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L Segu

Publications and source records attributed to L Segu.

At least 37 records · Page 2Linked to original sources
PubMed1994

The mouse 5-hydroxytryptamine1B receptor is localized predominantly on axon terminals.

The 5-hydroxytryptamine1B receptor is a serotonin receptor subtype which is expressed predominantly in the basal ganglia. It has been suggested to play a role in movement and appetite control as well as in certain pathological states such as migraine. The recent cloning of the 5-hydroxytryptamine1B gene as well as the discovery of a radioligand that labels in rodents 5-hydroxytryptamine1B and possibly 5-hydroxytryptamine1D alpha receptors (S-CM-G[125I]TNH2) allowed us to compare the distribution of the messenger RNA and of the protein in mouse brain sections. A high 5-hydroxytryptamine1B messenger RNA level is found in the caudate-putamen in medium spiny neurons that project to the globus pallidus and the substantia nigra. In contrast, no messenger RNA is expressed in the globus pallidus and substantia nigra although these structures reveal the highest level of 5-hydroxytryptamine1B binding sites. In the hippocampus, 5-hydroxytryptamine1B messenger RNA is localized in the cell bodies of pyramidal cells of the CA1 field while the protein is found predominantly in the dorsal subiculum, a projection zone for the CA1 pyramidal neurons. In the cerebellum, 5-hydroxytryptamine1B messenger RNA is expressed in the Purkinje cells, which display no receptor binding sites. Conversely, moderate binding is found in the deep nuclei of the cerebellum, the main projection zone of the Purkinje cells. 5-Hydroxytryptamine1B sites are also detected in the superficial gray layer of the superior colliculus and the lateral geniculate nucleus, brain regions containing the terminals of retinal ganglion cells. The soma of these ganglion cells express high levels of 5-hydroxytryptamine1B messenger RNA while no 5-hydroxytryptamine1B binding sites were found in the retina. This study demonstrates that the main brain regions, expressing 5-hydroxytrypamine1B messenger RNA contain low densities of 5-hydroxytryptamine1B binding sites. Conversely, the major projection areas of these anatomical structures do not express detectable levels of 5-hydroxytryptamine1B messenger RNA, but present a high density of binding sites. In addition, our data suggest that the distribution of the 5-hydroxytryptamine1D alpha binding sites is different from that of the 5-hydroxytryptamine1D alpha messenger RNA. These results together with previous lesion studies, indicate that the 5-hydroxytryptamine1B and possibly the 5-hydroxytryptamine1D alpha receptors are localized predominantly on axon terminals, while their expression is low or absent at the somatodendritic level. The 5-hydroxytryptamine1D alpha proteins might therefore contain an addressing signal allowing their transport toward nerve endings.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Differences in ketanserin binding in the ventromedial hypothalamus of ewes responsive or refractory to short days.

Participation of central 5HT receptors in the inhibition of LH pulsatility during refractoriness to short days (SD) in ewes has been suggested by previous in vivo studies using various 5HT-antagonist such as ketanserin. In the present study, binding of [3H]ketanserin in ewe brain sections was similar to that described in the brain of other species and could correspond with an interaction at 5HT2 receptors sites. Rosenthal analysis from the caudate nucleus was linear (Kd = 3 nM). The displacement studies from the cortex slices showed that the 5HT antagonists such as methysergide, ketanserin, cyproheptadine and spiperone competed with the labelled ligand at nanomolar concentrations whereas serotonin was less active. However, the first 3 drugs recognized different populations of binding sites. Prazosin, an alpha 1-adrenergic antagonist was inactive, but a slight inhibition of [3H]ketanserin binding was induced by pyrilamine, an H1 histaminic antagonist, within a nanomolar range. Methysergide (10(-6) M), which does not bind to H1 receptors, was therefore used to determine the nonspecific binding. Quantitative analysis of the binding of 3 nM [3H]ketanserin on sections of the ewe brain at the preopticohypothalamic level was then carried out by autoradiography. The highest binding densities were observed in the caudate nuclei (64.0 fmol/mg tissue Eq) and the mammillary bodies (52.7 fmol/mg tissue Eq) whereas intermediate or low densities were found in the other structures. The anatomical distribution of the labelling was similar to that described in other species for 5HT2 receptors. Ketanserin binding in these areas was compared between two groups of ovariectomized estradiol-treated Ile-de-France ewes, submitted to artificial short days (SD: 8L:16D), one group with a high LH pulsatility (responsive to SD) and the other one with a low LH pulsatility (photorefractory to SD). Binding densities were similar for each one of the studied regions between the two groups, except in the ventrolateral part of the mediobasal hypothalamus, where ewes exhibiting high LH pulsatility had a more than 2-fold higher binding density than those with a low LH pulsatility (mean +/- SEM, 14.6 +/- 1.4 vs. 5.7 +/- 1.0 fmol/mg tissue Eq, respectively; p < 0.0016). These results suggest that [3H]ketanserin binding sites in the ventromedial part of the mediobasal hypothalamus could be associated to the regulation of the photoperiodic inhibition of LH at the time of establishment of refractoriness to short days in the Ile-de-France ewe.

