Maintaining the stability of neural function: a homeostatic hypothesis.

The precise regulation of neural excitability is essential for proper nerve cell, neural circuit, and nervous system function. During postembryonic development and throughout life, neurons are challenged with perturbations that can alter excitability, including changes in cell size, innervation, and synaptic input. Numerous experiments demonstrate that neurons are able to compensate for these types of perturbation and maintain appropriate levels of excitation. The mechanisms of compensation are diverse, including regulated changes to synaptic size, synaptic strength, and ion channel function in the plasma membrane. These data are evidence for homeostatic regulatory systems that control neural excitability. A model of neural homeostasis suggests that information about cell activity, cell size, and innervation is fed into a system of cellular monitors. Intracellular- and intercellular-signaling systems transduce this information into regulated changes in synaptic and ion channel function. This review discusses evidence for such a model of homeostatic regulation in the nervous system.