EXPRESSION OF INTRINSIC BURSTING PROPERTIES IN NEURONS OF MATURING SENSORIMOTOR CORTEX

Intrinsically bursting (IB) neurons, responding with a burst of action potentials to just threshold intracellular depolarizing current pulse s, are encountered in layer V of mature rodent sensorimotor cortex. We report the results of intracellular recordings performed on neocortic al slices obtained from immature rats between postnatal day (P) 7 and P21, as compared to adult animals (above P60). The bursting properties are here reported to mature abruptly around P14. After this time a su bpopulation of IB neurons was recognizable on the basis of both physio logical and morphological characteristics (i.e. extensive apical and b asal dendrites arborization, axon collaterals limited to layers V-VI). Maturational changes in number and distribution of Ca2+/K+ channels m ay account for this developmental step. The immaturity of IB neurons m ay be correlated with the poorly synchronized character of cortical ac tivities in the very young animals.