Field potential analysis in elasmobranch cerebellum.
Stimulation of cerebellar white matter (WM) in the skate, an elasmobranch fish, evokes a distinctive set of cortical field potentials characterized by 3 negativities and a positivity. The first negativity (N1) has 1 msec latency and is largest in the lateral regions of the corpus cerebelli where Purkinje cells and white matter are most densely congregated. The second negativity (N2) occurs at 2--4 msec latency and is localized to the granular layer. The third negativity (N3) follows with a latency of 4--6 msec and is prominent in the molecular layer. The positivity (P) correlates with N2 in time course and dominates in the midline where granule cell axons ascend en masse to form parallel fibers in the molecular layer. A preceding WM stimulus blocks the N1 potential for 20 msec and the N2 potential for 60 msec and the N2 potential for 20 msec. A conditioning stimulus, applied to the parallel fibers in the dorsal midline (LOC), suppresses the N1 potential for 20 msec and the N2 potential for 40 msec. Intracellular recordings from the Purkinje cell layer reveals short latency action potentials correlating in time with N1. These findings suggest that N1 derives from antidromic Purkinje cell activation and mossy fiber excitation, that N2 represents orthodromic granule cell excitation by white matter fibers, and that N3 stems from parallel fiber activity. Because of its close association with parallel fibers and the similarity of its time course to N2, the positivity is attributed to current sources in parallel fibers generated by granule cell current sinks. Differences between the cerebellar field potentials found in elasmobranchs and mammals can be explained by the unique anatomic arrangement of granule cell axons in the former.
D000818:Animals; D001369:Axons / Q000502:physiology; D002531:Cerebellum / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials; D005399:Fishes; D009474:Neurons / Q000502:physiology; D011689:Purkinje Cells / Q000502:physiology