Alteration of central catecholamine metabolism following acute administration of ethanol

Lead and ethanol coexposure: implications on the dopaminergic system and associated behavioral functions

The present investigation involves ethanol's effects on the lead-induced alterations in the dopaminergic system. Ethanol, at a dose of 3 g/kg body weight for 8 weeks, resulted in a marked increase in the accumulation of lead in the blood and brain of animals receiving 50 mg lead/kg body weight. Levels of dopamine were found to decrease significantly, and were accompanied with increased norepinephrine levels in lead and ethanol coexposed animals. Uptake of tyrosine as well as the activities of tyrosine hydroxylase and monoamine oxidase were seen to increase significantly in lead as well as ethanol-treated animals, and these were increased to a greater extent when animals were administered lead and ethanol simultaneously. Dopamine receptor binding studies revealed a significant elevation in the number of binding sites in lead and ethanol-coexposed animals. The altered dopaminergic functions were reflected by the neurobehavioral deficits in terms of motor incoordination, aggressiveness, and hyperactivity of animals exposed to lead, the effect being more pronounced in lead- and ethanol-coexposed animals. In brief, results of this study suggests that ethanol potentiates lead-induced cellular damage at the neurochemical and neurobehavioral level.

Ethanol, but not the anxiolytic drugs buspirone and diazepam, produces a conditioned place preference in rats exposed to conditioned fear stress

The present study was designed to investigate the role of an anxiolytic effect in the development of a drug-associated place preference in rats exposed to conditioned fear stress, using the conditioned place-preference paradigm. The administration of a low dose of ethanol (300 mg/kg, IP) and the anxiolytic drugs, buspirone (1 and 2 mg/kg, IP) and diazepam (1.25 and 2.5 mg/kg, IP), did not produce a place preference in rats that were not exposed to conditioned fear stress. In rats that were exposed to conditioned fear stress, ethanol produced a significant place preference, while buspirone and diazepam failed to produce a place preference. In addition, ethanol, buspirone, and diazepam produced no place preference in rats treated with an anxiogenic dose of pentylenetetrazole (20 mg/kg, IP). A significant decrease in locomotor activity was observed in rats exposed to conditioned fear stress. Ethanol, but not buspirone and diazepam, significantly recovered or increased locomotor activity in rats exposed to conditioned fear stress. Further, the locomotor-stimulating effect of ethanol was markedly enhanced by repeated exposure to conditioned fear stress. These results suggest that the stimulating effect may be strongly related to the development of the rewarding effect of a low dose of ethanol under psychological stress, and that the conditioned place preference paradigm with conditioned fear stress may be useful for studying the rewarding mechanism of ethanol with regard to the interaction between ethanol and psychological stress.

Disrupted melatonin-secretion during alcohol withdrawal

1. The synthesis of the pineal hormone, melatonin, is under adrenergic control. The brain's rhythm generating system (suprachiasmatic nucleus and associated systems) which is synchronised by the light-dark cycle controls norepinephrine release from the sympathetic nerve terminal resulting in cAMP accumulation. Increased cAMP leads to induction of the rate-limiting enzyme, N-acetyltransferase and synthesis of melatonin. The pineal exhibits a circadian rhythm with highest blood levels of the hormone being present during the night. The circadian rhythm of melatonin production provides important time-of-day and time-of-year information and, as a result, this hormonal cycle drives other 24-hour rhythms as well as seasonal cycles of reproduction, at least in photoperiodic mammals. 2. Chronic alcoholics were withdrawn from alcohol during a continued period of 4 days and nights. Blood samples were drawn from an indwelling venous catheter and sleep was monitored with polysomnography. No medication was used. No alcohol intake was allowed after admission. Bright light treatment was applied during day 3 of the study. 3. During the 4 days of alcohol-withdrawal the night time melatonin-secretion was disrupted. More than 50% of the patients had a very low secretion (< 30 pg/ml) which did not normalize during the study period. Psychopathology, sleep quality and sleep architecture improved significantly. The melatonin secretion pattern showed low values throughout the study. This low melatonin secretion might reflect the long lasting toxic influence of alcohol on the biological clock and/or a direct inhibitory effect on pineal function. These are different effects, although interrelated. 4. Ethanol has a direct inhibitory effect on pineal melatonin synthesis. A well-recognized action of ethanol is its ability to permeate and perturb the structure of cell membranes and may be related to its lipophilic properties. The changes in membrane fluidity seem to last longer than the study period of 4 days.

