Journal of Neuroscience, Vol 7, 1741-1751, Copyright © 1987 by Society for Neuroscience
Immunocytochemical and pharmacological evidence for GABAergic spiking local interneurons in the locust
AH Watson and M Burrows
In the locust thoracic nervous system, spiking local interneurons within a
ventral midline population are stained by a polyclonal antibody raised
against GABA. Their cell bodies, their primary neurites in ventral
commissure II, and their prominent neurites in the perpendicular tract
linking ventral and dorsal fields of fine branches are all stained.
Individual interneurons in this population were labeled with Lucifer yellow
after their receptive fields had been determined physiologically. Alternate
sections were stained with the antibody. Some, but not all, of the spiking
local interneurons labeled with Lucifer yellow are also stained with the
antibody. Apart from having somata that lie more posteriorly within the
midline population, the antibody-stained interneurons cannot be
distinguished on morphological or physiological grounds from those that are
unstained. The way in which this cytochemical heterogeneity within an
otherwise homogenous population might arise during development is
discussed. A second group of spiking local interneurons with similar
sensory input to that of the ventral midline population, but with cell
bodies in the anterior lateral region of the ganglion and primary neurites
in ventral commissure I, are not stained. Interneurons in the midline group
receive direct inputs from sensory neurons and some directly inhibit
particular leg motor neurons that mediate interjoint and tactile reflexes.
Picrotoxin reversibly blocks the inhibition of the motor neurons and
therefore abolishes these reflexes. Immunocytochemical and pharmacological
experiments thus suggest that inhibition by some spiking local interneurons
may be mediated by GABA.