temperature of 34 degrees C. Irrespective of the body temperature it was found that the concentration of the major metabolites of dopamine and serotonin in brain tissue was significantly increased. Thus, the change in brain monoamine metabolite levels in rats after administration of ethanol are not due to ethanol-induced hypothermia.

The effect of ethanol on the brain catecholamine systems in female mice, rats, and guinea pigs

The effect of acute ethanol administration on the concentrations of dopamine (DA), norepinephrine (NE) and their metabolites (3,4-dihydroxyphenylacetic acid [DOPAC], homovanillic acid [HVA], 3,4-dihydroxyphenylglycol [DHPG] and 4-hydroxy-3-methoxyphenylglycol [HMPG]) in brains of female mice, rats, and guinea pigs were investigated. A subhypnotic dose (2 g/kg) or a hypnotic dose (4 g/kg) of ethanol was administered intraperitoneally and the animals were killed 45 min later. In the rat the DA levels were unchanged, while the NE concentrations were decreased after both doses of ethanol. The DA levels did not change in the mouse and guinea pig, while the concentrations of NE showed a minor decrease in the mouse but were unaffected in the guinea pig. After 4 g/kg of ethanol the DOPAC and HVA concentrations were elevated significantly in all three species, and after 2 g/kg the DOPAC levels were increased in the rat and guinea pig brains and the HVA levels in the mouse and guinea pig brains. In the mouse and rat brain the DOPAC + HVA concentrations indicated a dose response relationship: 4 g/kg was significantly more effective than 2 g/kg. The DHPG concentration increased in the rat brain after both 2 and 4 g/kg, while the HMPG concentrations increased significantly only after 2 g/kg. In the mouse and guinea pig the brain DHPG concentrations remained unchanged, while the HMPG concentrations increased after both 2 and 4 g/kg ethanol. These data suggest, that the turnover of both DA and NE was increased 45 min after a subhypnotic as well as after a hypnotic dose of ethanol in all three species studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the interaction between ethanol and amfonelic acid

Amfonelic acid (AFA), a non-amphetamine central stimulant dose-dependently reduced the hypnotic effect of ethanol in C57B1/6 mice. It did not enhance the elimination of ethanol. Amfonelic acid failed to modify the duration of pentobarbitone-induced hypnosis or the ethanol-induced hypothermia in these animals. Combined treatment with amfonelic acid and a lipophilic alpha 1-adrenoceptor agonist was not more effective than amfonelic acid alone in blocking ethanol hypnosis. The stimulation of locomotor activity by amfonelic acid in C57B1/6 mice was more sensitive to the blocking effect of ethanol than stimulation induced by d-amphetamine. The blocking effect of amfonelic acid, but not that of d-amphetamine, on the effects of ethanol developed tolerance. In pimozide-pretreated mice, amfonelic acid failed to reduce the ethanol-induced hypnosis. Hence it appears that dopamine (DA) released by amfonelic acid is responsible for its antagonism of ethanol. However, though amfonelic acid acted as a strong releaser of DA in Swiss-Webster, CD-1, DBA-2 and BALB/c mice, in these strains it failed to reduce the effect of ethanol. Moreover, methylphenidate, a dopaminergic stimulant, which acts by a mechanism similar to that of amfonelic acid was not effective in reducing the hypnotic effect of ethanol in C57B1/6 mice. For these reasons, additional mechanisms may have to be considered to explain this strain-dependent effect of amfonelic acid.