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G Doucet

Publications and source records attributed to G Doucet.

33 records · Page 2Linked to original sources
PubMed1990

Intrastriatal implants of mesencephalic cell suspensions in weaver mutant mice: ultrastructural relationships of dopaminergic dendrites and axons issued from the graft.

Dissociated cell suspensions were prepared from the ventral midbrain of normal mouse foetuses and stereotaxically implanted into the neostriatum of 2-3 months old homozygous weaver mutant mice, which are severely deficient in dopamine. In tests of amphetamine-induced turning behaviour 60 days after grafting, recipient animals displayed a rotational bias opposite to the grafted side. Prior to perfusion, which was carried out at 80 days after transplantation surgery, the grafted striata of the weaver recipients were deprived of their intrinsic mesostriatal dopamine input by local injections of 6-hydroxydopamine into the ipsilateral substantia nigra in order to selectively study the innervation derived from the graft. Grafts were found to contain an estimated 100-700 tyrosine hydroxylase immunoreactive neurones. An ultrastructural analysis demonstrated that both axons and dendrites immunoreactive for tyrosine hydroxylase extended from the graft into the recipient striatum. In the host striatum proximal to the graft (i.e. at a distance of 0.0-0.5 mm from the graft) the proportion of dendrites to axons was about 1:2, whereas distal to the graft (i.e. at a distance of 0.5-1.0 mm) it was 1:20. Graft-derived tyrosine hydroxylase immunoreactive axons were primarily found in apposition with unlabelled dendrites or spines of the recipient striatum (greater than 90%). Graft-derived dopaminergic dendrites received synaptic input from unlabelled axon terminals and were opposed to the unlabelled somata of striatal neurones in a few instances. In conclusion, this study shows that mesencephalic cell suspensions survive in the weaver striatum and provide a functional dopamine innervation which comprises both axonal and dendritic processes.

Animals↗
PubMed1989

Degeneration and graft-induced restoration of dopamine innervation in the weaver mouse neostriatum: a quantitative radioautographic study of [3H]dopamine uptake.

A recently introduced quantitative radioautographic technique was used to characterize the striatal dopaminergic deficit in weaver mutant mice and to evaluate the extent of DA reinnervation resulting from cell suspension grafts of fetal ventral mesencephalic tissue. Brain slices from normal mice and unilaterally grafted weaver mice were incubated in [3H]DA, in the presence of desipramine and pargyline 3-5 months after graft surgery. Semi-thin sections from the fixed and resinembedded slices were subsequently exposed on tritium sensitive film and afterwards dipped in nuclear emulsion for light microscope radioautography. Alternative slices were embedded in Epon for post-embedding tyrosine hydroxylase (TH) immunocytochemistry. The grain density of the film radioautographs matched well the distribution of TH positive fibers. Both methods revealed an almost complete absence of DA axons in the dorsomedial quadrant of the weaver neostriatum and an increasing density of DA innervation towards the ventrolateral areas. In the light microscope radioautographs, only the ventral striatum (i.e. nucleus accumbens and olfactory tubercle) and a narrow ventral and periventricular zone of the caudate-putamen were covered by silver grain clusters typical of DA varicosity labeling. Such labeled varicosities were nevertheless found in reduced numbers the lateral portion of both nucleus accumbens and the olfactory tubercle. The remaining neostriatum was overlaid by diffuse silver grains. suggesting a deficient DA uptake and storage mechanism in the residual DA fibers in this region. Immunocytochemistry using antibodies specific for DA or TH provided further evidence that the residual DA innervation in the weaver neostriatum was biochemically defective. Weaver mice with grafts of ventral mesencephalic tissue in the right neostriatum showed an amphetamine-induced rotational bias to the contralateral side, which was not seen in the sham-operated animals. In contrast to the intrinsic weaver neostriatal DA innervation, DA fibers of graft origin exhibited the normal, clustered type of varicosity labeling. The computerized image analysis of silver grain density in film radioautographs was calibrated by counting these labeled varicosities in selected areas of light microscope radioautographs from the same sections. Results showed a mean DA reinnervation of neostriatal tissue surrounding the graft of about 20%, in some cases up to 80%, of the density seen in wild type mice, with a gradual decrease with distance up to 1-1.4 mm from the graft. The ventral parts of the neostriatum, which contained higher numbers of residual intrinsic DA fibers, were much more sparsely reinnervated than the dorsal and dorsomedial areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Amphetamines↗
PubMed1989

Host afferents into intrastriatal transplants of fetal ventral mesencephalon.

