Effects of Morphine on Metabolism of Dopamine and Serotonin in Brains of Alcohol-Preferring AA and Alcohol-Avoiding ANA Rats

Morphine induces a larger locomotor stimulation in the alcohol-preferring AA rats than in the alcohol-avoiding ANA rats. We have now studied the acute effects of morphine (1 and 3 mg/kg) on metabolism of dopamine and serotonin (5-HT) in the dorsal and ventral striatum of the AA and ANA rats. The basal level of dopamine release, as reflected by the concentration of dopamine metabolite 3-methoxytyramine (3-MT), was lower in the caudate-putamen and nucleus accumbens of the AA rats than in the ANA rats. In the caudate-putamen, morphine increased dopamine metabolism and release more in the AA than in the ANA rats. In the nucleus accumbens and olfactory tubercle, the effects of morphine on dopamine metabolism and release did not differ between the rat lines. Morphine elevated the metabolism of 5-HT in the caudate-putamen and nucleus accumbens of the AA but not in those of the ANA rats. The results suggest that the larger morphine-induced psychomotor stimulation of the AA rats in comparison with the ANA rats is associated with the larger effect of morphine on dopamine metabolism in the caudate-putamen and 5-HT metabolism in the caudate-putamen and nucleus accumbens. Furthermore, low basal dopamine release may play a role in the high alcohol-preference of AA rats.     

Effects of ethanol and low-carbohydrate diet on contents of noradrenaline, dopamine, serotonin and their metabolites in rat brain]

Effects of ethanol consumption and intake of low-carbohydrate (low-CHO) diet on noradrenaline (NA), dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), serotonin (5HT) and its metabolite, 5-hydroxyindoleacetic acid (5HIAA) contents in six brain regions of rats were investigated. 1) Change of DA neuron Ethanol-containing control diet (hypercaloric ethanol diet) did not affect DA content in any area of brain, but decreased HVA in cortex and hypothalamus and increased DOPAC and HVA in midbrain. Low-CHO diet increased DA content in striatum, DOPAC and HVA in midbrain, but decreased DOPAC in hippocampus and hypothalamus, and HVA in cortex, pons and medulla, hippocampus and hypothalamus. Ethanol-containing low-CHO diet (isocaloric ethanol diet) increased DA level in striatum, DOPAC and HVA in midbrain, but decreased HVA in cortex, hippocampus, striatum and hypothalamus. These results suggest that i) hypercaloric ethanol diet has an opposite effect to carbohydrate on DA metabolism: hypercaloric ethanol diet and lowered carbohydrate intake per se enhance DA metabolism in midbrain, whereas inhibit it in cortex and hypothalamus, ii) lowered carbohydrate intake also declines DA metabolism in pons and medulla and hippocampus, whereas enhances DA synthesis in striatum, iii) the combined effect of ethanol and carbohydrate intake on DA metabolism is inhibited each other in the rats of isocaloric ethanol diet feeding, and this diet decreased DA metabolism in striatum. 2) Change of 5HT neuron Hypercaloric ethanol diet did not affect the contents of 5HT and 5HIAA in any region of brain.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Effect of ethanol on ascorbate release in the nucleus accumbens and striatum of freely moving rats.

An in vivo voltammetry technique was used to monitor the extracellular ascorbate (AA) concentration in the nucleus accumbens and striatum of unanesthetized, freely moving rats. A single injection of ethanol, 1.0 g/kg intraperitoneally (IP), induced a significant increase in extracellular AA concentration in both the nucleus accumbens and striatum. This effect was dose dependent within a dose range from 0.5-2.0 g/kg. 4-Methylpyrazole (50 mg/kg, IP), which inhibits alcoholdehydrogenase, could not prevent the increase in AA concentration, evoked by ethanol. Furthermore, systemic administration of acetaldehyde (20 mg/kg, IP), the main metabolite of ethanol, did not have any effect on the level of AA in the nucleus accumbens or striatum. These results show that ethanol can alter the brain extracellular AA levels and that this effect seems to be attributed to ethanol itself and not to acetaldehyde. Consequently, these results indicate that a role for AA in the action of ethanol in the brain should be considered.     

