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At least 1,261 records · Page 70Linked to original sources
PubMed1986

Effects of excitatory amino acid antagonists on evoked and spontaneous excitatory potentials in guinea-pig hippocampus.

Evoked and spontaneous excitatory post-synaptic potentials (e.p.s.p.s) at the mossy fibre input to CA3 pyramidal neurones were recorded intracellularly in slices from the guinea-pig hippocampus. The effects of several amino acid antagonists on these responses were examined. L-2-amino-4-phosphonobutyrate (L-AP4), L-serine-O-phosphate (L-SOP), kynurenate, and N-(p-bromobenzoyl)piperazine-2,3-dicarboxylate (pBB-PzDA) reduced the amplitude of evoked mossy fibre e.p.s.p.s without affecting membrane potential or input resistance. Antagonism of mossy fibre spontaneous miniature e.p.s.p.s (m.e.p.s.p.s) by these compounds fell into two groups. L-AP4 and L-SOP applied at concentrations that blocked evoked e.p.s.p.s did not affect amplitude distributions of spontaneous m.e.p.s.p.s. Kynurenate and pBB-PzDA significantly affected the amplitude distributions and reduced the mean amplitude of spontaneous m.e.p.s.p.s. These results are consistent with a presynaptic site of action for L-AP4 and L-SOP and a post-synaptic site of action for kynurenate and pBB-PzDA as antagonists of e.p.s.p.s at the guinea-pig mossy fibre-CA3 pyramidal neurone synapse.

Action Potentials↗
PubMed1986

Ascending fibers from the gigantocellular nucleus to the centromedian nucleus of the thalamus in cats.

Centrum medianum (CM) afferent pathways, which are involved in pain sensation, were analyzed using physiological techniques. Thirty-four neurons in the gigantocellular nucleus (nucleus gigantocellularis medullae oblongatae, GC) in cats were recorded intracellularly. Of these, 5 (15%) did not respond to electrical stimulation applied to any of the 4 limbs. Twenty-nine (85%) showed spike potentials that were superimposed on excitatory post-synaptic potentials (EPSPs) with an amplitude of 7.2 mV (n = 101) and a duration of 6.8 ms. The latencies from contra- and ipsilateral forelimb, contra- and ipsilateral hindlimb to the GC were 9.3 (n = 25), 7.2 (n = 23), 12.9 (n = 28), and 10.9 ms (n = 25), respectively. Of these responding neurons, 19 (66%) responded to stimuli to all 4 limbs, 7 (24%) to 3 limbs, 1 (3%) to 2 limbs, and 2 (7%) to 1 limb. These afferent neurons in the GC showed spike potentials without EPSPs after stimulation of the CM in the thalamus. Extracellular activities of 37 CM neurons were also tested. Of these, 4 neurons responded to GC stimulation with a short latency of 1.6 ms. Another 33 responded with a long latency of 6.7, and 11 of them were able to follow GC stimulation of over 200 Hz with a fixed long latency; 22 responded with varying long latencies but were not able to follow stimuli over 15 Hz. Three-quarters of the CM neurons received ipsilateral inputs from the GC, and the other contralateral inputs. Three CM neurons responded to stimulation of the GC in quasi-intracellular records. These findings suggest that some ascending fibers from the GC terminate on CM neurons and play a role in pain sensation.

Animals↗
PubMed1989

Dye-coupling in the neostriatum of the rat: II. Decreased coupling between neurons during development.

Physiological and morphological evidence for coupling between neostriatal neurons was obtained from the developing rat. Intracellular injections of Lucifer Yellow-CH (LY) were made in rat neostriatal slices to study dye transfer (coupling) between neurons. The incidence of interneuronal coupling was 70% in early postnatal (P) periods and declined gradually to 10% in the adult. The number of neurons filled by a single intracellular injection also declined with age. LY injection into single neurons commonly marked aggregates of 4 to 6 cells in neonates. Single injections never produced more than one coupled pair in P20 or older rats. Neurons in which fast prepotentials (FPPs) could be evoked were consistently found to be dye-coupled. FPPs were resistant to collision with action potentials generated by intracellular current injection. When chemical synaptic transmission was blocked Mn2+, short-latency depolarizations (SLDs) could be evoked by extracellular stimulation. The SLDs were distinguished from chemical synaptic potentials by their "all or none" nature and by their insensitivity to changes in membrane potential. No SLDs were observed in adult neurons. FPPs and SLDs may be indicators of electronic transmission between coupled cells. The high incidence of coupling early in development might reflect intercellular communication that contributes to the differentiation and growth of neostriatal neurons.

