SELECTIVE DISTRIBUTION OF THE NMDA-R1 GLUTAMATE-RECEPTOR IN ASTROCYTES AND PRESYNAPTIC AXON TERMINALS IN THE NUCLEUS LOCUS-COERULEUS OF THERAT-BRAIN - AN IMMUNOELECTRON MICROSCOPIC STUDY
Ej. Vanbockstaele et Eeo. Colago, SELECTIVE DISTRIBUTION OF THE NMDA-R1 GLUTAMATE-RECEPTOR IN ASTROCYTES AND PRESYNAPTIC AXON TERMINALS IN THE NUCLEUS LOCUS-COERULEUS OF THERAT-BRAIN - AN IMMUNOELECTRON MICROSCOPIC STUDY, Journal of comparative neurology, 369(4), 1996, pp. 483-496
The regional and cellular distribution of the different classes of exc
itatory amino acid receptors with respect to the noradrenergic neurons
of the nucleus locus coeruleus (LC) are unknown. We therefore combine
d immunoperoxidase labeling for the R1 subunit of the N-methy-D-aspart
ate (NMDA) receptor with immunogold-silver localization of the catecho
lamine synthesizing enzyme, tyrosine hydroxylase (TH), in single secti
ons through the rat LC to determine the subcellular localization of th
is glutamate receptor subtype with respect to the noradrenergic neuron
s. At the light microscopic level, there was light to moderate labelin
g for the NMDA-R1-like (li) receptor in the caudal pole of the LC and
dense labeling in the dorsolateral aspect of the LC adjacent to the su
perior cerebellar peduncle. In the rostral pole of the LC which is enr
iched with noradrenergic dendrites, significant overlap between both i
mmunoreactivities could be observed. At the ultrastructural level, imm
unoperoxidase labeling for NMDA-R1 was selectively distributed in astr
ocytic processes and within presynaptic axon terminals but was rarely
seen in catecholamine-containing somata or dendrites. Peroxidase label
ing for NMDA-R1, however, was occasionally observed in dendrites in th
e rostral pole of the LC. Most of these dendrites lacked detectable le
vels of TH, although TH immunoreactivity was apparent in the neuropil.
Dendrites containing NMDA-R1-li immunoreactivity often received asymm
etric (excitatory-type) contacts from unlabeled terminals. NMDA-R1-li-
immunoreactive axon terminals usually contained small clear, as well a
s large dense-core vesicles and were often apposed to unlabeled dendri
tes, axon terminals and/or glial processes. These results provide the
first ultrastructural evidence that NMDA-R1-li immunoreactivity is sel
ectively distributed within astrocytic processes and presynaptic axon
terminals within the LC. (C) 1996 Wiley-Liss, Inc.