Effect of leu-enkephalin on potassium currents in neurons of the respiratory center of rats in vitro

Action of opioid peptide: leu-enkephalin (10 nM - 1 microM), on K+A-current and inward rectifier in neurons of two divisions of the respiratory center: ventrolateral area of the solitary tract nucleus and the pre-Botzinger complex, was investigated in brainstem slices of Wistar rats by whole-cell voltage-clamp recordings. A-current and inward rectifier were found in all the neurons under study. A-current did not change after the application of leu-enkephalin to the bath solution while the amplitude of inward rectifier did reversibly increase. The data obtained suggest that the inhibitory effect of leu-enkephalin on neurons of the respiratory center, at least in part, can be based on its ability to modulate inward rectifier.     

Effect of thyroliberin on membrane potential and pattern of spontaneous activity of neurons of the respiratory center in rats in vitro

On frontal brainstem slices of rat by means of whole-clamp recordings, we investigated effects of TRH (10(-8) [symbol: see text]) on membrane potential and firing pattern of the neurones in ventrolateral area of the solitary tract nucleus and pre-Botzinger complex. TRH induced a membrane depolarisation and an increase in spontaneous activity of the respiratory centre neurones. After TRH administration, a shortening of time intervals between the beginning of bursts was found in bursting neurones of the pre-Botzinger complex. In some silent neurones, TRH elicited appearance of firing activity, so the silent neurones of the solitary tract nucleus were transformed into tonic while the silent pre-Botzinger complex neurones were transformed into bursting ones. Thus, there is a direct regulatory effect of TRH on the respiratory centre neurones at the level of their membrane.     

Synchronization of activity of rhythm-forming neurons in the respiratory center

The method of determination of the basic parameter of the mathematical model of respiratory centre using temporal characteristics of respiratory neurons has been suggested. The model's behaviour depending on the meaning of this parameter and possibility of respiratory neuron's activity sinchronization have been investigated. The influence of feedback shorting on the mechanico-receptor outline on this process has been described.     

The effect of high energy irradiation on the membrane potential and impulse activity of neurons in the brain of Helix pomatia

In electrophysiological experiments with a preparation of the isolated Helix pomatia brain, a study was made of the effect of pulsed irradiation with high-energy electrons (20 MeV) on membrane potentials and pulse activity of "silent", pacemaking and postsynaptic neurons. It was shown that after irradiation with 150 and 300 Gy (dose rate 5 Gy/s and pulse frequency 50 Hz) "silent" neurons retain their excitability. Pacemaking neurons responded to radiation by a drastic increase in spontaneous pulse activity followed by its transfer to a clipped then to an irregular one. At the same time, the discharge frequency increased in the postsynaptic neurons.     

Thyroliberin blocks potassium A-current in neurons of the respiratory center of adult rats in vitro

TRH is a well-known respiratory active neuropeptide. To study neuronal mechanisms of its activity, we have tested the effects of TRH on the potassium A-current in neurons of the ventrolateral solitary tract nucleus and pre-Botzinger complex in voltage-clamp experiments on adult rat brain slices. A-current was present in the neurons and it was partially and reversibly blocked by administration of THR (10(-8) M) to the bath solution. The significant decrease in amplitude of A-current was accompanied by the increase in inactivation constant (t). The effect of TRH on A-current amplitude was simulated by 5 mM 4-aminopyridine. The results presented here indicate that the stimulatory effects of TRH on neurons of the respiratory centre can be at least partially explained by its ability to block the potassium A-current.     

γ-氨基丁酸对离体大鼠延髓头端腹外侧区神经元单位放电的抑制作用

在７３张脑片上观察了γ－氨基丁酸（ＧＡＢＡ）对１０６个延髓头端腹外侧区（ＲＶＬＭ）神经元单位放电的影响。外源性的ＧＡＢＡ（０．１￣３．０ｍｍｏｌ／Ｌ）抑制了１０６神经元中的８４个神经元的电活动,这些抑制效应呈剂量－反应关系。ＧＡＢＡ的抑制效应大部分可被ＧＡＢＡＡ受体选择性拮抗剂荷苞牡丹碱甲基碘化物（ＢＭＩ）和Ｃｌ＾－通道阻断剂印防己毒素（ＰＴＸ）所阻断,而单独灌流ＢＭＩ和ＰＴＸ对ＲＶＬＭ神经元主要     

Stimulating effect of gamma-aminobutyric acid on rat hippocampal neurons in vitro

Effects of GABA on the background and electrically stimulated activity of single neurons and population spikes were investigated in isolated hippocampal slices. Application of relatively large GABA concentrations (10(-3) mol/l and more) depressed an antidromic population spike, field EPSP and neuronal background activity. Low concentrations of GABA (less than 10(-3) mol/l) added to the bath increased the population spikes amplitude and the late component of field EPSP, facilitated single neurone responses, their background activity and epileptiform discharges. GABA-evoked depolarization was observed in the majority of the studied neurons. The duality of the GABA action on central neurons are discussed.     

