DEVELOPMENT OF FIRING PATTERNS AND ELECTRICAL-PROPERTIES IN NEURONS OF THE RAT VENTROBASAL THALAMUS

The electrophysiological properties of thalamic neurons of the rat ven trobasal complex (VB) in vitro were studied during early postnatal dev elopment. Current clamp recordings using the whole cell patch clamp me thod revealed that immature thalamic neurons had less negative membran e potential and higher input resistance than mature neurons. One of th e most remarkable differences was the absence of spike bursts riding o n the low threshold calcium spike (LTS) in VB neurons before postnatal day 12 (P12). Action potentials recorded from immature neurons had lo nger duration than those of mature cells and were followed by a longer afterhyperpolarization (spike-ahp). The spike-ahp became shorter as m aturation progressed, reaching mature characteristics around P12, coin ciding with the appearance of spike bursting on the LTS. The calcium a ctivated potassium conductance, Ic, played a prominent role in the spi ke-ahp in immature neurons. In conclusion, the major differences in in trinsic membrane properties of VB neurons occur during the first 12 po stnatal days. The appearance of spike bursting riding on the LTS at P1 2 is consistent with the emergence of synchronized thalamocortical osc illations in rats around that age.