Quantitative analysis of the recurrent collaterals derived from Purkinje cells in zone X of the cat's vermis

Abstract

Intracellular electrodes filled with 4% horseradish peroxidase (HRP) were used to impale Purkinje cells in zone x of the cat's cerebellum. Subsequent to recording responses to bilateral stimulation of the ulnar, radial, and sciatic nerves, the cells were injected with HRP. Intracellularly labeled Purkinje cells were located and correlated with the physiological data. Purkinje cells in zone x respond primarily to stimulation of the ipsilateral forelimb. However, they have broad receptive fields in that most also receive inputs from stimulation of the contralateral forelimb or from more than one forelimb nerve; a few respond to activation of the hindlimb. The distribution of the recurrent collaterals of zone x Purkinje cells has several features that are similar to those from zones a,b, and c: 1) they have a similar number of varicosities within the plexus; 2) they distribute primarily in the sagittal as compared to the transverse plane; and 3) most varicosities in the plexus are located within the Purkinje cell layer. However, several characteristics distinguish the collaterals of zone x Purkinje cells. First, they have a greater transverse extent than those derived from Purkinje cells in zones a,b, and c. Second, they have a higher percentage of collaterals that extend to more superficial aspects of the molecular layer as well as to deep levels of the granule cell layer. The rostral extent of zone x has not been clearly defined in previous studies. On the basis of anatomical and physiological data derived from the present study it appears that Purkinje cells located in lobule Va have physiological and morphological properties similar to those observed for Purkinje cells in more caudal folia of lobule V. Thus, on the basis of the organization of local circuits, it appears that zone x extends at least to the most rostral folia of lobule V. In conclusion, these data suggest that Purkinje cells in zone x may not be involved in controlling the movements of specific muscles, as may be the case in other cortical zones. Rather, it could be hypothesized that Purkinje cells in zone x have a more generalized role in coordinating agonist and antagonist muscle groups in one limb or regulating patterns of movement between limbs.