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P Leroux

Publications and source records attributed to P Leroux.

At least 73 records · Page 4Linked to original sources
PubMed1987

alpha-Melanocyte-stimulating hormone (alpha-MSH) release from perifused rat hypothalamic slices.

A perifusion system was developed to investigate the control of alpha-melanocyte-stimulating hormone (alpha-MSH) release from rat brain. Hypothalamic slices were perifused with Krebs-Ringer bicarbonate (KRB) medium supplemented with glucose, bacitracin and bovine serum albumin. Fractions were set apart every 3 min and alpha-MSH levels were measured by means of a specific and sensitive radioimmunoassay method. Hypothalamic tissue in normal KRB medium released alpha-MSH at a constant rate corresponding to 0.1% of the total hypothalamic content per 3 min. The basal release was not altered by Ca2+ omission in the medium or addition of the sodium channel blocker tetrodotoxin (TTX). Depolarizing agents such as potassium (50 mM) and veratridine (50 microM), which is known to increase Na+ conductance, significantly stimulated alpha-MSH release in a Ca2+-dependent manner. When Na+-channels were blocked by TTX (0.5 microM) the stimulatory effect of veratridine was completely abolished whereas the K+-evoked release was unaffected. These findings suggest that: voltage-dependent sodium channels are present on alpha-MSH hypothalamic neurons; depolarization by K+ induces a marked stimulation of alpha-MSH release; K+- and veratridine-evoke releases are calcium-dependent. Altogether, these data provide evidence for a neurotransmitter or neuromodulator role for alpha-MSH in rat hypothalamus.

Animals↗
PubMed1987

Induction and Characterization of Penicillium caseicolum Mutants Resistant to Ergosterol Biosynthesis Inhibitors.

The isolation of Penicillium caseicolum mutants resistant to different fungicides which inhibit ergosterol biosynthesis is reported. Mutational frequencies for resistance were high (3 x 10 to 3 x 10). The levels of resistance toward the inhibitors of sterol C-14 demethylation were always low (<10), whereas high values were obtained with mutants resistant to inhibitors of sterol Delta14 reduction or Delta8-->Delta7 isomerization, or both. Generally, there was a positive cross-resistance between fungicides showing the same biochemical mode of action but not between compounds of two different groups. Mycelial growth rate and sporulation were tested; several mutants were not affected for these characteristics. We conclude that resistance to ergosterol biosynthesis inhibitors may be used as a good marker for genetic studies through protoplast fusion.

Journal Article↗
PubMed1987

[Experimental study on osteosarcoma of local chemotherapy diffusing from surgical acrylic cement and plaster].

An experimental study has been made to explore the possibility of using plaster or surgical cement as a vehicle for the diffusion of local chemotherapeutic agents in osteosarcoma. In vitro, leeching out of methotrexate from plaster or acrylic cement occurred with a peak during the first few hours followed by a decreasing curve lasting for an average of two weeks. In dogs suffering from a spontaneous osteosarcoma, the loss of substance produced by excision was filled with cement to which methotrexate had been added extemporaneously. This method of administration produced a general diffusion of methotrexate whose blood levels were measured for three to five days. In laboratory rats into which osteosarcomata had been grafted, tablets of plaster containing antimitotic drug were implanted into the tumour, which was left in situ. This made it possible to show that the local chemotherapy was having a true effect, particularly when the antimitotic used was cisplatinum. In patients who had acrylic cement containing methotrexate inserted during operation, local diffusion resulted in very high concentrations, evidenced by the concentration found in fluid obtained from suction drains during the early days after operation.

Animals↗
PubMed1986

Localization and identification of alpha-melanocyte-stimulating hormone (alpha-MSH) in the frog brain.

