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Background and purpose Insufficient prefrontal dopamine 1 (D1 ) receptor signalling has been linked to cognitive dysfunction in several psychiatric conditions. Because the PDE1 isoform B (PDE1B) is postulated to regulate D1 receptor-dependent signal transduction, in this study we aimed to elucidate the role of PDE1 in cognitive processes reliant on D1 receptor function. Experimental approach Cognitive performance of the D1 receptor agonist, SKF38393, was studied in the T-maze continuous alternation task and 5-choice serial reaction time task. D1 receptor/PDE1B double-immunohistochemistry was performed using human and rat prefrontal brain sections. The pharmacological activity of the PDE1 inhibitor, ITI-214, was assessed by measuring the increase in cAMP/cGMP in prefrontal brain tissue and its effect on working memory performance. Mechanistic studies on the modulation of prefrontal neuronal transmission by SKF38393 and ITI-214 were performed using extracellular recordings in brain slices. Key results SKF38393 improved working memory and attentional performance in rodents. D1 receptor/PDE1B co-expression was verified in both human and rat prefrontal brain sections. The pharmacological activity of ITI-214 on its target, PDE1, was demonstrated by its ability to increase prefrontal cAMP/cGMP. In addition, ITI-214 improved working memory performance. Both SKF38393 and ITI-214 facilitated neuronal transmission in prefrontal brain slices. Conclusion and implications We hypothesize that PDE1 inhibition improves working memory performance by increasing prefrontal synaptic transmission and/or postsynaptic D1 receptor signalling, by modulating prefrontal downstream second messenger levels. These data, therefore, support the use of PDE1 inhibitors as a potential approach for the treatment of cognitive dysfunction.

Background and Purpose Insufficient prefrontal dopamine 1 (D1) receptor signalling has been linked to cognitive dysfunction in several psychiatric conditions. Because the PDE1 isoform B (PDE1B) is postulated to regulate D1 receptor‐dependent signal transduction, in this study we aimed to elucidate the role of PDE1 in cognitive processes reliant on D1 receptor function. Experimental Approach Cognitive performance of the D1 receptor agonist, SKF38393, was studied in the T‐maze continuous alternation task and 5‐choice serial reaction time task. D1 receptor/PDE1B double‐immunohistochemistry was performed using human and rat prefrontal brain sections. The pharmacological activity of the PDE1 inhibitor, ITI‐214, was assessed by measuring the increase in cAMP/cGMP in prefrontal brain tissue and its effect on working memory performance. Mechanistic studies on the modulation of prefrontal neuronal transmission by SKF38393 and ITI‐214 were performed using extracellular recordings in brain slices. Key Results SKF38393 improved working memory and attentional performance in rodents. D1 receptor/PDE1B co‐expression was verified in both human and rat prefrontal brain sections. The pharmacological activity of ITI‐214 on its target, PDE1, was demonstrated by its ability to increase prefrontal cAMP/cGMP. In addition, ITI‐214 improved working memory performance. Both SKF38393 and ITI‐214 facilitated neuronal transmission in prefrontal brain slices. Conclusion and Implications We hypothesize that PDE1 inhibition improves working memory performance by increasing prefrontal synaptic transmission and/or postsynaptic D1 receptor signalling, by modulating prefrontal downstream second messenger levels. These data, therefore, support the use of PDE1 inhibitors as a potential approach for the treatment of cognitive dysfunction.

Background and purpose: A functional link between seizure-induced P-glycoprotein overexpression at the blood–brain barrier and therapeutic failure has been suggested by several studies using rodent epilepsy models and human epileptic tissue. Recently, we reported that interference with the mechanisms that up-regulate P-glycoprotein in response to seizure activity might provide a novel approach to control its expression in the epileptic brain. Based on these data, we hypothesized that blocking the appropriate signalling cascade by cyclooxygenase-2 inhibition should improve brain penetration of antiepileptic drugs and help to overcome drug resistance. Experimental approach: Effects of the selective cyclooxygenase-2 inhibitor celecoxib on the response to the P-glycoprotein substrate, phenobarbital, was evaluated in a chronic model of drug-resistant temporal lobe epilepsy in rats. Drug-resistant rats selected from this model exhibit a marked overexpression of P-glycoprotein in the hippocampus and other limbic brain regions. Key results: Responders and non-responders were selected from a group of rats with spontaneous recurrent seizures after prolonged treatment with phenobarbital at maximum tolerated doses. The efficacy of phenobarbital was re-evaluated following a 6 day treatment with celecoxib and the frequency of spontaneous recurrent seizures was significantly reduced in both groups of rats, phenobarbital responders or non-responders selected from the previous drug trial. Conclusions and implications: Pretreatment with the cyclooxygenase-2 inhibitor restored the anticonvulsant activity of phenobarbital in rats that failed to exhibit a relevant response before celecoxib treatment. Our data provide further support for a novel therapeutic approach to overcome transporter-mediated drug resistance in epilepsies.