Alcohol intake, ethanol-induced narcosis and intoxication in rats following neonatal 6-hydroxydopamine or 5, 7-dihydroxytryptamine treatment

The influence of drug class on reward in substance use disorders

In the United States, the societal costs associated with drug use surpass $500 billion annually. The rewarding and reinforcing properties that drive the use of these addictive substances are typically examined concerning the neurobiological effects responsible for their abuse potential. In this review, terms such as "abuse potential," "drug," and "addictive properties" are used due to their relevance to the methodological, theoretical, and conceptual framework for understanding the phenomenon of drug-taking behavior and the associated body of preclinical and clinical literature. The use of these terms is not intended to cast aspersions on individuals with substance use disorders (SUD). Understanding what motivates substance use has been a focus of SUD research for decades. Much of this corpus of work has focused on the shared effects of each drug class to increase dopaminergic transmission within the central reward pathways of the brain, or the "reward center." However, the precise influence of each drug class on dopamine signaling, and the extent thereof, differs considerably. Furthermore, the aforementioned substances have effects on several neurobiological targets that mediate and modulate their addictive properties. The current manuscript sought to review the influence of drug class on the rewarding effects of each of the major pharmacological classes of addictive drugs (i.e., psychostimulants, opioids, nicotine, alcohol, and cannabinoids). Our review suggests that even subtle differences in drug effects can result in significant variability in the subjective experience of the drug, altering rewarding and other reinforcing effects. Additionally, this review will argue that reward (i.e., the attractive and motivational property of a stimulus) alone is not sufficient to explain the abuse liability of these substances. Instead, abuse potential is best examined as a function of both positive and negative reinforcing drug effects (i.e., stimuli that the subject will work to attain and stimuli that the subject will work to end or avoid, respectively). Though reward is central to drug use, the factors that motivate and maintain drug taking are varied and complex, with much to be elucidated.

Central Noradrenergic Interactions with Alcohol and Regulation of Alcohol-Related Behaviors

Alcohol use disorder (AUD) results from disruption of a number of neural systems underlying motivation, emotion, and cognition. Patients with AUD exhibit not only elevated motivation for alcohol but heightened stress and anxiety, and disruptions in cognitive domains such as decision-making. One system at the intersection of these functions is the central norepinephrine (NE) system. This catecholaminergic neuromodulator, produced by several brainstem nuclei, plays profound roles in a wide range of behaviors and functions, including arousal, attention, and other aspects of cognition, motivation, emotional regulation, and control over basic physiological processes. It has been known for some time that NE has an impact on alcohol seeking and use, but the mechanisms of its influence are still being revealed. This chapter will discuss the influence of NE neuron activation and NE release at alcohol-relevant targets on behaviors and disruptions underlying alcohol motivation and AUD. Potential NE-based pharmacotherapies for AUD treatment will also be discussed. Given the basic properties of NE function, the strong relationship between NE and alcohol use, and the effectiveness of current NE-related treatments, the studies presented here indicate an encouraging direction for the development of precise and efficacious future therapies for AUD.

Selective destruction of midbrain raphe nuclei by 5,7-DHT: is brain 5-HT involved in alcohol drinking in Sprague-Dawley rats?

