Endogenous BDNF in the dorsolateral striatum gates alcohol drinking

Abstract

We previously found that brain-derived neurotrophic factor (BDNF)-haplodeficient mice exhibit greater ethanol-induced place preference and psychomotor sensitization, and greater ethanol consumption after deprivation, than control mice. We further observed that, in mice, voluntary ethanol intake increases BDNF expression in the dorsal striatum (DS). Here, we determined whether BDNF within the DS regulates ethanol self-administration in Long-Evans rats trained to self-administer a 10% ethanol solution. We observed a greater increase in BDNF expression after ethanol self-administration in the dorsolateral striatum (DLS) than in the dorsomedial striatum (DMS). We further found that downregulation of endogenous BDNF using viral-mediated siRNA in the DLS, but not in the DMS, significantly increased ethanol self-administration. Infusion of exogenous BDNF (0.25 microg/microl/side into the DMS; 0.25 and 0.75 microg/microl/side into the DLS) attenuated responding for ethanol when infused 3 h before the beginning of the self-administration session. Although the decrease in ethanol intake was similar in the DLS and DMS, BDNF infused in the DLS, but not in the DMS, induced an early termination of the drinking episode. Furthermore, the action of BDNF in the DLS was specific for ethanol, as infusion of the neurotrophic factor in the DMS, but not DLS, resulted in a reduction of sucrose intake. Together, these findings demonstrate that the BDNF pathway within the DLS controls the level of ethanol self-administration. Importantly, our results suggest that an endogenous signaling pathway within the same brain region that mediates drug-taking behavior also plays a critical role in gating the level of ethanol intake.

Figure 1.

Ethanol self-administration differentially upregulates BDNF expression within the DLS and the DMS. Rats were killed 30 min after the end of a 30 min self-administration session, and brain samples were collected for RT-PCR analysis and compared with naive animals (n = 4). To avoid inaccuracy of the analysis due to the low baseline levels of BDNF expression in the naive groups, quantification was not conducted.

Figure 2.

Knockdown of BDNF expression within the DLS increases ethanol self-administration. a, Rats were stereotaxically infused with siBDNF-1 (10¹⁰ TU/ml) into the DLS. Fifteen days after the microinjection, striatal slices were prepared and stained for virus-expressed GFP (green) along with either NeuN (top panel, red), or GFAP (bottom panel, red). The scale bar represents 100 μm. b, siBDNF-1 or siCT were stereotaxically injected into the DLS of rats. Five, 15, and 25 d after the microinjection, DLS were collected for RT-PCR analysis. siBDNF-1 time-dependently decreased BDNF expression in the DLS. Histograms depict the mean ratios of BDNF/GAPDH ± SEM normalized to BDNF levels obtained from control animals. The insert is a representative image of BDNF mRNA levels from samples collected 15 d after infection by the siCT- or siBDNF-1-expressing virus. (n = 7), *p < 0.05, **p < 0.01. c, Rats were treated as described in b and brain samples were collected, 5, 15, or 25 d after injection, and analyzed by Western blot to determine BDNF protein levels. The samples from the three different time points were separated on three different gels to ensure comparison between siBDNF-1 and siCT injections within each time points. The insert is a representative image of BDNF protein levels from samples collected 15 d after infection by the siCT- or siBDNF-1-expressing virus. (n = 3–4), ***p < 0.001. d, e, Rats were stereotaxically infused with siBDNF-1 or siCT (10¹⁰ TU/ml) into the DLS 2 months after the beginning of ethanol self-administration training. d, Injection of siBDNF-1 increases ethanol self-administration 15–16 d after infusion. Results are expressed as mean ± SEM ethanol consumed in grams per kilogram. siBDNF-1: n = 12; siCT: n = 11; *p < 0.05. e, BDNF knockdown in the DLS increases the number of ethanol deliveries. The results are expressed as mean ± SEM ethanol deliveries by blocks of 2 d. siBDNF-1: n = 12; siCT: n = 11; *p < 0.05.

