The depressing effect of GABA on synaptic excitation in isolated rat hippocampal slices

The action of various gamma-aminobutyric (GABA) concentrations on the amplitude of population EPSPs (PEPSPs) recorded from dendrites was examined in hippocampal slices. GABA produced reversible dose-dependent diminishing of the amplitude of PEPSPs without features of desensitization. CA1 hippocampal PEPSPs were much more sensitive to GABA (threshold concentrations--3.10(-5)-2.10(-4)mol/l; IC50--5.10(-4)-1.10(-3) mol/l) the action of GABA on PEPSPs was not depressed by bicuculline, picrotoxin or penicillin. The inhibitory action of GABA on dendritic antidromic population spike (DAPS) (post-synaptic inhibitory effect) was greatly reduced by these drugs. Baclofen was more potent inhibitor of CA1 PEPSPs than GABA (threshold concentration--1.10(-6)mol/l; IC50--3.10(-6)mol/l), but even in high concentration it induced only slight reduction of DAPS amplitude. It is concluded that GABA inhibitory effects on CA1 hippocampal PEPSPs are caused in the main by its presynaptic action mediated by GABA(B)-receptors located probably on axon terminals of the Schaffer collaterals.     

The postsynaptic effects of substance P in the frog neuromuscular synapse]

The effect of substance P on the end-plate currents (EPC) and miniature EPC (MEPC) was studied in the "cut" sartorius muscle of the frog using voltage-clamp technique after acetylcholinesterase inhibition. Substance P in the concentration 5.10(-7)-1.10(-6) mol/l had no effect on the amplitude and time course of the single EPC and MEPC, but promoted significant prolongation of EPC decay during repetitive nerve stimulation (10/s), which indicated development of postsynaptic potentiation. Elevation of the substance P concentration to 5.10(-6) mol/l has led to the shortening of single EPS decay and more significant depression of the EPC amplitude in trains. This effect was connected with a decrease of the postsynaptic membrane sensitivity to acetylcholine, i. e. development of desensitization.     

The effect of intracellular calcium on an increase in the cAMP-mediated calcium current]

Intracellularly perfused neurons of Helix pomatia in which serotonin-induced increase of calcium current (Ica) is mediated by cAMP were studied by the voltage clamp technique. It was established that an increase of the calcium intracellular concentration ([Ca2+]i) caused inhibition of the serotonin (5-HT) effect. The 5-HT effect value at 10(-6) and 10(-7) mol/l [Ca2+]i was 60 and 32% of the control one, respectively. Addition of the calmodulin antagonist (5.10(-5) M trifluoperasine) and phosphodiesterase blockers (5 mM theophylline or 10(-4) mol/l IBMX) sharply reduced the Ca2+ ability to inhibit the 5-HT effect. It is concluded that the Ca(2+)-calmodulin-dependent phosphodiesterase is a key link in the interaction between two signal transduction pathways--Ca2+ and cAMP in modulation of the calcium channel activity.     

Effects of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Vasoactive Intestinal Polypeptide (VIP) onHormone Secretion from Sheep Pituitary Cells in vitro

