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, 73 (6), 1173-83

GABA Neurons of the VTA Drive Conditioned Place Aversion

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GABA Neurons of the VTA Drive Conditioned Place Aversion

Kelly R Tan et al. Neuron.

Abstract

Salient but aversive stimuli inhibit the majority of dopamine (DA) neurons in the ventral tegmental area (VTA) and cause conditioned place aversion (CPA). The cellular mechanism underlying DA neuron inhibition has not been investigated and the causal link to behavior remains elusive. Here, we show that GABA neurons of the VTA inhibit DA neurons through neurotransmission at GABA(A) receptors. We also observe that GABA neurons increase their firing in response to a footshock and provide evidence that driving GABA neurons with optogenetic effectors is sufficient to affect behavior. Taken together, our data demonstrate that synaptic inhibition of DA neurons drives place aversion.

Figures

Figure 1.
Figure 1.. Excitation of GABA Neurons In Vivo Inhibits DA Neurons of the VTA
(A) Immunohistochemical staining for tyrosine hydroxylase (TH, red) and α1 subunit isoform of the GABAA receptor (blue, soma highlighted with stars) in VTA slices of GADcre+ mice infected with AAV5-flox-ChR2-YFP (green) in the VTA. Concentric pie charts represent the fraction of ChR2-YFP-positive cells (inner segment) and quantification of the two cell types (outer segment, n = 4 mice). Overlap between inner and outer segments represents colocalization (violet color represents colocalization of TH and GAD). (B) Coronal slice of a VTA expressing ChR2-eYFP in GABA cells showing the restriction of the expression of ChR2-eYFP to the VTA and the path of the guide cannula down to the VTA. Substantia nigra compacta and reticulata (SNc/SNr). (C) Schematic showing the positioning of the in vivo recording pipette relative to the optic fiber. A guide cannula was stereotaxically implanted in vivo above a VTA expressing ChR2-eYFP in GABA cells. The recording pipette was then lowered down to the VTA with a 10°C angle to avoid contact with the guide cannula. The red box locates the image shown in (B). (D) Single-unit recording, PSTH and raster plot of a ChR2-eYFP-expressing GABA neuron excited by a blue light stimulation for 1 s. (E) Same as in (D) for non ChR2-eYFP-expressing DA neuron inhibited by a 1 s blue light stimulation. (F) Boxplot representation showing the relative effect of 1 and 2 s blue light stimulation on GABA and DA neurons, respectively ***p ≤ 0.001 n = 8–12. (G) Normalized firing rate of GABA neurons that were excited during the 1 s blue light stimulation. The black trace shows the average for 8 cells and the gray area correspond to the SD. (H) Normalized firing rate of DA neurons that were inhibited during the 2 s blue light stimulation. The gray trace shows the average for 12 cells and the light gray area correspond to the SD. See also Figure S1.
Figure 2.
Figure 2.. Effect of Electrical Footshock on Spontaneous Activity of VTA Neurons
(A) Single-unit recording, peristimulus histograms(PSTH), and rasterplot ofatypical putative DAneuron inhibited byasingleelectrical footshock.The insetshows that 90% of the recorded cells were inhibited whereas the other 10% did not respond. (B) Same as in (A) for a putative GABA neuron, which is excited by the stimulus. The pie chart shows that the footshock stimulation induced an excitation of all GABA neurons. (C) Same as in (A) and (B) for a putative DA neuron, which is excited by the stimulus. This putative DA cell population represents a minority of recorded putative DA cells. (D) Average action potential waveform from the three representative cells in (A), (B), and (C). The vertical dotted lines represent the limit (1.1 ms) for which a cell is considered a DA or a GABA cell. (E) Boxplot representation of latencyt(70) = 2.3 *p < 0.01, response duration t(77) = 3.52 ***p < 0.01 and response magnitude(46) = 5.98 ***p < 0.01 for putative DA and GABA neurons, n = 21–56. Data are expressed as median (line), interquartile (box) 75th and 25th percentiles, and SD (error bars). (F) Example of effects of a single electrical footshock on the firing rate of a putative GABA and a putative DA neuron. See also Figure S2.
Figure 3.
Figure 3.. The Footshock-Induced Inhibition of DA Neurons Is Mediated by GABAA Receptors
