Journal of Neuroscience, Vol 13, 2821-2828, Copyright © 1993 by Society for Neuroscience
Ultrastructural localization of 5'AMP odorant receptor sites on the dendrites of olfactory receptor neurons of the spiny lobster
DN Blaustein, RB Simmons, MF Burgess, CD Derby, M Nishikawa and KS Olson
Department of Biology, Georgia State University, Atlanta 30302-4010.
A unique probe--biotinylated adenosine-5'-monophosphate (5'AMP-biotin)--
was used in transmission electron microscopic (TEM) studies to localize
5'AMP odorant binding sites on the dendrites of olfactory receptor neurons
in the aesthetasc sensilla of the spiny lobster, Panulirus argus. This
probe is capable of both binding to and exciting 5'AMP- sensitive olfactory
receptor neurons, as revealed through biochemical and electrophysiological
assays. TEM studies showed that 5'AMP-biotin binding sites are distributed
along the entire dendritic region that is exposed to odorants, including
the transitional zone (between the inner and outer dendritic segments,
including the ciliary segment) and all of the outer dendritic segment. The
density of 5'AMP binding sites per micron2 of membrane is similar along the
length of the olfactory dendrite. However, the relative number of
5'AMP-biotin binding sites per micron2 of sensillar area diminishes in the
distal 30% of the aesthetasc due to a decrease in the amount of dendritic
membrane in that region. The distribution of these 5'AMP binding sites is
therefore much more extensive than that of enzymes that inactivate 5'AMP--
5'ectonucleotidase/phosphatase--which are restricted to the transitional
zone (Gleeson et al., 1991). Taken together, these results suggest that
5'AMP-biotin is labeling 5'AMP-specific olfactory receptor sites that are
located along the entire outer dendritic segment and that can be coupled to
olfactory transduction. This study represents the first in situ
localization of specific olfactory receptor sites using a specific,
functionally defined ligand.