In vivo microdialysis study of brain ethanol concentrations in rats following oral self-administration

The influence of chromosome 4 on high ethanol consumption and blood pressure

The Spontaneously Hypertensive Rats (SHR) strain was developed through selective breeding for high systolic blood pressure. In our laboratory, we established a congenic rat strain named SHR.Lewis-Anxrr16 (SLA16). The SLA16 rat strain is genetically identical to the SHR except for the inserted Anxrr16 region in chromosome 4. Our objective was to evaluate the influence of this genomic region on ethanol consumption and blood pressure. First, we exposed SHR and SLA16 male and female rats to ethanol consumption. Results showed that, regardless of strain, females consumed more ethanol than males during forced (10% v/v) and spontaneous ethanol consumption (SEC; 2.5-20% v/v). Then, females from both strains were used to evaluate sensitivity to ethanol. No strain differences in the loss of righting reflex were observed after ethanol treatment (3 g/kg, 20% w/v, intraperitoneal [i.p.]). But, in the triple test, female SHR rats presented lower sensitivity to the ethanol (1.2 g/kg, 14% w/v, i.p.). Surprisingly, female SHR rats also presented higher blood pressure after SEC (10% v/v). Finally, losartan treatment was effective in decreasing the blood pressure of female rats of both strains, but had specific effects on SHR ethanol consumption. Our data suggest that SLA16 female rats consume less ethanol (10%), are more sensitive to its effects, and present lower blood pressure than SHR female rats. We demonstrated that the Anxrr16 locus in chromosome 4 is a genetic candidate to explain high ethanol consumption and blood pressure, at least in females.

Common effects of fat, ethanol, and nicotine on enkephalin in discrete areas of the brain

Fat, ethanol, and nicotine share a number of properties, including their ability to reinforce behavior and produce overconsumption. To test whether these substances act similarly on the same neuronal populations in specific brain areas mediating these behaviors, we administered the substances short-term, using the same methods and within the same experiment, and measured their effects, in areas of the hypothalamus (HYPO), amygdala (AMYG), and nucleus accumbens (NAc), on mRNA levels of the opioid peptide, enkephalin (ENK), using in situ hybridization and on c-Fos immunoreactivity (ir) to indicate neuronal activity, using immunofluorescence histochemistry. In addition, we examined for comparison another reinforcing substance, sucrose, and also took measurements of stress-related behaviors and circulating corticosterone (CORT) and triglycerides (TG), to determine if they contribute to these substances' behavioral and physiological effects. Adult Sprague-Dawley rats were gavaged three times daily over 5 days with 3.5 mL of water, Intralipid (20% v/v), ethanol (12% v/v), nicotine (0.01% w/v) or sucrose (22% w/v) (approximately 7 kcal/dose), and tail vein blood was collected for measurements of circulating CORT and TG. On day five, animals were sacrificed, brains removed, and the HYPO, AMYG, and NAc processed for single- or double-labeling of ENK mRNA and c-Fos-ir. Fat, ethanol, and nicotine, but not sucrose, increased the single- and double-labeling of ENK and c-Fos-ir in precisely the same brain areas, the middle parvocellular but not lateral area of the paraventricular nucleus, central but not basolateral nucleus of the AMYG, and core but not shell of the NAc. While having little effect on stress-related behaviors or CORT levels, fat, ethanol, and nicotine all increased circulating levels of TG. These findings suggest that the overconsumption of these three substances and their potential for abuse are mediated by the same populations of ENK-expressing neurons in specific nuclei of the hypothalamus and limbic system.

