C. Delbende

The novel antidepressant, tianeptine, reduces stress-evoked stimulation of the hypotalamo-pituitary-adrenal axes

The possible effect of tianeptine, a novel antidepressant agent, on the neuroendocrine response to stress was investigated in adult male rats. Tube restraint stress for 30 min induced a marked increase of plasma ACTH and corticosterone. A single i.p. injection of tianeptine (10 mg/kg), 120 min before stress caused a significant decrease of ACTH and corticosterone levels. In order to investigate the kinetics of the effect of tianeptine, the drug was injected at various times (from 15 min to 12 h) before restraint stress. The inhibitory effect of tianeptine on stress-induced elevations of plasma ACTH and corticosterone occurred from 1 to 3 h after the injection. Administration of increasing doses of tianeptine revealed that only the highest doses (10 and 20 mg/kg) had a significant effect on stress-evoked stimulation of ACTH and corticosterone secretion. These results show that the antidepressant, tianeptine, reduces the activation of the hypothalamo-pituitary-adrenal (HPA) axis induced by restraint stress. Since depressed patients generally exhibit an elevated cortisol level, the present data suggest that part of the therapeutic properties of tianeptine could be accounted for by the effect of this antidepressant to modulate the activity of the HPA axis.

Effect of chronic treatment with the antidepressant tianeptine on the hypothalamo-pituitary-adrenal axis

The effects of acute and chronic administration of tianeptine, a novel antidepressant agent, on the hypothalamo-pituitary-adrenal axis were studied in the adult male rat. A single injection of tianeptine did not alter the activity of the hypothalamo-pituitary-adrenal axis. In contrast, chronic administration of tianeptine (10 mg/kg twice a day for 15 days) induced a significant decrease in the concentration of corticotropin-releasing factor (CRF) in the hypothalamus and adrenocorticotropin (ACTH) in the anterior lobe of the pituitary. Chronic tianeptine treatment did not modify CRF levels in the cerebral cortex and hippocampus, and did not alter alpha-melanocyte-stimulating hormone and beta-endorphin levels in the neurointermediate lobe of the pituitary. Using the in situ hybridization technique, we observed that chronic administration of tianeptine did not modify CRF mRNA levels in the paraventricular nucleus of the hypothalamus. The effect of chronic tianeptine treatment on the neuroendocrine response to stress was also investigated. Tube restraint stress for 30 min induced a significant depletion of hypothalamic CRF and a substantial increase of plasma ACTH and corticosterone. Tianeptine abolished the stress-induced reduction of hypothalamic CRF concentration and markedly reduced the stress-induced increase in plasma ACTH and corticosterone levels. Taken together, these results suggest that tianeptine acts primarily at the level of the hypothalamus: (1) in unstressed rats, tianeptine reduces hypothalamic CRF and pituitary ACTH contents; (2) in stressed animals, tianeptine attenuates the activation of the hypothalamo-pituitary-adrenal axis.

Melanin-concentrating hormone (MCH) immunoreactivity in the brain and pituitary of the dogfish Scyliorhinus canicula. Colocalization with alpha-melanocyte-stimulating hormone (α-MSH) in hypothalamic neurons

The distribution of melanin-concentrating hormone (MCH) in the central nervous system of the dogfish Scyliorhinus canicula was determined by indirect immunofluorescence and peroxidase-anti-peroxidase techniques, using an antiserum raised against synthetic salmon MCH. Three groups of MCH-positive cell bodies were localized in the posterior hypothalamus. The most prominent cell group was detected in the nucleus sacci vasculosi. Scattered MCH-immunoreactive cells were observed in the nucleus tuberculi posterioris and in the nucleus lateralis tuberis. At the pituitary level, the caudal part of the median lobe of the pars distalis contained strongly MCH-positive perikarya. Some of these cells were liquor-contacting-type. Immunoreactive fibers originating from the hypothalamic perikarya projected throughout the dorsal wall of the posterior hypothalamus. Positive fibers were also detected within the thalamus and the central gray of the mesencephalon. The distribution of MCH-containing neurons was compared to that of alpha-MSH-immunoreactive elements using consecutive, 5-micron thick sections. Both MCH- and alpha-MSH-immunoreactive peptides were found in the same neurons of the nucleus sacci vasculosi. These data suggest that MCH and alpha-MSH, two neuropeptides which exert antagonistic activities on skin melanophores, may also act in a coordinate manner in the central nervous system of cartilaginous fish.