Host afferents into fetal ventral mesencephalic tissue grafted to the neostriatum of adult rats have been studied by using anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and immunocytochemistry for serotonin (5-HT), Substance P (SP), and dopamine-adenosine 3':5'-monophosphate-regulated-phosphoprotein-32 (DARPP-32). Numerous fibers of cortical origin were detected in the transplants following multiple (11-15) iontophoretic injections of PHA-L into the frontal and anterior cingulate cortex. The labeled fibers occurred with an apparently random distribution throughout the graft tissue. Their overall density was lower than that of the surrounding striatum but similar to that found in the host nigra-ventral tegmental area. The majority of the PHA-L-labeled fibers in the grafts were thin and tortuous with varicosities or lateral clubs with terminal boutons. Dual labeling showed frequent close appositions between PHA-L-labeled terminals and dopamine-immunoreactive cell bodies. In parallel electron microscopy, synaptic contacts were observed between PHA-L-labeled terminals and unlabeled neuronal profiles in the graft. Other labeled fibers in the grafts were thick and smooth, corresponding probably to labeled myelinated axons observed in the electron microscope. These thick fibers were often seen to give off collaterals of the thin type. The virtual absence of such thick fibers in the normal striatal neuropil suggests that at least some of the cortical afferents to the grafts may have sprouted from axons normally projecting to diencephalic or brain stem regions. Serotonin fibers occurred in patches or as scattered single fibers in both deep and superficial portions of the nigral transplants. In the electron microscope some of these terminals were seen to establish synaptic contacts with nonimmunoreactive elements in the graft. These fibers were present also when the graft tissue had been pretreated with 5,7-dihydroxytryptamine at the time of transplantation. This treatment eliminated all 5-HT-containing neurons from the grafts without any noticeable adverse effect on the survival of the dopaminergic neurons. The serotonin fibers in the grafts were thus most likely of host origin. SP-positive fibers formed a dense plexus inside the grafts. Since many SP-positive cell bodies were visualized inside the transplant after colchicine pretreatment, it is unclear, however, whether any of these fibers were of host origin. Intrastriatal injections of PHA-L or DARPP-32 immunocytochemistry indicated that the deep portions of the nigral grafts were entirely devoid of host striatal afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1988

Quantified regional and laminar distribution of the noradrenaline innervation in the anterior half of the adult rat cerebral cortex.

The regional and laminar distribution of the noradrenaline (NA) innervation in the adult rat cerebral cortex was quantified in radioautographs of semithin sections from whole hemisphere slices incubated with tritiated catecholamines and a monoamine oxidase inhibitor. Uptake-labeled axonal varicosities (aggregates of silver grains) were counted with the help of a computerized image analyzer in seven cytoarchitectonic areas of the rostral half of the cortex: Cg3, rostral AID, Cg2, Fr1, Par1, caudal AID, and Pir (prepiriform) according to Zilles's nomenclature. Both dopamine (DA) and NA terminals were detected after incubation with [3H]DA and citalopram or with [3H]NA alone. In the presence of desipramine (DMI), DA terminals alone were demonstrated; the number of NA terminals was then obtained by subtraction from counts in adjacent slices incubated with or without DMI. These counts suggested that DA and NA varicosities were fully visualized only after labeling with their respective tritiated amine. Similar numbers of labeled NA varicosities as inferred after [3H]NA incubation with or without DMI were observed after [3H]NA incubation in the presence of benztropine (BZ). This indicated that NA terminals were then maximally detected to the exclusion of the DA ones, and the latter approach was adopted for the acquisition of normative data. Since the average diameter of the labeled NA varicosities was known from earlier measurements in electron microscope radioautographs, the initial counts of labeled sites/mm2 of histological section could be expressed as numbers of varicosities/mm3 of tissue following a double correction for incomplete detection at the chosen duration of radioautographic exposure and section thickness. The overall density of NA innervation was thus estimated at 1.2 million varicosities/mm3 of tissue, with no statistically significant differences between the seven cortical areas examined. In every region, the number of NA terminals was the greatest in the molecular layer (1.5-2 times the density in the rest of cortex) and then progressively decreased in the underlying cortex, with a two- to threefold difference between upper and lower layers. These numerical data allowed an estimation to be made of the possible number of cortical NA varicosities per locus coeruleus nerve cell body of origin (at least 300,000), of their average number per cortical neuron (30-50), their actual incidence among all terminals in the cortex (1/1,000), their mean endogenous amine content per varicosity (0.22 fg), and the mean number of recognition sites for the uptake blocker DMI (4,500/varicosity).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Radioautographic method for quantifying regional monoamine innervations in the rat brain. Application to the cerebral cortex.