Reduced alcohol drinking in adult rats exposed to sucrose during adolescence

Intake of sweet-alcoholic drinks during adolescence is believed to favor alcohol abuse and dependence in adulthood. This study examined the influence of early exposure to ethanol with or without sucrose on the consumption of sweet or alcoholic solutions in adulthood. Adolescent rats (from post-natal day 30-46) were given continuous free access to tap water and either 5% sucrose, 5% ethanol or mixed 5% sucrose-5% ethanol. The control group was given access to water only. Upon reaching adulthood (post-natal day 60), rats were tested for saccharin (sweet), quinine (bitter) and ethanol consumption using a two-bottle free-choice paradigm. The results indicated that pre-exposure to ethanol did not alter the intake of sweet or ethanol solutions in adulthood. However, rats exposed to sucrose during adolescence showed a decreased consumption of both sweet and ethanol solutions. Because alcohol has a sweet taste component, an additional group of rats, pre-exposed to either 5% sucrose or water during adolescence, was tested for intravenous ethanol self-administration (preventing oral sensory stimulation) and in a new model of simultaneous access to oral saccharin and intravenous ethanol that results in higher total ethanol intake. Relative to controls, sucrose-exposed rats showed reduced operant self-administration of saccharin, yet no differences were found for intravenous ethanol self-administration. Altogether, these findings indicate that sucrose exposure during adolescence persistently affected the perception of sweet taste reward and thereby alcohol's acceptance in adulthood.

Positive association between ethanol consumption and anxiety-related behaviors in two selected rat lines

The Floripa H and L rat lines were selectively bred, respectively, for high and low scores of locomotion in the central aversive area of an open field (OF), which is a putative index of experimental anxiety. In the present study, we used these lines to examine the relationship between anxiety-related behaviors and ethanol intake through the use of three animal tests used to investigate anxiety (OF, elevated plus maze, and black/white box) and one oral ethanol consumption procedure. Males and females of the Floripa L line were more anxious-like than their counterparts in the three behavioral tests. No line differences in the tests of taste control solutions (saccharin and quinine) and forced ethanol (10%) were found. However, Floripa L female rats consumed more ethanol than their Floripa H counterparts at concentrations of 6 and 10% in a two-bottle choice protocol. Moreover, Floripa L females showed a higher ratio of ethanol to total fluids consumed, regardless of the concentration offered, than all other subgroups (males of both lines and Floripa H females). Males showed no line differences for ethanol consumption. Taken together, the results of this study confirm that there are important sex differences in both anxiety-related behaviors and ethanol consumption. Accordingly, these data suggest a positive genetic relationship between anxiety-related behaviors and ethanol intake, at concentrations of 6 and 10%, in females but not in males. This supports the use of both sexes in animal experiments involving anxiety- and ethanol-related behaviors. Finally, the results and the existing literature indicate that selectively bred laboratory animals constitute a useful tool in the search for genes influencing both anxiety and ethanol consummatory behavior.

Acute ethanol administration rapidly increases phosphorylation of conventional protein kinase C in specific mammalian brain regions in vivo

BACKGROUND

Protein kinase C (PKC) is a family of isoenzymes that regulate a variety of functions in the central nervous system including neurotransmitter release, ion channel activity, and cell differentiation. Growing evidence suggests that specific isoforms of PKC influence a variety of behavioral, biochemical, and physiological effects of ethanol in mammals. The purpose of this study was to determine whether acute ethanol exposure alters phosphorylation of conventional PKC isoforms at a threonine 674 (p-cPKC) site in the hydrophobic domain of the kinase, which is required for its catalytic activity.

METHODS

Male rats were administered a dose range of ethanol (0, 0.5, 1, or 2 g/kg, intragastric) and brain tissue was removed 10 minutes later for evaluation of changes in p-cPKC expression using immunohistochemistry and Western blot methods.

RESULTS

Immunohistochemical data show that the highest dose of ethanol (2 g/kg) rapidly increases p-cPKC immunoreactivity specifically in the nucleus accumbens (core and shell), lateral septum, and hippocampus (CA3 and dentate gyrus). Western blot analysis further showed that ethanol (2 g/kg) increased p-cPKC expression in the P2 membrane fraction of tissue from the nucleus accumbens and hippocampus. Although p-cPKC was expressed in numerous other brain regions, including the caudate nucleus, amygdala, and cortex, no changes were observed in response to acute ethanol. Total PKCgamma immunoreactivity was surveyed throughout the brain and showed no change following acute ethanol injection.

