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17 juillet 2005
Experientia
1968;24(1):47
lexique
Cyclic variation in the amplitude of a brainstem reflex during sleep and wakefulness
Chase MH, McGinty DJ, Sterman MB.

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In recent years, attention has been drawn to variations in the amplitude of spinal reflexes which ocçur during the different stages of sleep and wakefulness. We were interested in determining if similar variations take place in reflex activity at a brain-stem level. For this purpose we chose as a test reflex the masseteric monosynaptic reflex. It is our intent to determine the fluctuations in brainstem reflex transmission during various behavioral states; the initial ones studied were sleep and wakefulness.
 
A second objective of these studies arose as the result of experiments in acute preparations in which we observed complete inhibition of this reflex and others following orbital-cortical or basal forebrain stimulation. We are presently investigating the behavioral conditions during which the orbital cortex and basal forebrain may induce this reflex inhibition. Our first step, however, was the documentation of the normative variations in the amplitude of the masseteric monosynaptic reflex during sleep and waking states in unanesthetized, unrestrained cats.
 
Each of the 8 adult cats which were studied was prepared in the following manner. While the animal was under sodium methohexital (Brevital) anesthesia, electrodes to induce and record the reflex response, as well as others to monitor the ERG, eye movements, and posterior neck muscle EMG, were permanently fixed in place for chronic recording and stimulation. Anesthesia was then discontinued, the incisions closed, and the animal allowed to recover for a period of one week.
 
Data were collected while the animal was within an environmental chamber to which he had been habituated. The length of each recording session was approximately 5 h. During these sessions a liminally induced reflex was evoked continuously at the rate of 2/sec. In addition to oscilloscopic records of the reflex potentials, we were able to obtain, with the aid of a peakreading amplifying circuit, simultaneous polygraphic records of the amplitude of the reflex motor potential along with the activity of the EEG, eyes, and neck muscles. This method of data collectiôn allowed us to correlate closely variations in reflex amplitude with the specific state of the animal. Sleep and wakefulness were divided into the following 4 states: (1) alert; (2) drowsy; (3) quiet sleep; (4) active sleep.
 
The amplitudes of the reflex motor responses are plotted in histographic form in Figure 1 for the 4 states of sleep and wakefulness. During the alert state a large number of moderate and high-amplitude reflex potentials - as observed (Figure 1A). The drowsy state was characerized by a decrease in the frequency of the highermplitude potentials (Figure 1B), as compared with the lert state. During quiet sleep the mean amplitude of the eflex response decreased when compared with the drowsy tate (Figure 1C). At times during quiet sleep reflex reponses failed to occur following stimulation of the
mesencephalic nucleus. These events are indicated by the frequency of zero amplitude potentials (arrow at zero in figure 1). The majority of the reflex responses was completely suppressed during active sleep (Figure 1D).
 
A statistical analysis of the change in mean amplitude of the reflex during the successive states in the sleep cycle utilized planned comparison tests based on an analysis of variance. The changes in state - waking compared with drowsy, drowsy with quiet sleep, and quiet - sleep with active sleep - were each marked by a significant reduction in the amplitude of the reflex response (p<0.05).
chase