The influence of membrane potential on chloride channels activated by GABA in rat cultured hippocampal neurons

Chloride currents were activated by a low concentration of GABA (0.5 m) in neonatal rat hippocampal neurons cultured for up to 14 days. Currents elicited by 0.5 m GABA in neurons, voltage-clamped using the whole-cell technique with pipettes containing 149 mm Cl^–, reversed close to 0 mV whether pipettes contained 144 mm Na⁺ or 140 mm Cs⁺, and were blocked by 100 m bicuculline. Current-voltage curves showed outward rectification. Single channel currents appeared in cell-attached patches when the pipette tip was perfused with pipette solution containing 0.5 m GABA and disappeared when a solution containing 100 m bicuculline plus 0.5 m GABA was injected into the pipette tip. The channels showed outward rectification and, in some patches, had a much lower probability of opening at hyperpolarized potentials. The average chord conductance in 10 patches hyperpolarized by 80 mV was 7.8±1.6 pS (sem) compared with a chord conductance of 34.1±3.5 pS (sem) in the same patches depolarized by 80 mV. Similar single channel currents were also activated in cell-free, inside-out patches in symmetrical chloride solutions when 0.5 m GABA was injected into the pipette tip. The channels showed outward rectification similar to that seen in cell-attached patches, and some channels had a lower probability of opening at hyperpolarized potentials. The average chord conductance in 13 patches hyperpolarized by 80 mV was 11.8±2.3 pS (sem) compared with 42.1±3.1 pS (sem) in the same patches depolarized by 80 mV.We are grateful to B. McLachlan and M. Robertson for their general assistance, to C. McCulloch and M. Smith for writing computer programs and to W. O'Hare for making the pipette injection device.     

The effect of acoustic cavitation on the contraction force and membrane potential of rat papillary muscles

Acoustic cavitation induced by continuous focused ultrasound (1.4 W/cm2, 543 Hz) was found to result in reversible membrane depolarization (by 54 mV), loss of excitability and contracture in the rat papillary muscles. The same intensities of impulse ultrasound had positive inotropic effects.     

Interaction of serotonin and leu-enkephalin on the habituating central neurons of Helix pomatia L. in situ and in vitro

1. Habituating neurons (a, b and c) of Helix pomatia reacted to the serotonin (10(-5)-10(-4)M) with depolarization evoking oscillatory waves and burst firing at the range of -35 to -55 MP values. 2. Isolated habituating cells were hyperpolarized by serotonin and failed to generate membrane oscillation or bursting pattern. 3. Only the isolated habituating neurons reacted to the application of leu-enkephalin (10(-5)-10(-4)M) by depolarization. 4. Neither membrane oscillation nor burst firing were evoked by leu-enkephalin. 5. On the cells a, b and c leu-enkephalin modulated the serotonin effect through cyclic 3',5'-AMP system both in situ and in vitro. 6. The membrane oscillation and burst firing of the habituating cells are connected to the regulation of various rhythmic processes including pneumostoma movements.     

Resting membrane potential of rat ventroposteriomedial thalamic neurons during postnatal development

Resting membrane potential is a critical parameter determining tonic or bursting mode of the thalamic neurons. Previous studies using whole-cell recordings showed that immature ventroposteriomedial (VPM) and lateral geniculate thalamic neurons are strongly depolarized and have resting membrane potential near ?50 mV. Yet, whole-cell recordings are associated with an introduction of the shunting conductance via the gigaseal that may lead to membrane depolarization in small neurons with high, in the gigaohm range, membrane resistance. Therefore, we have performed measurements of resting potential of VPM neurons in slices obtained from neonatal rats of postnatal days P2-P7 using cell-attached recordings of NMDA channels as voltage sensors. Because currents through the NMDA channels reverse near 0 mV, we assumed that the resting potential should equal the reversal potential of currents through NMDA channels in cell-attached recordings. Analysis of the current-voltage relationships of NMDA currents revealed that the resting potential in the immature VPM neurons is around ?74 mV and that it does not change during the first postnatal week. This suggests that VPM neurons may operate in the bursting mode during the early postnatal period and support the oscillatory activity (spindle-like bursts) in the developing thalamocortical networks.     

