Neuroseience Letters, 13 (1979) 117--120

© Etsevier/North'H011and Scientific Publishers Ltd.

117

,

K-OC

AR

THE aASBW

TATEOWARABIand JUNICHI MATSUSH]~,IiA

Department o f Physiology, Hokkddo U~r,'-ity School of Medicine, Sapporo, ,SO6

(Japan) (Received January 28th, 1979) ( R e ~ version received April 1 lth,, 1979) (Accepted April 13th, 1979)

SUMMARY The trunk-ocular reflex of the rabbit was investigated by recording EMGs of right lateral rectus and spleniu~, muscles. The skuU and th~ chest of the rabbit were restrained and the lower part of the ~mnk was flexed laterally around the ~axis at the TH~0-~z in~t;erw;rtebral joint. Two kinds of eye movements, small with short latencies and large with longer latencies, were induced counter to the direction c~f the lateral flexion. The latency of the former was 1158 msec (range: 64--200 msec) and that of the latter was 255 msec (range: 1'80--380 msec). Recently, we have shown that a trm~,k~cular reflex was induced by twisting the trunk of human subject [ 8]. It was suggested that the po~ural relation between the upper and lower trunk influences the axis of vision. Such -dsual orientation chm~ges related to postural relations [ 2,5] between head and t n m k are due not only to the cervico~cular zefiex but also to the think-ocular reflex. Suzuki and Takemori [6,7] obse~ed changes in extraocular muscle of electromyogram (EMG) activity when tb_e thoracic nerve was stimulated in anesthetized rabbits. The aim of this experiment was to covfirm this tnmk~cularlreflex in awaked rabbits. A study we~ made of the EMG of extraocular and neck muscle when the trunk-ocular reflex was in&Lced. H o ~ z o n t ~ eye m o v e m e n ~ were produced when the trt~n k of the rabbit wv~ flexed laterally, but, in contrast t~ human beings, not when the trunk was twisted around the axis of the ve~ebl~l column. 1~e experiments were carried out on 4 rabbits (1.8--2.4 kg). An initial sterile condi:tions and deep pentobarbital O0 ~ m diameter copper wires) were. implantright splenius muscles for recording E M G , .~affu:ed to the rabbit's skull. In ,~orne

118 experiments, the bolts were employed to rigidly fix the skull of the rabbit to a metal bar, thereby eliminating vestibular influences. After a recovery period of several days, the rabbit was placed in a p r o n e position of a specially designed table with fixed ~ d : r o t a t i n g p0~i0tlSi~(Fig.::'l). A platform was connected to a stable, fixed table via a pin which served as an axis around which the platform could rotate over the surface of the t~b]e. The upper and lower parts of t h e chest were fzstened tightly to two U~haped panels anchored to the fixed table. The waist was fastened to the r,~tating platform. Eye and head movements were initially observed in a lightened room• In order to eliminate the effects of visual input, the EMG activities of lateral rectus and splenius muscles were recorded in a darkened room with the skull restrained. Sinusoidal (0.05--0.5 Hz) and lateral ramp (15--150 degree/sec) flexions of the lower trunk were applied by moving the platform manually. ~/hen the platform was rotated to one side, the rabbit's vertebral column was f:exed laterally from the level of Th~o. The movement of the trunk was monitored by a potentiorneter connected to the axis of rotation. The range cf movement was limited to within 30 degrees in both lateral directions. In the lightened room it was observed that horizontal eye movements were induced in the direction opposite to the lateral flexion of the lower trunk. ~,'or example, as the trunk was quickly flexed to the right, a quick and lar[~,~edeviation of the eyes occurred to th~ left. When the trunk was flexed slowly (less than 0.1 Hz), slow eye deviations of small amplitude were induced in only some cases. When similar stimuli were applied to the rabbit

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L. Fi~. 1. E:~perimental set-up. The skull and chest were secured ~ the lower (!,r fixed): table and the lower half of the trunk w u fastened to the up~r (0~:ro~ting) platform. The plattorm could' Slide laterally around a connecting ~in: When ~he platform was rotated, l~heloWer trunk of the rabbit Was flexed laterally, ......'

