Morphological and Physiological Differentiation of Purkinje Neurons in Cultures of Rat Cerebellum

During ontogeny, vertebrate CNS neurons differentiate from relatively simple stem cells to complex units that express unique morphological and electrophysiological characteristics. We have examined several aspects of this developmental process in an identified CNS neuronal type, the Purkinje neuron (PN) of the cerebellum. Our approach has included the use of a tissue culture preparation and immunohistochemical and electrophysiological techniques. Using immunohistochemical techniques, we have identified immature PNs in culture and examined their morphological and synaptic development. These studies have shown that PNs undergo extensive morphological and synaptic development in culture, the morphological characteristics of the immature PNs in culture and the developmental sequence and time course are reflective of that described for PNs in vivo, synapse formation is initiated at an early stage of PN development in culture and proceeds concurrently with the morphological development, and the main period of synapse formation is associated with the main period of dendritic development, reflecting the preferential location of synaptic sites at the dendritic region of mature PN. Using electrophysiological techniques, we have examined the physiological development of PNs in culture and have correlated the stages in physiological, morphological, and synaptic development. Results from these studies show the following. Mature PNs in culture exhibit complex electrophysiological properties, including the ability to generate 2 types of spike events, simple and complex spikes, and endogenously generated activity. Expression of electrophysiological properties begins at an early stage in PN development, when the PNs consist of little more than a soma with a few fine perisomatic processes. The earliest physiological characteristics to be expressed by the PN include sensitivity to transmitters, the ability to respond to synaptic input, and the ability to generate simple spikes. Synaptic input produces spontaneous activity in young PNs, but the patterns of activity change during development as mechanisms underlying endogenously generated activity and complex spike generation are expressed, and synapse formation proceeds.(ABSTRACT TRUNCATED AT 400 WORDS)