Decreased glial and synaptic glutamate uptake in the striatum of HIV-1 gp120 transgenic mice.

The mechanisms leading to the neurocognitive deficits in humans with immunodeficiency virus type 1 (HIV-1) are not well resolved. A number of cell culture models have demonstrated that the HIV-envelope glycoprotein 120 (gp120) decreases the reuptake of glutamate, which is necessary for learning, memory, and synaptic plasticity. However, the impact of brain HIV-1 gp120 on glutamate uptake systems in vivo remains unknown. Notably, alterations in brain glutamate uptake systems are implicated in a number of neurodegenerative and neurocognitive disorders. We characterized the kinetic properties of system XAG (sodium-dependent) and systems xc- (sodium-independent) [3H]-L-glutamate uptake in the striatum and hippocampus of HIV-1 gp120 transgenic mice, an established model of HIV neuropathology. We determined the kinetic constant Vmax (maximal velocity) and Km (affinity) of both systems XAG and xc- using subcellular preparations derived from neurons and glial cells. We show significant (30-35 %) reductions in the Vmax of systems XAG and xc- in both neuronal and glial preparations derived from the striatum, but not from the hippocampus of gp120 mice relative to wild-type (WT) controls. Moreover, immunoblot analysis showed that the protein expression of glutamate transporter subtype-1 (GLT-1), the predominant brain glutamate transporter, was significantly reduced in the striatum but not in the hippocampus of gp120 mice. These extensive and region-specific deficits of glutamate uptake likely contribute to the development and/or severity of HIV-associated neurocognitive disorders. Understanding the role of striatal glutamate uptake systems in HIV-1 gp120 may advance the development of new therapeutic strategies to prevent neuronal damage and improve cognitive function in HIV patients.

The effect of repeated exposure to ethanol on pre-existing fear memories in rats.

RATIONALE: There is a high degree of comorbidity between alcohol use disorder and post-traumatic stress disorder (PTSD), but little is known about the interactions of ethanol with traumatic memories. OBJECTIVES: Using auditory fear conditioning in rats, we asked if repeated exposure to ethanol could modify the retrieval of fear memories acquired prior to ethanol exposure. METHODS: Following auditory fear conditioning, Sprague-Dawley rats were given daily injections of ethanol (1.5 g/kg) or saline over 5 days. Two days later, they were given 20 trials of extinction training and then tested for extinction memory the following day. In a separate experiment, conditioned rats were given repeated ethanol injections and processed for c-Fos immunohistochemistry following a fear retrieval session. RESULTS: Two days following the cessation of ethanol, the magnitude of conditioned fear responses (freezing and suppression of bar pressing) was significantly increased. This increase persisted the following day. Waiting 10 days following cessation of ethanol eliminated the effect on fear retrieval. In rats conditioned with low shock levels, repeated exposure to ethanol converted a sub-threshold fear memory into a supra-threshold fear memory. It also increased c-Fos expression in the prelimbic prefrontal cortex, paraventricular thalamus, and the central and basolateral nuclei of the amygdala, areas implicated in the retrieval of fear memories. CONCLUSIONS: These results suggest that repeated exposure to ethanol may exacerbate pre-existing traumatic memories.

The ventral pallidum: Subregion-specific functional anatomy and roles in motivated behaviors.

The ventral pallidum (VP) plays a critical role in the processing and execution of motivated behaviors. Yet this brain region is often overlooked in published discussions of the neurobiology of mental health (e.g., addiction, depression). This contributes to a gap in understanding the neurobiological mechanisms of psychiatric disorders. This review is presented to help bridge the gap by providing a resource for current knowledge of VP anatomy, projection patterns and subregional circuits, and how this organization relates to the function of VP neurons and ultimately behavior. For example, ventromedial (VPvm) and dorsolateral (VPdl) VP subregions receive projections from nucleus accumbens shell and core, respectively. Inhibitory GABAergic neurons of the VPvm project to mediodorsal thalamus, lateral hypothalamus, and ventral tegmental area, and this VP subregion helps discriminate the appropriate conditions to acquire natural rewards or drugs of abuse, consume preferred foods, and perform working memory tasks. GABAergic neurons of the VPdl project to subthalamic nucleus and substantia nigra pars reticulata, and this VP subregion is modulated by, and is necessary for, drug-seeking behavior. Additional circuits arise from nonGABAergic neuronal phenotypes that are likely to excite rather than inhibit their targets. These subregional and neuronal phenotypic circuits place the VP in a unique position to process motivationally relevant stimuli and coherent adaptive behaviors.

