INFORMATION-PROCESSING BY GRADED-POTENTIAL TRANSMISSION THROUGH TONICALLY ACTIVE SYNAPSES

Many neurons use graded membrane-potential changes, instead of action potentials, to transmit information. Traditional synaptic models featu re discontinuous transmitter release by presynaptic action potentials, but this is not true for synapses between graded-potential neurons. I n addition to graded and continuous transmitter release, they have mul tiple active zones, ribbon formations and L-type Ca2+ channels. These differences are probably linked to the high rate of vesicle fusion req uired for continuous transmitter release. Early stages of sensory syst ems provide some of the best characterized graded-potential neurons, a nd recent work on these systems suggests that modification of synaptic transmission by adaptation is a powerful feature of graded synapses.