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Cognitive function is closely linked to functional outcomes in psychiatric disorders such as schizophrenia, however developing effective treatments for cognitive dysfunction have proven elusive. Potential reasons for this may include the complexity of diseases, the absence of appropriate and translatable animal tests of cognitive dysfunction, and the reproducibility of findings. Attention is a key component of cognitive function traditionally assessed in the clinic using a variant of the continuous performance test (CPT). The 5-choice (5C)-CPT was developed as a translational cross-species version of this task. Given the association between glutamatergic abnormalities and cognitive dysfunction in schizophrenia, we hypothesized that the NMDA receptor antagonist MK-801 would impair 5C-CPT in rats across different laboratories, and determined whether the dopamine D1 receptor agonist SKF38393 or the nonspecific nicotinic agonist nicotine would remediate such deficits. Rats were trained in the 5C-CPT at Beacon Discovery and UCSD. These rats were then treated with MK-801, agonist treatment, and combinations of the two. MK-801 produced 5C-CPT deficits in the same domains of rats across sites at similar doses. Neither nicotine nor SKF38393 treatment alone improved performance. Importantly, SKF38393, but not nicotine, remediated the MK-801-induced deficits. Convergent observation of MK-801-induced deficits in 5C-CPT was seen across laboratories, resulting in deficits consistent with those seen in people with schizophrenia. Treatment with SKF38393 but not nicotine reversed these deficits. More work is needed, but the 5C-CPT is a reliable method for detecting NMDA receptor disruption-induced deficits in attention.

Rationale Synergistic or supra-additive interactions between the anorectics (dex)fenfluramine and phentermine have been reported previously in the rat and in the clinic. Studies with 5-HT2C antagonists and 5-HT2C knockouts have demonstrated dexfenfluramine hypophagia in the rodent to be mediated by actions at the 5-HT2C receptor. Given the recent FDA approval of the selective 5-HT2C agonist lorcaserin (BELVIQ®) for weight management, we investigated the interaction between phentermine and 5-HT2C agonists on food intake. Objectives This study aims to confirm dexfenfluramine-phentermine (dex-phen) synergy in a rat food intake assay, to extend these findings to other 5-HT2C agonists, and to determine whether pharmacokinetic interactions could explain synergistic findings with particular drug combinations. Methods Isobolographic analyses were performed in which phentermine was paired with either dexfenfluramine, the 5-HT2C agonist AR630, or the 5-HT2C agonist lorcaserin, and inhibition of food intake measured in the rat. Subsequent studies assessed these same phentermine-drug pair combinations spanning both the full effect range and a range of fixed ratio drug combinations. Satellite groups received single doses of each drug either alone or in combination with phentermine, and free brain concentrations were measured. Results Dex-phen synergy was confirmed in the rat and extended to the 5-HT2C agonist AR630. In contrast, although some synergistic interactions between lorcaserin and phentermine were observed, these combinations were largely additive. Synergistic interactions between phentermine and dexfenfluramine or AR630 were accompanied by combination-induced increases in brain levels of phentermine. Conclusions Dex-phen synergy in the rat is caused by a pharmacokinetic interaction, resulting in increased central concentrations of phentermine.