Journal of Neuroscience, Vol 7, 3171-3190, Copyright © 1987 by Society for Neuroscience
Light microscopic immunocytochemical localization of pyruvate dehydrogenase complex in rat brain: topographical distribution and relation to cholinergic and catecholaminergic nuclei
TA Milner, C Aoki, KF Sheu, JP Blass and VM Pickel
Department of Neurology, Cornell University Medical College, New York, New York 10021.
Pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12 and EC
1.6.4.3) includes 3 catalytically active mitochondrial enzymes involved in
the formation of cellular energy through the tricarboxylic acid cycle and
in the synthesis of ACh. We sought to determine whether
immunocytochemically detected PDHC was enriched in neurons of the rat CNS,
and, if so, whether the perikarya containing higher levels of PDHC
immunoreactivity were differentially distributed with respect to their size
or location within nuclear groups containing ACh, catecholamines or other
unidentified transmitters. Under the labeling conditions used in this
study, the peroxidase-antiperoxidase immunoreaction product for PDHC was
detectable principally in neuronal perikarya. The intensity of
immunoreactivity within perikarya was variable as judged visually and by
cellular, computer-assisted densitometry. In the forebrain, the most
intensely labeled perikarya were seen in the medial septal nuclei, the
nuclei of the diagonal band, the nuclei basalis, the dorsal and ventral
striatum, and the entorhinal cortex. More caudally, intense
immunoreactivity was detected in perikarya in the supraoptic hypothalamic
nuclei, reticular thalamic nuclei, lateral substantia nigra, most of the
tegmental nuclei, lateral nuclei of the trapezoid body, raphe pontis and
obscuris, and the caudal part of the lateral reticular nuclei. In addition,
many of the motor nuclei of the cranial nerves, including the dorsal motor
nuclei of the vagus and the hypoglossal nuclei, and the nucleus ambiguus
contained perikarya with intense PDHC labeling. Densitometry revealed no
differences in intensity of immunoreactivity in soma of varying sizes.
However, the intensity of neuronal labeling for PDHC was significantly
greater in several nuclear groups that were shown in adjacent sections to
contain cholinergic, but not catecholaminergic, enzymes. In contrast, the
primary olfactory cortex, pyramidal cell layer of the regio inferior of
hippocampus, and the Purkinje cell layer of the cerebellum were regions
having perikarya with intense PDHC immunoreactivity but lacking both the
synthetic and the degradative enzymes for ACh. These results provide the
first morphological evidence that PDHC, a general metabolic enzyme complex,
is enriched in selective perikarya that are heterogeneously distributed in
brain and are especially abundant in many of the regions containing
cholinergic neurons. The heterogeneity of PDHC immunoreactivity suggests
that certain cholinergic as well as noncholinergic nuclei may be
selectively vulnerable to mitochondrial diseases involving pyruvate
utilization.