Distribution of NADPH-diaphorase reactivity in the spinal cord of metamorphosing and adult Xenopus laevis

The histochemical NADPH-diaphorase reaction has identified distinct neuronal populations in the nervous system of several species. Considerable evidence suggests that NADPH-d is a neuronal nitric oxide synthase (NOS). We examined spinal cords of adult and metamorphosing Xenopus laevis (XL) for developmental differences in NADPH-d reactivity. In adult XL, labeling was found in all dorsal root ganglia (DRGs) and in their termination sites within the dorsal horn (cutaneous afferent field) and intermediate gray (muscle afferent field). Cell bodies in the intermediate gray regions containing the autonomic preganglionic neurons were labeled in thoracic and sacral sections. Neurons located in the medial (MMC) and lateral motor columns (LMC) of the ventral horn were also stained. In metamorphosing XL, reactivity was detected in neurons in the intermediate gray, in the MMC and in the LMC as in the adult. Additionally, primary motoneurons including those innervating tail musculature were labeled. Neurons in the DRGs were stained at all stages; in the dorsal horn, the density of staining reflected the development of the sensory afferent fields. The conservation of NADPH-d reactivity in adult and metamorphosing XL spinal neurons suggests that NOS may be involved in processes independent of developmental changes occurring in XL spinal cord.