Squirrel monkey platform runway test. A preliminary report

Baseline Running on a Straight Platform by Squirrel Monkeys

An improved task of locomotor balance for use by squirrel monkeys, employing a shuttle-avoidance paradigm, consisted of a straight alley runway with pressure sensors on the floor to detect footsteps. Training and pre-experimental baseline performance for animals used later in vestibular end organ deafferentation experiments, etc. were described. Subjects learned the task within a few days ( Mdn = 5.81 days to first criterion session) as indicated by the skewed distribution of trial sessions to criterion. This test is an improvement over a perviously described measure of locomotor balance in that it eliminates the requirement of physical fitness inherent in the other task.

Training adaptations of baboons to light and moderate treadmill exercise

We evaluated training adaptations by 18 baboons (Papio cynocephalus anubis) to low and moderate quadrupedal walking exercise on a motorized treadmill. Moderate training produced 47% increases in lactate threshold, 63% increases in muscle citrate synthetase activity, increases in percentage of Type IIc muscle fibers, and reduced plasma insulin concentrations. Low training produced only reduced plasma insulin concentrations. Only results indicate that the baboon response to exercise training was similar to that of Homo sapiens, and dependent on exercise intensity.

Amino acid assay of vestibular nuclei 10 months after unilateral labyrinthectomy in squirrel monkeys

Amino acids were assayed by HPLC in bilateral vestibular nuclei from normal squirrel monkeys (n = 3) and those 10-month post-unilateral labyrinthectomy (n = 4). Findings of vestibulo-spinal and vestibulo-oculomotor functions were identical for both groups. No left-right asymmetry of amino acids was found within either group, nor between groups with the exception of GABA: GABA was significantly reduced in the bilateral vestibular nuclei of the 10-month post-lesion animals. This may be indicative of a reduction of cerebello-vestibular inhibitory control which could be secondary to the reduction of excitatory inputs to the system.

Early sensory determinants of locomotor speed in adult cats: I. Visual compensation after bilabyrinthectomy in cats and kittens

After a study of locomotion in cats deprived of their vestibular receptors early in life, the average speed of locomotion was measured in 3 adult cats, first before and then several months after bilateral labyrinthectomy, in a task involving free locomotion across platforms, rails or ladders and under normal illumination versus stroboscopic illumination or darkness. In the absence of visual cues, cats which received lesions as adults showed, on both wide and narrow supports, the same speed deficits as those of subjects which underwent lesions soon after birth. Visual cues were, however, used by some cats with early lesions to recover near normal performances on wide platforms. Evidence was found that the vestibular deficit comprised at least 3 components: a severe loss of dynamic balance occurred in all subjects with lesions and was mostly not compensated for by vision; a loss of the ability to keep to a straight course in darkness was observed on wide platforms, but vision considerably improved this function, even under stroboscopic illumination; a slight paw adjustment deficit was also observed on irregular supports, due to the fact that vision played a decreased role after the vestibular lesion. These effects point to the specificity of the vestibular control of balance, the availability of several sensorimotor strategies for orientation, and the complementarity of vestibular and visual inputs in guiding the subjects' step. We confirm here that vestibular inputs do not play a critical role during locomotor development, and stress the fact that peripheral visual cues about position or orientation (rather than motion), play a leading role in compensatory strategies.

Effect of physical exercise prelabyrinthectomy on locomotor balance compensation in the squirrel monkey

This study examines the effectiveness of physical exercise, during a prepathology state, on locomotor balance compensation after subsequent unilateral labyrinthectomy in squirrel monkeys. An experimental group underwent 3 hr. of daily running exercise on a treadmill for 3 mo. prior to the surgery, whereas a control group was not exercised. Postoperatively, the locomotor balance function of both groups was tested for 3 mo. There was no significant difference in gait deviation counts in the acute phase of compensation. However, in the chronic compensation maintenance phase, the number of gait deviation counts was fewer in the exercise group, which showed significantly better performance stability.

