SELECTIVE REGULATION OF CURRENT DENSITIES UNDERLIES SPONTANEOUS CHANGES IN THE ACTIVITY OF CULTURED NEURONS

We study the electrical activity patterns and the expression of conduc tances in adult stomatogastric ganglion (STG) neurons as a function of time in primary cell culture, When first plated in culture, these neu rons had few active properties, After 1 d in culture they produced sma ll action potentials that rapidly inactivated during maintained depola rization, After 2 d in culture they fired large action potentials toni cally when depolarized, and their properties resembled very closely th e properties of STG neurons pharmacologically isolated in the ganglion , After 3- 4 d in culture, however, their electrical properties change d and they fired in bursts when depolarized, We characterized the curr ents expressed by these neurons in culture, They included two TTX-sens itive sodium currents, a calcium current, a delayed-rectifier-like cur rent, a calcium-dependent potassium current, and two A-type currents, The changes in firing properties with time in culture were accompanied by an increase in inward and decrease in outward current densities, A single-compartment conductance-based model of an STG neuron was const ructed by fitting the currents measured in the biological neurons, Whe n the current densities in the model neuron were matched to those meas ured for the biological neurons in each activity state, the model neur on closely reproduced each state, indicating that the changes in curre nt densities are sufficient to account for the changes in intrinsic pr operties, These data indicate that STG neurons isolated in culture cha nge their intrinsic electrical properties by selectively adjusting the magnitudes of their ionic conductances.