1,721,006 research outputs found
Thyroid hormones reduce nicotinic receptor mediated currents in SH-SY5Y neuroblastoma cells
No full textBackground: Thyroid hormones (THs) are crucial for maturation and functioning of mammalian CNS. THs “classical” signaling involves nuclear receptors binding but also their non genomic actions, as rapid modulators of cell activity, are widely recognized. Since THs imbalance affects cognition and the cholinergic system is deeply involved in learning and memory processes we have studied THs effects at the level of the nicotinic acetylcholine receptors (nAchR). Methods: We used the patch-clamp technique to analyze T3 and T4 modulation of nicotine (NIC)-mediated current in SH-SY5Y neuroblastoma cells. Results: Both hormones decreased NIC-evoked current in a dose dependent fashion. The antagonism was reversible, not competitive and not blocked by Tetrac, an integrin αVβ3 receptor antagonist. A similar effect was detected with the endogenous agonist Acetylcholine. THs potencies were higher at 100 μM NIC (IC50 = 4.6 ± 2 μM for T3 and 4.8 ± 2 μM for T4) compared to those measured at 10 μM NIC (IC50 = 10 ± 4 μM for T3 and 8 ± 4 μM for T4). Furthermore, the efficacy of THs reached almost 90% at 100 μM NIC while was about 30 % at 10 μM NIC. THs inhibited nAchR-mediated currents by enhancing receptor desensitization and this effect was more pronounced at high agonist concentrations. Conclusions: Our results make light on a new non genomic activity of THs at the level of nAchR. This mechanism of action of THs can provide a new explanation for the cognitive deficits associated with tyroid dysfunction
Triazolam is more efficacious than diazepam in a broad spectrum of recombinant GABAA receptors
No full textBenzodiazepine-induced modifications of GABA (γ-aminobutyric acid) activated Cl- currents were studied in native GABAA receptors expressed in neonatal rat brain cortical neurons in primary cultures and in recombinant GABAA receptors expressed in transformed human embryonic kidney cells (293) after a transient transfection with cDNAs encoding for different molecular forms of α, β, and γ subunits of GABAA receptors. The efficacy of triazolam in cortical neurons was higher than that of diazepam. In transfected cells, triazolam showed a greater efficacy as a positive modulator of GABA-elicited Cl- currents in α1β1γ1, α1β1γ2, α1β1γ3, α6β1γ2 and α1β3γ2 receptors than diazepam, except in α3β1γ2 receptors where diazepam was more efficacious. When triazolam and diazepam were applied together to GABAA receptors assembled by transfecting cDNAs encoding for α1β1γ1 subunits, the action of triazolam was curtailed in a manner related to the dose of diazepam. In recombinant receptors assembled with α1β1γ1 receptors, maximally active doses of triazolam were more efficacious than those of clonazepam, alpidem, zolpidem, diazepam or bretazenil. © 1993
The density and distribution of six GABAA receptor subunits in primary cultures of rat cerebellar granule cells
No full textIn cultured cerebellar granule neurons (seven daysin vitro) the expression of GABAA receptor subunits was quantified by using freeze-fracture immunocytochemical techniques with antibodies that specifically recognize the α1, α6, β2-3, γ2 and δ subunits of the GABAA receptor. In some experiments we have also used a less specific antibody that recognizes several α receptor subunits (α-total). The specificity of these antibodies was verified in human embryonic kidney cell line no. 293 cells transfected with complementary DNAs codifying for various GABAA receptor subunits. The most abundant labeling in granule cells was generated by the antibody against the β2-3 subunits (∼44 colloidal gold particles/μm2), while the specific antibodies against α1 and α6 subunits show a labeling of about 16 colloidal gold particles/μm2. The α-total antibody shows a labeling of ∼37 gold particles/μm2. Both the γ2 and δ antibodies show a labeling of about 10 gold particles/μm2. In granule cells, the relative proportion of the label density revealed with antibodies against α-total, β2-3, γ2 and δ subunits is approximately 4:4:1:1. Assuming that one molecular form of the α subunit is assembled in a GABAA receptor, it can be estimated that in granule cells about 50% of receptors include the α1 subunit. A similar relative abundance can be estimated for the α6 subunit. The proportion of GABAA receptors containing the γ2 or δ subunits can be estimated to be about 50% in each case. Cerebellar granule cells express various abundances of GABAA receptor subunits which can be estimated by freeze-fracture immunocytochemistry. Fifty to sixty percent of these subunits form small receptor clusters, which appear to be associated with neuronal cytoskeleton proteins. © 1995 IBRO
Development of voltage-dependent ionic currents in rat cerebellar granule cells grown in primary culture
No full textDifferent sites of action of neurosteroids and benzodiazepines on natural and recombinant GABAA receptors
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