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Localization of nitric oxide synthase in the brain of the frog, Xenopus laevis.
Brüning G
,
Mayer B
.
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Nitric oxide synthase was localized in the brain of the South african clawed frog by NADPH diaphorase histochemistry and immunohistochemistry. All structures stained by the antiserum also displayed NADPH diaphorase activity. The fiber bundles of the terminal nerve, however, were positive for NADPH diaphorase but were not immunoreactive. In the forebrain, neurons expressing nitric oxide synthase were concentrated to the pallium, striatum, nucleus accumbens and anterior entopeduncular nucleus. Strongly stained neurons in the diencephalon were detected in the lateralthalamus, the tuberculum posterior and in the ventralhypothalamus. In the mesencephalon, the tectum and the magnocellular nucleus of the torus semicircularis contained many positive cells. Farther caudally, intensely stained neurons were abundant in an area corresponding to the anuran locus coeruleus, in the descending nucleus of the trigeminus and the inferior reticular nucleus. In the cerebellum, Purkinje cells were weakly stained. In summary, the expression pattern of nitric oxide synthase in the anuran brain reveals similarities to that of other vertebrates. The strongly positive cell group in the locus coeruleus may correspond to cholinergic cell groups in the mesopontine area in mammals.
Fig. 1, Schematic drawings of coronal sections through the brain of Xenopus laeuis providing a qualitative evaluation of the distribution of NOS-positive
neurons, rated as either weakly (O) or strongly stained (O).
Fig. 2. NOS in the telencephalon of Xenopus laevis, NADPH diaphorase histochemistry (A,B,D) and immunofluorescence (C). A: overview of stained
neurons in the medial (Mp), dorsal (Dp) and lateral pallium (Lp). Bar = 200 /zm. B: large multipolar neuron in medial pallium. Bar + = 25 /zm. C,D:
identical section. Corresponding cells and fibers indicated by arrowheads. Bundles of terminal nerve labelled by arrows in B. Bars = 200 /zm.
Fig. 3. NOS in the posterior telencephalon of Xenopus laevis. Immunofluorescence (A,C) and NADPH-diaphorase histochemistry (B,D). Coresponding
cells in identical sections indicated by arrowheads. Terminal nerve stained by NADPH diaphorase only (arrows in B,D). A,B: identical section. Stained
neurons in the anterior entopeduncular nucleus (Ea) and lateral part of the amygdala (Apl). Medial is to the right. Bars = 200 ~m. C,D: Identical section
through the lateral part of the amygdala. Dashed line in C indicates ventricular margin. Medial is to the left. Bars = 50 /zm.
Fig. 4. NOS in the diencephalon of Xenopus laevis. Immunofluorescence (A,C) and NADPH-diaphorase histochemistry (B,D). A,B: identical section.
Intense sraining in the superficialventral thalamic nucleus. Medial is to the left. Bars = 100 /xm. C: NOS-positive neurons in the posterior tuberculum.
Dashed line indicates ventricular margin. Bar = 50 /xm. D: NOS-positive neurons in the ventralhypothalamus. Cerebrospinal fluid-contacting processes
(arrows). Bar = 100 #rn.
Fig. 5. NOS in the mesencephalon of Xenopus laevis. Immunofluorescence (A,E) and NADPH-diaphorase histochemistry (B,C,D,F). A,B: identical
section through the tectum. Neurons of the mesencephalic trigeminal nucleus indicated by arrows. Bars = 50 ktm. C: overview of the tectum mesencephali.
Bar = 100 #m. D-F: NOS-positive neurons in the ventral mesencephalon. Bar = 100 /zm. E,F: identical section. Corresponding neurons labelled by
arrowheads. Bars = 100 /xm.
Fig. 6. NOS in the metencephalon of Xenopus laevis. Immunofluorescence (A,B,D) and NADPH-diaphorase histochemistry (C). A: section through the
superior reticular nucleus (locus coeruleus) and isthmic nucleus (Is). Medial is to the left. Bar = 100/xm. B: section through the descending nucleus of the
trigeminus (Vd) and the root of the trigeminal nerve (nV). Bar = 200 /xm. C: cell cluster in the descending nucleus of the trigeminus. Bar = 50 /xm. D:
cerebellum. NOS-positive Purkinje cells and horizontal fibers. Bar ~ 50 /~m
Fig. 7. NOS in the metencephalon of Xenopus laevis. NADPH-diaphorase histochemistry. A: level of the cerebellum. Positive Purkinje cells (arrowheads)
and fiber bundles invading the cerebellum (arrow). Caudal continuation of nucleus reticularis superior (Rs). Bar = 200 /zm. B: level of the eighth nerve
(nVIlI). Fibers coursing between the dorsal nucleus (VIIId) and the superior olive (SO). Cluster of positive ceils in the central gray (GC). Bar = 200 p,m.
Fig. 8. NOS in the medulla oblongata of Xenopus laevis. NADPH-diaphorase histochemistry. A: level of the ninth nerve. B: level of the dorsal column
nucleus (DCN). Arcuate fibers originating in the inferior reticular nucleus (Ri) and the DCN. Group of small cells and terminal plexus dorsal to Ri (arrow).
Bars = 200 p,m.
