The central cervical nucleus in the rat : studies on connectivity, function and chemical transmission

The central cervical nucleus (CCN) is a spinocerebellar cell group in the upper cervical spinal cord (rat: Cl-C3), that is known to receive a powerful primary afferent input from, the upper cervical spinal nerves (C 1-C4), originating mainly from muscle spindle afferents in deep dorsal neck muscles and from the ipsi- and contralateral vestibular nuclei. It projects to the cerebellar vermis bilaterally and to all the vestibular nuclei contralaterally.

In this thesis, several aspects of CCN neurons were examined: their cerebellar projection; their neurophysiology; and by immunocytochemistry at the electron microscopic level, the transmitter content of both the neck muscle afferents and the vestibular afferents. The cerebellar projection was visualized with a neuronal tract tracer (CTB), and was found as mossy terminals in the cerebellar cortex, distributed mediolaterally in mainly three regions, that formed parasagittal bands aligned apico-basally. These mossy fiber terminals were seen mostly subjacent to zebrin I immunopositive Purkinje cell clusters, that formed clear parasagittal bands, alternating with zebrin I immunonegative bands. The borders between the regions of labeled mossy fiber terminals and those of immunopositive Purkinje cell clusters did not completely coincide. The CCN neurons responded to stretching and electrical stimulation of the ipsilateral neck muscles biventer cervicis et complexus and splenius. The primary afferent boutons producing this response were found at the ultrastructural level to be enriched with glutamate-like immunoreactivity. Ia synapses with CCN neurons were further shown to be immunoreactive for AMPA receptors, and also NMDA receptors. The CCN neurons also responded to electrical stimulation of, in particular, the contralateral vestibular apparatus and also by movement of the experimental animal in the gravitational field. Neurons responded to sinusoidal movements of roll and pitch, i.e. utricular stimulation, but unexpectedly, also to otolith stimulation. Bulbospinal afferents, most likely the vestibulospinal fibers responsible for these responses were labeled with the tracer CTB, and found at the ultrastructural level to contact CCN neurons. Such vestibulo-CCN synapses were enriched with glutamate-like immunoreactivity and had synaptic contacts immunoreactive to AMPA receptors.