Journal of Neuroscience, Vol 8, 445-457, Copyright © 1988 by Society for Neuroscience
Ectopic dendritogenesis and associated synapse formation in swainsonine- induced neuronal storage disease
SU Walkley, DA Siegel and S Wurzelmann
Department of Neuroscience, Rose F. Kennedy Center for Research in Mental Retardation and Human Development, Albert Einstein College of Medicine, Bronx, New York 10461.
Ectopic dendrite growth and new synapse formation are known to occur on
select kinds of neurons in a wide variety of neuronal storage diseases. As
these changes in connectivity occur just proximal to the axonal initial
segment, it has been hypothesized that they underlie the generation of
abnormal neuronal function in these diseases. We have studied certain
aspects of this phenomenon through the use of a plant- derived indolizadine
alkaloid, swainsonine, which specifically inhibits the lysosomal hydrolase,
alpha-mannosidase. These studies fully document the close morphological
similarity between swainsonine-induced and inherited feline
alpha-mannosidosis. This includes the presence of clear and floccule-filled
storage vacuoles, as seen with routine EM, and axon hillock neurite growth
on select cell types, as seen with Golgi staining. The latter was found
only on cortical pyramidal neurons and multipolar cells of amygdala, and
these same cell types are known to be involved in ectopic neuritogenesis in
other storage diseases. Combined Golgi-electron-microscopic studies
demonstrated the presence of normal-appearing synapses on these aberrant
neuritic processes and also unusual, membranous inclusions specifically
within the neurite- bearing pyramidal cells. The latter may be indicative
of unique metabolic changes in these neurons and is consistent with the
hypothesis that storage of gangliosides or other glycolipids underlies the
recapitulation of dendritic growth features in these diseases. Experimental
manipulation of the disease process using the swainsonine model indicated
that induction of cortical pyramidal neuron neurite growth could be
influenced by both age of onset and intensity of intraneuronal storage.
Although Golgi studies clearly demonstrated neuritic sprouting in animals
with disease onset as late as at 1 year, cortical pyramidal cells of older,
adult animals appeared to undergo significant storage without a similar
induction of neurite growth. These studies support the view that induced
neuritogenesis in neuronal storage disease is associated with changes in
metabolism, specifically within the neurite-bearing cells, that this change
possibly involves gangliosides, and that the neuritogenic response may be
limited to pre- adult stages of brain maturation.