Since serotonin (5-HT) reportedly is involved in aberrant drinking of ethyl alcohol, the present study examined a possible role of the concentration of 5-HT in systems originating in the dorsal raphe nucleus (DRN), median raphe nucleus (MRN) or both nuclei. The preference for alcohol offered in concentrations increased over 10 days from 3% to 30% was determined for each Sprague-Dawley rat. After the rats were anesthetized with sodium pentobarbital, either 10 microg 5,7-DHT or artificial cerebrospinal fluid (CSF) was micro-injected stereotaxically into the DRN, MRN or both nuclei. After 10 days, a second alcohol preference test was offered to the animals. Then the rats were decapitated, each brain removed, and the block of tissue containing injection sites was saved for histological analysis. The remaining portion was dissected into separate regions for analysis by HPLC of 5-HT, 5-hydroxyindoleacetic-acid (5-HIAA), norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The 5,7-DHT lesion of the DRN depleted the levels of 5-HT and 5-HIAA by 50-55% in the midbrain and pons and by 70-80% in the frontal cortex, whereas, the 5,7-DHT lesion of MRN reduced 5-HT in all regions except the corpus striatum. The depletion of 5-HT was lower in MRN-lesioned than in DRN-lesioned rats in the frontal cortex and nucleus accumbens. The combined lesion of both DRN and MRN produced a massive decline of >90% of 5-HT and 5-HIAA in all structures except the pons where 5-HT was reduced by 70%. Whereas the level of NE was reduced mainly in the frontal cortex, the levels of DA and its metabolites were essentially unaffected by the 5,7-DHT lesions. Although single or combined lesions of the DRN and MRN failed to alter the intake of alcohol of the rats, the combined serotonergic lesions increased significantly the ingestion of water but not food. Correlational analyses in the sham groups showed a negative association between the intake of alcohol and cortical dopamine and possible hippocampal 5-HT and NE as well as between the ingestion of food and of 5-HT in the frontal cortex. Taken together, these observations in the Sprague-Dawley rat suggest that lower levels of these monoamines in certain regions of the brain may play a role in the maintenance of the basal intake of alcohol but not in the drinking after the injection of 5,7-DHT. Explanations of our findings include: (1) a compensatory neurochemical change in pre- or postsynaptic 5-HT receptors subsequent to the dysfunction of serotonergic neurons in the forebrain; (2) a unique characteristic of the Sprague-Dawley strain of rat; and (3) residual quanta of 5-HT which sustains the pattern of alcohol drinking.

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 and delta-sleep-inducing peptide: effects on brain monoamines

The brain content of dopamine (DA) and its metabolites [dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)] were the same in rats with different immobilization times in forced swimming test, while the serotonin (5-HT) concentration was higher in high active (HA, immobilization < 2 min) than low active (LA, immobilization > 5 min) animals. Ethanol (2 g/kg, PO) tended to increase the DA level in the striatum and nucleus accumbens in LA rats and decrease the 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentration in HA rats. delta-Sleep-inducing peptide (DSIP) injection reduced the level of 5-HT in the medial prefrontal cortex (MFC) in both groups, did not affect the concentration of DA or DOPAC, but increased HVA in the striatum of HA rats. DSIP injected before ethanol administration augmented the ethanol effects on 5-HT in the MFC and attenuated the action of ethanol on 5-HIAA in the nucleus accumbens. A relationship between the different levels of voluntary alcohol consumption and sensitivity to stress among LA and HA rats and the differences in DA and 5-HT concentrations is suggested. The use of LA and HA rats in developing models for testing of stress-shielding compounds is also described.

The effects of alpha-methyl-p-tyrosine pretreatment on ethanol-induced narcosis and hypothermia, as well as in the development of tolerance to these effects in UChA and UChB rats

We have previously reported that UChA rats (genetically low ethanol consumer) develop tolerance to narcosis time easier than UChB rats (genetically high ethanol consumer). We also have reported that UChA rats develop tolerance to the hypothermic effect of ethanol, while in UChB rats the repeated administration of ethanol induces sensitization towards this effect. In the present paper the effects of alpha-methyl-p-tyrosine (AMPT)--a competitive inhibitor of norepinephrine synthesis--on ethanol-induced narcosis and hypothermia, as well as in the development of tolerance to these effects, were studied in both strains of rats. Results obtained show that AMPT pretreatment induced a significantly higher increase in narcosis time and hypothermia, as well as, greater susceptibility to ethanol toxicity in UChB than UChA rats. Furthermore, the simultaneous treatment with AMPT and ethanol did not change the development of tolerance to narcosis time in both strains and to hypothermia and sensitization in UChA and UChB rats respectively.