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c

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Fig. 2. EMG activities of (;he right lateral rectus muscle (a) and the right splenius muscle (b) when the t r u n k was flexed laterally (c). Vertical bars represent 200/JV ~and 20 ° ,respectively. Left is upward in c. (1) T r u n k w ~ flexed sinusoidally by about + 30 °. (2) When a quick ramp m o v e m e n t was applied to the trunk, coordinated head end eye m o y e m e n t s were induced. EMG activity of the ocular muscle (a) was associz,ted ~vith EMG of the t neck muscle (b). EMG of the ocular muscle was integrated in a .

without restrainingthe skull,a quick eye deviation was followed by a quick head movement in the same direction. However, when the magnitude of the flexion was less than 20 degrees, ~uad when the trunk was flexed at the level of Li vertebral column, these phenomena were observed in about half the trials. In the dark, the E M G activitiesof the lateralrectus and neck muscles on one side increased when the trunk was flexed in the con1~ralateraldirection and decreased when flexion was in the ipsilateraldirection. When sinusoidal flexion of the trunk was applied at speeds slower than 0.1 Hz, gradual increments and decrements of E M G activitieswere obseTved in the lateral rectus muscle (Fig. 2(1)). W h e n quick ramp {Fig. 2(2'c)) or sinusoidal flexions of faster than 0.1 Hz were applied to the trunk, gradual increments of smaller motor unit activitieswere followed by an abrupt recruitment of the la~est motor units. Such recruitment was observed in 65% of the 65 quick ranlp flexions (Fig. 2(2a)). This differentialactivation of small and large motor unit activity is shown more clearly in Fig. 2(2a'),as indicated by the do-~mwardi and upward arrows respectively. This marked activation of the largest motor units x~s usually associated with E M G activityof the neck muscle of the smTie side (Fig. 2(2b). The average latency of the Iv~gestmotor units was 255 mse.c (range: 180--380 msec), that of the small motor units was 158 msec (range: 64--200 msec),

120

and that of 35% of t h e

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Suzuki snd "Pakemor] [~,Tj reporte-d that e l e c ~ c a l ~ u l a t i o n o f ~ h i g h cervical m~d thoracic spinal nerves induced horizontal eye movements; the cervico~cular reflex was induced by st'~tmulation of high cervical nerves (C~-3) and the think-ocular reflex was inducedby stimulation of thoracic

nerves, although ~ e bier reflex w ~ lessi n ~ ~ d I m conmstent. As to more natural stmltflation,the c ~ c o - o c ~ reflex was elicited by twisting the neck [1--3,5] and the tmnk~culsx reflex was induced by lateral flexion of t h e t ~ k as,was described in the pmsent~exp eriment. In human subjects i t was i n d u c ~ by tWisting t h e ~ n k , Thertrunk-ocular reflex, therefore, represents a reflex eye movement produced by postural infovzation arising in the trunk in the horizontal plane. Sensory organs which are responsible for the production of the trunk-ocular reflex are presumed to be joint receptors of the vertebral column [4,8]. The latency of smaller moto~ units induced by trunk flexion is compatible with that of the tr~mk-ocular reflex in human subjects. Slow eye movements were effectively induced in the dark as B~r~ny [1] described for the cervico-ocular reflex of rabbits. The latencies of the large and quick eye movements were longer than these of the small ~-ld slow eye movements and were associated with the activity of the neck muscles or with head movements. Them results suggest that there exist two separate systems for inducing the eye movements. REFERIENCES

1 Bir~ny, R., Augenbewegunge, dutch Thorax Bewegunge~ ausgelSst,Zbl. Physiol., 20 (1906) 298--302. 2 Cohen, L,A., Role of eye and neck proprioceptive mechanisms in bod~ orientation and motor coo~ination, J, Neurophysiol,, 24(1961) 1--11. 3 De Kleijn, A:, T o n i c Lab~nth und Hals Reflex auf die Augen, Pfl~igers, Arch, ges.Physiol.; 189 (1921) 82-'-97. 4 Friedrickson, J.M,, Schwarz, D. and Kornhuber, H.H,, Convergence and interaction of vestibular andd~p ~m~!c afferents upon neurons in the vestibular nuclei of cat,

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5 Magnus,P., Physi010gyof p0sture, ~ncet, 2 i l , Part 2(1926) 531-536. 6 Suzu]ki,J. movements i n d u ~ from the spinal nerves, Equi33~0, ~ 7 Suzuki.J, ~ d Te~kemddiS, Infraction of sp'mal:and.vestibulareye movements. In Pealtz, C,R' (Ed), Advan~S in O~-Rhino-Larjngology,S. Karger, S ~ l , 197 3, pp, 149--155. 8 Warabi,T., Trunk~cul~ reflex ~ man, Neurosel. I~tt., 9(1978) 267"270 i

Trunk-ocular reflex in the rabbit.

Neuroseience Letters, 13 (1979) 117--120 © Etsevier/North'H011and Scientific Publishers Ltd. 117 , K-OC AR THE aASBW TATEOWARABIand JUNICHI MAT...
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