Regulation of α‐Melanocyte‐Stimulating Hormone Release from Hypothalamic Neuronsa

a-Melanocyte-stimulating hormone (a-MSH) is a tridecapeptide amide that was initially isolated and characterized from the intermediate lobe of the pituitary. a-MSH derives from a multifunctional precursor protein, called proopiomelanocortin (POMC), which can generate through proteolytic cleavage various regulatory peptides including corticotropin, melanotropins, lipotropins and endorphins . I The gene encoding POMC is expressed in corticotrope cells of the pars distalis, in melanotrope cells of the pars intermedia, and in two populations of neurons located respectively in the arcuate nucleus of the hypothalamus? and in the caudal portion of the nucleus s01itariu.s.~ POMC neurons of the arcuate nucleus project in a number of brain areas including several hypothalamic nuclei, the median eminence, the septum, the periventricular region of the thalamus, the amygdala, and the rh~mbencephalon.~ POMC-producing neurons of the nucleus sotitarius innervate the caudal rhombencephalon and the spinal cord.5 Processing of POMC occurs in a tissue-specific manner, depending on the enzymatic equipment that is available in each cell type. In corticotrope cells, POMC is cleaved at the level of three dibasic amino acid residues, thus generating a large terminal fragment (16 K peptide), the joining peptide, ACTH, and P-lipotropin. In melanotrope cells and in hypothalamic neurons, further processing occurs leading to the formation of several y-MSHs, a-MSH, corticotropinlike intermediate lobe peptide (CLIP), y-LPH, and P-end~rphin.~.’ A large body of evidence indicates that the neuropeptide a-MSH can be regarded as an authentic neurotransmitter and/or neuromoduiator. Intracerebral injection of a-MSH affects a number of behavioral processes8 such as learning, memory, attention, motivation, and grooming behavior. Furthermore, a-MSH exerts a trophic action on the central nervous system and induces a marked antipyretic effect. Electron microscopic studies revealed that a-MSH-immunoreactive material is sequestered in dense core secretory vesicle^.^ Concurrentiy, it

Characterization of α-MSH-related peptides released from rat hypothalamic neurons in vitro

Abstract Reverse-phase high-performance liquid chromatography analysis, coupled with a sensitive radioimmunoassay for α-melanocyte-stimulating hormone (α-MSH), was used to characterize the α-MSH-related peptides stored in the rat hypothalamus or released from perifused hypothalamic slices. Four peaks of α-MSH-like immunoreactivity (α-MSH-LI) co-eluting with synthetic des-Nα-acetyl α-MSH, α-MSH and their respective sulfoxide derivatives were resolved and quantified. In hypothalamic extract, deacetyl α-MSH which was the predominant peptide represented 94.4% of total α-MSH-LI content, while the relative amount of α-MSH was only 5.6%. Analysis of α-MSH-related peptides contained in effluent perifusates showed that deacetyl α-MSH and its oxidized form were the major peptides released from neurons in basal conditions or under KCl-induced depolarization (50 mM KCl for 75 min). However, the proportion of acetylated peptide was 3–4 times higher in the perifusion medium than in hypothalamic extracts. Our data indicate that acetylation of des-Nα-acetyl α-MSH may occur during the process of exocytosis. Since acetylation of α-MSH markedly increases the behavioural potency of the peptide, these results suggest that regulation of the acetyltransferase activity could be a key mechanism to modulate the bioactivity of α-MSH-related peptides in the brain.