Repeated cycles of chronic intermittent ethanol exposure leads to the development of tolerance to aversive effects of ethanol in C57BL/6J mice.

BACKGROUND: Repeated cycles of chronic intermittent ethanol (CIE) exposure lead to increased voluntary ethanol (EtOH) intake in C57BL/6J mice. This study evaluates the development of tolerance to EtOH's aversive effects in CIE exposure. METHODS: Adult male C57BL/6J mice were trained to drink 15% EtOH (vs. water) in a limited access procedure and then exposed to CIE (EtOH mice) or air (control [CTL] mice) for 5 cycles alternating with weekly access to EtOH drinking. Following the 4th CIE cycle, the aversive effects of EtOH were evaluated using a conditioned taste aversion (CTA) paradigm with 1% saccharin as the conditioned stimulus. Several doses of EtOH (0, 1, 2, and 3 g/kg) and LiCl (0.4 M, 0.02 ml/g) served as unconditioned stimuli. Finally, mice underwent a 5th CIE cycle to measure blood and brain concentrations following a 2 g/kg EtOH dose. RESULTS: CIE exposure increased EtOH drinking in EtOH mice while drinking in CTL mice remained stable. The lowest EtOH dose (1 g/kg) did not induce CTA in either group, but the highest dose (3 g/kg) produced CTA in both groups (49% reduction for CTL vs. 25% reduction for EtOH) although the group differences were not statistically significant. However, the 2 g/kg EtOH dose induced a significant aversion in CTL mice (27% reduction) but not in EtOH mice (20% increase), indicating tolerance to EtOH's aversive effects. LiCl caused a similar aversion in CTL and EtOH mice (50% reduction). Finally, blood and brain ethanol concentrations were not different between CTL and EtOH mice following a 2 g/kg EtOH dose. CONCLUSIONS: The data indicate that CIE exposure produces tolerance to the aversive effects of 2 g/kg EtOH. This effect does not appear to be related to a learning deficit or altered EtOH pharmacokinetics. These data support the notion that tolerance to EtOH's aversive effects may contribute to excessive EtOH drinking in EtOH-dependent mice.

Up-regulation of the neuronal nicotinic receptor α7 by HIV glycoprotein 120: potential implications for HIV-associated neurocognitive disorder.

Approximately 30-50% of the >30 million HIV-infected subjects develop neurological complications ranging from mild symptoms to dementia. HIV does not infect neurons, and the molecular mechanisms behind HIV-associated neurocognitive decline are not understood. There are several hypotheses to explain the development of dementia in HIV(+) individuals, including neuroinflammation mediated by infected microglia and neuronal toxicity by HIV proteins. A key protein associated with the neurological complications of HIV, gp120, forms part of the viral envelope and can be found in the CSF of infected individuals. HIV-1-gp120 interacts with several receptors including CD4, CCR5, CXCR4, and nicotinic acetylcholine receptors (nAChRs). However, the role of nAChRs in HIV-associated neurocognitive disorder has not been investigated. We studied the effects of gp120(IIIB) on the expression and function of the nicotinic receptor α7 (α7-nAChR). Our results show that gp120, through activation of the CXCR4 chemokine receptor, induces a functional up-regulation of α7-nAChRs. Because α7-nAChRs have a high permeability to Ca(2+), we performed TUNEL staining to investigate the effects of receptor up-regulation on cell viability. Our data revealed an increase in cell death, which was blocked by the selective antagonist α-bungarotoxin. The in vitro data are supported by RT-PCR and Western blot analysis, confirming a remarkable up-regulation of the α7-nAChR in gp120-transgenic mice brains. Specifically, α7-nAChR up-regulation is observed in mouse striatum, a region severely affected in HIV(+) patients. In summary, CXCR4 activation induces up-regulation of α7-nAChR, causing cell death, suggesting that α7-nAChR is a previously unrecognized contributor to the neurotoxicity associated with HIV infection.

Brain region-specific gene expression changes after chronic intermittent ethanol exposure and early withdrawal in C57BL/6J mice.