The distribution of alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system of the frog Rana ridibunda was determined by immunofluorescence using a highly specific antiserum. alpha-MSH-like containing perikarya were localized in the infundibular region, mainly in the ventral hypothalamic nucleus. A rich plexus of immunoreactive fibers directed towards the ventral telencephalic region was detected. Reverse-phase high-performance liquid chromatography and radioimmunoassay were used to characterize alpha-MSH-like peptides in the frog brain. Chromatographic separation revealed that immunoreactive alpha-MSH coeluted with synthetic des-N alpha-acetyl alpha-MSH, authentic alpha-MSH and their sulfoxide derivatives. The heterogeneity of alpha-MSH-like material in the frog brain was in marked contrast with the figure observed in the intermediate lobe of the pituitary gland where only des-N alpha-acetyl alpha-MSH is present. These findings support the existence of discrete alpha-MSH immunoreactive neurons in the frog brain containing both desacetyl and authentic alpha-MSH.

Animals↗
PubMed1985

Localization and characterization of brain somatostatin receptors as studied with somatostatin-14 and somatostatin-28 receptor radioautography.

The localization and characterization of receptors for somatostatin-14 (S-14) and somatostatin-28 (S-28) were studied in the rat brain using the iodinated agonists [Tyr0,D-Trp8]S-14 and [Leu8,D-Trp22,Tyr25]S-28 as tracers. Slide-mounted frozen sections were used for the radioautographic localization and biochemical characterization of somatostatin receptors. In the latter case counting was performed on scraped off serial sections from rostral regions of the brain. Specificity studies demonstrated that either tracer could be displaced with S-28, S-14 or their agonists. The N-terminus fragment (1-12) of S-28 as well as a number of unrelated peptides were unable to compete with either tracer, indicating that the binding capacity for ligand-receptor recognition is located in the C-terminal portion of S-28. Scatchard analysis of saturation curves gave a one-site interaction with Kd values of 0.42 +/- 0.09 nM and 0.32 +/- 0.04 nM for the S-14 and S-28 iodinated agonists, respectively. By radioautography, the distribution of receptors for both S-14 and S-28 appeared very similar with high levels of binding in the deep layers of the cortex, the cingulate cortex, the claustrum, the locus coeruleus and most structures of the limbic system. Treatment with cysteamine, which caused a somatostatin depletion in the brain, was required to observe labeling in the hypothalamus. In some caudal areas of the brain, especially in the cerebellar nuclei, the solitary tract nucleus and the nucleus of the vagus nerve, only labeling with the S-28 agonist could be detected. This S-28 binding could be displaced by native S-14 (10(-6) M). Generally, there was a correlation between the localization of somatostatin receptors and that of immunoreactive somatostatin, as evaluated by immunocytochemistry. However, in some areas, an inverse correlation between receptor and peptide concentrations was observed. These results are in agreement with previous data suggesting that somatostatin could act as a neurotransmitter or neuromodulator in several brain areas.

Animals↗
PubMed1985

Localization and characterization of somatostatin-14 and somatostatin-28 receptors in the rat pituitary as studied by slide-mounted frozen sections.

The localization and characterization of somatostatin-14 (SS-14) and somatostatin-28 (SS-28) receptors were studied in the rat pituitary using the iodinated agonists [Tyr0, D-Trp8]-SS-14 and [Leu8, D-Trp22, Tyr25]-SS-28 as tracers. Slide-mounted frozen sections were used for the autoradiographic localization and biochemical characterization of somatostatin receptors. In the latter case, counting was performed on scraped off serial sections which contained both anterior and posterior pituitary. Specificity studies demonstrated that either tracer could be displaced with SS-28 and SS-14. A number of unrelated peptides were unable to compete with either tracer. Scatchard analysis of saturation curves gave one-site interactions with KD values of 0.53 +/- 0.08 nM and 0.22 +/- 0.03 nM for the SS-14 and SS-28 iodinated agonists, respectively. Using autoradiography, SS-14 and SS-28 receptors were shown to be distributed in the anterior pituitary only. Using densitometry, displacement and saturation curves could be also obtained.

Animals↗
PubMed1985

Ultrastructural autoradiographic localization of somatostatin-28 in the rat pituitary gland.

