Volume 16, Number 16,
Issue of August 15, 1996
pp. 5225-5232
Copyright ©1996 Society for Neuroscience
Haltere Afferents Provide Direct, Electrotonic Input to a
Steering Motor Neuron in the Blowfly, Calliphora
Received April 10, 1996; revised May 28, 1996; accepted May 30, 1996.
Amir Fayyazuddin1 and
Michael H. Dickinson1, 2
1 Committee on Neurobiology and
2 Department of Organismal Biology and Anatomy, The
University of Chicago, Chicago, Illinois 60637
The first basalar muscle (b1) is one of 17 small muscles in flies
that control changes in wing stroke kinematics during steering
maneuvers. The b1 is unique, however, in that it fires a single
phase-locked spike during each wingbeat cycle. The phase-locked firing
of the b1's motor neuron (mnb1) is thought to result from
wingbeat-synchronous mechanosensory input, such as that originating
from the campaniform sensilla at the base of the halteres. Halteres are
sophisticated equilibrium organs of flies that function to detect
angular rotations of the body during flight. We have developed a new
preparation to determine whether the campaniform sensilla at the base
of the halteres are responsible for the phasic activity of b1. Using
intracellular recording and mechanical stimulation, we have found one
identified haltere campaniform field (dF2) that provides strong
synaptic input to the mnb1. This haltere to mnb1 connection consists of
a fast and a slow component. The fast component is monosynaptic,
mediated by an electrical synapse, and thus can follow haltere
stimulation at high frequencies. The slow component is possibly
polysynaptic, mediated by a chemical synapse, and fatigues at high
stimulus frequencies. Thus, the fast monosynaptic electrical pathway
between haltere afferents and mnb1 may be responsible in part for the
phase-locked firing of b1 during flight.
Key words:
haltere;
gap junctions;
sensory motor reflex;
flight;
mechanosensory;
thoracic ganglion