Nitric oxide synthase and background adaptation in Xenopus laevis

Abstract

Adaptation of the skin colour to the background light condition in the amphibian Xenopus lae6is is achieved by migration of pigment granules in the skin melanophores, a process regulated by h-MSH secretion from melanotrope cells in the pituitary pars intermedia (PI). h-MSH secretion in turn, is regulated by various stimulatory and inhibitory messengers synthesized in brain nuclei, especially the hypothalamic suprachiasmatic and magnocellular nuclei and the locus coeruleus in the hindbrain.In the present study, the roles in background adaptation of nitric oxide (NO) and NO synthase (NOS) enzyme activity were evaluated. In situ, using both immunohistochemistry with anti-human brain NOS (bNOS) serum in paraffin-embedded material and using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry in cryo-sections, we showed NOS in neurons in the optic tectum and in the locus coeruleus. NADPH-d reactivity was also found in neurons in the lateral amygdala, the ventral hypothalamic nucleus and in fibers in the median eminence. Using a Western blot stained with an anti-human bNOS serum, we demonstrated a 150 kDa band in Xenopus hindbrain lysates, which is similar to the NOS protein present in the rat anterior pituitary, but which was not detectable in the lysates from both the neurointermediate and distal lobes in Xenopus. No differences in histochemical staining pattern or on Western blotting were observed between animals adapted to a black or a white background.Paraffin sections of the endocrine PI and pars distalis did not reveal bNOS-like immunoreactivity. NADPH-d reactivity was observed in the endothelia of this gland. However, using a new procedure of thin cryo-sections of pituitary neurointermediate lobes, we observed bNOS-immunoreactive fibers as well as cyclic 3%,5% guanosine monophosphate (cGMP)-accumulating fibers in the PI.The PI may be regulated by NOergic neurons from higher brain centers. The possibility that NOergic neurons in the locus coeruleus are involved in the innervation of the PI needs further investigation. The latter neurons are probably not noradrenergic because double labeling studies show no co-localization of NADPH-d reactivity and tyrosine hydroxylase immunoreactivity in locus coeruleus neurons. © 1997 Elsevier Science B.V.

Nitric Oxide Synthase and NADPH Diaphorase Distribution in the Bullfrog <i>(Rana catesbeiana)</i> CNS: Pathways and Functional Implications

“…A similar pattern is found in other amphibians [Artero et al, 1995;González et al, 1996González et al, , 2002Muñoz et al, 1996;Lázár and Losonczy, 1999]. For example, in X. laevis, nitrergic cells are located in the optic tectum [Brüning and Mayer, 1996], as well as the locus coeruleus and hypothalamic suprachiasmatic and magnocellular nuclei [Allaerts et al, 1997b]. It is likely that NO participates in higher level visual processing in these areas, as it does in other vertebrates [Cudeiro and Sillito, 2006].…”

Pattern of Nitrergic Neuronal System Organization in the Brain of Two Holostean Fishes (Actinopterygii: Ginglymodi)

“…Comparatively, intensely NOS-ir cells are present in the paraventricular area of cladistians [López et al, 2016] and their projections could be followed towards the neurohypophysis. Similar nitrergic groups with hypothalamo-hypophysial projections have been reported in the electric ray [Pérez et al, 1995], in the teleost Clarias batrachus [Gaikwad et al, 2009], and in anuran amphibians [Allaerts et al, 1997;Prasada Rao et al, 1997], although some amphibian species may lack nitrergic cells in the paraventricular region [Pinelli et al, 2014]. In mammals, the NADPH-d-reactive cells of the neurosecretory hypothalamic nuclei coexpress vasopressin/oxytocin [Arévalo et al, 1992;Miyagawa et al, 1994;Sánchez et al, 1994], where the NO probably regulates the release of these neurohormones [Vanhatalo and Soinila, 1995], whereas this colocalization is absent in the hypothalamus of birds [Sánchez et al, 1996].…”

Organization of the nitrergic neuronal system in the primitive bony fishesPolypterus senegalusandErpetoichthys calabaricus(Actinopterygii: Cladistia)

“…This innervation probably arises from the nitrergic cells in the paraventricular area, although tract‐tracing techniques are needed to confirm this hypothesis. A similar hypothalamohypophysial tract has been described for the electric ray (Pérez et al, ), the teleost Clarias batrachus (Gaikwad et al, ), and the anuran amphibians (Allaerts et al, ; Prasada Rao et al, ). In addition, partial colocalization between NOS and vasopressin/oxytocin was demonstrated in mammals (Arévalo et al, ; Miyagawa et al, ; Sánchez et al, ), and a similar approach would be necessary to clarify the neurosecretory nature of the nitrergic group in the paraventricular area of cladistians.…”