To identify the anterior pituitary cell type(s) containing somatostatin-28 (SS-28)-binding sites and to study the internalization processes of this peptide by the target cells, autoradiography was performed on rat anterior pituitaries removed at specific intervals (2-60 min) after iv injection of the [125I]iodo-SS-28 agonist [Leu8,D-Trp22,Tyr25]SS-28 into intact, adrenalectomized, or castrated male rats. At the light microscopic level, the silver grains were found in 75% of cells. Concomitant injection of an excess of unlabeled peptide prevented the binding of label, verifying the specificity of binding. No specific labeling could be detected in the adrenocorticotrophs of adrenalectomized rats or gonadotrophs (castration cells) of castrated rats. At the electron microscopic level, three cell types (somatotrophs, thyrotrophs, and mammotrophs) appear to contain radiolabeled SS-28. The time-course study in somatotrophs of intact animals showed that 2 min after injection, most silver grains were associated with the plasma membrane. Five to 15 min after injection, label was found over both the plasma membrane and cytoplasmic organelles, especially the Golgi apparatus, lysosomes, and secretory granules. At the longest time interval (60 min), labeling was mostly associated with the cytoplasmic organelles. These results indicate that SS-28-binding sites are present only in those cell types in which somatostatin is known to regulate secretory functions. The present data also show that a rapid internalization of the radiolabeled peptide occurs.

Animals↗
PubMed1985

[Role of alpha-MSH and related peptides in the central nervous system].

Alpha-melanocyte stimulating hormone (alpha-MSH) is a tridecapeptide secreted by intermediate lobe cells and synthesized in the brain as well. As a hormonal peptide, the physiological function of alpha-MSH consists mainly in the control of pigment movements within dermal melanophores. At the pituitary level, alpha-MSH secretion is under multifactorial control: it is inhibited by dopamine and GABA and stimulated by corticoliberin (CRF), thyroliberin (TRH), beta-adrenergic agonists and (or) serotonin. Identification of alpha-MSH containing neurons in the hypothalamus and other brain regions (septum, thalamus, mid-brain, striatum, hippocampus, cerebral cortex and spinal cord) has been carried out by means of immunological and biochemical techniques combined with bioassays. In the central nervous system (CNS) as in the hypophysis, alpha-MSH is synthesized from a high molecular weight precursor, pro-opiomelanocortin (POMC). Maturation of this protein yield similar end products in the hypothalamus and the intermediate lobe. Several peptides chemically related to alpha-MSH are generated including the desacetyl and monoacetyl (authentic alpha-MSH) forms; the latter has the greatest behavioral activity. The demonstration that alpha-MSH has numerous central nervous system effects has raised the possibility that this neuropeptide acts as a neuromodulator or a neurotransmitter. In the rat, intra-cerebroventricular administration of ACTH/MSH peptides induces the stretching-yawning syndrome (SYS) which is frequently preceded by excessive grooming. This excessive grooming is blocked by neuroleptics indicating that the central dopaminergic neurons are implicated in this behavioral effect of the peptide. alpha-MSH is involved in memory, arousal and attention; in hypophysectomized animals, the learning ability is restored after administration of MSH or related peptides. Injection of alpha-MSH delays also extinction of passive avoidance behavior and affects performances motivated by hunger as well as aggressive behavior. Recent studies concerning the role of alpha-MSH have been undertaken in human beings. The effects of MSH-related peptides favour a role of these peptides in arousal: they maintain a high level of vigilance and improve visual discrimination. These behavioral changes were accompanied by marked changes in CNS electrophysiology. Current studies, which aim at establishing a neurotransmitter function for alpha-MSH, concern the distribution and characterization of alpha-MSH receptors in the central nervous system and the mechanism controlling the release of neuronal alpha-MSH.

Aggression↗
PubMed1985

[Intermediate lobe of the amphibian pituitary gland: an endocrine gland with multiple secretions and under multi-hormonal control].