CONCLUSIONS

These results suggest that ethanol rapidly promotes phosphorylation of cPKC in limbic brain regions, which may underlie effects of acute ethanol on the nervous system and behavior.

Evidence for a female-specific effect of a chromosome 4 locus on anxiety-related behaviors and ethanol drinking in rats

Previous studies using the inbred rat strains Lewis (LEW) and spontaneously hypertensive rats (SHR) led to the mapping of two quantitative trait loci, named Ofil1 (on chromosome 4 of the rat) and Ofil2 (on chromosome 7), for open-field inner locomotion, a behavioral index of anxiety. Studies using other strains showed that the region next to Ofil1 influences measures of not only anxiety but also ethanol consumption. In view of the high prevalence of psychiatric disorders such as anxiety and alcoholism, as well as the comorbidity between them, the present study was designed to better characterize the contribution of these two loci to complex emotional and consummatory responses. Rats deriving from an F2 intercross between the LEW and the SHR strains were selected according to their genotype at markers flanking the loci Ofil1 and Ofil2 and bred to obtain lines of rats homozygous LEW/LEW or SHR/SHR for each of the two loci, thus generating four genotypic combinations. These selected animals as well as purebred LEW and SHR rats of both sexes were submitted to a battery of tests including measures of locomotor activity, anxiety, sweet and bitter taste reinforcement and ethanol intake. Lewis rats displayed more anxiety-like behavior and less ethanol intake than SHR rats. Ofil1 (on chromosome 4) affected both the activity in the center of the open field and ethanol drinking in females only. These results suggest that Ofil1 contains either linked genes with independent influences on anxiety-related responses and ethanol drinking or a pleiotropic gene with simultaneous effects on both traits.

Glial cell line-derived neurotrophic factor mediates the desirable actions of the anti-addiction drug ibogaine against alcohol consumption

Alcohol addiction manifests as uncontrolled drinking despite negative consequences. Few medications are available to treat the disorder. Anecdotal reports suggest that ibogaine, a natural alkaloid, reverses behaviors associated with addiction including alcoholism; however, because of side effects, ibogaine is not used clinically. In this study, we first characterized the actions of ibogaine on ethanol self-administration in rodents. Ibogaine decreased ethanol intake by rats in two-bottle choice and operant self-administration paradigms. Ibogaine also reduced operant self-administration of ethanol in a relapse model. Next, we identified a molecular mechanism that mediates the desirable activities of ibogaine on ethanol intake. Microinjection of ibogaine into the ventral tegmental area (VTA), but not the substantia nigra, reduced self-administration of ethanol, and systemic administration of ibogaine increased the expression of glial cell line-derived neurotrophic factor (GDNF) in a midbrain region that includes the VTA. In dopaminergic neuron-like SHSY5Y cells, ibogaine treatment upregulated the GDNF pathway as indicated by increases in phosphorylation of the GDNF receptor, Ret, and the downstream kinase, ERK1 (extracellular signal-regulated kinase 1). Finally, the ibogaine-mediated decrease in ethanol self-administration was mimicked by intra-VTA microinjection of GDNF and was reduced by intra-VTA delivery of anti-GDNF neutralizing antibodies. Together, these results suggest that GDNF in the VTA mediates the action of ibogaine on ethanol consumption. These findings highlight the importance of GDNF as a new target for drug development for alcoholism that may mimic the effect of ibogaine against alcohol consumption but avoid the negative side effects.

Effects of ethanol on locomotor and anxiety-like behaviors and the acquisition of ethanol intake in Lewis and spontaneously hypertensive rats

