Journal of Neuroscience, Vol 8, 4565-4575, Copyright © 1988 by Society for Neuroscience
The projection of individual axons from the parabrachial region of the brain stem to the dorsal lateral geniculate nucleus in the cat
DJ Uhlrich, JB Cucchiaro and SM Sherman
Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794.
In mammals, the retinogeniculocortical pathway is the primary afferent
route to visual cortex. The flow of information along this pathway can be
modulated at the thalamic level (i.e., at the lateral geniculate nucleus)
as a function of arousal, attention, and phenomena such as eye movements.
Physiological studies indicate that an important source of this
state-dependent influence on geniculate neuronal responsiveness is the
parabrachial region of the brain stem. We used the anterograde tracer
Phaseolus vulgaris leucoagglutinin to study the anatomical connections
between the parabrachial region and the lateral geniculate nucleus. Labeled
parabrachial axons are found throughout the thalamus, including all laminae
of the lateral geniculate nucleus, the lateral posterior-pulvinar complex,
the ventral lateral geniculate nucleus, the perigeniculate nucleus, and the
reticular nucleus of the thalamus. Within these nuclei, the axons exhibit
sporadically branched terminal arbors with boutons mostly en passant.
Serial reconstructions indicate that individual parabrachial axons that
innervate the lateral geniculate nucleus may terminate in other visual
thalamic nuclei as well, but not in thalamic nuclei that subserve other
modalities. Finally, the labeled parabrachial axons are morphologically
heterogeneous; they differ in their innervation targets, terminal arbor
shape, and the size spectrum of their boutons. These data suggest that this
portion of the ascending parabrachial pathway, which may be functionally
diverse, coordinates the responsiveness of the varied thalamic nuclei
involved with vision.