Analysis of the biphasic locomotor response to ethanol in high and low responders to novelty: a study in Nijmegen Wistar rats

The aim of the study was to investigate the biphasic locomotor response to ethanol in rats. Based on the recent finding that high responders to novelty (HR) and low responders to novelty (LR), selected from an outbred Nijmegen Wistar rat population, show differences in ethanol intake and preference, it was initially investigated to what extent HR and LR differ in their locomotor response to ethanol. A dose-response curve (0.2-2.0 g/kg, i.p.) was established using standardized activity boxes. HR showed a significant increase at 0.5 g/kg, followed by a significant decrease at doses 1.0-2.0 g/kg; LR showed only a decrease at doses 1.0-2.0 g/kg. Secondly, it was investigated to what extent stress altered the ethanol-induced increase and decrease, respectively. For that purpose, the ethanol-induced locomotor effects (0.5 and 1.0 g/kg) were analyzed in habituated and non-habituated (stressed) HR and LR; habituation consisted of a 15-min adaptation period to the activity cages. Stress significantly enhanced the excitatory effects in HR, but had no effect on the sedative effects in HR and LR. Finally, the locomotor effects of sub-chronic treatment (7 days) with an excitatory (0.5 g/kg) or sedative (1.0 g/kg) dose were analyzed in HR and LR. The excitatory effect of 0.5 g/kg disappeared throughout the treatment in HR, whereas the sedative effects of 1.0 g/kg remained the same in HR and LR. It is concluded that the mechanism underlying the ethanol-induced motor excitation differs completely from that underlying the ethanol-induced sedation. Given the known differences in the make-up of the brain and endocrine system between HR and LR, these animals are suggested to be good models for studying the mechanisms underlying the biphasic locomotor response to ethanol in rats.

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.

Alterations in dopamine metabolism by intraperitoneal ethanol in rats selected for high and low ethanol preference: a 3-methoxytyramine study

Effects of an ethanol dose (1 g/kg, IP) on the metabolism of dopamine (DA) in the nucleus accumbens, striatum and hypothalamus of ethanol-naive alcohol-preferring (AA) and alcohol-avoiding (ANA) rats were studied. Rats were sacrificed by focused-beam microwave irradiation of the brain 20 minutes after ethanol administration, and the concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), assumed to reflect DA metabolism, and of 3-methoxytyramine (3-MT), assumed to reflect DA release, were measured using gas chromatography-mass spectrometry. Basal striatal DOPAC and HVA concentrations were higher in the AA rats in comparison with ANA rats. Ethanol increased HVA, but not DOPAC, concentration in the nucleus accumbens and striatum, but not in the hypothalamus. There was a significant rat line x ethanol treatment interaction with respect to HVA concentration in the nucleus accumbens. The increase in HVA was higher in the AA than ANA rats. Basal 3-MT concentration was not changed by ethanol, except in the nucleus accumbens, where a significant rat line x ethanol treatment interaction was found. A decrease in 3-MT concentration was only detected in the ANA rats. After inhibition of monoamine oxidase with pargyline hydrochloride (75 mg/kg, IP, 10 min before sacrifice), 3-MT accumulation was decreased by ethanol, especially in the nucleus accumbens of both AA and ANA rat lines as well as in that of nonselected Wistar rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of CA antagonists on ethanol-induced excitation in habituated and nonhabituated mice: interaction with stress factors?

