Two kinds of peripheral afferent neurons in the earthworm reflex arc

Abstract

1. 1. Two kinds of neurons were identified in the body-wall longitudinal muscle layer of the earthworm, Amynthas hawayanus, by the simultaneous potential recording and Lucifer Yellow-CH injection method with a single microelectrode. 2. 2. Both kinds of neurons have their somata, neuntes and longitudinal processes imbedded in the longitudinal muscle layer. Those with two circular processes extending into the third segmental nerve trunk are tentatively named “intra-nerve-trunk” neurons and those with four circular processes extending into four setae shafts are tentatively named “intramural” neurons. 3. 3. Both kinds of neurons responded to electrical and mechanical stimuli applied in an afferent direction to them. 4. 4. The “intra-nerve-trunk” neuron decreased its response amplitudes to these stimuli after the third nerve trunk was sectioned in correlation to the response amplitude decrease recorded from the nerve trunk after it was sectioned. 5. 5. The response amplitude decrease due to denervation implies a nonlinear structure of the earthworm reflex circuits. 6. 6. The “intramural” neurons are believed to be primary sensory neurons connected to the mechanoreceptors in the setae.