The effects of electronic nicotine vapor on voluntary alcohol consumption in female and male C57BL/6 J mice

SIGNIFICANCE

Alcohol drinking and nicotine vaping often co-occur and dependence on both substances is common. However, the impact of nicotine vaping on alcohol consumption is not fully understood.

METHODS

We examined the effects of nicotine vaping on ethanol drinking in female and male C57BL/6 J mice using an electronic nicotine delivery system and intermittent access two-bottle choice (IA-2BC) drinking. Mice were exposed to electronic nicotine vapor (3%) or propylene glycol/vegetable glycerol (PG/VG) control for 3 h sessions daily for 4 weeks and voluntary alcohol consumption was monitored. Nicotine vapor exposure was stopped and voluntary alcohol drinking was measured for a 2 week abstinence period. We also examined the effects of alcohol and nicotine on locomotion, temperature, and nicotine metabolism.

RESULTS

Following acute nicotine vapor exposure, alcohol drinking was increased in males but not in females. Thermoregulation was disrupted following nicotine vapor exposure and voluntary drinking. Male and female mice displayed increased locomotor activity immediately following chronic nicotine vapor exposure, and an anxiolytic effect was seen in males. In nicotine vapor abstinence, female mice displayed increased alcohol consumption. Locomotor activity and anxiolytic effects remained elevated in male but not female mice. Female mice displayed higher levels of serum nicotine and hydroxycotinine, suggesting impaired metabolism following chronic drinking and nicotine vapor exposure.

CONCLUSION

Collectively, these results suggest that while both male and female ethanol-drinking mice experience the stimulatory effects of nicotine vapor, only in males is there a parallel increase in ethanol drinking and only females display impairments in nicotine metabolism after drinking.

Sex-specific plasticity in CRF regulation of inhibitory control in central amygdala CRF1 neurons after chronic voluntary alcohol drinking

Despite strong preclinical evidence for the ability of corticotropin releasing factor 1 (CRF1) antagonists to regulate alcohol consumption, clinical trials have not yet demonstrated therapeutic effects of these compounds in alcohol use disorder (AUD) patients. Several confounding factors may limit the translation of preclinical CRF1 research to patients, including reliance on experimenter-administered alcohol instead of voluntary consumption, a preponderance of evidence collected in male subjects only and an inability to assess the effects of alcohol on specific brain circuits. A population of particular interest is the CRF1-containing neurons of the central amygdala (CeA). CRF1 CeA neurons are sensitive to ethanol, but the effects of alcohol drinking on CRF signalling within this population are unknown. In the present study, we assessed the effects of voluntary alcohol drinking on inhibitory control of CRF1+ CeA neurons from male and female CRF1:GFP mice using ex vivo electrophysiology and determined the contributions of CRF1 signalling to inhibitory control and voluntary alcohol drinking. Chronic alcohol drinking produced neuroadaptations in CRF1+ neurons that increased the sensitivity of GABA_A receptor-mediated sIPSCs to the acute effects of alcohol, CRF and the CRF1 antagonist R121919, but these adaptations were more pronounced in male versus female mice. The CRF1 antagonist CP-154,526 reduced voluntary alcohol drinking in both sexes and abolished sex differences in alcohol drinking. The lack of alcohol-induced adaptation in the female CRF1 system may be related to the elevated alcohol intake exhibited by female mice and could contribute to the ineffectiveness of CRF1 antagonists in female AUD patients.

On the use of hyperpolarized helium MRI for conformal avoidance lung radiotherapy

We wanted to illustrate the feasibility of using hyperpolarized helium magnetic resonance imaging (HPH-MRI) to obtain functional information that may assist in improving conformal avoidance of ventilating lung tissue during thoracic radiotherapy. HPH-MRI images were obtained from a volunteer patient and were first fused with a proton density-weighted (PD(w)) MRI to provide corresponding anatomic detail; they were then fused with the treatment planning computed tomography scan of a patient from our treatment planning database who possessed equivalent thoracic dimensions. An optimized treatment plan was then generated using the TomoTherapy treatment planning system, designating the HPH-enhancing regions as ventilation volume (VV). A dose-volume histogram compares the dosimetry of the lungs as a paired organ, the VV, and the lungs minus the VV. The clinical consequences of these changes was estimated using a bio-effect model, the parallel architecture model, or the local damage (f(dam)) model. Model parameters were chosen from published studies linking the incidence of grade 3+ pneumonitis, with the dose and volume irradiated. For two hypothetical treatment plans of 60 Gy in 30 fractions delivered to a right upper-lobe lung mass, one using and one ignoring the VV as an avoidance structure, the mean normalized total dose (NTD(mean)) values for the lung subvolumes were: lungs = 12.5 Gy₃ vs. 13.52 Gy₃, VV = 9.94 Gy₃ vs. 13.95 Gy₃, and lungs minus VV = 16.69 Gy₃ vs. 19.16 Gy₃. Using the f(dam) values generated from these plans, one would predict a reduction of the incidence of grade 3+ radiation pneumonitis from 12%-4% when compared with a conventionally optimized plan. The use of HPH-MRI to identify ventilated lung subvolumes is feasible and has the potential to be incorporated into conformal avoidance treatment planning paradigms. A prospective clinical study evaluating this imaging technique is being developed.

Effects of mGlu1-receptor blockade on ethanol self-administration in inbred alcohol-preferring rats

The Group I family of metabotropic glutamate receptors includes subtype 1 (mGlu1) and subtype 5 (mGlu5) receptors. This family of receptors has generated interest as potential targets for different areas of therapeutic development, including intervention for alcohol and drug abuse. Most of this interest is driven by findings showing involvement of mGlu5 receptors in the regulation of drug self-administration; however, studies examining the role of mGlu1 receptors in drug self-administration are limited. The purpose of this work was to examine the role of mGlu1-receptor antagonism in the maintenance of ethanol self-administration and the self-administration of an alternate nondrug reward, sucrose. Male alcohol-preferring inbred rats were trained to self-administer ethanol (15% vol/vol) versus water on a concurrent schedule of reinforcement, and the effect of the mGlu1-receptor antagonist JNJ16259685 (0.1-1.0mg/kg intraperitoneal [IP]) was evaluated on self-administration. The rats were then trained to self-administer sucrose (0.4% wt/vol) versus water, and the same dose range of JNJ16259685 was tested. Locomotor activity was tested in a separate assessment to evaluate potential nonspecific motor effects of the antagonist. Ethanol self-administration was dose dependently reduced by JNJ16259685. This reduction was likely due to a motor impairment as the lowest effective dose (0.1mg/kg) significantly reduced locomotor behavior. Sucrose self-administration was reduced by the highest JNJ16259685 dose (1.0mg/kg), and this reduction was also likely due to a motor impairment. Interestingly, ethanol self-administration was more sensitive to mGlu1-receptor antagonism than sucrose self-administration as lower JNJ16259685 doses reduced ethanol-reinforced responding and motor behavior. Together, these results suggest that mGlu1 receptors do not play a specific role in modulating ethanol self-administration or the self-administration of an alternate nondrug reward (i.e., sucrose).