The effects of CA antagonists on ethanol induced locomotion in habituated (N) and nonhabituated (NH) mice was examined. H-mice were exposed to the testing apparatus for 4 days before testing. Mice were pretreated with pimozide (D2 antagonist), Schering 23390 (D1 antagonist), phenoxybenzamine (alpha 1 antagonist), or yohimbine (alpha 2 antagonist). Mice were then treated with ethanol. H mice had lower activity scores compared to NH mice. Ethanol produced an increase in activity for both groups. In NH animals, pimozide attenuated excitation in inverse relation to the ethanol dosage. In H mice, pimozide attenuated excitation only at doses that in themselves produced a decrease in activity. Schering 23390 reduced excitation only at doses that affected activity per se in both groups. Phenoxybenzamine reduced excitation dose-dependently in both groups. Yohimbine decreased excitation in both groups. Results suggest that stress emanating from a novel environment may affect not only activity per se but also the interaction between CA antagonists and ethanol.

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.

Ethanol reduces norepinephrine-stimulated melatonin synthesis in rat pinealocytes

In this study, the in vitro effects of ethanol on norepinephrine-stimulated cyclic AMP (cAMP), N-acetyltransferase (NAT), and melatonin (MT) production were examined in dispersed rat pinealocytes. Cellular cAMP content was determined 15 min after treatment; whereas NAT activity and MT release in the medium were determined 4.5 h after treatment. It was found that ethanol less than or equal to 200 mM had no effect on norepinephrine-stimulated cAMP response, whereas 25 mM ethanol resulted in a significant inhibition of norepinephrine-stimulated NAT and MT levels. Furthermore, ethanol was equally effective in inhibiting the dibutyryl cAMP-stimulated NAT and MT levels. The inhibitory action of ethanol was not due to a direct effect or a delay in the onset of NAT activity. When alcohols with different chain lengths were used, it was found that their inhibitory potencies were related to their chain lengths with butanol greater than propanol greater than ethanol greater than methanol. Taken together, these findings indicate that (1) ethanol has an inhibitory action on norepinephrine-stimulated MT synthesis, (2) one site of ethanol action is distal to cAMP elevation, and (3) the inhibitory effect of ethanol on pineal MT synthesis appears to be secondary to its hydrophobic action.

Differential effects of catecholamine antagonists on ethanol-induced excitation in mice

Catecholamine antagonists were assessed for their effects on ethanol-induced motor excitation. Motor excitation was measured in male Swiss-Webster mice using an open-field apparatus. Mice were treated with several doses of ethanol and at each dose, mice were pretreated with pimozide, a dopamine D2 antagonist, Schering 23390, a dopamine D1 antagonist, phenoxybenzamine, a noradrenergic alpha-1 antagonist, or yohimbine, a noradrenergic alpha-2 antagonist. Each mouse was subjected to only one dose regimen, and all injections were given IP. Ethanol produced an increase in locomotor activity. The degree to which pimozide attenuated ethanol excitation decreased with increasing ethanol dosage. At the highest dose of ethanol, pimozide increased ethanol excitation. Schering 23390 attenuated ethanol-induced excitation only at doses which affected motor activity per se. Phenoxybenzamine produced a dose-dependent reduction in ethanol excitation. Yohimbine had its greatest effects at the medium dose (4.0 mg/kg). These observations seem to indicate a role for both the dopamine D2 receptor and the noradrenergic alpha-1 receptor in ethanol-induced motor excitation.

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.

Transdihydrolisuride, a partial dopamine receptor antagonist: effects on monoamine metabolism

