Monoamine and metabolite levels in CNS regions of the P line of alcohol-preferring rats after acute and chronic ethanol treatment

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

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

Higher sensitivity to ethanol's aversive properties in WLP (Warsaw Low Preferring) vs. WHP (Warsaw High Preferring) rats

Ethanol can have both an aversive and rewarding effect, which may have a significant relationship to its individual preference. So far, the reasons for the high and low ethanol preference in the WHP (Warsaw High Preferring) and WLP (Warsaw Low Preferring) lines have not been found. WHP rats spontaneously drink over 5 g/kg/day of ethanol, while WLP rats drink under 2 g/kg/day. The purpose of the work was to study the sensitivity of WHP and WLP rats to the aversive effects of ethanol at doses of 1.5 g/kg and 2.0 g/kg in the conditioned taste aversion (CTA) procedure. Lower doses (0.5 and 1.0 g/kg, i.p. [intraperitoneally]) were tested earlier and only 1.0 g/kg produced a slight aversion in WLP rats. The secondary aim was to check the additional potential factors (blood ethanol concentration, pain sensitivity, anxiety-related behavior, learning, and memory) that may constitute an important differentiating feature of the WHP and WLP lines. For this purpose, the following tests were conducted: blood ethanol concentration, novel object recognition (NOR), flinch-jump, hot-plate, and elevated plus maze (EPM). The 1.5 g/kg i.p. dose of ethanol caused the development of an aversion only in WLP rats and the aversion extinguished in the post-conditioning phase. The 2.0 g/kg i.p. dose of ethanol resulted in the development of an aversion in both the tested groups, with the aversion being maintained throughout the whole post-conditioning period only in the WLP rats. There were no differences between the lines in terms of the blood ethanol concentration and the EPM tests. WHP rats had a higher pain sensitivity compared to WLP rats in flinch-jump and hot-plate tests. WLP rats showed a shorter exploration time for both objects compared to WHP in the NOR test. In conclusion, WHP and WLP rats differ in sensitivity to the aversive effects of ethanol. This difference may partially explain their opposite ethanol preference.

Behavioral, neurobiological, and neurochemical mechanisms of ethanol self-administration: A translational review

Alcohol use disorder has multiple characteristics including excessive ethanol consumption, impaired control over drinking behaviors, craving and withdrawal symptoms, compulsive seeking behaviors, and is considered a chronic condition. Relapse is common. Determining the neurobiological targets of ethanol and the adaptations induced by chronic ethanol exposure is critical to understanding the clinical manifestation of alcohol use disorders, the mechanisms underlying the various features of the disorder, and for informing medication development. In the present review, we discuss ethanol's interactions with a variety of neurotransmitter systems, summarizing findings from preclinical and translational studies to highlight recent progress in the field. We then describe animal models of ethanol self-administration, emphasizing the value, limitations, and validity of commonly used models. Lastly, we summarize the behavioral changes induced by chronic ethanol self-administration, with an emphasis on cue-elicited behavior, the role of ethanol-related memories, and the emergence of habitual ethanol seeking behavior.

Are genes coding for dopamine receptors implicated in alcoholism?

Part of the familial factor of alcoholism is associated with the existence of genetic vulnerability. Genetic factors which interact with the pathogenesis of alcoholism are nevertheless complex, partial and for the moment partly unknown at the biological level. Recently, many association studies have been published concerning alcohol-dependence and genes coding for the second dopamine receptor. These associations, which have had positive replications, raise many questions. First of all, should the inheritance of alcoholism be regarded as a definitive fact? Secondly what is inherited? It could be alcoholism in general, a component of this disease (for instance, dependence on, sensitivity to or the seeking-process for alcohol), a specific pattern of drinking, presence of complications linked to alcohol abuse, or more general features, common to many addiction diseases. Thirdly, how could dopamine be linked to alcoholism? Furthermore, how should these positive associations be considered, given that two of these studies were negative, and that all linkage studies were negative. Lastly, are there other clues and ways of finding genetic vulnerability factors for alcohol abuse?

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.

Oxytocin inhibits ethanol consumption and ethanol-induced dopamine release in the nucleus accumbens

Alcohol (EtOH) is one of the most widely abused recreational drugs and is arguably the most harmful. However, current treatment options for alcohol-use disorders generally have limited efficacy and poor uptake in the community. In this context, the neuropeptide oxytocin (OXT) has emerged as a promising potential treatment option for a number of substance-use disorders, including alcoholism. The utility of OXT in reducing consumption of and craving for a wide range of substances may lie in its ability to modulate drug-induced neurochemical effects within the mesolimbic dopamine pathway. However, the impact of OXT on EtOH actions in this pathway has yet to be explored. Here, we reveal that an acute intracerebroventricular (icv) infusion of OXT (1 µg/5 µl) attenuated voluntary EtOH (20 percent) self-administration after chronic intermittent access to EtOH for 59 days (28 drinking sessions) in male Wistar rats. Next, we demonstrated that an acute intraperitoneal (ip) injection of EtOH (1.5 g/kg, 15 percent w/v) increased dopamine release within the nucleus accumbens in both EtOH-naive rats and rats that had received 10 daily ip injections of EtOH. Icv OXT completely blocked the EtOH-induced dopamine release in both EtOH-naive and chronically treated rats. The attenuation of EtOH-induced dopamine release by OXT may help to explain the reduced EtOH self-administration observed following icv OXT infusion.

Early ethanol and water consumption: accumulating experience differentially regulates drinking pattern and bout parameters in male alcohol preferring (P) vs. Wistar and Sprague Dawley rats

Alcohol-preferring (P) rats develop high ethanol intake over several weeks of water/10% ethanol (10E) choice drinking. However, it is not yet clear precisely what components of drinking behavior undergo modification to achieve higher intake. Our concurrent report compared precisely measured daily intake in P vs. non-selected Wistar and Sprague Dawley (SD) rats. Here we analyze their drinking patterns and bouts to clarify microbehavioral components that are common to rats of different genetic backgrounds, vs. features that are unique to each. Under sole-fluid conditions P, Wistar and SD rats all consumed water at a high initial rate followed by a slow maintenance phase, but 10E - in a distinctly different step-like pattern of evenly distributed bouts. During choice period, 10E vs. water patterns for P rat appeared as an overlap of sole-fluid patterns. The SD rat choice patterns resembled sole-fluid patterns but were less regular. Choice patterns in Wistar differed from both P and SD rats, by consisting of intermixed small frequent episodes of drinking both 10E and water. Wistar and SD rats increased choice ethanol intake by elevating the number of bouts. A key finding was that P rat increased choice ethanol intake through a gradual increase of the bout size and duration, but kept bout number constant. This supports the hypothesis that genetic selection modifies microbehavioral machinery controlling drinking bout initiation, duration, and other pattern features. Precision analysis of drinking patterns and bouts allows differentiation between genetic lines, and provides a venue for study of localized circuit and transmitter influences mediating mesolimbic control over ethanol consumption.

