Chronic opipramol treatment extinguishes cocaine craving through Rac1 in responders: A rat model study.

Ras-related C3 botulinum toxin substrate 1 (Rac1), of the Rho small GTPase family, is a key regulator of actin cytoskeleton rearrangement and plays an important role in dendritic morphogenesis. Cocaine produces neuronal alterations, including structural changes in dendritic number and morphology. Emerging data indicate sigma-1 receptors (σ-1Rs) as a promising candidate for the prevention of cocaine craving. Opipramol is a σ-1R agonist approved in some European countries for depression and anxiety. Here we report that opipramol, mediated by Rac1, attenuates cocaine-seeking behavior in a rat model of self-administration. The opipramol effect was shown in two phases. It decreased cocaine-seeking behavior throughout the withdrawal phase and, interestingly, showed a significant reduction of cocaine-primed reinstatement in 75% of the opipramol-treated group (termed 'responders'). All opipramol-treated rats showed a decrease in σ-1R mRNA expression levels in the nucleus accumbens (NAc) versus controls. Responders also exhibited significantly decreased NAc Rac1 mRNA expression levels, compared with non-responder rats. Hence, Rac1 differentiated responders from non-responders. Rac1 correlated positively with σ-1R mRNA levels in opipramol responders. In another experiment, Rac1 inhibitor injected directly into the NAc core decreased active lever presses on the first day of extinction, indicating the critical role of Rac1 in the opipramol effect on drug seeking. We postulate that chronic activation of σ-1R, through a dynamic interaction with Rac1, may suggest a new approach to treat substance use disorder (SUD). Rac1 inhibition is a prerequisite for decreasing drug seeking and rehabilitation, and this can be achieved by opipramol, a medication that can be given during detoxification.

ApoE4 Exacerbates Hippocampal Pathology Following Acute Brain Penetration Injury in Female Mice.

The ɛ4 allele of apolipoprotein E (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease. ApoE4 is also associated with poor recovery and functional outcome following traumatic brain injury. This study examined the effects of the apoE genotype on brain pathology following acute injury, induced by penetration of a needle through the cortex and hippocampus, at 3 and 14 days following the injury in female apoE3 and apoE4 α-synuclein-deficient targeted replacement (TR) mice. The results obtained revealed a marked inflammatory, synaptic and vascular response following the needle penetration injury (NPI). These results were found to be affected by the apoE genotype such that the inflammatory response, as measured utilizing the astrocytic marker GFAP and the microglial marker iba1, was faster and more prolonged in the apoE4 than in the apoE3 mice. The synaptic changes following the injury included a transient increase in synaptophysin levels in the apoE3 and not in the apoE4 mice, which was associated with a subsequent decrease in glutamatergic synapses, as measured utilizing VGluT1, in apoE4 and not in the apoE3 mice. Unlike these effects, measurements of the vasculature utilizing collagen IV as a marker revealed a significant increase which was similar in both apoE3 and apoE4 mice. Taken together, these results show that following acute brain injury, there is an apoE4-specific inflammatory and neuronal response to the injury. The NPI model provides a useful tool for studying the mechanism underlying the effects of apoE4 following acute brain injury and for the development of a corresponding anti-apoE4-targeted treatment.

Neurodegeneration of lateral habenula efferent fibers after intermittent cocaine administration: implications for deep brain stimulation.

Deep brain stimulation (DBS) is an emerging technique for effective, non-pharmacological intervention in the course of neurological and neuropsychiatric diseases. Several brain targets have been suggested as suitable for DBS treatment of drug addiction. Previously, we showed that DBS of the lateral habenula (LHb) can reduce cocaine intake, facilitate extinction and attenuate drug-induced relapse in rats trained to self-administrate cocaine. Herein, we demonstrated that cocaine self-administration dose-dependently decreased connectivity between the LHb and midbrain, as shown by neurodegeneration of the main LHb efferent fiber, the fasciculus retroflexus (FR). FR degeneration, in turn, may have caused lack of response to LHb stimulation in rats trained to self-administer high-dose cocaine (1.5 mg/kg; i.v.). Furthermore, we show that the micro-structural changes caused by cocaine can be non-invasively detected using magnetic resonance imaging and diffusion tensor imaging. Detection of cocaine-induced alterations in FR anatomy can aid the selection of potential responders to LHb stimulation for treatment of drug addiction.