Intracellular stimulation of sensory cells elicits swimming activity in the medicinal leech

Abstract

Intracellular stimulation of each of three different types of mechanoreceptors, the T, P and N cells, evokes swimming behavior in leech preparations. Stimulation of an individual N cell or P cell evoked swimming in 75% and 53% respectively, of the preparations tested. Stimulation of an individual T cell was ineffective in eliciting swimming; however, simultaneous stimulation of two T cells evoked swimming in 59% of our preparations. Stimulation of mechanosensory neurons elicited swimming activity for a limited number of trials; i.e. the response habituated. The number of swim episodes evoked before habituation to criterion did not differ significantly for the different types of mechanoreceptors. The duration of swim episodes declined significantly over the course of N cell stimulation. The tendency for swim length to decline with repeated stimulation was present as well for swim episodes elicited by P or T cell stimulation. Swim initiation recovered spontaneously following habituation resulting from T cell stimulation. Spontaneous recovery following N cell stimulation was not demonstrated. However, N cell stimulation evoked swimming again after DP nerve shock or to a limited extent, after cell 204 stimulation. Spontaneous recovery of swim initiation to P cell stimulation was not investigated. A previous study detailed habituation of swimming activity to mechanical stimulation of the body wall (Debski and Friesen 1985). Only the T cells are activated significantly by this stimulus. Stimulation of sensory receptors other than mechanoreceptors was not effective in eliciting swimming in our preparation. We conclude that T cells mediate swim initiation elicited by stroking of the body wall and that the cessation of swimming to this stimulus is not due to sensory adaptation.

Physiological, pharmacological, and behavioral evidence for a TRPA1 channel that can elicit defensive responses in the medicinal leech

“…The initiation of swim behavior in the leech is quite complex, but one possibility is that swimming is elicited via direct activation of the P cells by AITC. Previous studies have found that both P and lN cell activity can produce swimming behavior, although P cells may be more effective (Brodfuehrer and Friesen, 1986;Debski and Friesen, 1987). At 500 µmol l −1 all of the animals produced a swim behavior, but there was a large variance in the duration of swimming elicited.…”

Intersegmental Coordination: Influence of a Single Walking Leg on the Neighboring Segments in the Stick Insect Walking System

“…This result clearly differs from that of activation of other well-investigated locomotor systems, where activation of one part of the system by the CNS of the animal itself was found to be sufficient to result in a coordinated motor output of the whole. Experiments in vitro on the leech (Debski and Friesen 1987) and in vivo and in vitro in crayfish (Cattaert et al 1992;Davis and Kennedy 1972a,b,c;Larimer 1976;Wiesma and Ikeda 1964) and lamprey (Brodin et al 1988) belong to these. In the crayfish swimmeret system, for example, stimulating one swimmeret's CBCO induces rhythmical activity in the whole multisegmental swimmeret system (Cattaert et al 1992).…”

Positive feedback loops sustain repeating bursts in neuronal circuits

“…Swimming locomotion in leeches is initiated, and can also be terminated, by sensory triggers [38,60]. During normal leech behavior, such sensory-induced swim termination occurs when the leech encounters some physical barrier.…”

“…Excitatory synapses connect Tr1 to swim-gating neurons cells 204/205 located in the posterior midbody ganglia (M9-M16) [36,37]. Depolarization of a single cell 204 by intracellular current injection is sufficient to drive fictive swimming; such episodes usually end with, but may continue beyond, the evoking cell 204 stimulus [36,38]. Cells 204 provide excitatory drive to a set of segmentally repeated swim oscillator interneurons (INs; cells 28, 115 and 208) via excitatory synapses [39].…”