Second-phase optokinetic after-nystagmus and vestibular compensation

To evaluate the direction-specific effect of optokinetic storage function on balance compensation after unilateral labyrinthectomy, squirrel monkeys (n = 12) were exposed to a prolonged (30 min) daily optokinetic stimulus (horizontal, constant speed-90 degrees/sec) for 14 days; either in the ipsilateral direction to the slow phase of spontaneous nystagmus, or in the contralateral direction, or without any optokinetic stimulus. The effect of optokinetic stimulus in ipsilateral direction (slow phase of OKAN-II in the opposite direction) was significantly more (p less than 0.001) in the vestibulo-oculomotor balance (static) regainment than the other two groups, but this group showed the severest gait deviation in the vestibulospinal balance function (p less than 0.05).

Autonomic effects on R-R variations of the heart rate in the squirrel monkey: an indicator of autonomic imbalance in conflict sickness

To assess the contribution of the autonomic nervous system (ANS) to beat-to-beat (R-R interval) variations in the squirrel monkey, heart rate was analyzed after atropine, propranolol, carbachol, or isoproterenol administration, using a computer analyzing system. Heart rate variations were expressed as coefficient of variance (CV) of mean R-R interval. CV of R-R interval clearly was reduced by atropine but not by propranolol, indicating that the effect could be mediated through the parasympathetic nerve. CV of R-R interval was measured also under vestibulo-visual conflict (VVC) situation in pitch. Although CV of R-R interval increased during VVC, this variation almost was abolished after atropine administration. Monkeys with unilateral labyrinthectomy showed smaller variations than those without operation during exposure to VVC. CV of R-R interval is a useful parameter for the objective and quantitative evaluation of ANS function and may be a good indicator to demonstrate the severity of motion sickness without invasive methods.

Post-labyrinthectomy balance compensation influenced by pre-placement of descending medial longitudinal fasciculus lesion

To characterize the functional role of the descending medial longitudinal fasciculus (d-MLF) in vestibular compensation, vestibulo-ocular and vestibulo-spinal balance functions were studied comparatively in the squirrel monkey. When a unilateral lesion was made on the d-MLF, the animals showed a slight head deviation to the intact side, slight locomotor ataxia and irregular spontaneous nystagmus. About 2 months later, the ipsilateral labyrinthectomy was placed, and the compensatory process was compared between 3 experimentals and 3 controls (labyrinthectomy without pre-lesion). During the acute stage of the vestibular compensation, locomotor deviation was clearly greater in experimentals than those in controls. However, no significant difference existed in the final attainment and maintenance of the balance. The same result was found in the spontaneous nystagmus, although the difference in the two groups was less remarkable.

Effect of thyrotropin-releasing hormone on vestibular compensation in primates

Continual administration of thyrotropin-releasing hormone (TRH) (250 micrograms/kg/day) for 14 days using an osmotic mini-pump in unilateral labyrinthectomized squirrel monkeys induced accelerated vestibular compensation. Decrease in total gait deviation counts and reduction of slow-phase eye velocity of spontaneous nystagmus were significantly faster in the TRH-treated group as compared with the control group.

Apparatus for measurement of dynamic body equilibrium in the guinea pig

An apparatus for the measurement of dynamic bodily equilibrium function in guinea pigs was made and its applicability was investigated. This apparatus consists of two cubical boxes (one of them is the starting box, and the other the goal box) connected by a 30 cm wide, 150 cm long, and 20 cm high straight platform. From the grids mounted on the floor of the starting box, an electric stimulation was given to make them run fully on the platform toward the goal box. On the floor of the platform, except for the 7 cm wide center line, 6 channels (3 channels on each side) of pressor-sensor-type recording system are installed. Thus, the animal's running performance is recorded by multi-channel pen recorder. At first, the animals should be screened and trained. Mostly the animals have learned to run with minimal deviations in several tens of training runnings. Thus, when the training period was over, five animals were selected to determine the recovery process of locomotion after the unilateral labyrinthectomy. The obtained results depicted through the gradual decrement of deviation count and running time were consistent with the previously reported results using other animals. Therefore, it could be concluded that this recovery process of bodily dysequilibrium measured by this test procedure must reflect the vestibular compensation of this animal.

