The synapse between LE sensory neurons and gill motoneurons makes only a small contribution to the Aplysia gill-withdrawal reflex.
The monosynaptic connection between the mechano-sensory neurons in the LE cluster and gill motoneurons has been extensively studied and used as a model for the gill-withdrawal reflex and its behavioural plasticity. In an attempt to evaluate the contribution of this synapse to the behaviour, we used voltage-sensitive dye recording to determine the number of activated LE neurons and the number of spikes made by each neuron in response to a light touch. In five preparations, light touch activated a median of five sensory cells with a median of 1.6 spikes per cell. From a comparison of the sizes of the motoneuron synaptic potentials elicited by LE spikes and elicited by a light siphon touch, we estimate that the LE sensory neurons contribute approximately 5% of the motoneuron synaptic potential in response to this touch. This result casts doubt on the validity of using this synaptic connection as a model for gill-withdrawal behaviour. Siphon nerve recordings reveal the existence of short-latency, low-threshold neurons that may provide much of the sensory input in response to a light touch.
Hickie
C
C
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06510, USA.
Cohen
L B
LB
Balaban
P M
PM
D000818:Animals; D001048:Aplysia / Q000502:physiology*; D005071:Evoked Potentials; D005880:Gills / Q000294:innervation; D066298:In Vitro Techniques; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010812:Physical Stimulation; D012018:Reflex / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*