Peripheral reflex pathways involving abdominal viscera: transmission of impulses through prevertebral ganglia

In neurophysiological terms, divergence describes the transmission of impulse traffic from a single afferent line, through an integrating nervous system, and out into multiple efferent lines. This feature has been ascribed to the vertebrate central nervous system and invertebrate ganglionic systems but has not yet been associated with the autonomic nervous system in mammals. Therefore, this study investigated the degree of divergence of afferent impulse traffic through a mammalian autonomic ganglion, the inferior mesenteric ganglion (IMG) in guinea pig. Multiunit discharges were recorded extracellularly from the peripheral nerves, which emerge from the IMG, to determine the lines of efferent outflow (i.e., divergence) of impulse traffic generated by stimulating central efferent and peripheral afferent nerves. Pathways interrupted by a cholinergic ganglion synapse were identified by using hexamethonium. Pathways running directly through the IMG were identified by studying the effects of dividing nerves surgically. A complex arrangement of ascending and descending pathways was revealed, showing a neural network that interconnects the upper gastrointestinal tract, distal colon, and pelvic viscera via prevertebral ganglia.