The cells of the frog pars intermedia synthesize a 36 000 (36K) protein called proopiomelanocortin (POMC). After [3H]glucosamine incorporation, separation of newly synthesized products by SDS-polyacrylamide gel electrophoresis showed that this 36K protein was glycosylated. Tryptic mapping revealed only one site of glycosylation and showed that the carbohydrate side-chain was located in the N-terminal region of POMC. The 36K protein was not released by the melanotrophs, but it generated, through specific intracellular proteolytic cleavage, a number of smaller peptides which were subsequently released. These peptides were identified by various methods including selective amino-acid incorporation, HPLC purification, acid-urea gel electrophoresis, tryptic and chymotryptic mapping, assay of melanotropic activity, radioimmunoassays and immunoprecipitations. Some of the newly synthesized N-terminal (18K) fragment of the POMC was secreted intact while a portion of it was further processed, via an intermediate peptide, to give mature gamma-MSH. All three of these peptides were glycosylated. In addition, the mature peptide (gamma-MSH) exhibited a low but significant melanotropic activity. The C-terminal portion of the prohormone was very rapidly processed to give des N alpha-acetyl alpha-MSH, corticotropin-like-intermediate lobe peptide (CLIP) and beta-endorphin. Authentic alpha-MSH was always absent in cellular extracts: acetylation to give rise to alpha-MSH was a late enzymatic process strictly linked to hormonal release. Since acetylation of alpha-MSH is required for full biological activity of this peptide, it is possible to conceive that this later step could be under neuroendocrine control. Using the perifusion technique we have been able to show the complexity of the control mechanisms regulating amphibian melanotrophs. It is generally accepted that the aminergic innervation of the intermediate lobe of the pituitary is involved in the hypothalamic control of melanotropin release. We have demonstrated that, in amphibians, dopamine inhibits alpha-MSH secretion through D2-type dopaminergic receptors whereas norepinephrine and (or) epinephrine stimulate alpha-MSH secretion via beta-adrenergic receptors. The existence of peptidergic fibers within parenchymal cells of the pars intermedia has been demonstrated. Evidence for TRH-containing fibers has been obtained by immunohistochemistry. Using a specific radioimmunoassay for TRH, we have confirmed the presence of TRH in the neurointermediate lobe of the frog. We have shown that TRH is a powerful MSH-releasing factor in these animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Amphibians↗
PubMed1984

Radioautographic study of binding and internalization of corticotropin-releasing factor by rat anterior pituitary corticotrophs.

In order to identify the anterior pituitary cell type(s) containing corticotropin-releasing factor (CRF) receptors and to study the internalization processes of this peptide by the target cells, radioautography was performed on rat anterior pituitaries removed at specific intervals (2-60 min) after intracarotid injection of [125I]iodo-CRF into intact and adrenalectomized female rats. In intact animals, all corticotrophs were labeled, whereas in the adrenalectomized animals about 80% of the hypertrophied corticotrophs (adrenalectomy cells) were. In control animals injected with both iodinated CRF and an excess of unlabeled peptide, no specific reaction could be detected. The time-course study in intact animals showed that 2 min after injection most silver grains were found over or within 160 nm of the plasma membrane. At the 5-min time intervals, grains were observed both over the plasma membrane and within the cytoplasm, associated with lysosomes, and the Golgi apparatus. Fifteen minutes after injection, grains were mostly found over lysosomes and the Golgi apparatus, whereas at the longest time intervals (30 and 60 min) almost no labeling could be detected. The results obtained in this study indicate that in the anterior pituitary CRF receptors are restricted to corticotrophs (as identified by electron microscopy) and that, after binding to the plasma membrane, CRF is rapidly internalized to Golgi elements and lysosomes.

Animals↗
PubMed1984

Characterization and localization of vasoactive intestinal peptide receptors in the rat lung.

Experiments were performed to characterize vasoactive intestinal peptide (VIP) receptors in rat lung and to study their localization by means of light and electron microscope autoradiography. [125I]Iodo-VIP binding to lung homogenate was inhibited by synthetic VIP, [Val5]secretin, secretin, and 7-27 secretin with half-maximal inhibition (ID50) values of 1.62, 13, 121 nmol/liter and up to 0.1 mmol/liter, respectively. The relative potency of [Val5]secretin and 7-27 secretin to displace the tracer indicated that [125I]iodo-VIP binds to specific VIP receptors. Kinetic studies showed two sites of binding, a site of high affinity with equilibrium dissociation constant (KD) values of 0.32 +/- 0.09 nM and Bmax of 88.7 +/- 28.6 fmol/mg protein and a lower affinity binding site with a KD value of 23.0 +/- 2.9 mM and Bmax of 584 +/- 136.9 fmol/mg protein. The localization of VIP receptors was performed by radioautography both in vivo after iv injection of [125I]iodo-VIP and in vitro by the direct application of the radiolabeled peptide to cryostat sections of unfixed lung tissue. After iv injection of label, silver grains were detected only over alveoli. Electron microscopy indicated that radioactivity was mostly associated with alveolar capillaries. In vitro localization studies showed specific binding not only to alveoli but also to bronchi. These studies suggest that VIP can act at different sites and that the peptide could gain access to alveoli via the general circulation.

