Effects of ceftriaxone on ethanol intake: a possible role for xCT and GLT-1 isoforms modulation of glutamate levels in P rats

Abstract

Rationale: Evidence suggests that glutamate transporter 1 (GLT-1) and cystine/glutamate exchanger transporter (xCT) are critical in maintaining glutamate homeostasis. We have recently demonstrated that ceftriaxone treatment induced upregulation of GLT1 levels and attenuated ethanol intake; however, less is known about the involvement of xCT on ethanol intake. In this study, we investigated the effects of ceftriaxone on the levels of xCT in both continuous and relapse-like ethanol drinking, as well as GLT-1 isoforms, and glutamate aspartate transporter (GLAST) in relapse-like ethanol intake.

Methods: P rats received free choice of 15 and 30 % ethanol and water for 5 weeks and then deprived of ethanol for 2 weeks. Rats were treated with ceftriaxone (100 mg/kg, i.p.) or saline during the last 5 days of the 2-week deprivation period. After deprivation period, P rats were re-exposed to free choice of 15 and 30 % ethanol and water for nine consecutive days. A second group of P rats was given continuous ethanol access for 5 weeks, then ceftriaxone (100 mg/kg, i.p.) or saline throughout the week 6.

Results: Ceftriaxone significantly attenuated relapse-like ethanol intake. Importantly, this effect of ceftriaxone was associated in part with upregulation of the levels of GLT-1a and GLT-1b isoforms and xCT in the prefrontal cortex (PFC) and the nucleus accumbens (NAc). There were no significant differences in GLAST expression among all groups. We also found that ceftriaxone treatment increased xCT levels in both PFC and NAc in continuous ethanol intake.

Conclusion: These findings suggest that xCT and GLT-1 isoforms might be target proteins for the treatment of alcohol dependence.

Fig. 1

Graph represents average daily ethanol and water intake and body weight during the 9 days of ethanol re-exposure. a Daily ethanol intake of male P rats for 9 days of ethanol re-exposure, following 5 days of treatment with ceftriaxone (CEF) or saline during ethanol deprivation. (*p<0.01; **p<0.001); b daily water intake of male P rats for 9 days, following 5 days of treatment during ethanol deprivation (*p<0.05; **p<0.01). All data are expressed as mean ± SEM. Saline (ethanol saline group, n=6); CEF (ethanol CEF group at 100 mg/kg body weight, n=6)

Fig. 2

Effects of ceftriaxone (CEF) on GLT-1a expression in the PFC and NAc in relapse-like ethanol-drinking paradigm. a Immunoblots for GLT-1a expression in the PFC and β-tubulin as a control-loading protein. b CEF treatment significantly increased GLT-1a level in the PFC as compared to ethanol-naïve saline and ethanol saline groups. c Immunoblots for GLT-1a expression in the NAc and β-tubulin as a control-loading protein. d CEF treatment significantly increased GLT-1a level in the NAc as compared to ethanol-naïve saline and ethanol saline groups. Data are expressed as mean ± SEM. (*p<0.05, **p<0.01); N=6 for each group

Fig. 3

Effects of ceftriaxone (CEF) on GLT-1b expression in the PFC and NAc in relapse-like ethanol-drinking paradigm. a Immunoblots for GLT-1b expression in the PFC and β-tubulin as a control-loading protein. b CEF treatment significantly increased GLT-1b level in the PFC as compared to ethanol-naïve saline and ethanol saline groups. c Immunoblots for GLT-1b expression in the NAc and β-tubulin as a control-loading protein. d CEF treatment significantly increased GLT-1b level in the NAc as compared to ethanol-naïve saline and ethanol saline groups. Data are expressed as mean ± SEM. (*p<0.05, **p<0.01); N=6 for each group

Fig. 4

Effects of ceftriaxone (CEF) on xCT expression in the PFC and NAc in relapse-like ethanol-drinking paradigm. a Immunoblots for xCT expression in the PFC and β-tubulin as a control-loading protein. b CEF treatment significantly increased xCT level in the PFC as compared to ethanol-naïve saline and ethanol saline groups. c Immunoblots for xCT expression in the NAc and β-tubulin as a control-loading protein. d CEF treatment significantly increased xCT level in the NAc as compared to ethanol saline group. Data are expressed as mean ± SEM. (*p<0.05, **p<0.01); N=6 for each group

Fig. 5

Effects of ceftriaxone (CEF) on xCT expression in the PFC and NAc in continuous ethanol-drinking paradigm. a Immunoblots for xCT expression in the PFC and β-tubulin as a control-loading protein. b There was significant difference in xCT level in the PFC between ethanol-naïve saline and ethanol saline groups. CEF treatment significantly increased xCT level in the PFC as compared to ethanol saline group. c Immunoblots for xCT expression in the NAc and β-tubulin as a control-loading protein. d There was significant difference in the xCT level in the NAc between ethanol-naïve saline and ethanol saline groups. CEF treatment significantly increased the xCT level in the NAc as compared to ethanol-naïve saline and ethanol saline groups. Data are expressed as mean ± SEM. (*p<0.05, ***p<0.001); (N=5–6)