Adrenergic Antagonists↗
PubMed1993

Increase of central 5-HT1B binding sites following 5,7-dihydroxytryptamine axotomy in the adult rat.

The effects of selective axotomy of serotoninergic neurons produced by an intracerebroventricular injection of 5,7-dihydroxytryptamine (200 micrograms free base) on 5-HT1B binding sites labeled with S-CM-G-[125I]TNH2 were investigated by quantitative autoradiography in the rat brain. Results show, 21 days after surgery, an upregulation of 5-HT1B receptors in the entorhinal cortex and the dorsomedial and suprachiasmatic nuclei of the hypothalamus. The cellular localization of those 5-HT1B receptors exhibiting post-lesion plastic properties is discussed.

5,7-Dihydroxytryptamine↗
PubMed1992

Biochemical and pharmacological characterization of serotonin-O-carboxymethylglycyl[125I]iodotyrosinamide, a new radioiodinated probe for 5-HT1B and 5-HT1D binding sites.

There is a lack of radioactive probes, particularly radioiodinated probes, for the direct labeling of serotonin-1B (5-HT1B) and serotonin-1D (5-HT1D) binding sites. Serotonin-O-carboxymethylglycyltyrosinamide (S-CM-GTNH2) was shown previously to be specific for these two subtypes; we, therefore, linked a 125I to its tyrosine residue. Biochemical and pharmacological properties of S-CM-G[125I]TNH2-binding sites were studied by quantitative autoradiography on rat and guinea pig brain sections. S-CM-G[125I]TNH2 binding is saturable and reversible with a KD value of 1.3 nM in the rat and 6.4 nM in the guinea pig. Binding is heterogeneous, paralleling the anatomical distribution of 5-HT1B sites in the rat and of 5-HT1D sites in the guinea pig. The binding of 0.02 nM S-CM-G[125I]TNH2 was inhibited by low concentrations of 5-HT, S-CM-GTNH2, CGS 12066 B, 5-methoxytryptamine, and tryptamine in both species. Propranolol inhibited the radioligand binding with a greater affinity in the rat than in the guinea pig. Conversely, 8-hydroxy-2-(di-n-propylamino)tetralin inhibited S-CM-G[125I]TNH2 binding with a greater affinity in the guinea pig than in the rat. Other competitors, specific for 5-HT1C, 5-HT2, 5-HT3, and adrenergic receptors, inhibited S-CM-G[125I]TNH2 binding in rat and guinea pig substantia nigra and in other labeled structures known to contain these receptors, but only at high concentrations. S-CM-G[125I]TNH2 is then a useful new probe for the direct study of 5-HT1B and 5-HT1D binding sites.

Animals↗
PubMed1991

Healing of erosive esophagitis with sucralfate and cimetidine: influence of pretreatment lower esophageal sphincter pressure and serum pepsinogen I levels.

