Modulatory effect of oxytocin and arginine-vasopressin on functional properties of three types of acetylcholine receptors in molluscan neurons.

It was found that 10(-7)-10(-8) mol/l oxytocin (OT) or arginine-vasopressin (AVP) applications produced effects on functional properties of three types of acetylcholine (ACh) receptors on various neurons identified in the ganglia of Helix pomatia under voltage clamp conditions. OT and AVP depressed ACh-induced sodium-potassium-calcium current in neuron RBc3 without shift of reversal potential. Our data show that there are two types (subtypes) of ACh receptors which are connected with chloride current in neurons of Helix pomatia. OT decreased ACh-induced chloride current in neuron D4 and enhanced ACh-induced chloride current in neuron D5. These effects of OT were mimicked by the intracellular injection of cyclic AMP or application of isobutylmethylxanthine and an active cyclic AMP analog. AVP as a rule mimicked the effects of OT on functional properties of ACh receptors, but in neuron F8 effects of OT and AVP were independent. The present results suggest that cyclic AMP may be the second messenger mediating the OT- and AVP-induced modulations of functional properties of three types of ACh-receptors.     

Modulatory effects of diadenosine polyphosphates on different types of calcium channels in the rat central neurons

Modulatory effects of diadenosine tetraphosphate (Ap₄A) and diadenosine pentaphosphate (Ap₅A) on Ca²⁺ channels were studied on isolated hippocampal neurons and synaptosomes taken from the rat midbrain. In experiments on synaptosomes obtained from the whole brain, Ap₅A applied at a concentration of 100 µM increased the intrasynaptosomal calcium level (measured by means of spectrofluorometry) for 26±1.8 nM, i.e., by 24±2%. Nifedipine failed to block this effect in synaptosomes and in hippocampal neurons. The high voltage-activated Ca²⁺ currents were identified by recording from freshly isolatedCA3 neurons using a whole-cell patch-clamp technique. Current-voltage relationships were measured in control and after incubation with 5 µM Ap₅A. In the majority of tested pyramidal neurons, the latter procedure resulted in a reversible increase in the high voltage-activated currents through Ca²⁺ channels measured at a holding potential of –100 mV, but not of –40 mV. Potentiation of the currents through Ca²⁺ channels in hippocampal neurons as well as an increase in intrasynaptosomal [Ca²⁺] could be irreversibly blocked by 5 µM -conotoxin, but not by 200 nM -Aga-IVA. These data indicate that diadenosine polyphosphates enhance the activity of N-type but not of L-type or P-type Ca²⁺ channels in many central neurons of the rat brain.Neirofiziologiya/Neurophysiology, Vol. 26, No. 6, pp. 409–416, November–December, 1994.     

Reaction of cholinoreceptors from an isolated molluskan neuron with analogs of acetylcholine and tetramethylammonium

The effect of 13 acetylcholine and tetramethylammonium derivatives on cholinoreceptors of isolated neurone on the pond snail has been investigated by the analysis of membrane current fluctuations at 10 and 20 degrees C. The elementary current was independent from the agonist structure. The channel open time and its Q10 coefficient were found to be maximum for acetylcholine. At low concentrations, acetylcholine derivative with four groups in its methylene chain exhibited the weakest activity. Agonist activity at higher concentrations was evaluated by maximum increase in the membrane current. With respect to this character, the derivative with two ethyl radicals in its cation group was found to be the weakest one. Possible causes of low activities of the agonists studied in comparison with that of acetylcholine are discussed.     

The pharmacological characteristics of two types of cholinoreceptors in the membrane of dialyzed neurons

1. The ramped voltage clamp technique was developed as a rapid means of studying the effects of certain nicotinic and muscarinic agents on ionic involvement and conductance changes during acetylcholine (ACh) responses of Helix pomatia neurons. 2. Atropine was found to be a potent cholinolytic on A-type neurons, ACh responses of which are blocked by ouabain and mediated by Na+ and Cl- permeabilities, while d-tubocurarine blocked B-type ACh responses which are insensitive to ouabain and mediated by Na+ and K+ permeabilities. 3. Nicotinic agent butyrylcholine was found to be a potent cholinomimetric on B-type cells. 4. The results suggest that ACh receptors on A-type cells are more "muscarinic" while those on B-type cells are more "nicotinic". 5. It was also suggested that both muscarinic and nicotinic ACh receptors may coexist in the Helix neuronal membrane and the possibility of ACh interacting with one of them is determined by the level of phosphorylation of the membrane proteins.     

