Effects of varenicline (Champix), a nicotinic partial agonist, were evaluated on subjective effects of nicotine (drug discrimination), motivation for nicotine taking (progressive-ratio schedule of intravenous nicotine self-administration) and reinstatement (cue-induced reinstatement of previously extinguished nicotine-seeking behavior). Effects on motor performance were assessed in rats trained to discriminate nicotine (0.4 mg/kg) from saline under a fixed-ratio (FR10) schedule of food delivery and in rats trained to respond for food under a progressive-ratio schedule. At short pretreatment times (5–40 min), varenicline produced full or high levels of partial generalization to nicotine’s discriminative-stimulus effects and disrupted responding for food, while there were low levels of partial generalization and no disruption of responding for food at 2- or 4-hour pretreatment times. Varenicline (1 and 3 mg/kg, 2-hour pretreatment time) enhanced discrimination of low doses of nicotine and to a small extent decreased discrimination of the training dose of nicotine. It also dose-dependently decreased nicotine-taking behavior, but had no effect on food-taking behavior under progressive-ratio schedules. Finally, varenicline significantly reduced the ability of a nicotine-associated cue to reinstate extinguished nicotine-seeking behavior. The ability of varenicline to reduce both nicotine-taking and nicotine-seeking behavior can contribute to its relatively high efficacy in treating human smokers.

The dopamine D3 receptor (DRD3) has been suggested to be involved in the mechanisms underlying stimulus-controlled drug-seeking behaviour. Ligands acting as DRD3 antagonists (SB 277011-A) or DRD3 partial agonists (BP 897) have shown some promise for reducing the influence of drug-associated cues on motivational behaviour. Here, effects of SB 277011-A and BP 897 were evaluated on cue-induced reinstatement of nicotine-seeking in rats. The effects of BP 897 on nicotine self-administration under a fixed-ratio 5 (FR5) schedule of reinforcement were also evaluated. SB 277011-A (1-10 mg/kg) was able to block cue-induced reinstatement of nicotine-seeking, indicating that DRD3 selective antagonism may be an effective approach to prevent relapse for nicotine. In contrast, BP 897 did not block the cue-induced reinstatement of nicotine-seeking or nicotine-taking under the FR5 schedule. In a control study, rats did not respond to the light stimuli without nicotine delivery, indicating that the responding for the drug-associated cues was induced by the previous pairing of light stimuli with nicotine's effects. These findings validate the role of DRD3 on reactivity to drug-associated stimuli and suggest that the DRD3 antagonist, but perhaps not the DRD3 partial agonist, could be used to prevent relapse in tobacco smokers.

Purpose To explore whether changes in dietary protein sources can lower plasma branched-chain amino acids (BCAAs), aromatic amino acids and sulfur amino acids (SAAs) that are often elevated in the obese, insulin-resistant state and in type 2 diabetes.MethodsThirty-six subjects (mean age 31 ± 2 years) underwent a voluntary abstinence from meat, poultry, eggs, and dairy products for 6 weeks, while enriching the diet with fish, in fulfillment of a religious fast. Subjects were assessed 1 week before the fast (V1), 1 week after initiation of the fast (V2) and in the last week of the fast (V3). Thirty-four subjects completed all three visits.ResultsFasting plasma BCAAs decreased at V2 and remained low at V3 (P < 0.001 for all). Valine showed the greatest decline, by 20 and 19 % at V2 and V3, respectively. Phenylalanine and tryptophan, but not tyrosine, also decreased at V2 and V3. The two proteinogenic SAAs, methionine and cysteine, remained stable, but the cysteine product, taurine, decreased from 92 ± 7 μmol/L to 66 ± 6 (V2; P = 0.003) and 65 ± 6 μmol/L (V3; P = 0.003). A progressive decline in plasma glutamic acid, coupled with an increase in glutamine, was observed. Plasma total and LDL cholesterol decreased at V2 and V3 (P < 0.001 for all).ConclusionChanging dietary protein sources to plant- and fish-based sources in an ad libitum setting lowers the plasma BCAAs that have been linked to diabetes risk. These findings point to habitual diet as a potentially modifiable determinant of fasting plasma BCAA concentrations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00394-016-1237-6) contains supplementary material, which is available to authorized users.

Dopamine D 3 receptors are implicated in cue-induced relapse to drug seeking. We have previously shown that systemic administration of a selective D 3 antagonist reduces cue-induced reinstatement of nicotine seeking in rats. The current study sought to investigate potential neural substrates mediating this effect. The D 3 antagonist SB-277011-A (0.01-1 mg/0.5 ml/side) infused into the basolateral amygdala or the lateral habenula, but not the nucleus accumbens, significantly attenuated cue-induced reinstatement of nicotine seeking. Moreover, infusion of SB-277011-A (1 mg/0.5 ml/side) into the basolateral amygdala or lateral habenula had no effect on food selfadministration. Together with the finding that systemic SB-277011-A had no effect on extinction responding, this suggests that the effects observed here were on reinstatement and cue seeking, and not due to nonspecific motor activation or contextual-modified residual responding. The further finding of binding of [ 125 I]7-OH-PIPAT to D 3 receptors in the lateral habenula and in the basolateral amygdala is consistent with an important role of D 3 receptors in these areas in nicotine seeking. It was also found that systemic administration of the selective D 2 antagonist L741626 decreased cue-induced reinstatement, consistent with a role of D 2 and D 3 receptors in modulating this behavior. The current study supports an important role for D 3 receptors in the basolateral amygdala and lateral habenula in cue-induced reinstatement.