Forty-eight patients with erosive reflux esophagitis were allocated to either sucralfate tablets, 4 g/day, or cimetidine, 1.6 g/day, for 8 weeks in a randomized, prospective, single-blind, cross-over therapeutic trial. Pretreatment lower esophageal sphincter (LES) pressure and serum pepsinogen I (PG-I) levels were investigated as possible predictors of healing with either drug. The trial was completed by 41 patients (21 in the sucralfate group and 20 in the cimetidine group); one patient in each group was removed because of side effects. Symptom improvement occurred to a similar extent in both groups. Endoscopic results after 8 weeks of treatment with sucralfate revealed complete healing of esophageal erosions in 48% (cimetidine, 55%) and improvement in an additional 19% (cimetidine, 20%). Neither of these differences was statistically significant. Some patients refractory to one drug had endoscopic healing of esophagitis when treated with the other drug after crossover. LES pressure did not influence outcome in patients treated with sucralfate, whereas significantly (p = 0.024) more patients refractory to cimetidine had an LES pressure less than 7 mm Hg than did those with a good response to the histamine-2 (H2)-receptor blockade. Patients whose esophagitis healed or improved after sucralfate tended to have lower serum PG-I levels than those with treatment failure (104 +/- 35 ng/mL vs 125 +/- 45 ng/mL), whereas the opposite occurred in patients treated with cimetidine (132 +/- 58 ng/mL in responders vs 78 +/- 27 ng/mL in nonresponders, p = 0.048). The results confirm that sucralfate is a valuable alternative to H2-receptor inhibitors for the treatment of reflux esophagitis. They also provide preliminary evidence that LES pressures and serum PG-I levels may have predictive value of the response to one or the other of these two drugs.

Adult↗
PubMed1991

Transient increase in [3H]Ro 15-4513 specific binding in the superficial gray layer of the rat superior colliculus induced by visual deafferentation.

The imidazodiazepine compound [3H]Ro 15-4513, a partial inverse agonist of benzodiazepine receptors of the central type, binds with high affinity (order of 10(-8) M) to a single population of benzodiazepine binding sites in the mammalian central nervous system. A quantitative autoradiographic study was carried out to determine the effects of one eye removal on [3H]Ro 15-4513 specific binding to rat brain sections in the superficial gray layer or stratum griseum superficiale (SGS) of the superior colliculus. Retinal afferent degeneration due to right eye removal, performed 3 and 7 days before sacrifice, led to a significant and symmetrical increase in the [3H]Ro 15-4513 specific binding in both right and left SGS by enhancing the binding affinity of the radioligand. This transient phenomenon disappeared when a longer survival period of 45 days was allowed to elapse. Conversely, unilateral lesion of the primary visual areas had no apparent effects on the specific binding of the radioligand. The absence of any loss of binding sites after either type of lesion suggests that the benzodiazepine receptors are probably not situated on the optic nerve axon terminals, nor on the cortical axon terminals originating from primary visual areas. In the SGS, as in other rat brain structures, benzodiazepine receptors of the central type are functionally coupled with GABAA receptors and form 'GABAA receptors/benzodiazepine receptors/chloride channel' complexes. The involvement of the local GABAergic system in the postlesion plasticity of benzodiazepine receptors was studied by testing the effects of exogenously applied GABA on [3H]Ro 15-4513 specific binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

A new 5-hydroxy-indole derivative with preferential affinity for 5-HT1B binding sites.

The affinities of several 5-hydroxy-indole derivatives for serotonin-1 (5-HT1) binding site subtypes, labeled with 2 nM [3H]5-HT, were assessed by quantitative autoradiography on rat brain sections. The results obtained with known ligands, namely 5-hydroxytryptamine (5-HT), 5-methoxytryptamine (5-Me-OT), 5-methoxy-N,N- dimethyl-tryptamine (5-Me-ODMT), 5-hydroxy-N,N-dimethyl-tryptamine (bufotenine) and 8-hydroxy-2-[di-N-propylamino]tetralin (8-OH-DPAT) demonstrate the reliability and the advantages of this technique for pharmacological studies. Novel serotonin derivatives were synthesized by carboxymethylation of the hydroxyl group. One of those new ligands, serotonin-O-carboxy-methyl- glycyl-tyrosinamide (S-CM-GTNH2), inhibited 2 nM [3H]5-HT binding to the substantia nigra with an IC50 of 22.4 nM, a value which is 22 times lower than that found in the dentate gyrus and choroid plexus. This demonstrates the preferential affinity of S-CM-GTNH2 for 5-HT1B versus 5-HT1A and 5-HT1C binding sites. S-CM-GTNH2 contains a tyrosine residue, which may be useful for the synthesis of a radioactive iodinated molecule and for the preparation of 'long-lasting ligands' linked through peptide bonds with a protein. These derivatives could be of great interest for ultrastructural and behavioral studies relevant to 5-HT1B sites.