Although vasoactive intestinal polypeptide (VIP) is thought to be a prolactin releasing factor, in vivo studies on sheep suggest that it is inactive in this species. Recent studies, based primarily on the rat, suggest that the related pituitary adenylate cyclase-activating polypeptide (PACAP) is also a hypophysiotrophic factor but again in sheep, this peptide has no in vivo effects on hormone secretion despite being a potent activator of adenylate cyclase in vitro. This lack of response to either peptide in vivo in sheep could be due to the low concentration of peptide that reaches the pituitary gland following peripheral injection. In the present study we therefore adopted an alternative approach of evaluating in vitro effects of these peptides on GH, FSH, LH or prolactin secretion from dispersed sheep pituitary cells. In a time-course study, PACAP (1 μmol/l) increased GH concentrations in the culture medium between 1 and 4 h and again at 12 h but had no effect in the 6 and 24 h incubations. Prolactin, LH and FSH were not affected by PACAP. The response to various concentrations of PACAP (1 nmol/l–1 μmol/l) were then evaluated using a 3 h incubation. Again prolactin and LH were not affected by PACAP and there was a small increase in GH concentrations but only at high concentrations of PACAP (0.1 and 1 μmol/l; P<0.05). PACAP also stimulated FSH secretion in cells from some animals although this effect was small. The GH response to PACAP was inhibited by PACAP(6–38), a putative PACAP antagonist, but not by (N-Ac-Tyr¹, D-Arg²)-GHRH(1–29)-NH_2, a GH-releasing hormone (GHRH) antagonist. The cAMP antagonist Rp-cAMPS was unable to block the GH response to PACAP suggesting that cAMP does not mediate the secretory response to this peptide. At incubation times from 1–24 h, VIP (1 μmol/l) had no effects on prolactin, LH or GH secretion and, in a further experiment based on a 3 h incubation, concentrations of VIP from 1 nmol/l–1 μmol/l were again without effect on prolactin concentrations. Interactions between PACAP and gonadotrophin releasing hormone (GnRH), GHRH and dopamine were also investigated. PACAP (1 nmol/l–1 μmol/l) did not affect the gonadotrophin or prolactin responses to GnRH or dopamine respectively. However, at a high concentration (1 μmol/l), PACAP inhibited the GH response to GHRH. In summary, these results show that PACAP causes a modest increase in FSH and GH secretion from sheep pituitary cells but only at concentrations of PACAP that are unlikely to be in the physiological range. The present study confirms that VIP is not a prolactin releasing factor in sheep.     

Analysis of postsynaptic currents in the phasic and tonic muscle fibers of the extraocular muscles of the rat

The miniature end-plate currents (MEPCs), miniature postjunctional currents (MPJCs) and mean values of life-time of open ionic channels (tau chan) were compared in experiments on fast and tonic muscle fibres. The rise-time and decay-time constants of MPJCs in tonic fibres were 2.5 and 4-5 times (respectively) longer than those of MEPCs in fast fibres; tau chan in tonic synapses was 2.2 times higher than in fast ones. Inhibition of AChE induced more pronounced prolongation of MEPCs (4.4 times) than MPJCs (1.8 times). As a result, the difference between the time decay of MPJCs and MEPCs reduced to 1.6 times. Thus, a more prolonged decay of MPJCs in tonic fibres in comparison with MEPCs in fast fibres was due to a larger value of tau chan and lower activity of AChE, that favours repetitive interaction between ACh-molecules and choline receptors causing prolongation of the decay of the synaptic response. The time course of MEPCs and tau chan in skeletal slow-twitch muscle fibres was significantly shorter than those in extraocular tonic muscle fibres.     

The characteristics of the action of calcium ions on miniature end-plate currents after the disruption of mediator hydrolysis

Effect of calcium on the miniature end-plate currents (MEPC) at the frog neuromuscular junction was studied by the voltage-clamp technique. Rise of the calcium concentration in the Ringer solution up to 9 mmol/l caused a decrease of the MEPC amplitude which was related to the reduction of the end-plate channel conductance. Calcium had no effect on the time course of MEPCs at the active acetylcholinesterase (AChE) but accelerated MEPC decay by 26% after AChE inhibition by neostigmin or armin. It is supposed that the shortening effect of calcium on the MEPC decay phase is based on the ability of calcium to modulate the block of ionic channels by acetylcholine or to accelerate the process of desensitization of the postsynaptic membrane.     

