Identified Octopaminergic Neurons Provide an Arousal Mechanism in the
Locust Brain.
Bacon, Jonathan P., Kevin S.J. Thompson, and Michael Stern.
Sussex Centre for Neuroscience, School of Biological Sciences, University
of Sussex, Brighton, BN1 9QG, U.K., Universit[grave]et Hamburg, Zoologisches
Institut, Neurophysiologie, Martin-Luther-King-Platz, D-20146 Hamburg,
Germany.
APStracts 2:0280N, 1995.
SUMMARY AND CONCLUSIONS
1. Habituation is the declining responsiveness of a neural circuit (or
behaviour) to repetitive stimulation. Dishabituation (or arousal) can be
brought about by the sudden presentation of an additional, novel stimulus. A
clear example of arousal in the locust is provided by the visual system: the
habituated response of the descending contralateral movement detector (DCMD)
interneuron to repetitive visual stimuli can be dishabituated by a variety of
other visual and tactile stimuli. 2. Application of octopamine to the locust
brain and optic lobes dishabituates the DCMD in a manner similar to the effect
of visual and tactile stimulation. 3. The locust CNS contains 2 pairs of
octopamine-immunoreactive cells, the protocerebral medulla 4 (PM4) neurons,
that could potentially mediate this dishabituation effect; PM4 neurons
arborise in the optic lobe, they contain octopamine, and they respond to the
same visual and tactile stimuli which dishabituate the DCMD. 4. To investigate
whether PM4 activity dishabituates the DCMD, we recorded intracellularly from
one of the PM4 neurons while recording extracellularly from the DCMD. When the
PM4 neuron is injected with hyperpolarizing current to render it completely
inactive, the DCMD exhibits its characteristic habituation to a moving visual
stimulus. However, depolarising the PM4 neuron, to produce action potentials
at approximately 20Hz, significantly increases the number of DCMD action
potentials per stimulus. 5. The PM4 neurons may therefore play an important
role in dishabituating the DCMD to novel stimuli. This effect is presumably
mediated by PM4 neurons releasing endogenous octopamine within the optic lobe.
Received 8 May 1995; accepted in final form 29 August 1995.
APS Manuscript Number J307-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.