Deletion of the 5-HT(3A)-receptor subunit blunts the induction of cocaine sensitization

Serotonin (5-HT) receptors are classified into seven groups (5-HT(1-7)), comprising at least 14 structurally and pharmacologically distinct receptor subtypes. Pharmacological antagonism of ionotropic 5-HT(3) receptors has been shown to modulate both behavioral and neurochemical aspects of the induction of sensitization to cocaine. It is not known, however, if specific molecular subunits of the 5-HT(3) receptor influence the development of cocaine sensitization. To address this question, we studied the effects of acute and chronic intermittent cocaine administration in mice with a targeted deletion of the gene for the 5-HT(3A)-receptor subunit (5-HT(3A)-/-). 5-HT(3A) (-/-) mice showed blunted induction of cocaine-induced locomotor sensitization as compared with wild-type littermate controls. 5-HT(3A) (-/-) mice did not differ from wild-type littermate controls on measures of basal motor activity or response to acute cocaine treatment. Enhanced locomotor response to saline injection following cocaine sensitization was observed equally in 5-HT(3A) (-/-) and wild-type mice suggesting similar conditioned effects associated with chronic cocaine treatment. These data show a role for the 5-HT(3A)-receptor subunit in the induction of behavioral sensitization to cocaine and suggest that the 5-HT(3A) molecular subunit modulates neurobehavioral adaptations to cocaine, which may underlie aspects of addiction.

Increased response to morphine in mice lacking protein kinase C epsilon

The protein kinase C (PKC) family of serine-threonine kinases has been implicated in behavioral responses to opiates, but little is known about the individual PKC isozymes involved. Here, we show that mice lacking PKCepsilon have increased sensitivity to the rewarding effects of morphine, revealed as the expression of place preference and intravenous self-administration at very low doses of morphine that do not evoke place preference or self-administration in wild-type mice. The PKCepsilon null mice also show prolonged maintenance of morphine place preference in response to repeated testing when compared with wild-type mice. The supraspinal analgesic effects of morphine are enhanced in PKCepsilon null mice, and the development of tolerance to the spinal analgesic effects of morphine is delayed. The density of mu-opioid receptors and their coupling to G-proteins are normal. These studies identify PKCepsilon as a key regulator of opiate sensitivity in mice.

Feasibility report of stereotactic body radiotherapy with tomotherapy for early stage medically inoperable lung cancer using extreme hypofractionation

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Background: This is a report on the technical feasibility, dosimetric aspects, and daily image-guidance capability with megavoltage computed tomography (MvCT) imaging of stereotactic body radiotherapy (SBRT) using tomotherapy for patients with medically inoperable early stage non-small cell lung cancer (NSCLC). Methods: Treatment planning was performed using 4D PET-CT in a BodyFix device. A pilot group of 4 patients with <5 cm T1/2, N0 tumors, was treated using IMRT (tomotherapy), utilizing daily image guidance with MvCT. Patients received 60 Gy within 10 days, delivered in five 12Gy fractions. The primary endpoint of this study was evaluation of acute and sub-acute treatment related toxicities. The secondary endpoint was radiographic evaluation for objective tumor response. Results: All 20 fractions were successfully delivered. MvCT provided excellent tumor visualization for daily image guidance. No significant tumor regression was observed in any patient during the 2 weeks of therapy, using volumetric contouring on MvCT images. The relevant dosimetric aspects, measured as median normalized total dose (NTD) were as follows: tumor = 116.5 Gy10; whole lung = 6.8 Gy3. Maximum fraction-size equivalent dose (FED) demonstrated median values as follows: esophagus = 4.04 Gy3; spinal cord = 6.53 Gy3. All patients are alive at a median follow-up of 6 months, with no grade 2 or higher acute pulmonary toxicities. Early radiographic follow-up demonstrates all 4 patients experienced a partial response. The mean tumor regression is 79% (range 64–85%). Conclusions: 4D PET-CT permits precise target delineation. In this, the first reported clinical experience, IMRT delivery of SBRT using tomotherapy is feasible, safe and free of major acute toxicities. The conformality which is obtained by helical delivery of the therapeutic dose makes it well-suited for dose escalation through extreme hypofractionation, with extremely low mean NTD to normal tissue. The ability to obtain on-treatment megavoltage CT scans to confirm tumor localization is a substantial advantage. Further studies and longer follow-up are warranted to evaluate the efficacy of this treatment modality.

[Table: see text]

GABA(A) receptor alpha-1 subunit deletion alters receptor subtype assembly, pharmacological and behavioral responses to benzodiazepines and zolpidem

Potentiation of GABA(A) receptor activation through allosteric benzodiazepine (BZ) sites produces the anxiolytic, anticonvulsant and sedative/hypnotic effects of BZs. Using a mouse line lacking alpha1 subunit expression, we investigated the contribution of the alpha1 subunit to GABA(A) receptor pharmacology, function and related behaviors in response to BZ site agonists. Competitive [(3)H]flunitrazepam binding experiments using the Type I BZ site agonist, zolpidem, and the Type I and II BZ site non-specific agonist, diazepam, demonstrated the complete loss of Type I BZ binding sites in alpha1(-/-) mice and a compensatory increase in Type II BZ binding sites (41+/-6%, P<0.002). Chloride uptake analysis in alpha1(-/-) mice revealed an increase (108+/-10%, P<0.001) in the efficacy (E(max)) of flunitrazepam while the EC(50) of zolpidem was increased 495+/-26% (alpha1(+/+): 184+/-56 nM; alpha1(-/-): 1096+/-279 nM, P<0.01). An anxiolytic effect of diazepam was detected in both alpha1(+/+) and alpha1(-/-) mice as measured on the elevated plus maze; however, alpha1(-/-) mice exhibited a greater percentage of open arm entries and percentage of open arm time following 0.6 mg/kg diazepam. Furthermore, alpha1(-/-) mice were more sensitive to the motor impairing/sedative effects of diazepam (1-10 mg/kg) as measured by locomotor activity in the open field. Knockout mice were insensitive to the anticonvulsant effect of diazepam (1-15 mg/kg, P<0.001). The hypnotic effect of zolpidem (60 mg/kg) was reduced by 66% (P<0.001) in alpha1(-/-) mice as measured by loss of righting reflex while the effect of diazepam (33 mg/kg) was increased 57% in alpha1(-/-) mice (P<0.05). These studies demonstrate that compensatory adaptations in GABA(A) receptor subunit expression result in subunit substitution and assembly of functional receptors. Such adaptations reveal important relationships between subunit expression, receptor function and behavioral responses.

Stimulation of endorphin neurotransmission in the nucleus accumbens by ethanol, cocaine, and amphetamine

Numerous studies have demonstrated that drugs of abuse activate the mesolimbic dopamine reward pathway, and it is widely held that this activation contributes to the motivational and positive reinforcing properties of these substances. However, there is evidence that endogenous opioid systems within this brain reward circuit also play a role in drug reinforcement and drug-seeking behavior. Using microdialysis in freely moving rats, we sought to determine whether various drugs of abuse (i.e., ethanol, cocaine, d-amphetamine, and nicotine) would increase neurotransmission of endogenous opioid peptides (i.e., endorphins) in the nucleus accumbens. Drugs were administered intraperitoneally twice at 3 h intervals, and the endorphin content of microdialysates was analyzed by a solid-phase radioimmunoassay. Acute administration of ethanol, cocaine, and d-amphetamine transiently elevated extracellular levels of endorphins in the nucleus accumbens, whereas nicotine and saline were without effect. We hypothesize that this drug-induced release of endorphins may contribute to the positive reinforcing and motivating properties of ethanol and psychostimulants.