Neuroadaptations that participate in the ontogeny of alcohol dependence are likely a result of altered gene expression in various brain regions. The present study investigated brain region-specific changes in the pattern and magnitude of gene expression immediately following chronic intermittent ethanol (CIE) exposure and 8 hours following final ethanol exposure [i.e. early withdrawal (EWD)]. High-density oligonucleotide microarrays (Affymetrix 430A 2.0, Affymetrix, Santa Clara, CA, USA) and bioinformatics analysis were used to characterize gene expression and function in the prefrontal cortex (PFC), hippocampus (HPC) and nucleus accumbens (NAc) of C57BL/6J mice (Jackson Laboratories, Bar Harbor, ME, USA). Gene expression levels were determined using gene chip robust multi-array average followed by statistical analysis of microarrays and validated by quantitative real-time reverse transcription polymerase chain reaction and Western blot analysis. Results indicated that immediately following CIE exposure, changes in gene expression were strikingly greater in the PFC (284 genes) compared with the HPC (16 genes) and NAc (32 genes). Bioinformatics analysis revealed that most of the transcriptionally responsive genes in the PFC were involved in Ras/MAPK signaling, notch signaling or ubiquitination. In contrast, during EWD, changes in gene expression were greatest in the HPC (139 genes) compared with the PFC (four genes) and NAc (eight genes). The most transcriptionally responsive genes in the HPC were involved in mRNA processing or actin dynamics. Of the few genes detected in the NAc, the most representatives were involved in circadian rhythms. Overall, these findings indicate that brain region-specific and time-dependent neuroadaptive alterations in gene expression play an integral role in the development of alcohol dependence and withdrawal.

Intermittent (every-other-day) drinking induces rapid escalation of ethanol intake and preference in adolescent and adult C57BL/6J mice.

BACKGROUND: Using adult C57BL/6J (B6) mice, we previously developed a procedure that causes a progressive increase in ethanol intake and preference (i.e., alcohol escalation effect) following weekly (intermittent) access to ethanol (Melendez et al., 2006). A limitation of this procedure is that it requires many weeks of testing, which limits its use to study ethanol escalation (i.e., binge-like drinking) during adolescence. Previous studies have shown that intermittent every-other-day (EOD) access to ethanol is sufficient to induce ethanol escalation in rats. The objective of this study was to verify whether EOD access is sufficient to induce escalated levels of ethanol intake and preference in adult and adolescent B6 mice. METHODS: Male B6 mice received free-choice 24-hour access to 15% ethanol and water on an EOD or daily basis for 2 weeks. Food and water were available at all times. Using adult mice, Experiment 1 characterized the induction of ethanol escalation following EOD access at 6 (i.e., drinking in the dark) and 24-hour intervals, whereas Experiment 2 determined whether daily drinking reverses escalation induced by EOD drinking. Experiment 3 compared ethanol-drinking capacity following daily versus EOD drinking in adolescent (P30-45) and adult (P70-85) mice. RESULTS: Experiment 1 revealed that EOD drinking leads to a significant (nearly 2-fold) increase in ethanol intake and preference over mice given daily access. Experiment 2 demonstrated that EOD-elicited escalation is blocked and subsequently reversed following daily drinking. Experiment 3 revealed that ethanol drinking was greater in adolescent mice compared with adults following daily drinking and EOD (escalated) drinking. Although the escalated levels of ethanol intake were greater in adolescent mice, the rate or onset of escalation was comparable between both age-groups. CONCLUSIONS: This study is the first to demonstrate that EOD drinking leads to escalation of ethanol intake and preference in adolescent and adult mice. Moreover, our results indicate that daily ethanol reverses ethanol escalation induced by intermittent drinking. The study also revealed that adolescent mice have a greater capacity to drink ethanol under both daily (controlled) and EOD (escalated) conditions, which further supports the notion of adolescent's susceptibility to heavy drinking.

Ceftriaxone restores glutamate homeostasis and prevents relapse to cocaine seeking.

