Between in and out: linking morphology and physiology of cerebellar cortical interneurons.

We used the juxtacellular recording and labeling technique of Pinault (1996) in the uvula/nodulus of the ketamine anesthetized rat in an attempt to link different patterns of spontaneous activity with different types of morphologically identified cerebellar cortical interneurons. Cells displaying a somewhat irregular, syncopated cadence of spontaneous activity averaging 4-10 Hz could, upon successful entrainment and visualization, be morphologically identified as Golgi cells. Spontaneously firing cells with a highly or fairly regular firing rate of 10-35 Hz turned out to be unipolar brush cells. We also found indications that other types of cerebellar cortical neurons might also be distinguished on the basis of the characteristics of their spontaneous firing. Comparison of the interspike interval histograms of spontaneous activity obtained in the anaesthetized rat with those obtained in the awake rabbit points to a way whereby the behaviorally related modulation of specific types of interneurons can be studied. In particular, the spontaneous activity signatures of Golgi cells and unipolar brush cells anatomically identified in the uvula/nodulus of the anaesthetized rat are remarkably similar to the spontaneous activity patterns of some units we have recorded in the flocculus of the awake rabbit. The spontaneous activity patterns of at least some types of cerebellar interneurons clearly have the potential to serve as identifying signatures in behaving animals.

Locomotion coincides with c-Fos expression in related areas of inferior olive and cerebellar nuclei in the rat.

Rats that had been walking on a rotating drum for a period of 75 min, demonstrated expression of the immediate early gene c-Fos in specific areas of the inferior olive and cerebellar nuclei. Non-walking control rats did not show consistent Fos-like immunoreactive labelling in these nuclei. Fos-like immunoreactive olivary neurons were consistently found in the caudolateral parts of the dorsal accessory olive and in its dorsal fold, and within specific areas of the medial accessory and principal olives. In the cerebellar nuclei, immunoreactive cells were found in the medial part of the anterior interposed nucleus, in the interstitial cell groups, and within specific parts of the medial, posterior interposed, and lateral nuclei. The lateral vestibular nucleus as well as the ventral part of the magnocellular red nucleus also displayed positive neurons. Most of these positive areas are known (1) to be related to the spinal cord and (2) to be anatomically linked. These results are in line with a presumptive role of the olivo-cerebellar system in ongoing movement control.