Single-channel and whole-cell studies of calcium currents in young and aged rat hippocampal slice neurons

The hippocampal slice preparation has contributed greatly to analysis of the basic neurophysiology of brain neurons. In addition, because traumatic dissociative procedures are not used, the in vitro slice is particularly well suited for studies of electrophysiological properties of hippocampal neurons in young and aged rodent brain. Using the slice, we have previously observed an aging-dependent enhancement of voltage-activated Ca²⁺ influx using a combination of intracellular sharp electrode current-clamp and voltage-clamp techniques. The Ca²⁺-dependent afterhyperpolarization as well as the Ca²⁺ action potential were significantly larger in aged rat neurons. Using the sharp electrode switch clamp method, similar effects were found for high voltage-activated whole-cell Ca²⁺ currents. In order to study the mechanistic bases of these aging phenomena at the single-channel level, we have recently focused on recording cell-attached patches from neurons in the partially dissociated hippocampal slice ('zipper' slice). This technique, developed by Gray et al. in 1990, subjects slices to a mild enzymatic treatment resulting in the exposure of individual neurons for patch-clamp procedures. Using this technique, we are currently recording single Ca²⁺ channel activity in hippocampal slices from 4- to 29-month-old rats.