The Journal of Neuroscience, February 1, 2002, 22(3):766-774
Novel Microglomerular Structures in the Olfactory Bulb of
Mice
Brian W.
Lipscomb1, 2,
Helen B.
Treloar2, and
Charles A.
Greer1, 2, 3
1 Interdepartmental Neuroscience Graduate Program,
2 Department of Neurosurgery, and 3 Section of
Neurobiology, Yale University School of Medicine, New Haven,
Connecticut 06520
The murine olfactory system consists of two primary divisions: (1)
a main olfactory system, in which olfactory sensory neurons (OSNs)
located in the main olfactory epithelium (MOE) send their axons to
glomeruli in the main olfactory bulb (MOB); and (2) an accessory
olfactory system, in which OSNs located in the vomeronasal organ send
their axons to glomeruli in the accessory olfactory bulb (AOB). In
labeling studies using the lectin Ulex europaeus agglutinin (UEA), we discovered a novel subset of small neuropilar structures in the MOB that are distinct from other glomeruli both in
the MOB and AOB. These "microglomeruli" are morphologically similar
to MOB glomeruli in many respects: they receive innervation from
processes present in the olfactory nerve layer and are isolated from
other glomeruli by juxtaglomerular cells; in addition, the compartmental pattern of UEA labeling suggests the presence of UEA
processes within their neuropil.
Microglomeruli contained processes that express the olfactory marker
protein, a marker common to mature OSN axons. However, unlike other
glomerular structures, the microglomeruli did not contain neural
cell adhesion molecule-labeled processes. Within microglomeruli,
UEA+ processes interdigitated with
MAP2+ dendrites, some of which likely originate from
interneurons, as indicated by glutamic acid decarboxylase labeling.
Synaptophysin labeling in microglomeruli strongly suggested that
synapses occur between UEA+ processes and dendrites.
Anterograde labeling of OSNs, by injection of rhodamine-dextran into
one naris, demonstrated that UEA+ processes in
microglomeruli originated in the MOE. The unique morphology, protein
expression, and location of microglomeruli have led us to hypothesize
that they represent a novel class of glomerular structures in the
murine olfactory system.
Key words:
glomeruli; olfactory nerve; Ulex europaeus
agglutinin; NCAM
Copyright © 2002 Society for Neuroscience 0270-6474/02/223766-09$05.00/0