Allopregnanolone and pentobarbital infused into the nucleus accumbens substitute for the discriminative stimulus effects of ethanol

BACKGROUND

The discriminative stimulus effects of ethanol are mediated in part by the gamma-aminobutyric acid type A (GABA(A)) receptor system. We have previously shown that microinjections of the competitive GABA(A) agonist muscimol in the nucleus accumbens and amygdala fully substitute for the discriminative stimulus effects of systemic ethanol. However, it is not known whether allosteric binding sites on GABA(A) receptors located within specific limbic brain regions contribute to the discriminative stimulus effects of ethanol.

METHODS

Male Long-Evans rats were trained to discriminate between intraperitoneal injections of ethanol (1 g/kg) and saline under a fixed-ratio 10 schedule of sucrose (10% w/v) reinforcement. Injector guide cannulae, aimed at both the nucleus accumbens core and the hippocampus area CA1, were then implanted to allow site-specific infusion of GABA(A)-positive modulators.

RESULTS

Infusion of the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone, or 3alpha-5alpha-P) in the nucleus accumbens resulted in dose-dependent full substitution for intraperitoneal ethanol (50% effective dose = 0.38 ng/microl per side). Likewise, injection of the barbiturate pentobarbital into the nucleus accumbens also substituted dose-dependently for ethanol (50% effective dose = 1.55 microg/microl per side). However, infusions of either 3alpha-5alpha-P or pentobarbital in the hippocampus failed to substitute for ethanol and produced inverted U-shaped dose-response curves.

CONCLUSIONS

These results demonstrate that allosteric positive modulation of GABA(A) receptors in the nucleus accumbens produces full substitution for the stimulus effects of ethanol. This suggests that GABA(A) receptors in the nucleus accumbens may play a more influential role in the discriminative stimulus effects of ethanol than those in the hippocampus.

Reduced ethanol withdrawal severity and altered withdrawal-induced c-fos expression in various brain regions of mice lacking protein kinase C-epsilon

Withdrawal from chronic ethanol consumption can be accompanied by motor seizures, which may be a result of altered GABA(A) receptor function. Recently, we have generated and characterized mice lacking the epsilon isoform of protein kinase C as being supersensitive to the behavioral and biochemical effects of positive GABA(A) receptor allosteric modulators, including ethanol. The aim of the present study was to determine whether protein kinase C-epsilon null mutant mice display altered seizure severity during alcohol withdrawal. In addition, we used c-fos immunohistochemistry immediately following seizure assessment to identify potential brain regions involved in any observed differences in withdrawal severity. Mice were allowed to consume an ethanol-containing or control liquid diet as the sole source of food for 14 days. During the 7-h period following removal of the diet, both ethanol-fed wild-type and protein kinase C-epsilon null mutant mice displayed an overall increase in Handling-Induced Convulsion score versus control-fed mice. However, at 6 and 7h following diet removal, the Handling-Induced Convulsion score was reduced in ethanol-fed protein kinase C-epsilon null mutant mice compared to ethanol-fed wild-type mice. Ethanol-fed protein kinase C-epsilon null mutant mice also exhibited a decrease in the number of Fos-positive cells in the lateral septum, and an increase in the number of Fos-positive cells in the dentate gyrus, mediodorsal thalamus, paraventricular nuclei of the thalamus and hypothalamus, and substantia nigra compared to ethanol-fed wild-type mice. These data demonstrate that deletion of protein kinase C-epsilon results in diminished progression of ethanol withdrawal-associated seizure severity, suggesting that selective pharmacological inhibitors of protein kinase C-epsilon may be useful in the treatment of seizures during alcohol withdrawal. These data also provide insight into potential brain regions involved in generation or suppression of ethanol withdrawal seizures.

Alcohol actions on GABA(A) receptors: from protein structure to mouse behavior

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were R. Adron Harris and Susumu Ueno. The presentations were (1) Protein kinase Cepsilon-regulated sensitivity of gamma-aminobutyric acid type A (GABAA) receptors to allosteric agonists, by Robert O. Messing, A. M. Sanchez-Perez, C. W. Hodge, T. McMahon, D. Wang, K. K. Mehmert, S. P. Kelley, A. Haywood, and M. F. Olive; (2) Genetic and functional analysis of a GABAA receptor gamma2 subunit variant: A candidate for quantitative trait loci involved in alcohol sensitivity and withdrawal, by Kari J. Buck and Heather M. Hood; (3) Tryptophan-scanning mutagenesis in GABAA receptor subunits: Channel gating and alcohol actions, by Susumu Ueno; and (4) Can a single binding site account for actions of alcohols on GABAA and glycine receptors? by R. Adron Harris, Yuri Blednov, Geoffrey Findlay, and Maria Paola Mascia.

The discriminative stimulus properties of self-administered ethanol are mediated by GABA(A) and NMDA receptors in rats

RATIONALE

The neurobiological systems that mediate the discriminative stimulus effects of self-administered drugs are largely unknown. The present study examined the discriminative stimulus effects of self-administered ethanol.

METHODS

Rats were trained to discriminate ethanol (1 g/kg, IP) from saline on a two-lever drug discrimination task with sucrose (10% w/v) reinforcement. Test sessions were conducted with ethanol (0 or 10% v/v) added to the sucrose reinforcement to determine if self-administered ethanol would interact with the discriminative stimulus effects of investigator-administered ethanol, or with the ethanol-like discriminative stimulus effects of the GABAA-positive modulator pentobarbital or the non-competitive NMDA antagonist MK-801.

RESULTS

During a saline test session, ethanol (10% v/v) was added to the sucrose reinforcement. Responding by all animals began accurately on the saline-appropriate lever and then switched to the ethanol-appropriate lever after rats self-administered a mean dose of 1.2 +/- 0.14 g/kg ethanol. During cumulative self-administration trials, responding initially occurred on the saline lever and then switched to the ethanol-appropriate lever after ethanol (0.68 +/- 0.13 g/kg) was self-administered. Investigator-administered MK-801 (0.01-1.0 mg/kg, cumulative IP) and pentobarbital (0.3-10.0 mg/kg, cumulative IP) dose-dependently substituted for ethanol. When ethanol (10% v/v) was added to the sucrose reinforcer, MK-801 and pentobarbital dose-response curves were shifted significantly to the left.

CONCLUSIONS

Self-administered ethanol substituted for and potentiated the stimulus effects of investigator-administered ethanol, suggesting that the discriminative stimulus effects of self-administered ethanol are similar to those produced by investigator-administered ethanol. Self-administered ethanol enhanced the ethanol-like discriminative stimulus effects of MK-801 and pentobarbital, which suggests that the discriminative stimulus effects of self-administered ethanol are mediated by NMDA and GABAA receptors.

