Electrophysiological study of the corticonuclear projection in the cat cerebellum

Experiments were designed to examine the relationship between the responses of Purkinje cells to natural peripheral stimuli and the location of these neurons within identified zones of the corticonuclear projection in lobule V of the cat cerebellar cortex. It was hypothesized that the corticonuclear zones are sharply demarcated and that the responses of Purkinje cells to a restricted natural stimulus is not localized to only one zone but rather is present and varies in character across these 3 zones. Initially the spatial distribution of the antidromic field potential evoked by stimulating in the fastigial (FN), lateral vestibular (LVN), and anterior interposed nuclei (AIN) was determined in sublobules Va-Vc in unanesthetized decerebrate cats. In some animals the corticonuclear projection was further examined by evaluating the location of Purkinje cells responding antidromically to stimuli in the FN, LVN and AIN, or FN, AIN and the posterior interposed nuclei (PIN). Once a Purkinje cell was identified, its simple and complex spike responses to a step-like flexion-extension passive movement of the ipsilateral forepaw were determined. The boundary based on the antidromic activation of Purkinje cells between the fastigial zone (FZ) and the anterior interposed zone (AIZ) in sublobules Va-Vc of the cerebellar cortex was highly reproducible from cat to cat, although there was a slight overlap between these zones based on the antidromic field potential. The FZ-AIZ border was located at 2.1 +/- 0.12 mm lateral and parallel to the midline. The FZ also contained a few cells projecting to the LVN. However, the AIZ only contained neurons projecting to the AIN. The boundary between AIZ and PIZ in lobule Va-Vc was between 3.3 and 3.8 mm from the midline and ran parallel to it. The peristimulus time histograms (PSTHs) of the simple and complex spike activity to a passive forepaw displacement revealed extensive modulation of neurons located across the mediolateral extent of the AI and PIZ. Both the simple and complex spike discharge of Purkinje cells projecting to the FN also were modulated, but to a lesser degree than cells in AIZ or PIZ. The spatial distribution of simple and complex spike responses recorded from Purkinje cells overlapped extensively. The data support previous findings that the corticonuclear projection is organized into longitudinally oriented sagittal zones. Electrophysiologically the boundaries were remarkably reproducible from animal to animal. The results also show that information processing involving the modulation of Purkinje cell activity in response to the forepaw stimulus occurs in all 3 zones examined.(ABSTRACT TRUNCATED AT 400 WORDS)