Effect of ACTH-(4-10) on equilibrium compensation after unilateral labyrinthectomy in the squirrel monkey

Daily injection of ACTH-(4-10) was given to squirrel monkeys for a 28 day period to modify the characteristics of the post-unilateral labyrinthectomy symptoms along the course of the equilibrium compensation. When compared to the results of the control group, the ACTH-(4-10) injection groups (daily dose 250 micrograms/kg or 500 micrograms/kg) showed a significant improvement of acquisition and maintenance of compensation both in the spinal locomotor balance function and the oculomotor balance function.

Effect of atropine and carbachol on vestibular compensation in squirrel monkeys

The central cholinergic system's involvement in vestibular compensation has been clearly demonstrated in the infra-human primate model. In the squirrel monkey, long after unilateral labyrinthectomy, atropine injection produced significant reduction of slow-phase eye velocity of the spontaneous nystagmus. The atropine effect was also depicted through the dynamic vestibular inputs, reducing the maximum slow-phase eye velocity of damped pendular rotation nystagmus. Contrary results (increased slow-phase eye velocities) were found after carbachol injection. After atropine injection, the locomotor deviation count increased significantly, more to the nonlesion side. Carbachol injection engendered the opposite result. After bilateral labyrinthectomy, no significant effect was found from drug injection. Thus, our findings suggest that atropine's major site of action after unilateral labyrinthectomy is the vestibular nuclei on the intact side.

Post-labyrinthectomy balance compensation with preplacement of cerebellar vermis lesion

Post-unilateral labyrinthectomy compensation was compared between squirrel monkeys; one group with the pre-placement of posterior vermectomy next group with uvulonodulectomy, and the other group without any vermic lesions. The comparison was made by characterizing behavioral locomotor imbalance (by squirrel monkey platform runway test) and oculomotor imbalance (spontaneous nystagmus). Post-posterior vermectomy + unilateral labyrinthectomy group showed a much slower regainment of locomotor balance function when compared to that after uvulonodulectomy + unilateral labyrinthectomy group (which results was almost identical to that after unilateral labyrinthectomy alone). In contrast, the former group exhibited faster decay in spontaneous nystagmus, whereas the latter group showed delayed reduction of slow phase eye velocity. Thus, posterior vermis could have more functional linkage to the vestibulo-spinal system, whereas, uvula and nodulus, to the vestibulo-oculomotor system.

Effect of diazepam on vestibular compensation in squirrel monkeys

The effect of the chronic administration of diazepam on vestibular compensation (post-unilateral labyrinthectomy) was studied in squirrel monkeys. An intramuscular injection of diazepam (2 mg/kg) was given daily for a period of 4 weeks post-operatively. After daily injection, reduction of the slow-phase eye velocity ( SPEV ) of spontaneous nystagmus and enhancement of locomotor body dysequilibrium were found in the early post-operative stage. However, these pharmacological effects decreased gradually and almost no remarkable effect was found about 3 weeks after surgery. When compared to control animals, no marked differences was found in SPEV reduction of spontaneous nystagmus in injected animals during the vestibular compensation period. Platform runway tests showed that the average number of calendar days needed to regain the pre-operative level of locomotor balance function in the group injected with diazepam was even less than that of the control group. Thus, post-operative daily diazepam injections did not retard the vestibular compensation. The possible neural mechanism responsible for this phenomenon is discussed.

