Metabolism of ( 14 C)-serotonin in the caudate nucleus, hypothalamus and reticular formation of the rat after ethanol administration

Influences of ethanol ingestion on olfactory function in humans

RATIONALE

Although ethanol is known to influence, in humans, psychophysical measures of visual, auditory, and vestibular function, the influence of this drug on the ability to smell is not clear.

OBJECTIVES

To evaluate, in eight men and eight women, the influences of ethanol ingestion on four well-validated measures of olfactory function: an ethanol odor detection threshold test, a phenyl ethyl alcohol odor detection threshold test, a 40-item smell identification test, and an odor discrimination/short-term odor memory test.

METHODS

In this double-blind experiment, grape juice alone was administered prior to the olfactory tests on one test occasion, and a grape juice-vodka mixture, designed to produce blood levels of ethanol near the legal level of intoxication, on another. The order of the two drug conditions was counterbalanced, as was the order of the presentation of the olfactory tests.

RESULTS

Ethanol ingestion markedly influenced the detection threshold for ethanol (all 16 subjects exhibited higher thresholds under the ethanol than under the non-ethanol condition) and had a significant, albeit small, influence on odor discrimination performance, as measured by the total number of correct responses independent of delay interval. Women performed significantly better than men on the latter measure. No influences of ethanol on odor identification, the phenyl ethyl alcohol detection threshold, or the delay interval (memory) component of the odor discrimination/memory test were observed.

CONCLUSIONS

Alcohol ingestion markedly and selectively alters olfactory sensitivity to ethanol, perhaps via habituation processes, and may subtly influence some measures of odor discrimination.

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Ethanol self-administration restores withdrawal-associated deficiencies in accumbal dopamine and 5-hydroxytryptamine release in dependent rats

Basal forebrain dopamine (DA) and 5-HT neurotransmission has been implicated in the mediation of the acute reinforcing actions of ethanol. Neuroadaptation theories predict that compensatory changes in neurochemical systems that are activated by alcohol acutely may underlie symptoms of withdrawal after chronic administration. To test this hypothesis, the release of DA and 5-HT was monitored by microdialysis in the nucleus accumbens of dependent male Wistar rats at the end of a 3-5 week ethanol (8.7% w/v) liquid diet regimen, during 8 hr of withdrawal, and during renewed availability of ethanol involving (1) the opportunity to operantly self-administer ethanol (10% w/v) for 60 min, followed by (2) unlimited access to the ethanol-liquid diet. Results were compared to control groups pair-fed with ethanol-free liquid diet and trained to self-administer either ethanol or water. In nondependent rats, operant ethanol self-administration increased both DA and 5-HT release in the NAC. Withdrawal from the chronic ethanol diet produced a progressive suppression in the release of these transmitters over the 8 hr withdrawal period. Self-administration of ethanol reinstated and maintained DA release at prewithdrawal levels but failed to completely restore 5-HT efflux. 5-HT levels recovered rapidly, however, within 1 hr of reexposure to ethanol liquid diet. These findings suggest that deficits in accumbal monoamine release may contribute to the negative affective consequences ethanol withdrawal and, thereby, motivate ethanol-seeking behavior in dependent subjects.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Ethanol challenge alters amino acid neurotransmitter release from frontal cortex of the aged rat

In two groups of male rats having an average age of either 90 days or two years, guide cannulae for bilateral push-pull perfusion were implanted stereotaxically to rest upon the superficial frontal cerebral cortex. On post-operative recovery, either 1.5 or 3.0 g/kg 20% ethanol (V/V) was given by intragastric gavage to each unrestrained rat. Sequential samples of venous blood were obtained from the tail and analyzed for alcohol levels by gas chromatography. A set of push-pull perfusions of the cortical sites was carried out with an artificial CSF before gavage and at 25, 50 and 150 min after the administration of ethanol. An individual perfusion was continued for 5.0 min at a rate of 25 microliters/min. Using high performance liquid chromatography with electrochemical detection (HPLC-EC) each sample of perfusate was then assayed for its content of glutamate (Glu), aspartate (Asp), glutamine (Gln), glycine (Gly), taurine (Tau) and GABA with homoserine used as the internal standard. The results showed that the 3.0 g/kg dose of ethanol resulted in a higher level of blood ethanol in the older animals, which persisted over the 150 min time interval. Further, the 1.5 g/kg dose of ethanol administered to the older rats reduced the cortical activity of Glu and Gln relative to the younger animals. In addition, the 3.0 g/kg dose augmented the cortical efflux of Tau in the aged rats. Neither dose of ethanol affected the efflux of Asp or Gly from the perfused frontal cortex of either the young or old group, nor was the release of GABA detectable under either the control condition or following treatment with ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

