Journal of Neuroscience, Vol 5, 2930-2939, Copyright © 1985 by Society for Neuroscience
Responses to odors mapped in snail tentacle and brain by [14C]-2- deoxyglucose autoradiography
R Chase
The method of 2-deoxyglucose (2-DG) autoradiography has been widely used to
map functional neuronal systems in vertebrates, but in invertebrate
species, where morphological dimensions favor its use, the applications
have been minimal. This study uses [14C]-2-DG to map the olfactory system
of a terrestrial snail, Achatina fulica. The olfactory organ in the snail's
tentacles bears a striking resemblance to the vertebrate olfactory mucosa.
There are also complex neural structures in the tentacle and brain that are
devoted to subsequent processing. These facts make the molluscan olfactory
system a suitable complement to the traditional vertebrate and insect
models in olfaction. The experiments utilized intact snails in which one
tentacle was exposed to a controlled odor environment while the
contralateral tentacle was held in a retracted position. The dose of
[14C]-2-DG (2 microCi/gm) was injected into the hemocele. Tissue processing
involved freeze- substitution with acetone, dry sectioning, and the
preparation of liquid film autoradiographs. Optical density measurements
permitted quantitative comparisons between experimental conditions. The
natural odors of conspecific snails and of carrots elicited significantly
more uptake of 2-DG in the exposed tentacle than in the unexposed tentacle
and, in the exposed tentacle, significantly more label over the axons of
the primary sensory neurons than was elicited by exposure to clean air.
Amyl acetate and octanol were less effective. A small number of
superficially placed sensory neurons were labeled in all stimulus
conditions, including clean air, and may represent the mechanosensors.
Stimulus-dependent labeling in the brain was limited to the procerebrum and
included both neuropilar and cellular parts. In contrast to vertebrate and
insect olfactory systems, there was no evidence of spatial coding for odor
quality.
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