The purpose of the present study was to investigate whether Lewis (LEW) and spontaneously hypertensive rats (SHR), characterized in numerous behavioral tests as strains with high-anxiety and low-anxiety, respectively, could differ in their sensitivity to the effects of ethanol in the elevated plus maze (EPM) and the open field (OF), two classical models of anxiety/emotionality, as well as in the acquisition of ethanol drinking behavior. It was also of interest to examine the relationship between sweet and bitter fluids preference and ethanol intake. SHR and LEW rats were given saline or ethanol injections (0.6 or 1.2 g/kg, ip.) and tested in the EPM and OF. Subsequently the same animals were given continuous free choice between water and ethanol solution (2-8%). Additional groups of animals were exposed to a free-choice regimen between saccharin (0.002-0.09%) or quinine (0.0001-0.0015%) and water. The low dose of ethanol (0.6 g/kg) induced anxiolytic-like effects and intensive locomotor activation mainly in SHR rats tested in the OF arena. Overall, LEW counterparts were unaffected in OF test. In oral self-administration paradigm, SHR rats consumed significantly more ethanol than LEW rats. Concerning other solutions, SHR rats consumed large amounts of saccharin compared with LEW rats. These data indicate that the SHR preference for ethanol intake may be positively related to their differential sensitivity to the anxiolytic/stimulant effects of ethanol and to the sensitivity of this strain for saccharin reinforcement. In addition, these findings provide evidence that the SHR strain may represent a useful genetic and pharmacological tool to investigate ethanol drinking traits.

Microdialysis for the determination of acetaldehyde and ethanol concentrations in the striatum of freely moving rats

The subject of the present paper is the simultaneous determination of ethanol (EtOH) and acetaldehyde (AcH) concentrations in the striatum of freely moving rats using an in vivo microdialysis followed by head-space gas chromatography (GC). Major operation conditions of GC were as follows: column, injector and detector temperatures 90, 110 and 200 degrees C, respectively; Supelcowax wide bore capillary column (60 m length, 0.53 mm i.d., 2 microm film thickness); carrier gas, nitrogen; flow rate, 20 ml/min. The recovery of EtOH and AcH at a concentration 40 mM and 250 microM, respectively, by microdialysis showed a maximum of 83.8+/-12.2 and 51.2+/-6.5%, respectively, at a flow rate of 0.8 microl/min. A good linear calibration curve in the concentration range of 5-50 mM for EtOH (r=0.998), and 10-250 microM for AcH (r=0.988) was observed. Microdialysates were collected for 10 min each after insertion of probe into the striatum. Rats were treated with cyanamide (100mg/kg, a potent aldehyde dehydrogenase inhibitor) and 60 min later with EtOH (1g/kg) intraperitoneally. A 10 min sample was about 8 microl. This volume was mixed with 40 microl of 0.002% t-butanol as an internal standard in 0.6N perchloric acid, and then analyzed by head-space GC method. The peak EtOH and AcH concentrations in the striatal dialysates reached maximum at 30 min, and then gradually decreased. This method represents a reasonable tool to quantify in vivo both AcH and EtOH levels simultaneously in rat brain.

Involvement of non-exocytotic mechanisms in ethanol-induced in vivo dopamine release: comparisons with cocaine

In order to determine whether a non-exocytotic mechanism was involved in ethanol-induced in vivo dopamine release in the nucleus accumbens, extracellular dopamine concentrations were measured via intracerebral microdialysis in freely moving Sprague-Dawley rats. Effects of ethanol on dopamine release in the nucleus accumbens were compared with those by cocaine, a drug that increases synaptic dopamine by a mechanism, which depends on neuronal activity and involves an exocytotic process. Administration of ethanol (80 mM) or cocaine (10 microM) via a dialysis probe increased extracellular dopamine concentrations in the nucleus accumbens. Pretreatments with tetrodotoxin (2 microM) or Ca2+ withdrawal did not block the ability of ethanol to increase nucleus accumbens dopamine. The blockade of dopamine autoreceptors by local infusion of sulpiride did not significantly alter the effect of ethanol on nucleus accumbens dopamine either. As opposed to ethanol, however, cocaine-induced increases in nucleus accumbens dopamine were sensitive to tetrodotoxin or Ca2+ omission. In addition, pretreatments with sulpiride significantly potentiated the effect of cocaine on extracellular dopamine concentrations. These differences in responses to tetrodotoxin, Ca2+ withdrawal and inhibition of dopamine autoreceptors suggest that a non-exocytotic mechanism may be involved in dopamine release in the nucleus accumbens evoked by focally applied ethanol.

