Selective phosphodiesterase inhibitors improve performance on the ED/ID cognitive task in rats

A number of selective phosphodiesterase (PDE) inhibitors have been demonstrated to improve learning in several rodent models of cognition. Given that schizophrenia is associated with impairments in frontal lobe-dependent cognitive functions (e.g., working memory and cognitive flexibility), we examined whether PDE inhibitors would attenuate cognitive deficits associated with schizophrenia. Persistent suppression of N-methyl-D-aspartate (NMDA) receptor function produces enduring structural changes in neocortical and limbic regions in a pattern similar to changes reported in schizophrenia. This similarity suggests that subchronic treatment with NMDA receptor antagonists (e.g., phencyclidine, PCP) may represent a useful preclinical model of neurobiological and related cognitive deficits associated with schizophrenia. We treated male Long-Evans rats with subchronic PCP (5 mg/kg, ip, BID, 7 d) or saline and then examined the effects of acute treatment with selected doses of PDE inhibitors that have been demonstrated to regulate both intracellular levels of cAMP and/or cGMP, and to improve cognitive function. We used an extradimensional-intradimensional (ED/ID) test of cognitive flexibility similar to those used in humans and non-human primates for assessing executive function. Subchronic treatment with PCP produced a selective impairment on ED shift (EDS) performance without significant impairment on any other discrimination problem when compared to saline-treated control animals. Selected doses of the four PDEIs evaluated (PDE2: BAY 60-7550; PDE4: rolipram; PDE5: sildenafil; PDE10A: papaverine) were able to significantly attenuate this cognitive deficit in EDS performance. This suggests that this rodent model of executive function was sensitive to pro-cognitive effects of intracellular effects resulting from PDE inhibition. Together, these data suggest that inhibition of PDE activity may represent valuable therapeutic targets to improve cognition associated with neuropsychiatric disorders that feature cognitive dysfunction as a key symptom.