Early ethanol and water intake: choice mechanism and total fluid regulation operate in parallel in male alcohol preferring (P) and both Wistar and Sprague Dawley rats

The goal of this study was to clarify similar and distinctly different parameters of fluid intake during early phases of ethanol and water choice drinking in alcohol preferring P-rat vs. non-selected Wistar and Sprague Dawley (SD) rats. Precision information on the drinking amounts and timing is needed to analyze micro-behavioral components of the acquisition of ethanol intake and to enable a search for its causal activity patterns within individual CNS circuits. The experiment followed the standard ethanol-drinking test used in P-rat selective breeding, with access to water, then 10% ethanol (10E) as sole fluids, and next to ethanol/water choice. The novelty of the present approach was to eliminate confounding prandial elevations of fluid intake, by time-separating daily food from fluid access. P-rat higher initial intakes of water and 10E as sole fluids suggest adaptations to ethanol-induced dehydration in P vs. Wistar and SD rats. P-rat starting and overall ethanol intake during the choice period were the highest. The absolute extent of ethanol intake elevation during choice period was greatest in Wistar and their final intake levels approached those of P-rat, contrary to the hypothesis that selection would produce the strongest elevation of ethanol intake. The total daily fluid during ethanol/water choice period was strikingly similar between P, Wistar and SD rats. This supports the hypothesis for a universal system that gauges the overall intake volume by titrating and integrating ethanol and water drinking fluctuations, and indicates a stable daily level of total fluid as a main regulated parameter of fluid intake across the three lines in choice conditions. The present findings indicate that a stable daily level of total fluid comprises an independent physiological limit for daily ethanol intake. Ethanol drinking, in turn, stays under the ceiling of this limit, driven by a parallel mechanism of ethanol/water choice.

Early exposure to ethanol differentially affects ethanol preference at adult age in two inbred mouse strains

Although the acute effects of ethanol exposure on brain development have been extensively studied, the long term consequences of juvenile ethanol intake on behavior at adult age, regarding especially ethanol consumption, are still poorly known. The aim of this study was to analyze the consequences of ethanol ingestion in juvenile C57BL/6J and DBA/2J mice on ethanol intake and neurobiological regulations at adulthood. Mice were given intragastric ethanol at 4 weeks of age under different protocols and their spontaneous ethanol consumption was assessed in a free choice paradigm at adulthood. Both serotonin 5-HT(1A) and cannabinoid CB1 receptors were investigated using [(35)S]GTP-γ-S binding assay for the juvenile ethanol regimens which modified adult ethanol consumption. In DBA/2J mice, juvenile ethanol ingestion dose-dependently promoted adult spontaneous ethanol consumption. This early ethanol exposure enhanced 5-HT(1A) autoreceptor-mediated [(35)S]GTP-γ-S binding in the dorsal raphe nucleus and reduced CB1 receptor-mediated G protein coupling in both the striatum and the globus pallidus at adult age. In contrast, early ethanol ingestion by C57BL/6J mice transiently lowered spontaneous ethanol consumption and increased G protein coupling of postsynaptic 5-HT(1A) receptors in the hippocampus but had no effect on CB1 receptors at adulthood. These results show that a brief and early exposure to ethanol can induce strain-dependent long-lasting changes in both behavior toward ethanol and key receptors of central 5-HT and CB systems in mice.

Neurodrinking: is alcohol a substrate in a novel, endogenous synthetic pathway for norepinephrine?

A number of preclinical and clinical studies indicate multiple types of interaction between ethanol intake and the mood-related neurotransmitter, norepinephrine (NE). For example, ethanol interacts with dopamine beta-hydroxylase (DBH), an enzyme that plays an essential role in the only well-established endogenous synthetic pathway for NE, whereby dopamine is hydroxylated to form NE. While the DBH pathway may indeed be the only endogenous mechanism for producing NE, another possibility is that multiple means have evolved for the biosynthesis of this very important neurotransmitter, where some pathways may be independent of DBH. If so, such redundancy would provide greater assurance that enough NE is available for the body to use in this neurotransmitter's various physiological roles. This paper puts forth the hypothesis ethanol is a substrate in a novel, endogenous synthetic pathway for NE, consistent with some studies showing that intake of ethanol increases the concentration of endogenous NE. Also consistent with this hypothesis, the molecular structure of ethanol is a physical subset of the structure of NE itself. If the hypothesis is correct, it may have important implications for understanding the physiological basis of alcohol use, abuse, and dependence in humans, as well as modeling these phenomena in animals. Importantly, the hypothesis is directly testable in rodents by presenting ethanol to DBH knockout mice, which are thought to lack NE, and then measuring if NE is synthesized in these animals.

Biogenic Amines in Striatum of Rats that Had Been Treated with Ethanol, and Their Brains Later Stored in Different Temperatures

The purpose of this study was to investigate how ethanol pretreatment and storage temperatures of brain striatum affect levels of biogenic amines in this tissue. Adult Wistar male rats were injected with 25% ethanol (5.0 g/kg i.p.) while the control rats were administered i.p. with the same volume of saline. Two hours later the rats were decapitated, their brains removed, and the striatum separated. Each striatum was divided into three parts: one part was immediately frozen on dry ice and kept at -70 degrees C; a second fragment was kept in a household refrigerator (+4 degrees C); and the third fragment was kept at +22 degrees C. Twenty-four hours later, levels of DA, DOPAC, HVA, 3-MT, 5-HT, and 5-HIAA in the striatum were assayed by HPLC/ED. Immediately after decapitation; ethanol levels were assayed in the serum of ethanol-pretreated and saline-pretreated rats using gas chromatography. Our results indicate that levels of striatal DA, DOPAC, and HVA in saline-pretreated rats decreased significantly when the storage temperature of the striatum was raised from -70 degrees C, through +4 degrees C, to +22 degrees C, while levels of striatal 5-HT and 5-HIAA remained constant within the temperature range tested and levels of 3-MT fluctuated. In ethanol-pretreated rats, striatal levels of DOPAC, HVA, and 5-HIAA were increased in all three storage temperatures, while levels of DA, 5-HT, and 3-MT were decreased in those temperatures. Those decreases were most profound in striatal samples kept at +22 degrees C. We conclude that concern about possible interactions between drugs and biogenic amines should be exercised.

Ethanol-induced effects on the dopamine and serotonin systems in adult Wistar rats are dependent on early-life experiences

Some individuals control their ethanol consumption throughout life, but others escalate their intake to levels that increase the risk for addiction. The early environment influences the individual response to ethanol and affects the underlying physiological processes that lead to a transition from a voluntary to a compulsive use of ethanol. However, the neurobiological substrates for these processes are not understood. The present study aimed to test the hypothesis that early environmental experiences affect the neurobiological effects that are induced by voluntary ethanol consumption. Rat pups were subjected to three different rearing environments: conventional animal facility rearing or separation from dam and littermates for either 15 or 360min. In adulthood, the rats were exposed to a two-bottle free choice between ethanol and water for seven weeks. Tissue levels of dopamine, 5-hydroxytryptamine (5-HT) and their metabolites were measured in brain areas that have been implicated in reward and addiction processes. Differences in ethanol-induced effects were noted in 5-HT-related measurements in the nucleus accumbens and ventral tegmental area and in dopamine-related measurements in the dorsal raphe nucleus (DRN). These results provided evidence of an early environmental impact on interactive neuronal circuits between the DRN and reward pathways. The amygdala, a key area in addiction processes, was particularly sensitive to early-life conditions. The animals that experienced the longest separation differed from the others; they had low basal 5-HT levels and responded with an increase in 5-HT after ethanol. These altered responses to initial ethanol consumption as a result of early environmental factors may affect the transition from habitual to compulsive drinking and contribute to individual vulnerability or resilience to addiction.

