Hj. Wenzel et al., ULTRASTRUCTURAL-LOCALIZATION OF NEUROTRANSMITTER IMMUNOREACTIVITY IN MOSSY CELL AXONS AND THEIR SYNAPTIC TARGETS IN THE RAT DENTATE GYRUS, Hippocampus, 7(5), 1997, pp. 559-570
Electrophysiologically identified and intracellularly biocytin-labeled
messy cells in the dentate hilus of the rat were studied using electr
on microscopy and postembedding immunogold techniques. Ultrathin secti
ons containing a labeled messy cell or its axon collaterals were react
ed with antisera against the excitatory neurotransmitter glutamate and
against the inhibitory neurotransmitter gamma-aminobutyric acid (GABA
). From single-and double-immunolabeled preparations, we found that 1)
messy cell axon terminals made asymmetric contacts onto postsynaptic
targets in the hilus and stratum moleculare of the dentate gyrus and s
howed immunoreactivity primarily for glutamate, but never for GABA; 2)
in the hilus, glutamate-positive messy cell axon terminals targeted G
ABA-positive dendritic shafts of hilar interneurons and GABA-negative
dendritic spines; and 3) in the inner molecular layer, the messy cell
axon formed asymmetric synapses with dendritic spines associated with
GABA-negative (presumably granule cell) dendrites. The results of this
study support the view that excitatory (glutamatergic) messy cell ter
minals contact GABAergic interneurons and non-GABAergic neurons in the
hilar region and GABA-negative granule cells in the stratum molecular
e. This pattern of connectivity is consistent with the hypothesis that
messy cells provide excitatory feedback to granule cells in a dentate
gyrus associational network and also activate local hilar inhibitory
elements. (C) 1997 Wiley-Liss, Inc.