Modulatory effects of acid-sensing ion channels on action potential generation in hippocampal neurons

Extracellular acidification has been shown to generate action potentials (APs) in several types of neurons. In this study, we investigated the role of acid-sensing ion channels (ASICs) in acid-induced AP generation in brain neurons. ASICs are neuronal Na⁺ channels that belong to the epithelial Na⁺ channel/degenerin family and are transiently activated by a rapid drop in extracellular pH. We compared the pharmacological and biophysical properties of acid-induced AP generation with those of ASIC currents in cultured hippocampal neurons. Our results show that acid-induced AP generation in these neurons is essentially due to ASIC activation. We demonstrate for the first time that the probability of inducing APs correlates with current entry through ASICs. We also show that ASIC activation in combination with other excitatory stimuli can either facilitate AP generation or inhibit AP bursts, depending on the conditions. ASIC-mediated generation and modulation of APs can be induced by extracellular pH changes from 7.4 to slightly <7. Such local extracellular pH values may be reached by pH fluctuations due to normal neuronal activity. Furthermore, in the plasma membrane, ASICs are localized in close proximity to voltage-gated Na⁺ and K⁺ channels, providing the conditions necessary for the transduction of local pH changes into electrical signals. cellular excitability; neuronal signaling; pH     

17β-雌二醇对大鼠脑片穹隆下器神经元放电活动的调变作用

用细胞外记录技术 ,在大鼠脑片穹隆下器 (subfornicalorgan ,SFO)上观察了 17β 雌二醇 (17β estradiol,E2 )对SFO神经元放电的影响 ,并进而分析其作用机制。实验结果如下 :(1) 15个SFO神经元在给予小剂量E2(0 1nmol/L)时 ,放电频率由 3 2 1± 0 37增至 6 79± 0 71Hz(P <0 0 0 1) ;而在给予大剂量E2 (10 0nmol/L)时 ,则放电频率由 3 44± 0 40Hz降至 1 44± 0 36Hz (P <0 0 1) ;(2 )在 7个SFO神经元应用谷氨酸NMDA受体阻断剂MK 80 1(5 0pmol/L) ,可阻断小剂量E2 (0 1nmol/L)对SFO神经元的兴奋效应 ;(3)在 7个SFO神经元应用NO生理性前体L 精氨酸 (L arginine ,1mmol/L)时 ,SFO神经元放电减少 ,且可阻断小剂量E2 (0 1nmol/L)对神经元的兴奋效应 ;(4 )在 6个SFO神经元应用NOS抑制剂L NG 硝基精氨酸甲酯 (L NAME ,10mmol)引起SFO神经元放电增加 ,并阻断大剂量E2 (10 0nmol/L)对SFO神经元的抑制效应。结果提示 :E2 对SFO神经元有双重作用。小剂量E2 使SFO神经元放电增加 ,这一效应可能与谷氨酸受体激活有关 ;而大剂量E2 则导致神经元放电减少 ,此效应可归因于NOS激活而引发NO生成。     

Mechanisms of tubocurarine action on nicotinic cholinoreceptors of rat sympathetic ganglia neurons

The effects of tubocurarine (TC) on current induced by acetylcholine (ACh) in neurons of rat upper cervical ganglia were investigated using techniques for voltage-clamping at the membrane. Reinforcement of TC-induced blockade was achieved by paired application of ACh following prior activation of nicotinic cholinoreceptors, indicating that TC blocked the channels opened by ACh. On average, the TC-open channel complex persisted for 9.8±0.5 sec (n=7) at –50 mV and 20–24°C. It was found that increases exponentially with hyperpolarization at the membrane (a shift in membrane potential of 61 mV corresponds to an e-fold change). Suppression of ACh-induced current (ACh current) was eliminated completely under the effects of 3–30 M with depolarization of up to 80–100 mV at the membrane. Suppression of ACh current produced by membrane potential at negative levels is intensified with increasing doses of ACh. Findings would indicate that blockade of ionic channels opened by ACh is the only mechanism of TC action on nicotinic cholinoreceptors in rat sympathetic ganglia.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 672–680, September–October, 1988.     

