Fractured Somatotopy in Granule Cell Tactile Areas of Rat Cerebellar Hemispheres Revealed by Micromapping; pp. 106–115

Abstract

We defined spatial patterns of tactile projections to cerebellar cortex of anesthetized albino rats using microelectrode micromapping methods. Low threshold natural stimulation of cutaneous mechanoreceptors of specific body structures evokes brisk, short latency, localized responses within the granule cell layer. These projections terminate within columnar assemblies of granule cells within the folia of crus I, crus II and paramedian lobule of the cerebellar hemispheres. These columnar inputs appear as individuated patches and the overall array of patches make up mosaics. The somatotopic organization of single patches is precise but that among the patches within the mosaic is fractured. Electrode puncture densities of as high as 65/mm were required to delineate the miniature projectional features within the patches and mosaics. The cutaneous sources contributing to the bulk of the granule cell inputs were smallest from perioral structures which are those prominently utilized in discriminative action sequences of rats. This suggests an important perceptual function of these circuits. Ipsilateral projections were predominant but bilateral and contralateral projections were also found. These data reinforce Snider'searly contention that tactile afferents (rather than just proprioceptive inputs) play an important role in cerebellar functions. All these findings necessitate reexamination of several current views of cerebellar functions.

Neurons of the inferior olive respond to broad classes of sensory input while subject to homeostatic control

“…Although the precise somatotopy of climbing fibre projections to crus 1 is not known, it has been shown that the mossy fibre projections to crus 1 convey somatosensory input mainly from the mystacial vibrissae and the surrounding skin, while the somatosensory input from the lips predominantly targets crus 2 (Shambes et al . ). The stimuli were given using a Von Frey filament (target force = 0.686 mN) attached to a piezo actuator.…”

“…The predominant somatosensory input to crus 1 stems, according to the classification of mossy fibre inputs, from the facial whiskers (Shambes et al . ). Here, we show at single cell resolution that climbing fibres indeed do convey somatosensory input from different facial areas, with Purkinje cells having the same receptive fields being located preferably in each other's proximity.…”

Different responses of rat cerebellar Purkinje cells and Golgi cells evoked by widespread convergent sensory inputs

“…Short‐latency excitations of mossy fibres and Purkinje cells in Crus I and II have been reported to be evoked principally by trigeminal inputs (e.g. Shambes et al 1978; Bower & Woolston, 1983), like the excitations of Golgi cells (Vos et al 1999; and Fig. 5).…”

Cerebellar Golgi cells in the rat receive multimodal convergent peripheral inputs via the lateral funiculus of the spinal cord

“…Analyses of information processing within the cerebellar cortex have largely focused on the precise spatial organization of mossy fibre inputs. In the rat, the best‐studied region of cerebellar cortex in terms of input is Crus II in the posterior lobe, and in this region the granule cell layer comprises ‘patches’ with focally specific mossy fibre inputs (Shambes et al 1978). Most of the patches in Crus II have both direct inputs from specific territories of the trigeminal nerve, and long loop cerebropontocerebellar inputs via the sensorimotor cortex conveying information from the same receptive field, which are reflected in the responses of granule cells and Purkinje cells (Bower & Woolston, 1983; Bower & Kassel, 1990; Morissette & Bower, 1996) and also Golgi cells (Vos et al 1999; Holtzman et al 2006).…”