J Taxi

Pierre and Marie Curie University - Paris 6, Lutetia Parisorum, Île-de-France, France

Are you J Taxi?

Claim your profile

Publications (15)18.53 Total impact

  • J Taxi, D Eugene
    [Show abstract] [Hide abstract]
    ABSTRACT: Without Abstract
    Neuroscience and Behavioral Physiology 01/1999; 29(4):439-43.
  • J Taxi, D Eugene
    [Show abstract] [Hide abstract]
    ABSTRACT: This work is based on the selective section of the B or C preganglionic fibres innervating respectively the B or C neurons of the last two abdominal ganglia of the sympathetic chain in the frog. A quantitative study of three morphological features of their synapses was performed for each of the two neuronal types. Significant differences were observed in the mean size of the preganglionic ending sections; on the contrary there were no differences in the mean length of the active zones. The subsynaptic apparatus, which is fairly frequent in this material, is not restricted to one neuronal type, although much more frequent in the synapses of B neurons. The modifications of the innervation of ganglionic neurons after selective section of one type of preganglionic fibres were followed measuring the synaptic density, using a synaptic index and an index of simple contacts. It appeared that, after selective degeneration of preganglionic C fibres, their regeneration being prevented, the preganglionic B fibres were able to from functional synapses on C neurons with a short latency, normal values of synaptic density being reached within 2 months. On the contrary, after degeneration of the preganglionic B fibres, the preganglionic C fibres reinnervated B neurons with a limited efficiency, in such a way that the synaptic density remained after several months much lower than normal and that electrophysiological recordings of synaptic transmission were limited to 44% of the impaled neurons. Possible interpretations of these data are discussed.
    Morfologiia (Saint Petersburg, Russia) 02/1998; 114(4):36-40.
  • D Eugene, G Lascar, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: Selective transection of the B or C preganglionic nerve fibres respectively innervating the B and C sympathetic neurons was carried out on the last two ganglia of the sympathetic chain of the frog Rana esculenta. At different times thereafter, the cross-reinnervation of one type of denervated neuron by nerve endings sprouting within the ganglia from intact fibres innervating the other type was investigated by both the quantitative morphology of the synaptic contacts and related structures and electrophysiological recordings of ganglionic transmission. As there are no fine ultrastructural criteria for distinguishing B from C neurons, the overall density of synapse, simple contact, and 'vacated' postsynaptic differentiation profiles was measured in the two cases of selective section and compared with the values for normal ganglia, therefore permitting the progress of cross-reinnervation with time for each type of neuron to be followed. At ten days after section of the C preganglionic fibres, immunocytochemistry showed that there were no anti-LH-RH-like peptide containing fibres within the ganglia. The B myelinated preganglionic fibres were able to reinnervate the denervated C neurons, with return to normal values of synaptic density and fully efficient transmission at two months in all tested C neurons. However, the latency of orthodromic action potentials was close to that of normally innervated B neurons. In contrast, the C non-myelinated preganglionic fibres reinnervated the denervated B neurons with limited efficiency, the synaptic density being two-thirds the normal value after five months, while subthreshold excitatory postsynaptic potentials or action potentials were only recorded in 44% of the tested B neurons. The latency of these orthodromic responses was close to that of normally innervated C neurons. It is postulated that the poor cross-reinnervation of B neurons could be due to insufficient sprouting of C fibres and/or lack of 'affinity' between C fibres and B neurons. In addition, these experiments demonstrated that the subsynaptic apparatus, fairly characteristic of frog ganglionic synapses, is present in both types of sympathetic neurons, although predominantly in B neurons.
    Journal of Neurocytology 01/1997; 25(12):763-75. · 1.94 Impact Factor
