The Journal of Neurophysiology Vol. 87 No. 1 January 2002, pp. 1-14
Copyright ©2002 by the American Physiological Society
Modifications of Vestibular Responses of Individual
Reticulospinal Neurons in Lamprey Caused by Unilateral
Labyrinthectomy
T. G.
Deliagina and
E. L.
Pavlova
The Nobel Institute for Neurophysiology, Department of
Neuroscience, Karolinska Institute, SE-171 77 Stockholm, Sweden
Deliagina, T. G. and
E. L. Pavlova.
Modifications of Vestibular Responses of Individual
Reticulospinal Neurons in Lamprey Caused by Unilateral
Labyrinthectomy. J. Neurophysiol. 87: 1-14, 2002. A
postural control system in the lamprey is driven by vestibular input
and maintains the dorsal-side-up orientation of the animal during
swimming. After a unilateral labyrinthectomy (UL), the lamprey
continuously rolls toward the damaged side. Normally, a recovery of
postural equilibrium ("vestibular compensation") takes about 1 mo.
However, illumination of the eye contralateral to UL results in an
immediate and reversible restoration of equilibrium. Here we used eye
illumination as a tool to examine a functional recovery of the postural
network. Important elements of this network are the reticulospinal (RS)
neurons, which are driven by vestibular input and transmit commands for
postural corrections to the spinal cord. In this study, we
characterized modifications of the vestibular responses in individual
RS neurons caused by UL and the effect exerted on these responses by
eye illumination. The activity of RS neurons was recorded from their
axons in the spinal cord by chronically implanted electrodes, and
spikes in individual axons were extracted from the population activity
signals. The same neurons were recorded both before and after UL.
Vestibular stimulation (rotation in the roll plane through 360°) and
eye illumination were performed in quiescent animals. It was found that
the vestibular responses on the UL-side changed only slightly, whereas
the responses on the opposite side disappeared almost completely. This
asymmetry in the bilateral activity of RS neurons is the most likely
cause for the loss of equilibrium in UL animals. Illumination of the eye contralateral to UL resulted, first, in a restoration of vestibular responses in the neurons inactivated by UL and in an appearance of
vestibular responses in some other neurons that did not respond to
vestibular input before UL. These responses had directional sensitivity
and zones of spatial sensitivity similar to those observed before UL.
However, their magnitude was smaller than before UL. Second, the eye
illumination caused a reduction of the magnitude of vestibular
responses on the UL side. These two factors tend to restore symmetry in
bilateral activity of RS neurons, which is the most likely cause for
the recovery of equilibrium in the swimming UL lamprey. Results of this
study are discussed in relation to the model of the roll control system
proposed in our previous studies as well as in relation to the
vestibular compensation.