The relationship between baseline prepulse inhibition levels and ethanol withdrawal severity in rats

Baseline prepulse inhibition (PPI) of the acoustic startle reflex is thought to reflect the functioning of the sensorimotor gating system in the brain. The current literature indicates that similar neurotransmitter systems may play roles both in the regulation of PPI and in the development of ethanol withdrawal syndrome (EWS). The aim of the present study was to test if individual baseline PPI levels have any relationship to the behavioral and neurochemical consequences of EWS in rats. A batch of rats (n=30) was sorted according to baseline PPI levels and classified as either high-inhibitory (HI) or low-inhibitory (LI) rats (n=10 in each group). Ethanol was administered in a liquid diet for 21 days. On the 22nd day, ethanol was removed from the diet, and EWS was induced. At the 2nd, 4th, and 6th hours of EWS, locomotor activity and behavioral symptoms were evaluated. Brain tissue concentrations of dopamine, serotonin and noradrenaline in hippocampus, cortex, and striatum were measured after the 6th hour of EWS testing. Another batch of rats (n=30) was classified using the same procedure and fed with regular diet. On the 22nd day, rats were decapitated and neurochemical measurements were repeated. HI and LI rats consumed similar amounts of ethanol. However, EWS signs such as stereotyped behaviors, wet-dog shakes, and tremor were more intense in LI rats compared to their HI counterparts. Audiogenic seizures occurred in both groups in a similar manner. Although the catecholamine concentrations in the brains of both groups were parallel under baseline conditions, dopamine levels increased in the cortex of LI and in the striatum of HI rats, whereas striatum serotonin levels decreased only in LI rats after the 6th hour of EWS. In conclusion, the data suggest that the behavioral symptoms and neurochemical changes observed in EWS may be associated with baseline PPI levels.

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.

Chronic voluntary ethanol intake hypersensitizes 5-HT(1A) autoreceptors in C57BL/6J mice

Alcoholism is a complex disorder involving, among others, the serotoninergic (5-HT) system, mainly regulated by 5-HT(1A) autoreceptors in the dorsal raphe nucleus. 5-HT(1A) autoreceptor desensitization induced by chronic 5-HT reuptake inactivation has been associated with a decrease in ethanol intake in mice. We investigated here whether, conversely, chronic ethanol intake could induce 5-HT(1A) autoreceptor supersensitivity, thereby contributing to the maintenance of high ethanol consumption. C57BL/6J mice were subjected to a progressive ethanol intake procedure in a free-choice paradigm (3-10% ethanol versus tap water; 21 days) and 5-HT(1A) autoreceptor functional state was assessed using different approaches. Acute administration of the 5-HT(1A) receptor agonist ipsapirone decreased the rate of tryptophan hydroxylation in striatum, and this effect was significantly larger (+75%) in mice that drank ethanol than in those drinking water. Furthermore, ethanol intake produced both an increased potency (+45%) of ipsapirone to inhibit the firing of 5-HT neurons, and a raise (+35%) in 5-HT(1A) autoreceptor-mediated stimulation of [(35)S]GTP-gamma-S binding in the dorsal raphe nucleus. These data showed that chronic voluntary ethanol intake in C57BL/6J mice induced 5-HT(1A) autoreceptor supersensitivity, at the origin of a 5-HT neurotransmission deficit, which might be causally related to the addictive effects of ethanol intake.

Delta-opioid receptor expression in the ventral tegmental area protects against elevated alcohol consumption

Alcoholism is a complex and debilitating syndrome affecting approximately 140 million people worldwide. However, not everyone who consumes ethanol develops abuse, raising the possibility that some individuals have a protective mechanism that inhibits elevated alcohol consumption. We tested the hypothesis that the delta-opioid receptor (DOR) plays such a protective role. Here we show that DOR activity in the ventral tegmental area (VTA) robustly decreases ethanol consumption in rats and that these effects depend on baseline ethanol consumption. Intra-VTA microinjection of the DOR agonist DPDPE decreases drinking, particularly in low-drinking animals. Furthermore, VTA microinjection of the DOR selective antagonist TIPP-Psi increases drinking in low, but not high, drinkers and this increase is blocked by comicroinjection of the GABA(A) antagonist bicuculline. Using electrophysiological techniques we found that in VTA brain slices from drinking rats DPDPE presynaptically inhibits GABA(A) receptor mediated IPSCs in low drinkers, but not in high drinkers or naive animals, most likely through activation of DORs on GABA terminals. This DOR-mediated inhibition of IPSCs also correlates inversely with behavioral correlates of anxiety measured in the elevated plus maze. In contrast, presynaptic inhibition of VTA GABA(A) IPSCs by the mu-opioid receptor agonist DAMGO is significantly reduced in both high- and low-drinking rats (<30%) compared with age-matched nondrinking controls (>70%). Together, our findings demonstrate the protective nature of VTA DORs and identify an important new target for therapeutic intervention for alcoholism.

Effects of chronic alcohol and repeated deprivations on dopamine D1 and D2 receptor levels in the extended amygdala of inbred alcohol-preferring rats

BACKGROUND

Dopaminergic (DA) activity in the extended amygdala (EA) has been known to play a pivotal role in mediating drug and alcohol addiction. Alterations of DA activity within the EA after chronic exposure to alcohol or substances of abuse are considered a major mechanism for the development of alcoholism and addiction. To date, it is not clear how different patterns of chronic alcohol drinking affect DA receptor levels. Therefore, the current studies investigated the effects of chronic ethanol consumption, with or without deprivations, on D1 and D2 receptor densities within the EA.

METHODS

Inbred alcohol-preferring (iP) rats were divided into 3 groups with the following treatments: (1) water for 14 weeks; (2) continuous alcohol (C-Alc) for 14 weeks [24-hour concurrent access to 15 and 30% (v/v) ethanol]; or (3) repeatedly deprived of alcohol (RD-Alc) (24-hour concurrent access to 15 and 30% ethanol for 6 weeks, followed by 2 cycles of 2 weeks of deprivation of and 2 weeks of reexposure to ethanol access). At the end of 14 weeks, the rats were killed for autoradiographic labeling of D1 and D2 receptors.

RESULTS

Compared with the water control group, both the C-Alc and the RD-Alc groups displayed increases in D1 receptor binding density in the anterior region of the Acb core, whereas the RD-Alc group displayed additional increases in D1 receptor binding density in anterior regions of the lateral and intercalated nuclei of the amygdala. Additionally, both C-Alc and RD-Alc rats displayed increases in D2 receptor binding density in anterior regions of the Acb shell and core, whereas RD-Alc rats displayed additional increases in D2 receptor binding density in the dorsal striatum.