  • G Lascar, D Eugene, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: The synaptic organization of the amphibian sympathetic ganglia was studied, especially in the last two abdominal paravertebral ganglia of the frog. These ganglia appear to form a monosynaptic relay, not containing interneurons. They consist of two systems working in parallel: the principal neurons, by far the most numerous, and a small number of chromaffin (i.e., SIF) cells, usually arranged in clusters. Each principal neuron is innervated by a preganglionic branch forming a set of cholinergic synapses which exhibit classical ultrastructure. The only peculiarity is the presence of a subsynaptic apparatus in a variable percentage of synaptic complexes. Electrophysiological studies have demonstrated that synaptic transmission is due to ACh release and involves several postsynaptic potentials. Moreover, the principal neurons are of two types, B and C, whose preganglionic axons and their own axons have different conduction velocities. C neurons tend to be small in diameter, and B neurons are larger, but the size distribution of the two populations overlaps. More recently, it was demonstrated that these two neuronal systems have different immunocytochemical features. The C preganglionic fibers contain an LHRH-like peptide, which is responsible for late synaptic events. The B preganglionic fibers contain CGRP, whose role has not yet been established. The principal neurons all contain adrenaline, but neuropeptide Y is also present in C neurons and could be a second transmitter at peripheral junctions. SP-containing fibers also pass through the ganglia, but give rise to intraganglionic synapses only rarely, except in the celiac plexus. Galanin can coexist with neuropeptide Y in certain C neurons. Numerous principal neurons are immunoreactive for VIP. Chromaffin cells contain noradrenaline and metenkephalin, and some contain SP or LHRH; they are endocrine cells controlled by preganglionic fibers and can have a modulatory effect on principal neurons endowed with appropriate receptors. The accessibility of frog abdominal ganglia and the anatomical separation of B and C preganglionic fiber pathways provide interesting systems in which to carry out experimentation on the stability and specificity of synaptic contacts. After postganglionic axotomy, the majority of synapses disappear by disruption of synaptic contacts. There is a certain discrepancy between the recovery of synaptic transmission and the reappearance of morphologically identifiable synapses, suggesting that a certain amount of transmission is possible at contacts devoid of synaptic complexes. The selective deafferentation of B or C neurons showed that the subsynaptic apparati are mainly found at B neuron synapses. The course of reinnervation following selective deafferentation reveals the existence of different specificities at B and C synapses: C neurons are easily reinnervated by B preganglionic fibers, whereas C fibers appear fairly ineffective at reinnervating B neurons, even after a long interval. Attempts were made to reinnervate ganglionic neurons with somatic motor nerve fibers. Reinnervation was achieved only rarely, and it is concluded that the ganglionic synapses in the frog have a higher specificity and lower plasticity than in mammals.
    Microscopy Research and Technique 11/1996; 35(2):157-78. · 1.59 Impact Factor
  • D Eugène, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: The formation of synapses in the last two ganglia of the sympathetic chain of the frog Rana esculenta was investigated after anastomosing the 6th spinal nerve to the denervated ganglia in order to evaluate the reinnervation of deafferented sympathetic neurons with somatic cholinergic axons. The same ganglia were examined both electrophysiologically and morphologically from 25 to 280 days after the operation. In response to electrical stimulations of the anastomosed spinal nerve, synaptic transmission was analysed with intracellular microelectrodes placed into B or C sympathetic neurons. Synaptic density was quantified using electron microscopy by a synaptic index defined as the ratio of the number of synapses encountered to the number of perykarya examined. After ganglionic deafferentation, post-synaptic membrane differentiations persisted without any pre-synaptic element and an index of the 'vacated' post-synaptic differentiations was calculated. Although somatic axons were growing into all ganglia studied, no sign of neuronal reinnervation was detected in ganglia of 8 of the 31 frogs (26%) taken from 29 to 210 days after the anastomosis. Moreover, in 18 out of 31 frogs (58%) analysed at different times after the operation, the ganglia were reinnervated with regenerating preganglionic axons in spite of care taken to