Conditions leading to selective and complete labeling of the noradrenaline (NA) and serotonin (5-HT) innervations in rat cerebral cortex were sought by incubating 200-micron-thick whole hemisphere slices with various combinations of tritiated monoamines and uptake blockers at different concentrations in the presence of a monoamine oxidase inhibitor. After fixation with glutaraldehyde, post-fixation with osmium tetroxide and flat-embedding in Epon, 4-micron-thick sections of the entire slices were radioautographed by dipping in nuclear emulsion. As previously reported, dopamine (DA) terminals could be specifically visualized and counted following incubation with 1 micron [3H]DA and 5 microM desipramine (DMI) with or without 5 microM citalopram (CITAL). The number of NA terminals could thus be obtained by subtracting DA varicosities from the total number of sites labeled in adjacent slices incubated without DMI but in presence of CITAL to eliminate some interspecific labeling of 5-HT terminals. NA terminals could also be identified exclusively and counted after labeling with 1 microM [3H]NA in the presence of 10 microM benztropine. 5-HT terminals were specifically detected after incubation with 1 microM [3H]5-HT in the presence of 10 microM non-radioactive NA. The labeled varicosities were counted in areas FR1 and PAR1 of the frontal and the parietal neocortex, respectively, with the aid of a microcomputer-based image analysis system. DA varicosities were concentrated mainly in layer VI of these regions and were more numerous in the frontal than the parietal area. NA terminals were equally distributed in the two regions but approximately twice as numerous in layer I than subjacent layers. The 5-HT innervation also showed a comparable overall density in the two cortical regions but with a differing intracortical distribution. In the frontal area, 5-HT terminals were slightly more concentrated in layer I (1.3-fold) than underlying layers where they were rather uniformly distributed. In the parietal area, layer I was again the most densely innervated (1.8 times the average), but a second zone of higher density (1.5 times average) was present in the outer part of layer V. The remaining layers showed lower numbers of 5-HT terminals than in the frontal region. To obtain absolute estimates of these innervation densities, the number of detected varicosities was assessed experimentally as a function of radioautographic exposure time and of histological section thickness, and their 'equivalent circle diameter' was measured in electron microscope radioautographs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Density of the dopamine innervation in rat cerebral cortex after neonatal 6-hydroxydopamine or adult stage DSP-4 noradrenaline denervations: a quantitative radioautographic study.

An in vitro radioautographic approach was used to count dopamine axon terminals (varicosities) of the mediofrontal and the supragenual cingulate cortex in 30-40-day-old rats treated with 6-hydroxydopamine at birth or with N(2-chloro-ethyl)N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) 7-10 days earlier. Compared to controls, there were no increases in the density of dopamine innervation in either region of the noradrenaline-denervated cortex after either treatment. The results, therefore, did not support the hypothesis of a sprouting of dopamine terminals reported to account for augmented cortical dopamine levels under these conditions. In line with earlier observations, such biochemical changes might rather be indicative of altered dopamine steady-state levels.

Animals↗
PubMed1987

Serotonin innervation in adult rat neostriatum. I. Quantified regional distribution.