Modulatory effects of catecholamines on neurons of the rat visual cortex: single-cell iontophoretic studies

The catecholamines noradrenaline and dopamine have been proposed as neuromodulators of cortical neuron excitability, and such a regulation could be mediated by specific adrenergic and dopaminergic receptors. We characterized electrophysiologically some of the types of responses to the iontophoretic application of adrenergic and dopaminergic agonists and antagonists on single cells in the rat visual cortex (areas occipital 1 monocular or Oc1M and occipital 1 binocular or Oc1B). For the majority of spontaneously active and visual cortical cells, noradrenaline and dopamine decreased the firing frequency. In the case of visually driven (synaptically activated) neurons, background firing was the main component of the response to be inhibited by the administration of noradrenaline, clonidine, and oxymetazoline, leading to an enhancement of the signal-to-noise ratio. Since these effects could be reduced or blocked by a previous ejection of the specific alpha 2-antagonist idazoxan, the findings support a role for alpha 2-adrenergic receptors in the transmission of sensory inputs to the visual cortex. These effects were not found with the mixed alpha-adrenergic agonist phenylephrine nor with the beta-agonist isoproterenol. Finally, the use of the inhibitory amino acid GABA rules out a simple hyperpolarizing response as the mechanism underlying noradrenaline modulatory effects in the cerebral cortex.     

Identification of cholinoreceptors on the soma of snail neurons RPa3 and LPa3

Identification of cholinoreceptors (CR) of the soma of neurons RPa3 and LPa3 of the snail is performed using selective cholinomimetics and cholinolytics during the recording of transmembrane ionic currents. Agonists of the nicotinic (NCR) and muscarinic (MCR) types of cholinolytics evoked a brief activation of the receptors, with the exception of carbamylcholine, followed by an irreversible blocking. All selective cholinomimetics bonded with the same membrane centers which acetylcholine (AC) activated. The nicotinic and muscarinic cholinolytics decreased the amplitude of the input current elicited by AC; however, the use of scopolamine and platyphylline was without effect. It is speculated that the soma of neurons RPa3 and LPa3 exhibits NCR and MCR which have a number of pharmacological features distinguishing them from the corresponding CR of vertebrates. The MCR of these neurons must be classed as a special subtype differing from the well-known M₁ and M₂ subtypes.M. V. Lomonosov State University of Moscow. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 77–86, January–February, 1992.     

The excitable properties of three types of motor axons

1. Three anatomically different types of lobster motor axons have been shown to possess different excitabilities under identical conditions. 2. The type, openers, which fired the longest trains of repetitive responses also had the lowest rheobase values, the longest utilization times, and the least accommodation. 3. A relationship between the time course of the local potential and the time course of the excitatory state has been disclosed. 4. The characterization of the excitatory state by simple two factor equations has been discussed and found to be only approximate since both the excitatory state and the local response tend to be somewhat oscillatory.     

Modulatory effects of the GABAergic basal ganglia neurons on the PPN and the muscle tone inhibitory system in cats

Pedunculopontine tegmental nucleus (PPN) contributes to the control muscle tone by modulating the activities of pontomedullary reticulospinal systems during wakefulness and rapid eye movement (REM) sleep. The PPN receives GABAergic projection from the substantia nigra pars reticulata (SNr), an output nucleus of the basal ganglia. Here we examined how GABAergic SNr-PPN projection controls the activity of the pontomedullary reticulospinal tract that constitutes muscle tone inhibitory system. Intracellular recording was made from 121 motoneurons in the lumbosacral segments in decerebrate cats (n=14). Short train pulses of stimuli (3 pulses with 5 ms intervals, 10-40 mA) applied to the PPN, where cholinergic neurons were densely distributed, evoked eye movements toward to the contralateral direction and bilaterally suppressed extensor muscle activities. The identical PPN stimulation induced IPSPs, which had a peak latency of 40-50 ms with a duration of 40-50 ms, in extensor and flexor motoneurons. The late-latency IPSPs were mediated by chloride ions. Microinjection of atropine sulfate (20 mM, 0.25 ml) into the pontine reticular formation (PRF) reduced the amplitude of the IPSPs. Although conditioning stimuli applied to the SNr (40-60 mA and 100 Hz) alone did not induce any postsynaptic effects on motoneurons, it reduced the amplitude of the PPN-induced IPSPs. Subsequent injection of bicuculline (5 mM, 0.25 ml) into the PPN blocked the SNr effects. Microinjections of NMDA (5 mM, 0.25 ml) and muscimol (5 mM, 0.25 ml) into the SNr reduced and increased the amplitude of the PPN-induced IPSPs, respectively. These results suggest that GABAergic basal ganglia output controls postural muscle tone by modulating the activity of cholinergic PPN neurons which activate the muscle tone inhibitory system. The SNr-PPN projection may contribute to not only control of muscle tone during movements in wakefulness but also modulation of muscular atonia of REM sleep. Dysfunction of the SNr-PPN projection may therefore be involved in sleep disturbances in basal ganglia disorders.     

