173 research outputs found
Pharmacology of GABA receptors in Ascaris suum muscle: an electrophysiological study
The aim of this work was to describe the pharmacological profile of the Ascaris
muscle GABA receptor, and to compare its properties to those of GABA receptors in
vertebrates. The interest of such study is to show the existence of pharmacological
differences between Ascaris and vertebrate GABA receptors, which may be exploited in
antiparasitic drug research. A short review will be presented first on the anatomy,
physiology and pharmacology of the neuro-muscular system of Ascaris, and on the
pharmacological characteristics of GABA receptors in vertebrates and invertebrates. It
will be followed by a simplified presentation of the receptor theory and the subsequent
development of drug-receptor interaction theories.The effects of GABA and various GABA-agonists on the membrane input
conductance of Ascaris muscle cells were studied using a current-clamp technique.
Dose-response curves were obtained and described by a modified Hill equation for each
agonist tested. The relative potencies of GABA-agonists in Ascaris are compared to
those obtained at vertebrate GABA-A receptors. Despite some differences: inactivity of
sulphonic acid derivatives and the loss of relative potency of rigid analogues of GABA,
such as muscimol, THIP and isoguvacine, the agonist profile of Ascaris muscle
GABA receptor appears correlated with the agonist profile of vertebrate GABA-A
receptors.In contrast, the antagonist profile of Ascaris GABA receptors differs greatly from
the antagonist profile of the vertebrate GABA-A receptor. The two classical GABA-A
antagonists, picrotoxin and bicuculline, were found very weak or inactive at
antagonizing GABA responses in Ascaris. The steroid derivative, RU5135, a very
potent competitive antagonist in vertebrate (IC50=5nM, rat cuneate nucleus, Simmonds
and Turner, 1985), was found to hold back some activity in Ascaris , but in a non
competitive manner and with an IC50 of 117μM.The effects of the arylaminopyridazine GABA derivatives SR95103 and SR95531
on GABA responses were investigated on GABA-induced conductance changes using a
current-clamp technique. Arylaminopyridazine GABA derivatives are specific and
competitive antagonists at the vertebrate GABA-A receptor, SR95531 being the most
potent analogue. In Ascaris SR95103 was found more potent than SR95531 at
antagonizing GABA responses. This potency order contrasts with that at vertebrate
GABA-A receptors. The antagonism of SR95103 was associated with a parallel shift to
the right in the GABA dose-response relationship. A modified Schild plot was used to
describe the action of SR95103, the data is consistent with a competitive mechanism
involving two molecules of GABA but one molecule of antagonist interacting with the
receptor. The estimated KB for SR95103 is 64±13μM (mean±SE, n=14) and the
pA₂=4.The actions of SR95103 were further examined on GABA-activated single-channel
currents using an outside-out patch-clamp technique. The presence of SR95103 (30-
100μM) did not alter the GABA-activated channel main conductance, but reduced the
open-probability of the channels. No effect on the mean burst duration, corrected mean
open-time and the distribution of burst-durations, was observed with 30μM SR95103.
However, when a higher concentration was used, 100μM, mean open-time and mean
burst duration were reduced, and the proportion of short bursts (mainly represented by
single openings) was increased. The mode of action of SR95103 is discussed, and it is
suggested that most of the antagonism is competitive and produced by a single molecule
of SR95103 combining with the receptor-channel complex, as suggested by the
current-clamp data. However, an additional non-competitive component, possibly a
channel block, is detected at high concentrations. This non-competitive component
accounts only for a small proportion of the antagonism, since no reduction in the
maximal response was detected by the current-clamp technique, even when high
antagonist concentrations were used (ImM).Other arylaminopyridazine derivatives were tested on GABA response in Ascaris
using a current-clamp technique. The order of potency of these compounds on Ascaris
muscle GABA receptor, was found different from the order of potency at the vertebrate
GABA-A receptor. One analogue, SR95132, virtually inactive in vertebrate
preparations was found equipotent to SR95103 in Ascaris. When tested on GABA
dose-response curves, SR95132 (KB=65μM) and other potent analogues, displaced
GABA dose-response curves to the right without decrease in the maximal response.
The modified Schild plots for these compounds, were also consistent with a
competitive mechanism involving two molecules of GABA and only one molecule of
antagonist interacting with the receptor. Structure-activity relationships for this series of
compounds are examined in Ascaris and compared to the vertebrates. Substitution on
the pyridazine ring in 4-position, while detrimental for the antagonist potency at the
vertebrate GABA-A receptor, appears to be a prerequisite for antagonistic activity on
Ascaris muscle GABA receptor. Newly synthesized arylaminopyridazine derivatives
confirmed that the presence of a substituent in the 4-position is very important for the
antagonistic activity at the Ascaris GABA receptor. The ethyl-4-substituted derivative,
NCS247-90 with Kb=55μM, was found to be more potent than SR95103 and
SR95132. Benzyl- (NCS251-90) and the isopropyl-(NCS252-90) 4-substituted
derivatives also appeared to be potent antagonists. Besides the role of the 4-position, the length of the side chain and the acidic function were also investigated. A longer
side-chain (5C), as in NCS194-83, decreaseithe potency but does not produce a
complete loss of potency. Replacement of the carboxylic acid group by a sulphonic acid
group produceja total inactivation of the compound, as seen with NCS249-90 and
NCS250-90. This is in agreement with the lack of potency of sulphonic acid derivatives
as agonists. These results are discussed in terms of the accessory binding sites theory
of Ariens, and suggest the existence of different accessory sites responsible for the
binding of antagonists on Ascaris GABA receptor.In conclusion, the Ascaris muscle GABA receptor differs from vertebrate GABA-A
receptors in terms of antagonist properties, whereas its agonist properties are very
similar to those of vertebrate GABA-A receptors. Among GABA antagonists, the
exploration of the arylaminopyridazine GABA derivatives family may lead to the
discovery of a new generation of anthelminthics. Already, one analogue, SR95132,
shows an antagonistic activity in Ascaris but not in vertebrates
Neuro-glial plasticity of neuroendocrine networks
Neuro-glial plasticity of neuroendocrine networks is a major mechanism involved in key events of physiological
functions such as parturition and lactation (oxytocinergic system) and preovulatory surge
(GnRH system). This type of plasticity is classically described as rearrangements between glial cells and
neuroendocrine neurones. Neuro-glial plasticity can occur within several hours. Cellular and molecular
mechanisms involved are complex and imply an active regulation of neuroendocrine networks
activity. In the present study we show that GnRH pulsatile secretion studied in vitro is regulated by
gap junction communication between glial cells. Glial cells forming the microenvironment of GnRH
neuronal network could represent a new system for integrating environmental cues and for regulating
GnRH secretionLa plasticité neuro-gliale des réseaux neuroendocrines est un élément majeur de la régulation d’évènements
clés de grandes fonctions, comme la plasticité du système ocytocinergique lors de la parturition
et de la lactation et celle du système GnRH dans le déclenchement du pic pré-ovulatoire de LH.