Effects of "non-quantal" acetylcholine on the sensitivity of the postsynaptic membrane: action of ouabain and imitation of these effects by exogenous acetylcholine]

Development of postsynaptic potentiation (PSP) and desensitization (DS) caused by "non-quantal" acetylcholine after acetylcholinesterase inhibition was studied by means of ouabain, an agent known to modulate (initially increase and then decrease) the level of non-quantal secretion of ACh. Ouabain had no effect on the MEPC parameters when AChE was active. After AChE inhibition ouabain initially increased the decay time constant of MEPC (tau), i.e. caused postsynaptic potentiation (PSP). This effect of ouabain grew with time between inhibition of AChE and application of ouabain. The PSP stage was followed by shortening of MEPCs decay, due to the development of desensitization (DS), and that process was more pronounced than in control. Applied before AChE inhibition, ouabain had no effect on tau. Thus neither PSP nor DS developed under those conditions. Exogenous ACh (20 nmol/l) applied simultaneously with inhibitor of AChE partially prevented the shortening of MEPCs decay, but decreased the amplitude of MEPC. Applied after MEPCs shortening, exogenous ACh (50 nmol/l) tended to return the initial value of tau. It is concluded that nonquantal ACh produces PSP and DS on the postsynaptic membrane after inhibition of ACh and that the DS persists after cessation of nonquantal secretion for a long time.     

Tryptamine as an endogenous modulator of neuronal sensitivity to serotonin

Tryptamine has been studied for its effect on the 5-hydroxytryptamine-induced responses of the dorsal root ganglion neurons in rat with intracellular registration of the membrane potential and conductance and application of drugs from micropipettes under pressure. It was found that tryptamine applied in high concentrations acted like 5-hydroxytryptamine; but in the concentration range when it has no effect on the membrane potential and membrane conductance it either enhanced (10(-7) mol/l) or diminished (10(-5) mol/l) 5-hydroxytryptamine responses mediated by 5-HT1A- but not by 5-HT2-receptors. Harmane acted like tryptamine, but its derivatives either only enhanced or only inhibited the 5-hydroxytryptamine effects. The allosterical nature of 5-hydroxytryptamine-modulating action of tryptamine, harmane and its derivatives is discussed.     

不同浓度维甲酸诱导体外培养人羊膜上皮细胞分化为神经样细胞的研究

目的探讨维甲酸诱导人羊膜上皮细胞向神经样细胞分化。方法以DMEM/F12培养基培养原代人羊膜上皮细胞,并将细胞分为5组:对照组;1×10-8mol·L-1维甲酸组;1×10-7mol·L-1维甲酸组;1×10-6mol·L-1维甲酸组;1×10-5mol·L-1维甲酸组。各维甲酸组经维甲酸处理7 d后,用免疫组化检测神经干细胞巢蛋白(nestin)、微管相关蛋白2(MAP-2)、神经胶质纤维酸性蛋白(GFAP)和细胞全能性标记物Oct-4表达,并计数阳性细胞比例。结果与对照组比较,各维甲酸组显著提高人羊膜上皮细胞分化为神经样细胞的比例,其中1×10-6mol·L-1维甲酸组阳性细胞比例最高;结论维甲酸体外能诱导人羊膜上皮细胞向神经样细胞分化,最适诱导浓度为1×10-6mol·L-1。     

Inhibitory action of dopamine on excitatory transmission in the isolated spinal cord of the rat

The effect of dopamine on the ventral root potential evoked by single supramaximal dorsal root stimulation was studied in the experiment in the isolated superfused spinal cord of 10-16 days old rats. It was discovered that application of dopamine caused the reversible dose-dependent inhibition of the mono- and polysynaptic ventral root reflex responses. The minimal effective concentration was 1 X 10(-8) mol/l. Dopamine applied in concentrations of 1 X 10(-4) mol/l and 1 X 10(-3) mol/l decreased the amplitude of the monosynaptic ventral root potential by 20% and 87% as against the control, respectively. Under the same conditions the amplitude of the polysynaptic ventral root potential decreased by 18% and 87% as against the control, respectively. The obtained results demonstrate that the dopaminergic brainstem-spinal pathways take part in the control of the transmission in the segmentary reflex arc.     