The distributional features of the serotonin (5-HT) innervation in adult rat neostriatum were examined and quantified using two complementary chemoanatomical methods: 5-HT-immunohistochemistry on serial histological sections and radioautography after [3H]5-HT uptake in whole cerebral hemisphere slices. As visualized and measured after peroxidase-antiperoxidase immunostaining, the neostriatal 5-HT fiber network pervading the entire neostriatum was 2-3 times denser in its ventral than dorsal parts, and showed a slight rostrocaudal increase in density. Its axonal length ranged from 1.06 to 4.18 m per mm3 of striatal tissue. Radioautographic counts of the [3H]5-HT-labeled axon varicosities within comparable sectors of the neostriatum showed good correlation with this distribution pattern. As extrapolated after appropriate corrections for incomplete detection at the chosen exposure time and from the thickness of sections examined, the number of neostriatal 5-HT varicosities (innervation density) ranged from 1.5 to 4.8 millions and averaged 2.6 millions per mm3 of tissue. These quantitative results provided new insights into the topographical organization of the dorsal raphe-neostriatal 5-HT projection system. They already allow for meaningful correlations with currently available microchemical data on intrastriatal 5-HT levels and should also be of considerable significance when as precise information becomes available on the number and localization of different 5-HT receptors and uptake carriers within rat neostriatum.

Animals↗
PubMed1987

Regional and laminar density of the dopamine innervation in adult rat cerebral cortex.

The topographic distribution and density of the dopamine innervation in adult rat cerebral cortex were investigated by means of a recently improved radioautographic procedure for the light microscopic visualization and counting of monoamine axonal varicosities. Dopamine terminals were specifically labeled by high-affinity uptake in whole cerebral hemisphere slices incubated for 15 min at 35 degrees C with 10(-6) M tritiated dopamine in the presence of 10(-4) M pargyline and 5 X 10(-6) M desipramine. The slices were subsequently fixed, embedded in Epon and processed for light microscope radioautography as large 4-micron-thick (whole hemisphere) or smaller, semi-thin sections (selected areas). In radioautographs of serial semi-thin sections exposed for various periods of time, the number of labeled axonal varicosities reached a plateau after 12-14 days of exposure. Counts on such sections of increasing thickness allowed to calculate a correcting factor to transform numbers obtained from 4-micron-thick sections into their equivalent for a tissue thickness of 0.5 micron from which all varicosities were detected. The number of labeled varicosities could then be expressed per mm3 of tissue after measuring their mean caliper diameter in electron microscope radioautographs. As visualized at 3 transverse levels representing most of the major cytoarchitectonic divisions of cerebral cortex, two novel aspects were recognized in the topographic distribution of dopamine terminal: (1) the presence of a dopamine innervation in layer VIb of the frontal, parietal, temporal and occipital neocortex, and (2) a significant contingent of dopamine varicosities within the deep and not only upper layers of supragenual cingulate cortex. A fair number of dopamine varicosities were also detected in the upper layers of the dorsomedial frontal area, in the retrosplenial and adjacent occipital cortex as well as in the ventral subiculum and field CAl of the hippocampus. As measured in 10 sectors representing different cortical regions, the highest density of dopamine innervation was found in the supragenual cingulate cortex (1.7 X 10(6] and particularly in its layers II and III (3.1 X 10(6)). A slightly lower density was measured in the anteromedian "prefrontal" cortex (1.0 X 10(6)). The rostrorhinal and the perirhinal cortex showed moderate dopamine innervation (3.0 and 5.5 X 10(5)) with varicosities in every layer. The piriform and the posterior entorhinal cortex were also moderately and ubiquitously innervated (2.5 and 3.0 X 10(5)).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Multifactorial study of prognostic factors in differentiated thyroid carcinoma and a re-evaluation of the importance of age.

A multivariate analysis of prognostic factors has been carried out with 375 cases of differentiated thyroid cancer (DTC) treated in the same centre by total thyroidectomy and 131I therapy. The patients have been followed for 5 to 23 years. The isolated prognostic roles of age, sex, clinical stage and histology were confirmed, but these factors were found to be strongly interrelated. Multifactorial analysis was conducted following Cox's model. It demonstrated that the prevalent role of clinical staging (nodular versus lobar or massive form) is as important as the initial presence of metastases (P = 0.0001). Histological assessment of differentiation, age and sex were of lesser importance. Thus, the most significant prognostic variable is clinical stage. These data must be taken into account when formulating management protocols for DTC.

Adolescent↗
PubMed1986

Quantification of the dopamine innervation in adult rat neostriatum.

