Electrophysiological Study of Spatial Distribution of Vestibulospinal Neurons in the Frog Rana ridibunda

In experiments on a perfused brain preparation of the frog Rana ridibunda, the vestibulospinal neurons were identified, based on the excitatory postsynaptic potentials (EPSP) that appeared in response to an ipsilateral stimulation of the vestibular nerve and on the antidromic activity in response to stimulation of the cervical and lumbar enlargements of the spinal cord. The cells that could be antidromically activated only by stimulation of the cervical cord were designated as C-neurons. The cells that could be antidromically activated by stimulation of the lumbar cord were designated as L-neurons. The intracellular activity was recorded in 244 neurons of the vestibular nuclear complexes, out of which 127 cells (52%) were C-neurons and 117 (48%), L-neurons. The antidromic action potentials were recorded from the cells of lateral (143 neurons, 58.6%), descending (75 neurons, 30.7%), and medial (26 neurons, 10.6%) vestibular nuclei. The axon conduction velocity was determined to amount, on average, to 10.67 m/s for C-neurons and 15.84 m/s for L-neurons. In the vestibular nuclear complex, distribution of the fast and slow C- and L-neurons was studied. This study confirmed the previously made suggestion that C- and L-neurons of the frog, as sources of vestibular fibers, are distributed separately or, more often, as small groups, which leads to a patch-like somatotopy, rather than to formation of clearly separated fields.