Effect of ethanol on brain catecholamines in rat lines developed for differential ethanol-induced motor impairment

The importance of the central catecholamines, with the emphasis on the noradrenergic neurons in the differential sensitivity to ethanol between the AT (alcohol-tolerant) rats selected for low and the ANT (alcohol-nontolerant) rats selected for high sensitivity to ethanol-induced (2 g/kg) motor impairment, was clarified by studying the effects of ethanol (2 and 4 g/kg, IP) on the utilization of norepinephrine (NA) and dopamine (DA), and on the metabolism of NA. The utilization of the catecholamines was estimated from the disappearance of the amines after inhibition of the brain tyrosine hydroxylase by alpha-methyl-p-tyrosine (200 mg/kg, IP), given 15 min after the administration of ethanol. The formation of 3-methoxy-4-hydroxy-phenylglycol (MHPG) was used as an estimate of NA metabolism, and was measured 30 min after the administration of ethanol. The basal utilization rate of NA and DA was similar between the two rat lines, but the increased formation of MHPG suggested that the naive AT rats had a higher noradrenergic activity in the limbic forebrain, hypothalamus, and cerebellum than did ANT rats. In the brain of both lines, ethanol accelerated the utilization and metabolism of NA in the same manner. Ethanol also increased the utilization of DA in the limbic forebrain of the AT and ANT rats. The higher sensitivity of the ANT rats' DA neurons to ethanol in the limbic forebrain and striatum was revealed by the significant rat line X ethanol interaction. The present findings suggest that the AT and ANT rats differ in the dopaminergic, but not in the noradrenergic responses to ethanol.

The alcohol tolerant and alcohol nontolerant rat lines selected for differential sensitivity to ethanol: a tool to study mechanisms of the actions of ethanol

Genetic selection work conducted in the Research Laboratories of State Alcohol Company (Alko Ltd), Helsinki, Finland, has resulted in the establishment of the ethanol sensitive Alcohol Nontolerant (ANT) and ethanol insensitive Alcohol Tolerant (AT) rat lines which differ in their sensitivity to ethanol induced motor impairment. These lines have been used in attempts to identify the mechanisms controlling ethanol induced motor impairment. The Alcohol Tolerant rats show a lower sensitivity to ethanol induced motor impairment on a tilting plane over a wide range of doses, but the lines do not differ in all behavioral measures of ethanol sensitivity. Furthermore, the Alcohol Tolerant line shows a higher capacity to develop acute tolerance and less calm behaviour, which may contribute to the line difference. Neurochemical work has shown differences in the functioning and sensitivity to ethanol of the catecholaminergic and GABAergic systems in the two lines, suggesting a role for both of these systems in the control of ethanol induced motor impairment.

Further studies on the neurochemical mechanisms mediating differences in ethanol sensitivity in LS and SS mice

Long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differences in CNS sensitivity to ethanol with LS mice exhibiting much greater sensitivity to hypnotic doses of ethanol (4.0-4.5 g/kg) than SS mice. The influence of peripheral and central catecholamine neuronal systems on ethanol sensitivity (sleep time) in LS and SS mice was examined following administration of reserpine, alpha-methyl-p-tyrosine and 6-hydroxydopamine. Ten days after a single dose of reserpine, tyrosine hydroxylase activity was increased in the brain and adrenal gland of LS mice but only in the brain of SS mice relative to untreated mice. Brain catecholamine levels in the reserpine-treated mice were 25-50% lower in both LS and SS mice compared to levels in untreated mice. These changes were associated with a 41% reduction in LS sleep time, but a 90% increase in SS sleep time. SS mice were also more susceptible to the lethal effects of reserpine. The increased mortality of SS mice may relate to a greater degree of reserpine-induced hypothermia and a slower rate of recovery of brain catecholamine levels. Neonatal LS and SS mice treated with 6-hydroxydopamine exhibited increased levels of catecholamines in the locus ceruleus, decreased levels in the cerebellum and unchanged levels in the hypothalamus at 60 days of age. These changes were associated with a modest decrease (10%) in LS sleep time and a marked increase (200%) in SS sleep time. alpha-Methyl-p-tyrosine decreased brain catecholamine levels of both lines by 30-50% while LS sleep times were unchanged and SS sleep times were increased by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ethanol, barbital, and lorazepam on brain monoamines in rat lines selectively outbred for differential sensitivity to ethanol

