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L Descarries

Publications and source records attributed to L Descarries.

At least 109 records · Page 6Linked to original sources
PubMed1979

Radioautographic characterization of a serotonin-accumulating nerve cell group in adult rat hypothalamus.

Intensely labeled nerve cell bodies were identified by radioautography within the pars ventralis of nucleus dorsomedialis hypothalami (hdv), following intraventricular perfusion with 10(-5) or 10(-4) M tritiated serotonin [3H]5-HT in adult rats pretreated with a monoamine oxidase inhibitor. This selective reaction, which involved approximately 1000 neurons on each side of the third ventricle, was unaltered by concomitant administration of 10(-3) M non-radioactive norepinephrine, and was absent after intraventricular injection of 10(-5) or 10(-4) M tritiated norepinephrine. The 3H-labeled 5-HT nerve cell bodies were loosely grouped within the inner and caudal half of the hdv, and appeared morphologically similar to the unreactive neurons among which they were interspersed. Within the same region, numerous labeled axonal varicosities were also detected, which were never found in synaptic contact with the reactive cells. If the 3H-labeled 5-HT neurons contain endogenous 5-HT, they might constitute an intrinsic source of 5-HT innervation in the adult rat hypothalamus.

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PubMed1978

[Adaptation of the deoxyglucose method to the cellular level: histologic preparation of the central nervous system for high resolution radioautography].

Vascular perfusion of all products required for primary fixation, postfixation, dehydration and embedding of nervous tissue in Epon permits radio-autographic detection of radioactivity accumulated in the central nervous system after intravenous injection of [3H]deoxyglucose. This histological technique should allow application of the deoxyglucose method at cellular if not subcellular level, since a high proportion of the tracer appears to be retained in situ in specimens adequately preserved for light and electron microscope radio-autography.

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PubMed1978

[Radioautographic identification of central monoaminergic neurons by local micro-instillation of tritiated serotonin or noradrenaline in cats].

Monoaminergic neurons in nuclei raphe dorsalis and locus coeruleus of the Cat may be visualized by radioautography after local micro-instillation of tritiated serotonin and noradrenaline. The concomitant administration of the appropriate tracer with the other biogenic amine in non radioactive form permits a specific identification of serotoninergic and catecholaminergic nerve cell bodies. A small contingent of presumptive serotoninergic neurons is thus demonstrated in the region of the locus coeruleus.

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PubMed1978

Serotonin nerve terminals in the locus coeruleus of adult rat: a radioautographic study.

Serotonin (5-HT) nerve terminals in the locus coeruleus (LC) of adult rat were visualized by high-resolution radioautography, in order to examine their distribution, fine structural features and intimate relationships with norepinephrine neurons. In animals pretreated with a monoamine oxidase inhibitor, prolonged intraventricular perfusion of 10(-4) M [3H]5-HT resulted in a specific identification of most if not all 5-HT axonal varicosities in LC. These terminals were equally distributed between the dorsal and ventral divisions of the nucleus. Their density was approximated at 10(7) per cu.mm within the middle third of the LC. In electron microscope radioautographs, the labeled 5-HT varicosities averaged 0.9 micron in diameter. They all exhibited a distinctive storage organelle, in the form of microvesicles and microcanaliculi (15-25 nm in diameter) partly filled with electron-dense material and usually aggregated in association with several large dense-core vesicles. While this finding of intrinsic morphological characteristics appeared compatible with a special cellular origin or regional differentiation, it was also suggestive of particular functional properties and/or mode of action. In a sample comprised of some 500 sectional profiles from labeled 5-HT varicosities in LC, a small proportion only (less than 10%) exhibited morphologically defined synaptic junctions. These rare contacts were invariably made with dendritic processes and never observed on the noradrenergic perikarya. It is therefore concluded that, in the LC, non-synaptic as well as synaptic mechanisms might be involved in the modulation and transneuronal regulation of norepinephrine neurons by 5-HT afferents.

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PubMed1976

Quantitative data on serotonin nerve terminals in adult rat neocortex.

