Neuro-Anatomical Evidence Indicating Indirect Modulation of Macrophages by Vagal Efferents in the Intestine but Not in the Spleen

Abstract

BackgroundElectrical stimulation of the vagus nerve suppresses intestinal inflammation and normalizes gut motility in a mouse model of postoperative ileus. The exact anatomical interaction between the vagus nerve and the intestinal immune system remains however a matter of debate. In the present study, we provide additional evidence on the direct and indirect vagal innervation of the spleen and analyzed the anatomical evidence for neuroimmune modulation of macrophages by vagal preganglionic and enteric postganglionic nerve fibers within the intestine.MethodsDextran conjugates were used to label vagal preganglionic (motor) fibers projecting to the small intestine and spleen. Moreover, identification of the neurochemical phenotype of the vagal efferent fibers and enteric neurons was performed by immunofluorescent labeling. F4/80 antibody was used to label resident macrophages.ResultsOur anterograde tracing experiments did not reveal dextran-labeled vagal fibers or terminals in the mesenteric ganglion or spleen. Vagal efferent fibers were confined within the myenteric plexus region of the small intestine and mainly endings around nNOS, VIP and ChAT positive enteric neurons. nNOS, VIP and ChAT positive fibers were found in close proximity of intestinal resident macrophages carrying α7 nicotinic receptors. Of note, VIP receptors were found on resident macrophages located in close proximity of VIP positive nerve fibers.ConclusionIn the present study, we show that the vagus nerve does not directly interact with resident macrophages in the gut or spleen. Instead, the vagus nerve preferentially interacts with nNOS, VIP and ChAT enteric neurons located within the gut muscularis with nerve endings in close proximity of the resident macrophages.

Enteric Neuronal Regulation of Intestinal Inflammation

“…These interactions involve the action of neurotransmitters, neuromodulators, and cytokines that carry signals, often bidirectionally, between enteric neurons and immune cells [19,20]. Disappointingly, neurons do not form traditional synapses with immune cells, which complicates the use of anatomical tools to investigate neuroimmune interactions; however, axons and immune cells do form ‘close associations’ that are often interpreted to be the anatomical substrate of functional interactions [21,22]. In the case of neurons and macrophages, the bidirectional link is dependent on macrophage secretion of bone morphogenetic protein 2 (BMP2) and neuronal secretion of colony stimulating factor 1 [22].…”

Vagus nerve stimulation mediates protection from kidney ischemia-reperfusion injury through α7nAChR+ splenocytes

“…As part of the CAP (13)(14)(15), acetylcholine-producing (ACh-producing) lymphocytes might have an important role. Although the intervening steps between VNS and splenic activation are not clearly defined (10,16), norepinephrine (NE) that is released from the splenic sympathetic nerve binds to β2-adrenergic receptors (β2AR) on nearby choline acetyltransferase-expressing (ChAT-expressing) splenic memory T cells (CD4 + CD44 hi CD62L lo ) and B cells (17). This subset of splenic ACh-producing T cells likely activates adjacent splenic macrophages via the α7nAChR (15), which leads to suppression of proinflammatory cytokines.…”

Type 3 Muscarinic Receptors Contribute to Clearance of Citrobacter rodentium

“…Cholinergic tone exerts anti-inflammatory effects on macrophages via the α7 NR (40–42); however, the effect of muscarinic specific tone on macrophages is uncertain. Expression of Nos-2 , a marker for CAM, was increased significantly in WT BMDM treated with bethanechol indicating that WT BMDM differentiate into CAM upon muscarinic stimulation (Figure 8A).…”