Action Potentials↗
PubMed1982

Electrophysiological properties of neurons contained in the locus coeruleus and mesencephalic nucleus of the trigeminal nerve in vitro.

Intracellular recordings were made from neurones contained in the locus coeruleus and mesencephalic nucleus of the trigeminal nerve (MNV), in tissue slices cut from guinea-pig pons and maintained in vitro. Locus coeruleus neurones were of -52.7 +/- 2.7 mV resting membrane potential; had an input resistance of 58.0 +/- 7.6 M omega and a membrane time constant of 7.3 +/- 1.0 ms. These neurones fired action potentials in response to depolarizing current pulses. Depolarizing synaptic potentials (DSPs) were recorded in locus coeruleus neurones in response to focal stimulation of the surface of the slice. MNV neurones were of -51.9 +/- 3.6 mV resting membrane potential; had an input resistance of 15.0 +/- 1.8 M omega and a membrane time constant of 1.35 +/- 0.16 ms. These neurones were also excitable but differed from locus coeruleus neurones in that they showed accommodation to depolarizing current pulses and time-dependent anomalous rectification with hyperpolarizing current pulses. In MNV neurones focal stimulation did not give rise to DSPs. Intracellular injection of Lucifer yellow revealed that the cell bodies of locus coeruleus neurones were small and multipolar whereas MNV neurones had larger, monopolar cell bodies.

Animals↗
PubMed1985

Action of norepinephrine in the dentate gyrus. I. Stimulation of locus coeruleus.

The effect of stimulating locus coeruleus (LC) on the response of dentate gyrus granule cells to medial perforant pathway stimulation was studied in anesthetized rats. Field responses were recorded simultaneously at the mid-dendritic and granule cell levels. Two types of responses were recorded: those due to the synchronous firing of granule cell action potentials (population spikes) and those produced by excitatory synaptic activity (evoked synaptic potentials or ESPs). Stimulation of LC prior to stimulating the perforant pathway resulted in a decrease in the ESP (inward current) measured at the dendrites and, in most animals, an increase of the population spike measured at the granule cell level. Although LC stimulation decreased the ESP at the dendrites, the ESP at the granule cell body level (outward current) was not affected. The changes in granule cell responses following LC stimulation are discussed in relation to previous findings in freely moving rats.

Animals↗
PubMed2006

Imaging membrane potential in dendrites and axons of single neurons.

This review focuses on the use of imaging techniques to record electrical signaling in the fine processes of neurons such as dendrites and axons. Voltage imaging began with the use and development of externally applied voltage-sensitive dyes. With the introduction of internally applied dyes and advances in detection technology, it is now possible to record supra-threshold action potential responses, as well as sub-threshold synaptic potentials, in fine neuronal processes including dendritic spines. The development of genetically coded sensors, as well as variants of laser scanning microscopy such as second harmonic generation, offers promise for further advances in this field. Through the use and further development of these methods, optical imaging of membrane potential will continue to be a valuable tool for investigators wishing to explore the electrical events underlying single neuronal computation.

Action Potentials↗
PubMed1986

Evidence for a catecholamine-mediated slow hyperpolarizing synaptic response in parasympathetic ganglia.

Stimulation of preganglionic nerve trunks in the presence of muscarinic and nicotinic cholinoceptor and purinoceptor antagonists produced a slow-hyperpolarizing synaptic potential that was mimicked by exogenously applied norepinephrine. Both responses were blocked by yohimbine, an alpha-adrenoceptor antagonist, and enhanced by imipramine and cocaine, inhibitors of norepinephrine reuptake. These findings fulfill pharmacological criteria suggesting that norepinephrine is a neurotransmitter in cat bladder parasympathetic ganglia.

