Functional role of dendritic spines.
A number of speculations have been made on the functional role of dendritic spines. Some emphasize that a spine modulates the effect of a chemical synapse on the spine head. Others propose that spines isolate neighboring synapses from each others' effects. Still others suggest that spines play a role in short- or long-term plasticity, while others deny any functional role for spines at all. This paper brings some quantitative calculations to bear on these questions. In contrast to previous studies of the steady-state voltage attenuation in dendrites having spines, our calculations predict the voltage transient throughout a dendrite due to activation of a chemical synapse on a spine-head, causing a time-dependent postsynaptic conductance change associated with a depolarizing reversal potential. We assume passive membrane in the spine and the dendrite. Computations were performed using a compartmental model of a long dendrite and a single spine, having parameters described by Jack et al. (1975). Voltage-divider approximations to the spine-neck were compared with direct compartmental models and with eigenfunction expansions to check the validity of the numerical integrations. In the spine-head, a pronounced transient depolarization is produced, more than twice that predicted by Jack et al. (1975) for steady-state current injection. The EPSP amplitude at the base of the spine was much smaller, and was slightly reduced by placing the synapse on the head of the spine rather than on the dendritic shaft.(ABSTRACT TRUNCATED AT 250 WORDS)
D003712:Dendrites / Q000502:physiology*; D008959:Models, Neurological; D009473:Neuronal Plasticity; D009474:Neurons / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology*