Blockade of protein phosphatase 2B activity in the amygdala increases anxiety- and depression-like behaviors in mice

Organ transplant patients receive chronic administration of the calcineurin inhibitor cyclosporin-A (CsA) and demonstrate increased incidence of mood disorders. Significant calcineurin expression can be observed with immunohistochemistry in the amygdala, a brain area important for behaviors related to mood disorders and anxiety. It is therefore important to determine whether chronic blockade of calcineurin might contribute to symptoms of anxiety and depression in these patients.

Taken together, these data demonstrate that decreasing calcineurin activity in the amygdala increases anxiety- and depression-like behaviors. These studies suggest that chronic administration of CsA to organ transplant patients could have significant effects on anxiety and mood and that this should be recognized as a clinical consequence of treatment to prevent transplant rejection.

Pharmacological CsA and viral-mediated gene transfer (adeno-associated viral expression of short hairpin RNA [AAV-shRNA]) approaches were used to inhibit calcineurin activity globally and selectively in the amygdala of the mouse brain to determine the role of calcineurin in behaviors related to depression and anxiety.

Systemic inhibition of calcineurin activity with CsA or local downregulation of calcineurin levels in the amygdala with AAV-delivered shRNAs targeting calcineurin A increased behavioral measures of anxiety in both the elevated plus maze and light/dark tests with no changes in locomotor activity. In the forced swim and tail suspension models of depression-like behavior, calcineurin blockade in the amygdala increased immobility similarly to manipulations that lead to a depression-like phenotype. Conclusions: Taken together, these data demonstrate that decreasing calcineurin activity in the amygdala increases anxiety- and depression-like behaviors. These studies suggest that chronic administration of CsA to organ transplant patients could have significant effects on anxiety and mood and that this should be recognized as a clinical consequence of treatment to prevent transplant rejection.