Linking dynamical and functional properties of intrinsically bursting neurons

Several studies have shown that bursting neurons can encode information in the number of spikes per burst: As the stimulus varies, so does the length of individual bursts.Therepresented stimuli, however, vary substantially among different sensory modalities and different neurons.The goal of this paper is to determine which kind of stimulus features can be encoded in burst length, and how those features depend on the mathematical properties of the underlying dynamical system.We show that the initiation and termination of each burst is triggered by specific stimulus features whose temporal characteristsics are determined by the types of bifurcations that initiate and terminate firing in each burst. As only a few bifurcations are possible, only a restricted number of encoded features exists. Here we focus specifically on describing parabolic, square-wave and elliptic bursters. We find that parabolic bursters, whose firing is initiated and terminated by saddle-node bifurcations, behave as prototypical integrators: Firing is triggered by depolarizing stimuli, and lasts for as long as excitation is prolonged. Elliptic bursters, contrastingly, constitute prototypical resonators, since both the initiating and terminating bifurcations possess well-defined oscillation time scales. Firing is therefore triggered by stimulus stretches of matching frequency and terminated by a phase-inversion in the oscillation. The behavior of square-wave bursters is somewhat intermediate, since they are triggered by a fold bifurcation of cycles of well-defined frequency but are terminated by a homoclinic bifurcation lacking an oscillating time scale. These correspondences show that stimulus selectivity is determined by the type of bifurcations. By testing several neuron models, we also demonstrate that additional biological properties that do not modify the bifurcation structure play a minor role in stimulus encoding. Moreover, we show that burst-length variability (and thereby, the capacity to transmit information) depends on a trade-off between the variance of the external signal driving the cell and the strength of the slow internal currents modulating bursts. Thus, our work explicitly links the computational properties of bursting neurons to the mathematical properties of the underlying dynamical systems.     

Comparative studies on the functional roles of N- and C-terminal regions of molluskan and vertebrate troponin-I

Vertebrate troponin regulates muscle contraction through alternative binding of the C-terminal region of the inhibitory subunit, troponin-I (TnI), to actin or troponin-C (TnC) in a Ca(2+)-dependent manner. To elucidate the molecular mechanisms of this regulation by molluskan troponin, we compared the functional properties of the recombinant fragments of Akazara scallop TnI and rabbit fast skeletal TnI. The C-terminal fragment of Akazara scallop TnI (ATnI(232-292)), which contains the inhibitory region (residues 104-115 of rabbit TnI) and the regulatory TnC-binding site (residues 116-131), bound actin-tropomyosin and inhibited actomyosin-tropomyosin Mg-ATPase. However, it did not interact with TnC, even in the presence of Ca(2+). These results indicated that the mechanism involved in the alternative binding of this region was not observed in molluskan troponin. On the other hand, ATnI(130-252), which contains the structural TnC-binding site (residues 1-30 of rabbit TnI) and the inhibitory region, bound strongly to both actin and TnC. Moreover, the ternary complex consisting of this fragment, troponin-T, and TnC activated the ATPase in a Ca(2+)-dependent manner almost as effectively as intact Akazara scallop troponin. Therefore, Akazara scallop troponin regulates the contraction through the activating mechanisms that involve the region spanning from the structural TnC-binding site to the inhibitory region of TnI. Together with the observation that corresponding rabbit TnI-fragment (RTnI(1-116)) shows similar activating effects, these findings suggest the importance of the TnI N-terminal region not only for maintaining the structural integrity of troponin complex but also for Ca(2+)-dependent activation.     

Modulatory effects of metanil yellow on immunity in rodents.

Pathomorphological and immunological studies were carried out on rodents following oral administration of 0, 0.1, 0.25 and 0.5% (w/w) metanil yellow, mixed in diet, for 30 days. No significant change in hematologic parameters and histologic architecture of liver, kidney, mesenteric lymph node, thymus and urinary bladder was observed except for mild desquamation of intestinal villi and moderate changes in Peyer's patches of small intestine with higher doses. Among immunological parameters, significant enhancement in the primary humoral immune response (anti-SRBC IgM plaque forming cells of spleen) was observed with the lowest dose of metanil yellow while higher doses produced opposing effects. An elevated cutaneous delayed type hypersensitivity (DTH) reaction to SRBC was seen in 0.1% metanil yellow treated animals but higher doses did not influence the reaction. The treatment also caused changes in functional capabilities of macrophages. Although these immune alterations could hardly influence the local immunity of gut, as measured by the capacity of animals to cause rejection of Nippostrongylus brasiliensis parasite, the potential to modulate the immunity in general by metanil yellow however assumes considerable biological significance.     