Central Ca++-channel blockade reverses ethanol-induced poikilothermia in the rat

Two series of experiments were performed to determine the possible involvement of Ca++ channels in the thermolytic action of ethanol administered at a room temperature of 22 degrees C. In one group of 11 adult female Sprague-Dawley rats, stainless steel guide cannulae were implanted stereotaxically above the lateral cerebral ventricle. Prior to an experiment, a thermistor probe was inserted into the colon so that core temperature could be monitored continuously for up to six hours or until the temperature had returned to a previous baseline level. When the animal's body temperature had stabilized, a dose of 4.0 g/kg in a v/v solution of 20% ethanol was given by intragastric gavage. After the body temperature had declined by about 2.0 degrees C, ordinarily 30 min after ethanol administration, either control CSF or the vehicle plus one of four doses of verapamil (8.3, 25, 50 and 100 micrograms) was infused intracerebroventricularly (ICV) in a volume of 10 microliter. In a second group of 7 unoperated rats, either 4.0 g/kg ethanol or a physiological saline control solution was administered isovolumetrically by intragastric gavage; then, 30 min later, either 3.0 or 10.0 mg/kg verapamil was injected intraperitoneally. At an ambient temperature of 22 degrees C, ethanol gavage produced a significant decline in colonic temperature which was unaffected by physiological saline given by the same route. Although the CSF control vehicle was without effect, verapamil administered ICV attenuated the thermolytic action of ethanol in all doses tested; however, the lowest dose exerted its antagonist effect but with a longer latency. Conversely, when verapamil was given systemically, the hypothermic action of ethanol was significantly potentiated in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxyindoleacetic acid and 5-hydroxytryptophol levels in rat brain: effects of ethanol, pyrazole, cyanamide and disulfiram treatment

The two serotonin metabolites 5-hydroxyindoleacetic acid (5HIAA) and 5-hydroxytryptophol (5HTOL) were measured in two regions of rat brain (pons medulla and diencephalon) using a gas chromatographic-mass spectrometric (GC-MS) method. Acute ethanol intoxication effected an elevation of 5-hydroxytryptophol levels, while 1 week of treatment with ethanol appeared to have no effect on either metabolite when measured 24 h after the last dose. Disulfiram and cyanamide treatment produced an approximately 2-fold increase in 5-hydroxytryptophol and a slight reduction in 5-hydroxyindole-acetic acid. Pyrazole treatment produced an increase in both metabolites. This effect was, however, counteracted by the simultaneous administration of ethanol.

5-hydroxytryptophan-induced conditioned taste aversion to ethanol in the rat

This experiment was conducted to determine the efficacy of 5-HTP in producing conditioned taste aversions (CTAs) to ethanol in rats restricted to a one-hour daily access to fluid. Administration of 100 mg/kg of DL-5-HTP immediately following novel exposure to ethanol resulted in an aversion of such magnitude that some rats refused to consume the ethanol solution. Since ethanol was the only fluid available to these rats, they eventually died, presumably of dehydration. By comparison, LiCl administration also produced a CTA to ethanol, but no such persistent rejection was observed. Both 5-HTP and LiCl also produced CTAs when saccharin and tartaric acid solutions were used as novel fluids, but these aversions were short-lived and all rats resumed drinking. The causative factor(s) in the persistent ethanol rejection until death observed in rats treated with 5-HTP remain undetermined but the results have indicated that simple CS-UCS associative learning mechanisms are probably not a primary causative factor.

Ethanol metabolism and striatal dopamine turnover

In recent reports it has been indicated that acute and chronic ethanol treatments affect the central dopaminergic system. In particular, after acute ethanol administration it has been detected an increase of dopamine (DA) turnover measured as dihydroxyphenylacetic acid (DOPAC) content in rat corpus striatum. In order to verify the correlation between these neuronal events and the metabolism of ethanol, we measured striatal DA activity after different experimental manipulations of liver function. Ethanol metabolic rate has been stimulated by administering phenobarbital sodium, while liver ethanol metabolism was decreased with a subtotal hepatectomy. In these conditions we found a shift to the left of the time curve for DOPAC levels and a significant reduction of the peak of DOPAC increase respectively. In this paper we report that acetaldehyde induces modifications of the striatal DOPAC content, which become significant after a shorter latency period in comparison with the acute ethanol injection. Our data suggest the hypothesis that the neurochemical effects of ethanol may be mediated by the formation of specific metabolic products.

