Structure of intraglomerular dendritic tufts of mitral cells and their contacts with olfactory nerve terminals and calbindin-immunoreactive type 2 periglomerular neurons
K. Kosaka et al., Structure of intraglomerular dendritic tufts of mitral cells and their contacts with olfactory nerve terminals and calbindin-immunoreactive type 2 periglomerular neurons, J COMP NEUR, 440(3), 2001, pp. 219-235
Intraglomerular dendritic tufts of Golgi-impregnated and biotinylated dextr
an amine (BDA)-labeled mitral cells in the rat main olfactory bulb were ana
lyzed in detail. In particular, the relationships of BDA-labeled tufts with
olfactory nerve (ON) terminals and processes of calbindin D-28K-immunoreac
tive (CB-IR) cells were investigated with confocal laser-scanning light mic
roscopic (CLSM) and electron microscopic (EM) analyses. CB-IR cells were ty
pe 2 periglomerular cells that restricted their processes in the ON-free (n
on-ON) zone of the glomerulus and received few synapses from ON terminals.
The mitral tufts varied in complexity, but individual branches were rather
simple, smooth processes that bore some branchlets and spines and extended
more or less in a straight line or a gentle curve rather than winding tortu
ously within glomeruli as though they did not consider the compartmental or
ganization, which consisted of ON and non-ON zones that interdigitated in a
complex manner with one another. Conventional EM analysis revealed that bo
th thin and thick, presumed proximal branches of mitral/tufted cell dendrit
ic tufts received asymmetrical synapses from ON terminals. Correlated CLSM-
EM analysis confirmed direct contacts between the BDA- and CB-labeled proce
sses detected in the CLSM examinations, and synapses were recognized at som
e of those sites. Furthermore, ON terminals and CB-IR processes were distri
buted on both proximal and distal dendritic branches in a more or less mosa
ic pattern. These findings revealed that, on the mitral dendritic tufts, ON
terminals and processes of type 2 periglomerular neurons were not clearly
segregated proximodistally but, rather, were arranged in a mosaic pattern,
which may be important in fine tuning the output from individual glomeruli.
J. Comp. Neurol. 440:219-235, 2001. (C) 2001 Wiley-Liss, Inc.