The acute effects of ethanol, barbital, and lorazepam on the synthesis and metabolism of brain monoamines were studied in the AT (Alcohol Tolerant) and ANT (Alcohol Nontolerant) lines of rats, which have been selected for differential motor impairment after ethanol administration. The ethanol-sensitive ANT rats are also more sensitive than the ethanol-insensitive AT rats to the motor impairment caused by barbital and lorazepam. Ethanol increased, whereas barbital and lorazepam decreased, the synthesis of catecholamines in several regions of the brain. Ethanol did not affect the formation of DOPAC, whereas barbital and lorazepam reduced it. Similarly, the accumulation of 5-HTP was increased after administration of ethanol, but was decreased after administration of barbital or lorazepam. Ethanol, barbital and lorazepam decreased the formation of 5-HIAA. The rat lines did not differ in any of these responses. Some differences could, however, be demonstrated between the AT and ANT rats in the effects of the three drugs on the levels of the brain monoamines. Although the importance of these differences in the differential sensitivity to these drugs between the two lines is difficult to determine, the role of central monoaminergic mechanisms cannot be excluded. These findings also suggest that the motor impairment induced by ethanol, barbiturates, and benzodiazepines is probably not primarily based on the monoaminergic systems.

CNS monoamine levels and the effect of DSP4 on ethanol sensitivity in LS and SS mice

Brain area monoamine levels were determined in selectively-bred ethanol sensitive (LS) and insensitive (SS) mice. Norepinephrine, dopamine and serotonin were measured using high performance liquid chromatography coupled with electrochemical detection. Brain regions studied included cerebellum, brain stem, striatum, frontal cortex, hippocampus and hypothalamus. LS and SS mice exhibited similar regional monamine levels with the exception of differences in brain stem and cerebellar norepinephrine levels. The role of norepinephrine in regulating ethanol sensitivity of these mice was investigated using the neurotoxin, DSP4 (selectively lesions central noradrenergic pathways). Treatment with DSP4 did not alter ethanol sensitivity in the LS or SS mice, measured by duration of righting response loss and blood ethanol concentration at its recovery. Differences in brain stem and cerebellar norepinephrine levels between the LS and SS mice were considerably smaller than the large decreases in levels produced in both lines by DSP4. It is concluded that although synaptically-released monoamines may influence ethanol responses, norepinephrine probably does not directly mediate differences in behavioral sensitivity to ethanol between these mouse lines.

Effect of neonatal nomifensine exposure on adult behavior and brain monoamines in rats

The aim of the study was to examine the effects of early postnatal exposure to nomifensine, an inhibitor of catecholamine uptake, on concurrent active (REM) sleep, on later alcohol related behavior and on monoamine concentrations in various brain regions of rats. For these purposes rats were given daily injections of 10 mg/kg nomifensine s.c. between the 7th and the 18th postnatal days. During the nomifensine exposure active sleep, expressed as a percentage of total sleeping time, was reduced. At one month of age, the nomifensine rats showed increased ambulation and had lower defecation scores in the open-field than the controls. Neonatal exposure to nomifensine increased voluntary intake of 10% (v/v) alcohol when the rats were 2-3 months of age. The rats, however, did not exhibit preservation in the T-maze, and similarly to control rats suppressed drinking 0.1 M lithium chloride even when thirsty. Measurement of cerebral monoamine concentrations at the age of 3 months suggested that neonatal nomifensine treatment interferes with the noradrenergic and serotonergic systems in several regions of the brain. Concentrations of noradrenaline and 5-hydroxyindoleacetic acid (5-HIAA) were decreased in the cerebral cortex and frontal cortex, concentration of 5-HIAA was decreased in the neostriatum, and concentrations of noradrenaline, 5-hydroxytryptamine (5-HT) and 5-HIAA were elevated in the lower brain stem. Taken together, these findings show that exposure to nomifensine during the 2nd and 3rd postnatal weeks suppresses neonatal active sleep, causes changes in the adult open-field behavior, and increases voluntary alcohol intake, perhaps due to a long-lasting alteration in brain monoamines.

