Saccular influence on the otolith-spinal reflex and posture during sudden falls of the cat

Abstract

Hypothesis: The saccule provides important input for the otolith spinal reflex during sudden falls in the cat.

Background: Previous studies on cats have identified two distinct components of muscle activity in response to sudden falls: an early otolith-dependent component (OSR) and a later nonlabyrinthine component associated with landing. The presence of an otolith-dependent reflex suggests a discrete role of the otolith organs in the control of posture and locomotion.

Methods: The influence of saccular input on the OSR during sudden falls was studied by simultaneous video and electromyographic (EMG) recordings obtained from saccular-deficient deaf white cats and white cats with normal hearing.

Results: A total of 628 sudden falls from five cats (two normal, one unilaterally deaf and two bilaterally deaf) were studied. Normal cats had a total of 337 drops, 276 of which (82%) were acceptable; a unilaterally deaf cat had a total of 79 drops, 56 of which (71%) were acceptable; deaf cats had a total of 212 drops, 177 of which (83%) were acceptable. The earliest of five observed behavioral events was that of forelimb extension which had a mean latency of 98 +/- 32 msec in normal cats and 139 +/- 28 msec in deaf cats (p < 0.0001). The mean latency of early EMG activity in normal cats was 19 +/- 7 msec and in deaf cats was 30 +/- 13 msec (p < 0.0001). The unilaterally deaf cat exhibited behavior and early EMG responses that were similar to those of normal cats. Deaf cats displayed poor body control during landings that improved with experience.

Conclusions: These data demonstrate that the saccule provides important input for the otolith spinal reflex in the cat, and cats that lack both saccules have discernible behavioral and EMG differences in response to sudden falls, when compared with normal cats.