Cutaneo-pressure Reflex and Neck-torsion Nystagmus in Rabbits

Abstract

To clarify the relationship between the exteroceptive and proprioceptive reflexes in the occurrence of nystagmic responses of cervical origin, the following experiments were carried out. That is, a piece of cloth is wrapped around the trunk of rabbits to suspend them in the air so that their four limbs do not touch the ground. The head is then rotated about 90 degrees clockwise around the longitudinal axis of the body. The nystagmus thus induced is termed neck-torsion nystagmus. The nystagmus is recorded from the right eye using an electronystagmograph (ENG) and either the electromyograph (EMG) of the deep neck muscles or the electroencephalograph (EEG) was also recorded. Alteration of the neck-torsion nystagmus is then observed when cutaneo-pressure stimulation is given to the auricle, the trunk and limbs.The following results were obtained.(1) The cutaneo-pressure reflex plays a certain role in the enhancement and/or suppression of neck-torsion nystagmus.(2) The cutaneo-pressure reflex elicited in the auricle reduces the activity of the contralateral deep neck muscles increased due to the torsion of the neck, whereas that elicited in the hindlimb increases the activity of the ipsilateral neck muscles.(3) The former cutaneo-pressure reflex decreases the activity of the brain through the decrease in the activity of the deep neck muscles. In contrast, the latter cutaneopressure reflex increases the activity of the brain through the increase in the activity of the same neck muscles. Thus, the former decreases the neck-torsion nystagmus, while the latter is related to the increased neck-torsion nystagmus.(4) The cutaneo-pressure reflex elicited in the trunk suppresses the neck-torsion nystagmus and it is more markedly suppressed when cutaneo-pressure stimulation of the trunk is given on the side of the chin.(5) The cutaneo-pressure reflex elicited in the forelimbs is not related to the development of neck-torsion nystagmus.