Peri-adolescent drinking of ethanol and/or nicotine modulates astroglial glutamate transporters and metabotropic glutamate receptor-1 in female alcohol-preferring rats

Abstract

Impairment in glutamate neurotransmission mediates the development of dependence upon nicotine (NIC) and ethanol (EtOH). Previous work indicates that continuous access to EtOH or phasic exposure to NIC reduces expression of the glutamate transporter-1 (GLT-1) and cystine/glutamate antiporter (xCT) but not the glutamate/aspartate transporter (GLAST). Additionally, metabotropic glutamate receptors (mGluRs) expression was affected following exposure to EtOH or NIC. However, little is known about the effects of EtOH and NIC co-consumption on GLT-1, xCT, GLAST, and mGluR1 expression. In this study, peri-adolescent female alcohol preferring (P) rats were given binge-like access to water, sucrose (SUC), SUC-NIC, EtOH, or EtOH-NIC for four weeks. The present study determined the effects of these reinforcers on GLT-1, xCT, GLAST, and mGluR1 expression in the nucleus accumbens (NAc), hippocampus (HIP) and prefrontal cortex (PFC). GLT-1 and xCT expression were decreased in the NAc following both SUC-NIC and EtOH-NIC. In addition, only xCT expression was downregulated in the HIP in both of these latter groups. Also, glutathione peroxidase (GPx) activity in the HIP was reduced following SUC, SUC-NIC, EtOH, and EtOH-NIC consumption. Similar to previous work, GLAST expression was not altered in any brain region by any of the reinforcers. However, mGluR1 expression was increased in the NAc in the SUC-NIC, EtOH, and EtOH-NIC groups. These results indicate that peri-adolescent binge-like drinking of EtOH or SUC with or without NIC may exert differential effects on astroglial glutamate transporters and receptors. Our data further parallel some of the previous findings observed in adult rats.

Keywords: Co-abuse; Ethanol; GLT-1; Nicotine; mGluR1; xCT.

Fig. 1.

Time-line and group conditions for binge-like drinking of SUC or EtOH with or without NIC in female P rats.

Fig. 2.

Average last five sessions binge-like drinking of; (A) SUC (g/kg of average body weight) and SUC-NIC (g/kg of body weight), (B) NIC (Ryu et al.) (mg/kg of body weight) and NIC (EtOH) (mg/kg of body weight) NIC (mg/kg of body weight) in female P rats, and (C) EtOH (g/kg of body weight) and EtOH-NIC (g/kg of body weight). Unpaired t-test revealed that addition of NIC reduced SUC consumption, however, the analysis did not show any change in EtOH consumption following addition of NIC. Unpaired t-test revealed that NIC consumption was higher in SUC-NIC group compared to EtOH-NIC group. Data are represented as mean ± SEM (n = 9 for each group), (# p < 0.0001).

Fig. 3.

Effects of binge-like drinking of SUC and SUC-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST, and (D) mGluR1 in the NAc. One way ANOVA followed by Newman-Keuls analysis revealed that SUC-NIC but not SUC exposure reduced GLT-1/GAPDH and xCT/GAPDH ratios in the NAc. The analysis did not show any significant reduction in GLAST/GAPDH ratio in the NAc. One way ANOVA followed by Newman-Keuls analysis revealed that SUC-NIC but not SUC exposure increased mGluR1/ratio in the NAc. Data are represented as mean ± SEM (n = 6 for each group), (* p < 0.05 and ** p < 0.01).

Fig. 4.

Effects of binge-like drinking of EtOH and EtOH-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST, and (D) mGluR1 in the NAc. One way ANOVA followed by Newman-Keuls analysis revealed that EtOH-NIC but not EtOH exposure reduced GLT-1/GAPDH and xCT/GAPDH ratios in the NAc. The analysis did not show any significant reduction in GLAST/GAPDH ratio between the groups in the NAc. One way ANOVA followed by Newman-Keuls analysis revealed that EtOH-NIC and EtOH exposure increased mGluR1/GAPDH ratio in the NAc. Data are represented as mean ± SEM (n = 6 for each group), (* p < 0.05 and ** p < 0.01).

Fig. 5.

Effects of binge-like drinking of SUC and SUC-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST, and (D) mGluR1 in the HIP. One way ANOVA followed by Newman-Keuls analysis revealed that SUC-NIC but not SUC exposure reduced xCT/GAPDH ratio in the HIP. The analysis did not show any significant reduction in GLT-1/GAPDH, GLAST/GAPDH and mGluR1/GAPDH ratios between all groups in the HIP. Data are represented as mean ± SEM (n = 6 for each group), (* p < 0.05 and ** p < 0.01).

Fig. 6.

Effects of binge-like drinking of EtOH and EtOH-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST and (D) mGluR1 in the HIP. One way ANOVA followed by Newman-Keuls analysis revealed that EtOH-NIC but not EtOH exposure reduced xCT/GAPDH ratio in the HIP. The analysis did not show any significant reduction in GLT-1/GAPDH, GLAST/GAPDH and mGluR1/GAPDH ratios between the groups in the HIP. Data are represented as mean ± SEM (n = 6 for each group), (* p < 0.05).

Fig. 7.

Effects of binge-like drinking of SUC and SUC-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST, and (D) mGluR1 in the PFC. One way ANOVA followed by Newman-Keuls analysis did not show any significant reduction in GLT-1/GAPDH, xCT/GAPDH GLAST/GAPDH and mGluR1/GAPDH ratios between all groups in the PFC. Data are represented as mean ± SEM (n = 6 for each group).

Fig. 8.

Effects of binge-like drinking of EtOH and EtOH-NIC on relative expression (R) of (A) GLT-1, (B) xCT, (C) GLAST, and (D) mGluR1 in the PFC. One way ANOVA followed by Newman-Keuls analysis did not show any significant reduction in GLT-1/GAPDH, xCT/GAPDH GLAST/GAPDH and mGluR1/GAPDH ratios between all groups in the PFC. Data are represented as mean ± SEM (n = 6 for each group).

Fig. 9.

Effects of binge-like drinking of SUC, SUC-NIC EtOH, or EtOH-NIC on the activity of GPx in the HIP. A) One way ANOVA followed by Newman-Keuls analysis revealed that SUC and SUC-NIC exposure reduced GPx activity the HIP. B) One way ANOVA followed by Newman-Keuls analysis revealed that EtOH and EtOH-NIC exposure reduced GPx activity in the HIP. Data are represented as mean ± SEM (n = 6 for each group), (* p < 0.05).