Alpha-melanocyte-stimulating hormone (α-MSH) in the brain of the cartilagenous fish. Immunohistochemical localization and biochemical characterization

The distribution of immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system and pituitary of the elasmobranch fish Scyliorhinus canicula was determined by the indirect immunofluorescence and the peroxidase-antiperoxidase methods using a highly specific antiserum. Perikarya containing alpha-MSH-like immunoreactivity were localized in the dorsal portion of the posterior hypothalamus, mainly in the tuberculus posterioris and sacci vasculosus nuclei. Immunoreactive alpha-MSH cell bodies were found in the dorsal wall and ventral region of the caudal part of the tuberculum posterioris. These structures were densely innervated by fine beaded immunoreactive fibers. Some alpha-MSH immunoreactive cells were occasionally detected in the ventral part of the nucleus periventricularis. Scattered cell bodies and fibers were also observed in the dorsal wall of the posterior recess. Outside the hypothalamus very few fibers were detected in the dorsal thalamus and mesencephalon. No immunoreactivity was found in any other parts of the brain. The alpha-MSH immunoreactive material localized in the brain was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological detection. Brain and pituitary extracts exhibited displacement curves which were parallel to that obtained with synthetic alpha-MSH. The concentrations of alpha-MSH immunoreactive material were determined in 5 different regions of the brain. The highest concentration was found in the hypothalamus. HPLC analysis resolved two major forms of immunoreactive alpha-MSH in the hypothalamus, which had been same retention times as des-N alpha-acetyl-alpha-MSH and its sulfoxide derivative. These results provide the first evidence for the presence of alpha-MSH-like peptides in the fish brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Proopiomelanocortin (POMC)-related peptides in the brain of the rainbow trout, Salmo gairdneri.

We have investigated the presence of ACTH, alpha-MSH and beta-endorphin, three peptides which derive from the multifunctional precursor protein proopiomelanocortin (POMC) in the brain of the rainbow trout Salmo gairdneri. Using both the indirect immunofluorescence and peroxidase-antiperoxidase techniques, a discrete group of positive cells was identified in the hypothalamus, within the anterior part of the nucleus lateralis tuberis. alpha-MSH-containing neurons represented the most abundant immunoreactive subpopulation. Coexistence of alpha-MSH, ACTH and beta-endorphin was observed in the lateral part of the nucleus. ACTH- and beta-endorphin-containing cells were mainly distributed in the rostral and caudal regions of the nucleus. In the medial portion of the nucleus lateralis tuberis, numerous cells were only stained for alpha-MSH. Moderate to dense plexuses of immunoreactive fibers were observed in the ventral thalamus and the floor of the hypothalamus. Some of these fibers projected towards the pituitary. The concentrations of ACTH, alpha-MSH and beta-endorphin-like immunoreactivities were measured in microdissected brain regions by means of specific radioimmunoassays. Diencephalon, mesencephalon and medulla oblongata extracts gave dilution curves which were parallel to standard curves. The highest concentrations of POMC-derived peptides were found in the diencephalon (alpha-MSH: 4.28 +/- 0.43 ng/mg prot.; ACTH: 1.08 +/- 0.09 ng/mg prot.; beta-endorphin: 1.02 +/- 0.1 ng/mg prot.), while lower concentrations were detected in the mesencephalon, medulla oblongata and telencephalon. The present results demonstrate that various peptides derived from POMC coexist within the same cell bodies of the fish hypothalamus. Taken together, these data suggest that expression and processing of POMC in the fish brain is similar to that occurring in pituitary melanotrophs.

γ-Aminobutyric acid inhibits the release of α-melanocyte-stimulating hormone from rat hypothalamic slices

Abstract The effect of γ-aminobutyric acid (GABA) on release of α-melanocyte-stimulating hormone (α-MSH) from hypothalamic neurons was investigated in vitro using the perifusion technique. Rat hypothalamic slices were continuously superfused with Krebs-Ringer medium and the release of α-MSH in the effluent perifusate was monitored by means of a sensitive and specific radioimmunoassay method. Infusion of 50 mM K + for 15 min induced a transient increase of α-MSH release (5- to 8-fold above the spontaneous level). Infusion of the same dose of K + for 75 min caused a brief discharge of α-MSH during the first 30 min followed by sustained release of the neuropeptide. The effect of GABA was investigated 27 min after the onset of KCl infusion. Application of GABA (5 × 10 −5 M) resulted in a significant and reversible inhibition of K + -induced α-MSH release. The GABA A agonist, muscimol (10 −4 M), produced a prolonged inhibition of K + -evoked α-MSH release, while the GABA B agonist, baclofen (10 −4 M), was devoid of effect on hypothalamic α-MSH release. Bicuculline (10 −4 M), a specific GABA A antagonist, had no effect when added alone to the medium but totally reversed the inhibitory effect of GABA on K + -induced α-MSH release. Taken together these data suggest that exogenous GABA exerts an inhibitory control on α-MSH neurons. Our data also show that the effect of GABA on α-MSH release by hypothalamic neurons is mediated through GABA A -type receptors. To investigate further the involvement of GABA neuronal systems in the regulation of α-MSH release, rats were treated with the GABA transaminase inhibitor AOAA and the α-MSH content was assessed in both the intermediate lobe of the pituitary and in the hypothalamus. Three hours after intraperitoneal injection of aminooxyacetic acid hemihydrochloride (AOAA; 30 mg/kg), a significant increase of α-MSH concentration was observed in pars intermedia and hypothalamic extracts. These results, together with the presence of an abundant network of GABAergic nerve terminals in the basal hypothalamus, support the notion that the neurotransmitter GABA may play a physiological role in the regulation of α-MSH release by hypothalamic neurons.

