Calcium Current Modulation as a Mechanism in the Synaptic Plasticity Underlying Habituation and Sensitization in Aplysia
Habituation and sensitization are two simple forms of learning which occur widely throughout the animal kingdom (26). Habituation is the decline in reflex responsiveness which occurs when a stimulus is presented repeatedly, while sensitization is the increase in responsiveness which results from the transient presentation of a novel stimulus. Although this definition does not exclude the possibility that what happens in sensitization might simply be the opposite of what happens during habituation, earlier work has shown that sensitization is in actuality a distinct process, superimposable on habituation and having its own discernible properties and time course (3,9). In this report, I present experiments which address the question of the cellular mechanisms of both habituation and sensitization, and which confirm, at the level of the biophysics of single neurons, the distinctiveness of sensitization as a process in its own right, independent of habituation. To be more specific, the results of these experiments imply that both habituation and sensitization result from changes in transmitter release consequent to modulation of the influx of calcium ions into the terminals of the presynaptic element in the reflex pathway. They also imply, however, that habituation results from a decrease in calcium influx due to the properties of the calcium channels themselves, whereas sensitization occurs because of an increased calcium influx which results from a change in the properties of a different set of ionic channels in the presynaptic membrane.
KeywordsSensory Neuron Synaptic Plasticity Action Potential Duration Outward Current Calcium Current
Unable to display preview. Download preview PDF.
- 5.Castellucci, V. F. and Kandel, E. R., Presynaptic facilitation as a mechanism for behavioral sensitization in Aplysia,Science, 194 (1976) 1176–1178.Google Scholar
- 11.Kandel, E. R., A Cell-Biological Approach to Learning, Grass Lecture Monograph 1, Society for Neuroscience, Bethesda, Md. (1978).Google Scholar
- 12.Kandel, E. R. and Tauc, L., Heterosynaptic facilitation in neurones of the abdominal ganglion of Aplysia depilans, J. Physiol. (London), 181 (1965) 1–27.Google Scholar
- 13.Katz, B. and Miledi, R., The timing of calcium action during neuromuscular transmission, J. Physiol. (London), 189 (1967) 535–544.Google Scholar
- 14.Katz, B. and Miledi, R., Tetrodotoxin-resistant electrical activity in presynaptic terminals, J. Physiol. (London), 203 (1969) 459–487.Google Scholar
- 14a.a.Katz, B. and Miledi, R., The effects of prolonged depolarization on synaptic transfer in the stellate ganglion of the squid, J. Physiol. (London), 216 (1971) 503–512.Google Scholar
- a.Klein, M. and Kandel, E. R., Mechanism of calcium current modulation underlying presynaptic facilitation and behavioral sensitization in Aplysia, Proc. Nat. Acad. Sci. U.S.A., (1980) in press.Google Scholar
- b.Klein, M., Shapiro, E. and Kandel, E. R., Synaptic plasticity and the modulation of the Ca2+ current, J. Exp. Biol., (1980) in press.Google Scholar
- 16.Llinas, R. R., Calcium and transmitter release in squid synapse, In: Society for Neuroscience Symposia, Vol. 2, M. W. Cowan and J. A. Ferendellí, eds., Society for Neuroscience, Bethesda, Md. (1977) 139–160.Google Scholar
- 18.Nicholls, J. and Wallace, B. G., Modulation of transmission at an inhibitory synapse in the central nervous system of the leech, J. Physiol. (London), 281 (1978) 157–170.Google Scholar
- 21.Pinsker, H., Kupfermann, I., Castellucci, V. and Kandel, E. R., Habituation and dishabituatíon of the gill-withdrawal reflex in Aplysia, Science, 167 (1970) 1740–1742.Google Scholar