Chester R. Wilpizeski

Motion-induced sickness following bilateral ablation of area postrema in squirrel monkeys.

Using squirrel monkeys as experimental subjects, we reexamined the disputed role of the area postrema (AP) in motion‐induced vomiting. After anesthetization, the obex and rhomboid fossa were exposed surgically, and the AP was ablated by thermal coagulation using either a battery cautery or a CO2 microsurgical laser. Sham operations were performed on another sample of monkeys. Two or more weeks after surgery, all animals were given 10 daily 2‐hour horizontal rotations at 30 rpm. Every monkey in both the lesions and sham samples vomited on two or more test days. While the vomiting characteristics were modified following ablation of AP, its function is not indispensible for the development of motion sickness in horizontally‐rotated squirrel monkeys.

Experimental motion sickness induced in squirrel monkeys by continuous off-axis horizontal rotation**

Under a variety of experimental conditions, nonrestrained adult male squirrel monkeys were subjected to continuous rotation in the horizontal plane at 33 rpm. Severity of motion-induced sickness was quantified by measuring latencies of three responses associated with sickness. Per- and postrotational nystagmus was recorded from a subsample of monkeys with permanent recording electrodes implanted in the bony orbits. Incidence of sickness depended on the time limits of stimulation imposed, and it occurred in a maximum of about 90 per cent of test sessions if rotation was continued for two hours. When subjected to ten once-per-day rotation sessions, only a few monkeys showed evidence of developing transient habituation of onset of motion sickness. Mean frequency of emetic episodes, however, declined over the latter half of the rotation series. Restricting visual cues by blindfolding the monkeys prevented most subjects from vomiting.

Subjective concomitants of motion sickness: quantifying rotation-induced illness in squirrel monkeys.

It has been suggested by numerous researchers that the development of conditioned food aversion (CFA) in experimental animals represents the presence of a subjective state of illness. Squirrel monkeys with proven susceptibility to rotation-induced vomiting were given surgical bilateral labyrinthectomies, a procedure known to abolish signs and symptoms of motion sickness in human beings. Postoperatively, labyrinthectomized monkeys neither vomited nor revealed any reduction in food consumption when exposed to provocative rotation. Other samples of monkeys known to be refractory to horizontal rotation and to sinusoidal vertical motion also exhibited little tendency to acquire a conditioned aversion to banana. But monkeys who had sham operations and those who revealed weak-to-strong signs of motion sickness exhibited a marked CFA (significant reduction in food intake). The strength of CFA was much greater when elicited in the test vehicle when compared with response in the home cage. The findings are interpreted as support for a limited application of CFA procedures for inferring the presence of motion-induced nausea and malaise.

Otological Applications of Lasers

The purpose of this chapter is to discuss the rationale and instrumentational requirements for laser otological microsurgery, and to review the literature on ablative and analytical applications of lasers as they relate to the ear.

Behavioral conditioning and experimental motion-induced sickness

Adult male squirrel monkeys were the subjects of experiments conducted to determine whether or not repeated exposures to sickness-inducing horizontal rotation would result in behavioral conditioning of emetic responses. The development of conditioned food aversion and feeding suppression as a consequence of pre- and postrotation eating was quantified. It was concluded that neither instrumental conditioning nor classical conditioning were valid alternative hypotheses for the occurrence of repeated vomiting episodes over a period of ten daily exposures to motion. Conditioned aversion to fresh banana and feeding suppression developed gradually if rotation, which induced multiple bouts of vomiting, was sustained for 1- or 2-hour sessions. If spinning was terminated immediately after the first emetic response, no aversion or suppression emerged. The occurrence of food aversion, by itself, is questioned as a valid index of the presence of subjective concomitants of motion sickness in animals.

Intensification and habituation of experimental motion sickness in squirrel monkeys by repeated horizontal rotation

The aim of this research was to quantify the development of habituation or intensification of experimental motion sickness induced in Bolivian squirrel monkeys by repeated exposures to horizontal rotation. Incidence, frequency, and latency of vomiting responses were recorded from monkeys rotated daily in a transparent testing chamber at 30 rpm for periods of 1 or 2 hours. Data showed that more than half of the subjects revealed habituation in terms of increased latencies for vomiting. Some showed a tendency to vomit increasingly earlier with multiple daily exposures to rotation. The development of habituation and intensification was evident as early as the second day of rotation. The number of emetic episodes per day decreased as a consequence of repeated rotation, but intensification of vomiting frequency did not occur beyond the fifth day.

A two-factor model of rotation-induced motion sickness syndrome in squirrel monkeys.

Nonrestrained squirrel monkeys were rotated repeatedly in the horizontal plane once per day for preset times or until a vomiting response occurred. Emesis latencies and frequencies were recorded. Some subjects were fed fresh banana immediately before and after each rotation. The amount consumed provided a measure of conditioned food aversion or feeding suppression. A two-factor model of the motion-sickness syndrome was formulated to account for the data. According to the model, appropriate stimulation of the semicircular canals accompanied by visual and proprioceptive stimulation generates two independent physiologic processes or states: an objective emesis and a subjective nausea process. The emesis process is revealed by vomiting responses and the nausea process is inferred from the appearance of conditioned food aversion. Susceptible monkeys (type I) and resistant monkeys (type II) have different emesis processes, but both have similar nausea processes. Refractory monkeys have no well-developed emesis or nausea processes. Time and order characteristics of the motion-sickness syndrome depend on specific interactions of emesis and nausea processes.

Horizontal Nystagmus in Methylmercury Poisoned Squirrel Monkeys

Chronic states of methylmercurialism were induced in squirrel monkey subjects. Principal neurological signs included ataxia, abnormal gait, incoordination and amaurosis. Although slight to moderate vacuolization occurred in supporting cell layers of the cristae and maculae, receptor cell function was essentially normal. Except for a lowered cold threshold, bithermal caloric‐induced nystagmus was not significantly different from control values. Pre and postrotatory (Barany chair) tests revealed a reduction only in frequency related variables. The development of spontaneous and positional nystagmus (sometimes with eyes open) coupled with the behavioral signs and the evidence of normal receptor response suggested cerebellar dysfunction. Severe pathologic changes were present in the cerebral cortex, but no lesions were found in the cerebellar cortex. Substantial neuronal degeneration and gliosis, however, were observed in several subcortical nuclei, including cerebellar and vestibular nuclei.

Experimental labyrinthotomy in monkeys by argon and carbon dioxide lasers.

The horizontal semicircular canal of squirrel monkeys was irradiated unilaterally with either an argon or carbon dioxide laser. Postoperatively, there was a small but significant reduction in caloric-induced ENG responses to 45° thermal stimulation. The principal morphologic effect of laser irradiation was a plug of fibrous tissue or new bone within the lumen of the lesioned semicircular canal.

Temperature characteristics of squirrel monkey horizontal semicircular canals during caloric irrigation.

Current assumptions concerning body temperature of experimental animals, particularly as it relates to the selection of caloric test stimuli, are likely to be inaccurate guesses. Although the temporal bone of squirrel monkeys attenuates irrigation temperature by a factor of nearly 10, there is a high correlation between thermal changes in inner ear fluid and irrigation values. In this study, nystagmus (defined by electronystagmographic thresholds) occurred when horizontal canal temperatures deviated from resting temperature by ±0.14 C.