Modulation of extracellular neurotransmitter levels in the nucleus accumbens by a taurine uptake inhibitor

Using in vivo microdialysis, we examined the effect of local perfusion of the taurine uptake inhibitor guanidinoethyl sulfonate on extracellular levels of various neurotransmitters in the rat nucleus accumbens. Guanidinoethyl sulfonate (500 microM-50 mM) produced a concentration-dependent increase in extracellular taurine levels. While 500 microM and 5 mM concentrations of guanidinoethyl sulfonate were largely without effect, 50 mM guanidinoethyl sulfonate produced a significant decrease in extracellular levels of aspartate, glutamate and glycine, with no effect on extracellular dopamine levels. These results indicate that guanidinoethyl sulfonate can modulate extracellular amino acid levels in the nucleus accumbens.

Expression profiling of neural cells reveals specific patterns of ethanol-responsive gene expression

Adaptive changes in gene expression are thought to contribute to dependence, addiction and other behavioral responses to chronic ethanol abuse. DNA array studies provide a nonbiased detection of networks of gene expression changes, allowing insight into functional consequences and mechanisms of such molecular responses. We used oligonucleotide arrays to study nearly 6000 genes in human SH-SY5Y neuroblastoma cells exposed to chronic ethanol. A set of 42 genes had consistently increased or decreased mRNA abundance after 3 days of ethanol treatment. Groups of genes related to norepinephrine production, glutathione metabolism, and protection against apoptosis were identified. Genes involved in catecholamine metabolism are of special interest because of the role of this pathway in mediating ethanol withdrawal symptoms (physical dependence). Ethanol treatment elevated dopamine beta-hydroxylase (DBH, EC 1.14.17.1) mRNA and protein levels and increased releasable norepinephrine in SH-SY5Y cultures. Acute ethanol also increased DBH mRNA levels in mouse adrenal gland, suggesting in vivo functional consequences for ethanol regulation of DBH. In SH-SY5Y cells, ethanol also decreased mRNA and secreted protein levels for monocyte chemotactic protein 1, an effect that could contribute to the protective role of moderate ethanol consumption in atherosclerotic vascular disease. Finally, we identified a subset of genes similarly regulated by both ethanol and dibutyryl-cAMP treatment in SH-SY5Y cells. This suggests that ethanol and cAMP signaling share mechanistic features in regulating a subset of ethanol-responsive genes. Our findings offer new insights regarding possible molecular mechanisms underlying behavioral responses or medical consequences of ethanol consumption and alcoholism.

Reduced operant ethanol self-administration and in vivo mesolimbic dopamine responses to ethanol in PKCepsilon-deficient mice

There is increasing evidence that individual protein kinase C (PKC) isozymes mediate specific effects of ethanol on the nervous system. In addition, multiple lines of evidence suggest that the mesoaccumbens dopamine reward system is critically involved in the rewarding and reinforcing effects of ethanol. Yet little is known about the role of individual PKC isozymes in ethanol reinforcement processes or in regulation of mesolimbic systems. In this study, we report that mice lacking the epsilon isoform of PKC (PKCepsilon) show reduced operant ethanol self-administration and an absence of ethanol-induced increase in extracellular dopamine levels in the nucleus accumbens. PKCepsilon null mice exhibited a 53% decrease in alcohol-reinforced operant responses under basal conditions, as well as following ethanol deprivation. Behavioural analysis revealed that while both genotypes had the same number of drinking bouts following deprivation, PKCepsilon null mice demonstrated a 61% reduction in number of ethanol reinforcers per bout and a 57% reduction in ethanol-reinforced response rate. In vivo microdialysis experiments showed that, in contrast to wild-type mice, PKCepsilon null mice exhibited no change in extracellular levels of dopamine in the nucleus accumbens following acute administration of ethanol (1 and 2 g/kg i.p.), while mesolimbic dopamine responses to cocaine (20 mg/kg i.p.) or high potassium (100 mM) in these mice were comparable with that of wild-types. These data provide further evidence that increases in extracellular mesolimbic dopamine levels contribute to the reinforcing effects of ethanol, and indicate that pharmacological agents inhibiting PKCepsilon may be useful in the treatment of alcohol dependence.

Co-localization of PKCepsilon with various GABA(A) receptor subunits in the mouse limbic system

The distribution of PKCepsilon and its co-localization with various GABA(A) receptor subunits within limbic structures of the mouse brain was examined by fluorescence immunohistochemistry. Levels of PKCepsilon immunoreactivity were highest in the cingulate cortex and dentate gyrus, moderate in the nucleus accumbens, and lowest in the prelimbic cortex and basolateral amygdala. Co-localization of PKCepsilon immunoreactivity with the GABA(A) receptor alpha1, beta 2/3, and gamma2 subunits varied by subunit and brain region examined, with the majority of co-localization occuring in the dentate gyrus, nucleus accumbens and basolateral amygdala. These results demonstrate that PKCepsilon may interact with GABA(A) receptors in a subunit- and region-specific manner, and provide a potential anatomical basis for recent behavioral and biochemical evidence that PKCepsilon modulates GABA(A) receptor function.

Microdialysis in the mouse nucleus accumbens: a method for detection of monoamine and amino acid neurotransmitters with simultaneous assessment of locomotor activity

Microdialysis has been extensively used to characterize the effects of drugs of abuse on extracellular levels of various neurotransmitters in nucleus accumbens (NAc) of the rat brain. However, recent advances in mouse genetics have prompted the need for studying the in vivo neurochemical correlates of drug intake in genetically engineered mice. While an earlier study has shown the feasibility of measuring monoamines in the NAc of behaving transgenic mice [I. Sillaber, A. Montkowski, R. Landgraf, N. Barden, F. Holsboer, R. Spanagel, Enhanced morphine-induced behavioural effects and dopamine release in the nucleus accumbens in a transgenic mouse model of impaired glucocorticoid (type II) receptor function: influence of long-term treatment with the antidepressant moclobemide, Neuroscience, 85 (1998) 415-425 [16] ], in this protocol we demonstrate a method for measuring both monoamine and amino neurotransmitters from the NAc of freely moving mice combined with open field locomotor activity monitoring. Mice were implanted with guide cannulae aimed at the NAc and allowed 4 days of recovery before being implanted with microdialysis probes equipped with 1-mm cuprophane membranes. On the following day, mice were placed in plexiglass chambers equipped with infrared photobeams, where microdialysis samples and locomotor activity data were collected in 10-min intervals. Immediately after collection, microdialysis samples were split into two equal aliquots for separate analysis of monoamine and amino acid neurotransmitter content. High performance liquid chromatography (HPLC) analysis revealed that norepinephrine, dopamine, serotonin, aspartate, glutamate, glycine, taurine, and gamma-aminobutyric acid (GABA) could be detected in each microdialysis sample. Thus, we have shown it is feasible to monitor extracellular levels of multiple neurotransmitters with simultaneous measurement of locomotor behavior in the mouse, making this model suitable for studying differential neurochemical and behavioral responses to drugs of abuse in genetically engineered mice.

