Ultrastructural identification of physiologically recorded neurons in the cat cerebellum.

Abstract

Neurons from the cerebellar cortex of cats were examined in electron microscopic preparations after intracellular recording and pressure injections of horseradish peroxidase (HRP). Neurons that contained HRP reaction product within dendrites were identified as either Purkinje or Golgi II cells. This identification was based on specific ultrastructural criteria that included the presence of synapses on the surfaces of dendritic shafts or spines, the identification of the presynaptic component of these synapses, and the presence of certain visible intracellular organelles. In addition, we examined specimens that contained two types of labeled dendrites after a single HRP injection. These dendrites were identified as arising from Purkinje and Golgi II cells and were shown to interdigitate with each other in a dendritic glomerulus. Dendritic appendages or sheet-like spines emanated from the Purkinje cell dendrite and sent small finger-like protrusions that surrounded and invaginated the Golgi II cell dendrite. In this glomerulus, the dendrites were shown to approach each other, and preliminary results suggest the presence of a gap junction at this site of direct apposition. This finding supports physiologic data which suggest electrical coupling between Purkinje and Golgi II cells. In addition, the results of this study demonstrate the usefulness of combining intracellular electrophysiology with HRP staining for the ultrastructural identification of recorded neurons. © 1980