Cette plasticité est décrite par des réarrangements neuroanatomiques des cellules gliales associées aux
neurones neuroendocrines. Elle peut se mettre en place en quelques heures. Les mécanismes cellulaires
et moléculaires sont complexes et mettent en jeu une régulation active de l’activité des neurones par
les cellules gliales. Dans l’étude présentée ici, nous montrons que la pulsatilité de sécrétion des neurones
à GnRH étudiés in vitro est régulée par la communication des cellules gliales via des jonctions
gap. Les cellules gliales du microenvironnement des neurones à GnRH pourraient ainsi représenter un
nouveau système d’intégration des signaux environnementaux et de régulation de la sécrétion de GnR
Protective Effects of a Rhodiola Crenulata Extract and Salidroside on Hippocampal Neurogenesis against Streptozotocin-Induced Neural Injury in the Rat
Previously we have demonstrated that a Rhodiola crenulata extract (RCE), containing a potent antioxidant salidroside, promotes neurogenesis in the hippocampus of depressive rats. The current study was designed to further investigate the protective effect of the RCE on neurogenesis in a rat model of Alzheimer's disease (AD) induced by an intracerebroventricular injection of streptozotocin (STZ), and to determine whether this neuroprotective effect is induced by the antioxidative activity of salidroside. Our results showed that pretreatment with the RCE significantly improved the impaired neurogenesis and simultaneously reduced the oxidative stress in the hippocampus of AD rats. In vitro studies revealed that (1) exposure of neural stem cells (NSCs) from the hippocampus to STZ strikingly increased intracellular reactive oxygen species (ROS) levels, induced cell death and perturbed cell proliferation and differentiation, (2) hydrogen peroxide induced similar cellular activities as STZ, (3) pre-incubation of STZ-treated NSCs with catalase, an antioxidant, suppressed all these cellular activities induced by STZ, and (4) likewise, pre-incubation of STZ-treated NSCs with salidroside, also an antioxidant, suppressed all these activities as catalase: reduction of ROS levels and NSC death with simultaneous increases in proliferation and differentiation. Our findings indicated that the RCE improved the impaired hippocampal neurogenesis in the rat model of AD through protecting NSCs by its main ingredient salidroside which scavenged intracellular ROS
Alternative culture conditions for isolation and expansion of retinal progenitor cells
L'hypothalamus est-il sexué ? Sécrétion pulsatile de GnRH et synchronisation neuronale
absen
Glial gap-jonction mediated regulation of GnRH neurons network activity
International audienc
Régulation des neurones à Gonadotropin Releasing Hormone (GnRH) par les cellules gliales
National audienc
Développement de la signalisation calcique dans les neurones à GnRH
La gonadotropin releasing hormone est essentielle à la reproduction. Sécrétée de manière pulsatile, elle contrôle la sécrétion des hormones gonadotropiques hypophysaires. Les neurones à GnRH, peu nombreux, dispersés dans l'aire préoptique, ont une origine extracérébrale. Une phase migratoire au cours de la vie embryonnaire précède la mise en place de la sécrétion. Les mécanismes de la migration et de la sécrétion, en particulier la pulsatilité, restent méconnus. Avec des cultures d'explants olfactifs, nous avons étudié les conductances calciques au cours du développement et les facteurs impliqués dans la synchronisation. Nos résultats montrent une maturation des conductances calciques et leur contribution relative dans les fluctuations calciques intracellulaires au cours du développement. Quant à la synchronisation, nos résultats montrent l'existence d'une rythmicité dans l'activité électrique des neurones et l'implication du GABA et de la GnRH sans écarter d'autres neurotransmetteurs.The gonadotropin releasing hormone is essential to the reproduction. Secreted in a pulsatile manner, it controls the gonadotropic hormones secretion. GnRH neurons are in small number and are spread in the hypothalamic preoptic area. A migratory phase during the embryonic life, precedes the set up of the secretion. Mechanisms involved in the migratory state, as well as those involved in secretion, in particularly pulsatility, remain unknown. Using two models of nasal explants cultures, we studied modifications in calcium conductances during the in vitro development and factors potentially involved in neuronal synchronization. Our results have underlined a maturation in calcium conductances and their relative contribution in intracellular calcium signaling occurring during the in vitro development. They have also shown the existence of rhythmicity in electrical activity, and confirmed the role for GABA and GnRH, even if the involvement of others neurotransmitters cannot be eliminated.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF
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