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Decreased sensitivity of NMDA receptors on dopaminergic neurons from the posterior ventral tegmental area following chronic nondependent alcohol consumption.

ABSTRACT: The mesocorticolimbic dopamine system mediates the reinforcing effects of salient stimuli, including drugs of abuse. Nondependent chronic alcohol consumption modifies this system, resulting in an increased number of spontaneously active dopamine neurons in the posterior ventral tegmental area (VTA) of alcohol-preferring (P) rats. Enhanced responses of postsynaptic glutamate receptors may contribute to the increase in active dopamine neurons. Thus, excitations of putative dopamine neurons to locally applied N-methyl-d-aspartic acid (NMDA; glutamate receptor subtype agonist) were evaluated.P rats were assigned to alcohol naïve (water only) or alcohol drinking (continuous access to 15% alcohol and water for 8 consecutive weeks) groups. Responses of 23 putative dopamine neurons from naïve rats and 19 putative dopamine neurons from drinking rats were assessed in vivo using microiontophoretically applied NMDA. Current-response curves for firing frequency and burst activity were constructed using nonlinear mixed effects models. Between-group comparisons were made for EC(50) (effective current producing a half maximal excitatory response), E(max) (maximal excitatory effect), and C(DB) (the current at which depolarization block-marked decrease in neuronal activity-occurred).Drinking P rats steadily consumed alcohol over the 8-week protocol and did not exhibit signs of dependence or withdrawal. Putative dopamine neurons from drinking rats exhibited resistance to depolarization block (higher C(DB) values) and required larger doses of NMDA to elicit moderate excitatory responses (higher EC(50) values), consistent with decreased receptor affinity. Maximal excitatory responses (E(max) ) did not differ between the groups, consistent with no change in receptor number. Blood alcohol was at undetectable levels at the time of experimentation.NMDA receptor sensitivity is decreased on posterior VTA putative dopamine neurons in P rats on a nondependent schedule of alcohol consumption. Mechanisms underlying increased spontaneous dopamine neuron activity may be independent of changes in NMDA receptor function. Decreased NMDA receptor sensitivity may precede the development of dependence.

SUBMITTER: Fitzgerald GJ

PROVIDER: S-EPMC3382036 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature

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Decreased sensitivity of NMDA receptors on dopaminergic neurons from the posterior ventral tegmental area following chronic nondependent alcohol consumption.

Fitzgerald Griffin J GJ Liu Hai H Morzorati Sandra L SL

Alcoholism, clinical and experimental research 20120320 10

<h4>Background</h4>The mesocorticolimbic dopamine system mediates the reinforcing effects of salient stimuli, including drugs of abuse. Nondependent chronic alcohol consumption modifies this system, resulting in an increased number of spontaneously active dopamine neurons in the posterior ventral tegmental area (VTA) of alcohol-preferring (P) rats. Enhanced responses of postsynaptic glutamate receptors may contribute to the increase in active dopamine neurons. Thus, excitations of putative dopam ...[more]

PMID: 22433065

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Project description:BackgroundChronic postsurgical pain (CPP) markedly impairs patients' quality of life. Research has shown that chronic stress may extend incisional nociception in male mice. Dopaminergic (DAergic) neurons in the ventral tegmental area (VTA) are integral to stress-related mental disorders (including major depressive disorder, anxiety disorders, and PTSD) and pain. However, the impact of chronic social defeat stress (CSDS) on mesolimbic dopamine (DA) transmission in the development of CPP is yet to be established. It remains uncertain whether the dopamine signals in the rostral anterior cingulate cortex (rACC), which regulate pain, derive from the VTA. This study aims to explore the role of VTA-rACC dopaminergic circuits in a mouse model of CPP induced by CSDS.MethodsWe conducted CSDS on C57BL/6 J wild-type male mice (n = 12-16 mice/group) and DAT-cre male mice (n = 10-12 mice/group). After 10 days of CSDS, a left posterior plantar incision was made to establish a mouse model of CPP. Paw withdrawal thresholds (PWTs) were evaluated using Von-Frey fibre stimulation. The open field test (OFT) and elevated plus maze test (EPM) were used to assess pain-related negative emotions. We used immunofluorescence staining and Western Blot to analyse D1, D2, c-Fos, and TH expression. DAergic fibre projections in the VTA-rACC neural pathway were traced using retrograde tracing and immunofluorescence staining. Optogenetics and Chemogenetics were employed to manipulate DAergic neurons in the VTA and their axons in the rACC.ResultsThe ipsilateral PWTs in male C57BL/6 J mice significantly decreased after surgery, returning to baseline after seven days. Conversely, in CSDS mice, ipsilateral PWTs remained reduced for at least 30 days post-incision. A significant reduction in TH-positive neurons expressing c-Fos in the VTA of CPP mice was observed 15 days post-incision. Activating DAergic neurons significantly improved ipsilateral PWTs and locomotor performance in the OFT and EPM in CPP mice post-incision. Additionally, D1 expression in the rACC was found to decrease in CPP mice, and this reduction counteracted the increase in PWTs caused by activating DAergic neuron axon terminals in the rACC.ConclusionCSDS results in chronicity of postsurgical nociception and anxiety-like negative emotions, with alterations in DA transmission playing a role in CPP. Specific activation of DAergic neurons mitigates nociceptive responses and anxiety-like bahaviors, possibly mediated by D1 receptors in the rACC.

Project description:The objective of this study was to determine changes in gene expression in the ventral tegmental area (VTA) following loss-of-control alcohol drinking by alcohol-preferring (P) rats. Adult female P rats (n = 7) were given concurrent access to 10, 20 and 30% EtOH for four 1-hr sessions daily for 10 weeks followed by 2 cycles of 2 weeks of abstinence and 2 weeks of EtOH access. Rats were killed by decapitation 3 hr after the 4th daily EtOH-access session at the end of the second 2-week relapse period. An age-matched water control group of female P rats (n = 8) was also killed. RNA was prepared from micropunch samples of the VTA from individual rats; analyses were conducted with Affymetrix Rat 230.2 chips. Ethanol intakes were 1.5-2.5 g/kg per sessions, resulting in blood levels >200 mg% at the end of the 4th session. There were 211 named genes that were significantly different (FDR = 0.1) between the water and EtOH groups. Bioinformatics analyses indicated alterations in (a) transcription factors that reduced excitation-coupled transcription and promoted exocitotic neuronal damage involving clusters of genes associated with Nfkbia, Fos and Srebf1; (b) genes that reduced cholesterol and fatty acid synthesis, and increased protein degradation; and (c) genes involved in cell-to-cell interactions and regulation of the actin cytoskeleton. Among the named genes, there were 62 genes in common with differences between alcohol-naïve P and non-preferring (NP) rats, with 43 of the genes changing in the opposite direction following excessive binge-like drinking. These genes are involved in a pro-inflammatory response, and enhanced response to glucocorticoids and steroid hormones. Overall, the results of this study indicated that excessive binge-like alcohol drinking by P rats may be altering the expression of genes that promote neuronal damage. Comparison of Differences in Gene Expression in the Ventral Tegmental Area of Rat Lines Selectively Bred for High or Low Alcohol Consumption

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Decreased sensitivity of NMDA receptors on dopaminergic neurons from the posterior ventral tegmental area following chronic nondependent alcohol consumption.

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Decreased sensitivity of NMDA receptors on dopaminergic neurons from the posterior ventral tegmental area following chronic nondependent alcohol consumption.

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