The effect of alcohol on dopamine metabolism in the caudate nucleus of an unanesthetized monkey

Previously it was shown that the acute administration of ethanol to the rat significantly alters the metabolism of the dopamine (DA) in liver but not in brain tissue. To extend this finding to the primate, two push-pull perfusion cannulae were implanted in the regions of the left and right caudate nucleus of a Macaca nemistrina. After 14C-DA was injected into the caudate, the site ws perfused with an artificial CSF and the perfusate analyzed for the major metalolites of DA. Ethanol was then administered in a dose of 6 g/kg by the nasopharyngeal route. The results show that very little alteration occurs in the metabolism of DA during or postethanol intoxication.

Brain monoamines and free choice ethanol consumption in rats

Rats given intraventricular (i.v.t.) injections of 6-hydroxydopa (90 microgran) showed reduced brain part noradrenaline levels but no change in free choice ethanol consumption, while rats given 6-hydroxydopamine (250 microgram) i.v.t. injections showed reduced brain part noradrenaline and dopamine levels and a reduced free choice ethanol intake. Rats given i.v.t. injections of 5,6-dihydroxytryptamine (50 microgram) showed a reduction of serotonin in the hippocampus and an increase in free choice ethanol consumption. Chronic forced ethanol consumption, achieved by placing rats on a Metrecal--ethanol diet, also increased subsequent free choice ethanol intake, but had no permanent effect on brain part monoamine levels. Rats exposed to ethanol prenatally were hyperactive at 5 weeks of age but not at 10 weeks. At 15 weeks, their ethanol preference was not different from that of controls nor did their brain part monoamine levels differ from those of controls at 16 weeks. These results indicate that disrupting the balance between the monoamine neuro-transmitter systems with the neurotoxins alters the free choice ethanol consumption of rats but that prior chronic exposure to ethanol also changes free choice ethanol consumption in the absence of any permanent change in monoamine levels. The long-term behavioral changes seen in rats exposed to ethanol are not due to permanent alterations in the brain levels of noradrenaline, dopamine, or serotonin.

The effects of ethanol on dopamine metabolism in rat liver and brain

Levels of dopamine metabolites are drastically altered in the presence of ethanol in liver slices, however no change in brain metabolism of dopamine is observed in a conscious animal which has been administered ethanol. Though THP can be formed in the cell during the metabolism of dopamine, increasing DOPAL levels does not cause an increase in THP formation. Thus if this compound is important in the overall alcohol problem more subtle ways of looking at its formation in individual synaptic regions will have to be developed in order to determine if ethanol will alter its level.

The metabolism of biogenic amines in experimental animals and in human subjects during acute and chronic administration of ethanol

Ethanol has been shown to induce a shift in catecholamine metabolism peripherally from normally oxidative pathways to reductive pathways. The mechanisms of this effect may result from competitive inhibition of aldehyde dehydrogenase by acetaldehyde. The shift in metabolism cannot be found in brain and alterations in catecholamine function may reflect changes in the turnover of these amines.

Intraventricular ethanol and ethanol intake: a behavioral and radiographic study

Ethanol (10% w/v) was infused intraventricularly at a rate of 11 mul/hr, delivered over 50 sec every 10 min for 10 days into 5 Sprague-Dawley and 5 Wistar rats. Thereafter, preference testing with ascending concentrations of alcohol solutions vs . water vs. food gave no significant differences between treated and sham-operated controls, in contradiction to previously reported increases in alcohol consumption. Ethanol's rate of elimination from the ventricle and its pattern of diffusion into the brain were determined using radioactive ethanol: elimination from the brain is rapid with a half-like of 24 to 35 sec, and the amount diffused throughtout the brain small, with a maximal concentration in any one section of 0.004% (such a concentration is at least 20 times less than would result from a moderately intoxicating parenteral dose of ethanol). The character of the elimination and the lack of effect on alcohol intake found here indicate that intraventricularly administered ethanol is a technique with no usefulness in elucidating the processes affecting alcohol addiction.