Effect of ethanol on (R)- and (S)-salsolinol, salsoline, and THP in the nucleus accumbens of AA and ANA rats.

Tetrahydroisoquinolines (TIQ) are active metabolites of dopamine. Intracerebral application stimulates the voluntary ethanol intake. In the present study, the levels of several TIQ's [(S)- and (R)-salsolinol, salsoline and tetrahydropapaveroline (THP)] were measured in the extracellular space of the nucleus accumbens of alcohol-preferring AA and alcohol-avoiding ANA rats. Ethanol (2 g/kg i.p.) caused an increase in dopamine levels in ANA but not in AA rats. Neither (R)- nor (S)-salsolinol concentrations changed after ethanol application, though (S)-salsolinol concentrations were higher in ANA than in AA rats. Ethanol caused an increase in salsoline concentrations in ANA but not in AA rats. THP increased following ethanol, which tended to be stronger in ANA rats. The study revealed differences in the TIQ levels of the nucleus accumbens between AA and ANA rats. In case of changes following ethanol application (dopamine, salsoline, THP), the AA rats were less sensitive. The findings resemble observations in high-risk sons of alcoholics with reduced sensitivity to ethanol in young age and increased risk to become alcoholic.     

Striatal and hypothalamic neurotransmitter changes during ethanol withdrawal in mice

The alterations in striatal and hypothalamic GABA, DA and its metabolites DOPAC and HVA, and in hypothalamic NE were investigated immediately after ethanol removal and during the withdrawal phase following 10 or 30 days of chronic ethanol administration. After 10 days of ethanol, GABA levels were increased immediately after ethanol removal in both the corpus striatum and the hypothalamus. The concentration of striatal DA was increased at days 2 and 3 of withdrawal and was unchanged at any other time. There was no change in the concentration of DOPAC and HVA in the hypothalamus at any time during withdrawal. Striatal DOPAC and HVA levels were increased only at day 7 of withdrawal after 10 and 30 days of ethanol feeding which was associated with a return of striatal DA to control levels. The concentration of NE in the hypothalamus was increased at days 1, 2 and 7 of withdrawal. After 30 days of ethanol, striatal GABA was increased only at day 7 of withdrawal whereas striatal DA levels were only increased at days 2 and 3 of withdrawal. Hypothalamic NE was markedly increased at days 2, 3 and 7 of withdrawal. The increase in DA concentration associated with no change in DOPA accumulation following inhibition of DOPA decarboxylase and a decrease in the striatal disappearance of DA after alphamethylparatyrosine (alpha-MT) suggests the presence of a hypodopaminergic state. On the other hand an increase in the disappearance of NE in the hypothalamus after alpha-MT suggests an increased NE turnover and a hyperadrenergic state during withdrawal. The increase in striatal GABA at day 7 of withdrawal after 30 days of ethanol may be a rebound phenomenon and may reflect the presence of a hypogabaergic state which has been shown to occur during ethanol withdrawal.     

Extracellular levels of dopamine in the nucleus accumbens in AA and ANA rats after reverse microdialysis of ethanol into the nucleus accumbens or ventral tegmental area.

Ethanol is known to increase the release of dopamine in the nucleus accumbens. The question of whether this is a result of a direct or an indirect effect of ethanol on mesolimbic dopaminergic neurons was examined by investigating the extracellular levels of dopamine and its metabolites in the nucleus accumbens of alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Non-Alcohol) rats after application of ethanol locally into either the nucleus accumbens or the ventral tegmental area with the use of reverse microdialysis. Application of ethanol (200, 400, or 800 mM in dialysate) into the nucleus accumbens, but not into the ventral tegmental area, temporarily increased the accumbal levels of dopamine in a dose-dependent manner. The ethanol-evoked increase in the level of extracellular dopamine was more prominent in AA rats than in ANA rats. Ethanol tended to suppress levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid. Because the concentrations of ethanol found to elevate the extracellular level of dopamine can hardly be considered pharmacologically relevant, the increase in accumbal dopamine levels after application of ethanol may be due to nonspecific membrane effects of ethanol. The findings support the suggestion that the increase in the extracellular level of dopamine in the nucleus accumbens after systemic administration of ethanol may involve other sites on dopamine neurons or even different neurotransmitter systems, rather than the action of ethanol at the mesolimbic dopaminergic terminals.     