Effect of quinine on the calcium currents of mollusk neurons

The effects of quinine on the peak amplitude and relaxation of calcium current (ICa) were examined on isolated unidentified snail neurons. Quinine (1 X 10(-5)-5 X 10(-4) mol/l) reversibly slowed the relaxation of ICa in a dose-dependent manner (early effect) and suppressed the peak amplitude of ICa in a dose-dependent and time-dependent manner (delayed effect). Quinine induced a shift of the current-voltage relationship for peak ICa by 5-10 mV in the hyperpolarizing direction. A half inhibition of ICa peak amplitude was induced by 6 X 10(-5) mol/l quinine. The results show that quinine is an effective inhibitor of calcium channels in snail neurons.     

维甲酸体外诱导大鼠胚胎垂体生长激素细胞的分化

目的 探讨维甲酸(RA)在体外诱导大鼠胚胎垂体生长激素(GH)细胞的分化作用.方法 原代培养大鼠胚胎垂体细胞,采用不同浓度的维甲酸(10-8、10-7、10-6、10-5 mol/L)诱导大鼠胚胎垂体细胞分化,以DMEM培养基为作为对照组,诱导2、4、6d后,利用免疫组化检测GH细胞百分比,放射免疫分析检测细胞上清GH...     

The extrasynaptic effect of the neuropeptides vasopressin, oxytocin and vasotocin on the electrically controlled ion channels of the membrane in mollusk neurons]

Extrasynaptic effects of vasopressin, oxytocin, vasotocin on the membrane electrosensitive ionic channels were studied in model experiments using isolated somata from the CNS of mollusc Lymnaea stagnalis. The neuropeptide in concentrations of 1.10(-16)-1.10(-6) mol/l either blocked or induced biphasic dose-dependent effect on amplitudes of the membrane ionic currents.     

Immunosuppressive effects of clozapine and haloperidol: enhanced production of the interleukin-1 receptor antagonist

In schizophrenic patients, multiple immune abnormalities have been reported, including increased production of proinflammatory cytokines. There is some evidence that antipsychotic drugs may have immunosuppressive effects. The aim of this study was to examine the in-vitro effects of different concentrations of antipsychotic agents on cytokine production by human whole blood. We examined the effects of clozapine and haloperidol, 10(-4), 10(-6) and 10(-8)M, on the unstimulated and stimulated (lipopolysaccharide+phytohemagglutinin) production of interleukin-6 (IL-6), IL-10, interferon-gamma (IFNgamma), and the IL-1 receptor antagonist (IL-1RA). Clozapine, 10(-6) and 10(-8)M, and haloperidol, 10(-4), 10(-6), and 10(-8)M, significantly increased the unstimulated and stimulated production of IL-1RA. Clozapine 10(-6)M significantly increased the stimulated production of IFNgamma. Clozapine 10(-4)M significantly suppressed the unstimulated production of IL-6 and IL-1RA and the stimulated production of IL-6, IL-10, IFNgamma and IL-1RA. The results suggest that both clozapine and haloperidol, at concentrations within the therapeutic range, may exert immunosuppressive effects through an enhanced production of IL-1RA.     

CSF acetylcholinesterase activity in central neurological diseases involving cholinergic systems]

The enzymatic activity of acetylcholinesterase (AchE) in the cerebrospinal fluid (CSF) is considered to be a marker of central cholinergic neuron integrity. Then, we evaluated CSF AchE activity in 90 cases of neurological diseases involving cholinergic system and their related disease, and 28 control cases without central organic lesions or abnormal findings in routine CSF study. AchE activity was evaluated according to Ellman's method using acetylthiocholine iodide as a substrate and tetraisopropyl-pyrophosphoramide, a specific inhibitor of butyrylocholinesterase. CSF AchE of Alzheimer type dementia (AD/SDAT, N = 12: 21.9 +/- 4.7 nmol/ml/min) showed no significant change from those of both control group (22.1 +/- 3.9) and vascular dementia (9: 21.7 +/- 6.7). In extrapyramidal diseases, reduction of the activity was observed in Huntington's chorea (HC, 4: 16.3 +/- 1.4) and progressive supranuclear palsy (PSP, 4: 17.6 +/- 1.7), whereas normal activity was shown in Parkinson's disease (PD, 19: 22.5 +/- 4.6), dentatorubropallidoluysian atrophy (DRPLA, 4: 22.6 +/- 4.2) and striatonigral degeneration (SND, 4: 20.4 +/- 4.3). In olivopontocerebellar atrophy (OPCA, N = 16), we disclosed reduced CSF AchE activity (15.8 +/- 2.4) which had significant correlations with the atrophy of the pontine base (r = 0.6017, p less than 0.02) and cerebellar vermis (r = 0.5450, p less than 0.05) in MRI. AchE activity in cerebellar cortical atrophy (CCA, 5: 20.6 +/- 2.2) remained within the control values. Normal activity was demonstrated in both amyotrophic lateral sclerosis (6: 24.3 +/- 7.3) and spinal muscular atrophy (4: 22.9 +/- 3.9).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of L-arginine on the afferent resting activity in the cephalopod statocyst.