BACKGROUND: The cystine-glutamate exchanger is downregulated after chronic cocaine, resulting in reduced extracellular levels of nucleus accumbens glutamate. The importance of cocaine-induced loss of glutamate homeostasis is revealed by N-acetylcysteine restoring cystine-glutamate exchange and attenuating reinstatement to cocaine seeking. Another regulator of extracellular glutamate is the glial glutamate transporter GLT-1. We hypothesized that cocaine self-administration reduces GLT-1 and that GLT-1 upregulation inhibits cocaine seeking. METHODS: We measured [(3)H] glutamate uptake and protein expression of GLT-1 and xCT, the catalytic subunit of the cystine-glutamate exchanger, following cocaine self-administration and 3 weeks of extinction training. We also examined the affect of ceftriaxone (previously shown to increase GLT-1) and N-acetylcysteine treatment on the expression of GLT-1 and xCT. Ceftriaxone was also tested for the capacity to inhibit cue- and cocaine-induced relapse. RESULTS: Cocaine self-administration reduced glutamate uptake and the expression of both GLT-1 and xCT. Ceftriaxone restored GLT-1 and xCT levels and prevented cue- and cocaine-induced reinstatement of drug seeking. N-acetylcysteine also restored GLT-1 and xCT levels. CONCLUSIONS: These results indicate that glutamate transport and cystine-glutamate exchange may be coregulated and provide further evidence that targeting glutamate homeostasis is a potential method for treating cocaine relapse.

Nrf2 gene deletion fails to alter psychostimulant-induced behavior or neurotoxicity.

The transcription factor NF-E2-related factor (Nrf2) regulates the induction of phase 2 detoxifying enzymes by oxidative stress, including synthesis of the catalytic subunit (xCT) of the heterodimeric cystine-glutamate exchanger (system xc-). Repeated cocaine treatment in rats causes persistent neuroadaptations in glutamate neurotransmission in the nucleus accumbens that result, in part, from reduced activity of system xc-. Since in vitro under- or over-expression of Nrf2 regulates system xc- activity and xCT content, it was hypothesized that in vivo deletion of the Nrf2 gene would: 1) decrease system xc- activity, 2) produce a behavioral phenotype resembling that elicited by chronic cocaine administration, and 3) enhance dopamine depletion after methamphetamine-induced oxidative stress. In all three experiments no genotypic difference was measured between mice sustaining homozygous Nrf2 gene deletion and wild-type littermates. Thus, while Nrf2 is a transcriptional regulator of xCT and capable of protecting cells from oxidative stress, following Nrf2 gene deletion this role can be partially compensated by other mechanisms and methamphetamine-induced oxidative stress and dopamine toxicity does not significantly involve Nrf2.

Development of an alcohol deprivation and escalation effect in C57BL/6J mice.

BACKGROUND: Relapse-like drinking has been studied through the expression of the alcohol deprivation effect (ADE), which is measured by a pronounced increase in ethanol preference and consumption after imposed abstinence. No studies have characterized the ADE in C57BL/6J (B6) mice. The present study examined the effects of length and number of deprivations on the expression of the ADE in B6 mice. METHODS: Adult male B6 mice received 24-hour continuous access to ethanol and water for 6 weeks (baseline). Experiment 1 determined the ADE in mice receiving weekly access to 15% ethanol (i.e., exposed 1 day a week and deprived during the other 6 days) for a total of 10 weeks. Experiments 2 and 3 determined the ADE after a single 2-week deprivation period in mice receiving a single concentration of 15% ethanol or multiple concentrations of 7.5, 15, and 30% ethanol, respectively, followed by weekly access to their respective ethanol solutions for 10 weeks. Experiment 4 determined the ADE after a single 2-week deprivation period, followed by daily access to 15% ethanol. Mice never deprived of ethanol (i.e., continuous access) were used as age-matched drinking controls. RESULTS: The ADE was observed after the initial 6-day deprivation period and was profoundly enhanced (i.e., escalation of the ADE) following weekly reexposure to 15% ethanol. Compared with a single concentration of 15% ethanol, concurrent access to multiple ethanol concentrations resulted in a near 2-fold increase in baseline ethanol consumption. Regardless of having access to single or multiple concentrations of ethanol, the ADE was not observed immediately after a 2-week deprivation period. The ADE was observed (although to a lesser magnitude and duration) following weekly reexposure to single or multiple concentrations of ethanol. Alternatively, following a 2-week deprivation period, mice receiving daily access to 15% ethanol showed a significant decrease in ethanol intake and preference (i.e., negative ADE). CONCLUSIONS: Short-term deprivations followed by repeated intermittent (weekly) reexposure to ethanol produces a robust ADE in B6 mice. Increasing the initial deprivation length to 2 weeks produces various opposing effects, including erasure of an initial ADE, diminished expression and magnitude of the ADE following weekly exposure, and complete reversal of the ADE following daily exposure to ethanol.