Effects of repeated morphine treatment on metabolism of cerebral dopamine and serotonin in alcohol-preferring AA and alcohol-avoiding ANA rats

The alcohol-preferring AA (Alko Alcohol) rats are more rapidly sensitized to the locomotor activity-stimulating effects of small doses of morphine than the alcohol-avoiding ANA (Alko Non-Alcohol) rats. To study the involvement of dopaminergic and serotonergic transmission in this behaviour, the effects of acute morphine (1 mg/kg) challenge on the concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were estimated in three dopaminergic areas in AA and ANA rats on the fourth day after a 3-day morphine or saline treatment. Acute administration of morphine enhanced DA metabolism in the caudate-putamen in the AA, but not in the ANA, rats; in the nucleus accumbens and in the olfactory tubercle the acute effect of morphine was similar in rats of both lines. Morphine pretreatment did not significantly enhance acute morphine's effects on DA metabolites in any of the brain areas studied in rats of either line. Acute administration of morphine enhanced brain 5-HT metabolism in the AA rats but not in the ANA rats, but after repeated treatment it induced no enhancement of 5-HT metabolism. With the methods used, no significant differences were found between the AA and ANA rats in the effects of repeated morphine on cerebral dopaminergic or serotonergic mechanisms which could account for the different behavioural sensitization found previously in rats of these lines. However, both monoamines studied might be involved in the acute locomotor stimulatory effects of morphine.     

In vivo effects of inorganic mercury (HgCl(2)) on striatal dopaminergic system

In the present study, the effects of intrastriatal administration of different concentrations (40 microM, 400 microM, and 4 mM) of inorganic mercury (HgCl(2)) on the dopaminergic system of rat striatum were evaluated, using a microdialysis technique coupled to liquid chromatography-electrochemical detection. In previous studies, we discussed the effects of organic mercury (MeHg) administration on the striatal dopaminergic system on the basis of changes in the release and metabolism of striatal dopamine (DA). In the present study it is demonstrated that intrastriatal administration of all concentrations of HgCl(2) produced significant increases in the output of DA (1240, 2500, and 2658% for the concentrations of 40 microM, 400 microM, and 4 mM HgCl(2), respectively) from rat striatal tissue, associated with significant decreases in striatal levels of its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) with the concentrations of 400 microM and 4 mM HgCl(2) (74.4 and 3.4% for DOPAC and 71.0 and 50.6% for HVA, respectively), whereas no changes in metabolite levels were observed with the concentration of 40 microM HgCl(2). These effects are explained as a result of stimulated DA release and/or changed DA metabolism. The effects of intrastriatal administration of HgCl(2) were compared with those of MeHg on DA extracellular levels.     

In Vivo Effects of Inorganic Mercury (HgCl2) on Striatal Dopaminergic System

In the present study, the effects of intrastriatal administration of different concentrations (40 μM, 400 μM, and 4 mM) of inorganic mercury (HgCl₂) on the dopaminergic system of rat striatum were evaluated, using a microdialysis technique coupled to liquid chromatography-electrochemical detection. In previous studies, we discussed the effects of organic mercury (MeHg) administration on the striatal dopaminergic system on the basis of changes in the release and metabolism of striatal dopamine (DA). In the present study it is demonstrated that intrastriatal administration of all concentrations of HgCl₂ produced significant increases in the output of DA (1240, 2500, and 2658% for the concentrations of 40 μM, 400 μM, and 4 mM HgCl₂, respectively) from rat striatal tissue, associated with significant decreases in striatal levels of its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) with the concentrations of 400 μM and 4 mM HgCl₂ (74.4 and 3.4% for DOPAC and 71.0 and 50.6% for HVA, respectively), whereas no changes in metabolite levels were observed with the concentration of 40 μM HgCl₂. These effects are explained as a result of stimulated DA release and/or changed DA metabolism. The effects of intrastriatal administration of HgCl₂ were compared with those of MeHg on DA extracellular levels.     

