Ethanol enhances GABAergic transmission onto dopamine neurons in the ventral tegmental area of the rat - PubMed (original) (raw)

Ethanol enhances GABAergic transmission onto dopamine neurons in the ventral tegmental area of the rat

Jonathan W Theile et al. Alcohol Clin Exp Res. 2008 Jun.

Abstract

Background: Activation of the dopaminergic (DA) neurons of the ventral tegmental area (VTA) by ethanol has been implicated in its rewarding and reinforcing effects. At most central synapses, ethanol generally increases inhibitory synaptic transmission; however, no studies have explored the effect of acute ethanol on GABAergic transmission in the VTA.

Methods: Whole-cell patch clamp recordings of inhibitory postsynaptic currents (IPSCs) from VTA-DA neurons in midbrain slices from young rats.

Results: Acute exposure of VTA-DA neurons to ethanol (25 to 50 mM) robustly enhanced GABAergic spontaneous and miniature IPSC frequency while inducing a slight enhancement of spontaneous IPSC (sIPSC) amplitude. Ethanol (50 mM) enhanced paired-pulse depression of evoked IPSCs, further suggesting enhanced GABA release onto VTA-DA neurons. The frequency of sIPSCs was suppressed by the GABA(B) agonist, baclofen (1.25 microM) and enhanced by the antagonist, SCH50911 (20 microM); however, neither appeared to modulate or occlude the effects of ethanol on sIPSC frequency.

Conclusions: The present results indicate that ethanol increases postsynaptic GABA(A) receptor sensitivity, enhances action potential-independent GABA release onto VTA-DA neurons, and that this latter effect is independent of GABA(B) auto-receptor inhibition of GABA release.

PubMed Disclaimer

Figures

Fig. 1

Fig. 1

Ethanol (25 mM) potentiates sIPSC frequency. (A) sIPSCs recorded from a VTA-DA neuron under control conditions, in the presence of 15 and 25 mM ethanol, and after a washout. (B) A bar graph representing the percent change ± SEM above control sIPSC frequency for the conditions shown in (A). Event frequency under control conditions was 4.62 ± 0.75 Hz. (C) A bar graph representing the percent change ± SEM above control sIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 52.82 ± 2.28 pA. (n = 7, *p < 0.05 by ANOVA/Dunnett C posthoc different from control).

Fig. 2

Fig. 2

Ethanol (50 mM) potentiates sIPSC frequency and amplitude. (A) sIPSCs recorded from a VTA-DA neuron under control conditions, in the presence of 25 and 50 mM ethanol, and after a washout. (B) Time course for a sample representative neuron under conditions shown in (A). The dotted lines represent the average frequency under each condition for that neuron. (C) A bar graph representing the percent change ± SEM above control sIPSC frequency for the conditions shown in (A). Event frequency under control conditions was 5.48 ± 0.93 Hz. (D) A bar graph representing the percent change ± SEM above control sIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 54.49 ± 5.56 pA. (E) Cumulative probability histogram of sIPSC inter-event intervals for epochs from same neuron shown in (B). (F) Cumulative probability histogram of sIPSC event amplitudes from the same neuron shown in (B), (E). (n = 8, *p < 0.05 by ANOVA/Dunnett C posthoc different from control, *†p < 0.05 by ANOVA/Dunnett C posthoc different from wash).

Fig. 3

Fig. 3

Cumulative results show ethanol-induced potentiation of sIPSC frequency and amplitude at varying concentrations. (A) A bar graph representing the percent change ± SEM above control sIPSC frequency in the presence of 15, 25, and 50 mM ethanol. Event frequency under control conditions was 4.92 ± 0.44 Hz. (B) A bar graph representing the percent change ± SEM above control sIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 52.92 ± 2.06 pA. (n = 7 for 15 mM, n = 22 for 25 mM, n = 11 for 50 mM; *p < 0.05, **_p_ < 0.01 by ANOVA/Dunnett C posthoc different from control) (**C**) A sample cell was analyzed that showed a maximal ethanol-induced (50 mM) enhancement in sIPSC frequency (∼86% above control) to determine the percent change in the number of events at their respective amplitude distribution. The events were binned into 5 pA groups, for example, the point at 30 pA represents all events >25 and <30 pA. All events at 105 pA represent those events greater than 100 pA in size. The total number of events was 1,148 and 2,135 in control and ethanol conditions, respectively, taken from a time course of 5 minutes for each condition (note: the 300% change in events <15 pA represents an increase from only 4 to 12 events).

