WIDESPREAD MECHANOSENSORY ACTIVATION OF THE SEROTONERGIC SYSTEM OF THE
MEDICINAL LEECH.
Szczupak, Lidia and William B. Kristan.
Biology Department 0357, University of California, San Diego. La Jolla, CA
92093-0357.
APStracts 2:0227N, 1995.
SUMMARY AND CONCLUSIONS
The serotonergic system of the medicinal leech comprises a small number of
iterated, identified neurons, of which the Retzius (Rz) neurons are major
components. Activity in pressure mechanosensory (P) cells sufficient to elicit
locomotory and defensive behaviors also excites Rz neurons. We characterized
the interactions between P and Rz neurons within the ganglion and at different
distances along the nerve cord. ¯Within a ganglion: (1) P cells excited both
Rz neurons, electrically close to the site of electrical coupling between the
Rz neurons; (2) each of the four P cells had similar effects on the Rz
neurons; (3) homologous contralateral P cells shared interneuronal pathways.
These data show that P cells provide nearly identical bilateral information
onto Rz neurons. ¯Along the nerve cord: (1) Every P cell excited Rz neurons
in ganglia anterior and posterior to the site of stimulation; (2) the signal
was carried the entire length of the nerve cord along interneuronal pathways
with similar overall (but regionally different) conduction velocities in the
two directions; (3) the amplitude of the Rz responses was smaller as the
distance to the activated P cell increased; (4) the rate of change of the
amplitude along the cord was larger when the signal traveled from front-to-
back than in the opposite direction. These data shows that mechanosensory
input from any segment could excite Rz neurons along the cord, in proportion
to the intensity of the stimulus.
Received 17 March 1995; accepted in final form 10 July 1995.
APS Manuscript Number J180-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.