Supersensitivity to allosteric GABA(A) receptor modulators and alcohol in mice lacking PKCepsilon

Several of the actions of ethanol are mediated by gamma-aminobutyrate type A (GABA(A)) receptors. Here we demonstrated that mutant mice lacking protein kinase C epsilon (PKCepsilon) were more sensitive than wild-type littermates to the acute behavioral effects of ethanol and other drugs that allosterically activate GABA(A) receptors. GABA(A) receptors in membranes isolated from the frontal cortex of PKCepsilon null mice were also supersensitive to allosteric activation by ethanol and flunitrazepam. In addition, these mutant mice showed markedly reduced ethanol self-administration. These findings indicate that inhibition of PKCepsilon increases sensitivity of GABA(A) receptors to ethanol and allosteric modulators. Pharmacological agents that inhibit PKCepsilon may be useful for treatment of alcoholism and may provide a non-sedating alternative for enhancing GABA(A) receptor function to treat other disorders such as anxiety and epilepsy.

A novel nociceptor signaling pathway revealed in protein kinase C epsilon mutant mice

There is great interest in discovering new targets for pain therapy since current methods of analgesia are often only partially successful. Although protein kinase C (PKC) enhances nociceptor function, it is not known which PKC isozymes contribute. Here, we show that epinephrine-induced mechanical and thermal hyperalgesia and acetic acid-associated hyperalgesia are markedly attenuated in PKCepsilon mutant mice, but baseline nociceptive thresholds are normal. Moreover, epinephrine-, carrageenan-, and nerve growth factor- (NGF-) induced hyperalgesia in normal rats, and epinephrine-induced enhancement of tetrodotoxin-resistant Na+ current (TTX-R I(Na)) in cultured rat dorsal root ganglion (DRG) neurons, are inhibited by a PKCepsilon-selective inhibitor peptide. Our findings indicate that PKCepsilon regulates nociceptor function and suggest that PKCepsilon inhibitors could prove useful in the treatment of pain.

The discriminative stimulus effects of ethanol are mediated by NMDA and GABA(A) receptors in specific limbic brain regions

This study was conducted to assess the involvement of N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA) receptor systems, located in specific limbic brain regions. in the discriminative stimulus effects of ethanol. Male Long-Evans rats were trained to discriminate between intraperitoneal (i.p.) injections of ethanol (1 g/kg) and saline on a two-lever drug discrimination task. The rats were then implanted with bilateral injector guides aimed at the nucleus accumbens core (AcbC), prelimbic cortex (PrLC), hippocampus area CA1 (CA1), or extended amygdala (i.e., at the border of the central and basolateral nuclei). Infusions of the non-competitive NMDA antagonist MK 801 in the AcbC or CA1 resulted in dose-dependent full substitution for i.p. ethanol. MK 801 infusion in the PrLC or amygdala failed to substitute for ethanol. Injection of the competitive NMDA antagonist CPP in the AcbC also failed to substitute for ethanol. Co-infusion of MK 801 in the hippocampus potentiated the effects of MK 801 in the AcbC, whereas NMDA infusion in the hippocampus attenuated the ability of MK 801 in the AcbC to substitute for ethanol. The direct GABA(A) agonist muscimol resulted in dose-dependent full substitution for i.p. ethanol when it was injected into the AcbC or amygdala, but failed to substitute when administered in the PrLC. Co-infusion of MK 801, but not CPP, potentiated the effects of muscimol in the AcbC. These results demonstrate that ethanol's discriminative stimulus function is mediated centrally by NMDA and GABA(A) receptors located in specific limbic brain regions. The data also suggest that the discriminative stimulus effects of ethanol are mediated by interactions between ionotropic GABA(A) and NMDA receptors in the nucleus accumbens, and by interactions among brain regions.

The effects of local application of ethanol in the n. accumbens on dopamine overflow and clearance

The actions of ethanol on extracellular dopamine levels in the n. accumbens were examined in both anesthetized and unanesthetized rats using either in vivo voltammetry or microdialysis. In the voltammetry studies, ethanol was microinjected directly into the accumbens. For the microdialysis studies, the ethanol was injected systemically. The voltammetry studies failed to find any direct effect of local ethanol on extracellular dopamine levels. However, exposure to high ethanol concentrations directly injected into the n. accumbens showed the rise rate and the return to baseline rate to a n. accumbens KCl-stimulated dopamine release. In the microdialysis studies, increased levels of extracellular dopamine in the n. accumbens were found in unanesthetized rats, similar to those reported in the literature. However, in the anesthetized rats, the extracellular dopamine levels were not increased, even with similar local ethanol levels measured in the dialysate. Taken together, the data suggest that the actions of ethanol to increase extracellular dopamine levels in the n. accumbens are most likely not an effect of ethanol at the level of the accumbens but rather an action which increases neural activity within the mesoaccumbens pathway, perhaps via actions at the ventral tegmental area.

Alcohol self-administration: further examination of the role of dopamine receptors in the nucleus accumbens

One of the functions of the mesolimbic dopamine (DA) system is to regulate the process of reinforcement, a process that is thought to influence drug self-administration. This study tested the effects of centrally administered DA receptor ligands on ethanol self-administration behavior. Long-Evans rats were trained to lever press on a fixed-ratio 4 schedule of ethanol (10% v/v) reinforcement. DA agonists and antagonists were then bilaterally microinjected (0.5 microliter/side) into the nucleus accumbens (N Acc) 10-min before sessions to test for effects on the onset, maintenance, and termination of ethanol self-administration. Infusions of the D1-like agonist SKF 38393 (0.03 to 3.0 micrograms) produced no effect on ethanol self-administration. The D1-like antagonist SCH 23390 (0.5 to 2.0 micrograms) reduced total responding by decreasing the time course of self-administration without altering response rate. The D2-like agonist quinpirole produced a biphasic effect on self-administration. Quinpirole (1.0 microgram) increased total responses and response rate, whereas higher doses (4.0 to 10.0 micrograms) decreased total responding as a result of early termination. The D2-like antagonist raclopride (0.1 to 1.0 microgram) reduced total responding by decreasing time course and response rate. Co-administration of either SKF 38393 or SCH 23390 with quinpirole prevented the behavioral effects observed with the low doses of quinpirole. Thus, in the N Acc either increased activation of D1-like receptors or their blockade can affect the expression of the behavioral effects of the D2-like agonist. This suggests that some intermediate level of D1 activation is required to observe the D2 effect. The decreases in total responding produced by raclopride were enhanced by co-administration of SKF 38393, but not altered by SCH 23390, thus suggesting that D1-like and D2-like receptors in the N Acc interact in the regulation of ethanol self-administration in a manner similar to their interactive regulation of other behaviors.

