c‐fos expression and (14C) 2‐deoxyglucose uptake in the caudal cerebellum of the rat during motor/sensory cortex stimulation

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Abstract
Fos, the protein product of the c‐fos gene, is induced in neurons in response to a variety of stimuli. In order to see if Fos could be used to map activity in the brain, the pattern of Fos staining was compared to the pattern of (14C) 2‐deoxyglucose (2DG) uptake in the seventh and eighth lobules of the cerebellum during electrical stimulation of the cerebral cortex.Electrical stimulation of hindlimb motor/sensory cortex of awake rats increased 2DG uptake in the contralateral and ipsilateral cerebellum. The largest increases occurred in granule cell patches in the contralateral copula pyramidis (Cop P) and pyramis (P), the hemispheric and vermal portions of the eighth cerebellar lobule, respectively. The granule cell patches formed parasagittal bands that extended short distances mediolaterally, and extended long distances anteroposteriorly over much of the Cop P.Forelimb motor/sensory cortex stimulation increased 2DG uptake bilaterally in the seventh, paramedian (PM) cerebellar lobule. The greatest increases occurred in the granule cell layer contralateral to the stimulation. These and the above results generally agree with classical studies that localize forelimb on the seventh lobule anterior to the hindlimb on the eighth lobule. However, hindlimb cortical stimulation activated parts of the PM, and forelimb cortical stimulation activated portions of the rostral Cop P. In general, nonoverlapping portions of Cop P and PM were activated during the two types of cortical stimulation. These results are consistent with a fractured somatotopy (Welker and Shambes, '85) in which nonadjacent body parts are consistently represented in adjacent granule cell patches on each lobule, with the fractured somatotopy being different for every lobule.No region of cerebellum expressed Fos in unstimulated, electrode implanted, control subjects. However, following 15 minutes of electrical stimulation of hindlimb cortex, Fos was expressed 4 hours later in patches of granule cell nuclei in Cop P and P. These patches of Fos immunostained granule cells occurred in similar locations in Cop P to the patches of highest glucose metabolism observed with the 2DG method.Zones of Purkinje cell nuclei also expressed Fos. These Purkinje cell zones were often directly over similar sized granule cell patches in P. In the hemisphere however, the zones of Purkinje cells in ventrolateral Cop P expressing Fos only partially overlapped underlying granule cell patches that expressed Fos. Moreover, Fos was not induced in any Purkinje cells adjacent to the Fos‐stained granule cell patch in dorsolateral Cop P. These results demonstrate that somatotopically organized granule cell patches representing activated cerebellar afferents may be congruent with somatotopically organized zones of Purkinje cells representing activated cerebellar efferents‐particularly in the vermis (P). However, in the cerebellar hemisphere activated cerebellar affer‐ ents and efferents from the same body part often only partially overlap one another or do not overlap at all.

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