Rapamycin Regulates The Electrophysiological Properties Of Cortical L5Pyramidal Cells In Developing Brain

BACKGROUDmTOR (the mammalian target of Rapamycin), a pivotal regulatory cascade, mediates many important physiological processes. Impairment of mTOR could result in a lot of disorders such as obesity, diabetes, cancer, and etc. In the central nervous system, mTOR mainly takes part in axon formation, neuronal cell migration, and cortical plate formation. Its abnormality leads to seizures, cognitive disorders, ischemic strokes and Schizophrenia.Rapamycin (RMC) is one of the inhibitors of the mTOR signaling pathway. Clinically, RMC is used as a kind of immunosuppressant to treat tumors. It has been demonstrated that RMC can inhibit the occurrence of seizures, improve cognition and recovery after ischemic strokes, and protect neuron from injury. Recent studies prove that RMC can regulate the electrophysiological properties of the neurons, but with a relatively long time lasting12-72hours. Generally, this long-time application blocks all the changes including neurophysiologic and morphological alterations. mTOR regulates synaptic transmission not only through changes in the number of synapses, but also by modifying the function and information coding properties of individual synapses. However, dose RMC identically affect the electrophysiological properties of excitatory neurons among different stages of developing brain, and what happens for the electrophysiological properties with a short-time treatment of RMC? To answer these questions, using developing brain slices, we carried out whole cell recording from cortical Layer5pyramidal cells, which play key roles in cerebral information processing. Our results will provide a better understanding on the mechanisms of neural function regulated by RMC.METHODThe electrophysiological features of cortical layer5pyramidal cells from P4/P10SD rats and P90adult C57mouse are studied separately with patch clamp technique, including I/V curve, rest membrane potential (RMP), spontaneous electrical activity including excitatory postsynaptic potential (EPSP), spontaneous or triggered action potential (AP). Further, we studied the influences of RMC (0.5μg/ml) on these electrophysiological properties.RESULTSIn the present study,1-3min RMC treatments all have impacts on the electrophysiological properties from the cortical L5pyramidal cells in developing brain, but it varies a lot in each. Firstly, it changes the I/V curves, which mainly enhance the reactivity of the pyramidal neuron to current stimulation in P4and P10rats. As to P90rats, the enhancement is smaller. Secondly, RMP of each developing brain are notably increased by RMC. Also, RMC is able to trigger some slow inward currents. The spontaneous electrical activities of the pyramidal neurons are also changed, such as the significant increases in SD of baseline variant, peak aptitudes of the baseline changes, the onset of EPSP and spontaneous AP, which also differs in each period. Finally, our finding indicated that the frequency of triggered APs was significantly declined in burst spiking (BS) cells by RMC. Meanwhile, the BS firing pattern was transferred to the regular spiking (RS) firing pattern without changing the level of trigger currents.CONCLUSIONRMC could exert a transient and direct effect on the electrophysiological properties of excitatory neurons among three developing stages in the brain, but the affection is uneven. Our findings suggest mTOR signaling pathway could become a new target for childhood neuropsychical diseases. Our findings also enhance the understandings of the mechanism of some childhood neuropsychical diseases.