Limited access to ethanol increases the number of spontaneously active dopamine neurons in the posterior ventral tegmental area of nondependent P rats

Microdialysis experiments in alcohol-preferring (P) rats have shown that chronic ethanol exposure increases extracellular levels of dopamine (DA) in the nucleus accumbens. Because DA neuronal activity contributes to the regulation of DA overflow in terminal regions, we hypothesized that posterior ventral tegmental area (VTA) DA neuronal activity (firing frequency, burst activity, and/or the number of spontaneously active DA neurons) would be increased in P rats consuming ethanol compared with P rats consuming only water. In vivo electrophysiological techniques were used to evaluate the activity of single DA neurons in the posterior VTA. Our findings show that voluntary ethanol intake by nondependent P rats significantly increased the number of spontaneously active DA neurons in the posterior VTA compared with P rats that consumed only water. Firing frequency and burst activity did not differ between the two groups. These results suggest that adaptive changes occur in the mesolimbic DA system of nondependent P rats to increase the excitability of posterior VTA DA neurons and enhance DA release from nerve terminals in the nucleus accumbens.     

拟除虫菊酯对大鼠脑黑质纹状体系统多巴胺及其代谢产物的影响

目的 初步探讨拟除虫菊酯类农药对雄性SD大鼠脑黑质纹状体多巴胺(DA)系统的毒性作用及其可能机制。方法 采用不同剂量的溴氰菊酯(DM,6.25、12.50 mg/kg)、氯菊酯(PM,200、400mg/kg)给雄性SD大鼠连续10 d经口灌胃给药后,HPLC荧光检测法分别检测其脑黑质、纹状体内DA及其代谢产物3,4-二羟基苯乙酸(DOPAC)、3-甲氧基-4-羟基苯乙酸(HVA)的含量。结果 给药各组大鼠纹状体内DA含量都有不同程度的下降,且12.50 mg/kg DM组(6.14±0.57μg/g湿重)与对照组(9.46±1.95 μg/g湿重)的差异有统计学意义(P<0.05);200、400 mg/kg PM组和6.25、12.50 mg/kgDM 4个组的DA更新率[(DOPAC HVA)/DA]与对照组相比,分别增加了133.33％、166.67％、166.67％和266.67％,差异均有统计学意义(P<0.05或P<0.01);而黑质内DA及其代谢产物水平均无明显变化。结论 DM可能抑制酪氨酸羟化酶合成DA,使其在纹状体内的含量下降,PM和DM都可以加强DA的代谢。     

Chronic ethanol consumption increases dopamine uptake in the nucleus accumbens of high alcohol drinking rats.

Past research has indicated that chronic ethanol exposure enhances dopamine (DA) neurotransmission in several brain regions. The present study examined the effects of chronic ethanol drinking on dopamine transporter (DAT) function in the nucleus accumbens (Acb) of High-Alcohol-Drinking replicate line 1 (HAD-1) rats. HAD rats were given concurrent 24-h access to 15% ethanol and water or water alone for 8 weeks. Subsequently, DA uptake and the V(max) of the DAT were compared between the two groups using homogenates of the nucleus accumbens. DA uptake was measured following a 2 min incubation at 37 degrees C in the presence of 8 nM [(3)H]DA. For kinetic analyses, DA uptake was assessed in the presence of 5 concentrations of [(3)H]DA ranging from 8 nM to 500 nM. Analyses of the data revealed a significant increase in DA uptake in the ethanol group compared to water controls. Kinetic analyses revealed the change in DA uptake to be a consequence of an increase in the V(max) of transport. These findings demonstrate that chronic free-choice oral ethanol consumption in HAD-1 female rats increases DA uptake in the Acb by increasing the V(max) of the transporter. However, it is not known whether the ethanol-induced change in V(max) is caused by differences in the actual number of available transporter sites or from a difference in the velocity of operation of a similar number of transporters. Overall, the data indicate that chronic ethanol consumption by HAD-1 rats produces prolonged neuroadaptations within the mesolimbic DA system, which may be important for the understanding of the neurobiological basis of alcoholism.     

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.     

