Neurotoxic effects of colchicine: differential susceptibility of CNS neuronal populations.

Colchicine injected into the dentate gyrus of the hippocampus in adult rats preferentially destroys dentate granule cells. In the present study, we examine the light- and electron-microscopic correlates of the degeneration and evaluate whether the selectivity is preserved across the range of doses between 0.18 and 25 micrograms. Colchicine in a similar dose range was also injected into the cerebellum, olfactory bulb, striatum and cerebral cortex to examine local and regional differences in susceptibility to colchicine. The morphological changes accompanying degeneration in the dentate gyrus include fragmentation of the granule cell layer, appearance of small dark staining bodies in the cell layer, massive microglial invasion and profound disruption of granule cell axons and dendrites. Electron-microscopic observations suggest that the small dark bodies are probably condensed nuclei. The preferential vulnerability of dentate granule cells following intrahippocampal injection was observed at all doses. At doses between 0.18 and 2.5 micrograms there was little evidence of damage to neurons other than dentate granule cells. At the highest dose tested (25 micrograms) some pyramidal cells of regio superior near the injection site were destroyed, while granule cell destruction extended several mm from the injection site. Injection of 0.5-25 micrograms into the cerebellum resulted in the destruction of both granule cells and Purkinje cells, while cells which appeared to be neurons in the molecular layer were less affected. Following injection of 0.5 microgram into the olfactory bulb, granule cells were extensively destroyed and there appeared to be some loss of mitral cells and an overall shrinkage of the injected bulb. Neuronal destruction in the striatum was observed with colchicine injections ranging from 2.5 to 25 micrograms, but at a given dose, the destruction was less extensive than for any other region tested except cerebral cortex. A possible application of this method and the implications of these results for other investigators using colchicine in the brain are discussed.

On the role of hippocampal connections in the performance of place and cue tasks: comparisons with damage to hippocampus.

Behavioral changes following interruption of the main connections of hippocampus and closely related areas (entorhinal cortex, mammillary bodies, dentate gyrus) were determined and compared with findings of previous research that involved direct damage to hippocampus. By a within-subjects design, rats were trained to run in a radial maze with a procedure that involved two kinds of learning (place and cue) and two memory functions (working and reference memory). Rats with fimbria-fornix and entorhinal cortex lesions were impaired on both the place and the cue task. Specifically, the animals suffered a general impairment in working memory on both tasks but were impaired in reference memory only on the place task. Animals with lesions of the dentate gyrus and mammillary bodies were able to perform the complex place and cue tasks with minimal problems. In previous research it was found that direct damage to hippocampus (including all cell fields, alveus, fimbria) resulted in impaired performance only on the place task (Jarrard, 1983). Taken together, these findings indicate that interruption of hippocampal input/output pathways and/or damaging some closely related structures has a greater effect on the behaviors studied than does direct damage to hippocampus.

Fate of afferents to the dentate gyrus following destruction of granule cells with colchicine.

Granule cells of the dentate gyrus can be selectively destroyed by intrahippocampal injections of colchicine. The present study evaluates the consequences of this selective neuronal destruction on the afferent axon terminals which have been deprived of their normal targets. The area of the neuropil in the dentate gyrus (the molecular layer) was evaluated in sections stained using the Timm's method for heavy metals, which selectively marks the terminal fields of the different afferent systems. The molecular layer was examined electron microscopically to determine the fate of afferent terminals. Anterograde transport of HRP or [3H]proline was used to define the location and extent of afferent terminal fields of the entorhinal and commissural projections to the dentate gyrus in which the granule cells had been destroyed. There was a substantial reduction in the size of the dentate gyrus molecular layer after destruction of granule cells with colchicine. Electron microscopic analyses revealed that there were very few axon terminals or synapses remaining in the shrunken molecular layer. Tract tracing methods revealed that both the entorhinal and commissural pathways were still present in their normal terminal zones in the dentate gyrus, however, the density of the projections was greatly reduced. There was no evidence to suggest the formation of ectopic projections to unusual locations, such as the contralateral dentate gyrus. Pathways passing through the hippocampus appeared to survive the colchicine injections. These results suggest that target destruction in adult animals leads to the disappearance of the afferent axon terminals which normally innervate the cells which die.

Retrograde regulation of neuronal size in the entorhinal cortex: consequences of the destruction of dentate gyrus granule cells with colchicine.

