Cervical input to vestibulocollic neurons.

Extracellular responses of vestibulospinal neurons projecting to neck segments (vestibulocollic neurons) to stimulation of cervical afferents were studied in decerebellate cats anesthetized with chloralose or decerebrated intercollicularly. These neurons were antidromically activated by microstimulation in the C2 ventral horn ipsilateral or contralateral to the vestibular nuclei. Contralateral neck afferents produce in vestibulocollic neurons the same responses they produce in other vestibulo-spinal neurons, although the response (early excitation, inhibition) which predominates varies with type of preparation. In intercollicular decerebrate cats, the main effect of stimulating the contralateral C2 ganglion was inhibition (latency greater than or equal to 6 msec), often followed by late excitation. Early excitation, at a latency less than 6 msec, was rarely seen, although it occurred in half the vestibulospinal neurons projecting to the cervical enlargement. In contrast to the results in decerebrate cats, stimulation of the contralateral C2 ganglion produced early excitation in over one-third of the vestibulocollic neurons studied in chloralose-anesthetized cats. Results on vestibulocollic neurons were similar whether the cells projected ipsilaterally or contralaterally, or whether or not the cells also projected to the cervical enlargement (branching neurons). The influence of cervical afferents on vestibulocollic neurons demonstrates supraspinal paths by which cervical afferents may act upon the neck and might modify vestibular reflexes of the neck.