Molecular Mechanisms Underlying How Corticosterone Increases The Excitability Of Hippocampal Neurons In Mice

Most species（including humans）can adapt to a certain degree of stress.In the process of stress,the body regulates the body to better adapt to environmental changes by activating the hypothalamic pituitary adrenal axis（HPA axis）and releasing Glucocorticoid Corticosterone（Cort）.This is of great significance to the survival and evolution of species.Cort can exert the slow effect of nuclear gene transcription and the fast effect of cytoplasmic non gene transcription through glucocorticoid receptor（GR）.Cort rapidly increases the excitability of hippocampal pyramidal neurons within a few minutes（through a genome-independent fast signal pathway）,which is a kind of cellular plasticity of hippocampal neurons.The activation of hippocampal brain area can feedback inhibit the HPA axis and make Cort fall back to the normal level within a certain time after stress,so that the body can adapt to a certain degree of stress.However,how GR mediates Cort’s genome independent fast signal pathway to improve neuronal excitability is not very clear.In this study,we used patch clamp recording,conditional gene knockout/knockin mice,pharmacology and molecular biology to explore the molecular signal pathway of stress hormone Cort to rapidly improve the excitability of hippocampal pyramidal neurons.By adding Cort to the incubation solution of isolated brain slices,we found that Cort can quickly reduce the after hyperpolarization（AHP）of mouse hippocampal CA1pyramidal neurons and enhance the intrinsic excitability of neurons by shortening the release time of subsequent action potentials.Inhibition of GR can eliminate the excitatory effect of Cort.Soon after Cort combined with gr（within a few minutes）,it changed the excitability of neurons,which is obviously a rapid effect produced by non-genomic effects.In order to explore how Cort can activate the downstream fast signal pathway to reduce AHP and improve neuronal excitability,we detected the acetyltransferase activity of the coactivator SRC3（steroid receptor coactivator3）of GR.the results showed that GR combined with Cort could significantly enhance the ability of SRC3 to acetylate its cytoplasmic substrate calmodulin（Ca M）.In order to further explore whether SRC3 is involved in Cort improving neuronal excitability,on the one hand,we constructed Src3 spatio-temporal specific knockout mice.On the other hand,we used pharmacological methods to inhibit intracellular SRC 3 and found that SRC3 is necessary for Cort to improve neuronal excitability.In order to confirm whether acetylated cam is involved in transmitting the signal of Cort improving neuronal excitability,we constructed Cam1 gene conditional knockin mice with acetylation site mutation.It is found that the mutation of Ca M acetylation site can eliminate the enhancement of neuronal excitability caused by Cort,indicating that acetylated Ca M exists in the downstream rapid signal pathway of Cort to improve neuronal excitability.Further mechanism study found that direct injection of acetylated Ca M into cells could inhibit AHP and significantly increase neuronal excitability;And this effect can be blocked by Kv7/M channel（affecting AHP）inhibitors,suggesting that M channel may be involved in the regulation of Cort’s rapid improvement of neuronal excitability.In conclusion,this study reveals the rapid nongenomic mechanism of stress hormone Cort to improve neuronal excitability:Cort acts on M channel through GR-SRC3-^AcCa M signal,and rapidly improves neuronal excitability by inhibiting AHP.The results of this study enrich the neural plasticity mechanism of body adaptation to stress,and provide new insights for understanding the nongenomic effects of steroid hormones.