Studies in developing animals have documented that manipulations which increase or decrease the size of a neuron's axon arbor lead to increases or decreases respectively in the size of the neuron's soma. The present study evaluates whether similar dependencies exist in adult animals, by analyzing changes in cell size in the entorhinal cortex after selective destruction of dentate granule cells with colchicine. Neurons in layer II of the entorhinal cortex which had been deprived of their normal targets decreased in size by 32% relative to their contralateral homologs. Neurons in layer III which project to regio superior of the hippocampus were affected to only a slight extent, decreasing in size by 8% relative to their contralateral homologs. Neurons in layer V, which do not project to the hippocampus, were unaffected by colchicine injections into the hippocampus. These results indicate that neurons in adult animals which retract terminal arbors as a consequence of target loss also decrease in size.

Comparison of the neurotoxic effects of colchicine, the vinca alkaloids, and other microtubule poisons.

Previous studies have revealed that colchicine is selectively toxic to certain neuronal populations in the CNS, particularly granule cells of the dentate gyrus. The present study evaluates whether other microtubule poisons exhibit similar neurotoxic effects. Equimolar solutions of colchicine, colcemid, podophyllotoxin, vinblastine, vincristine and lumicolchine, the non-binding analog of colchicine, were injected into the dentate gyrus. Neurotoxicity was evaluated histologically. As previously reported, colchicine selectively destroyed dentate granule cells with minimal damage to other neurons including hippocampal pyramidal cells. Vincristine was very toxic and was not selective for granule cells. Vinblastine was relatively selective in destroying granule cells, but was not as potent as colchine. Colcemid and podophyllotoxin had minimal toxic effects. Lumicolchine injections caused no more damage than injections of vehicle. This ordering appears to correlate with the reversibility of binding tubulin.

Neurotoxicity of colchicine and other tubulin-binding agents: a selective vulnerability of certain neurons to the disruption of microtubules.

Colchicine and certain other agents which disrupt microtubules and interfere with axonal and dendritic transport are highly toxic to certain CNS neurons. The present chapter summarizes our knowledge about this selective neurotoxicity. Injections of colchicine into several bran regions lead to the death of selected populations of neurons within those regions. Intra-hippocampal injections selectively destroy granule cells of the dentate gyrus; hippocampal pyramidal cells are essentially unaffected. Injections into the cerebellum, olfactory bulb, and caudate nucleus also destroy resident neurons. In these areas several cell types are vulnerable. Neurons of the cerebral cortex appear to be much less affected by colchicine, although some neurons of paleocortical regions are vulnerable. Colchicine does not appear to be an excitotoxin like kainic acid. The neurotoxicity of colchicine appears to be related to the destruction of microtubules, since other agents which disrupt microtubules have similar toxic effects, and since analogs of colchicine which do not disrupt microtubules are non-toxic. Colchicine may induce an autotoxic response which leads to neuronal death in certain populations due to the accumulation of some toxic cellular product which is normally transported by a microtubule-dependent process. The selective vulnerability of neurons to the neurotoxic effects of colchicine may be a model for system degenerations of the central nervous system in which certain subpopulations of neurons are selectively vulnerable to abnormal accumulations of metabolic products.

Preferential neurotoxicity of colchicine for granule cells of the dentate gyrus of the adult rat.

Injections of 5-7 microgram (6-9 nmol) of colchicine into the dentate gyrus of the hippocampus of mature rats result in widespread destruction of dentate granule cells with little, if any, damage to other cell populations, including hippocampal pyramidal cells. Selective destruction of dentate granule cells is also observed after intraventricular injections. The destructive effects of colchicine appear as soon as 12 hr after the injection and lead to the disappearance of the granule cells over a period of days. Whereas the effects on nongranule cell populations in the hippocampus appear to be reversed by approximately 11 days after injection, the granule cells are almost completely absent at long intervals after injection. At the long postinjection survival intervals the disappearance of the granule cells is accompanied by elimination of their terminal projections, the mossy fibers, as revealed by Timm staining for heavy metals. Because the preferential neurotoxic effects of colchicine do not result in morbidity or obvious behavioral debilitation, the toxicity may prove useful for studying the functional consequences of removing specific cell populations in the central nervous system.

Experience with botulinum toxin in the treatment of cerebral palsy.

OBJECTIVES: To assess the effect of botulinum toxin on dynamic spasticity and dystonic posturing in children with cerebral palsy. DESIGN: Assessment and documentation of the motor disability of children with cerebral palsy followed by injection of botulinum toxin into selected muscle groups. Reassessment of motor function after injection. SUBJECTS: Fifteen children with cerebral palsy: 5 with dynamic spasticity, 5 with dystonia and 5 with a mixed picture. RESULTS: On a standard scoring system, 13 of the children showed improved function at reassessment. CONCLUSION: Intramuscular injection of botulinum toxin is effective in the treatment of selected children with spastic and dystonic forms of cerebral palsy. Improvement is not permanent, but the injection can be repeated.