TRPA1 is an ion channel and has been proposed as a thermosensor across species. In invertebrate and ancestral vertebrates such as fly, mosquito, frog, lizard and snakes, TRPA1 serves as a heat receptor, a sensory input utilized for heat avoidance or infrared detection. However, in mammals, whether TRPA1 is a receptor for noxious cold is highly controversial, as channel activation by cold was observed by some groups but disputed by others. Here we attribute the discrepancy to species differences. We show that cold activates rat and mouse TRPA1 but not human or rhesus monkey TRPA1. At the molecular level, a single residue within the S5 transmembrane domain (G878 in rodent but V875 in primate) accounts for the observed difference in cold sensitivity. This residue difference also underlies the species-specific effects of menthol. Together, our findings identify the species-specific cold activation of TRPA1 and reveal a molecular determinant of cold-sensitive gating.

Acute pharmacological blockade of central histamine H 3 receptors (H 3 Rs) enhances arousal/attention in rodents. However, there is little information available for other behavioral domains or for repeated administration using selective compounds. ABT-239 [4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile] exemplifies such a selective, nonimidazole H 3 R antagonist with high affinity for rat (pK i ϭ 8.9) and human (pK i ϭ 9.5) H 3 Rs. Acute functional blockade of central H 3 Rs was demonstrated by blocking the dipsogenia response to the selective H 3 R agonist (R)-␣-methylhistamine in mice. In cognition studies, acquisition of a five-trial, inhibitory avoidance test in rat pups was improved with ABT-239 (0.1-1.0 mg/kg), a 10-to 150-fold gain in potency, with similar efficacy, over previous antagonists such as thioperamide, ciproxifan, A-304121 [(4-(3-(4 -furamide], and A-349821 [(4Ј-(3-((R,R)2,5-dimethyl-pyrrolidin-1-yl)-propoxy)-biphenyl-4-yl)-morpholin-4-yl-methanone]. Efficacy in this modelwas maintained for 3 to 6 h and following repeated dosing with ABT-239. Social memory was also improved in adult (0.01-0.3 mg/kg) and aged (0.3-1.0 mg/kg) rats. In schizophrenia models, ABT-239 improved gating deficits in DBA/2 mice using prepulse inhibition of startle (1.0 -3.0 mg/kg) and N40 (1.0 -10.0 mg/kg). Furthermore, ABT-239 (1.0 mg/kg) attenuated methamphetamineinduced hyperactivity in mice. In freely moving rat microdialysis studies, ABT-239 enhanced acetylcholine release (0.1-3.0 mg/kg) in adult rat frontal cortex and hippocampus and enhanced dopamine release in frontal cortex (3.0 mg/kg), but not striatum. In summary, broad efficacy was observed with ABT-239 across animal models such that potential clinical efficacy may extend beyond disorders such as ADHD to include Alzheimer's disease and schizophrenia.

Background and purpose: Selective cannabinoid CB 2 receptor agonists have demonstrated analgesic activity across multiple preclinical pain models. AM1241 is an indole derivative that exhibits high affinity and selectivity for the CB 2 binding site and broad spectrum analgesic activity in rodent models, but is not an antagonist of CB 2 in vitro functional assays. Additionally, its analgesic effects are m-opioid receptor-dependent. Herein, we describe the in vitro and in vivo pharmacological properties of A-796260, a novel CB 2 agonist. Experimental approach: A-796260 was characterized in radioligand binding and in vitro functional assays at rat and human CB 1 and CB 2 receptors. The behavioural profile of A-796260 was assessed in models of inflammatory, post-operative, neuropathic, and osteoarthritic (OA) pain, as well as its effects on motor activity. The receptor specificity was confirmed using selective CB 1 , CB 2 and m-opioid receptor antagonists. Key results: A-796260 exhibited high affinity and agonist efficacy at human and rat CB 2 receptors, and was selective for the CB 2 vs CB 1 subtype. Efficacy in models of inflammatory, post-operative, neuropathic and OA pain was demonstrated, and these activities were selectively blocked by CB 2 , but not CB 1 or m-opioid receptor-selective antagonists. Efficacy was achieved at doses that had no significant effects on motor activity. Conclusions and implications: These results further confirm the therapeutic potential of CB 2 receptor-selective agonists for the treatment of pain. In addition, they demonstrate that A-796260 may be a useful new pharmacological compound for further studying CB 2 receptor pharmacology and for evaluating its role in the modulation of pain.

Background and purpose: The CB 2 receptor has been proposed as a novel target for the treatment of pain, and CB 2 receptor agonists defined in in vitro assays have demonstrated analgesic activity in animal models. Based on its in vivo analgesic efficacy, AM1241 has been classified as a CB 2 -selective agonist. However, in vitro characterization of AM1241 in functional assays has not been reported. Experimental approach: In this study, AM1241 was characterized across multiple in vitro assays employing heterologous recombinant receptor expression systems to assess its binding potencies at the human CB 2 and CB 1 receptors and its functional efficacies at the human CB 2 receptor. Key results: AM1241 exhibited distinct functional properties depending on the assay conditions employed, a unique profile in contrast to those of the agonist CP 55,940 and the inverse agonist SR144528. AM1241 displayed neutral antagonist activities in FLIPR and cyclase assays. However, when cyclase assays were performed using lower forskolin concentrations for stimulation, AM1241 exhibited partial agonist efficacy. In addition, it behaved as a partial agonist in ERK (or MAP) kinase assays. Conclusions and implications:The unusual phenomenon of inconsistent functional efficacies suggests that AM1241 is a protean agonist at the CB 2 receptor. We postulate that functional efficacies displayed by protean agonists in various assay systems may depend on the levels of receptor constitutive activities exhibited in the assay systems, and therefore, efficacies observed in in vitro assays may not predict in vivo activities.