SEROTONIN IS REDUCED IN THE FRONTAL CORTEX OF SARDINIAN ETHANOL-PREFERRING RATS

Ethanol-naive Sardinian alcohol-preferring (sP) and Sardinianalcohol-non-preferring (sNP) rats were tested to evaluate thelevels of serotonin (5-HT) and 5-hydroxyindol-3-yl-acetic acid(5-HIAA) in the frontal cortex, hypothalamus, and nucleus accumbens,and the levels of dopamine (DA) and 3,4-dihydroxyphenylaceticacid (DOPAC) in the hypothalamus and nucleus accumbens. Comparedwith the sNP line, the sP rats had lower 5-HT and 5-HIAA concentrationsin the frontal cortex, whereas no differences were found inthe other brain areas tested, neither for neurotransmittersnor their metabolites. As the decreased 5-HT function is a featureshared by different alcohol-preferring strains, it could belinked to the genetic predisposition to voluntary ethanol consumption.     

Effects of lifelong ethanol consumption on drinking behavior and motor impairment of alcohol-preferring AA and alcohol-avoiding ANA rats.

The effects of drinking ethanol throughout a lifetime on voluntary drinking behavior and ethanol-induced motor impairment were studied in alcohol-preferring AA (Alko, Alcohol) and alcohol-avoiding ANA (Alko, Non-Alcohol) rats of both sexes. At the age 3 months, the rats were tested for individual voluntary ethanol (10% vol./vol.) intake and ethanol-induced motor impairment (2 g/kg, i.p.). The rats were housed in group cages, half of them having 12% (vol./vol.) ethanol as the only source of fluid and the other half having free access to water. Food was always available for all animals. At the age of 23 months, their individual voluntary ethanol intake and ethanol-induced motor impairment were tested again. During forced drinking, the females of both strains consumed more ethanol than did the males. The ethanol consumption of the AA and ANA females and the ANA males increased significantly (P < .001) with age, but a slight decrease was seen in the ethanol consumption of the AA males. Time x strain interaction showed a significant (P < .05) difference in the ethanol consumption of male rats, with the AA males having a slight decrease in ethanol consumption with age, whereas the ANA males increased their ethanol consumption. After 19 months of forced ethanol exposure, AA males significantly decreased their individual voluntary ethanol consumption, and individual voluntary ethanol consumption by ethanol-exposed AA males was more pronounced (P < .001) than that of the AA rats that had free access to water (P < .05). For the female AA rats, those having free access to water significantly decreased their voluntary ethanol consumption (P < .05), but those having ethanol only did not. No significant changes in voluntary ethanol consumption with age or with different exposures were seen in the ANA rats. Body weights were higher in the groups having access to water than in the ethanol-only groups, but the differences were not significant within the AA and ANA strains. The ANA rats were significantly heavier in all groups. These results indicate that the voluntarily nondrinking ANA rats can drink almost as much ethanol as the voluntarily drinking AA rats when they are forced to drink ethanol and that lifelong forced ethanol drinking does not change their inherent drinking habits. When sensitivity to ethanol was measured with the tilting-plane test, the old AA female rats were more sensitive to ethanol than were the young ones. The young ANA females were more sensitive than the AA females when tested at 4 months. In males, aging did not produce any differences in ethanol sensitivity.     

Effects of exposure to moderate levels of ethanol during prenatal brain development on dendritic length,branching, and spine density in the nucleus accumbens and dorsal striatum of adult rats

Reductions in measures of dendritic morphology in the agranular insular cortex have been identified as consequences of prenatal exposure to moderate levels of ethanol in the rat. Motivated by the strong connectivity between this region of frontal cortex and the striatum and a growing body of data linking specific components of the mesocortical/limbic system to effects of ethanol and ethanol self-administration, the current study investigated the effects of moderate fetal ethanol exposure on the dendritic morphology of medium spiny neurons (MSNs) in several regions of the striatum. Throughout gestation, pregnant rat dams either consumed a saccharin solution (control) or achieved average daily blood ethanol concentrations of 84 mg% via voluntary consumption of a 5% ethanol solution. The brains of adult male offspring were extracted and processed for Golgi-Cox staining. MSNs from the dorsomedial striatum, dorsolateral striatum and the nucleus accumbens core and shell were sampled for analysis. Relative to saccharin controls, robust reductions in dendritic length and branching, but not spine density, were observed in the shell of the nucleus accumbens in fetal-ethanol-exposed rats. No significant prenatal ethanol effects were found in the other regions of the striatum. These findings suggest that exposure to moderate levels of ethanol in utero can have profound effects on brain regions related to reward processing and provide possible clues relevant to understanding increased self-administration of drugs of abuse in animals exposed to ethanol during brain development.     

