SIMULTANEOUS MULTISITE RECORDINGS AND STIMULATION OF SINGLE ISOLATED LEECH NEURONS USING PLANAR EXTRACELLULAR ELECTRODE ARRAYS

Planar extracellular electrode arrays provide a non-toxic, non-invasiv e method of making long-term, multisite recordings with moderately hig h spatial frequency (recording sites per unit area). This paper report s advances in the use of this approach to record from and stimulate si ngle identified leech neurons in vitro. A modified enzyme treatment al lowed identified neurons to be extracted with very long processes. Mul tisite extracellular recordings from the processes of such isolated ne urons revealed both the velocity and direction of action potential pro pagation. Propagation in two cell types examined was from the broken s tump towards the cell body (antidromic). This was true for spontaneous action potentials, action potentials produced by injecting current in to the cell body and extracellular stimulation of the extracted proces s via a planar extracellular electrode. These results extend previous findings which have shown that the tip of the broken stump of extracte d neurons has a high density of voltage-activated sodium channels. Mor eover they demonstrate the applicability of extracellular electrode ar rays for recording the electrical excitability of single cells.