Afferent Electrical Stimulation Research Articles

The responses of a single neuron of the vestibular nuclei to caloric stimulation in the cat.

Numerous studies on electrophysiological aspects of the single neuron in the vestibular nuclei have been presented since the investigation by Adrian (1). The vestibular nuclei consist of four groups: Schwalbe's, Bechterew's, Deiters' and Roller's nuclei. Among them the Deiters' nucleus is located in the most lateral region and its nerve cells are the largest in size. The pattern of the afferent and efferent fiber connections of the central vestibular system is extremely complex. The vestibular nuclei project the ascending fibers to the flocculonodular lobe and fastigial nucleus of cerebellum and to the reticular formation and motor nuclei in the brain stem. The descending fibers terminate near the spinal motor cells passing through the lateral vestibulo-spinal tract (2-7). There are several technical difficulties for recording the unitary discharges from the vestibular nuclei. Orientation of the structure is somewhat uncertain due to covering by the cerebellum. Vertical insertion of the microelectrode is obstructed by the tentorium cerebelli, and respiratory movement evokes the fluctuation of the recording areas. Many efforts to eliminate the difficulties, such as deep anesthesia, application of muscle relaxants and resection of the cerebellum have hitherto been devised. However, these procedures may affect the vestibular activity. Relative long-term recordings of the unitary discharges from the same single neuron in the vestibular nuclei have been developed by improvement of the microelectrode technique and the stable immobilization technique of the recording sites (8-11), but most of these experiments have been carried out in the anesthetized animals. In order to investigate the function of the vestibular nuclei in the experimental animals, following stimuli have been employed: afferent electrical stimulation of the vestibular nerve (12-20), postural rotation (14, 15, 21-24), tilting (21, 25-27), acoustic stimuli (28, 29), proprioceptive stimulation of the extremities (2, 30) and caloric stimulation (24, 31-34). Recently, direct and nongravidity stimulation in space attitude is also introduced (35). It is well-known that caloric stimulation is originally a clinical test of the vestibular function as the reliable diagnosis method for lesions of the vestibular system, but the responses of the vestibular nuclei to caloric stimulation in the unanesthetized animals still remain to be settled. In the present experiments, an attempt has been made to know the responses of the unitary discharges in the vestibular nuclei, mainly in the Deiters' nucleus, to caloric stimulation of the middle ear cavity in the pentobarbital-anesthetized cats and in the encephale isole preparations of unanesthetized cats.

EFFECTS OF DECASERPINE ON THE ELECTROENCEPHALOGRAM OF RABBIT

The dissociation between EEG and behavior produced by reserpine in rabbit was firstly demonstrated by Rinaldi and Himwich (1). Kikuchi (2) confirmed the result that the increase of the component of the resting waves in EEG at early period of reserpine action was followed by the arousal waves. He observed the appearance of the arousal waves of EEG in all of the animals which showed a clear-cut marked sedation during 4 to 10 hours after the administration of reserpine. He further showed that the pretreatment of rabbit with methamphetamine reversed the effect of reserpine on EEG. In the early period of reserpine action the EEG of rabbit showed an arousal pattern, and later it exhibited a pattern of the resting waves, which was observed within 10 hours or more after the administration. The pharmacological effects of decaserpine (10-methoxy deserpidine) have been reported by Mir and Lewis (3). Decaserpine did not produce sedation in a variety of animals and even large doses of decaserpine did not prolong barbiturate sleep in mice. The drug did not also produce ptosis or diarrhoea. However, when the initial blood pressure was considerably high in cat, the administration of decaserpine produced a gradual fall, and the same procedure depressed the pressor response elicited by electrical afferent stimulation of the cervical vagal nerve. The depletion of catecholamine in the brain, atrium and adrenal gland by the intravenous injection of decaserpine in rabbit has been shown by Higuchi et al. (4). The decrease of the level of brain noradrenaline was maximal about three hours after the injection. The duration of the depletion of brain noradrenaline produced by the intravenous injection of decaserpine was shorter than that produced by the sane procedure of reserpine. The decrease of the level of brain noradrenaline caused by decaserpine almost recovered twelve hours after the injection. The depletion of noradrenaline in brain shown by Higuchi et al. (4) urged strongly the present study of the effect of decaserpine on the spontaneous EEG in rabbit.

Changes in prepyriform evoked potential with food deprivation and consumption

Measurements on six cats of the mean absolute amplitude of prepyriform spontaneous activity disclosed that major changes took place under four conditions: (a) closure of the nostrils; (b) food deprivation; (c) food consumption; and (d) arousal from rest to readiness for overt action. These implied that measurable cortical activity was dependent on factors including stimulus input to the cortex, attentiveness to the input, motivation, and the initiation of an overt response. A search was made for concomitant changes in prepyriform evoked potential, on the assumption that constant intensity, afferent electrical stimulation would provide the basis for measuring changes in excitability of the cortex. Variations in attentiveness of the cats to the stimuli were reduced by daily electrical stimulation leading to habituation; several weeks of stimulation were required to achieve long-term stability. Two types of change were then observed in the frequency-response curves: an over-all increase in amplitude with deprivation; and a decrease in peakedness of the curves with the onset of food consumption. These two changes were also found in potentials evoked in cats made attentive to the electrical stimulus by conditioning to press a bar for milk on receipt of the stimulus. They were obscured by overlapping changes in the evoked potential of the type previously correlated with changes in attention. Separation of the change with attention from the change with consumption depended on the use of behavioral conditions that separated the alerting from the performing stages of the conditional response. Separation of the change with motivation in attentive cats was inadequate.