avoid it. However, even after 3 months, certain neurons of these ganglia were not reinnervated and the synaptic index approximated the value of normal ganglia only in the 8th ganglion. In addition, post-synaptic membrane differentiations could still persist and coexist with normal synapses. It was only beyond three months after the anastomosis that the ganglia of 5 of the 31 frogs (16%) were reinnervated with regenerating somatic axons. Reinnervated B and C neurons were polyinnervated. But in 3 out of these 5 frogs the ganglia were also reinnervated with preganglionic axons and several B and C neurons received a double reinnervation. The synaptic indices were far from the value of normal ganglia except for the 8th ganglion of one frog reinnervated by both types of axons and the indices of vacated differentiations were close to that of ganglia with no reinnervated neurons. Contrary to mammals, frog somatic axons are, therefore, relatively ineffective at reinnervating sympathetic neurons, probably because in amphibian ganglia, synapses between the pre- and post-synaptic elements require higher specificity.
    Journal of the Autonomic Nervous System 06/1995; 53(1):16-34.
  • J Taxi, D Eugène
    [Show abstract] [Hide abstract]
    ABSTRACT: The main physiological and morphological features of the synapses in the superior cervical ganglia of mammals and the last two abdominal ganglia of the frog sympathetic chain are summarized. The effects of axotomy on structure and function of ganglionic synapses are then reviewed, as well as various changes in neuronal metabolism in mammals and in the frog, in which the parallel between electrophysiological and morphological data leads to the conclusion that a certain amount of synaptic transmission occurs at "simple contacts." The effects of deafferentation on synaptic transmission and ultrastructure in the mammalian ganglia are reviewed: most synapses disappear, but a number of postsynaptic thickenings remain unchanged. Moreover, intrinsic synapses persist after total deafferentation and their number is strongly increased if axotomy is added to deafferentation. In the frog ganglia, the physiological and morphological evolution of synaptic areas is comparable to that of mammals, but no intrinsic synapses are observed. The reinnervation of deafferented sympathetic ganglia by foreign nerves, motor or sensory, is reported in mammals, with different degrees of efficiency. In the frog, the reinnervation of sympathetic ganglia with somatic motor nerve fibers is obtained in only 20% of the operated animals. The possible reasons for the high specificity of ganglionic connections in the frog are discussed.
    International Review of Cytology 02/1995; 159:195-263. · 6.09 Impact Factor
  • Source
    J Taxi
    Biology of the Cell 02/1994; 80(2-3):119-21. · 3.49 Impact Factor
  • D Eugene, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: Axotomy was carried out on frog sympathetic neurons of the two last lumbar chain ganglia. At different times thereafter, synaptic transmission was analysed electrophysiologically by intracellular microelectrodes and compared with synaptic density, measured by electron microscopy in the same ganglia. For this purpose, modifications in synaptic transmission were estimated first, by the numbers of B and C sympathetic neurons exhibiting subthreshold excitatory postsynaptic potentials in response to 10 Hz orthodromic stimulation of preganglionic fibres, and second, by the amplitude and number of excitatory postsynaptic potentials occurring over 5-10 s periods of 10 Hz stimulation. By distinguishing two types of morphological relationships between the pre- and postsynaptic elements, two contact indices were defined: a synaptic index (ratio of the number of synapses encountered to the number of perikarya explored) and a simple contact index corresponding to the same type of contacts, but without any membrane differentiation. Both the electrophysiological and morphological results showed that the first effects were detectable 4 days after axotomy, and that the main alterations in synaptic transmission and density occurred at 2 weeks. In addition, while in normal ganglia the excitatory postsynaptic potentials of B and C neurons reached the threshold for action potential generation in response to 10 Hz stimulation, about 29% of the axotomized neurons had subthreshold excitatory postsynaptic potentials 1 week after section. At 2 weeks, this proportion reached 65%, and the synaptic and simple contact indices, at 90% and 60% respectively, were significantly lower than the