Characterization of α-melanocyte-stimulating hormone (α-MSH)-like peptides in discrete regions of the rat brain. In vitro release of α-MSH from perifused hypothalamus and amygdala

The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is synthesized by discrete populations of hypothalamic neurons which project in different brain regions including the cerebral cortex, hippocampus and amygdala nuclei. The purpose of the present study was to identify the alpha-MSH-immunoreactive species contained in these different structures and to compare the ionic mechanisms underlaying alpha-MSH release at the proximal and distal levels, i.e. within the hypothalamus and amygdala nuclei, respectively. The molecular forms of alpha-MSH-related peptides stored in discrete areas of the brain were characterized by combining high-performance liquid chromatography (HPLC) separation and radioimmunoassay detection. In mediobasal and dorsolateral hypothalamic extracts, HPLC analysis confirmed the existence of a major immunoreactive peak which co-eluted with the synthetic des-N alpha-acetyl alpha-MSH standard. In contrast, 3 distinct forms of immunoreactive alpha-MSH, which exhibited the same retention times as synthetic des-, mono- and di-acetyl alpha-MSH, were resolved in amygdala nuclei, hippocampus, cortex and medulla oblongata extracts. The proportions of acetylated alpha-MSH (authentic alpha-MSH plus diacetyl alpha-MSH) contained in these extrahypothalamic structures were, respectively, 78, 80, 60 and 92% of the total alpha-MSH immunoreactivity. In order to compare the ionic mechanisms underlaying alpha-MSH release from hypothalamic and extrahypothalamic tissues, we have investigated in vitro the secretion of alpha-MSH by perifused slices of hypothalamus and amygdala nuclei. High potassium concentrations induced a marked increase of alpha-MSH release from both tissue preparations. However, a higher concentration of KCl was required to obtain maximal stimulation of amygdala nuclei (90 mM) than hypothalamic tissue (50 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of vasoactive intestinal peptide in brains from normal and parkinsonian subjects

The distribution of vasoactive intestinal peptide (VIP) in the post-mortem human brain was determined by radioimmunoassay using a highly specific antiserum. The detection limit of the assay was 4 fmol/tube. The highest concentrations of VIP were found in the cerebral cortex, amygdala, hypothalamus and hippocampus. The lowest levels of peptide were detected in basal ganglia including caudate nucleus, external pallidum, putamen and substantia nigra. All dilution curves of acetic acid extracts from different brain areas were strictly parallel to the standard curve. Sephadex G-50 gel filtration of frontal cortex extract showed that VIP-like immunoreactivity (VIP-LI) eluted as a major peak comigrating with synthetic hVIP. Detailed mapping of VIP in the human cerebral cortex showed the existence of a rostro-caudal gradient of VIP-LI concentrations: the frontal cortex exhibited the highest VIP levels, the parietal and temporal cortex contained medium values and the occipital cortex contained the lowest VIP levels. The concentrations of VIP-LI were compared in various regions of the human brain from normal and parkinsonian subjects. No significant changes in VIP-LI levels occurred in the brains of patients dying with Parkinsons disease. No difference in VIP levels could be found either when the parkinsonian group was subdivided into nondemented and demented patients. These data indicate that VIP-containing neurons are not affected in parkinsonian patients. Our results also suggest that VIP neuronal systems are not involved in the course of dementing process in Parkinsons disease.