CONCLUSION

The results of this study indicate that 14-week extended alcohol drinking with continuous chronic or repeated deprivations increase binding sites of D1 and D2 receptors in specific regions of the EA with greater sensitivity in the anterior regions. The repeated deprivation has greater effect on altering D1 and D2 receptor binding sites in the Acb, dorsal striatum, and subamygdala regions. The current result indicates that the two drinking paradigms may have common as well as differential mechanisms on alteration of dopamine receptor-binding sites in specific regions of the EA.

Glutamate and dopamine synaptic terminals in extended amygdala after 14-week chronic alcohol drinking in inbred alcohol-preferring rats

Alcohol has been shown to affect glutamate (GLU) and dopamine (DA) release and their correlated receptors in the key reward center--extended amygdala--which includes the shell of nucleus accumbens (sNAc) and central nucleus of amygdala (cAmg). It is unclear to date whether there is an alteration in the number of presynaptic GLU/DA nerve terminals. In this study, we investigated the number of GLU and DA terminals in the extended amygdala of alcohol-preferring (P) rats that chronically drank ethanol. P rats have a propensity to drink ethanol to intoxication and develop an alcohol dependency. The P rats were divided into (1) Water group given ad libitum chow and water for 14 weeks; (2) Continuous alcohol group (C-Alc) given ad libitum chow and choice of 15 or 30% (v/v) ethanol or water for 14 weeks; and (3) Repeated deprivation (RD-Alc) group given the same choice of ethanol or water for 6 weeks, followed by a twice repeated cycle of 2 weeks without ethanol followed by 2 weeks with ethanol. Two subpopulations of GLU terminals were labeled by immunostaining for the vesicular GLU transporter 1 (vGLUT1) and vesicular GLU transporter 2 (vGLUT2). DA terminals were labeled by immunostaining for tyrosine hydroxylase (TH). The GLU and DA immunostained (im) varicosities were quantified and analyzed using stereological methods. We found that chronic alcohol did not alter the number of TH-im terminals in the extended amygdala in either the C-Alc or RD-Alc drinking paradigms. Thus, the increases in extracellular levels of DA previously reported following chronic alcohol are likely due to a change in the efficiency of DA release rather than a change in the number of DA terminals. The number of vGLUT1-im terminals was also unchanged in the extended amygdala; however, the number of vGLUT2-im terminals, which represent the greater population of GLU terminals, was increased in the sNAc of the RD-Alc group compared to the Water group. Chronic alcohol is known to affect GLU release, and our findings indicate that repeated alcohol deprivation may preferentially increase GLU terminals in the sNAc bearing the vGLUT2, which are primarily afferents from the thalamus. Our results further indicate that repeated deprivation of alcohol can change the ratio of GLU to DA innervation in the sNAc, a key region of the reward circuitry.

Locomotor-stimulating effects of indirect dopamine agonists are attenuated in Fawn hooded rats independent of postweaning social experience

The effects of the indirect dopamine (DA) agonists cocaine and D-amphetamine on locomotor activity were examined in Fawn hooded (FH) rats and Wistar rats. The effect of isolation rearing was also examined to determine if it might have different effects in these two strains. Contrary to previous findings in other rat strains, only small increases in locomotor-stimulating responses to low doses of cocaine were observed in the present study as a result of isolation rearing. However, at higher cocaine doses, locomotor activity was substantially attenuated in FH rats relative to Wistar rats. A similar pattern of effects was observed for amphetamine in FH rats but only at the intermediate dose. The effects of strain and rearing were independent. There was no evidence for interactions between these factors.

The DRD2 gene and the risk for alcohol dependence in bipolar patients

The high co-morbidity between bipolar disorder and alcohol dependence may have different explanations, one of them being the existence of common genetic factors for the two disorders. Several candidate genes may be involved but the genes acting in the dopaminergic pathway may be more specifically involved. We have thus tested the role of the gene encoding the D2 dopamine receptor (TaqI A1 allele) in the potentially shared vulnerability to alcohol dependence and bipolar disorder. One hundred and twenty-two French (for at least two generations) patients were recruited on the basis of hospital or outpatient files and were interviewed with the DIGS. The A1 allele frequencies were compared between four groups, namely, with bipolar patients and co-morbid alcohol dependence (N = 21), with bipolar patients without alcohol morbidity (N = 31), with alcohol dependence without mood disorder (N = 35) and unaffected controls (N = 35). The Hardy Weinberg equilibrium for the DRD2 Taq1 A1 genotypes was respected for the sample as a whole, and for each subsample. We observed that 42.9% of control subjects have at least one A1 allele, a frequency which is not significantly different from the one observed in the affected sample as a whole (39.1%), neither from patients with alcohol dependence (37.1%), patients with bipolar disorder (48.4%) nor patients with alcohol dependence and bipolar disorder (28.6%). The regression analysis based on the three variables (bipolar disorder, alcohol dependence and interaction between these two disorders) does not explain the presence of the A1 allele of the DRD2 gene. We thus found no evidence for a significant role of the A1 allele of the D2 dopamine receptor gene in the specific association between bipolar disorder and alcohol dependence in our sample.

Glycyl-L-glutamine injected centrally suppresses alcohol drinking in P rats

Recent reports show that central beta-endorphin (1-31) injection augments the volitional intake of alcohol. Correspondingly, alcohol drinking stimulates beta-endorphin (1-31) release from the hypothalamus of the rat. Glycyl-l-glutamine (Gly-Gln) is produced in beta-endorphin-containing neurons and is co-released with beta-endorphin(1-31) and other processing products. Because Gly-Gln is apparently an endogenous antagonist of beta-endorphin(1-31) in several systems, the present study was designed to investigate the hypothesis that Gly-Gln injected i.c.v. would alter voluntary alcohol drinking in the genetic, high-alcohol-preferring P rat. After a guide tube was implanted stereotaxically above the lateral cerebral ventricle, the rats were offered 3-30% alcohol over 10 days, and then given their maximally preferred concentration of alcohol in the presence of water for the remainder of the experiment. Gly-Gln or artificial cerebrospinal fluid (CSF) vehicle then was injected i.c.v. in a dose of 10 or 100 nmol for 3 consecutive days, which was followed by a 7-day postinjection interval. Gly-Gln suppressed significantly the intakes of alcohol in terms of both g/kg and proportion to total fluid. During the postinjection days, alcohol drinking continued to be suppressed, whereas neither the daily intakes of food or water nor the body weights of the rats were changed. The present results are consistent with the concept of a functional antagonism by Gly-Gln of the role of beta-endorphin(1-31) in mediating certain central functions. These results demonstrate that alcohol consumption is suppressed by the direct intracerebral application of this unique peptide.

