Functional consequences of cocaine re-exposure after discontinuation of cocaine availability

Residual deficits in functional brain activity after chronic cocaine self-administration in rhesus monkeys

Previous studies in humans and in animals have shown dramatic effects of cocaine on measures of brain function that persist into abstinence. The purpose of this study was to examine the neurobiological consequences of abstinence from cocaine, using a model that removes the potential confound of cocaine cues. Adult male rhesus monkeys self-administered cocaine (0.3 mg/kg/injection; N = 8) during daily sessions or served as food-reinforcement controls (N = 4). Two times per week, monkeys were placed in a neutral environment and presented with a cartoon video for ~30 min, sometimes pre- and sometimes post-operant session, but no reinforcement was presented during the video. After ~100 sessions and when the cocaine groups had self-administered 900 mg/kg cocaine, the final experimental condition was a terminal 2-[14C]-deoxyglucose procedure, which occurred in the neutral (cartoon video) environment; for half of the monkeys in each group, this occurred after 1 day of abstinence and for the others after 30 days of abstinence. Rates of local cerebral glucose metabolism were measured in 57 brain regions. Global rates of cerebral metabolism were significantly lower in animals 1 day and 30 days post-cocaine self-administration when compared to those of food-reinforced controls. Effects were larger in 30- vs. 1-day cocaine abstinence, especially in prefrontal, parietal and cingulate cortex, as well as dorsal striatum and thalamus. Because these measures were obtained from monkeys while in a neutral environment, the deficits in glucose utilization can be attributed to the consequences of cocaine exposure and not to effects of conditioned stimuli associated with cocaine.

The thalamus in drug addiction: from rodents to humans

Impairments in response inhibition and salience attribution (iRISA) have been proposed to underlie the clinical symptoms of drug addiction as mediated by cortico-striatal-thalamo-cortical networks. The bulk of evidence supporting the iRISA model comes from neuroimaging research that has focused on cortical and striatal influences with less emphasis on the role of the thalamus. Here, we highlight the importance of the thalamus in drug addiction, focusing on animal literature findings on thalamic nuclei in the context of drug-seeking, structural and functional changes of the thalamus as measured by imaging studies in human drug addiction, particularly during drug cue and non-drug reward processing, and response inhibition tasks. Findings from the animal literature suggest that the paraventricular nucleus of the thalamus, the lateral habenula and the mediodorsal nucleus may be involved in the reinstatement, extinction and expression of drug-seeking behaviours. In support of the iRISA model, the human addiction imaging literature demonstrates enhanced thalamus activation when reacting to drug cues and reduced thalamus activation during response inhibition. This pattern of response was further associated with the severity of, and relapse in, drug addiction. Future animal studies could widen their field of focus by investigating the specific role(s) of different thalamic nuclei in different phases of the addiction cycle. Similarly, future human imaging studies should aim to specifically delineate the structure and function of different thalamic nuclei, for example, through the application of advanced imaging protocols at higher magnetic fields (7 Tesla).This article is part of a discussion meeting issue 'Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists'.

HMG-CoA synthase 2 drives brain metabolic reprogramming in cocaine exposure

The brain is a high energy-consuming organ that typically utilizes glucose as the main energy source for cerebral activity. When glucose becomes scarce under conditions of stress, ketone bodies, such as β-hydroxybutyrate, acetoacetate and acetone, become extremely important. Alterations in brain energy metabolism have been observed in psychostimulant abusers; however, the mode of brain metabolic programming in cocaine dependence remains largely unknown. Here, we profiled the metabolites and metabolic enzymes from brain nucleus accumbens (NAc) of mice exposed to cocaine. We found that cocaine modified energy metabolism and markedly activated ketogenesis pathway in the NAc. The expression of HMG-CoA synthase 2 (HMGCS2), a critical rate-limiting ketogenesis enzyme, was markedly up-regulated. After switching metabolic pathways from ketogenesis to glycolysis through activation of glucokinase, cocaine-evoked metabolic reprogramming regained homeostasis, and the cocaine effect was attenuated. Importantly, both the pharmacological and genetic inhibition of HMGCS2 significantly suppressed cocaine-induced ketogenesis and behavior. In conclusion, cocaine induces a remarkable energy reprogramming in the NAc, which is characterized by HMGCS2-driven ketogenesis. Such effect may facilitate adaptations to cocaine-induced energy stress in the brain. Our findings establish an important link between drug-induced energy reprogramming and cocaine effect, and may have implication in the treatment of cocaine addiction.

Graphene–hemin hybrid nanosheets as a label-free colorimetric platform for DNA and small molecule assays

A novel colorimetric platform has been developed for detecting DNA and small molecules based on a graphene–hemin hybrid nanosheet in a homogenous solution.