内皮素对麻醉大鼠动脉压力感受器反射的调制作用

在27只隔离灌流颈动脉窦区的麻醉大鼠,观察了内皮素（ET-1）对动脉压力感受器反射的调制作用。结果如下：（1）在颈动脉窦区灌流1nmol／L的ET-1时,压力感受器机能曲线向左下方移位,曲线的最大斜率（PS）由0.40±0.02增至0.51±0.02kPa／kPa（P＜0.01）,压力感受器反射性血压下降幅度（RD）由5.66±0.23增至6.76±0.22kPa（P＜0.01）。由此提示,这一剂量的FT-1对压力感受器反射有易化作用。（2）用10nmol／L的ET-1灌流时,压力感受器机能曲线则向右上方移位,PS降至0.28±0.01kPa／kPa（P＜0.01）,RD降至4．16±0.19kPa（P＜0.01）;100nmol／L的ET-1可使压力感受器机能曲线向右上方移位更为明显,PS降至0.19±0.03kPa（P＜0.001）,RD进一步降至3.33±0.38kPa（P＜0.001）。这些结果表明,上述两种剂量的ET-1对压力感受器反射有抑制作用。（3）ETA受体选择性阻断剂BQ123（0.15μmol／L）可以阻断ET-1（10nmol／L）对压力感受器反射的抑制效应。（4）预先灌流KATP通道阻断剂格列苯脲（10μmol／L）,也可阻断ET-1的效应。综上所述,ET-1对压力感受器反射有双重效应,低剂量时有易化作用,而较高剂量时则有抑制作用,后一作用由ET-1型受体介导并有KATP通道的参与。     

Influence of hypergravity on hypothalamic vasopressin and oxytocin neurons in rats

This study was aimed to evaluate the reaction of the vasopressin (VP) and oxytocin (OT) neurons of the supraoptic nucleus (SON) in rats to single or repeated hypergravity (HG). Special attention was paid to the tyrosine hydroxylase (TH) expression in VP neurons as a marker of the neuron activation. Rats were revolved in a centrifuge with overloading 2G for 5 days or 34 days as well as for 34 days plus 5 days with an interval of 39 days between two rotations. Control rats were kept in a centrifuge room. Radioimmununoassay, quantitative and semi-quantitative immunocytochemistry and in situ hybridization were used to evaluate: a) VP concentration in the pituitary posterior lobe (PL) and in plasma; b) the number of VP-, OT- and TH-immunoreactive neurons in the SON; c) the optic density of VP-, OT- and TH-immunoreactive materials in cell bodies (SON) and distal axons (PL), d) the optic density of VP and OT mRNAs signals (S35) in the whole SON on microfilms. According to our data, VP neurons were strongly activated during HG (5 days or 34 days) that was manifested in the functional hypertrophy of the neurons, greatly increased concentrations of VP mRNA in the SON and VP in plasma, the onset of the TH expression. The neurons showed initially (5 days) the functional insufficiency (VP release > VP synthesis) followed by their adaptation (subsequent 29 days) to the increased need in VP (VP release < VP synthesis). No reaction of VP neurons was observed to repeated HG. In contrast to VP neurons, OT neurons did not react to short-term HG or showed functional depression after the long-term treatment.     

Antipyrogenic properties of oxytocin

Effects of oxytocin on pyrogenal or endogenous pyrogen-induced fever were studied. Intramuscular injection of oxytocin (0.2 micrograms/kg every half an hour) did not significantly affect the pattern of pyrogenal-induced fever. Constant intravenous injection of oxytocin (0.4 and 4 micrograms/kg/h) 2-4.5 h after pyrogenal decreased the rectal temperature, on an average, by 24% and 31%, respectively. Endogenous pyrogen fever was not attenuated by intravenous oxytocin (4 micrograms/kg/h). The antipyrogenic effect of oxytocin is related to inhibition of endogenous pyrogen synthesis rather than to blockade of its action, which is indicated by a decreased second peak of the temperature curve, inhibition of endogenous pyrogen synthesis in vitro, and persistence of the hyperthermic effect of endogenous pyrogen.