Multiunit Discharges Research Articles

Analysis of various factors involved in EEG synchronization during milk drinking in the cat

Electroencephalographic (EEG) and multineuronal activity (MUA) from several brain structures were recorded in 11 adult cats during milk drinking. Milk drinking elicited parietal and hippocampal EEG synchronization and inhibited multiunit discharge in several brain regions. The proportion of EEG synchronization varied considerably between animals, but remained more or less constant for each cat after several testing days. Neither modification of milk concentration nor fasting influenced the proportions of EEG synchronization during milk drinking. Adaptation of the animals to the experimental environment facilitated the appearance of EEG synchronization during milk drinking. Chlorpromazine (3 mg/kg) significantly increased the proportion of EEG synchronization observed during milk drinking. By contrast, displacement of the head, neck or postural body adjustments during milk drinking blocked EEG synchronization. Amphetamine also had a suppressive effect on the EEG parietal and hippocampal synchronic activity observed during milk drinking. Our results suggest that development of parietal EEG synchronization in response to pleasant stimulation is a complex phenomenon requiring a relaxed condition of the animal, including its adaptation to the experimental environment and relative immobility with the concomitant diminution of afferent inflow from some of the muscles involved in locomotion.

Postcontraction changes in sensitivity of muscle afferents to static and dynamic stretch

The effects on dynamic and static components of the afferent stretch response from a muscle were examined in the period after a brief tetanus, which previous study has shown is marked by a persisting elevation in sensory discharge. Afferent activity of the cat's triceps surae or medial gastrocnemius muscle was monitored as integrated multiunit discharge in a whole dorsal root, and the ventral roots were stimulated to produced a tetanus. The levels of activity at a static muscle length were found to be elevated in decreasing degree over several millimeters of lengthening beyond that at which the muscle was held during tetanus. During a ramp stretch, the velocity-related overshoot in dorsal root activity was also increased. Such changes were still detected after the elevated discharge had been made to disappear by momentary limited extension of the muscle. They are consistent with the hypothesis of residual effect on the intrafusal fibers, perhaps in the form of persisting actin-myosin crossbridges. Under sinusoidal stretch, the multiunit responses were generally decreased in the first few cycles following tetanus. Observations on single units indicated that the decrease was due chiefly to diminished responses of Ib afferents, which had incompletely recovered from adaptation brought on by excitation during the tetanus.

Observations on the expected decrease in proprioceptive discharge and purported advent of non-proprioceptive activity from the chronically tenotomized muscle

Uncertainties in present understanding of the net effect of chronic tenotomy on muscle sensory activity caused us to make comparisons of the multi-unit discharge from tenotomized medial gastrocnemius muscles in cats and rats. With the calf muscles fully relaxed, the dorsal root activity from the selectively denervated legs was less on the tenotomized side in 15 of 20 chronic cat preparations. In rats, activity recorded from the tenotomized muscle nerve was greater in a 2-week period following tenotomy, but not at later times. At intermediate degrees of stretch of the calf region induced by flexing the ankles activity levels from the tenotomized muscles were consistently less, whether the spindle receptors were passive or under fusimotor activation. However, with the muscles remaining as they had been throughout the chronic period, activity on the tenotomized side sometimes equalled or exceeded that developed contralaterally when flexion of the ankle approached its physiological limit. This observation was significant, since in the behaving animal, the ankle on the experimental side was often seen to be more sharply flexed than in the sound leg. Factors that might contribute to the specious appearance of increased activity in the peripheral nerve are discussed, and arguments adduced against the hypothesis that non-proprioceptive sensory endings are the source of increased discharge after tenotomy.