Alcohol stimulates the release of dopamine in the ventral pallidum but not in the globus pallidus: a dual-probe microdialysis study

The mesoaccumbens dopamine system has been hypothesized to be a common neural substrate mediating the actions of various drugs of abuse, including ethanol. However, the involvement of the mesopallidal dopamine system has received very little attention. The present study examined the effects of intraperitoneal (IP) ethanol administration on the extracellular levels of dopamine in the ventral pallidum (VP) and globus pallidus (GP) of Wistar rats. Rats were bilaterally implanted with microdialysis probes aimed at the VP and GP or nucleus accumbens (NAc) and dorsal striatum (dSTR). During microdialysis testing, rats with probes located in the VP and GP were injected IP with sterile saline or 15% (v/v) ethanol in saline at doses of 0.75, 1.5, or 2.25 g/kg. Rats with NAc and dSTR probes were injected with saline or 2.25 g/kg ethanol. The IP administration of 1.5 and 2.25 g/kg ethanol significantly (p <0.05) elevated the extracellular levels of dopamine in the VP (maximal increase: 136 and 182% of baseline, respectively) but not in the GP. No effects on extracellular dopamine levels were observed following the IP injections of 0.75 g/kg ethanol or saline. The IP administration of 2.25 g/kg ethanol significantly (p <0.05) elevated the extracellular levels of dopamine in the NAc (maximal increase: 198% of baseline) and dSTR (maximal increase: 155% of baseline). Analysis of the effects of 2.25 g/kg ethanol on dopamine release revealed greater increases in the VP, NAc, and dSTR compared to the GP. The data suggest that the mesopallidal, mesoaccumbens, and nigrostriatal dopamine systems are more sensitive to the effects of ethanol than the nigropallidal dopamine system.

Differential adaptive properties of accumbens shell dopamine responses to ethanol as a drug and as a motivational stimulus

Non-adaptive activation of dopamine transmission in the nucleus accumbens shell by drugs of abuse has been attributed a fundamental role in the mechanism of drug addiction. In order to test this hypothesis, we compared in the same subject the effect of an addictive drug (ethanol) and of taste stimuli, including ethanol's own taste, on dialysate dopamine in the nucleus accumbens shell as an estimate of dopamine transmission and on taste reactivity as an expression of motivational valence. Ethanol was also monitored in the dialysates. In naive rats, intraoral infusion of a 20% sucrose + chocolate solution elicited a monophasic increase of dialysate dopamine immediately after the intraoral infusion. In contrast, intraoral infusion of 10% ethanol, 10% ethanol + 20% sucrose or 10% ethanol + 20% sucrose + chocolate solutions elicited a biphasic increase of nucleus accumbens dopamine with an early taste-related rise and a late rise related to dialysate ethanol. Pre-exposure to the ethanol solutions 24 h before resulted in the absence of the early dopamine rise and permanence of the late dopamine rise. This late dopamine rise was actually increased as compared with that of the nonpre-exposed group when sucrose-containing ethanol solutions were tested. The results indicate that single trial pre-exposure to the ethanol solutions differentially affects the responsiveness of nucleus accumbens shell dopamine to the direct intracerebral action of ethanol and to the effect of its taste with potentiation, or no change of the first and abolition of the second. These observations point to the existence of major differences in the adaptive regulation of nucleus accumbens dopamine transmission in the shell after drug as compared with taste reward. These differences, in turn, are consistent with a role of nucleus accumbens shell dopamine in the mechanism of the behavioural effects of addictive drugs.