Adrenergic Fibers↗
PubMed1991

The effects of external calcium on the N-methyl-D-aspartate induced short-term potentiation in the rat hippocampal slice.

The effect of altered extracellular Ca concentration was studied on the N-methyl-D-aspartate (NMDA) induced short-term potentiation (STP) of the population excitatory post-synaptic potential recorded from the stratum radiatum of CA1 of the rat hippocampal slice. Perfusion of 130 microM of NMDA for 10 s in control media containing 2.0 mM extracellular Ca evoked an STP with a maximum amplitude of 46% and a duration of 16 min. Perfusion of media containing a reduced Ca concentration of 0.8 mM or 1.0 mM did not alter the amplitude or time course of the STP. However, raising the Ca concentration to 3.0 mM or 4.0 mM caused a significant reduction in the amplitude of the STP to 23% and 2% respectively. The abolition of the NMDA induced STP in 4 mM Ca could not have been produced by response saturation since an identical long-term potentiation (LTP) was produced in this high Ca media as in the control media. These studies show that the NMDA induced STP has a very different Ca dependency to LTP.

Animals↗
PubMed1991

Convergent inputs to Octopus oculomotor neurones demonstrated in a brain slice preparation.

A brain slice preparation was developed to permit recordings to be made from neurones in the anterior lateral pedal lobe of the octopus CNS. These are the first intracellular recordings obtained from identified neurones in the cephalopod CNS. The neurones had membrane resting potentials of around -40 mV and action potentials up to 20 mV in amplitude. Spontaneous synaptic potentials could be seen in some cells. All of the oculomotor neurones, identified by stimulation of the anterior oculomotor nerve to evoke an antidromic potential, received an excitatory input from the visual system, shown by electrical stimulation of the optic tract, and some also received an excitatory input from the statocyst, as shown by electrical stimulation of the macula nerve.

Action Potentials↗
PubMed1986

Separation of components of hippocampal field potentials by digital filtering on a PC-based microcomputer.

A versatile digital filtering system is described which enables separation of wave components of evoked potentials based on their frequencies. The utility of this technique is exemplified by application of digital filtering to hippocampal field potentials. Separation of population spikes from lower frequency synaptic potentials provides less ambiguous interpretation of the compound slope of the field potential during the first 5 milliseconds of the response. The entire procedure of stimulation, data acquisition, and digital filtering was implemented on a PC-compatible computer.

Animals↗
PubMed2005

Corticotrophin-releasing hormone decreases synaptic transmission in rat sensorimotor cortex in vivo.

Corticotrophin-releasing hormone is a key regulator of the mammalian stress response. Although its actions on behavior are well documented, the actions of corticotrophin-releasing hormone in cortical neuronal systems are poorly understood. In the present experiments, adult male Sprague-Dawley rats were anesthetized and field excitatory post-synaptic potential recordings were made from sensorimotor cortex layer II/III and layer V cells. Infusions of corticotrophin-releasing hormone (100 ng/nl) directly into the sensorimotor cortex produced a significant depression of the initial excitatory component of evoked responses that could be prevented by prior administration of a corticotrophin-releasing hormone antagonist. Although requiring the activation of corticotrophin-releasing hormone receptors, the depression was also dependent upon N-methyl-D-aspartate receptor activity and could be blocked by the competitive N-methyl-D-aspartate antagonist -3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonate. These findings demonstrate that corticotrophin-releasing hormone has a novel depressant-like action in sensorimotor cortex in vivo that may play a role in modulating motor activity during periods of stress.

Animals↗
PubMed2000

The neurotrophin hypothesis for synaptic plasticity.

The neurotrophin hypothesis proposes that neurotrophins participate in activity-induced modification of synaptic transmission. Increasingly, evidence indicates that the synthesis, secretion and actions of neurotrophins on synaptic transmission are regulated by electrical activity and that neurotrophins themselves can acutely modify synaptic efficacy. Neurotrophins appear to exert either a permissive or instructive role on activity-dependent synaptic potentiation and depression, which depends on the particular synaptic connections and developmental stages. The characteristics of synaptic changes that are induced by neurotrophins suggest that this family of proteins is crucial for providing a molecular background in which activity-dependent plasticity can occur at selective synaptic sites within the neural network.

