first objective is to investigate the neural control of arousal state. The
Arousal state appears to be controlled by neuromodulatory systems. To
address the issue of arousal at the cellular level, we have initiated a
pharmacological study on the neuromodulation of the cockroachís
locomotory circuitries using known insects neuromodulators as well as an
insect neurotoxin. The wasp Ampulla compressa subdues its prey by injecting
venom apparently directly into the central nervous system. While the vast
majority of venomous insects produce paralysis in their prey, A. compressa
utilizes a unique biochemical strategy: behavioral modulation.
The inflicted prey animal is rendered unable to organize an escape
sequence, but remains ambulatory and is subsequently led by the predator to
a suitable oviposition location, where it serves as a nutritional source
for the wasp's young. It is
hypothesized that the central nervous system of the prey animal loses its
normal ability to activate modulatory circuits involved in behavioral
arousal. The first
specific aim of our resarch is to describe the biochemical composition of A. compressa
venom, and identify the component(s) - termed here
"anti-arousal toxin(s)" (AAT) that are involved in behavioral
modulation of prey. This objective is accomplished through a combination of
liquid chromatography, mass spectrometry and protein sequencing.
Amino acid sequence information of candidate AATs will be used to
construct primers for use in PCR-based amplification of nucleotide
sequences for complete characterization of AAT primary molecular structure.
Our second aim is to determine the venomístarget in the
animalís CNS. We determine the location of venom injection and which
neurons are affected by the venom. By examining the behavior and the
physiology of stung animals, we are exploring the mechanism which controls
the responsiveness of the neuronal escape circuitry. We also study the
effects ofthe neurotoxin on membrane properties of identified neurons and
on synaptic transmission between these neurons. Our third aim is
to verify the identity of candidate AATs by their introduction into the
central nervous system in vivo and in vitro. We will assess their ability
to produce the previously described behavioral and physiological properties
syndrome caused by the natural stinging sequence.
These include lack of the escape response, characterized by failure
of appropriate stimuli to elicit normal escape responses in the prey and
selective failure to recruit fast motoneuron circuitry.
Finally, the last specific aim is to determine the precise
alterations in synaptic transmission and neuronal membrane properties that
underly anti-arousal behavioral modification.
This objective is approached in part through electrophysiological
analyses of pre-and postsynaptic responses to
appropriate escape stimuli. Changes in membrane properties are assayed by measurements of
membrane resistance, excitability and relevant changes in ion channel