Primary afferents sensitive to capsaicin and noxious heat express vanilloid receptor 1(VR1) in both their peripheral and central fibers and terminals. We used multiple immunofluorescence and confocal microscopy to characterize their pattern of termination in rat spinal cord, colocalization of neurochemical markers of primary afferents and other presynaptic receptors. VR1-positive unmyelinated fibers mainly terminate in lamina I, where they co-stain for CGRP, and to a limited extent for SP, and in lamina II, especially its medial half, where they co-stain for IB4. VR1 positive thin myelinated fibers terminate in lamina I and co-stain for the neurochemical tracer CTB, injected in the sciatic nerve. As revealed by simultaneous staining for the synaptic marker synaptophysin, VR1-positive terminals are abundant in lamina I and sparse in lamina II. In L6-S1 spinal cord, VR1-positive fibers and terminals were abundant in Lissauer's tract, lamina I-V, medial collateral path to lamina X, and lateral collateral path to sacral parasympathetic nucleus. Most of VR1 positive fibers in Lissuer's tract and LCP are colocalized with SP. In conclusion, it is suggested that VR1 positive fibers in spinal cord are both peptidergic and non-peptidergic, IB4 positive fibers, mediating both somatic and visceral sensations, and that peptidergic VR1 positive fibers are mainly related with visceral sense.
Animals ; Capsaicin ; Fluorescent Antibody Technique ; Ganglia, Spinal ; Hot Temperature ; Microscopy, Confocal ; Myelin Sheath ; Negotiating ; Rats* ; Receptors, Presynaptic ; Sciatic Nerve ; Sensation ; Spinal Cord ; Synaptophysin