ALLOPREGNANOLONE INCREASES MATURE EXCITATORY SYNAPSES ALONG DENDRITES VIA PROTEIN KINASE A SIGNALING

Allopregnanolone (AP alpha; 5 alpha-pregnan-3 alpha-ol-20-one) is synthesized in both the periphery and central nervous system and is known to be a potent positive allosteric modulator of the GABA(A) receptor. Because APa was suggested to improve the symptoms of depression and Alzheimer's disease (AD), which involve synaptic dysfunction and loss, we examined whether AP alpha affects excitatory synapses. Drebrin, which is an actin-binding protein, forms a unique stable actin structure in dendritic spines, and drebrin levels correlate positively with cognitive levels in AD and mild cognitive impairment. We investigated whether AP alpha increases excitatory synapse density along dendrites of mature hippocampal neurons using drebrin-imaging-based evaluation of mature synapses. We prepared primary cultures of hippocampal neurons and either transfected them with GFP or immunostained them against drebrin. Morphological analysis of GFP-transfected neurons revealed that a 24-h exposure to 0.3 or 1 mu M AP alpha significantly increased dendritic spine density without any morphological changes to spines. Drebrin cluster density was also increased by 0.3 and 1 mu M AP alpha. The protein kinase A (PKA) inhibitor H-89 inhibited the AP alpha-induced increase in drebrin cluster density. These data demonstrate that AP alpha increases mature excitatory synapses via activation of PKA. Therefore, the PKA-cAMP response element-binding protein (CREB) signaling pathway is likely to be involved in the AP alpha-induced increase of mature excitatory synapses. Another possibility is that the PKA-dependent increase in AMPA receptors at dendritic spines mediates the AP alpha function. In conclusion, our study indicates that AP alpha may improve neuropsychiatric disorder outcomes via increasing the numbers of mature excitatory synapses. (C) 2015 IBRO. Published by Elsevier Ltd. All rights reserved.