Cystine/glutamate exchange regulates metabotropic glutamate receptor presynaptic inhibition of excitatory transmission and vulnerability to cocaine seeking.

Withdrawal from chronic cocaine reduces extracellular glutamate levels in the nucleus accumbens by decreasing cystine/glutamate exchange (xc-). Activating xc- with N-acetylcysteine restores extracellular glutamate and prevents cocaine-induced drug seeking. It was hypothesized that the activation of xc- prevents drug seeking by increasing glutamatergic tone on presynaptic group II metabotropic glutamate receptors (mGluR2/3) and thereby inhibiting excitatory transmission. In the first experiment, the capacity of glutamate derived from xc- to regulate excitatory transmission via mGluR2/3 was determined. Physiological levels of cystine (100-300 nm) were restored to acute tissue slices from the nucleus accumbens or prefrontal cortex. Cystine increased glutamate efflux and decreased miniature EPSC (mEPSC) and spontaneous EPSC (sEPSC) frequency as well as evoked EPSC amplitude. These effects of cystine were presynaptic, because there was no change in mEPSC or sEPSC amplitude, and an increase in the evoked EPSC paired-pulse facilitation ratio. The cystine-induced reduction in EPSCs was reversed by blocking either xc- or mGluR2/3. In the second experiment, blocking mGluR2/3 prevented the ability of N-acetylcystine to inhibit the reinstatement of drug seeking in rats trained to self-administer cocaine. These data demonstrate that nonsynaptic glutamate derived from xc- modulates synaptic glutamate release and thereby regulates cocaine-induced drug seeking.

Regulation of extracellular glutamate in the prefrontal cortex: focus on the cystine glutamate exchanger and group I metabotropic glutamate receptors.

Microdialysis was used to determine the in vivo processes contributing to extracellular glutamate levels in the prefrontal cortex of rats. Reverse dialysis of a variety of compounds proved unable to decrease basal levels of extracellular glutamate, including Na+ and Ca2+ channel blockers, cystine/glutamate exchange (x(c)-) antagonists, and group I (mGluR1/5) and group II (mGluR2/3) metabotropic glutamate receptor (mGluR) agonists or antagonists. In contrast, extracellular glutamate was elevated by blocking Na+-dependent glutamate uptake (X(AG)-) with DL-threo-beta-benzyloxyaspartate (TBOA) and stimulating group I mGluRs with (R,S)-3,5-dihydroxy-phenylglycine (DHPG). The accumulation of extracellular glutamate produced by blocking X(AG)- was completely reversed by inhibiting system x(c)- with 4-carboxyphenylglycine (CPG), but not by Na+ and Ca2+ channel blockers. Because CPG also inhibits group I mGluRs, two additional group I antagonists were examined, LY367385 [(+)-2-methyl-4-carboxyphenylglycine] and (R,S)-1-aminoindan-1,5-dicarboxylic acid (AIDA). Whereas LY367385 also reduced TBOA-induced increases in extracellular glutamate, AIDA did not. In contrast, all three group I antagonists reversed the increase in extracellular glutamate elicited by stimulating mGluR1/5. In vitro evaluation revealed that similar to CPG, LY367385 inhibited x(c)- and that stimulating or inhibiting mGluR1/5 did not directly affect [3H]glutamate uptake via x(c)- or X(AG)-. These experiments reveal that although inhibiting x(c)- cannot reduce basal extracellular glutamate in the prefrontal cortex, the accumulation of extracellular glutamate after blockade of X(AG)- arises predominately from x(c)-. The accumulation of glutamate elicited by mGluR1/5 stimulation does not seem to result from modulating X(AG)-, x(c)-, or synaptic glutamate release.

Ethanol exposure decreases glutamate uptake in the nucleus accumbens.

