Spatiotemporal pattern of nicotinamide adenine dinucleotide phosphate-diaphorase reactivity in the developing central nervous system of premetamorphic Xenopus laevis tadpoles

We have catalogued the progressive appearance of putative nitric oxide synt hase (NOS)containing neurons in the developing central nervous system (CNS) of Xenopus laevis. Xenopus embryos and larvae were processed in wholemount and in cross section using nicotinamide adenine dinucleotide phosphate-dia phorase (NADPH-d) histochemistry as a marker for NOS within the CNS. The te mporal sequence of NADPH-d reactivity identified discrete groups and subgro ups of neurons in the forebrain, midbrain, and hindbrain on the basis of th eir morphology, location, and order of appearance during development. A pro portion of these groups of neurons appeared to be important in sensory proc essing and motor control. Staining also appeared at specific stages in the spinal cord, the retina, and the skin. After the appearance of labelling, N ADPH-d reactivity continued in each of the cell groups throughout the stage s examined. We found no evidence for staining that subsequently disappeared at later stages in any cell group, indicating a persistent rather than tra nsient role for NO in the Xenopus tadpole CNS. These results are discussed in light of recent findings on possible roles for NADPH-d-positive cell gro ups within the developing motor circuitry. J. Comp. Neurol. 437:350-362, 20 01. (C) 2001 Wiley-Liss. Inc.