Synaptic interactions between a muscle-associated proprioceptor and body
wall muscle motoneurons in larval and adult Manduca sexta.
Tamarkin, Dawn A. and Richard B. Levine.
Division of Neurobiology and Department of Physiology, 611 Gould-Simpson
Bldg., The University of Arizona, Tucson, AZ 85721.
APStracts 3:0075N, 1996.
SUMMARY AND CONCLUSIONS
1. Synaptic remodeling of a proprioceptive circuit during metamorphosis of the
insect, Manduca sexta, is described. The stretch receptor organ is a muscle-
associated proprioceptor which is innervated by a single sensory neuron. It
inserts dorsolaterally in the abdomen in parallel with the intersegmental
muscles of each abdominal segment. The synaptic input from the stretch
receptor sensory neuron to select abdominal internal (intersegmental) and
external muscle motoneurons was characterized in both the larva and adult. 2.
In the larva, the sensory neuron provides excitatory synaptic input to
motoneurons that innervate muscles ipsilateral to the stretch receptor organ
in the body wall; the strongest excitatory synaptic input is to motoneurons
that innervate targets in close proximity to the stretch receptor organ. The
sensory neuron also provides excitatory synaptic input to motoneurons that
innervate contralateral, dorsal targets. However, it inhibits, apparently
through a polysynaptic pathway, motoneurons innervating contralateral, lateral
and ventral targets. 3. The synaptic input to intersegmental muscle
motoneurons from the stretch receptor sensory neuron changes during
metamorphosis. In contrast to the larva, all motoneurons recorded in the adult
(both ipsilateral and contralateral) were excited by the sensory neuron. As in
the larva, the adult sensory neuron provides the strongest excitatory synaptic
input to motoneurons innervating targets in close proximity to the stretch
receptor organ. 4. The proprioceptive input to the body wall muscle
motoneurons was evaluated to determine whether the pathway is monosynaptic, as
has been described in other systems. Spike-triggered signal averaging and
synaptic latency measurements suggested that the strongest excitatory synaptic
input to motoneurons involves a monosynaptic pathway.
Received 8 September 1995; accepted in final form 4 April 1996.
APS Manuscript Number J600-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96