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Gangitano D, Salas R, Teng Y, Perez E, De Biasi M: Progesterone modulation of alpha5 nAChR subunits influences anxiety-related behavior during estrus cycle. Genes Brain Behav. 2009 Jun;8(4):398-406. Epub 2009 Feb 11.
Smokers often report an anxiolytic effect of cigarettes. In addition, stress-related disorders such as anxiety, post-traumatic stress syndrome and depression are often associated with chronic nicotine use. To study the role of the alpha5 nicotinic acetylcholine receptor subunit in anxiety-related responses, control and alpha5 subunit null mice (alpha5 (-/-)) were subjected to the open field activity (OFA), light-dark box (LDB) and elevated plus maze (EPM) tests. In the OFA and LDB, alpha5 (-/-) behaved like wild-type controls. In the EPM, female alpha5 (-/-) mice displayed an anxiolytic-like phenotype, while male alpha5 (-/-) mice were undistinguishable from littermate controls. We studied the hypothalamus-pituitary-adrenal axis by measuring plasma corticosterone and hypothalamic corticotropin-releasing factor. Consistent with an anxiolytic-like phenotype, female alpha5 (-/-) mice displayed lower basal corticosterone levels. To test whether gonadal steroids regulate the expression of alpha5, we treated cultured NTera 2 cells with progesterone and found that alpha5 protein levels were upregulated. In addition, brain levels of alpha5 mRNA increased upon progesterone injection into ovariectomized wild-type females. Finally, we tested anxiety levels in the EPM during the estrous cycle. The estrus phase (when progesterone levels are low) is anxiolytic-like in wild-type mice, but no cycle-dependent fluctuations in anxiety levels were found in alpha5 (-/-) females. Thus, alpha5-containing neuronal nicotinic acetylcholine receptors may be mediators of anxiogenic responses, and progesterone-dependent modulation of alpha5 expression may contribute to fluctuations in anxiety levels during the ovarian cycle. |
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