Lack of expression of the T-cell marker XTLA-1 in Xenopus tropicalis: exploitation in thymus restoration studies.

Flow cytometric studies employing the monoclonal antibody XT-1 reveal that, in contrast to other strains and species of Xenopus examined, thymocytes and splenocytes from X. tropicalis do not express the T lineage-specific antigen XTLA-1. Thymus dependence of XTLA-1 expression in splenocytes is confirmed in X. laevis by early thymectomy experiments. When X. tropicalis larval thymus is implanted to thymectomized X. borealis larvae, histological studies reveal extensive colonisation by host-derived (quinacrine-positive) cells following metamorphosis. Flow cytometry of propidium iodide-stained nuclei shows that within 3 months of xenothymus implantation, 90% of cells within the implant originate from the recipient; donor cells were undetectable in recipient spleens at this time. The emergence of near normal levels and distribution of XTLA-1 positive cells within xenogeneic thymus implants within 3 months of implantation is illustrated by flow cytometric observations and through immunofluorescence analysis of cryostat sections. These kinetic studies indicate that immigrant host cells require sojourn within the foreign thymus environment before they express the T-cell marker.     

Axon regeneration by developing limb motoneurones inXenopus laevis

Newly generated motoneurones invading the limb bud were labelled with horseradish peroxidase to identify them later in development. They were then axotomized by amputating the limb bud. The limb bud was replaced immediately in some animals. After the period of normal motoneurone death, which falls a few days after the operation, many horseradish peroxidase labelled motoneurones were still alive provided the limb bud had been replaced. Without a limb bud, labelled motoneurones were few or non-existent. The conclusion is that in spite of their immaturity, the labelled motoneurones must have grown new axons into the limb for their death to have been avoided. Axon regeneration therefore seems to be inherent to motoneurones of any age.     

Poly(A)~+mRNA翻译产生的GABA受体-氯离子通道复合体

采用生化药理学方法首次在注射了胚鸡脑poly(A)~+mRNA的非洲爪蟾卵母细胞表面检测到GABA受体复合体,从生化角度证实了移植GABA受体、安定受体的结合部位及其功能部位氯离子通道的存在。注射Barth液和poly(A)RNA的卵母细胞不能表达此受体复合体。放射性配体结合实验中,〔~3H〕FNZP终浓度高于0.6nmol/L时,结合趋于饱和,K_D=1.17nmol/L,B_(max)=1.5fmol/cell。此结合可被过量的氟安定抑制,而不受QNB的影响。蝇蕈醇(20μmol/L),内源性GABA受体激动剂(19μg/μl),苯巴比妥(500μmol/L)可以增强移植安定受体与〔~3H〕FNZP的结合。GABA(2μmol/L)及低浓度的印防己毒素(50μmol/L)对结合无影响,较高浓度(125μmol/L)的印防己毒素对结合有抑制作用。     

Morphological classification of retinal ganglion cells in adult Xenopus laevis

Summary Retrograde transport of horseradish peroxidase (HRP) was used to characterise the soma and dendritic arborization of retinal ganglion cells in adultXenopus laevis toad. HRP was administered to the cut end of the optic nerve and the morphological characteristics of HRP-filled ganglion cells were analysed in retinal wholemount preparations using computer assisted morphometry. Ganglion cells were classified according to their soma size, dendritic branching pattern, dendritic field and the number of shaft dendrites. Ganglion cells were divided into 3 major classes on the basis of soma sizes and extent of dendritic field: large (soma size, mean 258.04 μm²±52.03 SD; dendritic field size 0.104 mm²±0.23), medium size (126.7 μm²±37.01; 0.041 mm²±0.013) and small (87.3 μm²±22.69; 0.0061 mm²±0.0035). A more detailed analysis allowed 12 morphologically distinct subgroups to be identified (Types I–XII). Quantitative studies showed that large cells comprise about 1%, medium size about 8–9% and the small cells over 90% of total ganglion cell population. The number of large and medium size ganglion cells corresponded well with the number of myelinated optic fibres and the number of small neurons with the number of unmyelinated optic fibres in the optic nerve. Large ganglion cells were correlated with Class 4 and 5, medium size ganglion cells with Class 3 and small ganglion cells with Class 1 and 2 functionally characterized ganglion cells in the frog retina (Maturana et al. 1960). The retinal distribution of large ganglion cells appear to suggest certain similarities to mammalian alpha type ganglion cells.     