Dopaminergic and opiate agonists and antagonists differentially decrease multiple schedule responding maintained by sucrose/ethanol and sucrose

Similar neurobiological mechanisms are hypothesized to influence ethanol- and food-related reinforcement processes. This study examined the ability of compounds with dopaminergic or opiate activity to selectively alter responding maintained by a sucrose/ethanol solution in comparison to a sucrose solution. Long-Evans rats were trained to press a lever using 5% sucrose/10% ethanol and 5% sucrose as the reinforcers on a multiple Fixed Ratio 4 Fixed Ratio 4 schedule of reinforcement. When stable responding was established, the effects of intraperitoneally administered amphetamine (0.0-3.0 mg/kg), haloperidol (0.0-1.0 mg/kg), morphine (0.0-10.0 mg/kg), and naloxone (0.0-10.0 mg/kg) were examined on total session reinforcer presentation and presentation of each reinforcer within individual multiple schedule components. Prior to drug treatment, the total number of reinforcer presentations of the sucrose/ethanol solution was significantly greater than sucrose reinforcer presentations, suggesting the sucrose/ethanol solution was a more efficacious reinforcer. All agents administered decreased responding maintained by sucrose/ethanol and sucrose. The dose-effect curves for sucrose/ethanol were shifted to the left compared to sucrose, suggesting that although the compounds did not selectively impact sucrose/ethanol-maintained responding, sucrose/ethanol-maintained responding was more sensitive to the effects of these compounds.

Differential changes in sucrose/ethanol and sucrose maintained responding by independently altering ethanol or sucrose concentration

Increased reinforcing efficacy of sucrose/ethanol solutions in comparison to sucrose solutions has been previously demonstrated. However, the contribution of the components of the sucrose/ethanol solution is not well defined. The present study used a multiple schedule of reinforcement to evaluate the differential changes in reinforcer presentations as sucrose or ethanol concentrations were altered. Male Long-Evans rats were trained to press a lever on a multiple fixed ratio 4-fixed ratio 4 schedule which was composed of alternating 2-min components. During one component, 5% sucrose/10% ethanol was presented as the reinforcer and, in the second component, 5% sucrose was presented. Independent manipulations of the ethanol concentration (0, 5, and 20%) in the sucrose/ethanol solution or sucrose concentration (0, 10, and 20%) in the sucrose solution were then performed. Increasing the ethanol concentration in the sucrose/ethanol solution resulted in decreases in reinforcer delivery but increases in ethanol intake (grams per kilogram) and total session caloric intake. Increasing the sucrose concentration in the sucrose solution resulted in significant increases in sucrose reinforcer delivery and total session caloric intake. During the concentration manipulations, the number of reinforcers presented of the unchanged reinforcer was not affected. Differential changes in the pattern of reinforcer presentation after ethanol and sucrose concentration manipulations during successive access periods suggest that sucrose and sucrose/ethanol maintained responding are differentially regulated. Changes in sucrose maintained responding after increases in the sucrose concentration were observed early in the session suggesting a strong influence of taste in regulating intake. Changes in sucrose/ethanol maintained responding after increases in the ethanol concentration occurred later in the session and suggest that postingestive effects (i.e., pharmacology) play a major role in the regulation of sucrose/ethanol intake. In addition, the differential patterns of sucrose/ethanol and sucrose maintained behavior suggest that the ethanol component of the sucrose/ethanol solution plays an important role in maintaining sucrose/ethanol reinforced behavior.

Dopamine receptors in the medial prefrontal cortex influence ethanol and sucrose-reinforced responding

This study tested the role of dopamine receptors in the medial prefrontal cortex (mPFC) in the onset, maintenance, and termination of ethanol and sucrose-reinforced responding. Two groups of Long Evans rats were trained to lever press on a fixed-ratio 4 schedule of reinforcement with 10% ethanol (n = 10) or 5% sucrose (n = 5) presented as the reinforcer. After implantation of injector guide cannulae, the D2/3 agonist quinpirole and the D2 antagonist raclopride were administered bilaterally into the mPFC before behavioral sessions. During control conditions, sucrose reinforcement maintained a 2-fold greater number of responses per session than did ethanol reinforcement. Quinpirole (10.0 micrograms/microliter) reduced total ethanol-reinforced responses by delaying response onset and decreasing the duration of responding, but had no effect on response maintenance (i.e., response rate). A higher dose of quinpirole (20.0 micrograms/microliter) decreased total sucrose responses by simultaneously decreasing duration and response rate, without altering response latency. Thus, the effects of quinpirole on ethanol and sucrose-reinforced responding were similar on response total and duration, but differential on response latency and rate. Raclopride (0.05 and 1.0 microgram/microliter) decreased total ethanol responding and rate, but doses as much as 400-fold greater (20.0 micrograms/microliter) did not alter sucrose response totals. Raclopride alone had no effect on response latency or duration measures in either reinforcement condition. Coadministration of raclopride blocked the quinpirole-induced increase in response latency (ethanol reinforcement) and decrease in response rate (sucrose reinforcement), but had no effect on other response measures. These data are consistent with the interpretation that D2 and D3 receptors in the mPFC are differentially involved in ethanol and sucrose response onset and maintenance, but similarly involved in response termination. However, differences in baseline response parameters and group size may have contributed to the observed effects.

Norepinephrine and serotonin receptors in the paraventricular nucleus interactively modulate ethanol consumption

The homeostatic function of the hypothalamus has long been recognized. In particular, the role of the paraventricular nucleus (PVN) in regulating ingestive behavior has been of interest. Infusions of serotonin and norepinephrine into the PVN are correlated with nutrient selective decreases and increases in consumatory behavior, respectively. Given the wide range of homeostatic functions of the hypothalamus, it is plausible that similar hypothalamic mechanisms may also be involved in the regulation of ethanol intake. This study examined the effects of PVN infusions of serotonin (5-HT) and norepinephrine (NE) on ethanol intake in a 1-hr limited-access two-bottle paradigm. When intake of 6% (v/v) ethanol versus water stabilized, male Wistar rats were implanted with stainless steel guide cannulae aimed at the PVN. After recovery, NE (20, 50, and 100 nmol), 5-HT (5 and 25 nmol), and their combination (NE 50 nmol + 5-HT 5 nmol) were microinjected into the PVN in a volume of 0.5 microliter/side over 1 min. Baseline ethanol intake was approximately 1.0 g/kg and ethanol preference (milliliters ethanol per total milliliters) was approximately 60%. Both 20 and 50 nmol of NE significantly increased absolute ethanol intake by 50% and relative ethanol intake by approximately 30%. Corresponding decreases were observed in water intake. Neither dose of 5-HT when administered alone altered ethanol or water consumption, but the 5-nmol dose of 5-HT attenuated the increase observed after NE (50 nmol) administration. These data demonstrate that NE and 5-HT receptors in the PVN interact in the modulation of ethanol ingestion. This finding suggests that homeostatic regulatory functions of the hypothalamus are involved in ethanol intake, and a perturbation of this system may influence excessive drinking.