Effect of ethanol on extracellular dopamine in the nucleus accumbens of alcohol-preferring AA and alcohol-avoiding ANA rats

The role of central monoamines in the genetically determined influences on voluntary ethanol consumption were examined by studying the extracellular levels of monoamines in the nucleus accumbens of the alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Nonalcohol) rats with in vivo microdialysis. Dialysate samples for the assay of monoamines with small bore HPLC were collected from freely moving animals at 15 min intervals after administration of ethanol (0.5, 1, or 2 g/kg, i.p.). Ethanol significantly increased the extracellular levels of dopamine, DOPAC, and HVA, suggesting stimulation of dopamine release by ethanol, while the effect on 5-HIAA did not reach significance. No difference in the extent or time course of stimulation of dopamine release between the AA and ANA rats was found. The results could so far give no indication that the differential ethanol consumption by AA and ANA rats could be explained in terms of differences in ethanol-induced stimulation of dopamine release in the nucleus accumbens.

Genetics of alcoholism: simultaneous presentation of a chocolate drink diminishes alcohol preference in high drinking HAD rats

Through selective crossbreeding of the N/Nih heterogeneous stock of rats, two genetic lines of rats have been developed that are categorized by their preference for ethyl alcohol as high alcohol drinking (HAD) and low alcohol drinking (LAD) animals. Corresponding to other strains of rat bred for alcohol selection or rejection, they were subdivided on the basis of their intake of a solution of 10% alcohol vs. water. The present experiments were designed to determine whether the HAD-1 and LAD-1 lines are similar to the P and NP rats in their profile of alcohol consumption. Five successive three-bottle preference tests for alcohol drinking in the presence of water were undertaken in both HAD (n = 9) and LAD (n = 10) rats as follows: 10% alcohol for 5 days; 3-30% concentrations of alcohol increased over 11 days; the maximally preferred concentration of alcohol for 5 days; this maximally preferred concentration of alcohol plus either chocolate Slender for 5 days, or an aspartame solution for 5 days. The intake of alcohol of the LAD rats during the 10% test was 0.4 g/kg/day, whereas during the 3-30% test, the maximum intake was 1.7 g/kg/day; their maximally preferred concentrations ranged between 7% and 9% alcohol. In contrast, the intake of 10% alcohol of the HAD rats was 6.5 g/kg/day, whereas during the 3-30% test the mean daily intake was 6.6 g/kg/day; the maximally preferred solutions of the HAD rats ranged between 13 to 20%, with the mean maximum intake of 10.57 g/kg/day reached at the 20% concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Reduction of voluntary alcohol intake in the rat by modulation of the dopaminergic mesolimbic system: transplantation of ventral mesencephalic cell suspensions

The dopaminergic mesolimbic system plays a major role in the mechanisms of reward and positive reinforcement, and is also known to be a primary target for the action of substances that are self-administered and are considered drugs of abuse. Even though alcohol administration has been shown, by physiological and pharmacological manipulations, to cause changes in the mesolimbic dopaminergic system, it has not yet been determined whether, conversely, experimentally induced changes in this system are effective in regulating the voluntary intake of ethanol. In the present study we assessed the effects of the intrastriatal transplantation of fetal dopaminergic grafts on the regulation of voluntary alcohol intake in the rat. Fetal dopaminergic transplants from ventral mesencephalon--but not dopamine-poor transplants or sham-operated animals--reduced the voluntary intake of ethanol by about 40-50%. These results indicate that the effects obtained are due to the dopaminergic nature of the grafts, and not the consequence of a non-specific effect of the graft, or of the surgical procedure itself. These results support the hypothesis that the dopaminergic mesolimbic system plays an important role in the regulation of the voluntary intake of ethanol.

Adaptive changes of dopamine-D2 receptors in rat brain following ethanol withdrawal: a quantitative autoradiographic investigation

The effect of subchronic treatment with two doses of ethanol (5 and 10 vol% drinking fluid) on the density of dopamine-D2 receptors was investigated at two different phases of withdrawal, namely 24 h and 5 days after the cessation of the ethanol application. The number of dopamine-D2 receptors was affected in regions receiving projections from both the substantia nigra as well as the ventral tegmentum. Twenty-four hours after the replacement of the ethanol solution by water, a dose-dependent decrease of D2 receptors was found in all regions (N. caudatus dorsalis, medialis and ventralis, N. accumbens lateralis and medialis, tuberculum olfactorium) and most of the analyzed planes [interaural 7.7-10.2 according to the atlas of Paxinos and Watson (35)]. At day 5 of withdrawal, the number of dopamine-D2 receptors of the animals treated with 5 vol% ethanol reached the level of water controls in most planes. In contrast, two- to three-fold higher numbers were detected in animals treated with the higher dose. Only in the most caudal parts of the investigated regions, was the number of receptors decreased with the higher dose. The mesocorticolimbic system seems to be less sensitive to the effects of ethanol than the nigrostriatal neurones. The findings of the present study suggest an increased activity of dopaminergic neurons with an adaptive reduction of dopamine-D2 receptors during the subchronic treatment with ethanol during the first day(s) of withdrawal. This phase is followed by a reduced turnover rate for up to 7 days (21). The reduced activity of dopaminergic neurones induces a compensatory increase of the number of receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol enhances the release of dopamine and serotonin in the nucleus accumbens of HAD and LAD lines of rats

The effects of intraperitoneal administration of ethanol, 0.5, 1.0, and 2.0 g/kg body weight, on the extracellular concentrations of dopamine (DA), serotonin (5-HT), and their major metabolites were studied in the nucleus accumbens (ACC) of alcohol-naive, selectively bred high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) lines of rats using the technique of microdialysis. In both lines, the extracellular levels of DA were increased following the injection of 1.0 and 2.0 g of ethanol/kg body weight while only the 2.0-g/kg dose elevated the concentration of 5-HT. None of the ethanol doses altered the extracellular levels of the major metabolites of DA and 5-HT. Dose-response curves for DA and 5-HT release indicated no marked difference in the sensitivity to ethanol between the lines. Local perfusion with 60 mM K+ through the microdialysis probe markedly enhanced the release of DA and 5-HT in the ACC of both lines; there was a small difference between the lines in the amounts of DA, but not 5-HT, released by K(+)-stimulation. Overall, the results indicate that (1) the ACC DA system is more sensitive than the ACC 5-HT system to intraperitoneal ethanol administration in both lines and (2) there is no evidence for a relationship between alcohol preference and sensitivity of the ACC DA and 5-HT systems to acute intraperitoneal ethanol administration.

Regulation of nucleus accumbens dopamine release by the dorsal raphe nucleus in the rat

The effects of microinfusing L-glutamate, serotonin (5-HT), (+-)-8-hydroxy-2-(di-N-propylamino) tetralin (8-OH DPAT; a 5-HT1A agonist), and muscimol (a GABAA agonist) into the dorsal raphe nucleus on the extracellular levels of 5-HT, dopamine (DA) and their metabolites in the nucleus accumbens were studied in unanesthetized, freely moving, adult male Wistar rats, using the technique of microdialysis coupled with small-bore HPLC. Administration of 0.75 micrograms L-glutamate produced a 25-50% increase (P less than 0.05) in the extracellular levels of both 5-HT and DA. On the other hand, infusion of 8-OH DPAT and, to a lesser extent, 5-HT produced a significant (P less than 0.05) decrease in the extracellular levels of both 5-HT and DA. Muscimol (0.25 or 0.50 microgram) had little effect on the extracellular concentrations of 5-HT or DA following its administration. In general, the extracellular levels of the major metabolites of 5-HT and DA in the nucleus accumbens were not altered by microinfusion of any of the agents. The data indicate that (a) the 5-HT neurons projecting to the nucleus accumbens from the dorsal raphe nucleus can be activated by excitatory amino acid receptors and inhibited by stimulation of 5-HT1A autoreceptors, and (b) the dorsal raphe nucleus 5-HT neuronal system may regulate the ventral tegmental area DA projection to the nucleus accumbens.