Conditions leading to specific and integral visualization of dopamine axon terminals (varicosities) were tested in adult rat cerebral hemisphere slices incubated with [3H]dopamine and processed for high resolution radioautography. Specific visualization of the dopamine endings was achieved after incubation with 10(-6) M [3H]dopamine in the presence of a monoamine oxidase inhibitor (pargyline 10(-4) M), and of desipramine (5 X 10(-6) M), an inhibitor of catecholamine uptake by noradrenaline and serotonin neurons. [3H]Dopamine varicosity labeling was eliminated by the addition of 5 X 10(-5) M benztropine (an inhibitor of catecholamine uptake by catecholamine neurons), and was almost absent when dopamine nerve cell bodies of the midbrain had been previously destroyed with 6-hydroxydopamine. In dopamine-denervated neostriatum incubated without desipramine, a second set of labeled terminals was also visible. These were identified as serotoninergic, since their labeling was suppressed by citalopram, an inhibitor of monoamine uptake highly specific for serotonin neurons. There was no desipramine-sensitive but citalopram-resistant varicosity labeling suggestive of neostriatal noradrenaline innervation. In normal striatum, incubation at 35 degrees C always resulted in a labeling of dopamine varicosities restricted to a narrow band which followed the contours and cut surface of this anatomical region. This unusual distribution was the result of an uptake barrier generated by the tightly packed dopamine varicosities. Indeed, the striatal dopamine varicosity labeling was more widespread after partial 6-hydroxydopamine denervation or in normal tissue incubated either with a higher [3H]dopamine concentration (5 X 10(-6) M), in the presence of relatively low benztropine concentrations (10(-5) M), or at lower temperature (15 degrees C). Material incubated at 15 degrees C for 90 min was suitable for purposes of quantification: labeled varicosities were then visualized throughout the striatum and across the full thickness of the slices; moreover, the number of labeled varicosities plotted against radioautographic exposure time increased in parallel and reached a plateau at the same time in neostriatal sectors with widely different innervation densities. At a rostral transverse level across neostriatum, the dorsolateral quadrant showed hyperdense "patches" of labeled terminals distinguishable from an already dense surrounding "matrix", whereas, ventromedially, the dopamine innervation appeared more uniform and somewhat less dense.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Quantified regional and laminar distribution of the serotonin innervation in the anterior half of adult rat cerebral cortex.

The regional and laminar distribution of the serotonin (5-HT) innervation in adult rat cerebral cortex was quantified in radioautographs of semi-thin sections from whole hemisphere slices incubated with tritiated 5-HT and a monoamine oxidase inhibitor. Uptake-labelled axonal varicosities (aggregates of silver grains) were counted with the help of a computerized image analyser, in seven cytoarchitectonic areas of the anterior half of the cortex: Cg3, rostral AID, Cg2, Fr1, Par1, caudal AID and Pir (prepiriform). Since the average diameter of cortical 5-HT varicosities had been previously measured in electron microscope radioautographs, the counts of labelled sites per mm2 of radioautograph could be transformed to numbers of varicosities per mm3 of tissue after a double correction for incomplete detection at the chosen duration of radioautographic exposure and from the thickness of section examined. The mean regional density of cortical 5-HT innervation was thus evaluated at 5.8 million varicosities per mm3 of tissue, ranging from 4.4 (Cg2) to 7.1 million (AIDr). Cg2, Par1 and Fr1 showed significantly lower regional densities than Cg3, AIDc, Pir and AIDr. The highest laminar density was that of layer I in all regions except Pir, but each region had a distinct pattern of 5-HT innervation. In Par1, for example, there was a second band of predilection amounting to 5.3 million varicosities per mm3 at the height of layer Va. On the basis of these figures, it was possible to extrapolate the average number of cortical 5-HT varicosities per midbrain raphe nerve cell body of origin (500,000 at least), their average number per cortical target neuron (145-230), their incidence among all axon terminals in cortex (1/200), their mean endogenous amine content (0.045 fg), and their mean number per varicosity of recognition sites for reuptake blockers such as paroxetine, citalopram or cyanoimipramine (5000-6200). Such quantitative data and further correlations between 5-HT innervation density and other measurable aspects of cortical structure and function should help to elucidate the role(s) of 5-HT in this part of the brain.

Animals↗