The effects of bath application of the nitric oxide (NO) precursor L-arginine (L-ARG) on the resting activity (RA) of afferent crista fibers were studied in isolated statocysts of the cuttlefish Sepia officinalis under various experimental conditions. L-ARG (threshold 10(-7) M) had three different effects: inhibition, excitation, and excitation followed by an inhibition; only the inhibitory effect of L-ARG was dose-dependent. D-Arginine (D-ARG) had no effect. When the preparation was pre-treated with NO synthase inhibitors (N(G)-Nitric-L-arginine methyl ester HCl (L-NAME), N(G)-Nitro-L-arginine (L-NOARG)), both the inhibitory and the excitatory effects of L-ARG significantly decreased at higher concentrations (10(-5 to -4) M), or were completely blocked at lower concentrations (10(-7 to -6) M), of L-ARG. When the preparation was pre-treated with guanylate cyclase inhibitors (1H-[1,2, 4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), methylene blue (M-BLU), cystamine (CYS)), L-ARG had only excitatory effects, whereas its effects were only inhibitory when the preparation was pre-treated with adenylate cyclase inhibitors 2',3'-dideoxyadenosine (DDA), MDL-12330A (MDL), nicotinic acid (NIC-A)). L-ARG had no effects when the pre-treatment was with a guanylate cyclase inhibitor and an adenylate cyclase inhibitor combined; in that situation, the RA of the afferent fibers remained. These data indicate that in cephalopod statocysts, a cGMP and a cAMP signal transduction pathway (presumably via the generation of NO) are responsible for the effects of L-ARG on the RA of crista afferent fibers. They also indicate that the L-ARG-cGMP pathway is the dominant pathway and is inhibitory, and that both pathways have only modulatory effects on, but are not essential for, the generation of the RA.     

The risk of Parkinson disease associated with urate in a community-based cohort of older adults

Background/Aims: Studies suggest an inverse association between urate concentration and the risk of Parkinson disease (PD). We investigated this in the Cardiovascular Health Study in an elderly community-based cohort of adults. Methods: The association of baseline urate (μmol/l) and incident PD over 14 years was assessed with locally weighted scatterplot smoothing (LOESS) regression from which categories of low (<300 μmol/l), middle (300-500 μmol/l), and high (>500 μmol/l) urate ranges were derived. Multivariate logistic regression models assessed the risk of PD for each urate range. Linear and quadratic terms were tested when modeling the association between urate and the risk of PD. Results: Women had significantly lower urate concentrations than did men [316.8 μmol/l (SD 88.0) vs. 367.4 μmol/l (SD 87.7), p < 0.0001] and in women no associations between urate and PD risk were observed. In men, LOESS curves suggested a U-shaped or threshold effect between urate and PD risk. With the middle range as reference, the risk of developing PD was significantly increased for urate <300 μmol/l (OR 1.69, 95% CI 1.03-2.78) but not for urate >500 μmol/l (OR 1.55, 95% CI 0.72-3.32) in men. A negative linear term was significant for urate <500 μmol/l, and across the entire range a convex quadratic term was significant. Conclusions: Results suggest a more complex relationship than previously reported between urate levels and the risk of PD in men. Low urate concentrations were associated with a higher PD risk and high urate concentrations were not associated with a further decrease in PD risk.     

