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This Article Full Text Full Text (PDF) All Versions of this Article: 93/5/2940    most recent 01202.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Evans, C. G. Articles by Cropper, E. C. Search for Related Content PubMed PubMed Citation Articles by Evans, C. G. Articles by Cropper, E. C.

Inhibition of Afferent Transmission in the Feeding Circuitry of Aplysia: Persistence Can Be as Important as Size

¹Department of Physiology and Biophysics, Mt. Sinai School of Medicine; and ²Phase Five Communications, New York, New York

Submitted 22 November 2004; accepted in final form 22 December 2004

We are studying afferent transmission from a mechanoafferent, B21, to a follower, B8. During motor programs, afferent transmission is regulated so that it does not always occur. Afferent transmission is eliminated when spike propagation in B21 fails, i.e., when spike initiation is inhibited in one output region-B21's lateral process. Spike initiation in the lateral process is inhibited by the B52 and B4/5 cells. Individual B52 and B4/5-induced inhibitory postsynaptic potentials (IPSPs) in B21 differ. For example, the peak amplitude of a B4/5-induced IPSP is four times the amplitude of a B52 IPSP. Nevertheless, when interneurons fire in bursts at physiological (i.e., low) frequencies, afferent transmission is most effectively reduced by B52. Although individual B52-induced IPSPs are small, they have a long time constant and summate at low firing frequencies. Once IPSPs summate, they effectively block afferent transmission. In contrast, individual B4/5-induced IPSPs have a relatively short time constant and do not summate at low frequencies. B52 and B4/5 therefore differ in that once synaptic input from B52 becomes effective, afferent transmission is continuously inhibited. In contrast, periods of B4/5-induced inhibition are interspersed with relatively long intervals in which inhibition does not occur. Consequently, the probability that afferent transmission will be inhibited is low. In conclusion, it is widely recognized that afferent transmission can be regulated by synaptic input. Our experiments are, however, unusual in that they relate specific characteristics of postsynaptic potentials to functional inhibition. In particular we demonstrate the potential importance of the IPSP time constant.

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				C. G. Evans, T. Kang, and E. C. Cropper Selective Spike Propagation in the Central Processes of an Invertebrate Neuron J Neurophysiol, November 1, 2008; 100(5): 2940 - 2947. [Abstract] [Full Text] [PDF]