Animals↗
PubMed1991

Pharmacological characterization of serotonin-O-carboxymethyl-glycyl-tyrosinamide, a new selective indolic ligand for 5-hydroxytryptamine (5-HT)1B and 5-HT1D binding sites.

The affinity of a new serotonin (S) derivative, serotonin-O-carboxymethyl-glycyl-tyrosinamide (S-CM-GTNH2), for the various 5-hydroxytryptamine (5-HT)1 receptor subtypes was tested using quantitative autoradiography on rat and guinea pig brain sections. In the rat, S-CM-GTNH2 is 57 and 24 times more potent at 5-HT1B sites (IC50 = 28 nM) than at 5-HT1A (IC50 = 1600 nM) and 5-HT1C sites (IC50 = 670 nM), respectively. In the guinea pig, the affinity of S-CM-GTNH2 for 5-HT1D sites (IC50 = 67 nM) is 21 times higher than at 5-HT1A sites (IC50 = 1400 nM). S-CM-GTNH2 shows a low affinity (less than 10 microM) for 5-HT2 and 5-HT3 binding sites. This new ligand is therefore highly specific for 5-HT1B and 5-HT1D binding sites and can be used to further characterize the involvement of these subtypes in physiological studies focusing particularly on behavioral effects.

Animals↗
PubMed1991

[Synthesis and pharmacological study of radioiodinated serotonin derivative specific of 5-HT1B and 5-HT1D binding sites of the central nervous system].

We describe here the synthesis of a new serotonin conjugate, S-CM-GTNH2, and its radioiodinated derivative. Quantitative autoradiographic studies on rat and guinea pig brain sections incubated with 2 nM [3H]5-HT showed a preferential affinity of S-CM-GTNH2 for 5-HT1B and 5-HT1D sites. Autoradiograms from brain sections incubated with 0.02 nM S-CM-G[125I]TNH2 showed a heterogeneous anatomical distribution of the labelling with high densities in regions rich in 5-HT1B or 5-HT1D binding sites, and with no labelling of those rich in 5-HT1A or 5-HT1C sites. The pharmacological profiles of the binding sites corresponded to those of 5-HT1B and 5-HT1D receptor subtypes. The radioligand S-CM-G[125I]TNH2 is a good probe for the study of these sites and will be used for their subcellular localization in electron microscopy.

Animals↗
PubMed1990

A new system for computer-assisted quantitative receptor autoradiography.

We have developed a computer-assisted analytic system for quantifying autoradiograms. The system was tested by studying the characteristics of high affinity serotonin binding sites (5-HT1) in rat brain sections, using [3H]5-HT as a radioligand. Autoradiographic data are digitized and transferred to a Macintosh II by means of a high speed, high resolution solid state camera. The physical characteristics of the device (uniformity, temporal stability, linearity) are such that the accuracy of the measurements obtained is highly satisfactory. The autoradiogram grey levels were measured and converted into radioligand concentrations (fmol/mg tissue) with the "BIOLAB" program which was specially written at our department in Macintosh Programming Workshop (MPW). The consistency of the measurements performed on small anatomical structures confirms the reliability of the system. The greatest discrepancies were due to the processing of the sections and also to the biological variability from one animal to another. The low cost of the device described, the high picture definition, the speed with which measurements can be obtained, the reliability of the system, and the original character of the program make it a valuable means to easier analyse quantitative autoradiography in pharmacological and physiological research.

