Neural Circuits Associated with 5-HT1B Receptor Agonist Inhibition of Methamphetamine Seeking in the Conditioned Place Preference Model

5-HT_1B receptors (5-HT_1BRs) modulate psychostimulant reward and incentive motivation in rodents. Here we investigated the effects of the 5-HT_1BR agonist CP94253 (10 mg/kg, IP) on the acquisition and expression of methamphetamine (Meth) conditioned place preference (CPP) in C57BL/6 male mice. We subsequently examined the potential brain regions involved in CP94253 effects using FOS as a marker of neural activity. In the acquisition experiment, mice received the agonist 30 min before each of the Meth injections given during conditioning. In the expression experiment, mice that had acquired Meth-CPP were given either saline or CP94253 and were tested for CPP 30 min later. We found that CP94253 attenuated the expression of Meth-CPP, but had no effect on acquisition. Mice expressing Meth-CPP had elevated numbers of FOS⁺ cells in the ventral tegmental area (VTA) and basolateral amygdala (BlA) and reduced FOS⁺ cells in the central amygdala (CeA) compared to saline controls. CP94253 given before the expression test, but not acutely in drug-naive mice, enhanced FOS⁺ cells in the VTA, the nucleus accumbens (NAc) shell and core, and the dorsomedial striatum and reversed the Meth-conditioned changes in FOS in the BlA and CeA. Approximately 50-70% of FOS⁺ cells in the NAc and VTA were GABAergic regardless of group. By contrast, we did not observe FOS-labeling in dopamine neurons in the VTA. The findings suggest that CP94253 attenuates the motivational effects of the Meth-associated environment and highlight the amygdala, VTA, NAc, and dorsomedial striatum as potential regions involved in this effect.

Fos expression in response to dopamine D3-preferring phenylpiperazine drugs given with and without cocaine

WC 44 and WC 10 are phenylpiperazines with low (23 fold) to moderate (42 fold) selectivity for dopamine D3 receptors (D3Rs) over D2Rs, respectively. WC 44 is a full D3R agonist in the forskolin-stimulated adenylyl cyclase (AC) assay, whereas WC 10 has little efficacy. In contrast to their opposite effects in the AC assay, these drugs often produce similar behavioral effects, suggesting that the AC assay does not predict the efficacy of these drugs in vivo. Here, we examined whether Fos protein expression induced by these drugs would be more consistent with their behavioral effects in vivo. Rats received either vehicle, WC 10 (5.6 mg/kg, i.p.), WC 44 (10.0 mg/kg, i.p), cocaine (10.0 mg/kg, i.p.), or cocaine with WC 10 (5.6 mg/kg, i.p.) or with WC 44 (10.0 mg/kg, i.p). Locomotion was monitored for 90 min and the brains were harvested for immunohistochemistry. Both WC 10 and WC 44 decreased spontaneous and cocaine-induced locomotion. Both compounds also increased Fos expression relative to saline in the dorsal striatum and nucleus accumbens core and shell, and relative to cocaine alone in the nucleus accumbens shell. The findings suggest that even though these compounds have different efficacy in the AC bioassy, they produce similar brain activation and attenuation of cocaine hyperlocomotion. Together with our previous research demonstrating that these compounds down-shift the cocaine self-administration dose-effect function, the findings support the idea that D3R-selective compounds may be useful for cocaine dependence medications development.

Animal models to guide clinical drug development in ADHD: lost in translation?

We review strategies for developing animal models for examining and selecting compounds with potential therapeutic benefit in attention-deficit hyperactivity disorder (ADHD). ADHD is a behavioural disorder of unknown aetiology and pathophysiology. Current understanding suggests that genetic factors play an important role in the aetiology of ADHD. The involvement of dopaminergic and noradrenergic systems in the pathophysiology of ADHD is probable. We review the clinical features of ADHD including inattention, hyperactivity and impulsivity and how these are operationalized for laboratory study. Measures of temporal discounting (but not premature responding) appear to predict known drug effects well (treatment validity). Open-field measures of overactivity commonly used do not have treatment validity in human populations. A number of animal models have been proposed that simulate the symptoms of ADHD. The most commonly used are the spontaneously hypertensive rat (SHR) and the 6-hydroxydopamine-lesioned (6-OHDA) animals. To date, however, the SHR lacks treatment validity, and the effects of drugs on symptoms of impulsivity and inattention have not been studied extensively in 6-OHDA-lesioned animals. At the present stage of development, there are no in vivo models of proven effectiveness for examining and selecting compounds with potential therapeutic benefit in ADHD. However, temporal discounting is an emerging theme in theories of ADHD, and there is good evidence of increased value of delayed reward following treatment with stimulant drugs. Therefore, operant behaviour paradigms that measure the effects of drugs in situations of delayed reinforcement, whether in normal rats or selected models, show promise for the future.

A case-control association study of serotonin 1A receptor gene and tryptophan hydroxylase 2 gene in attention deficit hyperactivity disorder

Serotonergic system-related genes are likely to be involved in mechanisms underlying attention deficit hyperactivity disorder (ADHD). We investigated the association of serotonin the 1A receptor C-1019G single nucleotide polymorphism (HTR1A C-1019G SNP) and tryptophan hydroxylase 2 gene -703G/T (TPH2 -703G/T) SNP with ADHD. All of the ADHD subjects completed a comprehensive and standardized diagnostic and psychological evaluation battery including the parents' Korean version of the ADHD Rating Scale-IV (ARS). The genotype and allele frequencies of 78 ADHD patients and 107 normal controls were analyzed for 5-HTR1A C-1019G and TPH2 -703G/T. There were statistically significant differences in the genotype distributions and allele frequencies of HTR1A C-1019G between the ADHD group and the control group. The homozygous allele C frequency was significantly higher in ADHD patients than in controls. However, no differences in either genotype distribution or in allele frequencies of TPH2 -703G/T were observed between the ADHD patients and the controls. In the ADHD patients, ANCOVA revealed that there were no significant differences in the subscales and total score between the ADHD probands with the CC genotype and those with the CG and GG genotypes in ARS and the Continuous Performance Test (CPT) when adjusting for age and gender. The odds ratio comparing the CC genotype group with the CG genotype group and the C allele with G was 2.12 and 1.79 respectively. Therefore, genotype CC was associated with higher risk of ADHD. Our results suggest that the HTR1A C-1019G SNP may affect susceptibility to ADHD. Further investigation with a larger number of subjects is needed in order to confirm this finding.