Compensation of postural effects of hemilabyrinthectomy in the cat. A sensory substitution process?

Abstract

A photographic technique was used to study the evolution of lateral head-tilt following hemilabyrinthectomy in adult cats. Animals were maintained post-operatively in normally lit conditions (LM cats), in total darkness (DM cats), or in stroboscopic light. In LM casts, the head tilt peaked at 45 degrees (with the lesionned side down) on the second post-operative day, and decreased to about 0 degree within about 10 days. This evolution was followed by rebounds of head-tilt to large angles before a stable compensated head postion could be maintained (approximately at the end of the third post-operative month). In DM cats the head remained tilted by a large angle throughout the duration of the dark period. Re-exposure to light was followed by a rapid decrease of head-tilt. In stroboscopic light, the evolution of head-tilt was found to be closely similar to that in the normally lit condition. Finally, when put back in the dark at a late post-operative stage, already compensated animals were found to loose their symmetrical head position, and to re-acquire a strong head tilt. This effect resumed on re-exposure to light. It is inferred that static visual input is a necessary condition for compensation of the postural deficits of hemi-labyrinthctomy in the cat. Maintenance of a stable head posture also depends upon continuous availability of visual input.

Head Tilt Produced by Hemilabyrinthectomy Does Not Depend on the Direct Vestibulospinal Tracts

“…The present results also reveal that contrary to a common belief [Putkonen et al, 1977], EMG activity recorded from the dorsal neck muscles (biventer cervicis and splenius) after hemilabyrinthectomies was not higher on the side ipsilateral to the lesion even when the cats showed typical head tilt to the lesioned side. Rather the activity was higher on the contra lateral side in 3 of the 5 cats tested.…”

“…This indicates that these dorsal neck muscles are not the primary muscles that produce head tilt; similar head tilt can be pro duced even after all dorsal neck muscles have been detached from the lamboidal ridge [Fukushima et al, 1987a], suggesting that some deep lateral neck mus cles are primarily responsible for the head tilt. All these results indicate that head tilt following hemilab yrinthectomy is not produced by a hyperactivity of the dorsal neck muscles on the side of the lesion via crossed direct excitatory vestibulocollic fibers as sug gested by some authors [Putkonen et al, 1977;Courjon and Jeannerod, 1979;Dutia, 1985], although this does not exclude a possible involvement of some deep lateral neck muscles on the lesioned side via polysyn aptic pathways [Fukushima et al, 1987a;see below]. Dutia [1985] reported that after acute hemilabyrin thectomy, tonic EMG activity in the biventer cervicis muscle was much higher on the side ipsilateral to the lesion compared to the EMG activity in the contralat eral muscle (actually it was abolished), contrary to our EMG observations.…”

“…Interruption of the vestibulospinal tracts (VSTs) was per formed in 13 cats: in 8 of the 13, VST lesions were combined with hemilabyrinthectomies, and in 5 cats single VST lesions were per formed. In the remaining 5 cats, electromyographic (EMG) activity was chronically recorded bilaterally from dorsal neck muscles (bi venter cervicis and splenius) 2-4 days after hemilabyrinthectomies to examine whether the dorsal neck muscles ipsilateral to the lesioned side show an increased EMG activity as expected from the current notion [Putkonen et a)., 1977: Courjon and Jeannerod, 1979: Dutia, 1985, since motoneurons of these neck muscles are shown to receive direct excitatory crossed vestibulocollic projec tions [Wilson and Melvill Jones, 1979). Teflon-coated silver wires (diameter 0.2 mm) were inserted into the muscles for EMG record ings.…”

“…McCabe and Ryu, 1969: McCabe et al, 1972, A current notion ascribes the neural mech anism of head tilt after hemilabyrinthectomy to an al tered balance of activity in the direct vestibulocollic pathways which have monosynaptic excitatory and inhibitory connections to the contralateral and ipsilateral neck motoneurons via the medial longitudinal fasciculus (MLF), i.e. the increased activity of vestibu lar nuclear neurons contralateral to the lesioned side produces increased tension of neck muscles on the side of the lesion via the direct crossed vestibulocollic pathways [Putkonen et al, 1977;Courjon and Jeannerod, 1979]. Although the known connections of ves tibulocollic fibers with neck motoneurons [see Wilson and Melvill Jones, 1979, for review] are compatible with this notion, it has never been critically tested.…”

Role of an enriched environment on the restoration of behavioral deficits in Lurcher mutant mice

“…The restoration of abilities following a lesion of a nervous structure depends on many factors:the nature of the neural structure, the extent of the lesion, the age at which the lesion was done, and the sensorimotor experience before and after the lesion (Auvray, Caston, Reber, & Stelz, 1989;Caston et al, 1995;Igarashi, Levy, O-Uchi, & Reschke, 1981;Jeannerod & Hecaen, 1979;Lacour & Xerri, 1980;Petrosini, 1983;Precht, 1983;Putkonen, Courjon, & Jeannerod, 1977;Zion, Auvray, Caston, Reber, & Stelz, 1990). However, the effects of the rearing environment on the behavioral expression of neural deficits of genetic origin have not been investigated in great detail.…”