Single cell isolation: a way to examine network interactions.

A procedure for isolating identified, small neurons from snail ganglia is described. The technique allows a particular neuron, previously identified by morphological and electrophysiological characteristics, to be marked and then isolated from the ganglia. This procedure was developed to permit the detailed comparison of the electrical characteristics of a neuron before and after isolation from an intact system. An earlier description has appeared. The cell somata is marked intracellularly by the iontophoretic injection of Procion navy blue H3RS which visually differentiates the cell from other cells in the ganglion. The ganglion is then treated with a trypsin-haluronidase solution to soften the ganglion sheath, which is then removed. The cells are gently shaken to isolate them from the ganglion and then examined electrophysiologically. A comparison of membrane properties, such as action potential height, duration and rate of rise and decay was made before and after all treatments were applied to assess deleterious effect. An analysis of network properties, such as burst duration, number of spikes per burst and presynaptic activity was also performed after each phase of the procedure. No significant differences were noted after dye injection, enzyme treatment, and where appropriate, after isolation. An increase in input resistance and corresponding decrease in the slope of the steady state current--voltage plot (I--V plot) were observed after isolation of a cell. These were expected results of removing the 'load' (i.e. axon or electrical coupling) from the cell soma. This method may be applied to many other systems to study the effects of network interactions on the properties of a single cell and should therefore facilitate the analysis of neuronal networks as well as single cell properties.