Animals↗
PubMedDate not supplied

Frequency-dependent involvement of NMDA receptors in the hippocampus: a novel synaptic mechanism.

Acidic amino acids, such as l-glutamate, are believed to be excitatory neurotransmitters in the mammalian brain and exert effects on several different receptors named after the selective agonists kainate, quisqualate and N-methyl-D-aspartate (NMDA). The first two receptors collectively termed non-NMDA receptors, have been implicated in the mediation of synaptic transmission in many excitatory pathways in the central nervous system (CNS), whereas NMDA receptors, with few exceptions do not appear to be involved; this is typified in the hippocampus where there is a high density of NMDA receptors yet selective NMDA receptor antagonists, such as D-2-amino-5-phosphonovalerate (APV), do not affect synaptic potentials. NMDA receptors have, however, been shown to be involved in long-term potentiation (LTP) in the hippocampus, a form of synaptic plasticity which may be involved in learning and memory. NMDA receptors have also been found to contribute to epileptiform activity in this region. We now describe how NMDA receptors can participate during high-frequency synaptic transmission in the hippocampus, their involvement during low-frequency transmission being greatly suppressed by Mg2+. A frequency dependent alleviation of this blockade provides a novel synaptic mechanism whereby a single neurotransmitter can transmit very different information depending on the temporal nature of the input. This mechanism could account for the involvement of NMDA receptors in the initiation of LPT and their contribution, in part, to epileptic activity.

2-Amino-5-phosphonovalerate↗
PubMed1976

Short-term synchronization of intercostal motoneurone activity.

1. The hypothesis is advanced that the joint occurrence of unitary excitatory post-synaptic potentials e.p.s.p.s) evoked in motoneurones by branches of common stem pre-synaptic fibres causes short-term synchronization of their discharge during the rising phases of the unitary e.p.s.p.s. 2. This hypothesis was tested using the pre- and post-stimulus time (PPST) histogram to detect synchronized firing among groups of intercostal motoneurones discharging in response to their natural synaptic drives. 3. Motor nerve action potentials were recorded monophasically from nerve filaments of the external intercostal muscles of anaesthetized, paralysed cats maintained on artificial ventilation. 4. Computer methods were used to measure peak spike amplitude, spike amplitude, spike interval and filament identification for simultaneous recordings from four filaments. The spike amplitude histograms were derived for each filament and groups of spikes were selected for analysis. 5. With spikes of one group designated as 'stimuli' (occurring at zero time) and those of a second as 'response' the PPST histogram was computed with different time bin widths. 6. With bin widths of 100 and 10 msec the central respiratory periodicity was apparent in the PPST histogram. With 1.0 msec bins the PPST histogram showed a narrow central peak extending to +/- 3.0 msec at its base. This 'short-term synchronization' supports the hypothesis of joint firing due to common presynaptic connectivity. 7. It was shown that detection of short-term synchronization was critically dependent on a sufficient quantity of data but that provided a simple criterion of adequate counts per bin in the PPST histogram was met, short-term synchronization could be detected between intercostal motoneurones of the same and adjacent segments.

Action Potentials↗
PubMed1980

Intracellular recordings from the paraventricular nucleus in slices of rat hypothalamus.

1. The electrical activity of thirty-five neurones in the lateral area of the paraventricular nucleus (p.v.n.) was recorded intracellularly in vitro from slices of rat hypothalamus. 2. Spontaneously occurring action potentials were observed in twenty-four of the neurones. The temporal pattern of action potentials was generally slow and irregular; occasionally some cells fired bursts of action potentials. 3. Depolarizations with a fast rising phase and slow decay occurred spontaneously in most cells. These depolarizations exhibited a wide range of amplitudes in each cell (up to 33 mV), showed temporal summation, and could serve as pre-potentials for spontaneously occurring action potentials. Presumably, these depolarizations were excitatory post-synaptic potentials (e.p.s.p.s.). 4. Depolarizing current injection could evoke action potentials. Extracellular stimuli dorsolateral to the fornix column occasionally elicited action potentials which had a short and invariant latency and which could respond to stimulation rates of 100 Hz. In some cases, extracellular stimuli in the same area evoked depolarizations which had long and variable latency and were similar to those occurring spontaneously. These two types of responses probably represent antidromic and orthodromic activation respectively. 5. Intracellular injections of horseradish peroxidase suggest that these recordings were obtained primarily, but not exclusively, from magnocellular neuroendocrine cells. This is consistent with previous anatomical studies on the location of magnocellular elements in p.v.n.