Discriminative stimulus function of ethanol: role of GABAA receptors in the nucleus accumbens

Because the subjective effects of drugs may be related to abuse potential, this study was conducted to assess the involvement of GABAA receptor systems in the nucleus accumbens (N Acc) in the discriminative stimulus effects of ethanol. Male Long-Evans rats were trained to discriminate between intraperitoneal (IP) injections of ethanol (1 g/kg) and saline under a fixed-ratio 10 schedule of sucrose (10% w/v) reinforcement. When performance during training sessions met the accuracy criteria (> 80% correct responding for five consecutive days), an ethanol generalization curve was determined. The rats were then surgically implanted with bilateral stainless-steel guide cannulae aimed at the N Acc. Intra-accumbens (IA) substitution test sessions were conducted during which the direct GABAA agonist muscimol (0.01, 0.04, 0.10, and 0.40 micrograms/microliter; IA) was administered in combination with saline (IP). The direct GABAA antagonist bicuculline (0.03, 0.10, and 0.30 micrograms/microliter; IA) was administered in combination with the training dose of ethanol (1 g/kg, ip). At 10-min postinjection, IA muscimol partially substituted for IP ethanol. However, at 15-min postinjection, muscimol (0.10 microgram/microliter; IA) fully substituted for IP ethanol. Bicuculline attenuated the discriminative stimulus properties of IP ethanol, but only at doses that significantly decreased response rate. At 10-min postinjection, muscimol (0.01 and 0.04 micrograms/microliter) potentiated (> 80% ethanol lever responding) the discriminative stimulus properties of a dose of ethanol (0.5 g/kg) that alone produced only partial generalization. These data suggest that ethanol discrimination is mediated centrally and demonstrate that infusions of the GABAA agonist muscimol in the N Acc are sufficient to produce the stimulus effects corresponding to a 1.0 g/kg training dose of ethanol. When taken together with data showing that GABAA receptor activation in the N Acc potentiates the termination of ethanol self-administration, these data suggest that ethanol's discriminative stimulus function may influence its reinforcement function.

Effects of ventral tegmental microinjections of the GABAA agonist muscimol on self-administration of ethanol and sucrose

Two groups of Long-Evans rats were trained to lever press on a fixed-ratio 4 (FR4) schedule of reinforcement with ethanol (10% v/v) or sucrose (75% w/v) presented as the reinforcer. After implantation of guide cannulae aimed at the ventral tegmental area (VTA), weekly bilateral injections of muscimol (10, 30, and 100 ng) were tested. During control conditions, response patterns for both groups were characterized by high rates that began shortly after the start of the session and terminated after approximately 10 min. Muscimol (10 ng) administration in the VTA increased the number of sucrose- but had no effect on the total number of ethanol-reinforced responses. Muscimol (30 ng) shifted the response patterns of both groups from high initial rates with early termination to slow initial rates with delayed termination, suggesting the possibility of nonspecific locomotor effects. These data suggest that ethanol- and sucrose-reinforced response totals are differentially sensitive to changes in GABAergic transmission in the VTA. The similar muscimol-induced changes in response patterns with the two reinforcers supports the hypothesis that GABAA receptors in the VTA are involved similarly in the maintenance of ethanol- and sucrose-reinforced responding. However, the failure of muscimol to increase ethanol-reinforced responding suggests that GABAergic systems in other brain regions may also be involved in the changes in ethanol intake seen following peripheral administration of GABAmimetic drugs.

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.

Morphine induced changes in ethanol-and water-intake are attenuated by the 5-HT3/4 antagonist tropisetron (ICS 205-930)

The opiate agonist morphine has been shown to increase ethanol intake and mesolimbic dopamine (DA) levels. Conversely, the 5-HT3/4 antagonist tropisetron has been shown to decrease ethanol intake and morphine-induced increases in mesolimbic DA levels. This study was designed to test the effects of acutely administered tropisetron on morphine-induced changes in ethanol (6% v/v) and water intake in a two-bottle test procedure. Ten water restricted male rats were injected with combinations of morphine (0.0, 0.56, 1.0, 1.5, 10.0, and 17.0 mg/kg, SC) and tropisetron (0.0, 1.0, 10.0, and 17.0 mg/kg, SC) prior to test sessions. Morphine (1.0 and 1.5 mg/kg) significantly increased absolute (g/kg) and relative ethanol intake (ethanol/total fluid). Tropisetron alone did not affect ethanol or water intake. When tropisetron (10.0 and 17.0 mg/kg) was administered in combination with morphine (1.5 mg/kg), the increase in ethanol intake induced by morphine was attenuated. Tropisetron (1.0 mg/kg) reversed a decrease in ethanol intake induced by morphine (17.0 mg/kg). The two highest doses of tropisetron partially attenuated a significant decrease in water intake produced by morphine (17.0 mg/kg). These data suggest that opiate and 5-HT3 mechanisms could interact in the regulation of ethanol intake. However, the doses of tropisetron tested were high and, therefore, the potential involvement of 5-HT4 receptors or other neurotransmitter systems in regulating ethanol intake is discussed.

Effects of intraaccumbens injections of dopamine agonists and antagonists on sucrose and sucrose-ethanol reinforced responding

The present experiment tested the effects of intraaccumbens injections of dopamine (DA) agonists and antagonists on operant responding reinforced by sucrose and sucrose/ethanol solutions. The mixed DA agonist d-amphetamine (20.0 micrograms/microliters) significantly reduced responding reinforced by a low concentration sucrose solution (2% w/v) by 48% and 38% compared to no injection and sham control values, respectively. The addition of ethanol (10%) to a low concentration sucrose solution (3%) presented as the reinforcer changed the response pattern from a continuous moderate response rate, over a 30 min session, to an initial high response rate that terminated after approximately 10 min. With sucrose/ethanol reinforcement, d-amphetamine slowed the initial high response rate but extended responding throughout the 30 min sessions. However, no significant changes were observed in number of responses per session. When 75% sucrose (w/v) was presented as the reinforcer, d-amphetamine did not change the total number of responses/session, but response patterns were again altered from high initial rates with early offset to slow steady rates that continued for the duration of sessions. The D2 DA antagonist raclopride (0.1-5.0 micrograms/microliters) resulted in a dose-dependent decrease in responding reinforced by 75% sucrose. The baseline patterns, response totals, and effects of the DA antagonists resemble our previously reported findings with 10% ethanol (v/v) reinforcement. These data support the conclusion that mesolimbic DA activity may be a common mechanism in ethanol reinforced behavior and behavior reinforced by other substances, but suggest that the nature of behavioral change may depend upon the reinforcer.

Comparison of the discriminative stimulus function of ethanol following intracranial and systemic administration: evidence of a central mechanism

Rats were trained using a two-lever drug discrimination procedure to press one lever following systemic administration of ethanol (1.0 mg/kg, IP) and another lever following IP injections of saline. After determination of an ethanol generalization curve (0.25-1.25 g/kg, IP), rats were surgically implanted with bilateral stainless steel guide cannulae that terminated in the lateral ventricles. Following surgery, the generalization curve was redetermined and did not differ from presurgery values. Then, generalization to bilateral intracerebroventricular (ICV) injections of ethanol (600.0 and 900.0 mM, 1.0 microliter/side) were administered alone and in combination with IP injections of ethanol. The ICV ethanol injections produced partial generalization, but the combination of ICV ethanol (600.0 and 900.0 mM) with IP ethanol (0.25 and 0.50 g/kg) injections were two- to threefold more potent then IP injections alone. Response rates were unaffected by any dose of ethanol tested. These data suggest central mediation of ethanol's discriminative stimulus function due to: 1) increased potency of systemically administered ethanol by centrally administered ethanol, and 2) partial generalization between centrally and peripherally administered ethanol.