Effects of acute acamprosate and homotaurine on ethanol intake and ethanol-stimulated mesolimbic dopamine release

The purpose of the present study was to determine the acute effects of the anticraving compound acamprosate (calcium acetylhomotaurinate) and the closely related compound homotaurine on ethanol intake and ethanol-stimulated dopamine release in the nucleus accumbens. Male rats were treated with acamprosate (200 or 400 mg/kg intraperitoneally, i.p.) or homotaurine (10, 50, or 100 mg/kg i.p.) 15 min prior to access to 10% ethanol and water for 1 h in a two-bottle choice restricted access paradigm. A separate group of rats was implanted with microdialysis probes in the nucleus accumbens and given an acute injection of ethanol (1.5 g/kg i.p.) that was preceded by saline, acamprosate, or homotaurine. Acamprosate and homotaurine dose-dependently reduced ethanol intake and preference. These compounds also delayed or suppressed ethanol-stimulated increases in nucleus accumbens dopamine release, suggesting that acamprosate and homotaurine may reduce ethanol intake by interfering with the ability of ethanol to activate the mesolimbic dopamine reward system.

Brain ethanol levels after voluntary ethanol drinking in AA and Wistar rats

Brain ethanol was monitored in the nucleus accumbens with one minute microdialysis and headspace gas chromatography in male Wistar and alcohol preferring AA (Alko Alcohol) rats after voluntary limited access consumption without food restriction. The rats drank 0.93 +/- 0.14 (Wistar) and 0.73 +/- 0.07 g/kg (AA), with a resulting mean maximal brain ethanol level of 15.9 mM and 14.1 mM, respectively. Maximum brain ethanol levels for individual AA rats were in the range 9.4-33.6 mM, median 15.5 mM and for the individual Wistar rats in the range 2.5-35.2 mM, median 17.8 mM. There was a significant but not perfect correlation between the amount ethanol drunk and the resulting ethanol level in the nucleus accumbens, probably because of the rats not being food deprived before the experiment. The results show that rats drink pharmacologically meaningful doses in a voluntary limited access situation and that blood samples can give us a hint about the level attained in the brain, but to know the early brain concentration after drinking, microdialysis is an excellent tool.

Bicuculline sensitive depressor response to ethanol infusion into the lateral hypothalamus

Decreased GABA function in the hypothalamus increases mean arterial pressure (MAP) and heart rate (HR). Since ethanol acts on GABA-A receptors, blocking GABA-A receptors can prevent a decrease of MAP and HR by ethanol in the lateral hypothalamus (LH). Ethanol at 5-30 mM, with or without 25 ng/microl bicuculline, was infused into the LH, and the activity of the site was validated with 100 nmoles of serotonin. Male rats were anesthetized with pentobarbital, and the femoral artery was catheterized to measure MAP and HR. Microinfusion was performed with a 28-gauge cannula placed into the LH. Serotonin increased MAP and HR within 15 sec. Ethanol decreased the MAP by -21.15 +/- 3.92 mmHg and HR by -53.61 +/- 14.95 BPM, at 15 min, which recovered by 15 min after the infusion was terminated. These maximum decreases were produced by 20 mM ethanol giving a U-shaped dose response. The aCSF vehicle had no effect. Bicuculline prevented ethanol-induced changes and had no effect when administered alone. Both serotonin and ethanol have direct effects on LH neurons with cardiovascular function. Ethanol produces this effect through GABA-A receptors.

Neuronal spike activity in the nucleus accumbens of behaving rats during ethanol self-administration

Many lines of evidence support the importance of the nucleus accumbens (NAC) for ethanol-reinforced behavior. The nature of the neuronal activity that occurs in this region during ethanol self-administration is not known. We recorded from ensembles of single-units primarily located within the shell of the NAC during operant responding for oral ethanol solutions by well-trained rats. Of 90 units recorded from seven sessions from seven rats, 41 (46%) did not exhibit significant changes in relation to the experimental events. Of the 49 units (54%) that did exhibit significant phasic changes, alterations in firing rate occurred in relation to the following experimental events: operant response (63%), tone stimulus (20%), and ethanol delivery (63%). In addition, changes in spike activity during the intervals between the three experimental events were noted in 33% of the units. Most units (55% of responsive units) responded to multiple experimental events. Thus different but overlapping populations of neurons in the NAC represent each event that occurs along the temporal dimension of a single trial performed to obtain ethanol reward. The data suggest that the NAC plays a crucial role in linking together conditioned and unconditioned internal and external stimuli with motor plans to allow for ethanol-seeking behavior to occur.