Ionic mechanisms of the effects of phenibut and GABA unrelated to changes in the function of chloride channels

It is established that beta-phenyl-GABA (phenibut) and partly GABA elicit direct depolarization of the isolated spinal cord motoneurons. The depolarizing effect of phenibut and a depolarizing component of GABA action do not alter in the presence of picrotoxin (10(-5) mol/l) and in the chloride-deficient medium. This depolarizing phenibut effect which is not bound with activation of GABAA-receptors and chloride channels coupled with them does not alter in Na+-deficient medium, enhances in the medium with excess of K+ ions (10 mol/l) and in presence of imidazol (5 . 10(-4) mol/l) and is completely abolished in the Ca2+-deficient medium with 2 mmol/l of Mn2+ or in the presence of 10(-4) mol/l theophylline. It is supposed that phenibut and partly GABA diminish intracellular concentration of cAMP via GABAB-receptor activation and decrease functional activity of voltage-dependent Ca2+-ionic channels and Ca2+-activated outward K+-currents.     

Pentobarbital interaction with the GABA-activated ion channels of the neurons in the rat cerebellum]

GABA and barbiturate-activated currents of isolated single neurons in the rat cerebellum were studied by means of the concentration clamp, voltage clamp and intracellular perfusion methods. The dissociation constant (Kd) was 3 +/- 0.8.10(-5) M. Pentobarbital potentiated the GABA-induced conduction of isolated neurons. The dose-effect for GABA shifted along the abscissa axes. Optimal concentrations which potentiated the GABA effect were within 10(-6)-10(-4) M. The pentobarbital concentrations above 5.10(-4) M without GABA activated the Cl conductance. The short-time conductance during fast pentobarbital washing off was found to increase.     

Concentration-dependent effects of neostigmine on the endplate acetylcholine receptor channel complex

The concentration-dependent actions of neostigmine, a carbamate anticholinesterase agent, were studied on the acetylcholine receptor channel complex in voltage-clamped twitch fibers of costocutaneous muscles of garter snakes. Low concentrations of neostigmine (10(-6) or 10(-5) M) increased miniature endplate current (MEPC) amplitude and the time constant of MEPC decay without changing the relationship between the MEPC decay time constant and membrane potential. Acetylcholine- or carbachol-induced endplate current fluctuation spectra were well fitted by a single Lorentzian curve with a characteristic frequency and single-channel conductance unaltered by low concentrations of neostigmine. Concentrations of neostigmine greater than 5 X 10(-5) M decreased MEPC amplitude and split the decay of MEPCs into two components, one faster and one slower than the control rate. These effects were both voltage and concentration dependent. Spectra of current fluctuations recorded in concentrations greater than or equal to 5 X 10(-5) M neostigmine required two time constants, one faster and one slower than the control. Two component spectra were also obtained with carbachol-induced current fluctuation spectra, indicating that these effects of neostigmine were direct and not a consequence of acetylcholinesterase inhibition. Similar results were also obtained in muscles pretreated with collagenase to remove junctional acetylcholinesterase. The fast and slow time constants obtained from current fluctuation spectra decreased and increased, respectively, with either increases in the concentration of neostigmine or membrane hyperpolarization when analyzed in the same fiber. The effects of neostigmine on channel lifetime were reversible with washing. These results indicate that the effects of neostigmine are concentration dependent. Concentrations greater than 2.5 X 10(-5) M exhibit direct effects on the endplate receptor channel complex which are unrelated to acetylcholinesterase inhibition. These actions include: a prolongation of the gating kinetics of the endplate receptor channel complex, the production of an altered state of the receptor channel complex evidenced by a high frequency component to current fluctuation spectra, and a direct action to block the acetylcholine receptor.