Comparison of the electrical properties of neocortical neurones in slices in vitro and in the anaesthetized rat.

Because neurones in isolated brain slices are abnormal in several respects, we have compared the electrical properties of neocortical neurones from the anaesthetized rat with neurones from slices of the same area of neocortex in vitro. Resting potentials were not significantly different but there was a small increase in mean spike amplitude and threshold in slices. The most striking observation was a doubling of the mean apparent input resistance (Rin) of neurones in slices (36 M omega cf. 18 M omega in vivo). To assess the extent to which the loss of surface membrane of neurones in slices might contribute to the raised Rin, we estimated the membrane capacity of neurones in the two samples from calculations of the membrane time constants. The mean membrane capacity was significantly lower in neurones from slices, being 2/3 that of the in vivo sample, showing that recordings were indeed mostly from smaller cells in the slices. Possible causes of the difference in mean input resistance not attributable to neuronal size are also discussed.