Animals↗
PubMed1984

[Chemodectoma of nerve X. Value and interest of the concept of the diffuse paraganglionic system].

Tenth nerve chemodectoma is one of the rarest varieties of cervicocephalic paragangliomas, far behind tumors developed from the carotid body. Based on findings in three patients, one reported previously, clinical and biological features of these formations are discussed. Recent data and those from personal studies are exposed, and arguments presented enabling the concept to be defended of a diffuse paraganglionic system in relation with the vagus nerve.

Adult↗
PubMed1983

Coexistence of vasoactive intestinal peptide and enkephalins in the adrenal chromaffin granules of the frog.

The chromaffin cells of the frog adrenal gland were studied at the electron microscopic level by means of the immunoperoxidase technique. Using specific antibodies against Met-enkephalin, Leu-enkephalin and vasoactive intestinal peptide (VIP), the coexistence of the three neuropeptides in the chromaffin cells was demonstrated. Furthermore, all three peptides were co-located in the 200-400 nm dense-core vesicles which also stained for dopamine-beta-hydroxylase. These results, which suggest concomitant release of catecholamines and neuropeptides by the chromaffin cells, support the concept that VIP is involved in the stimulation of adrenal steroid secretion during stress conditions.

Adrenal Medulla↗
PubMed1983

Co-localization of vasoactive intestinal peptide (VIP) and enkephalins in chromaffin cells of the adrenal gland of amphibia. Stimulation of corticosteroid production by VIP.

Recent studies have shown that biologically active peptides and monoaminergic neurotransmitters coexist in certain neuronal cell populations. Using the immunofluorescence technique, we have examined the localization of enkephalins, vasoactive intestinal peptide (VIP) and tyrosine hydroxylase in the adrenal gland of the frog Rana ridibunda. Most chromaffin cells which stained for tyrosine hydroxylase contained VIP-like immunoreactivity, whereas methionine- (Met-) and leucine- (Leu-) enkephalin-like immunoreactivity was detected in about 40% of the cells revealed by the anti-tyrosine hydroxylase serum. No VIP- or enkephalin-like immunoreactive nerve fibres were observed. Since in the frog, the chromaffin cells are in close contact with the adrenocortical (interrenal) tissue, a possible action of VIP and opiates on corticosteroidogenesis has been investigated. At doses 10(-6) and 10(-5) M, 20-min infusions of synthetic porcine or chicken VIP elicited a significant increase in corticosterone and aldosterone production by perifused frog adrenals, in a dose-dependent manner. As compared to ACTH, VIP was several orders of magnitude less effective in stimulating corticosteroid production. Morphine, Met- and Leu-enkephalins (10(-5) M) had no effect on spontaneous secretion of corticosteroids. In addition, Met- and Leu-enkephalins (10(-5) M) did not alter the production of corticosterone induced by ACTH. THese results suggest that VIP contained in the chromaffin cells of the frog adrenal gland may exert a local action in stimulating corticosteroid production by the interrenal tissue.

Acetylcholine↗
PubMed1983

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. II. Lack of action of thyroxine on TRH-induced alpha-MSH secretion.