Extracellular dopamine and serotonin after ethanol monitored with 5-minute microdialysis.

In order to determine potential rapid changes in extracellular dopamine (DA) and 5-hydroxytryptamine (serotonin, 5-HT) during the first 5-10 min after ethanol, intracerebral microdialysis coupled with microbore HPLC was used. Ethanol at the doses of 0.5, 1, and 2 g/kg was administered IP and extracellular DA and 5-HT in 5-min dialysates from the nucleus accumbens (NAC) of freely moving rats were determined. Ethanol at all doses significantly increased extracellular DA and 5-HT. DA and 5-HT peaked at 10, 15, 20 min and 20, 20, 55 min following 0.5, 1, and 2 g/kg, respectively. Based on previous reports showing that brain or blood ethanol levels peaked within 10-20 min after administration, the results indicate that peak increases in extracellular DA and 5-HT in the NAC occurred at approximately the same time, with the DA time course more temporally correlated with the blood or brain alcohol concentration curve reported in the literature. These results support the concept that the reinforcing properties of ethanol derive, at least in part, from its ability to stimulate DA release in the NAC. In addition, the present data are not in opposition with a role of 5-HT in the ethanol reinforcing effect.     

Binding of serotonergic ligands to brain membranes of alcohol-preferring AA and alcohol-avoiding ANA rats.

The alcohol-preferring AA rats have higher concentration of 5-hydroxytryptamine (5-HT) in the brain than the alcohol-avoiding ANA rats. In the present study, the 5-HT1, 5-HT2, and 5-HT3 receptors were studied with [3H]5-HT, [3H]ketanserin, and [3H]LY278584, respectively, in membrane homogenates from different brain regions of both rat lines using in vitro binding assays. No differences in the 5-HT1 and 5-HT2 receptor binding in the brainstem, hippocampus, frontal cortex, and hypothalamus or in the 5-HT3 receptor binding in the nucleus accumbens, amygdala, hippocampus, and frontal cortex were observed between the ethanol-naive animals of the rat lines. In rats given the opportunity to voluntarily consume alcohol, there was a tendency to increase 5-HT1 binding in the ANA rats, which tendency was, however, also found in their ethanol-naive controls subjected to the same handling and behavioral tests as the ethanol-experienced animals. The results do not, however, indicate that any genetic modifications of the 5-HT receptor-binding sites have occurred in the process of the selective breeding of AA and ANA rats for alcohol preference and avoidance, respectively.     

3H]ethylketocyclazocine binding to brain opioid receptor subtypes in alcohol-preferring AA and alcohol-avoiding ANA rats.

We measured brain regional patterns of [3H]ethylketocyclazocine binding to brain opioid receptors in ethanol-naive alcohol-preferring Alko, Alcohol (AA) and alcohol-avoiding Alko, Non-Alcohol (ANA) rats, by using quantitative autoradiography. This agonist ligand labels all opioid receptor subtypes. The proportions of mu- and delta-opioid receptor binding were evaluated by displacing the mu- and delta-opioid receptor components by the peptides Tyr-D-Ala-Gly-N(Me)Phe-Gly-ol (DAMGO, 100 nM) and Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE, 100nM), respectively, the K-component being the naltrexone-sensitive binding left after removal of the above two components. The labeling patterns in the brains of the AA and ANA rats were consistent with the well-known distributions of the opioid receptor subtypes in nonselected rat strains and there was no major difference between the lines. The mu-opioid receptor binding was greater in the AA than ANA rats in several brain regions, most interestingly in the substantia nigra pars reticulata and striatal clusters with elevated shell/core ratios in the nucleus accumbens. The delta-opioid receptor binding did not differ between the lines, whereas the AA rats had more K-opioid receptors than the ANA rats in several brain regions, including limbic areas and basal ganglia. The observed results might indicate altered action of the opioidergic system on dopaminergic pathways in rats with differential alcohol preference.