Impaired GABAergic transmission and altered hippocampal synaptic plasticity in collybistin-deficient mice

Collybistin (Cb) is a brain-specific guanine nucleotide exchange factor that has been implicated in plasma membrane targeting of the postsynaptic scaffolding protein gephyrin found at glycinergic and GABAergic synapses. Here we show that Cb-deficient mice display a region-specific loss of postsynaptic gephyrin and GABA(A) receptor clusters in the hippocampus and the basolateral amygdala. Cb deficiency is accompanied by significant changes in hippocampal synaptic plasticity, due to reduced dendritic GABAergic inhibition. Long-term potentiation is enhanced, and long-term depression reduced, in Cb-deficient hippocampal slices. Consistent with the anatomical and electrophysiological findings, the animals show increased levels of anxiety and impaired spatial learning. Together, our data indicate that Cb is essential for gephyrin-dependent clustering of a specific set of GABA(A) receptors, but not required for glycine receptor postsynaptic localization.     

Protective action of vitamins on the spermatogenesis in lead-treated Swiss mice

The protective action of vitamins C and E against lead acetate-induced reduced sperm count and sperm abnormalities in Swiss mice has been studied. Intraperitoneal injection of lead acetate (10mg/kg body weight) in the present study stimulates lipid peroxidation in the testicular tissue, indicated by a significant increase in malondialdehyde content in the experimental mice group. This is associated with an increased generation of noxious reactive oxygen species (ROS). Significantly reduced sperm count associated with increased sperm abnormality percentage in the lead-injected mice group compared to controls substantially proves the ongoing damaging effects of lead-induced ROS on developing germ cells. However, intraperitoneal administration of vitamin C (Vit C) at a concentration equivalent to the human therapeutic dose (10 mg/kg body weight) was able to minimize significantly the testicular malondialdehyde content with a concomitant increase in sperm count and significant decrease in the percentage of abnormal sperm population. Vitamin E (Vit E) (100 mg/kg body weight) treatment of a batch of lead-injected mice had a similar effect as Vit C but with a comparatively lower efficacy. On the other hand, coadministration of both vitamins (Vit C + Vit E) at the above mentioned doses to lead-treated mice led to the most significant decline in malondialdehyde content along with elevated sperm count and reduction in the percentage of abnormal sperm population. The protective action and the synergistic action of both vitamins (C and E) against lead-induced genotoxicity are discussed.     

An acetylcholine receptor alpha-subunit promoter conferring preferential synaptic expression in muscle of transgenic mice.

We have obtained transgenic mice expressing nuclearly targeted beta-galactosidase (nls-beta-gal) under the control of a chicken acetylcholine receptor alpha-subunit promoter. The expression of the transgene was detected in early somites, starting before embryonic day 9.5. In 13-day embryos, the expression pattern of the transgene closely paralleled that of the endogenous mouse alpha-subunit gene, assessed by in situ hybridization. Our results illustrate, with single-cell resolution, the tissue specificity of this alpha-subunit promoter during embryogenesis. After birth, the overall beta-galactosidase activity rapidly decreased with age. However, in diaphragms of newborn animals, beta-galactosidase activity selectively persisted in nuclei underlying the motor endplates. The latter were revealed by an acetylcholinesterase stain. Nls-beta-gal was also visualized by indirect immunofluorescence, while endplates were labelled with fluorescent alpha-bungarotoxin. Confocal microscopy unambiguously identified the more intensely stained nuclei as synaptic 'fundamental nuclei', and allowed estimates of relative staining levels. Thus an 842 bp acetylcholine receptor gene promoter confers preferential synaptic expression to a reporter gene within myofibres in vivo.     

NMDA受体参与小鼠的前额扣带回的神经突触传递

谷氨酸性突触是哺乳动物神经系统的主要兴奋性突触。在正常条件下,大多数的突触反应是由谷氨酸的AMPA受体传递的。NMDA受体在静息电位下为镁离子抑制。在被激活时,NMDA受体主要参与突触的可塑性变化。但是,许多NMDA受体拮抗剂在全身或局部注射时能产生行为效应,提示NMDA受体可能参与静息状态的生理功能。此文中,我们在离体的前额扣带回脑片上进行电生理记录,发现NMDA受体参与前额扣带回的突触传递。在重复刺激或近于生理性温度时,NMDA受体传递的反应更为明显。本文直接显示了NMDA受体参与前额扣带回的突触传递,并提示NMDA受体在前额扣带回中起着调节神经元兴奋的重要作用。     

Mechanisms of non-adrenergic non-cholinergic synaptic transmission in smooth muscle cells of the gastrointestinal tract