(A) Single-unit recording, PSTH, and raster plot of a representative putative DA neuron inhibited by an electrical stimulation, recorded in GIRK2/3 KO mice. The inset shows that all recorded cells were inhibited by the stimulus. (B) Boxplot representation of the response latency, duration and magnitude for wild-type (WT) and GIRK2/3 KO mice, n = 12–24; latency t(28) = 1,21 p = 0.24, duration t(28) = 1,1 p = 0.30, magnitude t(28) = 0.59 p = 0.56. (C) Same as in (A) for a representative putative DA cell that was inhibited by the footshock while haloperidol was i.v. injected. The inset shows that all cells were inhibited. (D) Same as in (B) when saline and haloperidol were i.v. injected to WT mice, n = 5; latency t(29) = 0.22 p = 0.82, duration t(29) = 0.10 p = 0.91, magnitude t(8) = .0.23 p = 0.82. (E) Same as in (A) and (C) for a representative putative DA neuron inhibited by an electrical stimulation while saline was applied via a guide cannula implanted above the VTA. The inset shows that all recorded cells were inhibited. (F) Same representation as in (E) for a representative putative DA neuron not inhibited by an electrical stimulation while bicuculline was applied via a guide cannula implanted above the VTA. The pie chart shows that 90% of putative DA neuron was inhibited and 10% was nonresponsive to the electrical stimulation. (G) Same as in (B) and (D) for saline and bicuculline in WT mice, n = 6–12; latency t(16) = 2.02 ***p ≤ 0.001, duration t(16) = 7.68 ***p ≤ 0.001, magnitude t(16) = 4.68 ***p % 0.001. Data are expressed as median (line), interquartile (box), and 75th and 25th percentiles and SD (error bars). See also Figure S3.
Figure 4.
Figure 4.. Indirect or Direct Inhibition of DA Neurons Is Sufficient to Drive Behavioral Aversion
(A) Aversive learning curve showing the relative time spent in light-paired chamber for each session. The two groups exhibited a significantly different performance (F(1,21) = 36.02, p ≤ 0.001). One conditioning session (blue box) is enough to induce an aversion of the conditioning chamber in GADcre+ mice (###, t(16) = 4.4 p ≤ 0.001). Only GADcre+ mice showed aversion during the whole experiment (F(3,63) = 9.98, ***p < 0.001) (GADcre+ versus GADcre on conditioning day 1 t(21) = 4.4 ***p < 0.001; GADcre+ versus GADcre on conditioning day 2 ***p < 0.001, t(5.01:21); GADcre+ versus GADcre on test day 1 t(21) = 4.9 ***p < 0.001). (B) Bar graph showing the aversion difference score measured as time spent in conditioned chamber a — time spent in unconditioned chamber b. Note that during the pretest there is no initial aversion as the time spend by the mice in both chambers is equal. After conditioning, mice expressing ChR2-eYFP in VTA GABA cells show a clear aversion on the test day for the conditioned chamber a (pretest day versus test day for GADcre+ mice t(21) = 4.9 ***p < 0.001 but not control mice (GADcre+ versus GADcre on test day t(16) = 5.74 ***p < 0.001 n = 9–14). (C) Tracking data from a representative trace of a GADcre+ and a GADcre mice on the conditioning day 2. The color code corresponds to the speed with blue representing resting state and red fast movement. (D) Bar graph showing the number of U turn each group of mice made at the entrance of each chamber. This measurement reveals the decision of the GADcre+ mice to avoid the light-paired chamber (F(1,21) = 14,68 ***p ≤ 0.001, GADcre+ versus GADcre in conditioned chamber t(21) = 3.31 **p ≤ 0.01, conditioned versus unconditioned chamber for GADcre+1(18) = 2.94 **p ≤ 0.01). (E) Bar graph showing the average speed for each group in the conditioned chamber F(1,21) = 8,47 ***p ≤ 0.001, GADcre+ versus GADcre on test day t(21) = 2.1 *p ≤ 0.05). (F) Bar graph showing the time spent in freezing status for each group in the unconditioned chamber (F(1,2) = 4,38 ***p ≤ 0.001, GADcre+ versus GADcre on test day t(19) = 3.18 p ≤ 0.01). (G) Same as in (A) with THcre+ mice infected in the VTA with AAV5-flox-eNpHR3.0-eYFP or AAV5-flox-eYFP. The two groups exhibited a significantly different performance (F(1,21) = 5, p ≤ 0.001). Two conditioning sessions (amber box) are sufficient to induce an aversion of the conditioning chamber in THcre+/eNpHR3.0-eYFP mice (t(14) = 3.3 **p ≤ 0.01). Only THcre+/eNpHR3.0-eYFP mice showed aversion during the whole experiment (F(3,21) = 7.7 ***p ≤ 0.001) (THcre+/eNpHR3.0-eYFP versus THcre+/eYFP on conditioning day 2 t(16) = 2.3 *p ≤ 05; THcre+/eNpHR3.0-eYFP versus THcre+/ eYFP on test day t(16) = 2.2 *p < 0.05). (H) Same as in (B). Note that during the pretest there is no initial aversion as the time spent by the mice in both chambers is equal. After conditioning, mice expressing eNpHR3.0-eYFP in VTA DA cells show a clear aversion on the test day for the conditioned chamber a (pretest day versus test day for THcre+/ eNpHR3.0-eYFP mice t(14) = 2.5 *p ≤ 0.05 but not control mice (THcre+/eNpHR3.0-eYFP versus THcre+/eYFP on test day t(16) = 2.2 *p ≤ 0.05 n = 10). Bars are means ± SD. See also Figure S4.

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