Physiological Properties of Gap Junction Channels in the Nervous System

Before the patch clamp technique was developed, large cells were desirable for the multiple microelectrode impalements that physiological studies of gap junctions required. For that reason, as well as the inherent interest in understanding electrotonic synapses, much of the initial characterization of gap junction function, biophysical and pharmacological experiments were performed on the gigantic coupled neurons of molluscs, the fused axons and large cell bodies of arthropod neurons and the identifiable neurons and glia within the segmental ganglia of the leech. A few vertebrate preparations also fulfilled these requirements, such as the giant Mauthner cells1 and electromotor nuclei of certain teleosts,2 Rohon-Beard cells in the frog spinal cord3 and neurons within the inferior olivary nucleus of mammals,4 but the tedious dissection required for these vertebrate studies led most investigators to pursue the simpler nervous systems of invertebrates. Moreover, 20 years ago a focus of neurobiology was to determine neural circuits in organisms with a limited number of neurons, each of which was identifiable from one animal to the next.5 If we understood the wiring diagram and activity patterns underlying the brains and behaviors of these animals, it was widely believed, we would progress in large measure toward understanding the human mind.