Figure 3.

Knockdown of BDNF expression within the DMS does not alter ethanol consumption. a, siBDNF-1 or siCT were stereotaxically injected into the DMS. Fifteen days after the microinjection, DMS were collected for RT-PCR analysis of the BDNF mRNA content. Histograms depict the mean ratios of BDNF/GAPDH ± SEM normalized to BDNF levels obtained from control animals. The insert is a representative image of BDNF mRNA levels from samples collected 15 d after infection by the siCT- or siBDNF-1-expressing virus. A Student's t test revealed a significant difference between the 2 treatments. (n = 3), *p < 0.05. b, Rats were treated as described in a and brain samples were collected 15 d after injection and analyzed by Western blot to determine BDNF protein levels. The insert is a representative image of BDNF protein levels from samples collected 15 d after infection by the siCT- or siBDNF-1-expressing virus. A Student's t test revealed a significant difference between the two treatments. n = 6; **p < 0.01. c, d, Rats were stereotaxically injected with siBDNF-1 or siCT into the DMS 2 months after the beginning of ethanol self-administration training. c, BDNF knockdown within the DMS does not alter the amount of ethanol consumed. The results are expressed as mean ± SEM ethanol consumed (in grams per kilogram). siBDNF-1: n = 7; siCT: n = 5; p values >0.05. d, BDNF knockdown in the DMS does not alter the number of ethanol deliveries. The results are expressed as mean ± SEM ethanol deliveries by blocks of 2 d. siBDNF-1: n = 7; siCT: n = 5.

Figure 4.

BDNF injection into the DLS decreases ethanol self-administration by inducing an early termination of the drinking episode. Rats were microinjected with PBS or BDNF into the DLS 10 min (0.75 μg/μl/side over 2 min) or 3 h (0.08, 0.25, and 0.75 μg/μl/side over 2 min) before the beginning of the self-administration session. a, BDNF injected into the DLS dose-dependently decreases ethanol self-administration only when injected 3 h before the beginning of the session. Data are expressed as mean ± SEM number of presses. n = 8; **p < 0.01, ***p < 0.001 versus PBS group. b, Data are presented as mean ± SEM ethanol consumed in grams per kilogram. n = 8; *p < 0.05, **p < 0.01. c, BDNF induces an early termination of the drinking episode. Results are expressed as the mean ± SEM time of the last press in minutes. PBS and BDNF 0.08 μg/μl: n = 8; BDNF 0.25 μg/μl: n = 7; BDNF 0.75 μg/μl: n = 4; *p < 0.05. d, BDNF injection into the DLS does not alter sucrose self-administration. BDNF was injected into the DLS 3 h before the session of rats trained to self-administer sucrose for at least 2 months. The data are represented as mean ± SEM number of presses. n = 12.

Figure 5.

BDNF injection into the DMS decreases ethanol and sucrose self-administration. Rats were microinjected with PBS or BDNF (0.08 and 0.25 μg/μl/side) into the DMS 3 h before the beginning of the self-administration session. a, BDNF infused into the DMS decreased the number of presses on the ethanol lever. Data are expressed as mean ± SEM number of presses. n = 10; ***p < 0.001. b, BDNF injected into the DMS decreases ethanol consumption. n = 10; ***p < 0.001. c, BDNF injected into the DMS does not induce an early termination of the drinking episode. Results are expressed as mean ± SEM time of the last press in minutes. n = 11. d, BDNF microinjected into the DMS decreases sucrose self-administration. n = 7; ***p < 0.001.

Figure 6.

BDNF injection into the shell of the NAc does not alter ethanol self-administration. Rats were microinjected with PBS or BDNF (0.25 μg/μl/side and 0.75 μg/μl/side) into the shell of the NAc 3 h before the beginning of the operant ethanol self-administration session. Number of lever presses (a) and ethanol consumption (b) were similar between the two groups. n = 5.