The effect of PKC activity on the TTX-R sodium currents from rat nodose ganglion neurons

To determine how protein kinase C (PKC) activity influences properties of the tetrodotoxin-resistant sodium current (TTX-R I(Na)) in neonatal rat nodose ganglion (NG) neurons, we assessed the effects of phorbol,-12-myristate,13-acetate (PMA), one of the PKC activators, and staurosporine, one of the PKC inhibitors, on the current. PMA (30 and 100 nM) induced an increase in the peak current amplitude of normalized current-voltage curves, a leftward shift in the potential for half activation (V(1/2)) of normalized conductance-voltage curves and a leftward shift of V(1/2) potential for steady-state inactivation curves. The effects of staurosporine (0.1 and 1 muM) on the peak current amplitude and the V(1/2) potential for activation were opposite compared with those seen after PMA application. Staurosporine (1 muM) antagonized PMA (100 nM)-induced modification of TTX-R I(Na). These results suggest that the basal TTX-R I(Na) obtained from neonatal NG neurons is controlled by the level of PKC activity.     

下丘脑Orexin神经元对呼吸活动的调节

半个世纪前,就有报道提示来自下丘脑外侧区的电脉冲可刺激呼吸。近年研究显示,下丘脑对呼吸的调节可能起源于下丘脑的Orexin神经元,其神经纤维投射到有Orexin受体分布的脑干呼吸中枢,微量注射Orexin于脑干呼吸中枢可刺激呼吸。在Orexin基因敲除的小鼠上,CO2引起呼吸增加的反应变弱,且使自发性睡眠呼吸暂停发生的频率增加。更有意义的发现是,下丘脑Orexin神经元能感受细胞外H+和CO2的变化,起到中枢化学感受器的作用而调节呼吸活动。本文简述Orexin的生物学特点,着重对呼吸活动的调节,以及参与相关呼吸系统疾病的病理生理过程作一综述。     

Enkephalin-like substance in aplysia nervous tissue and actions of leu-enkephalin on single neurons

Extract from the abdominal ganglia of Aplysia was fractionated by high performance liquid chromatography. Several large uv absorbing peaks were found. One of these peaks from the ganglionic extract was analyzed by displacement assay with the use of Mytilus edulis membranes. The results revealed the substance in this peak was able to displace 3H-D-Ala2, met5-enkephalinamide. In electrophysiological studies of abdominal and cerebral neurons, depolarizing and hyperpolarizing responses were obtained from some neurons, including neurons in the identified cerebral B cell cluster. A smaller population of cells exhibited biphasic responses. Some of the responses could be depressed by prior naloxone treatment. In conclusion, an endogenous opioid system, using substance related to but distinct from the enkephalins, may exist in Aplysia.     

The effect of thyroid hormones on the membrane adenylate cyclase activity in sickle red blood cells in vitro

A comparative study of thyroid hormone responsive membrane adenylate cyclase activity has been carried out on normal (Hb-AA) and sickle cell (Hb-SS) subjects. Thyroid hormones (T3 and T4) and selected analogues (TRIAC and DLT) enhanced adenylate cyclase activity in Hb-AA membranes. The interaction of Hb-SS membranes with the hormones and analogues was not significant except for T3 which moderately stimulated Hb-SS membrane adenylate cyclase. We suggest that circulating irreversibly sickled cells, in view of their membrane phospholipid defect, probably contribute to the low response of membrane adenylate cyclase to effector stimulation.     

Spectral characteristics of electrical activity of the respiratory center in brain processes in fetus and newborn rats in vitro

Power spectral analysis of inspiratory discharges of C3-C5 ventral roots in brainstem-spinal cord preparation from foetal (18 and 20 gestation days) and newborn (0-1 and 2-3 postnatal days) rats was performed. The respiratory centre perinatal development manifests itself by decreasing of respiratory rhythm variability and increasing of inspiratory burst duration. In foetal inspiratory bursts, low-frequency oscillations (1-10 Hz) dominate. In early postnatal stage, the relative power of low-frequency oscillations begin to decrease, and medium frequency oscillations (10-50 Hz) start to dominate over the inspiratory discharge. The data obtained suggests, that perinatal maturation of respiratory centre is characterised by stabilisation of the respiratory rhythm generation and developmental alteration of inspiratory activity's spectral and temporary parameters.