Effects of prolonged optokinetic stimulation on oculomotor and locomotor balance functions

Squirrel monkeys were exposed to optokinetic stimulus (90 degrees/sec constant speed, unidirectional) for 60 min. Eye movements during and after the stimulus exposure were recorded. Comparison of the data between very early and late stages of exposure showed the oculomotor gain increase and the nystagmic frequency decline. Slow phase eye velocity of bilaterally labyrinthectomized squirrel monkeys in the late exposure stage could reach almost to the level of normal animals. Post-stimulus analysis in normal monkeys showed that amphetamine enhanced the optokinetic after-nystagmus duration, the maximum slow phase eye velocity, and the time constant. In contrast, the effect of amphetamine on reversed optokinetic after-nystagmus was not at the significant level in all parameters studied. The manifestation of directional reciprocity of optokinetic after-nystagmus was inconsistent. In bilaterally labyrinthectomized animals, ipsilateral optokinetic after-nystagmus did not appear after the stimulus cessation. Instead, immediate reversed optokinetic after-nystagmus appeared. When the normal animal was kept in the light after the stimulus cessation, slow phase eye velocity of reversed optokinetic after-nystagmus declined relatively rapidly. Reversed optokinetic after-nystagmus and vestibular evoked nystagmus were summated or deducted, in velocity domain, depending upon the direction. Optokinetically induced system imbalance did not depict when the monkey's spinal locomotor function was measured by the platform runway test with the availability of vision.

An inexpensive automatic activity monitor for small primates

An activity cage has been designed to provide a quantitative measure of locomotor activity in small primates. Movement is detected by the interruptions of photocell beams, which are counted electronically and stored in on-board memory for subsequent display or entry into a computer. The device functions independently, and does not require a computer to be on-line during data collection. Data thus obtained have proven reliable, and are a valid record of the activity of the animal.

Further study of physical exercise and locomotor balance compensation after unilateral labyrinthectomy in squirrel monkeys

The effect of physical exercise on compensation for locomotor asymmetry after unilateral labyrinthectomy was studied in squirrel monkeys. Five monkeys were assigned to the motor-driven rotating cage exercise, and another five, non-exercise control. Daily exercise (cumulative time of 2 1/2 hours) was given for three weeks preoperatively and continuously (daily) post-operatively. The average number of calendar days to attain the locomotor balance compensation was 20 days in the exercise group, and 35 days in the non-exercise control group. Statistical analysis showed the former compensated (according to the previously established criterion) significantly faster than the latter ( less than 0.05). Furthermore, faster reduction of gait deviation was found in the exercise group. Therefore, when physical exercise was given extensively and continuously, and locomotor balance function was measured by the squirrel monkey platform runway test (Igarashi, 1974), physical exercise application enhanced the locomotor equilibrium compensation.

Modifications and development of spinal reflexes in the alert baboon (Papio papio) following an unilateral vestibular neurotomy

Unilateral vestibular neurotomy performed on 6 baboons was followed by the classical postural and locomotor postoperative disorders. Postoperative spinal reflex excitability was studied in these awake baboons by measuring monosynaptic recruitment ratios in soleus motoneuronal pool and the recovery cycle of the monosynaptic response. Vestibular neurotomy induces: (1) asymmetrical spinal reflexes with a decrease of the recruitment on the side of the section and an increase on the opposite side. (2) a modification of phases IV and V of the ipsilateral recovery cycle. The recovery during postoperative days of normal recruitment curves and recovery cycles is described. This recovery is relatively fast and relates closely to the compensation of postural and locomotor disorders. We note the importance of an early active motor exploration on the time-course of recovery: postoperative disorders in posture and locomotion are reduced much later when baboons are submitted to a motor restriction. These findings suggest a combined alpha and gamma-hypoexcitability of the ipsilateral hindlimb. The study of the recovery process suggests that the cerebellum is involved in the compensatory mechanisms. The regression of postural disorders, observed both in restrained and unrestrained baboons, demonstrates the importance of central regulations using proprioceptive afferents for recovery.