Neonatal desipramine or zimeldine treatment causes long-lasting changes in brain monoaminergic systems and alcohol related behavior in rats

To study the relationship between neonatal antidepressant administration, active (REM) sleep and adult alcohol-related behavior, rat pups were treated daily with 5 mg/kg desipramine (DMI) or 25 mg/kg zimeldine SC from the 6th to the 19th postnatal days. Movement sensitive mattress ("SCSB") measurements showed that zimeldine treatment suppressed active sleep throughout the whole treatment period, but DMI was more effective during the first 8 days than during the last treatment days. At the age of 70 days, the zimeldine-treated rats expressed a selective increase of some components of activity in the open field test, and the DMI rats had a higher defecation score compared to the controls. Furthermore, the zimeldine-rats responded with a decrease in ambulation in the open field to an alcohol dose which generally stimulates locomotion in rats. At the age of 3 months the DMI and zimeldine rats showed increased voluntary intake of 10% (v/v) alcohol. Measurement of brain monoamines revealed that the neonatal treatment with DMI or zimeldine interfered with the normal development and function of the monoamine neuronal systems: the concentrations of noradrenaline, dopamine and 5-hydroxytryptamine (5-HT), and their metabolites were altered in several brain regions. The results thus suggest that neonatal treatment with DMI or zimeldine suppresses active sleep and has an influence on later alcohol-related behavior, possibly due to a long-lasting defect in brain monoaminergic transmission.

Effect of neonatal clomipramine treatment on adult alcohol drinking in the AA and ANA rat lines

In order to test further the hypothesis that neonatal active (REM) sleep suppression by means of clomipramine, an inhibitor of monoamine reuptake, is involved in the subsequent increase of voluntary alcohol consumption in rats, the AA (alcohol preferring) and ANA (alcohol avoiding) rat lines were injected daily with 25 mg/kg clomipramine IP from the 7th to the 20th postnatal days. At the age of 3 months the clomipramine AA rats consumed significantly more 10% (v/v) alcohol solution than the control AA rats. Neonatal clomipramine treatment did not, however, affect the drinking patterns of the ANA rats. Secondly, in order to test the alcohol-deprivation effect; i.e., the increase in alcohol consumption after its deprivation, the AA and ANA rats were deprived of alcohol for 17 days. There was a significant difference between the temporal pattern of changes in alcohol drinking produced by alcohol deprivation in the AA rats and the pattern in the ANA rats. Furthermore, the clomipramine treated AA rats tended to show a decrease and the clomipramine ANA rats an increase in their post-deprivation alcohol intake compared to the control AA and ANA rats. The results are interpreted in terms of active sleep being important for later alcohol drinking and other genetically determined differences in behavior.

The effect of 5,7-dihydroxytryptamine treatment on the response to ethanol in mice

In order to assess the role of the serotonergic system in the development of tolerance to ethanol in the mouse, serotonin neurons in the CNS were lesioned with an intracerebroventricular injection of the neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). Mice injected with 5,7-DHT responded to an acute dose of ethanol with a longer sleep time and greater fall in body temperature than CSF-treated mice. The increased response to acute administration of ethanol was accompanied by higher circulating levels of ethanol in mice pretreated with 5,7-DHT. When mice were fed an ethanol-containing liquid diet for five days, a higher mortality rate was observed in the 5,7-DHT group compared to the CSF pretreated group of mice. When the groups of mice were tested for tolerance 24 hours after withdrawal, the 5,7-DHT group was less tolerant than the CSF group. Therefore, damage to the serotonin neurons results in altered ethanol disposition, altered initial sensitivity to ethanol, and an inhibition in the development of tolerance in the mouse.

Effects of TRH, ethanol, and TRH-ethanol combination on activity in rats with altered monoamine content

Investigations were undertaken with 5,7-dihydroxytryptamine and 6-hydroxydopamine treated rats to see whether activity changes induced by TRH, ethanol and the TRH-ethanol combination would be affected after reduced monoamine function. In keeping with earlier results, TRH increased activity, ethanol reduced activity and the TRH-ethanol combination produced activity counts greater than those for TRH alone. Neither the 5,7-dihydroxytryptamine-induced reduction of brain serotonin nor the 6-hydroxydopamine treatments which reduced brain catecholamines altered the hyperactivity induced by TRH or the TRH-ethanol combination. While reduction of brain serotonin did not affect the ethanol-induced changes in activity, preferential reduction of dopamine as well as reduction of both norepinephrine and dopamine significantly antagonized this measure of ethanol-induced depression. The reduction of dopamine alone produced the greatest effect on this action of ethanol. It can be concluded from the data that the increased locomotion induced by TRH and the TRH-ethanol combination does not depend upon endogenous monoamines, whereas the sedative effects of ethanol are apparently influenced by alterations in brain catecholamine function.

