Journal of Neuroscience, Vol 5, 2310-2317, Copyright © 1985 by Society for Neuroscience
FMRF-amide-like substances in the leech. II. Bioactivity on the heartbeat system
JR Kuhlman, C Li and RL Calabrese
In the preceding paper (Kuhlman, J. R., C. Li, and R. L. Calabrese (1985)
J. Neurosci. 5: 2301-2309) FMRF-amide-like immunoreactivity was localized
to a specific set of neurons in the leech. Three types of these neurons are
involved in controlling the animal's heartbeat: HE motor neurons and HA
modulatory neurons which directly innervate the hearts, and the
swim-initiating interneurons (cells 204) which can accelerate the heartbeat
central pattern generator. Application of synthetic FMRF-amide had effects
on the hearts and the heartbeat central pattern generator that mimicked the
actions of the HA and cell 204 neurons. Bath application of FMRF-amide
(10(-7) to 10(-6) M) to the hearts activated their myogenic rhythm and
increased their beat tension, thus mimicking the effects of activity in HA
cells. Bath application of lower concentrations of FMRF-amide (10(-9) to
10(-8) M) to the isolated central nervous system dramatically accelerated
the central motor program for heartbeat, thus mimicking the effects of
activity in cell 204. These observations suggest that an FMRF-amide- like
substance may be used as a chemical signal by HA and cell 204 neurons. The
role of the FMRF-amide-like substance contained in HE motor neurons remains
unclear, but it may be released along with the HE cell's neuromuscular
transmitter, acetylcholine.