Cocaine-induced loss of white matter proteins in the adult mouse nucleus accumbens is attenuated by administration of a β-lactam antibiotic during cocaine withdrawal

Abstract

We report significantly decreased white matter protein levels in the nucleus accumbens in an adult mouse model of chronic cocaine abuse. Previous studies from human cocaine abuse patients show disruption of white matter and myelin loss, thus supporting our observations. Understanding the neuropathological mechanisms for white matter disruption in cocaine abuse patients is complicated by polydrug use and other comorbid factors, hindering the development of effective therapeutic strategies to ameliorate damage or compliment rehabilitation programs. In this context, our data further demonstrate that cocaine-induced loss of white matter proteins is absent in mice treated with the β-lactam antibiotic, ceftriaxone, during cocaine withdrawal. Other studies report that ceftriaxone, a glutamate transporter subtype-1 activator, is neuroprotective in murine models of multiple sclerosis, thereby demonstrating potential therapeutic properties for diseases with white matter loss. Cocaine-induced white matter abnormalities likely contribute to the cognitive, motor, and psychological deficits commonly afflicting cocaine abusers, yet the underlying mechanisms responsible for these changes remain unknown. Our observations describe an adult animal model for the study of cocaine-induced myelin loss for the first time, and highlight a potential pharmacological intervention to ameliorate cocaine-induced white matter loss.

Copyright © 2012 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Effects of cocaine on white matter protein levels in the nucleus accumbens. A: Levels of MBP (*P < 0.05) PLP, MOG, MAG (**P < 0.001), PLP alternate isoform (DM20) (NS), in mice administered cocaine (15 mg/kg) for 14 days, followed by 30 days vehicle during withdrawal and a single challenge dose of cocaine. n = 8 to 10 mice per group with one-way analysis of variance with Bonferroni's multiple comparison post hoc testing. B and C: Double immunofluorescence labeling of nucleus accumbens from control (B), and mice treated with cocaine for 14 days, 30 days withdrawal (C), followed by cocaine challenge. Tissues are labeled with MBP in green, neurofilament in red, and nuclei are labeled in blue with DAPI. Original magnification, ×40. Scale bar = 10 μm.

Figure 2

Effects of ceftriaxone administration on WM during withdrawal from cocaine. A: Representative Western blot of 10 μg protein from NAc from one mouse from each group. GAPDH was used as a loading control. B–F: WM protein levels in control; 17 days ceftriaxone followed by 30 days vehicle during withdrawal (Ceft); 14 days cocaine followed by 30 days vehicle during withdrawal (Coc); 3 days ceftriaxone pretreatment followed by 14 days of ceftriaxone and cocaine, and 30 days of vehicle during withdrawal (Coc with Ceft); 14 days of cocaine followed by 30 days ceftriaxone (200 mg/kg) during withdrawal (Coc then Ceft). B: Quantification of MBP. *P < 0.05, **P < 0.01. C: PLP. *P < 0.001, **P < 0.05. D: PLP alternate isoform (DM20). *P < 0.05. E: Myelin oligodendrocyte glycoprotein (MOG). *P < 0.001, **P < 0.01. F: MAG. *P < 0.001, **P < 0.01 levels. n = 8 to 10 mice per group with one-way analysis of variance with Bonferroni's multiple comparison post hoc testing. G–I: Double immunofluorescence labeling of nucleus accumbens from (G) control; (H) cocaine (15 mg/kg) for 14 days, followed by 30 days vehicle during withdrawal and a single dose challenge of cocaine; (I) cocaine (15 mg/kg) for 14 days, followed by 30 days ceftriaxone during withdrawal and a single dose challenge of cocaine. Tissues are labeled with MBP in green, neurofilament in red, and nuclei labeled in blue with DAPI. Original magnification, ×40. Scale bar = 10 μm. DM20, PLP alternate isoform; MAG, myelin-associated glycoprotein.

Figure 3

Evidence of decreased glutamate subtype transporter-1 (GLT1) and increased caspase-3 activity in oligodendrocytes of cocaine-treated mice. A: GLT1 levels in NAc of control; 17 days ceftriaxone only (Ceft) followed by 30 days vehicle during withdrawal; 14 days cocaine only (Coc) followed by 30 days vehicle during withdrawal; 3 days Ceft pretreatment followed by 14 days of ceftriaxone and cocaine (Coc with Ceft) and 30 days of vehicle during withdrawal; 14 days of cocaine followed by 30 days ceftriaxone (Coc then Ceft) during withdrawal. *P < 0.01. B: Representative Western blot of GLT1 levels in 10 μg protein from NAc from one mouse from each group. GADPH was used as a loading control. C: Representative using Western blot of cleaved caspase-3 levels in 40 μg protein from NAc from one mouse from each group. GAPDH was used as a loading control. *P < 0.05, **P < 0.01. D: Cleaved caspase-3 protein levels in control; 14 days cocaine followed by 30 days vehicle during withdrawal (Coc); 14 days of cocaine followed by 30 days ceftriaxone during withdrawal (Coc then Ceft). n = 8 to 10 mice per group with one-way analysis of variance with Bonferroni's multiple comparison post-hoc testing. E–G: NAc tissues from representative mice are labeled with an antibody against cleaved caspase-3 in green, CC1, an oligodendrocyte-specific maker in red, and nuclei in blue with DAPI. E: NAc tissues from control show robust CC1-immunoreactivity (red) with no evidence of caspase-3 activity. F: NAc tissues from cocaine-treated mice show decreased CC1-immunoreactivity (red) with evidence of caspase-3 activity (green, arrowheads) associated with CC1-1+ oligodendrocytes (red). G: NAc tissues from cocaine treated mice that received ceftriaxone during withdrawal show CC1-immunoreactivity (red) with undetectable caspase-3 activity (green). Original magnification, ×100. Scale bar = 10 μm.