Molecular mechanism of the long-lasting change in the excitability of fetal brain neurons following dam's brain stimulation

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The influence of the dam's hypothalamus on the electrophysiological properties of neurons of the superior colliculus (SC) was studied in the fetal rats using the technique of in vivo whole cell recordings, while the fetus was still connected to the dam by the umibilical cord. The folowing results were obtained.1) The resting membrane potential of SC neurons ranged from 46 to 60 mV.2) The amplitude of action potential induced by intracellular injection of a small depolarizing current pulse was small, ranging from 31 to 48 mV, while the duration of action potential measured at half-maximal spike amplitude was 8 to 25 msec.3) Depolarizing current pulse often evoked a slow depolarization in the fetal SC neurons, which has been reported in previous experiments to occur in premature brain neurons.4) The amplitude of action potential of the fetal SC neurons was increased by approximately 15% following electrical stimulation of the dam's hypothalamus, while the duration of action potential was reduced by approximately 26%.5) The slow depolarization induced by depolarizing current pulse became less frequent after stimulation of the dam's hypothalamus.6) These results suggest that activation of the dam's hypothalamus influences the development of membrane properties of the fetal brain neurons through the placenta.