Posthypoxic myoclonus in the rat: natural history, stability, and serotonergic influences

Movement disorders after resuscitation from cardiac arrest

It is difficult to predict precisely the final neurologic outcome from cardiac arrest and accompanying cerebral hypoxia. Although rare, several movement disorders may arise as a consequence of hypoxic injury, including myoclonus, dystonia, akinetic-rigid syndromes, tremor, and chorea. Dys-function of various portions of the central nervous system, including the basal ganglia, thalamus, midbrain, and cerebellum, is implicated in the pathogenesis of these posthypoxic movement disorders. The development of animal models of posthypoxic movement disorders and of newer imaging techniques applied to human patients who have movement disorders after hypoxic episodes has improved understanding of the pathophysiology of posthypoxic movement disorders and has suggested newer treatments. Many outstanding questions remain, however. What factors promote susceptibility to the development of posthypoxic movement disorders? Why do patients who have similar clinical hypoxic insults develop markedly dis-similar movement disorders? Why are the basal ganglia especially vulnerable to cerebral hypoxia? Why do some movement disorders occur in delayed fashion and progress for years after the hypoxic insult? Is the pathogenesis of progressive posthypoxic movement disorders related to that of neurodegenerative diseases? What are the most effective medications for the various posthypoxic movement disorders? Is there a role for deep brain stimulation in the treatment of posthypoxic movement disorders? We anticipate that current and future research in the area of posthypoxic movement disorders will reveal answers to some of these important questions.

Estrogen supplementation in the posthypoxic myoclonus rat model

The objective of the study was to investigate the effects of estrogen on severity and duration of myoclonus in the rat cardiac arrest model of posthypoxic myoclonus. Female sex hormones affect a variety of movement disorders and alter dopaminergic and serotonergic pharmacology. Although women represented three-fourths of patients from the original report of Lance and Adams and 80% of the largest published series, the impact of estrogens on myoclonus has never been studied. Twelve previously ovariectomized female rats underwent 8 minutes of mechanically induced cardiac arrest and were resuscitated according to a standardized protocol. On the same day, they were randomly assigned to subcutaneous treatment with a 21-day, 0.5-mg, 17 beta-estradiol or matching placebo pellet. Animals were tested daily with 7 sets of 45 auditory stimuli for 10 days, and myoclonus scores were obtained using a 5-point interval scale. Comparisons were based on two-sample Wilcoxon rank-sum tests. Estrogen treatment significantly enhanced myoclonus intensity and duration: mean peak myoclonus score, 210.2 +/- 18.0 versus 180 +/- 28.5 (p = 0.031); mean number of days above baseline, 9.2 +/- 0.4 versus 5.7 +/- 2.3 (p = 0.004); mean score on day 10, 90.7 +/- 38.7 versus 27.0 +/- 20.6 (p = 0.016). All estrogen-treated animals were above baseline on day 10 compared with none in the placebo group. Estrogen enhances and prolongs posthypoxic myoclonus, suggesting that female gender and estrogen status may play a pivotal role as a risk factor for human posthypoxic myoclonus.