Transneuronal labeling of neurons in the adult rat central nervous system following inoculation of pseudorabies virus into the colon

Transneuronal tracing with pseudorabies virus (PRV) was used to identify si tes in the central nervous system involved in the neural control of colon f unction. PRV-immunoreactive (IR) cells were primarily localized to the caud al lumbosacral (L6-S1) and caudal thoracic-rostral lumbar (T13-L1) spinal s egments with the distribution varying according to survival time (72-96 h). In the lumbosacral spinal cord at all time points examined, significantly (P less than or equal to 0.005) greater numbers of PRV-IR cells were presen t in the region of the sacral parasympathetic nucleus (SPN) of the S1 spina l segment compared to that of the L6 segment. These studies also revealed m orphologically distinct cell types with a differential distribution (probab ly interneurons and preganglionic parasympathetic neurons) in the region of the SPN in the L6-S1 spinal segments following colon inoculation. PRV-labe led neurons were located at various levels of the neuraxis and at many site s had a distribution similar to that following injection of virus to other urogenital organs. However, some unique sites in the dorsal motor nucleus o f the vagus, nucleus of the solitary tract, nucleus ambiguus and area postr ema were also identified. To determine if labeling in these caudal medullar y sites was mediated by spinal or vagal pathways, the colon was inoculated with PRV in animals with a complete spinal cord (TX) transection (5-7 days prior). Following spinal transection, PRV-infected cells were detected in t he same caudal medullary regions; however, labeling in other regions (e.g., Barrington's nucleus) was eliminated or significantly reduced. These studi es have yielded several novel observations concerning the central neural co ntrol of colonic function: (1) the preganglionic efferent and primary affer ent innervation of the colon arises primarily from the S1 spinal segment; ( 2) the distribution of PRV-infected neurons in the central nervous system f ollowing colon inoculation was similar to that following PRV inoculation of other urogenital organs; (3) Barrington's nucleus, which has been identifi ed previously as the pontine micturition center, may have a role in colonic function; and (4) PRV infection in Barrington's nucleus following colon in oculation is mediated by bulbospinal pathways whereas labeling in caudal me dullary regions is mediated, at least in part, by vagal pathways.