Action Potentials↗
PubMed1983

Electrophysiological properties of rat spinal dorsal horn neurones in vitro: calcium-dependent action potentials.

1. The electrophysiological properties of dorsal horn neurones have been investigated in the immature rat in vitro spinal cord slice preparation. 2. Intracellular recordings from dorsal horn neurones show that direct or orthodromic stimulation generates action potentials followed by a brief after-hyperpolarization. Synaptic potentials were elicited by the activation of primary afferent fibres in the dorsal root. 3. Input resistance for dorsal horn neurones ranged from 48 to 267 M omega, and the membrane time constant was in the range of 4-19 ms. 4. In response to strong depolarizing currents dorsal horn neurones perfused with TTX and TEA frequently exhibit a slow regenerative depolarizing potential followed by a slow after-hyperpolarization. The depolarizing potential probably results from an influx of Ca. It is blocked by low concentration Ca, Co or Mn, and enhanced by high levels of extracellular Ca. 5. There is, in addition, a low-threshold Ca-dependent response which is activated at membrane potentials more negative than -65 mV and has a maximum rate of rise at the polarization level of about -80 mV. 6. The addition of Ba or TEA to the perfusing medium provided support for the Ca-dependence of the low- and high-threshold responses, and the lack of fast inactivation of the high-threshold Ca potential.

Action Potentials↗
PubMed1986

Venous mechanoreceptor input to neurones in the inferior mesenteric ganglion of the guinea-pig.

Intracellular recordings were made in vitro from neurones of guinea-pig inferior mesenteric ganglia (i.m.g.) attached to the mesenteric vasculature of the distal colon region. The inferior mesenteric vein was cannulated for distension. Non-evoked continuous excitatory post-synaptic potentials (e.p.s.p.s) and action potentials were recorded from 38% of neurones in the absence of the colon or any imposed perturbation. Continuous e.p.s.p.s were blocked by hexamethonium, tetrodotoxin and by transection of the lumbar colonic nerves. Distension of the inferior mesenteric vein altered the frequency of continuous activity in 23% of cells which exhibited continuous activity. Venous distension was associated with a depolarization in 31% of cells tested. The depolarization averaged 2.8 mV and in 89% of these was associated with an increase in membrane resistance. A further 14% of cells exhibited an increase in membrane resistance in the absence of depolarization. Venous distension increased the amplitude of fast e.p.s.p.s generated by stimulation of the lumbar splanchnic nerve or the intermesenteric nerve in 38% of cells tested. The results of this study demonstrate the existence of a mechanosensory pathway from the venous bed of the distal mesenteric region to the i.m.g. of the guinea-pig and suggest that distension may enhance neural transmission by increasing the excitability of ganglionic cells.

Action Potentials↗
PubMed1982

Extracellular potassium ions mediate specific neuronal interaction.

The giant interneurons from the nerve system of the cockroach Periplaneta americana exhibit a peculiar reciprocal synaptic interaction. The synaptic potentials are not blocked by addition of 5 millimolar cobalt chloride and have an extrapolated reversal potential close to 0 millivolt. Hyperpolarizing current injected into one cell does not spread to the other. Intracellular injection of tetraethylammonium ions into one giant interneuron increases the duration of the action potential of the injected cell to 30 milliseconds and reduces the rise time and amplitude of the postsynaptic response recorded in the other giant interneuron. These results indicate that the interaction between the interneurons is not mediated by conventional chemical or electrotonic synapses.. All evidence points to generation of the potentials by localized increases in extracellular potassium concentrations as a consequence of firing of one neuron.

Action Potentials↗