Pharmacogenetics of stimulant abuse liability: association of CDH13 variant with amphetamine response in a racially-heterogeneous sample of healthy young adults

Brain Glutamate Dynamics Predict Positive Agency in Healthy Women: Insights from Combined Application of Pharmacological Challenge, Comprehensive Affective Assessment, and Magnetic Resonance Spectroscopy

Contributions of brain glutamate (Glu) to conscious emotion are not well understood. Here, we evaluate the relationship of experimentally induced change in neocortical Glu (ΔGlu) and subjective states in well individuals, using combined application of pharmacological challenge, magnetic resonance spectroscopy (MRS), and comprehensive affective assessment. Drug challenge with d-amphetamine (AMP) (20 mg oral), methamphetamine (MA) (Desoxyn, 20 mg oral), and placebo (PBO) was conducted on three separate test days in a within-subjects double blind design. Proton MRS quantified neurometabolites in the right dorsal anterior cingulate cortex 140-150 min post-drug and PBO. Subjective states were assessed at half hour intervals over 5.5 h on each session, yielding 3792 responses per participant (91,008 responses overall, N = 24 participants), with self-reports reduced by principal components analysis (PCA). PCA produced a primary factor score of AMP- and MA-induced positive agency (ΔPA). MRS indicated drug-induced ΔGlu related positively to ΔPA (ΔGluMA r = +0.44, p < 0.05, N = 21), with large effects in females (ΔGluMA r = +0.52, p < 0.05; ΔGluAMP r = +0.61, p < 0.05, N = 11). Subjective states related to ΔGlu included rise in subjective stimulation, vigor, friendliness, elation, positive mood, positive affect (r's = +0.51 to +0.74, p < 0.05), and alleviation of anxiety in females (r = -0.61, p < 0.05, N = 11). These self-reports correlated with ΔGlu to the extent they loaded on ΔPA (r = 0.95 AMP, p = 5 × 10-10; r = 0.63 MA, p = 0.0015, N = 11), indicating the coherence of ΔGlu effects on emotional states. Timing data indicated Glu shaped positive emotion both concurrently and prospectively, with no relationship with pre-MRS emotion (ΔGluAMP r = +0.59 to +0.65, p's < 0.05; ΔGluMA r = +0.53, p < 0.05, N = 11). Together these findings indicate substantive, mechanistic contributions of neocortical Glu to positive agentic states in healthy individuals, which are most readily observed in women. The findings illustrate the promise of combined application of pharmacological challenge, comprehensive affective assessment, and MRS neuroimaging techniques in basic and clinical studies.

Brain Glutamate Dynamics Predict Positive Agency in Healthy Women

Contributions of brain glutamate to conscious emotion are not well understood. Here we evaluate the relationship of experimentally-induced change in neocortical glutamate (ΔGlu) and subjective states in well individuals. Drug challenge with d-amphetamine (AMP; 20 mg oral), methamphetamine (MA; Desoxyn®, 20 mg oral), and placebo (PBO) was conducted on three separate test days in a within-subjects double blind design. Proton magnetic resonance spectroscopy (MRS) quantified neurometabolites in the right dorsal anterior cingulate cortex (dACC) 140-150 m post-drug and PBO. Subjective states were assessed at half hour intervals over 5.5-hours on each session, yielding 3,792 responses per participant (91,008 responses overall, N=24 participants). Self-reports were reduced by principal components analysis to a single factor score of AMP- and MA-induced Positive Agency (ΔPA) in each participant. We found drug-induced ΔGlu related positively with ΔPA (ΔGluMA r=+.44, p<.05, N=21), with large effects in females (ΔGluMA r=+.52, p<.05; ΔGluAMP r=+.61, p<.05, N=11). States related to ΔGlu in females included rise in subjective stimulation, vigor, friendliness, elation, positive mood, positive affect (r's=+.51 to +.74, p<.05), and alleviation of anxiety (r=-.61, p<.05, N=11). Self-reports correlated with DGlu to the extent they loaded on ΔPA (r=.95 AMP, p=5×10-10; r=.63 MA, p=.0015, N=11), indicating coherence of ΔGlu effects. Timing data indicated Glu shaped emotion both concurrently and prospectively, with no relationship to pre-MRS emotion (ΔGluAMP r=+.59 to +.65, p's<.05; ΔGluMA r=+.53, p<.05, N=11). Together these findings indicate substantive, mechanistic contributions of neocortical Glu to positive agentic states in healthy individuals, most readily observed in women.

Rewarding effects of physical activity predict sensitivity to the acute subjective effects of d-amphetamine in healthy volunteers

While individual differences in reward sensitivity are believed to generalize across drugs and alternative rewards, this notion has received little empirical attention in human research. Here, we tested whether individual differences in the subjective rewarding effects of physical activity were associated with the subjective response to d-amphetamine administration. Healthy volunteers ( n=95; age 18-35 years) completed questionnaires measuring the self-reported pleasurable effects of physical activity and other covariates, and this was followed by two double-blind counterbalanced sessions during which they received either 20 mg oral d-amphetamine or placebo. Subjective drug effects measures were collected before and repeatedly after drug administration. Subjective d-amphetamine-related effects were then reduced via principal components analysis into latent factors of "positive mood," "arousal," and "drug high." Multiple regression models controlling for placebo-related scores, session order, demographics, body mass index, level of physical activity, and use of other drugs showed that degree of self-reported physical activity reward was positively associated with d-amphetamine-induced positive mood and arousal ( βs≥0.25, ps≤0.04), but was not associated with d-amphetamine-induced changes in drug high ( β=0.13, p=0.24). These results provide novel evidence suggesting that individual differences in reward sensitivity cross over between d-amphetamine reward and physical activity reward in humans.

Cdh13 and AdipoQ gene knockout alter instrumental and Pavlovian drug conditioning

Genome-wide association studies in humans have suggested that variants of the cadherin-13 (CDH13) gene are associated with substance use disorder, subjective response to amphetamine, and attention deficit hyperactivity disorder. To examine the role of the Cdh13 and its peptide ligand adiponectin (AdipoQ) in addiction-related behaviors, we assessed Cdh13 knockout (KO) rats and AdipoQ KO mice using intravenous cocaine self-administration and conditioned place preference (CPP) paradigms. During intravenous cocaine self-administration, male Cdh13 heterozygous (+/-) and KO (-/-) rats showed increased cue-induced reinstatement compared with wild-type (WT) rats when presented with a cocaine-paired stimulus, whereas female Cdh13 rats showed no differences across genotype. Cdh13 -/- rats showed higher responding for a saccharin reinforcer and learned the choice reaction time (RT) task more slowly than WTs. However, we found no differences between Cdh13 -/- and +/+ rats in responding for sensory reinforcement, number of premature responses in the RT task, tendency to approach a Pavlovian food cue, CPP and locomotor activation to cocaine (10 or 20 mg/kg). In AdipoQ -/- mice, there was a significant increase in CPP to methamphetamine (1 mg/kg) but not to a range of d-amphetamine doses (0.5, 1, 2 and 4 mg/kg). Taken together, these data suggest that Cdh13 and AdipoQ regulate sensitivity to psychomotor stimulants and palatable rewards without producing major changes in other behaviors. In humans, these two genes may regulate sensitivity to natural and drug rewards, thus influencing susceptibility to the conditioned drug effects and relapse.