Serotonin (5-HT) nerve terminals, specifically labeled with [3H]5-HT have been counted in light microscope radioautographs from the fronto-parietal neocortex of adult rats, following prolonged superfusions with relatively high concentrations of tracer (10(-5) M or 10(-4) M), and after 15 or 30 days of radioautographic exposure. Comparative analysis of the results indicated that all 5-HT varicosities did not possess the same capacity to accumulate the exogenous amine. Nevertheless, superfusions with 10(-4) M[3H]5-HT provided a sufficient loading of 5-HT boutons to allow their complete detection within any given layer of the neocortex. The labeled varicosities were found to be present within all cortical layers, except layer VI. Their total number was extrapolated to be approximately 1 X 10(6)/cu.mm of cortex. This figure represented a mean incidence of one 5-HT nerve terminal/850-1400 cortical synapses (0.07-0.12%). The intralaminar density of 5-HT innervation increased progressively from layer V to layer I, in a distribution pattern suggestive of unspecific afferents. Based on endogenous 5-HT levels of 346 +/- 32 ng/g for the fronto-parietal neocortex, the mean 5-HT content per varicosity could be estimated to be 0.35 X 10(-3) pg, and the concentration 1900 ng/g wet weight of terminal or 0.2%. In view of their particular ultrastructural features7, ubiquitous repartition and endogenous amine content, 5-HT nerve endings may be considered as capable of exerting a rather widespread influence in the neocortex.

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PubMed1975

Serotonin nerve terminals in adult rat neocortex.

Axonal processes which take up and retain exogenous tritiated serotonin ([3H]5-HT) have been demonstrated in the fronto-parietal cortex of adult rats, by means of high resolution radioautography. Prolonged topical superfusion with relatively high concentrations of ([3H]5-HT allowed detection of a maximal number of axonal reactions in the upper 3 layers of cortex. Comparison of results obtained from normal rats and animals pretreated with 6-hydroxydopamine or bearing midbrain raphe lesions established the specificity of this labeling. All reactive axons seemed to arise from the serotonin nerve cell bodies in groups B7 and B8 of Dahlström and Fuxe15. In electron microscope radioautographs, the serotonin fibers appeared as tenuous, naked axonal processes (0.1-0.5 mum in diameter) exhibiting small enlargements (0.7 mum in mean diameter) spaced at frequent intervals (1-3 mum). These boutons contained occasional mitochondria, small, round, agranular 'synaptic' vesicles and large granular vesicles. With axons, [3H]5-HT was concentrated in the boutons, and to a much lesser extent in connecting segments. This reactive pattern resembled that revealed by the fluorescence technique for endogenous serotonin. Preferential accumulations of the tracer by mitochondria and vesicular organelles indicated that these elements could sequester exogenous serotonin. Large granular vesicles were not necessarily visible in random thin sections of the labeled varicosities, and thus could not serve as the unique criterion for electron microscopic identification of 5-HT terminals. Moreover, these organelles are known to be present in other types of nerve endings. Topometric analysis of serial thin sections nevertheless demonstrated that large granular vesicles were potentially detectable in every 5-HT containing bouton, and also enabled extrapolation of their average number at 7 per varicosity. This low number makes it unlikely that large granular vesicles primarily represent storage sites. They could rather serve as a carrier for particle-bound enzymes essential to the local metabolism of serotonin or its precursors. A very small fraction of the serotonin varicosities exhibited the membrane differentiations of typical synaptic terminals. Extensive sampling in serial thin sections revealed junctional complexes in only 5% of labeled boutons, as opposed to 50% of unlabeled nerve endings in the surrounding neuropil. The data do not preclude the possibility that other monoaminergic neurons also share similar characteristics. It is probable that endogenous serotonin can be liberated from all axonal varicosities including those lacking strictu senso synaptic relationships. The overall configuration and ultrastructural features of cortical serotonin fibers suggest intrinsic dynamic properties which could assume particular significance in terms of function, plasticity and regrowth.

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PubMed1970

Intraneural distribution of exogenous norepinephrine in the central nervous system of the rat.

Catecholaminergic neurons, which take up and retain exogenous norepinephrine labeled with tritium, were studied by means of high resolution radioautography, in the substantia nigra, the substantia grisea periventricularis, and the locus coeruleus of the rat. Under the conditions required for the radioautographic detection of exogenous norepinephrine-(3)H, it was established that (1) glutaraldehyde was the most suitable fixative for preserving the labeled amine in situ; (2) norepinephrine-(3)H itself, rather than metabolites, accounted for most of the reactions detected in catecholaminergic neurons. At various time intervals after an intraventricular injection of norepinephrine-(3)H, the tracer reached a concentration 15-100 times higher, and disappeared at a slower rate, in presynaptic axons (t(1/2):4 hr) than in nerve cell bodies (t(1/2):0.8-1.3 hr). After pretreatment with a monoamine oxidase inhibitor, the radioautographic reactions increased and persisted longer, especially in the preterminal axons. Within neurons, the labeled amine was ubiquitously distributed in the nerve cell body and concentrated in presynaptic axons and synaptic terminals of various morphological types. Although large granular vesicles were usually present in the labeled axonal bulbs, no structural characteristic could be specifically ascribed to catecholaminergic neurons. It is suggested that exogenous norepinephrine bound to macromolecular complexes is present in all parts of catecholaminergic neurons and mainly concentrated within presynaptic axons.

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