Non-adrenergic non-cholinergic (NANCh) inhibitory synaptic potentials in smooth muscle cells (SMC) of the gastrointestinal tract are of a complex transmitter and ion nature. A blocker of ATP receptors, suramin, blocks the fast component, while a blocker of NO synthase, L-NOARG, blocks the slow component of NANCh inhibitory synaptic potentials. In the presence of both suramin and L-NOARG, SMC respond to stimulation of the intramural plexus by generating a low-amplitude hyperpolarization, and VIP is likely to be the transmitter for this effect. Low-conductance Ca²⁺-dependent potassium channels are involved in generation of the fast component of NANCh inhibitory synaptic potentials, and these channels are effectively blocked by apamin. The slow component of this potential is generated by high-conductance Ca²⁺-dependent potassium channels. In the presene of both apamin and L-NOARG (or charibdotoxin), SMC respond to intramural stimulations with non-cholinergic excitatory synaptic potentials, and ATP application evokes depolarization. Both effects are blocked by suramin. In the presence of apamin, noradrenaline also evokes depolarization in SMC, and this effect, similarly to hyperpolarization under normal conditions, is blocked by phentolamine. Our studies allow us to suggest that in smooth muscles of the gastrointestinal tract there are two types of synaptic transmission: the excitatory cholinergic, adrenergic, and ATP-ergic transmission and the inhibitory adrenergic, ATP-ergic, NO-ergic, and VIP-ergic transmission.     

Muscle specificity in tests of cervical flexor muscle performance.

The deep cervical flexor (DCF) muscles are considered to be of substantial clinical importance in the management of neck pain. While conventional cervical flexion (CF) dynamometry methods have been used frequently to assess the capacity of the cervical flexor muscles, it has been suggested that cranio-cervical flexion (CCF) methods may provide a more specific test of DCF muscle performance. This study compared the activation of the deep and superficial cervical flexor muscles between tests of isometric cranio-cervical flexion (CCF) and conventional cervical flexion (CF) dynamometry. Normalised root-mean-square values were recorded for the deep cervical flexor (DCF), sternocleidomastoid (SCM), anterior scalene (AS), and sternohyoid (SH) muscles during isometric CCF and CF tests at maximal voluntary contraction (MVC), 50% MVC, and 20% MVC in ten healthy volunteers. The results demonstrated significantly greater electromyography (EMG) amplitude for the SCM (P<.001-.002) and AS (P<.001-.001) muscles in the CF test conditions (MVC, 20%MVC, and 50%MVC) compared to CCF test conditions. Moreover, the SH muscle demonstrated significantly greater EMG amplitude during CF compared to CCF but only in the 50% MVC and 20% MVC conditions (P=.007 and .02 respectively). These results demonstrate that dynamometry tests of CF result in greater activity of the superficial cervical flexor muscles compared to tests of CCF. As a result, CCF dynamometry may provide a more specific method to assess and retrain DCF muscle performance, compared to conventional CF in which superficial muscle activity may mask impaired performance of the DCF muscles.     

Peptidergic synaptic transmission in sympathetic ganglia

Biologically active peptides have been localized in neuronal cell bodies, axons, and synaptic boutons of sympathetic ganglia; some of these peptides may be neurotransmitters. For example, substances immunologically similar to substance P and luteinizing hormone-releasing hormone appear to be released from nerve terminals in sympathetic ganglia. In each case, the postsynaptic action of the peptide lasts for several minutes and is accompanied by a combination of decreases and increases in the membrane conductance that are voltage dependent. These peripheral peptidergic synapses may be models for peptidergic transmission in the central nervous system where detailed analysis is more difficult.     

Effect of strychnine,hydrastine, and apamine on synaptic transmission in smooth muscle cells

The action of strychnine, hydrastine, and apamine on neuromuscular transmission in the stomach and taenia coli was investigated. Hydrastine and strychnine increase nonadrenergic IPSPs of smooth muscle cells. Under the influence of apamine the IPSP and hyperpolarization evoked by exogenous ATP are reversibly blocked and noncholinergic EPSPs appear; ATP, however, does not cause depolarization of the cell membrane. Consequently, apamine is a specific blocker of nonadrenergic inhibition, acting on the postsynaptic membrane, and ATP is a mediator both of this inhibition and of noncholinergic synaptic excitation discovered in smooth muscle cells.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 295–299, May–June, 1978.     