Specific decreases in ethanol- but not water-reinforced responding produced by the 5-HT3 antagonist ICS 205-930

The serotonin 5-HT3 antagonist ICS 205-930 has been shown to block the discriminative stimulus properties of ethanol and decrease voluntary intake, suggesting a possible role for 5-HT3 systems in the reinforcing effects of ethanol. ICS 205-930 (0.56, 1.0, 3.0, 10.0, and 17.0 mg/kg i.p.) was examined on ethanol and water self-administration in an operant paradigm. Following a sucrose-fading procedure, two groups of nondeprived rats responded on either a concurrent fixed ratio 4 schedule for ethanol (10% v/v) and water (CONC FR4 FR4), or a single FR4 schedule for ethanol (10% v/v). ICS 205-930 dose-dependently decreased ethanol-reinforced responding in the concurrent condition without decreasing water-reinforced responding, suggesting a specific effect on ethanol. Ethanol-reinforced responding was also dose-dependently decreased in the single FR4 condition, but the dose effect curve was shifted to the left. These data support the conclusions that 5-HT3 systems may play a specific role in ethanol self-administration that is independent of general appetitive and motor processes, and that 5-HT3 antagonists may have therapeutic efficacy in the treatment of alcohol abuse when multiple reinforcers are available.

Ventral tegmental microinjections of quinpirole decrease ethanol and sucrose-reinforced responding

The effects of microinjections in the ventral tegmental area (VTA) of the dopamine D2/D3 agonist quinpirole on ethanol- and sucrose-reinforced responding were tested. Two groups of Long-Evans rats were trained to lever press on a fixed-ratio 4 schedule with 10% ethanol (v/v) (n = 8) and 75% sucrose (w/v) (n = 10) presented as the reinforcer. Weekly bilateral injections of quinpirole were tested in the ethanol group (0.0, 0.001, 0.01, 0.1, and 1.0 micrograms/microliters) and sucrose group (0.0, 0.01, 0.1, 1.0, and 10.0 micrograms/microliters). Quinpirole dose dependently decreased ethanol- and sucrose-reinforced responding, but the dose-effect curve for sucrose was shifted two orders of magnitude to the right of the ethanol curve. Temporal response patterns during control sessions for both reinforcers were characterized by initial high rates that terminated after approximately 10 min. VTA injections of quinpirole dose dependently delayed the onset of the first response and the initial high rate period, and resulted in an early termination of responding following onset. These data support the hypothesis that dopamine activity in the VTA is involved in the regulation of ethanol-reinforced responding in a manner similar to that of other reinforcers.

Effect of dopamine agonists and antagonists on ethanol-reinforced behavior: the involvement of the nucleus accumbens

Rats initiated to self-administer 10% ethanol (v/v) in an operant situation using the sucrose-substitution technique received bilateral n. accumbens or caudate nucleus microinjections of d-amphetamine (4, 10, and 20 micrograms/brain), quinpirole (4 micrograms/brain), and/or raclopride (0.1, 0.5, and 1.0 micrograms/brain). Only microinjections into the n. accumbens produced changes in rate and pattern of responding. With d-amphetamine, an increase in total responding and a slowing of initial response rate was seen, whereas with raclopride administration a dose-related decrease in total responding was observed with no alteration in momentary response rates. Drug-dependent behavioral rate and pattern differences suggest that DA activity in the n. accumbens influences ethanol reinforced behavior.

Microinjections of dopamine agonists in the nucleus accumbens increase ethanol-reinforced responding

Long-Evans rats (N = 3) were trained to lever press on a fixed-ratio 4 (FR 4) schedule with ethanol (10% v/v) presented as the reinforcer. Each rat received a total of six bilateral nucleus accumbens microinjections, one per week. They were tested with one physiological saline control, three 20.0-microgram/brain d-amphetamine, and two 6.0-microgram/brain quinpirole injections given 10 min prior to operant sessions. Ethanol-reinforced responding terminated after approximately 10 min during control sessions. Microinjections of the D2 agonist quinpirole and the nonspecific dopamine (DA) agonist d-amphetamine increased total responding but produced slowed response rates that continued for 45-60 min. The slowed response rate produced by d-amphetamine resulted in a peak increase in interresponse times (IRTs) between 8-10 s, whereas quinpirole increased IRTs in the 14- to 16-s range, indicating that nonspecific DA activation resulted in higher rates of ethanol-reinforced responding than specific D2 activation although both drugs decreased local response rates. These data indicate that the amount and temporal extent of ethanol-reinforced responding are increased by microinjections of DA agonists in the nucleus accumbens and support the hypothesis that DA activity in this region is involved in the regulation of ethanol-reinforced responding.

Effects of morphine on acquisition and maintenance of ethanol and water intake patterns in rats

Two experiments were conducted to assess the effects of chronic subcutaneous injections of morphine (1.0 mg/kg) or saline on the pattern and amount of sweetened ethanol and water intake in fluid restricted Long-Evans rats. Following daily injections, 2-h two-bottle choice tests were conducted with water and an ethanol solution (15% ethanol v/v in 5% sucrose w/v). During a 20-day acquisition phase (Experiment 1), ethanol intake patterns and amounts did not differ between saline (n = 6) and morphine (n = 6) groups. Both groups exhibited ethanol intake patterns that decreased exponentially throughout the session suggesting control by fluid restriction procedures. Morphine decreased water intake during initial periods of each session and increased intake during later periods. In Experiment 2, morphine and saline injections were reversed across three phases with the same rats. Morphine increased total ethanol consumption during the first few days of each 15-day phase, but the groups did not differ thereafter, and the initial increases produced no statistically significant group differences. Additionally, morphine augmented ethanol intake in early portions of sessions, while water intake was decreased and increased during early and later portions of each session, respectively. Analysis of the data from the last 5 days of each phase indicated that, when injected with morphine, the group which received saline during acquisition consumed significantly more ethanol solution than the group injected with morphine during acquisition. The effect on patterns of water and ethanol intake were observed, regardless of the drug injected during acquisition.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Self-Administration: Role of Mesolimbic Dopamine

It appears clear that ethanol reinforcement, like that of many abused drugs, utilizes the mesolimbic DA pathways. From the data presented on microinjection of DA agonists and antagonists, it would seem that only part of the regulatory process controlling ethanol drinking is directly involved with this pathway. Once drinking has begun, the DA antagonist raclopride results in a rapid termination of drinking. This appears to be a blocking effect of what may be conditioned reinforcement resulting from prior ethanol reinforcement initiation procedures. Microinjection of the DA agonists d-amphetamine and quinpirole prolonged drinking, with little signs of normal termination apparent in the 30-min session in many animals. This appeared to be the result of interference with normal termination processes. While it remains to be demonstrated that oral ethanol consumption results in the release of DA in the nucleus accumbens, evidence from prior work and the present studies support a role for the mesolimbic DA system in ethanol reinforcement.