Search results for "action potential"
showing 10 items of 233 documents
An electrophysiological study of the ontogenesis of adenosine receptors in the CA1 area of rat hippocampus
1990
Abstract The depressant effect of adenosine (Ad) was studied electrophysiologically in hippocampal slices from 5-, 10-, 15-, 20-, 30- and 120-day-old rats. Ad (10μM) depressed the field EPSP in CA1 to the same extent in all age groups. Caffeine (Caf), an Ad receptor antagonist, enhanced and nitrobenzylthioinosine (NBI), an Ad uptake blocker, depressed the field EPSP. Both these effects were, however, less prominent in slices from younger animals, a finding consistent with lower extracellular levels of endogenous Ad in neonatal rats.
Pronounced cholinergic but only moderate purinergic effects in isolated atrial and ventricular heart muscle from cats.
1989
1 The effects of cholinergic and purinergic stimulation on action potential, force of contraction and 86Rb efflux were investigated in cat atrial and/or ventricular heart muscle. 2 Acetylcholine and carbachol exerted a concentration-dependent negative inotropic effect in cat atrial heart muscle. Carbachol 10 μmol l−1 completely abolished the force of contraction and increased the rate constant of 86Rb efflux 2–3 fold, whereas the action potential duration was shortened to about 1/10 of its length under control conditions. 3 The effects of acetylcholine and carbachol in cat atrial heart muscle were mimicked, qualitatively, by adenosine and its analogues 5′-(N-ethyl)-carboxamido-adenosine (NE…
Effects of melatonin on spontaneous electrical activity of neurons in rat suprachiasmatic nuclei: an in vitro iontophoretic study.
1989
Circadian rhythms, endogenously generated in suprachiasmatic nuclei (SCN), seem to be under the direct influence of melatonin. Therefore, the effect of iontophoretically applied melatonin on electrical activity of SCN neurons was investigated in vitro. Usually, melatonin had an inhibitory effect. In the 3-h periods before (2.00-5.00 p.m.) or after (5.00-8.00 p.m.) the light-dark transition the percentage of SCN neurons sensitive to melatonin was very high (80% and 100%, respectively). However, efficacy of melatonin was low in the periods preceeding (20%) and following (33%) this 6-h time interval.
Effects of histamine on spontaneous electrical activity of neurons in rat suprachiasmatic nucleus
1991
Abstract The hypothalamic suprachiasmatic nucleus (SCN) is thought to be a light-entrained pacemaker in mammals, inducing a wide range of endogenous circadian events. In rat brain, histaminergic (HAergic) fibres are particulary rich in the hypothalamus. This prompted an investigation of the influence of bath-applied HAergic compounds on the spontaneous electrical activity of SCN neurons, recorded extracellularly in the hypothalamic slice preparation. Cells activated by bath application of HA ( n = 28) outnumbered those inhibited by HA ( n = 6). 48% of cells tested ( n = 28) were unresponsive to HA application. HA-induced activation of SCN neurons' discharge rate could be suppressed by the H…
Contribution of both ?- and ?-adrenoceptors to the inotropic effects of catecholamines in the rabbit heart
1992
The functional role of alpha-adrenoceptors was investigated in different parts of the rabbit heart. Phenylephrine (PE) caused a marked increase in force of contraction (Fc) and a prolongation of the action potential (AP) in preparations from the left atrium and the right ventricle. The response was less pronounced in the right atrium and in the left ventricle, whereas APs of spontaneously beating sinoatrial preparations remained completely unchanged. Phentolamine as well as the diesters phorbol 12,13 dibutyrate (PDBu) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) eliminated the effects of PE. The contribution of alpha-adrenoceptors to the effects of adrenaline (Adr) and noradrenaline (NA) …
Inhibition of nitric oxide synthase influences the activity of striatal neurons in the rat
2002
The activity of single units in the striatum of urethane-anesthetized rats was recorded before and after the systemic administration of 7-nitro-indazole (7-NI; 50 mg/kg intraperitoneally), a selective inhibitor of neuronal nitric oxide (NO) synthase. Two neuronal types were clearly distinguishable electrophysiologically, on the basis of either discharge frequency pattern or features of the individual spike waveform (spike duration, negative phase/total duration ratio, and negative phase/total amplitude ratio). Only sporadically discharging neurons (basal firing rate, <0.1 spikes/s) were influenced by 7-NI, which caused a statistically significant increase in their firing rate. In contrast, …
Electrophysiological properties of rat pinealocytes: Evidence for circadian and ultradian rhythms
1984
Extracellular single-unit recordings were made during day- and night-time in the pineal gland of urethane-anesthetized adult male Sprague-Dawley rats. All cells exhibiting spontaneous electrical activity had firing frequencies from less than 1 Hz to about 100 Hz, and their discharge patterns were characterized as regular, irregular or bursting. While most of the spontaneously active cells (n = 163) showed a uniform activity level throughout the recording period (30-120 min), a group of 9 cells exhibited oscillatory rhythms with periods of 4-8 min. In addition, long-term recordings across day- and night-time from five cells revealed increasing activity during night-time in three cells, while…
Signal characteristics of EMG during fatigue
1977
Electromyographic (EMG) activity of m. rectus femoris muscle was registered from young male and female subjects during maintained isometric knee extension at 60% of maximal voluntary contraction. The following EMG parameters were analyzed for the entire fatigue time: integrated EMG (IEMG), averaged motor unit potential (AMUP) and power spectral density function (PSDF). The results indicated a slight but continuous rise of IEMG during the fatigue period. AMUP showed sensitivity to fatigue with increase in amplitude, rise time, and number of spikes counted. PSDF was also easily affected by fatigue so that the total power density curve was shifted towards lower frequencies with a high frequenc…
Effects of an Earth-strength magnetic field on electrical activity of pineal cells
1980
Although magnetic fields can influence biological systems, including those of man and other vertebrates1–5, no central nervous structure has been identified that might be involved in their detection. From a theoretical point of view, the pineal organ might be such a structure for the following reasons: (1) It is involved in the regulation of circadian rhythms6 and is thus essential for migratory restlessness (‘Zugunruhe’)7. Orientation at that time can be altered by an artificial magnetic field (MF) with a direction differing by 90° from that of the Earth. Circadian rhythms can be inhibited from phase shifting by compensation of the Earth's MF and can be influenced by an artificial MF8. (2)…
Impaired neuromuscular transmission during partial inhibition of acetycholinest-erase: The of stimulus-induced antiromic backfiring in the generation…
1992
Neuromuscular transmission was studied in the rat phrenic nerve-hemidiaphragm preparation with acetylcholinesterase (AChE) partially inactivated. Enzyme inhibition resulted in (1) increased single-twitch tension of the diaphragm; (2) compound muscle action potential (CMAP) containing repetitive discharges; (3) stimulus-induced antidromic backfiring (SIAB) seen in the phrenic nerve; and (4) repetitive nerve stimulation (RNS) eliciting a decrement-increment (D-I) phenomenon (i.e., amplitude reduction maximal with the second CMAP). Using a high-calcium and low-magnesium solution, SIAB and the decrement of the second CMAP during RNS were intensified, whereas closely spaced trains and (+)-tubocu…