The role of the synaptic vesicles in transmission at the insect nerve-muscle junction

The ultrastructure of nerve-muscle synapses on red and white fibres of locust ($\text{Schistocerca}$$\text{gregaria}$) retractor unguis muscle fibres was examined before and after stimulation. At a stimulation frequency of 15Hz, the synapses on the white fibres fatigued completely; those on the red fibres also fatigued, but during prolonged stimulation they showed intermittent periods of recovery. Synaptic vesicles at both types of fatigued synapses were reduced in volume compared with controls and at fatigued synapses on white fibres the vesicles had irregular outlines. Aggregation of vesicles were observed at fatigued synapses on red fibres and the synaptic cleft width at these synapses was less than at control synapses on red fibres. These results are discussed in the light of the vesicle hypothesis for synaptic transmission.     

Dehydration anorexia is attenuated in oxytocin-deficient mice

Evidence in rats suggests that central oxytocin (OT) signaling pathways contribute to suppression of food intake during dehydration (i.e., dehydration anorexia). The present study examined water deprivation-induced dehydration anorexia in wild-type and OT -/- mice. Mice were deprived of food alone (fasted, euhydrated) or were deprived of both food and water (fasted, dehydrated) for 18 h overnight. Fasted wild-type mice consumed significantly less chow during a 60-min refeeding period when dehydrated compared with their intake when euhydrated. Conversely, fasting-induced food intake was slightly but not significantly suppressed by dehydration in OT -/- mice, evidence for attenuated dehydration anorexia. In a separate experiment, mice were deprived of water (but not food) overnight for 18 h; then they were anesthetized and perfused with fixative for immunocytochemical analysis of central Fos expression. Fos was elevated similarly in osmo- and volume-sensitive regions of the basal forebrain and hypothalamus in wild-type and OT -/- mice after water deprivation. OT-positive neurons expressed Fos in dehydrated wild-type mice, and vasopressin-positive neurons were activated to a similar extent in wild-type and OT -/- mice. Conversely, significantly fewer neurons within the hindbrain dorsal vagal complex were activated in OT -/- mice after water deprivation compared with activation in wild-type mice. These findings support the view that OT-containing projections from the hypothalamus to the hindbrain are necessary for the full expression of compensatory behavioral and physiological responses to dehydration.     

Role of the synaptic microenvironment in functional modification of synaptic transmission

Experiments on hippocampal slices showed that perfusion with a dextran solution more effectively facilitates AMPA-mediated transmission in structurally complex synapses of mossy fibers of Shaffer collaterals. Estimates for changes in the extracellular Ca²⁺ concentration in the close vicinity of a reconstructed synapse during the action potential development are obtained. The results together with data about the rather small (0.5 μm) characteristics distance between neighboring synapses showed that the probability of mutual intersynaptic influence via the microenvironment is high. A probable functional role of such influences is discussed.     

Newly produced synaptic vesicle proteins are preferentially used in synaptic transmission

Aged proteins can become hazardous to cellular function, by accumulating molecular damage. This implies that cells should preferentially rely on newly produced ones. We tested this hypothesis in cultured hippocampal neurons, focusing on synaptic transmission. We found that newly synthesized vesicle proteins were incorporated in the actively recycling pool of vesicles responsible for all neurotransmitter release during physiological activity. We observed this for the calcium sensor Synaptotagmin 1, for the neurotransmitter transporter VGAT, and for the fusion protein VAMP2 (Synaptobrevin 2). Metabolic labeling of proteins and visualization by secondary ion mass spectrometry enabled us to query the entire protein makeup of the actively recycling vesicles, which we found to be younger than that of non‐recycling vesicles. The young vesicle proteins remained in use for up to ~ 24 h, during which they participated in recycling a few hundred times. They were afterward reluctant to release and were degraded after an additional ~ 24–48 h. We suggest that the recycling pool of synaptic vesicles relies on newly synthesized proteins, while the inactive reserve pool contains older proteins.     

Depression of glutamate-mediated synaptic transmission by benzyl alcohol.

The data obtained from this study suggest that the nonionizable anesthetic benzyl alcohol has two prominent actions on GABA- and glutamate-mediated synaptic transmission at the lobster neuromuscular junction. They are as follows: (1) depression of the excitatory end-plate potential and the postsynaptic membrane response to applied glutamate, and (2) a hyperpolarization of the postsynaptic resting membrane potential associated with a decrease in effective membrane resistance. No change in amplitude of the inhibitory end-plate potential or inhibitory reversal potential was seen. Excitatory miniature end-plate potential frequency was also unaffected. The depression of excitatory synaptic transmission appears to be due to a decreased responsiveness of the postsynaptic receptor-ionophore complex.     

Control of neural information transmission by synaptic dynamics.