BACKGROUND: An increased level of extracellular glutamate is a key neurochemical feature associated with ethanol exposure and withdrawal. METHODS: In the current study, extracellular levels of glutamate and glutamate transport in the nucleus accumbens were assayed 24 hr after repeated ethanol exposure (1 g/kg ip daily for 7 days) with use of in vivo no-net-flux microdialysis and in vitro [(3)H]glutamate uptake, respectively. RESULTS: Microdialysis revealed higher extracellular glutamate concentrations in the nucleus accumbens of rats that were given ethanol. The increase in basal extracellular glutamate levels was accounted for in part by a decrease in the in vivo probe recovery of glutamate. Moreover, an in vitro accumbens slice preparation measuring [(3)H]glutamate uptake revealed that Na(+)-dependent [(3)H]glutamate uptake was significantly reduced 24 hr after 7 days of repeated ethanol exposure. The ethanol-induced deficit in glutamate uptake was not associated with decreased total tissue levels of the transporters GLAST or GLT1. The in vivo and in vitro ethanol-induced changes in glutamate levels and uptake returned to control levels 14 days after discontinuing 7 days of repeated ethanol exposure. CONCLUSIONS: These results suggest that the previously reported increases in extracellular glutamate induced by ethanol exposure may be due in part to deficits in glutamate transport.

Dopamine receptor regulation of ethanol intake and extracellular dopamine levels in the ventral pallidum of alcohol preferring (P) rats.

Sufficient evidence exists for the inclusion of the ventral pallidum (VP) into the category of a dopaminoceptive brain region. The effects of inhibiting dopamine D(1)- or D(2)-like receptors in the VP on (a) ethanol intake and (b) extracellular levels of dopamine, were investigated in the alcohol-preferring (P) rat. The D(1)-like antagonist, SCH-23390, and the D(2)-like antagonist, sulpiride (0.25-2 microg/0.5 microl) were bilaterally injected into the VP and ethanol (15%, v/v) intake was assessed in a 1 h limited access paradigm. The results indicate that microinjections of sulpiride significantly increased ethanol consumption (65% increase at the 2.0 microg dose). Whereas the D(1) antagonists SCH-23390 tended to decrease ethanol intake, the effect was not statistically significant. In a separate group of rats, reverse microdialysis of sulpiride and SCH-23390 (10-200 microM) were conducted in the VP of P rats. Local perfusion of only the 200 microM sulpiride dose significantly increased the extracellular levels of dopamine (maximal increase: 250% of baseline). On the other hand, local perfusion of SCH-23390 (10-200 microM) dose dependently increased the extracellular levels of dopamine 180-640% of baseline. Overall, the results of this study suggest that (a) tonic activation of D(2) postsynaptic receptors in VP imposes a limit on ethanol intake in the P rat; (b) there are few D(2) autoreceptors functioning in the VP; (c) there is tonic D(1)-like receptor mediated inhibitory feedback regulation of VP-dopamine release.

Comparison of intracranial self-administration of ethanol within the posterior ventral tegmental area between alcohol-preferring and Wistar rats.

BACKGROUND: A previous study indicated that selectively bred alcohol-preferring (P) rats self-administered ethanol (EtOH) directly into the ventral tegmental area (VTA), whereas the alcohol-nonpreferring line did not. Wistar rats will also self-administer EtOH directly into the posterior VTA. Because Wistar rats also have a low preference for EtOH solutions but self-inject EtOH into the VTA, this study was undertaken to test the hypothesis that there is an association between EtOH preference and sensitivity of the VTA to the reinforcing effects of EtOH. METHODS: Adult P and Wistar rats were assigned to groups that received one of the following concentrations of EtOH: 0, 50, 75, 100, 150, or 200 mg/100 ml. Rats were connected to the microinjection system, placed into two-lever (active and inactive) experimental chambers, and given EtOH for the first four sessions (acquisition), artificial cerebrospinal fluid for sessions 5 and 6 (extinction), and EtOH again in session 7 (reinstatement). Responding on the active lever produced a 100-nl injection of the infusate. RESULTS: P rats self-infused 75 to 200 mg/100 ml EtOH and demonstrated lever discrimination, whereas Wistar rats reliably self-infused only 150 and 200 mg/100 ml EtOH. Both P and Wistar rats reduced responding on the active lever when artificial cerebrospinal fluid (aCSF) was substituted for EtOH and reinstated responding in session 7 when EtOH was restored, although P rats demonstrated a very robust enhancement of responding for 100 and 150 mg/100 ml EtOH, and this was not found for Wistar rats. CONCLUSIONS: These results suggest that, compared with Wistar rats, the posterior VTA of P rats was more sensitive to the reinforcing effects of EtOH. Furthermore, the reinstatement data suggest that the posterior VTA of P rats underwent neuronal alterations as a result of prior EtOH exposure and extinction that changed the reinforcing effects of EtOH within this region.

