Postnatal development of membrane properties of layer I neurons in rat neocortex.
Using whole-cell patch-clamp techniques in brain slices, we studied the postnatal development of electrophysiological properties of rat neocortical layer I neurons during the first three weeks of postnatal life. Neurons, including Cajal-Retzius cells, were visualized under Nomarski optics before recording. In the first postnatal week, all layer I neurons, including Cajal-Retzius cells, had low resting membrane potentials (-40 to -55 mV), high input resistances (1-5 G omega), and long membrane time constants (80-130 msec). Action potentials (APs) of layer I neurons early in postnatal development were lower in amplitude and longer in duration. The threshold for APs also was more depolarized than in older neurons. A medium after-hyperpolarization already was present at postnatal day 0 (PN0), but fast afterhyperpolarizations were not seen until PN10. At all postnatal ages, layer I neurons were capable of repetitive firing, displayed little or no frequency adaptation, and did not display slow afterhyperpolarizations. Early in development, layer I neurons had a prominent hyperpolarization-activation depolarizing sag that decreased with age. These results suggest that the membrane properties of rat neocortical layer I neurons mature rapidly during the first two postnatal weeks. Cajal-Retzius cells had electrical properties similar to other layer I neurons and did not show an earlier maturation of membrane properties.
Zhou
F M
FM
Neurobiology Research Center, University of Alabama at Birmingham 35294, USA.
Hablitz
J J
JJ
D000200:Action Potentials; D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D002540:Cerebral Cortex / Q000166:cytology* / Q000254:growth & development / Q000502:physiology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials; D009474:Neurons / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley
D007473:Ion Channels