The computational processing of a neural system is strongly influenced by the dynamical characteristics of the information transmission between neurons. In this work, the control of neural information transmission by synaptic dynamics is investigated by means of a master-equation-based stochastic model of pre-synaptic release of neurotransmitter-containing vesicles. The model incorporates facilitation of vesicle fusion with the pre-synaptic membrane due to intracellular calcium ions and depletion of readily releasable vesicles. The message to be transmitted is coded by the pre-synaptic firing sequence, and the received signal corresponds to the post-synaptic membrane potential response. At the sending end, the stochastic character of the vesicle release contributes to the entropy of the probability distribution of the number of vesicles released and represents noise with respect to information transmission. At the receiving end, the generation of post-synaptic membrane potentials is influenced by the temporal behaviour of ionic currents and membrane charging and is determined by means of a low-dimensional model. The rate and temporal types of neural coding are compatible with limiting cases of the synaptic information transmission as a function of initial vesicle release probability and pre-synaptic firing rate. The effects of the nonlinear dependencies of the vesicle release probability on intracellular calcium concentration and number of available vesicles are analysed. The model is compared with phenomenological and reduced models, a principal advantage being the capability of also determining fluctuations of dynamic variables Copyright 2002 Academic Press.     

Muscle-damaging exercise affects isokinetic torque more at short muscle length

The aim of this study was to investigate the differences in the length-dependent changes in quadriceps muscle torque during voluntary isometric and isokinetic contractions performed after severe muscle-damaging exercise. Thirteen physically active men (age = 23.8 ± 3.2 years, body weight = 77.2 ± 4.5 kg) performed stretch-shortening cycle (SSC) exercise comprising 100 drop jumps with 30-second intervals between each jump. Changes in the voluntary and electrically evoked torque in concentric and isometric conditions at different muscle lengths, muscle soreness, and plasma creatine kinase (CK) activity were assessed within 72 hours after SSC exercise. Isokinetic knee extension torque decreased significantly (p < 0.05) at all joint angles after SSC exercise. At 2 minutes and at 72 hours after SSC exercise, the changes in knee torque were significantly smaller at 80° (where 180° = full knee extension) than at 110-130°. At 2 minutes after SSC exercise, the optimal angle for isokinetic knee extension torque shifted by 9.5 ± 8.9° to a longer muscle length (p < 0.05). Electrically induced torque at low-frequency (20-Hz) stimulation decreased significantly more at a knee joint angle of 130° than at 90°. The subjects felt acute muscle pain and CK activity in the blood increased to 1,593.9 ± 536.2 IU·L?1 within 72 hours after SSC exercise (p < 0.05). This study demonstrates that the effect of muscle-damaging exercise on isokinetic torque is greatest for contractions at short muscle lengths. These findings have practical importance because the movements in most physical activities are dynamic in nature, and the decrease in torque at various points in the range of motion during exercise might affect overall performance.     

Electrophysiological aspects of synaptic transmission at the electromotor junction of Torpedo marmorata

Miniature and stimulus-evoked electroplaque potentials were recorded in Torpedo electrocytes intracellularly and extracellularly and analysed quantitatively. Tetrodotoxin reversibly blocked stimulus evoked potentials but hardly affected spontaneous miniature potentials in amplitude and frequency. The quantum content of stimulus-evoked potentials varied between 150 and 400 in normal saline and decreased in low Ca2+ high Mg2+ solution. Quantal release conformed to binomial statistics and allowed determination of the release parameters p and n. Analysis of the time constant of decay of spontaneous miniature electroplaque currents showed variation around a mean of 0.75 +/- 0.16 msec (SD) which was greatly prolonged by application of neostigmine.     

Synaptic transmission: ion concentration changes in the synaptic cleft.

Currents flowing through the postsynaptic membrane of an active synapse will tend to change the concentrations of ions in the synaptic cleft. Published experimental data are used to predict (a) the sodium and potassium concentration changes in the cleft at the frog neuromuscular junction, and (b) the sodium depletion in the cleft under a Ia synaptic bouton on a cat motoneuron. Significant concentration changes are predicted at both synapses. These changes will contribute to the time dependence of the observed current and will cause the reversal potential of the current to be time dependent. At the frog neuromuscular junction, the time course of the endplate current has been shown previously to depend on the magnitude of the current flowing (at a given potential). We attribute this to changes of the cleft ion concentration. The time dependent changes of the endplate current reversal potential that we predict for the neuromuscular junction are probably too small to be detected. This is because the effects of sodium depletion and potassium accumulation on the reversal potential almost cancel. We predict that near the reversal potential small currents of complex time course will remain, i.e. no true reversl potential exists. Such currents have previously been experimentally. At the cat Ia synapse, the synaptic current is predicted to deplete a significant fraction of the available extracellular sodium ions. Consequently, the magnitude of the synaptic current should be relatively independent of the number of postsynaptic channels activated, and of the membrane potental, as has previously been found experimentally.