Role of the Transcription Factor CREB in the NMDA Receptor Antagonist-Induced Attention Deficits

Abstract

This thesis is the result of a multidisciplinary approach which combines behavioral, biochemical and neurochemical assays to identify and delineate the molecular mechanisms involved in the control of attention. Blockade of prefrontocortical glutamate NMDAR is associated with attentional performance deficits as assessed in a task capable of measuring selective attention and response control such as the five choice serial reaction time (5-CSRT) task. I investigated whether phosphorylation of proteins linked to the PKA/CREB pathway in the prefrontal cortex (PFC) and in subcortical regions may be affected by NMDAR blockade. Pharmacological experiments using western blot and immunohistochemical techniques clearly demonstrated that increased CREB phosphorylation (p-CREB) in the PFC but not in subcortical regions may be associated to deficits in attention performance caused by the blockade of prefrontocortical NMDAR with the selective antagonist CPP. Attempts has been made to identify the intracellular pathways responsible for CPP-induced p-CREB changes by examining different protein kinases upstream to CREB such as protein kinase A (PKA), extracellular regulated protein kinases 1/2 (ERK1/2) and calcium/calmodulin kinase II (CaMKII). However, the precise role of these kinases in NMDAR antagonist induced changes in p-CREB is unclear and deserves further studies. The hypothesis that attention deficits induced by NMDAR blockade in the PFC might reflect excessive glutamate (GLU) release in the PFC was investigated by assessing the effects of intracortical CPP on attention, GLU release and p-CREB under basal conditions and in rats pre-treated with the mGlu2/3 receptor agonist LY379268. The results provide evidence that enhanced GLU release in the PFC and CREB phosphorylation are associated to attention deficit. As there are evidences that drug responses may be modulated by the behavioural state of animals, I evaluated the effect of blockade of NMDAR in the PFC on p-CREB in rats performing the 5-CSRT task. Intriguingly, I found that in these rats CPP-induced p-CREB in the PFC was decreased as opposed to the increase found in behaviourally naive rats at the same time point, suggesting that the direction of CPP-induced p-CREB changes critically depends on the behavioural state of animals. Moreover CPP-induced cognitive impairments were prevented by the intracortical administration of Sp-cAMP suggesting that the activation of the PKA/CREB cascade in the PFC is required for the correct performance of the task. In conclusion the present thesis support the role of CREB and provide new information on the mechanisms involved in the control of attention and executive functions associated with some neuropsychiatric disorders