Animals↗
PubMed1989

Regulation by estradiol of GABAA and GABAB binding sites in the diencephalon of the rat: an autoradiographic study.

Using in vitro quantitative autoradiography we studied the in vivo effects of estradiol on GABAA and GABAB receptors in the rat brain. In all the areas studied (suprachiasmatic nucleus, medial preoptic area, striatum, frontal cortex), estradiol failed to significantly affect the GABAA receptor density. Chronic treatment with estradiol led however in the suprachiasmatic nucleus and the striatum to a decrease in the density of GABAB receptors. GABAB receptor regulation by estradiol was found to be area-specific within the hypothalamus since it was not observed in the medial preoptic area. The down regulation of GABAB receptors in the suprachiasmatic nucleus induced by estradiol treatment might thus explain the inhibitory effect of the steroid on the GABA control of serotonin metabolism we recently reported.

Animals↗
PubMed1989

Changes in exploratory behaviour of hamsters following treatment with 8-hydroxy-2-(di-n-propylamino)tetralin.

The influence of the centrally active 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on the exploration of objects was studied in hamsters, using a radioactographic method. This spatial paradigm allows the study of the behavioural expression of underlying locomotor and cognitive (attentional, mnemonic, representative) mechanisms. The drug was found to enhance the cognitive components of the exploratory process, i.e. object-oriented exploration, habituation and, under certain temporal conditions, response-to-change, in a dose-dependent manner. Since drug-injected animals did not differ from controls when no object was present, 8-OH-DPAT probably has no role in non-oriented exploratory activity. The influence of time was further investigated by varying the duration of successive trials and intertrial intervals. In situations where the durations were extremely shortened (3-min trials/3-min intertrial intervals), drug-treated subjects, in contrast to control ones, exhibited a 'hypernormal' time course: they explored and habituated. 8-OH-DPAT appears to increase the efficiency of exploration possibly via a positive effect on arousal or attention. 8-OH-DPAT is assumed to act on 5-HT somatodendritic autoreceptors, lowering 5-HT utilization in the hippocampus, which is the main structure implicated in spatial memory. This exploration paradigm could be employed in the study of time components of environmental adaptation without the need to restrain subjects.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1988

Distribution of benzodiazepine receptors in the rat superior colliculus: a light and electron microscope quantitative autoradiographic study.

The distribution of benzodiazepine (Bdz) receptors of the central type was analysed in the superficial grey layer of the rat superior colliculus from light and electron microscope autoradiographs, using the highly specific partial reverse agonist [3H]Ro 15-4513, a radioligand which can be crosslinked to its binding sites by ultraviolet rays. Biochemical characteristics of the binding were first defined by liquid scintillation count on unfixed cryostat mesencephalic brain slices. Saturation curves (1.6-20 nM) and Scatchard plot indicated that the radioligand bound with a high affinity (Kd = 11 nM) to a single population of sites (Bmax = 650 fmol/mg dry tissue). A slight primary chemical fixation of the brain did not significantly modify the binding characteristics. The consolidation of the specific binding by ultraviolet light on prefixed brain slices was found to be optimal after a 45-min illumination period. The distribution of Bdz sites on light and electron microscope autoradiographs was then analysed by applying these binding conditions. Prefixed brain slices (50 micron thick, Vibratome) were incubated in the 15 nM radioligand in the absence (total binding) or in the presence (non-specific binding) of the non-radioactive antagonist Ro 15-1788 (10(-5) M). Quantitative light microscopic study of Epon-embedded semithin sections showed that 95% of the silver grains of the specific label were located on the neuropil to the detriment of the neuronal and glial cell compartments. In the electron microscopic study, the distribution of the specific binding sites was statistically analysed over a total of more than 10 identified single or junctional tissue compartments, using the 50% probability circle method (Williams, 1969). Apart from a slight labeling of varicose profiles, the specific labeling was found to be concentrated on two particular tissue compartments: the percentage of grains associated with contacts between varicosities and dendrites was 32%, and that associated with axodendritic synapses was 16% of the total specific labeling measured over all compartments combined. A low proportion (33%) of the labeled axodendritic interfaces was characterized by a synaptic differentiation. These results suggest that both synaptic and non-synaptic Bdz receptors are present in the rat superior colliculus, and may each modulate neuronal cell activity in a different way.

