Increased Expression of Cannabinoid Receptor 1 in the Nucleus Accumbens Core in a Rat Model With Morphine Withdrawal.

Increased Expression of Cannabinoid Receptor 1 in the Nucleus Accumbens Core in a Rat Model with Morphine Withdrawal.

Brain Res. 2013 Aug 1;
Yuan WX, Heng LJ, Ma J, Wang XQ, Qu LJ, Duan L, Kang JJ, Chen LW, Gao GD

Relapse is a major clinical problem and remains a major challenge in the treatment of drug addiction. There is strong evidence that the endocannabinoid system of the nucleus accumben core (NAcc) is involved in drug-seeking behavior, as well as in the mechanisms that underlie relapse to drug use. To reveal the mechanism that underlies this finding, we examined the expression pattern of the cannabinoid receptor 1 (CB1-R) in the NAcc of SD rats that had been undergoing morphine withdrawal (MW) for 1 day, 3 days and 3 weeks (acute, latent and chronic phases, respectively). Morphine exposure induced conditioned place preference (CPP) in rats. Significant increase of CB1-R expression in NAcc was observed in animals in the 1 day, 3 days and 3 weeks morphine withdrawal compare to the control group. Immunofluorescence labeling showed axonal fibers or terminals by fluorescence microscope observation. Immunoelectron microscopy detection showed silver-gold particles located in the presynaptic membranes that mainly give rise to symmetrical synapses. Quantitative electron microscopy showed an increase in number of CB1-R-positive terminals in the morphine withdrawal groups and the number of immunogold particles was significantly increased at these inhibitory terminals. We also confirmed that infusions of the CB1-R antagonist rimonabant into the NAcc attenuated the CPP during morphine withdrawal. Our present data have thus indicated that increasing pattern of CB1-R expression in the NAcc during above morphine withdrawal phases, which might underlie the relapse associated drug seeking behavior after morphine withdrawal. HubMed – addiction

Biological Mechanisms that Promote Weight Regain Following Weight Loss in Obese Humans.

Physiol Behav. 2013 Aug 1;
Ochner CN, Barrios DM, Lee CD, Pi-Sunyer FX

Weight loss dieting remains the treatment of choice for the vast majority of obese individuals, despite the limited long-term success of behavioral weight loss interventions. The reasons for the near universal unsustainability of behavioral weight loss in [formerly] obese individuals have not been fully elucidated, relegating researchers to making educated guesses about how to improve obesity treatment, as opposed to developing interventions targeting the causes of weight regain. This article discusses research on several factors that may contribute to weight regain following weight loss achieved through behavioral interventions, including adipose cellularity, endocrine function, energy metabolism, neural responsivity, and addiction-like neural mechanisms. All of these mechanisms are engaged prior to weight loss, suggesting that so called “anti-starvation” mechanisms are activated via reductions in energy intake, rather than depletion of energy stores. Evidence suggests that these mechanisms are not necessarily part of a homeostatic feedback system designed to regulate body weight or even anti-starvation mechanisms per se. Though they may have evolved to prevent starvation, they appear to be more accurately described as anti-weight loss mechanisms, engaged with caloric restriction irrespective of the adequacy of energy stores. It is hypothesized that these factors may combine to create a biological disposition that fosters the maintenance of an elevated body weight and work to restore the highest sustained body weight, thus precluding the long-term success of behavioral weight loss. It may be necessary to develop interventions that attenuate these biological mechanisms in order to achieve long-term weight reduction in obese individuals. HubMed – addiction

Opiate dependence induces network state shifts in the limbic system.

Neurobiol Dis. 2013 Jul 30;
Dejean C, Boraud T, Le Moine C

Among current theories of addiction, hedonic homeostasis dysregulation predicts that the brain reward systems, particularly the mesolimbic dopamine system, switch from a physiological state to a new “set point”. In opiate addiction, evidence show that the dopamine system principal targets, prefrontal cortex (PFC), nucleus accumbens (NAC) and basolateral amygdala complex (BLA) also adapt to repeated drug stimulation. Here we investigated the impact of chronic morphine on the dynamics of the network of these three interconnected structures. For that purpose we performed simultaneous electrophysiological recordings in freely-moving rats subcutaneously implanted with continuous-release morphine pellets. Chronic morphine produced a shift in the network state underpinned by changes in Delta and Gamma oscillations in the LFP of PFC, NAC and BLA, in correlation to behavioral changes. However despite continuous stimulation by the drug, an apparent normalization of the network activity and state occurred after two days indicating large scale adaptations. Blockade of ? opioid receptors was nonetheless sufficient to disrupt this acquired new stability in morphine-dependent animals. In line with the homeostatic dysregulation theory of addiction, our study provides original direct evidence that the PFC-NAC-BLA network of the dependent brain is characterized by a de novo balance for which the drug of abuse becomes a main contributor. HubMed – addiction

Tales from the dark side: Do neuromodulators of drug withdrawal require changes in endocannabinoid tone?

Prog Neuropsychopharmacol Biol Psychiatry. 2013 Aug 1;
Oleson EB, Cachope R, Fitoussi A, Cheer JF

Environmental and interoceptive cues are theorized to serve as ‘signals’ that motivate drug seeking, effects that may be augmented in the withdrawn state. Phasic dopamine release events are observed in the nucleus accumbens in response to such motivational salient stimuli and are thought to be necessary for drug-associated cues to trigger craving. We recently demonstrated how dopamine neurons encode stimuli conditioned to a negative event, as might occur during conditioned withdrawal, and stimuli predicting the avoidance of negative events, as might occur as an addict seeks out drugs to prevent withdrawal. In this review we first discuss how the subsecond dopamine release events might process conditioned withdrawal and drug seeking driven by negative reinforcement processes within the context of our dopamine data obtained during conditioned avoidance procedures. We next describe how the endocannabinoid system modulates phasic dopamine release events and how it might be harnessed to treat negative affective states in addiction. Specifically, we have demonstrated that endocannabinoids in the ventral tegmentum sculpt cue-induced accumbal surges in dopamine release and, therefore, may also be mobilized during drug withdrawal. HubMed – addiction