Role of arginine vasopressin and corticotropin-releasing factor in mediating alcohol-induced adrenocorticotropin and vasopressin secretion in male rats bearing lesions of the paraventricular nuclei

In male rats, lesions of the paraventricular nucleus (PVN) of the hypothalamus attenuate, but do not abolish, adrenocorticotropin (ACTH) secretion in response to acute alcohol injection. As the PVN is the major source of corticotropin-releasing factor (CRF) in the median eminence, this observation suggests that extra-PVN brain regions, and/or ACTH secretagogues other than CRF (e.g. arginine vasopressin (AVP)), mediate ACTH stimulation by alcohol. This hypothesis was tested by examining the effect of AVP immunoneutralization in PVN-lesioned (PVNx) rats. Removal of endogenous AVP diminished alcohol-evoked ACTH secretion in both sham-operated and PVNx animals, indicating that AVP from outside the PVN partially mediates the hypothalamic-pituitary-adrenal (HPA) axis response to alcohol. This led us to determine whether alcohol might also regulate AVP steady-state gene expression in the supraoptic nucleus (SON) and PVN, and/or CRF mRNA in the PVN and the central nucleus of the amygdala (AMY). In the magnocellular portion of the PVN, sham-operated animals showed significantly increased PVN levels of both CRF and AVP mRNAs 3 h after alcohol. In the SON, alcohol administration tended to decrease AVP gene expression in PVNx rats, while the drug increased AVP mRNA levels in the SON of sham-operated rats. AMY levels of CRF mRNA were unaffected by these manipulations. Finally, since the regulation of alcohol-induced AVP mRNA levels in the SON appeared to depend on the presence of the PVN, we measured peripheral levels of AVP in both sham-operated and PVNx animals after injection of vehicle or alcohol. Although AVP decreased in all groups, alcohol depressed AVP secretion to a greater extent in PVNx animals, suggesting that AVP systems are more sensitive to inhibition in the absence of the PVN. Our results demonstrate that although AVP of PVN origin may participate in regulating the stimulatory effect to AVP on ACTH secretion, AVP from areas other than the PVN also plays a role. Additionally, regulation of both AVP gene expression in the SON and secretion in the systemic circulation are altered in rats bearing lesions of the PVN.

Ethanol affects hypothalamic neurons projecting to the hippocampus and inhibits dentate granule cell LTP

In previous studies we demonstrated that ethanol inhibition of hippocampal granule cell long-term potentiation (LTP) is mediated by angiotensin II (AII), and the inhibition can be blocked by losartan, a specific AII receptor antagonist. The purpose of the present study was to demonstrate that this low-dose ethanol inhibition of dentate granule cell LTP induction is mediated by lateral hypothalamic (LH) afferents that project to the granule cells. In urethane anesthetized rats, we compared the effects of ethanol infusion, 6.0 microliter/30 min, by means of an open-ended push-pull type cannula, in both the LH and the dentate gyrus, on dentate granule cell LTP. Results demonstrate a dose-dependent inhibition of LTP induction when the LH is perfused that can be blocked by losartan, 10 mg/kg i.p.. Four doses of ethanol were used: 5, 10, 20, and 30 mM. There was no effect when the dentate gyrus was infused with 30 mM ethanol and normal granule cell LTP was observed. Also, these results demonstrate for the first time a low-dose ethanol effect on a physiological function, LTP in a specific neural pathway, directly related to the anterograde amnesia produced by ethanol on short-term memory. Therefore, these data support our hypothesis that ethanol inhibition of LTP induction at the medial perforant path-granule cell synapse can be attributed to a presynaptic release of AII and cannot be explained in terms of a direct postsynaptic effect on the granule cells.