Selective depletion of norepinephrine in brain by N-2-chloroethyl-N-ethyl-2-bromobenzylamine fails to alter the voluntary consumption of ethanol in rats

The effects of the selective norepinephrine neurotoxin, DSP-4, on the maintenance of voluntary consumption of ethanol was tested in male Long-Evans rats. The drug, DSP-4, produced a 51% reduction in whole brain levels of NE without affecting the consumption of ethanol. These results, however, do not rule out a role for NE in mediating this behavior.

Effects of neonatal treatment with clomipramine on adult ethanol related behavior in the rat

Male rat pups were deprived of active (REM) sleep by giving daily injections of clomipramine between 8 and 21 days after birth. At the age of 55 days their ambulation and defecation in the open-field were tested. Thereafter, beginning at the age of 66 days, the voluntary ethanol consumption of the rats was tested for 4 weeks. Compared to saline-treated rats, the CLM rats consumed more ethanol, tended to be more active in the open-field, and responded with a decrease in ambulation to an ethanol dose which stimulated locomotion in control rats. These results indicate that neonatal treatment with clomipramine has an influence on later ethanol-related behavior in rats.

Forebrain noradrenaline and oral self-administration of ethanol by rats

The effects of 6-hydroxydopamine-induced depletion of forebrain noradrenaline (NA) on oral intake of ethanol were studied in male Wistar rats. Prior depletion of NA produced a smaller and significantly less variable intake of a concentrated solution of ethanol than that of control rats, and this effect was not accompanied by hyperreactivity to aversive solutions of quinine. NA-depleted rats also displayed rejection 'thresholds' for ethanol solutions that were significantly lower than those of controls. Depletion of forebrain NA did not, however, affect the punishing effects of ethanol injections measured in the conditioned taste aversion paradigm. In contrast to these effects of NA depletion on initiation of ethanol intake, depletion of forebrain NA after a preference for ethanol had been established failed to affect subsequent intake of ethanol. These results suggest that forebrain NA is involved in the initiation of ethanol intake by naive rats but not in the maintenance of established patterns of intake by experienced rats. Possible mechanisms for this differential involvement of NA are discussed.

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.

Alcohol intake and ethanol intoxication in the rate: effect of a 6-OHDA-induced lesion of the ascending noradrenaline pathways

The ascending noradrenaline (NA) pathways were lesioned by injecting 6-hydroxydopamine (6-OHDA) 16 micrograms/4 microliters bilaterally into the posterior mesencephalon in male Long Evans rats. Another group of rats was pretreated with protriptyline (25 mg/kg), a NA uptake blocking agent, 15 min before they received the intracerebral injections of 6-OHDA. The controls received the vehicle only. Spectrofluorimetric determination of the catecholamine concentrations in various parts of the brain revealed a marked degeneration of the ascending NA systems in the group receiving 6-OHDA. Unexpectedly, the DA systems were also affected by the 6-OHDA treatments. Three weeks after the operation the 6-OHDA group showed a transient increase in ethanol intake. In the tilting-plane test, ethanol (2 g/kg. i.p.) impaired the performance of the 6-OHDA-treated rats significantly more than that of the controls. In contrast, the hypothermic effect of ethanol (4 g/kg, i.p.) was significantly smaller in the lesioned rats. Furthermore, the catecholamine levels in various parts of the brain could be significantly correlated with both the extent of ethanol intoxication and the hypothermia. However, the duration of ethanol-induced narcosis (4 g/kg, i.p.) was affected by the present treatments. These results give further support for the view that the central NA neurons are important in the control of ethanol intake, and that they are involved in the expression of the acute effects of ethanol administration.