Electrical activity in neocortical projection and association areas during slow wave sleep

Both EEG activity and multiunit discharges have been simultaneously recorded by transcortical electrode couples from different neocortical projection and association areas in the chronically implanted cat. Slow wave sleep (SWS) is characterized by the occurrence of surface negative slow waves (NSWs) systematically accompanied by a concomitant decrease in unitary discharges. Statistical study of the importance, spread and synchronization of these patterns in the different areas has been performed. NSWs of association areas are of higher amplitude than those of projection areas. The simultaneous decrease in the number of spikes is also more important. In the middle suprasylvian area, where a total discharge suppression occurs during NSWs, the wave amplitude is directly related to the duration of the unit activity pause. During the same SWS stage, two forms of sleep can be distinguished and may alternate many times. In the first form, occuring just after drowsiness, NSWs are rare in the auditory area and NSWs of primary areas only spread to the nearest association area. When this form changes into the second one, NSWs increase in number on auditory and association areas, while NSWs from visual and somesthetic areas extend to the whole association cortex. In both forms, visual area NSWs occur with a 50 msec lag when compared with those recorded simultaneously from association areas. NSWs may be considered as the EEG evidence of cortical inhibition, the characteristics of which might be correlated to some of the psycho-physiological changes observed during SWS.

A selective control of olfactory bulb electrical activity in relation to food deprivation and satiety in rats

The possible role of centrifugal neural pathways in a feedback control of the olfactory input related to regulatory mechanisms of feeding behavior, has been investigated in rats. Bipolar electrodes were chronically and bilaterally implanted and multiunit discharges of the mitral cell layer recorded in unanesthetized rats. From the basal level of integrated activity, three types of responses to odor stimulations were considered: positive (enhanced), negative (inhibited) and null (unchanged). Rats were tested in a first group either hungry, after food deprivation or satiated, immediately after a single 2hr-daily meal. In a second group, they were tested either hungry under the effect of 20 U/kg body weight, of injected insulin, or satiated after their daily meal. In both groups, rats either hungry or satiated, were stimulated in test series by two different odors: (a) the odor of their familiar stock-diet; and, (b) a control odor: isoamyl acetate in the first group, citral in the second. Stimulated by the food odor, food-deprived and insulin treated rats exhibited positive responses. They exhibited, when satiated, significantly different negative responses. Stimulated by control odors, rats either hungry or satiated showed a same pattern of negative or null responses. Results are discussed in terms of a motivation dependant feedback control of the olfactory input in which the anatomically identified olfacto-hypothalamic loop is likely involved.

Activité multi-unitaire de structures sous-corticales pendant le cycle veille-sommeil chez le chat

1. 1. Spontaneous multi-unit discharges have been studied during the sleep-wakefulness cycle in cats with chronically implanted electrodes. Fine tipped recording electrodes were placed in pontine reticular formation (PRF), mesencephalic reticular formation (MRF), raphe nuclei and hypothalamus. The discharges were transformed into a continuous integration curve in which the voltage was a function of frequency and amplitude. 2. 2. During slow wave sleep (SWS) the integration curve lowered progressively for all the structures recorded, indicating a decrease in activity. Furthermore, for the raphe nuclei, brief elevations of this curve were observed to be related to the occurrence of spindles. 3. 3. During the transition between SWS and sleep with fast cortical activity (paradoxical sleep, PS), the integration curve generally showed: for the raphe nuclei, a progressive elevation preceding the onset of PS by 20–50 sec; in the MRF and hypothalamus, an increase occurring later, at the time of cortical activation; in the PRF, no change. Only one of the sites (anterior hypothalamus) showed a decrease in the integration curve during the SWS-PS transition. 4. 4. During PS the curve was tonically elevated for raphe nuclei, MRF and hypothalamus, but remained at the SWS level for the PRF. During the phasic events of PS, especially bursts of rapid eye movements, sudden peaks of higher voltage were observed in the integration curve. These peaks were predominantly found in the PRF where they constituted the only variation observed; for the raphe nuclei and caudal portion of the MRF the peaks were superimposed on the tonic high level of activity. By contrast, the peaks were not observed for the anterior portion of the MRF and for the hypothalamus. 5. 5. Phasic phenomena induced by administration of reserpine were also accompanied by peaks of the integration curve, but only for the PRF. 6. 6. These results suggest, so far as PS is concerned, that the raphe nuclei may play an inducing role; the MRF may be implicated in maintenance of cortical activation and PRF may be a source of the brief depolarizations associated with phasic events.