Validation of beta2 containing nicotinic acetylcholinergic receptors as a potenti

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DESCRIPTION (provided by applicant): Bipolar disorder is a chronic, severe and devastating illness which exerts a crippling personal and financial toll on the individual, family and wider society. The main burden of illness in bipolar disorder is in the depressive pole i.e. bipolar depression. There are currently few effective, well-validated treatments for bipolar depression. It is clear that there is an urgent need for novel molecular targets and subsequently treatments in the pharmacotherapy of bipolar depression. One such target is the nicotinic acetylcholinergic receptor system which has been postulated to play a role in the pathophysiology of bipolar disorder. A number of recent studies implicate this system in the causation of bipolar disorder and it warrants justified attention. Until recently this system was not amenable to study in man due to logistical reasons including the lack of availability of appropriate ligands. The development of a novel single photon emission tomography (SPECT) nicotinic acetylcholinergic receptor (nAChR) radioligand now allows us to examine an important aspect of this receptor system; ¿2 subunit containing nicotinic acetylcholinergic receptors. These receptors are widespread in the brain and are assumed to play a key role in the system especially due to their location in mood regulating circuits. Our primary aim is therefore to determine ¿2 subunit containing nAChRs availability in patients with bipolar disorder, who are currently depressed and compare them with healthy control subjects. We propose a SPECT study of ¿2 subunit containing nAChRs in patients with bipolar depression to determine whether there is a dysfunction of this key element. We will study 18 patients with bipolar depression and 18 age-matched healthy control subjects. All subjects will have one MRI scan and one SPECT scan with the SPECT radioligand [123I]5-I-A-85380 to quantify ¿2 subunit containing nicotinic acetylcholinergic receptors in brain regions involved in mood regulating circuits. Based on previous studies and our preliminary data showing significant deficits of this system in unipolar and bipolar depression, we hypothesize that there will be a decrease in ¿2 subunit containing nAChRs in patients with bipolar depression compared with healthy control subjects. The results of this study will allow us to determine if this molecular target is worth pursuing in a larger sample. PUBLIC HEALTH RELEVANCE: It is clear that there is an urgent need for the development of novel therapeutic targets to better treat bipolar depression as there are currently few effective, well-validated treatments for bipolar depression. This study will validate one particular receptor system, the nicotinic acetylcholine receptor, as potentially having a central role in the causation of bipolar depression. If this proves successful then it would be possible to develop newer antidepressant drugs to better treat patients with bipolar depression.