Reduced [3H]Cyclic AMP Binding in Postmortem Brain from Subjects with Bipolar Affective Disorder

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Abstract
Findings of increased Gsα levels and forskolin‐stimulated adenylyl cyclase activity in selective cerebral cortical postmortem brain regions in bipolar affective disorder (BD) implicate increased cyclic AMP (cAMP)‐mediated signaling in this illness. Accumulating evidence suggests that intracellular levels of cAMP modulate the abundance and disposition of the regulatory subunits of cAMP‐dependent protein kinase (cAMP‐dPK). Thus, in the present study, we tested further whether hyperfunctional Gsα‐linked cAMP signaling occurs in BD by determining [3H]cAMP binding, a measure of the levels of regulatory subunits of cAMP‐dPK, in cytosolic and membrane fractions from discrete brain regions of postmortem BD brain. Specific [3H]cAMP (5 nM) binding was determined in autopsied brain obtained from 10 patients with DSM‐III‐R diagnoses of BD compared with age‐ and postmortem delay‐matched controls. [3H]cAMP binding was significantly reduced across all brain regions in cytosolic fractions of BD frontal (−22%), temporal (−23%), occipital (−22%) and parietal (−15%) cortex, cerebellum (−36%), and thalamus (−13%) compared with controls, but there were no differences in [3H]cAMP binding in the membrane fractions from these same regions. These results suggest that changes occur in the cAMP‐dPK regulatory subunits in BD brain, possibly resulting from increased cAMP signaling. The possibility that antemortem lithium and/or other mood stabilizer treatment may contribute to the above changes, however, cannot be ruled out.

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