Influence of dopaminergic and serotonergic neurons on intravenous ethanol self-administration in the rat

Rats implanted with chronic indwelling intravenous catheters and allowed access to a self-administration apparatus learned to self-inject intravenous ethanol. Ethanol concentrations of 0.5, 1.0, and 2.0%, corresponding to a dose/injection of 1, 2, and 4 mg/kg, respectively, were consistently self-injected. Self-injection was not acquired or maintained with ethanol doses of 0.5 or 8 mg/kg/injection. Saline replacement of ethanol reservoirs led to marked increases in lever-pressing response in animals self-injecting 1, 2, and 4 mg/kg ethanol/injection but not with 0.5 or 8 mg/kg/injection. Neurotoxin-induced lesions of dopamine-(DA) containing neurons in nucleus accumbens septi failed to alter the acquisition or maintenance of ethanol self-injection. Pretreatment with haloperidol (0.05 and 0.1 mg/kg, SC) failed to alter hourly or daily self-injection rates. On the other hand, p-chlorophenylalanine pretreatment increased, while fluoxetine (2.5 and 5.0 mg/kg) administration significantly reduced, self-injected intravenous ethanol. These data suggest that ethanol is self-injected by the rat in a narrow dose range and that 5-hydroxytryptamine (5-HT), but not DA-containing neurons, subserves some function in the reinforcing or aversive affects of ethanol.

Alcohol stimulates the release of dopamine and serotonin in the nucleus accumbens

The effects of acute IP administration (0.5, 1.0 or 2.0 g/kg) and local perfusion (25, 50 or 100 mM) of ethanol on the extracellular concentrations of dopamine (DA), serotonin (5-HT) and their metabolites in the nucleus accumbens (ACC) of the rat were studied with in vivo microdialysis coupled with a small-bore HPLC electrochemical detection procedure. The IP administration of 1.0 and 2.0 g/kg ethanol significantly (p less than 0.05) increased the extracellular levels of DA and 5-HT in the ACC whereas the 0.5 g/kg dose caused no change. In general, the extracellular levels of the 3 monoamine metabolites were not altered by IP ethanol except for a slight increase in the levels of homovanillic acid following the 2.0 g/kg dose. Local perfusion of 50 and 100 mM ethanol (but not 25 mM) through the microdialysis probe markedly increased (170-200% of control) the extracellular levels of DA in the ACC. Only the 100 mM concentration of ethanol altered the extracellular levels of 5-HT (2-fold increase), 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid. Addition of 100 microM ICS 205-930 (a 5-HT3 antagonist) to the perfusate markedly reduced the 100 mM ethanol-stimulated release of DA and 5-HT. Overall, the data suggest that ethanol can stimulate the release of both DA and 5-HT in the ACC and that the action of ethanol within the ACC may be mediated in part by 5-HT3 receptors.

Serotonergic sprouting is induced by dopamine-lesion in substantia nigra of adult rat brain

We have previously extracted a serotonin (5-HT) neurotrophic supernatant from the 5,7-DHT lesioned hippocampus. The current study shows that a new 5-HT neurotrophic signal was monitored in the striatum and nigra after DA-denervation. Such a signal may be involved in the heterotypic sprouting. Dopaminergic neurotoxin, 6-hydroxydopamine (6-OHDA), was injected directly into the substantia nigra of adult rats. Two months after surgery, immunocytochemical staining showed that tyrosine hydroxylase (TH)-positive cell bodies had mostly disappeared in the substantia nigra, and TH-positive terminals in the striatum were almost completely depleted. Meanwhile, the 5-HT fibers, which exist in the same areas with low density, sprouted in the nigra as well as in the striatum and became dense. Normally 5-HT fibers innervate the striatum sparsely and the globus pallidus densely with sharp delineation (in the control side), and become dense across both areas with no appreciable delineation (in the lesion side). The increase of 5-HT fibers was more prominent in the posterior than in the anterior striatum. A significant increase in 5-HT and 5-HIAA levels was also evident in the posterior striatum when the decrease in DA level exceeded 90% in the nigra and striatum. In addition, we found that induction of 5-HT sprouting requires a greater than 90% decrease of DA level. Current data support that 6-OHDA injection in the substantia nigra of adult rats triggered a trophic signal or removed an inhibition for the growth of 5-HT neurons which responded with sprouting in the nigra as well as in the striatum.

Regional distribution of ethanol-inducible cytochrome P450 IIE1 in the rat central nervous system

A specific form of cytochrome P450, P450 IIE1, active in ethanol oxidation, is known to be induced about 10-fold in rat liver following ethanol treatment. This isozyme of P450 participates effectively in the metabolic activation of precarcinogens, such as N-dimethylnitrosamines, and of solvents such as carbon tetrachloride and benzene. In the present investigation, two different polyclonal antisera against P450 IIE1 were used in order to map the regional distribution of this P450 form in the rat central nervous system. The presence of P450 IIE1 in various brain regions was confirmed by Western blot analysis. The P450 IIE1-immunoreactivity was heterogeneously distributed between brain areas. Neuronal cell bodies and glial cells of presumed astroglial as well as oligodendroglial identity contained immunoreactivity. All fiber tracts harbored P450 IIE1-immunoreactive glial cells as did the ependymal lining of the ventricular wall as well as small and large vessels throughout the brain. P450 IIE1-immunoreactive glial cells were present in all areas of the neocortex, in the olfactory bulb, in the piriform cortex and in several different thalamic nuclei. In the cerebellum, P450 IIE-immunoreactivity was found in all cell layers and was exclusively localized to glial cells and their processes. Staining of blood vessels was prominent in the white matter where P450 IIE1-immunoreactive glial cells were seen to have end-feet on the vessels. A subgroup of pyramidal cells of the frontal cortex showed strong P450 IIE1-immunoreactivity, as did a component of the olfactory nerve which innervates the accessory bulb. In the hippocampal region, the pyramidal cells of all subfields were P450 IIE1-immunoreactive. Some polymorphic cells of the hilus and subfield CA stained intensely with the P450 IIE1 antibodies. A high density of P450 IIE1-immunoreactivity was detected throughout the striatal complex. The immunoreactivity was localized to neuronal cell bodies as well as the neurophil. Fibers of the nigrostriatal system were strongly P450 IIE1-immunoreactive. Mechanical lesions of this pathway showed an accumulation of P450 IIE1-immunoreactivity proximal to the lesion relative to the striatum and a depletion in the reticular part of the substantia nigra, suggesting that the antigen may be transported from the striatum to the substantia nigra. In the brain stem a high density of P450 IIE-immunoreactive neurons was detected in the substantia nigra, the pontine nucleus, lateral superior olive and the nucleus of the trigeminal nerve and facial nucleus. A great number of large- to medium-sized immunoreactive neurons were situated in the central gray and in the reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional brain contents of serotonin, dopamine and their metabolites in the selectively bred high- and low-alcohol drinking lines of rats