Impoverished rearing environment alters metabotropic glutamate receptor expression and function in the prefrontal cortex.

Rearing rats in impoverished (IC) and enriched (EC) environmental conditions alters synaptic plasticity and cognitive processes. Metabotropic glutamate receptors (mGluRs) are known to play a key role in synaptic and behavioral plasticity. In the present study, the effect of rearing conditions on the expression of mGluR proteins in the prefrontal cortex (PFC) was assessed by immunoblotting. A significant difference in the content of prefrontal mGluR1 and mGluR5 (ie group I) and mGluR2/3 (ie group II) was observed between IC and EC rats. To functionally characterize this difference, in vivo microdialysis was used to verify differences in mGluR regulation of extracellular glutamate in the PFC. The results indicate that the capacity of group I and II mGluRs to elevate extracellular glutamate levels was significantly blunted in the PFC of IC rats compared to either EC subjects, or rats reared in normal environmental conditions (ie NIH standards). Group II mGluR receptors regulate performance in a forced T-maze spatial memory task that involves the PFC, and IC rats demonstrated deficits in this task relative to EC rats. These data suggest that reduced mGluR transmission in the PFC produced by impoverished, relative to enriched, rearing environments may contribute to cognitive deficits.

Involvement of the mesopallidal dopamine system in ethanol reinforcement.

The current study was designed to test the hypothesis that acquisition of signal-induced anticipation of self-administered ethanol and operant oral self-administration of ethanol increases the extracellular levels of dopamine in the ventral pallidum of alcohol-preferring (P) rats. The study was also designed to explore the association between behavioral activity and dopamine efflux in the ventral pallidum. Adult, female P rats were randomly assigned to operantly self-administer 15% (volume/volume) ethanol, 0.0125% (weight/volume) saccharin, or water. In addition, all groups were acclimated in the operant chambers to periods of habituation, anticipation, and postadministration. The ethanol group showed significant increases in extracellular levels of dopamine in the ventral pallidum during (1). the first 10 min of the anticipation period, (2). the last 10 min of the self-administration period, and (3). the initial 10 min of the postadministration period. There were no significant differences in motor activity during anticipation and self-administration of ethanol, saccharin, or water. These findings support the suggestion that dopaminergic activation in the ventral pallidum is involved in ethanol-seeking and ethanol-drinking behaviors and directly implicate the mesopallidal dopamine system in the reinforcing actions of ethanol.

Intracranial self-administration of ethanol within the ventral tegmental area of male Wistar rats: evidence for involvement of dopamine neurons.

Previous work from our laboratory indicated that female Wistar rats will self-administer ethanol (EtOH) directly into the posterior ventral tegmental area (VTA). These results suggested that VTA dopamine (DA) neurons might be involved in mediating the reinforcing actions of EtOH within this region. The objectives of this study were to determine (1) the dose-response effects for the self-administration of EtOH into the VTA of male Wistar rats, and (2) the involvement of VTA DA neurons in the reinforcing actions of EtOH within the VTA. Adult male Wistar rats were implanted stereotaxically with guide cannulas aimed at the posterior or anterior VTA. After 1 week, rats were placed in standard two-lever (active and inactive) experimental chambers for a total of seven to eight sessions. The first experiment determined the intracranial self-administration of EtOH (0-400 mg%) into the posterior and anterior VTA. The second experiment examined the effects of coadministration of the D2/3 agonist quinpirole on the acquisition and maintenance of EtOH self-infusions into the posterior VTA. The final experiment determined the effects of a D2 antagonist (sulpiride) to reinstate self-administration behavior in rats given EtOH and quinpirole to coadminister. Male Wistar rats self-infused 100-300 mg% EtOH directly into the posterior, but not anterior, VTA. Coadministration of quinpirole prevented the acquisition and extinguished the maintenance of EtOH self-infusion into the posterior VTA, and addition of sulpiride reinstated EtOH self-administration. The results of this study indicate that EtOH is reinforcing within the posterior VTA of male Wistar rats and suggest that activation of VTA DA neurons is involved in this process.