Characterization of the central nervous system innervation of the rat spleen using viral transneuronal tracing

Splenic immune function is modulated by sympathetic innervation, which in t urn is controlled by inputs from supraspinal regions. In the present study, the characterization of central circuits involved in the control of spleni c function was accomplished by injecting pseudorabies virus (PRV), a retrog rade transynaptic tracer, into the spleen and conducting a temporal analysi s of the progression of the infection from 60 hours to 110 hours postinocul ation. In addition, central noradrenergic cell groups involved in splenic i nnervation were characterized by dual immunohistochemical detection of dopa mine-beta -hydroxylase and PRV. Infection in the CNS first appeared in the spinal cord. Splenic sympathetic preganglionic neurons, identified in rats injected with Fluoro-Gold i.p. prior to PRV inoculation of the spleen, were located in T-3-T-12 bilaterally; numerous infected interneurons were also found in the thoracic spinal cord (T-1-T-13). Infected neurons in the brain were first observed in the A5 region, ventromedial medulla, rostral ventro lateral medulla, paraventricular hypothalamic nucleus, Barrington's nucleus , and caudal raphe. At intermediate survival times, the number of infected cells increased in previously infected areas, and infected neurons also app eared in lateral hypothalamus., A7 region, locus coeruleus, subcoeruleus re gion, nucleus of the solitary tract, and C3 cell group. At longer postinocu lation intervals, infected neurons were found in additional hypothalamic ar eas, Edinger-Westphal nucleus, periaqueductal gray, pedunculopontine tegmen tal nucleus, caudal ventrolateral medulla, and area postrema. These results demonstrate that the sympathetic outflow to the spleen is controlled by a complex multisynaptic pathway that involves several brainstem and forebrain nuclei. (C) 2001 Wiley-Liss, Inc.