The 9,10-transdihydro analogue of the dopaminergic ergot derivative lisuride, transdihydrolisuride (TDHL) stimulated the accumulation of dopa following inhibition of the aromatic amino acid decarboxylase with 3-hydroxybenzylhydrazine HCl in striatum (0.1-10 mg/kg i.p.), in the dopamine rich part of the limbic system (at 3 mg/kg i.p.) and in the neocortex (0.3-10 mg/kg i.p.). At a low dose (0.03 mg/kg) however, TDHL inhibited dopa accumulation in the limbic system. In gamma-butyrolactone-pretreated rats TDHL not only inhibited the accumulation of dopa in striatum and in the dopamine-rich part of the limbic system but also antagonized the inhibitory effect of lisuride on dopa accumulation. The accumulation of 5-hydroxytryptophan was reduced in striatum, in parts of the limbic system and neocortex only at high doses of TDHL (3 and 10 mg/kg i.p.). TDHL (0.03 or 3 mg/kg i.p.) did not change the alpha-methyl-p-tyrosine methylester HCl-induced disappearance of dopamine but accelerated the disappearance of noradrenaline at a dose of 3 mg/kg in all brain regions studied. The striatal level of dihydroxyphenylacetic acid was increased by TDHL dose dependently, the maximum effect being only half of that induced by haloperidol. TDHL (0.3 and 3 mg/kg i.p.) stimulated the accumulation of 3-methoxytyramine and normetanephrine following monoamine oxidase (MAO) inhibition with pargyline. The data suggest that TDHL is a mixed agonist-antagonist at central dopamine receptors. Under normal conditions the antagonistic component appears to predominate in the nigrostriatal and mesolimbic system. The stimulation of noradrenaline turnover was most likely due to an adrenoceptor antagonistic action of TDHL.

Effect of ethanol in preovulatory periods on brain monoamine levels

The effects of two doses of ethanol (2 and 4 g/kg, i.p.) on the concentration of catecholamines (noradrenaline and dopamine), serotonin and 5-hydroxyindoleacetic acid in various regions of the rat brain were studied. The ethanol administration of both doses induces a significant decrease in the levels of hypothalamic noradrenaline. Similarly, 5-hydroxyindoleacetic acid levels in the same region and hemispheres are increased. The high dose produces an elevation in the concentration of midbrain dopamine. It was concluded that the hypothalamus is the brain region most sensitive to the action of ethanol and the effect of this substance differs according to the brain area.

Neurochemical correlates of tolerance and strain differences in the neurochemical effects of ethanol

The behavioral and neurochemical effects of acute and chronic ethanol administration were studied in BALB/c, C57B1/6 and DBA/2 mice. The rates of dopamine synthesis and release in the striatum were estimated by measuring the accumulation of DOPA and DOPAC, respectively, after inhibition of aromatic amino acid decarboxylase with NSD-1024. Biphasic behavioral effects were found in BALB/c and DBA/2 mice, but not in C57B1/6 mice, with low doses of ethanol producing activation and high doses, depression. Biphasic effects were also found in the dopamine response to acute doses of ethanol. The BALB/c and DBA/2 mice showed larger suppressions of DA release in the lower dose ranges of ethanol, and smaller increases at the higher doses than did the C57B1/6 mice. Ethanol stimulated dopamine synthesis in a monophasic, dose-dependent manner, and C57B1/6 mice were less sensitive to this effect of ethanol compared to the other tested strains of mice. Chronic ethanol feeding produced behavioral tolerance to the high-dose depressant effects of ethanol, but not to the low-dose activating effects. Similarly, tolerance developed in the dopaminergic responses to a higher challenge dose of ethanol (3.5 g/kg). These findings demonstrate that genetically determined differences exist in the sensitivity of the dopaminergic systems of mice to ethanol, and suggest that central dopamine neurons may be important in the behavioral effects of ethanol.

Catecholamine metabolism in rat brain following the intracerebroventricular administration of cyclic nucleotides

The dibutyryl analogues of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were administered into the lateral ventricles and catecholamine metabolites were determined in brain 40 min later. Dibutyryl cAMP elevated the level of homovanillic acid in whole brain and dihydroxyphenyl acetic acid levels in striatum, the dopamine-rich part of the limbic system and hemispheres but neither affected the accumulation of 3-methoxytyramine following inhibition of MAO with pargyline nor dopamine and noradrenaline levels. Normetanephrine accumulating after MAO inhibition was elevated markedly by dibutyryl cAMP. Dibutyryl cGMP was without effect on the catecholamine metabolites investigated. Dibutyryl cAMP appears to stimulate dopamine metabolism within dopaminergic nerve endings but does not stimulate dopamine release. Dibutyryl cAMP-induced activation of noradrenaline metabolism, however, appears to coincide with a stimulation of noradrenaline release.