control ganglion indices. At longer times after axotomy, there was a discrepancy between the morphological and electrophysiological results: at 1 month, the synaptic index seemed to rise as the decline in the efficacy of synaptic transmission became more marked. The amplitude of the subthreshold excitatory postsynaptic potentials recorded in B neurons was 5.5 +/- 2.8 mV (mean +/- SD, n = 18); this value was significantly lower by about 50% than that measured 1 week after axotomy. In addition, the number of excitatory postsynaptic potentials in B neurons reached an average maximum of 83 +/- 29 for 100 stimuli applied at 10 Hz. Similar results were obtained for C neurons. Two months after axotomy, the physiological and morphological parameters of synaptic efficacy began to recover and return to normal values, but had not reached them by 4 months. These observations show that some synaptic transmission remains possible, even with a much reduced number of synaptic complexes. It is suggested that after axotomy, simple contacts also might be involved in synaptic transmission.
    Journal of Neurocytology 06/1991; 20(5):404-19. · 1.94 Impact Factor
  • G Lascar, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: Cell bodies and processes of SIF cells were found to be CCK-like immunoreactive within the mesenteric ganglion of the guinea-pig. Immunoreactivity was contained in granular vesicles, the labeling being chiefly associated with granules, about 100 nm in diameter. Asymmetric synaptic contacts between CCK-like immunoreactive SIF cells have been identified and a possible functional implication regarding intraganglionic connections for these SIF cells is discussed.
    Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie 02/1991; 312(2):77-84.
  • Source
    J Taxi, D Eugène
    [Show abstract] [Hide abstract]
    ABSTRACT: Changes in the shape of neuronal perikarya and other ganglionic structures were observed by electron microscopy in the frog sympathetic ganglia at different times after axotomy. Degenerating and hypertrophic profiles appeared to reflect a remodelling process affecting preganglionic fibres. The shape of neuronal perikarya was modified by the formation of infoldings occupied by preganglionic fibres and/or by that of short winding dendrites often bearing a synapse. The origin of these changes is discussed. In frog sympathetic ganglia, the period of recovery after axotomy was marked by specific reactions which affected neuronal shape and preganglionic fibres, and are not known to occur in the ganglia of mammals.
    Biology of the Cell 02/1991; 72(1-2):75-82. · 3.49 Impact Factor
  • D EUGENE, J TAXI
    Journal of The Autonomic Nervous System - J AUTONOM NERV SYST. 01/1991; 33(2):138-139.
  • D Eugène, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: In frog ganglia, efficacy of synaptic transmission was analyzed in parallel with the number of synapses at different times after axotomy of sympathetic neurons: the number of synapses was at their minimum at two weeks whereas depression of synaptic transmission was strongest at one month. The relationship between the presence of synaptic dense specializations and the existence of efficacious transmission is discussed.
    Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie 02/1990; 310(12):599-606.
  • G Lascar, J Taxi
    [Show abstract] [Hide abstract]
    ABSTRACT: Each adrenal gland of the Axolotl consists of a strip lying all along the medio-lateral edge on the ventral surface of the kidney. The gland is composed of interrenal cells (IC) and chromaffin cells (CC). The IC contained a great number of pleomorphic lipid droplets, smooth endoplasmic reticulum and elongated mitochondria with tubulo-vesicular cristae. Two types of CC, always disposed in clusters and exhibiting long cytoplasmic processes were described according to the electron density, size and shape of granules distributed in their cytoplasm; noradrenaline cells (NA) and adrenaline cells (A). The innervation and ultrastructural differences from the adrenal gland of other Anurans were discussed.
    Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie 02/1986; 303(6):211-6.
  • Comptes rendus des séances de l'Académie des sciences. Série III, Sciences de la vie 02/1982; 294(3):175-9.
  • J Taxi, G Lascar
    Trabajos del Instituto Cajal / Consejo Superior de Investigaciones Cientificas 02/1981; 72(2):83-109.

Publication Stats

55 Citations
18.53 Total Impact Points

Institutions

  • 1990–1999
    • Pierre and Marie Curie University - Paris 6
      Lutetia Parisorum, Île-de-France, France