Journal of Neurophysiology, Vol 70, Issue 5 1777-1786, Copyright © 1993 by APS

ARTICLES

The role of interneurons in controlling the tail-withdrawal reflex in Aplysia: a network model

J. A. White, I. Ziv, L. J. Cleary, D. A. Baxter and J. H. Byrne
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225.

1. The contributions of monosynaptic and polysynaptic circuitry to the tail-withdrawal reflex in the marine mollusk Aplysia californica were assessed by the use of physiologically based neural network models. Effects of monosynaptic circuitry were examined by the use of a two-layer network model with four sensory neurons in the input layer and one motor neuron in the output layer. Results of these simulations indicated that the monosynaptic circuit could not account fully for long-duration responses of tail motor neurons elicited by tail stimulation. 2. A three-layer network model was constructed by interposing a layer of two excitatory interneurons between the input and output layers of the two-layer network model. These interneurons had properties mimicking those of the recently described interneuron LP117, receiving excitatory input from pleural sensory neurons and evoking a biphasic excitatory postsynaptic potential (EPSP) in pedal motor neurons (Cleary and Byrne 1993). The three-layer model could account for long-duration responses in motor neurons. 3. Sensory neurons are a known site of plasticity in Aplysia. Synaptic plasticity was incorporated into the three-layer model by altering the magnitudes of conductance changes evoked in motor neurons and interneurons by presynaptic sensory neurons. In these simulations the excitatory interneurons converted an amplitude-coded input into an amplitude- and duration-coded output, allowing the three-layer network to support a large range of output amplitudes and durations. 4. Synaptic plasticity at more than one locus modified dramatically the input-output relationship of the three-layer network model. This feature gave the model redundancy in its plastic properties and points to the possibility of distributed memory in the circuitry mediating withdrawal reflexes in Aplysia. Multiple sites of control over the response of the network would likely allow a more diverse repertoire of responses.

This article has been cited by other articles:

				E. G. Antzoulatos and J. H. Byrne Long-Term Sensitization Training Produces Spike Narrowing in Aplysia Sensory Neurons J. Neurosci., January 17, 2007; 27(3): 676 - 683. [Abstract] [Full Text] [PDF]

				G. A. Phares, E. G. Antzoulatos, D. A. Baxter, and J. H. Byrne Burst-Induced Synaptic Depression and Its Modulation Contribute to Information Transfer at Aplysia Sensorimotor Synapses: Empirical and Computational Analyses J. Neurosci., September 10, 2003; 23(23): 8392 - 8401. [Abstract] [Full Text] [PDF]

				D. Barbas, L. DesGroseillers, V. F. Castellucci, T. J. Carew, and S. Marinesco Multiple Serotonergic Mechanisms Contributing to Sensitization in Aplysia: Evidence of Diverse Serotonin Receptor Subtypes Learn. Mem., September 1, 2003; 10(5): 373 - 386. [Abstract] [Full Text] [PDF]

				S. A. Prescott and R. Chase Sites of Plasticity in the Neural Circuit Mediating Tentacle Withdrawal in the Snail Helix aspersa: Implications for Behavioral Change and Learning Kinetics Learn. Mem., July 1, 1999; 6(4): 363 - 380. [Abstract] [Full Text]

				M. Storozhuk and V. Castellucci The synaptic junctions of LE and RF cluster sensory neurones of Aplysia californica are differentially modulated by serotonin J. Exp. Biol., January 1, 1999; 202(2): 115 - 120. [Abstract] [PDF]

				S. A. Prescott Interactions between Depression and Facilitation within Neural Networks: Updating the Dual-Process Theory of Plasticity Learn. Mem., November 1, 1998; 5(6): 446 - 466. [Abstract] [Full Text]

				L. J. Cleary, W. L. Lee, and J. H. Byrne Cellular Correlates of Long-Term Sensitization in Aplysia J. Neurosci., August 1, 1998; 18(15): 5988 - 5998. [Abstract] [Full Text] [PDF]

				S. A. Prescott, N. Gill, and R. Chase Neural Circuit Mediating Tentacle Withdrawal in Helix aspersa, With Specific Reference to the Competence of the Motor Neuron C3 J Neurophysiol, December 1, 1997; 78(6): 2951 - 2965. [Abstract] [Full Text] [PDF]

				J. R. Lieb Jr. and W. N. Frost Realistic Simulation of the Aplysia Siphon-Withdrawal Reflex Circuit: Roles of Circuit Elements in Producing Motor Output J Neurophysiol, March 1, 1997; 77(3): 1249 - 1268. [Abstract] [Full Text] [PDF]

				M. Stopfer and T. J. Carew Heterosynaptic Facilitation of Tail Sensory Neuron Synaptic Transmission during Habituation in Tail-Induced Tail and Siphon Withdrawal Reflexes of Aplysia J. Neurosci., August 15, 1996; 16(16): 4933 - 4948. [Abstract] [Full Text] [PDF]

				L J Cleary, J H Byrne, and W N Frost Role of interneurons in defensive withdrawal reflexes in Aplysia. Learn. Mem., January 1, 1995; 2(3-4): 133 - 151. [PDF]