Effects of exogenous ganglioside and cholesterol application on excitability of Aplysia neurons

The effects of pressure-ejected gangliosides GM1 and GMix ("Cronassial") and cholesterol dissolved in sea water on the electrophysiological characteristics of Aplysia neurons were studied using voltage-clamp recording techniques. Two types of electrophysiological effects were found. In about 5% of neurons brief pulses (0.1-0.2 sec) of GM1 or GMix elicited fast and large currents associated with an increase in membrane conductance and clear reversal potentials. These currents were similar to those elicited by common neuro-transmitters. Thus it appears that gangliosides may activate a membrane-bound receptor on at least some neurons. Most (about 85%) of the 121 neurons studied showed responses to longer pulses (1.0-2.5 sec) of gangliosides. These responses were much smaller, usually had a relatively slow component, and could be mimicked by application of cholesterol. The currents elicited were either inward or outward and were often biphasic, with an small initial outward component followed by a larger slow inward current. The responses often became larger upon repeated application at short intervals, and long periods of wash were required for recovery. This type of response appears to reflect changes in the electrical properties of the cell induced by incorporation of small amounts of gangliosides or cholesterol into the membrane.