The contents of dopamine (DA), serotonin (5-HT) and their primary acid metabolites were assayed in ten brain regions of the selectively bred high-alcohol drinking (HAD) and low-alcohol drinking (LAD) lines of rats. Compared with the LAD line, the contents of 5-HT and/or 5-hydroxyindoleacetic acid were approximately 10-20% (p less than 0.05) lower in several brain regions of the HAD line (cerebral cortex, striatum, nucleus accumbens, septal nuclei, hippocampus and hypothalamus). The levels of DA, 3,4-dihydroxyphenylacetic acid and homovanillic acid were also 10-20% lower in the nucleus accumbens and anterior striatum (p less than 0.05) of the HAD animals. These data are in agreement with previous findings that comparatively lower levels in 5-HT and DA systems are associated with high-alcohol drinking in rodents and support the involvement of certain 5-HT and DA pathways in the mediation of alcohol drinking behavior.

Measurement of monoamines and monoamine metabolites in various brain regions of six shark species

1. The concentrations of six monoamines or monoamine metabolites were measured in six brain regions of six shark species using high performance liquid chromatography with electrochemical detection. 2. Serotonin concentrations were greatest in the hypothalamus and tegmentum, intermediate in the midline ridge formation, spinal cord and forebrain, and lowest in the cerebellum in all species. 3. Specie differences in dopamien concentration were significant only in the forebrain; species differences in the levels of the norepinephrine, epinephrine and 5-hydroxyindoleacetic acid were significant in most brain regions, including the midline ridge formation. 4. Differences and similarities to the mammalian pattern of monoamine distribution in the brain are discussed.

Serotonin and ethanol preference

This chapter brings together evidence indicating the involvement of serotonin (5-HT) in ethanol preference using data mainly obtained from selectively bred alcohol-preferring and alcohol-nonpreferring lines of rodents. Although several laboratories have established rodent lines that will consume large quantities of ethanol daily, only one line thus far has been established that satisfied all the criteria for an animal model of alcoholism and that would be suitable for studying the biological basis of ethanol preference. This is the P line of alcohol-preferring rats that: (1) freely consumes 5-9 g ethanol/kg body wt/day; (2) drinks sufficient alcohol to produce intoxicating blood alcohol concentrations; (3) works to obtain alcohol; (4) self-administers ethanol for its CNS pharmacological effects; and (5) develops chronic tolerance to and dependence on alcohol with free-choice drinking. Relative to the NP line of alcohol-nonpreferring rats, the P rat has lower 5-HT levels in several CNS regions, including some, such as the nucleus accumbens, hypothalamus, and frontal cortex, which are involved in the brain reward circuitry. Furthermore, both acute and chronic ethanol administration have effects on the 5-HT pathway from the dorsal raphe nucleus to the nucleus accumbens in the P rat. Pharmacological studies have demonstrated that fluoxetine, a serotonin uptake inhibitor, reduced the oral consumption or intragastric self-administration of alcohol in the P rats. In addition, administration of a 5-HT1B agonist also attenuated the oral intake of ethanol by P rats. It is hypothesized that the serotonergic pathway from the dorsal raphe nucleus to the nucleus accumbens is involved in the reinforcing actions of alcohol in the P line of rats.

Autoradiographic analysis of [3H]imipramine binding in the human brain postmortem: effects of age and alcohol

In vitro quantitative autoradiography of high-affinity [3H]imipramine binding sites was performed on 16 human brains postmortem. The densities of binding sites were highest in the hypothalamus. Next, in descending order, were the basal and lateral nuclei of the amygdala; substantia innominata; insular cortex; the central nucleus of the amygdala; the anterior nucleus of the thalamus; the head of the caudate nucleus; portions of the frontal, parietal, and temporal cortex; claustrum; the granular layer of the dentate gyrus; substantia nigra; the pyramidal layer of CA fields; globus pallidus; red nucleus; and white matter. Imipramine binding was found to increase with age in a region-specific manner. The presence of alcohol had a similar effect, which was most pronounced in the hippocampus. Sex and time from death to autopsy did not affect imipramine binding, in our sample.

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)

Effects of acute ethanol administration on monoamine and metabolite content in forebrain regions of ethanol-tolerant and -nontolerant alcohol-preferring (P) rats

The contents of dopamine (DA), serotonin (5-HT) and their metabolites in the frontal cortex, anterior striatum, nucleus accumbens and hypothalamus of alcohol-tolerant and -nontolerant rats of the alcohol-preferring P line were determined one hour after the IP administration of 2.5 g ethanol/kg body wt. Compared with saline-injected controls, nontolerant P-rats injected with ethanol had (a) 60% higher levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the frontal cortex; (b) 30-60% higher levels of DOPAC and HVA in the anterior striatum and nucleus accumbens; and (c) 20% higher levels of 5-HIAA in all three forebrain regions. In the tolerant group, the effects of IP ethanol on DOPAC and HVA were markedly attenuated or completely eliminated in these three forebrain regions. However, in the case of 5-HIAA, an attenuated response was observed only in the nucleus accumbens of the tolerant group. The IP administration of ethanol had little effect on the contents of DA or 5-HT in any of these three forebrain regions, with the exception that 5-HT levels were elevated in the anterior striatum of both the tolerant and nontolerant groups. In the hypothalamus, there were no significant differences for the contents of DA, 5-HT or their metabolites between the nontolerant or tolerant P rats after IP ethanol. The data indicate that both acute ethanol administration and chronic alcohol intake by the P line of rats alters certain DA and 5-HT systems that may be involved in the brain reward circuitry and in DA pathways involved in motor functions.

Neurogenetic adaptive mechanisms in alcoholism

Clinical, genetic, and neuropsychopharmacological studies of developmental factors in alcoholism are providing a better understanding of the neurobiological bases of personality and learning. Studies of the adopted-away children of alcoholics show that the predisposition to initiate alcohol-seeking behavior is genetically different from susceptibility to loss of control after drinking begins. Alcohol-seeking behavior is a special case of exploratory appetitive behavior and involves different neurogenetic processes than do susceptibility to behavioral tolerance and dependence on the antianxiety or sedative effects of alcohol. Three dimensions of personality have been described that may reflect individual differences in brain systems modulating the activation, maintenance, and inhibition of behavioral responses to the effects of alcohol and other environmental stimuli. These personality traits distinguish alcoholics with different patterns of behavioral, neurophysiological, and neuropharmacological responses to alcohol.

Contents of monoamines in forebrain regions of alcohol-preferring (P) and -nonpreferring (NP) lines of rats

The contents of monoamine neurotransmitters and metabolites were assayed in the frontal cortex, nucleus accumbens and anterior striatum of rats from the selectively bred alcohol-preferring P and nonpreferring NP lines. Lower levels of serotonin (20-30%) in all three brain regions of P as compared with NP rats lends support to the hypothesis that a decreased metabolic activity and/or innervation by serotonin neurons is associated with the abnormally high volitional intake of ethanol. Of additional interest, however, were the approximately 25% lower contents of dopamine and its major metabolites in the nucleus accumbens of the P rats. This observation may indicate that P rats have a specific deficiency in the dopaminergic projections from the ventral tegmental area to the nucleus accumbens and, since the accumbens is an important structure in brain reward circuitry, it might also be an important determinant of the excessive volitional intake of alcohol by P rats.