GABAergic transmission in the nucleus accumbens is involved in the termination of ethanol self-administration in rats

Long-Evans rats (n = 12) were trained to lever-press on a fixed-ratio 4 schedule of reinforcement with ethanol (10% v/v) presented as the reinforcer. After implantation of bilateral stainless-steel guide cannulae aimed at the nucleus accumbens, site-specific microinjections of muscimol (1-30 ng) and bicuculline (1-10 ng) were tested for effects on ethanol-reinforced responding. Baseline response patterns were characterized by initial high rates that terminated abruptly after approximately 20 min. Muscimol administration in the nucleus accumbens decreased the total number of ethanol-reinforced responses and obtained reinforcers. Bicuculline also decreased ethanol-reinforced responses and reinforcers at the highest dose tested. When a dose of bicuculline (1 ng) that was ineffective by itself was coadministered with an effective dose of muscimol (10 ng), the muscimol-induced decreases in responding were blocked. Analysis of response patterns showed that muscimol decreased ethanol self-administration by terminating responding, normally lasting 20 min, after approximately 10 min with no changes in local response rate. Bicuculline decreased total responding by producing parallel, but nonsignificant, changes in time course and response rate. These data suggest that GABAergic transmission in the nucleus accumbens is involved in the termination, but not the onset or maintenance of ethanol self-administration. The specificity of this effect gives emphasis to the importance of measuring behavioral parameters, as well as products of behavior (such as intake volume) in the study of ethanol self-administration.

Pharmacology of ethanol and glutamate antagonists on rodent sleep: a comparative study

Twenty-five Sprague-Dawley rats were implanted with electrodes for standard sleep-wake cycle recordings. A guide cannula was stereotaxically implanted into the lateral ventricle. Rats were divided into five groups (n = 5) and challenged with an intraventricular administration of 10 microliters of a 5 nM solution of either: ethanol (EtOH), MK-801, AP5 (noncompetitive and competitive NMDA receptor antagonists, respectively), CNQX (AMPA receptor antagonist), or saline. Rats were recorded polygraphically for the following 4 h. Results showed that, at comparable doses, all tested drugs reduced REM sleep. No significant changes were detected in slow-wave sleep or wakefulness. This selective effect of glutamatergic antagonists suggests that glutamate may be a selective modulator of REM sleep. These findings also show that EtOH shares similar pharmacological effects on the sleep-wake cycle of the rat. Ultimately, glutamatergic mechanisms could contribute to the EtOH-mediated reduction of REM sleep.

Brain ethanol in AA, ANA, and Wistar rats monitored with one-minute microdialysis

A microdialysis system for measuring the ethanol concentration curve in the nucleus accumbens of the rat brain was developed and tested in three different rat lines (AA, ANA, and Wistar) after an intraperitoneal (IP) and an intragastric (IG) dose of 1.0 g/kg ethanol. The flow rate of the modified Ringer solution was set at 5 microliters/min; samples were taken every minute after ethanol administration and analyzed with headspace gas chromatography. After IP administration, the brain ethanol levels rose much more rapidly than tail blood ethanol levels in the same animals. The maximum brain ethanol level after IG administration was lower and occurred later, and were similar to the tail blood levels in AA and ANA rats. No clear difference between the lines was found after IP administration but there was some indication that ANA rats may absorb alcohol after IG intubation faster than AA or Wistar rats.

Oral ethanol self-administration in rats is reduced by the administration of dopamine and glutamate receptor antagonists into the nucleus accumbens

The purpose of this study was to assess the role of endogenous dopamine and glutamate systems within the nucleus accumbens in modulating responses for oral ethanol reinforcements (10% w/v) in a free-choice operant task. Pretreatment with both systemic (100 micrograms/kg) and intra-nucleus accumbens microinjection of fluphenazine (2 and 4 micrograms), a dopamine receptor antagonist, significantly decreased responding for ethanol, without significantly affecting responses for water. Ethanol self-administration was also attenuated by microinjection into the nucleus accumbens of 2-amino-5-phosphopentanoic acid (AP-5, 3 and 6 micrograms), a competitive NMDA receptor antagonist. These results suggest that dopamine and glutamate neurotransmission in the nucleus accumbens may regulate ethanol self-administration and its reinforcing effects.