Symposium overview and historical perspective: dendrodendritic synapses: past, present, and future.

Synapses between dendrites are at the core of mechanisms for processing odor stimuli, as well as for processing in many other brain systems. A perspective on the development of our understanding of these mechanisms may therefore be of interest. Studies of the olfactory bulb leading to the discovery of dendrodendritic synapses began in 1959. They involved a multidisciplinary approach that included Golgi cell morphology, electrophysiology, a microcircuit wiring diagram, membrane biophysics, theory of field potentials, cable theory, dendritic electrotonus theory, computational models of mitral and granule cells, prediction by the models of dendrodendritic synaptic interactions, confirmation with electron microscopy using single sections and serial sections, and final integration in the reports of feedback and lateral inhibitory interactions in 1966 and 1968. Following the discovery of glomerular odor maps in the 1970s, the functional significance of the dendrodendritic inhibition in processing the maps has been increasingly documented. Recent experimental and computational studies are revealing how these synapses are organized into distributed systems for processing the odor maps. Future studies need to situate dendrodendritic mechanisms in these distributed systems and correlate them with the tight functional loops between olfactory bulb and olfactory cortex. Studies in awake behaving animals will be increasingly important. The relations of dendritic mechanisms to perception, memory, and the pathogenesis of disorders such as Alzheimer’s will be rich fields for study. Dendrites and their synapses should continue to provide ideal models for the study of basic mechanisms of cortical integration and the neural basis of smell.