Fig. 4

Fig. 4

Ethanol enhances paired-pulse depression. (A), (B) Sample evoked IPSC recordings from a VTA-DA neuron prior to (A), and after exposure to ethanol (50 mM) (B). Each trace represents an averaged trace from 8 individual traces over a continuous 3.5-minute time period for each condition from a representative neuron. Both recordings exhibit paired-pulse depression (PPD); however after exposure to ethanol, the PPD is enhanced. (C) A bar graph representing the paired-pulse ratio (defined as IPS-C2/IPSC1) under control conditions and in the presence of ethanol (50 mM). (D) A bar graph representing the decay time as measured by the time constant, τ (milliseconds), under control conditions and in the presence of ethanol (50 mM). (n = 5 of 6, *p < 0.05 by a paired student's _t_-test different from control).

Fig. 5

Fig. 5

Baclofen does not inhibit ethanol-induced potentiation of sIPSC frequency. (A) sIPSCs recorded from a VTA-DA neuron under control conditions, in the presence of 1.25 μ_M baclofen, 50 mM ethanol with 1.25 μ_M baclofen, and after a washout. (B) A bar graph representing the percent change ± SEM above control sIPSC frequency for the conditions shown in (A). Event frequency under control conditions was 2.36 ± 0.23 Hz. (C) A bar graph representing the percent change ± SEM above control sIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 49.48 ± 3.41 pA. (n = 6, **p < 0.01 by ANOVA/Dunnett C posthoc different from control, *†_p < 0.05 by ANOVA/Dunnett C posthoc different from baclofen alone, **††_p < 0.01 by a paired student's _t_-test different from baclofen alone).

Fig. 6

Fig. 6

SCH50911 does not occlude ethanol-induced potentiation of sIPSC frequency. (A) sIPSCs recorded from a VTA-DA neuron under control conditions, in the presence of 20 _μ_M SCH50911, 50 mM ethanol with 20 μ_M SCH50911, and after a washout. (B) A bar graph representing the percent change ± SEM above control sIPSC frequency for the conditions shown in (A). Event frequency under control conditions was 1.89 ± 0.40 Hz. (C) A bar graph representing the percent change ± SEM above control sIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 51.58 ± 2.24 pA. (n = 6, *p < 0.05 by ANOVA/Tukey HSD posthoc different from control, **p < 0.01 by ANOVA/Tukey HSD posthoc different from control, *†_p < 0.05 by ANOVA/Tukey HSD posthoc and by paired student's t_-test different from SCH50911 alone, *††_p < 0.05 by ANOVA/Tukey HSD posthoc different from wash).

Fig. 7

Fig. 7

Ethanol (50 mM) potentiates mIPSC frequency. (A) mIPSCs recorded from a VTA-DA neuron under control conditions, in the presence of 50 mM ethanol, and after a washout. (B) A bar graph representing the percent change ± SEM above control mIPSC frequency for the conditions shown in (A). Event frequency under control conditions was 2.57 ± 0.45 Hz. (C) A bar graph representing the percent change ± SEM above control mIPSC amplitude for the conditions shown in (A). Event amplitude under control conditions was 43.13 ± 3.88 pA. (D) Cumulative time course for averaged cells. The dotted lines indicate the averaged value displayed in (B). (n = 11, *p < 0.05 by student's _t_-test different from control).

Similar articles

Cited by

References

    1. Albanese A, Minciacchi D. Organization of the ascending projections from the ventral tegmental area: a multiple fluorescent retrograde tracer study in the rat. J Comp Neurol. 1983;216:406–420. - PubMed
    1. Appel SB, McBride WJ, Diana M, Diamond I, Bonci A, Brodie MS. Ethanol effects on dopaminergic “reward” neurons in the ventral tegmental area and the mesolimbic pathway. Alcohol Clin Exp Res. 2004;28:1768–1778.
    1. Ariwodola OJ, Weiner JL. Ethanol potentiation of GABAergic synaptic transmission may be self-limiting: role of presynaptic GABA(B) receptors. J Neurosci. 2004;24:10679–10686. - PMC - PubMed
    1. Bonci A, Malenka RC. Properties and plasticity of excitatory synapses on dopaminergic and GABAergic cells in the ventral tegmental area. J Neurosci. 1999;19:3723–3730. - PMC - PubMed
    1. Brodie MS, Appel SB. The effects of ethanol on dopaminergic neurons of the ventral tegmental area studied with intracellular recording in brain slices. Alcohol Clin Exp Res. 1998;22:236–244. - PubMed

Publication types

MeSH terms

Substances

Grants and funding

LinkOut - more resources