MICROELECTRODE ANALYSIS OF PYRAMIDAL SYSTEM DURING TRANSITION FROM SLEEP TO WAKEFULNESS

Abstract

A new prepn.[long dash]the "pyramidal" cat[long dash]is descr. This unanesthetized animal, which retains only the continuity of the cerebral peduncles following mesencephalic transection, exhibits spontaneously the characteristic eeg. and behavioral patterns of sleep. Spike potentials have been recorded from the motor cortex of the cerebrum and from its efferent projections in the medulla oblongata through the use of fine wire microelectrodes. The units examined were those which were spontaneously active only during the spindle waves recorded from the surface of the motor cortex. This activity, when present, was intimately correlated with each wave of the spindle complex. Cortical activation, induced either by blowing unfiltered air into the nose or by electrical stimulation of appropriate regions of the thalamus was paralleled by a complete blockade of the spike potentials. This abolition may be a result of the failure of ephaptic excitation or of an active inhibition of the neurons selected for study. Local application of a dilute soln. of strychnine (0.2%) to the motor cortex produced characteristic high frequency outbursts of activity in the intrinsic cerebral neurons and in the corresponding pyramidal tract. The convulsive discharges and the corresponding strychnine waves were completely blocked for short intervals during olfactory or thalamic stimulation. The relation of this phenomenon to the mechanisms involved in the arousal reaction is discussed. More concentrated solns. of strychnine (1%) augmented the frequency of the spike outburst and the amplitude of the cortical wave. Stimuli previously effective in blocking the strychnine complex no longer produced a detectable change.