Transneuronal tracing of colonic-related afferent circuits in mice using herpes simplex virus 1 strain H129 expressing EGFP

The central circuits of spinal afferent pathways innervating pelvic visceral organs remain to be characterised in the mouse, despite the depth of knowledge on peripheral properties. To address this, we used anterograde transneuronal tracing with a strain of herpes simplex virus1 expressing EGFP (HSV-H129-EGFP). We injected HSV-H129-EGFP into the distal colon wall and neuronal expression of EGFP was tracked over time (24-120 hours; N=4/time)within thoracolumbar (TL; T10-L1) and lumbosacral (LS; L6-S1) dorsal root ganglia (DRG),spinal cord and brain. HSV-H129-EGFP was evident in LS DRG neurons 48 hours after colonic injection and in TL DRG after 72 hours. By 72-96 hours, EGFP labelled neurons were prevalent in the spinal cord, including LS dorsal horn laminae (LI-LV), dorsal grey commissure and sacral parasympathetic nucleus, and within the TL dorsal horn lamina I, the intermediolateral nucleus and around the central canal. After 96 hours, EGFP neurons were also evident within the caudal medulla, specifically within the dorsal motor vagal complex, reticular nuclei, nucleus raphe magnus and caudal locus coeruleus. After 120 hours, EGFP labelling had spread more rostral into the pontine locus coeruleus, Barrington’s nucleus, lateral parabrachial nucleus and pontine reticular formation. Dense labelling was also evident in the hypothalamic paraventricular nucleus, whilst sparse labelling was observed in the midbrain periaqueductal gray and thalamic nuclei (intermediodorsal and paraventricular) and medial-frontal cortex. These data provide the first description of the spinal cord and brain circuits relevant to the central neural control of colonic autonomic and sensory function in the mouse.