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

Abstract

Splenic immune function is modulated by sympathetic innervation, which in turn is controlled by inputs from supraspinal regions. In the present study, the characterization of central circuits involved in the control of splenic function was accomplished by injecting pseudorabies virus (PRV), a retrograde transynaptic tracer, into the spleen and conducting a temporal analysis of the progression of the infection from 60 hours to 110 hours postinoculation. In addition, central noradrenergic cell groups involved in splenic innervation were characterized by dual immunohistochemical detection of dopamine-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 ventrolateral 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 appeared in lateral hypothalamus, A7 region, locus coeruleus, subcoeruleus region, nucleus of the solitary tract, and C3 cell group. At longer postinoculation intervals, infected neurons were found in additional hypothalamic areas, Edinger-Westphal nucleus, periaqueductal gray, pedunculopontine tegmental 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.

Splenic nerve is required for cholinergic antiinflammatory pathway control of TNF in endotoxemia

“…5 G and H), indicating that nerve terminals found in juxtaposition to TNF-producing macrophages are catecholaminergic. In agreement with studies that indicate lack of vagus innervation of the spleen (14,16,17), staining of spleen sections with antibodies against choline acetyltransferase or vesicular acetylcholine transporter, markers of cholinergic neurons, failed to reveal cholinergic nerve fibers (data not shown). Together, these results indicate that the nerve fibers supplying the TNF-secreting macrophages are catecholaminergic, not cholinergic.…”

“…5 C and D). Previous studies indicate that innervation of the spleen is supplied by the splenic nerve, which is comprised principally of catecholaminergic fibers originating in the ganglia of the celiac-superior mesenteric plexus (15)(16)(17). Spleen tissue treated with glyoxylic acid, a standard procedure to stain catecholamines (26), revealed an extensive nerve fiber network that followed the same distribution as that of synaptophysin ( Fig.…”

“…This finding was surprising because experimental evidence indicates that efferent fibers from the celiac branch of the vagus nerve terminate in the celiac-superior mesenteric plexus ganglia (13), but not in the spleen (14). Innervation of the spleen is provided by catecholaminergic fibers that originate in the celiac-superior mesenteric plexus ganglia (15)(16)(17), which are in turn under the control of preganglionic neurons located in the intermediolateral gray column of the thoracic spinal cord (16). Here, we show that catecholaminergic splenic nerve fibers terminate adjacent to TNF-producing macrophages and that surgical ablation of the splenic nerve or catecholamine depletion by reserpine abrogates the suppressive effect of vagus nerve stimulation on TNF production.…”

Autonomic innervation and regulation of the immune system (1987–2007)

“…At longer survival times, virus labeling was detected in premotor sympathetic brain nuclei in the brain stem, pons and hypothalamus. While the central pattern of transneuronal labeling was comparable to what has been reported for the thymus and spleen (Cano et al, 2001;Trotter et al, 2007), the amount of central labeling of PRV infected neurons was very limited and likely was due to the high and neurotoxic doses of PRV required to initiate transneuronal transport from bone marrow. However, their results establish the origin of sympathetic neural input to bone marrow, and importantly, dual transneuronal labeling with two isogenic, but histochemically distinguishable, forms of PRV allowed a comparison between bone marrow versus the overlying skeletal muscles.…”

“…Similarly, immunohistochemical studies for vesicular acetylcholine transporter, a highly specific marker for cholinergic neurons and fibers, indicated their complete absence in lymphoid tissue (Schafer et al, 1998). Finally, a transneuronal study of the innervation of the spleen with PRV has verfied this conclusion (Cano et al, 2001) and demonstrated that sympathetic preganglionic neurons that innervate the spleen arise from the T1-T12 region of the thoracic spinal cord. Longer survival times identified sympathetic premotor brain nuclei projecting either directly or indirectly to the spinal sympathetic preganglionic neurons, and again consisted of many of the same nuclei in the brainstem, pons and hypothalamus that are activated by immune stimuli ( Wan et al, 1994).…”