Transmembrane signaling events at the dendrites and axons of olfactory rece
ptor neurons mediate distinct functions. Whereas odorant recognition and ch
emosensory transduction occur at the dendritic membranes of olfactory neuro
ns, signal propagation, axon sorting and target innervation are functions o
f their axons. The roles of G proteins in transmembrane signaling at the de
ndrites have been studied extensively, but axonal G proteins have not been
investigated in detail. We used immunohistochemistry to visualize expressio
n of or subunits of G(0) and G(i2) in the mouse olfactory system. G(0) is e
xpressed ubiquitously on axons of olfactory receptor neurons throughout the
olfactory neuroepithelium and in virtually all glomeruli in the main olfac
tory bulb. In contrast, expression of G(i2) is restricted to a sub-populati
on of olfactory neurons, along the dorsal septum and the dorsal recess of t
he nasal cavity, which projects primarily to medial regions of the olfactor
y bulb, with the exception of glomeruli adjacent to the pathway of the vome
ronasal nerve. In contrast to the overlapping expression patterns of G(0) a
nd G(i2) in the main olfactory system, neurons expressing G(0) and those ex
pressing G(i2) in the accessory olfactory bulb are more clearly separated,
in agreement with previous studies. Vomeronasal axons terminating in glomer
uli in the rostral region of the accessory olfactory bulb express G(i2), wh
ereas those projecting to the caudal region express G(0). Characterization
of the expression patterns of G(i2) and G(0) in the olfactory projection is
essential for future studies aimed at relating transmembrane signaling eve
nts to signal propagation, axon sorting and target innervation. (C) 1999 El
sevier Science B.V. All rights reserved.