Animals↗
PubMed1986

High-affinity serotonin binding sites: autoradiographic evidence for their location on retinal afferents in the rat superior colliculus.

High affinity 5-HT binding sites (5-HT1) were labeled in vitro on mounted rat brain slices using [3H]5-HT as a radioligand. In the first stage of experimentation, the bound radioactivity was measured on slices by liquid scintillation count in order to define the biochemical characteristics of the binding. Saturation curves were drawn, as well as association and elution curves for a 2 nM radioligand concentration. The mean affinity constant of the specific binding (Kd) was found to be 2.9 nM. In the second stage, the experimental parameters giving optimum binding were applied to the frozen slices prepared exactly as for the biochemical approach in order to investigate the effects of degeneration of retinal axon terminals on the distribution of 5-HT1 sites in the visual upper layers of the superior colliculus. The optical densities directly measured from tritium-sensitive film clearly indicate that the ablation of one eye causes a progressive reduction in the binding in the contralateral, largely deafferented, stratum griseum superficiale (SGS); with a 24-day survival period, the reduction was about 35-40%. In the homologous region of the ipsilateral colliculus, the binding decreased by about 10-15%. It is concluded that at least two populations of 5-HT1 binding sites coexist in the visual collicular layers, one of which is probably located on the axon terminals of retinal afferents. The present results confirm a previous hypothesis based on iontophoretic data, according to which this monoamine is involved in retino-collicular transmission. As far as the retinofugal terminal binding sites are concerned, 5-HT seems to exert a presynaptic control on visual inputs.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1981

A serotoninergic system in the nodose ganglia of the cat: radioautographic studies.

After the in vitro incubation of the cat nodose ganglia with 3H-5-HT, the radioautographic detection of the tracer at the light microscope level shows an intense labeling over some several hundred cell bodies. By ultrastructural studies, it has been possible to detect unmyelinated fibers intensely labeled and to characterize as neurons the labeled cell bodies. These data argue for the presence of 5-HT in some peripheral vagal afferents, obviously involved in vegetative regulatory mechanisms.

Animals↗
PubMed1978

The topographical distribution of serotoninergic terminals in the spinal cord of the cat: quantitative radioautographic studies.

In vitro uptake of labeled serotonin (5-HT) has allowed the radioautographic detection of serotoninergic fibers in the cat spinal cord at thoracic and lumbar levels. The specificity of labeling was ensured by the conditions of incubation ([3H]5-HT was 10(-7) M) and by test control experiments with concomitant 10(-6) M NA or 2 X 10(-6) M fluoxetine which led respectively to an unmodified or a negative radioautographic pattern. Macroscopic radioautography with [14C]5-HT gave the framework for analysis of 5-HT innervation at this level which appeared dense in the grey matter and more scattered in white matter except in the periphery. In the grey matter labeled structures appeared at histological level as randomly oriented fibers. They displayed enlargements which were identified by electron microscopy as varicosities (mean diameter 0.7 micrometer) containing clear and large granular vesicles. To estimate the density of 5-HT varicosities in grey matter, semi-automatic counting was performed on histological radioautographs, using an image analyzer. Maximal concentrations of boutons were found in the periependymal region, the sympathetic lateral column, the whole dorsal horn and the motor neuron area of ventral horn. In a densely innervated region, the number of boutons was estimated to be at least 2.65 X 10(6)/cu.mm. In white matter, labeled fibers were longitudinally oriented in the periphery and obliquely in other regions, except in the dorsal funiculus, where they were nearly absent. Previous histofluorescence and biochemical data are confirmed and completed by the results of this approach which displays several advantages in resolution, sensitivity and possibilities of automated quantification. Moreover owing to the dynamic abilities of the radioautographic method, the spinal cord provides a good model for the study of the properties (namely the axonal flow) and the functions of the serotoninergic neurons.

Animals↗