In vivo whole-cell recording from neurons of the superior colliculus in fetal rats.
In vivo whole-cell recording was made from neurons of the superior colliculus (SC) in rat fetuses which were connected with the dam by the umbilical cord. Fast action potentials could be generated by changing membrane potentials to depolarizing direction. The firing thresholds of fetal SC neurons appeared to be higher (between -50 and -35 mV) than those of brain neurons in later developmental stages. The action potentials of fetal SC neurons, which were smaller in amplitude and wider in duration as compared to mature brain neurons, revealed a small or no afterhyperpolarization. In addition to these fast action potentials, slow depolarizations of smaller amplitudes were evoked by intracellular injection of long depolarization pulses. Most neurons of the fetal SC (7/11) revealed linear current-voltage (I-V) relations, while the remaining neurons displayed marked rectification. In some fetal SC neurons, presumed EPSPs and IPSPs occurred spontaneously. These presumed postsynaptic potentials showed temporal summation. These results suggest that rat SC neurons are functionally active even before birth, though the membrane properties remain immature.
Department of Physiology, Yamaguchi University, School of Medicine, Yamaguchi, Japan. y.sakata@po.cc.yamaguchi-u.ac.jp
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Y
Sakata
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T
Fujioka
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Nakamura
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D005333:Fetus / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013477:Superior Colliculi / Q000166:cytology* / Q000196:embryology; D013569:Synapses / Q000502:physiology; D014470:Umbilical Cord