Journal of Neuroscience, Vol 7, 2794-2806, Copyright © 1987 by Society for Neuroscience
Electrophysiologically identified nigral dopaminergic neurons intracellularly labeled with HRP: light-microscopic analysis
JM Tepper, SF Sawyer and PM Groves
Intracellular recordings were obtained in vivo from neurons of the rat
substantia nigra, pars compacta. Neurons that were identified as
dopaminergic by a variety of electrophysiological criteria, including
antidromic activation from ipsilateral neostriatum or globus pallidus, were
microiontophoretically injected with horseradish peroxidase and examined at
the level of the light microscope. Dopaminergic neurons were of medium size
and had ovoid, polygonal, or fusiform cell bodies that emitted from 3-6
primary dendrites. Much of the sparse and relatively unbranched dendritic
arborization of these neurons remained within pars compacta, except for 1
or 2 large dendrites that were directed ventrally or ventrolaterally into
pars reticulata, roughly perpendicular to the plane of the pars compacta.
In coronal sections, the dendrites of ovoid- or polygonal-shaped pars
compacta neurons were oriented mainly along the dorsoventral axis, whereas
fusiform-shaped neurons had dendrites that were oriented primarily
mediolaterally. Although some of the dendrites of dopaminergic neurons
exhibited variations in diameter, most were not markedly varicose.
Dendrites were sometimes sparsely invested with spinelike appendages or
other dendritic extrusions, particularly along their distal portions. The
axons of dopaminergic pars compacta neurons were emitted from primary or
proximal secondary dendrites, and were extremely fine processes, 0.5 micron
or less in diameter. No local axon collaterals were observed.