Axonal transport of [S]Methionine labeled proteins in Xenopus optic nerve: Phases of transport and the effects of nerve crush on protein patterns

Axonal transport of proteins in the Xenopus optic nerve was examined by labeling proteins in the eye with [³⁵S]methionine injected intraocularly and then analyzing the labeled proteins in the eye, nerve, and tectum on linear gradient SDS polyacrylamide gels at different times after the injection. Because the optic nerve in Xenopus is short, in order to distinguish transported proteins from locally synthesized proteins, the optic nerve on one side of the animal was crushed at the orbit (to stop axonal transport) 5–30 min prior to injection and the crushed and normal nerve segments were compared. Proteins in the intact nerve which were absent in the crushed nerve were identified as axonally transported proteins. By such criteria several waves corresponding to transported material moving at 6mm/day, 1.6–2.8 mm/day, and approximately 0.2 mm/day were detected in the nerve. The most rapid phases of transport could be further resolved in the optic tectum into 3 additional components at 60–96 mm/day, 30–48 mm/day, and 6–11 mm/day.Analysis of labeled proteins in the crushed nerves distal to the crush, near the injury site, revealed several locally synthesized proteins (mol. wt. 54,000, 48,000, 43,000 daltons) which were not present in normal, uninjured nerves. Such proteins are probably synthesized by glia in response to injury.     

Choline acetyltransferase immunoreactive neurons innervating labyrinthine and lateral line sense organs in amphibians

The goal of the present study was to investigate aspects of the central organization of the neurons belonging to the octavolateralis efferent system of amphibians. The perikarya of three genera, Pleurodeles, Xenopus, and Discoglossus, were located in the brainstem by applying retrograde to the appropriate cranial nerves and choline acetyltransferase immunohistochemistry was used to identify cholinergic neurons. The efferent neurons supplying lateral line (Pleurodeles, Xenopus) and labyrinthine (Pleurodeles, Xenopus, and Discoglossus) end organs were found to intermingle in a single octavolateralis efferent nucleus. The neurons lie bilateral to the labelled nerves in Pleurodeles and ipsilateral in Xenopus and Discoglossus. Separate labelling of the anterior and posterior octavus rami provided no evidence for distinct groupings of efferent neurons that could be associated with auditory and vestibular end organs. In all three species many if not all octavolateral efferent neurons displayed immunoreactivity for choline acetyltransferase. They could be distinguished from the cholinergic facial motoneurons, with which they sometimes intermingle, on the basis of either their distinctive size and shape (Pleurodeles, Xenopus) or their location (Discoglossus). Double labelling in Xenopus confirmed the cholinergic nature of the efferent neurons. © 1993 Wiley-Liss, Inc.     

Complete sequence of a cDNA encoding an active rat choline acetyltransferase: a tool to investigate the plasticity of cholinergic phenotype expression

A cDNA clone encoding the complete sequence of an active rat choline acetyltransferase (ChoAcTase; acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6) has been isolated. Analysis of the deduced amino acid sequence reveals 85% and 31% identity with the porcine and Drosophila melanogaster enzymes, respectively. To further elucidate the molecular basis of neurotransmitter-related phenotypic plasticity, the expression of ChoAcTase mRNA was compared with that of tyrosine hydroxylase [TH; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2], in neurons from superior cervical ganglia grown in the following conditions: 1) normal medium, 2) high K+ medium, and 3) normal medium supplemented with 50% muscle-conditioned medium (CM). TH mRNA was expressed in all three media; its level rose in high K+ and decreased strikingly in the presence of CM. ChoAcTase mRNA could be visualized in CM, but fell to undetectable levels in normal and high K+ media. These results suggest that translational or post-translational mechanisms do not play a major role for the modulation of neurotransmitter-associated phenotype.     

Xenopus skin mucus induces oral dyskinesias that promote escape from snakes

African clawed frogs fed to American water snakes induced yawning and gaping which slowed ingestion and facilitated the frogs' escape without inducing flavor aversion. The peptide and/or indolealkylamine contents of the frog's poison glands caused the effect because frogs with purged glands did not induce these behaviors and rarely escaped. Poison gland mucus, applied orally, elicited similar oral movements. The frog's clear lubricating mucus was inactive. As several compounds in the poison glands have known neuroleptic properties, the oral behaviors may be induced by neural mechanisms reported to govern neuroleptic-induced orofacial dyskinesia in schizophrenics.     

Strong modulation by RFamide neuropeptides of the ASIC1b/3 heteromer in competition with extracellular calcium

Acid-sensing ion channels are excitatory receptors for extracellular H⁺. Since the extracellular H⁺ concentration can significantly increase during an inflammation, one of the proposed functions for ASICs is peripheral perception of pain. The ASIC1b and ASIC3 subunits are specifically expressed in sensory ganglia neurons and are candidate sensors of peripheral acidosis. However, the function of these ASIC subunits is limited by their steady-state desensitization during a small but persistent increase of the H⁺ concentration and by their desensitization after stronger H⁺ stimuli. Here we show that ASIC1b and ASIC3 form a heteromeric channel that, at steady-state, desensitizes at more acidic values than either homomeric ASIC1b or homomeric ASIC3 alone. Moreover, we show that RFamide neuropeptides, putative modulators of ASIC activity during inflammation, drastically slow down the desensitization of the ASIC1b/3 heteromer with an apparent dissociation constant of 24 μM. The apparent affinity for RFamide-induced effects was about 3-fold higher at low extracellular calcium concentrations. Our results suggest that the ASIC1b/3 heteromer is a possible target for RFamide neuropeptides in the peripheral nervous system.