OLFACTORY CONTROL OF A SIMPLE MOTOR SYSTEM

To understand how olfactory information controls certain behaviors, it is
necessary identify neural elements in the central nervous system that
process and relay olfactory information and to determine the mechanisms by
which such elements exert their influence over particular motor acts. In
favorable invertebrate preparations, the sensory afferent pathways and the
neural elements that govern stereotyped behaviors are accessible to
cellular study. These systems therefore serve as useful models for studies
of neural mechanisms leading from sensory inputs to motor outputs. As has
been demonstrated in numerous important cases, insights gained from such
model systems can provide a basis for, and guide research on, less
accessible vertebrate systems. One such useful model is the moth Manduca sexta, in which detection of
certain chemical cues by antennal olfactory receptors stimulates
stereotyped behaviors. For example, the sex pheromones released by a
receptive female trigger a characteristic flight response in a male, by
which he orients and moves toward, and eventually finds the signalling
female for mating. Olfactory information about sex pheromones is processed
in a specialized part of the brain that is found only in the antennal lobes
of normal males and gynandromorphic females (with antennal lobes innervated
by sensory axons from male antennae). Olfactory information integrated in
these and other, "higher" brain centers ultimately descends to thoracic
motor centers and to control flight. By means of intracellular recording and staining, this research will
explore the physiology and structure of nerve cells in the pathway from
olfactory centers in the brain to the flight-motor outputs in the thorax.
The proposed studies will focus on: (1) the control of flight motor
activity by odors (particularly sex pheromones) delivered to the antennae;
(2) descending projection neurons that carry the integrated olfactory
information from the brain to motor centers in the thoracic ganglia of
males and gynandromorphic females; and (3) the roles of identifiable
neurons in the thoracic ganglia as targets of the descending projection
neurons and as possible modulators of flight motor activity. This research
promises to expand our understanding of neural mechanisms of olfaction as
well as of motor control. Learning about the mechanisms by which olfactory
information exerts control over important behaviors in such a model system
will help to fill a major gap in our understanding of the chemical senses
and their roles in normal and abnormal neural and behavioral functions.