THE INFLUENCE OF THYROIDECTOMY ON THE VARIABILITY OF NEUROMUSCULAR ACTIVITY IN THE RAT

Abstract

IT is GENERALLY AGREED that thyroidectomy leads to a reduction in the level of neuromuscular activity (1). The converse, however, does not hold. Feeding thy roid hasbeen shown to result in a decrease rather than an increase in activity (2). The decreasedactivity following thyroidectomy may be attributed in part to lowered levels of excitation and irritability of the nervous system. This hypothesis tends to be confirmed by experiments indicating lowered resistance to narcotics (3), increased thresholds to light and sound stimulations (4), decreased speed of simple reaction to an electric shock (5), and lowered rate of cortical alpha-rhythms (6) in the hypothyroid state. Since the variabilityof behavior is in large part a function of sensitivity to environmental stimuli, andassuming that the thyroid secretion maintains the normal level of irritability of the nervoussystem, it is reasonable to predict that the daytO-day variability of spontaneous activity would be less in hypothyroid than in normal animals.