Chronic ethanol inhibits rat hippocampal "stimulus-secretion" coupling mechanism for 5-hydroxytryptamine in vitro

Effects of ethanol on serotonergic neurotransmission were investigated in crude mitochondrial fraction (P2 fraction) from rat brain hippocampus and hypothalamus. The [14C]5-HT preloaded P2 fraction was exposed to 45 mM KCl to induce 5-hydroxytryptamine release in vitro. Ethanol in vitro did not produce any significant inhibition of [14C]5-HT release until its concentration was greater than 100 mM. The K+-evoked 45Ca uptake of hippocampal P2 fraction was unaffected by 100 mM. However, 200 mM ethanol inhibited approximately 63% of K+-evoked 45Ca uptake. Chronic ethanol (10 g/kg/day) for 6 days inhibited [14C]5-HT release from hippocampus whereas it did not affect [14C]5-HT release from hypothalamus. Results indicate that chronic ethanol treatment may decrease serotonergic neurotransmission in selective brain regions. The reduction in 5-hydroxytryptamine release was the result of inhibition in "stimulus-secretion" coupling mechanism.

Effects of ethanol on monoamine and amino acid release from cerebral cortical slices of the alcohol-preferring P line of rats

The effects of 250 mg/100 ml ethanol on the efflux of 3,4-dihydroxyphenylacetic acid (DOPAC) and the 35 mM K+-stimulated, Ca2+-dependent release of norepinephrine (NE), dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), glutamate, and aspartate from cerebral cortical slices of the alcohol-preferring P line of rats and stock Wistar rats were studied. The K+-stimulated, Ca2+-dependent release of GABA for the P rats was 35% lower, while the release of glutamate was almost twice that of the stock animals. The release of the other compounds was similar for the two groups. Addition of 250 mg/100 ml ethanol to the superfusion media did not alter the release of NE, DA, and 5-HT nor the efflux of DOPAC from cortical slices of either group of rats. However, the K+-stimulated, Ca2+-dependent release of GABA, glutamate, and aspartate was significantly enhanced by ethanol for both the P and stock group of rats. These in vitro data do not support a direct action of ethanol on DA, NE, and 5-HT release or on DOPAC efflux, but suggest a direct action on the transmitter release process for GABA, glutamate, and aspartate in the cerebral cortex.

Reduced ethanol consumption during cyproheptadine administration in rats from a long-term alcohol-treated colony

The influence of cyproheptadine (CPH) on forced and voluntary ethanol intake was studied in long-term alcohol-treated rats. Wistar rats from a colony (WAC) that have been drinking alcohol as their only liquid fluid for the 25 previous generations and from a genetically related colony (WN) that had never been given alcohol were used. In the first experiment, daily IP doses of 15 mg/kg CPH were found to reduce forced ethanol consumption during CPH treatment in both WAC and WN rats which had been drinking ethanol for six months. In two additional groups of WAC and WN rats which were not given ethanol, water intake was not affected by CPH administration. In a second experiment, alcohol preference was reduced both during and after CPH, but total fluid intake (ethanol + water) was not affected. These findings suggest that the effect of CPH could be specific to ethanol. The decrease in ethanol consumption was associated with a significant body weight loss; this result may support the hypothesis of a link between the serotoninergic system, food intake, and alcohol drinking behavior that has been considered by earlier investigators.

Effects of 250 mg% ethanol on monoamine and amino acid release from rat striatal slices

A single IP injection of 2.5 g ethanol/kg body weight into the rat increased the striatal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) one hour later to 133 and 141% of control values, respectively. Blood alcohol concentrations at this time were approximately 250 mg%. The increased striatal tissue levels of DOPAC and HVA found after IP administration did not appear to be due to a direct effect of ethanol on the efflux of these two metabolites or on the release of dopamine (DA) since in vitro studies with striatal slices demonstrated that 250 mg% ethanol had no effect on the endogenous release of DOPAC, HVA, or DA. However, ethanol did enhance the K+-stimulated, Ca2+-dependent release of glutamate and aspartate from striatal slices to 168 and 214% of control values, respectively. The release of glutamate and aspartate from slices of midbrain (minus colliculi) was also increased by 250 mg% ethanol. On the other hand, the release of GABA, NE and 5-HT did not appear to be significantly altered by 250 mg% ethanol. The in vitro findings have led to the hypothesis that the elevated DOPAC and HVA levels observed in the striatum following an acute IP injection of 2.5 g/kg of ethanol are due to increased release of DA produced by the excitatory actions of glutamate (and/or aspartate) on dopaminergic neurons.

Monoamine uptake inhibitors attenuate ethanol intake in alcohol-preferring (P) rats

The P line of alcohol-preferring rats drink pharmacologically significant amounts of ethanol when given free choice between a 10 percent ethanol solution and water. Serotonin (5-HT) uptake inhibitors and desipramine, a norepinephrine (NE) uptake inhibitor, were found to significantly reduce their ethanol consumption for up to 24 hours after intraperitoneal injection. To determine if this effect of 5-HT uptake inhibitors could be altered by receptor antagonists, some of which are short acting, P rats were trained to drink ethanol by free choice during scheduled availability, with ethanol being presented one hour every four hours during the light cycle. The majority of the ethanol was consumed during the first hour of availability, and the ethanol intake was significantly reduced by the 5-HT uptake inhibitors, fluoxetine and fluvoxamine. Pretreatment with antagonists for 5-HT1, 5-HT2 and alpha- and beta-NE receptor systems failed to alter the fluvoxamine attenuation of ethanol intake. The mechanism by which 5-HT uptake inhibitors alter ethanol preference remains unclear.

Effects of alcohol on cerebrospinal fluid norepinephrine in rhesus monkeys

Alcohol (1-3 g/kg) significantly increased the concentration of cerebrospinal fluid (CSF) norepinephrine (NE) in rhesus monkeys. This effect is consistent with the previously demonstrated activational and possible antidepressant effect of low doses of alcohol. The greatest increase was observed in subjects with low baseline levels of CSF NE. Individual differences in activation or euphoria could be related to differential increases in CSF NE following alcohol consumption.

Intragastric self-infusion of ethanol by ethanol-preferring and -nonpreferring lines of rats

An ethanol-preferring line of rats, developed by selective breeding, consumed as much as 9.4 +/- 1.7 grams of ethanol per kilogram of body weight per day through intragastric self-infusions, yielding blood ethanol concentrations of 92 to 415 milligrams per 100 milliliters. By contrast, the ethanol- nonpreferring line self-administered only 0.7 +/- 0.2 gram per kilogram per day. These findings indicate that the reinforcing effect of ethanol is postabsorptive and is not mediated by the drug's smell or taste. Hence the ethanol-preferring line of rats may be suitable animal model of alcoholism.