Thyrotropin-releasing hormone (TRH) stimulates alpha-melanocyte-stimulating hormone (alpha-MSH) secretion in amphibia as well as thyrotropin-stimulating hormone (TSH) and prolactin secretions in mammals. Since thyroid hormones regulate the stimulatory effect of TRH on TSH and prolactin, the possible role of thyroxine (T4) in the control of alpha-MSH secretion in amphibia, has been investigated. Neurointermediate lobes of Rana ridibunda were perifused in amphibian culture medium for 7 hr and the amounts of alpha-MSH released into the effluent perfusate were measured by radioimmunoassay. In vivo treatment with T4 (0.5 mg/kg twice a day for 9 days) did not modify the in vitro response of the neurointermediate lobes to TRH (10(-9) to 10(-7) M). In addition, prolonged infusion of T4 in vitro did not alter spontaneous and TRH-induced alpha-MSH release. In spite of the inhibitory effect of T4 on TRH-induced TSH and prolactin secretions in mammals, the present data show that, in frogs, thyroid hormone does not modulate the stimulation of alpha-MSH secretion induced by TSH.

Animals↗
PubMed1983

Immunological characterization of endorphins, adrenocorticotropin, and melanotropins in frog hypothalamus.

To gain more information about the nature and regulation of opiomelanocorticotropic peptides in the frog diencephalon, radioimmunological determinations of alpha- and beta-MSH. ACTH, beta- and gamma-endorphins have been performed in hypothalamic extracts. Sephadex G-50 gel filtration revealed a single peak of alpha-MSH-like immunoreactivity (alpha-MSH-LI) comigrating with synthetic alpha-MSH. Two peaks of ACTH-LI were observed; the major one eluting slightly before human ACTH. Using a porcine beta-endorphin antiserum which exhibited 45% cross-reaction (on a molar basis) with ovine beta-LPH, one major peak of beta-endorphin-LI and two additional components were observed in the elution profile; none of these peaks coeluted with synthetic porcine beta-endorphin. No significant beta-MSH or gamma-endorphin-LI was detected. To investigate a possible role of glucocorticoids on the level of opiomelanocorticotropic peptides in frog hypothalamus, 60 male frogs were treated with dexamethasone (300 micrograms/day) during 8 days. Dexamethasone treatment did not modify the chromatographic distribution and the total amount of alpha-MSH-LI and ACTH-LI in hypothalamic extracts. A slight (15%) increase in beta-endorphin-LI was even observed after 8 days of dexamethasone treatment. From these results it is concluded that three classes of opiomelanocorticotropic peptides are present in the frog hypothalamus in the following order of concentration: beta-endorphin-LI greater than alpha-MSH greater than ACTH. In addition, circulating glucocorticoids which significantly reduce the concentration of opiomelanocorticotropic hormones in the distal lobe of the frog pituitary (S. Jégou, M. C. Tonon, F. Leboulenger, C. Delarue, J. Côté, G. Pelletier, and H. Vaudry (1981a). In "Adv. Physiol. Sci.' E. Stark, G. B. Makara, Zs. Acs, and E. Endröczi, eds., Vol. 13, pp. 129-133. Pergamon, Budapest.) do not modify the amount of these peptides in the hypothalamus.

Adrenocorticotropic Hormone↗
PubMed1983

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. III. Effect of neuropeptides on alpha-MSH secretion.

It has been previously demonstrated that thyrotropin-releasing hormone (TRH) stimulates in vitro the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in frog. In the present study, the effects of various neuropeptides on spontaneous and/or TRH-induced alpha-MSH secretion were investigated, using a well-defined perifusion system technique. Vasoactive intestinal peptide, (VIP) a neurohormone which stimulates TRH target cells in mammals, was totally devoid of effect on frog melanotrophs although VIP-like material could be detected in neurointermediate lobe extracts. Somatostatin-like immunoreactive material was found in high concentrations in the frog neurointermediate lobe complex, but synthetic somatostatin (from 10(-10) to 10(-6) M) did not modify the spontaneous release of alpha-MSH. At doses of 10(-8) and 10(-6) M, synthetic somatostatin did not modify TRH-induced alpha-MSH secretion. Morphine (10(-5) M) and opioid peptides (10(-10) to 10(-6) M) had no effect on spontaneous alpha-MSH secretion. In addition, methionine enkephalin (10(-5) M) did not modify the stimulatory effect of TRH on alpha-MSH secretion. From these results we conclude that, among the neuropeptides which modulate prolactin secretion in mammals, only TRH is involved in alpha-MSH secretion in the frog.

Animals↗