3-Methoxytyramine and normetanephrine as indicators of dopamine and noradrenaline release in mouse brain in vivo

Intraperitoneal administration of pargyline HCl induced a dose-dependent accumulation of 3-methoxytyramine and normetanephrine in mouse brain in vivo. As judged by the decrease of 5-hydroxyindole acetic acid levels a dose of 200 mg/kg of pargyline appeared to inhibit monoamine oxidase completely. This dose led to an approximately linear accumulation of 3-methoxytyramine and normetanephrine during the first 3 hours. gamma-Butyrolactone, 750 mg/kg i.p. reduced the accumulation of 3-methoxytyramine despite a marked increase of dopamine. (+)-Amphetamine stimulated 3-methoxytyramine as well as normetanephrine accumulation at doses of 3 and 10 mg/kg i.p. In line with the concept of receptor-mediated negative feedback control of catecholaminergic transmission the dopamine receptor agonists apomorphine, 0.3 mg/kg i.p., lisuride, 0.05--0.3 mg/kg i.p., and bromocriptine, 10 mg/kg i.p., decrease 3-methoxytyramine formation while the dopamine receptor blocking agent haloperidol, 1 mg/kg i.p., led to a 3-fold increase. The alpha-adrenoceptor agonist clonidine, 0.1 mg/kg i.p., reduced the formation of normetanephrine and the alpha-adrenoceptor antagonists yohimbine, 10 mg per kg i.p., phenoxybenzamine, 20 mg/kg i.p., and mianserine, 50 mg/kg i.p., stimulated normetanephrine accumulation 1.5- to 4-fold. 3-Methoxytyramine and normetanephrine accumulating after inhibition of monoamine oxidase appear to be reliable indicators of dopamine and noradrenaline release and metabolism.

Acute and chronic ethanol treatment changes endorphin levels in brain and pituitary

Acute ethanol administration increased methionine-enkephalin (met-enkephalin) and beta-endorphin levels in distinct areas of the rat brain, whereas chronically supplied ethanol caused a depression of met-enkephalin and beta-endorphin levels in most of the brain areas investigated. The beta-endorphin content of the intermediate/posterior lobe of the pituitary of rats and guinea pigs decreased by 70%. Withdrawal of ethanol resulted in a complete recovery of endorphin levels in brain and pituitary within two weeks. Whether the observed alterations in endorphin concentrations are causally related to the primary mechanisms underlying alcohol dependence is uncertain, since no obvious signs of physical dependence were observed in treated animals.

Antagonism of ethanol's central stimulation by catecholamine receptor agonists

The effect of ethanol (2 g/kg) on brain catecholamine neurons in the rat as well as its interaction with catecholamine receptor agonists was studied utilizing single unit recording techniques. Identified dopamine (DA) neurons of the zona compacta, substantia nigra as well as noradrenaline (NA) neurons of the locus coeruleus showed no alterations in firing rate at ethanol administration. Also the function of their presynaptic DA and NA receptors, respectively, appeared normal judging from the unaltered inhibitory response to systemically or microiontophoretically applied receptor agonists, apomorphine and clonidine, respectively, when applied in small doses. In contrast, the catecholamine releasing agent amphetamine caused inhibition of firing of the central catecholamine neurons in the same anesthetized preparation. The rate of tryosine hydroxylation in vivo in central DA and NA neurons measured as the amount of Dopa accumulated in various brain regions following inhibition of aromatic l-amino acid decarboxylase by NSD 1015, 150 md/kg i.p., was significantly increased by ethanol in anesthetized rats. Consequently, the present data do not support the hypothesis derived largely from behavioural evidence that ethanol causes inactivation of central DA and NA neurons. The antagonism by catecholamine receptor agonists, apomorphine and clonidine of ethanol's behaviourally stimulant action may thus be of unspecific character. The results indicate that alterations in tyrosine hydroxylase activity, when measured as Dopa formation after decarboxylase inhibition, can occur without concomitantly altered impulse activity in central DA or NA neurons. At present the action of ethanol on brain DA and NA neurons remains unclear and necessitates further studies.