Co‐cultures of inferior olive and cerebellum: Electrophysiological evidence for multiple innervation of Purkinje cells by olivary axons

Slices of inferior olive (IO) and cerebellum were co‐cultured for several weeks by means of the roller tube technique. Recordings were carried out intracellularly from Purkinje cells (PCs) which were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow, or by immunohistochemical stainings with antibodies raised against the 28 kD Ca²⁺‐binding protein calbindin. Following stimulation of olivary tissue, an all‐or‐none full complex spike response was recorded in some PCs consisting of a fast rising spike followed by a depolarizing potential. In other PCs, graded stimulation of the olivary explant induced synaptic potentials which were characterized by step‐wise variation in their amplitude and resembled the ones occurring spontaneously. In contrast, only smoothly graded synaptic potentials were observed in cerebellar mono‐cultures. These results indicate that some of the PCs in olivo‐cerebellar co‐cultures are innervated by several olivary neurons.