Journal of Neuroscience, Vol 9, 1375-1388, Copyright © 1989 by Society for Neuroscience
A morphometric analysis of functionally defined subpopulations of neurons in the paraventricular nucleus of the rat with observations on the effects of colchicine
JH Rho and LW Swanson
Neural Systems Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037.
Two populations of neurons in the paraventricular nucleus of the
hypothalamus that have different efferent projections and physiological
roles in the regulation of visceral responses were characterized
morphologically with a combined intracellular filling, retrograde tracer,
and immunohistochemical method. Neuroendocrine cells were retrogradely
labeled by an intravenous injection of Fast blue, and distinguished from
descending neurons that were retrogradely labeled by an injection of
fluorogold into the spinal cord. Retrogradely labeled neurons were
selectively penetrated and filled intracellularly with Lucifer yellow to
visualize detailed features of their morphology. Corticotropin-releasing
hormone (CRH)-containing neurons were distinguished from other
neuroendocrine cells by immunostaining the tissue with an antiserum to rat
CRH. Morphometric features of defined populations of neurons were then
quantified and reconstructed graphically to generate multicellular montage
drawings that demonstrate their spatial organization. Descending neurons
were further separated into dorsal and ventral medial parvicellular
components, while the neuroendocrine population was differentiated into
parvicellular and magnocellular groups. The mean somal areas, total
dendritic lengths, and spine densities were compared between groups of
neurons, and these showed significant differences across cell types. These
measures were also dramatically affected by colchicine, which appears to
induce the formation of new dendritic appendages, swelling of the soma, and
reduction of dendritic length. Whether colchicine is acting directly upon
cytoskeletal structures or indirectly by altering the physiology of the
cell is unclear. However, the precise effects of colchicine on mean somal
area, total dendritic length, and spine density appear to be dependent upon
individual cell type. Colchicine may therefore act in a nonspecific, but
nonetheless highly selective, manner in disrupting an endogenous mechanism
regulating the number, morphology, and location of spines.