Frequency Of Spontaneous Action Potentials Research Articles

Prostaglandins and neurotransmission at the guinea pig and rabbit urinary bladder

High concentrations of prostaglandins (PGE1, PGE2, or PGE2 alpha) (2 x 10(-6) M) produced a slow contraction of longitudinal strips of detrusor muscle taken from the bladders of guinea pigs and rabbits. At a lower concentration (10(-6) M) prostaglandins enhanced contractions produced by field stimulation of nerves in guinea pig but not rabbit strips. The contractions were not affected by indomethacin. Contractions of guinea pig strips in response to acetylcholine at 10(-4) M were enhanced by prostaglandins and unaffected by indomethacin. Membrane potentials of smooth muscle cells recorded with micro electrodes, were unchanged up to 10(-6) M PGE2. Above this the cells were depolarized with an increase in frequency of spontaneous action potentials. Synchronous recording of electrical and mechanical activity with the double sucrose gap indicated a decrease in amplitude of the evoked excitatory junction potential and action potential even when the contraction was enhanced in the presence of PGE2. Responses to repeated stimulation at 10 Hz for 1 min were progressively depressed. This trend was slightly reduced by PGE2 but unaffected by indomethacin. It is concluded that prostaglandins are not normally released by the nerves to the urinary bladder but are able to facilitate contraction in the guinea pig. This effect is probably on the excitatory-contraction coupling, possibly by mobilizing Ca2+. Some modification of transmitter release by the nerves may also occur.

Excitatory effects of cholecystokinin in rat hippocampus: pharmacological response compatible with ‘central’- or B-type CCK receptors

The effects of the sulfated octapeptide of cholecystokinin (CCK 8-S), the non-sulfated homolog (CCK 8-NS) as well as the C-terminal di-, tri- and tetrapeptidic fragments (respectively CCK 2, CCK 3 and CCK 4) were studied in vitro in rat hippocampal slices by extracellular recording of the spontaneous action potential discharge frequency of neurons located in the CA1 stratum pyramidalis. Bath-applied CCK 8-S concentration-dependently increased the action potential discharge frequency of hippocampal CA1-neurons in concentrations ranging from 0.05 to above 1 μM. Both CCK 8-NS and CCK 4 exhibited reversible and concentration-dependent excitatory effects. They were 4 and 10 times less potent than CCK 8-S,respectively, as concentrations of 2μM CCK 8-NS and 5 μM CCK 4 were needed to evoke the same excitation as that induced for a given neuron by 0.5 μM CCK 8-S. In contrast, none of the shorter fragments (CCK 2 and CCK 3) were effective in altering spontaneous discharge of CCK 8-S-sensitive neurons even at concentrations of 100μM. The pharmacologic profile of the excitatory response observed in the rat hippocampus follows the same pattern as the binding profile observed on brain membrane preparations. It is therefore concluded that the CCK receptors involved in this response seem to be related more to the ‘central’- or B-type CCK receptors rather than to the ‘peripheral’- or A-type CCK receptors.

The fade of the response to acetylcholine at the rabbit isolated sino-atrial node.

1. The effect of acetylcholine (ACh) on the frequency of spontaneous action potentials, recorded with glass microelectrodes from small preparations of the sino-atrial node of the rabbit, has been investigated. 2. On application of ACh there was a rapid increase in cycle length (the interval between successive action potentials) but then, despite the continued presence of the ACh, cycle length decreased once again; i.e. the response to ACh 'faded' in the presence of ACh. This fade of the chronotropic response to ACh has been characterized. 3. To observe fade it was found to be important to use a fast flow bath in order to increase the ACh concentration at the preparation abruptly. In other words, the response to ACh was sensitive to the rate of increase in the ACh concentration at the tissue. This may explain why in one study of the sino-atrial node of the guinea-pig the authors failed to observe fade. 4. The concentration dependence of fade was studied in two ways: either as the fade in the response with different doses of ACh, or as the decrease in the response to a fixed test dose applied after a variable conditioning dose. Both methods indicated that fade increased with concentration over the range of roughly 10(-7) to 10(-5) M-ACh. 5. The onset of fade, i.e. the decline in cycle length during an exposure to ACh, was monophasic with low doses of ACh and biphasic (with fast and slow phases) with higher doses. The mean half-times of the fast and slow phases of fade were 10 +/- 2 s and 240 +/- 30 s (mean +/- S.E.M.; n = 5). However, in some preparations, rather than a smooth decrease in cycle length, there were discontinuities and cycle length could decrease in a stepwise fashion or even transiently alternate between two distinct states. 6. Time was required for recovery from fade because a response to a test dose applied soon after a conditioning dose was depressed. Recovery was studied by applying test doses at different times after conditioning doses. Recovery occurred with a half-time of 40 +/- 8 s (mean +/- S.D.; n = 8) after a short exposure (30 s) to ACh, but was slower (half-time, 250 +/- 20 s; n = 6) after a longer exposure (5 min). 7. Immediately after washing off ACh, cycle length decreased below its original value, although it then returned to this value over several minutes.(ABSTRACT TRUNCATED AT 400 WORDS)

Non‐cholinergic neurotransmission and the effects of peptides on the urinary bladder of guinea‐pigs and rabbits.

Supramaximal repetitive field stimulation with pulses of 50 microseconds produced contraction of strips of bladder from rabbits and guinea-pigs. Atropine reduced responses at all frequencies to about 60% and the contraction was poorly maintained. With the double sucrose-gap technique large excitatory junction potentials (e.j.p.s) were recorded with superimposed action potentials. These were not reduced by atropine or phentolamine. Substance P (SP) produced contraction and increased the frequency of spontaneous action potentials recorded with micro-electrodes from bladder strips. Vasoactive intestinal peptide (VIP) produced relaxation and slowed action potentials in rabbit but had no effect in guinea-pig; neurotensin, somatostatin and leu-enkephalin were without action in either species. When the tissue was kept in contact with SP, a second application after 10 min produced only a small contraction suggesting that SP receptors were desensitized. However, the electrical response to field stimulation was unchanged and the mechanical response was increased. Chymotrypsin reduced mechanical responses to SP but had no effect on responses to field stimulation. The SP analogue, D-Pro2, D-Phe7, D-Trp9-SP, had no effect on responses to SP or to field stimulation. It is concluded that the bladder receives excitatory non-cholinergic innervation which is responsible for a large excitatory junction potential and contraction. Although SP can contract the detrusor muscle, it is unlikely that it is an excitatory transmitter or that any of the five peptides act as modulators of transmitter release.

Electrical properties and membrane currents in the ciliateDidinium

1. The electrical properties of the ciliateDidinium nasutum, aParamecium predator, have been investigated using techniques of constant current injection, voltage-clamp, exchange of solutions, and non-lethal deciliation. The electrical observations have been related to structural characteristics (Fig. 1). 2. The resting potential was primarily K-dependent. K concentrations beyond 1 mmol/1 depolarized the cell and reduced the input resistance. The resting conductance for Ca was low. Partial substitution of Ca by Mg changed the membrane potential very little and had no effect on the input resistance. Chloride did not influence the membrane properties. 3. The late V/I-relationship was characterized by pronounced outward and minimal inward rectification. It was very little modified by Ca concentrations ranging between 0.125 mmol/1 and 8 mmol/1. Raising the K concentration between 0.063 and 16 mmol/1 did not affect membrane rectification. 4. Membrane depolarization triggered a stimulus-graded action potential, which was Ca-dependent. The action potential rose with rates of up to 6 V/s; its overall duration was 100 to 500 ms. Repolarization occurred along a fast and a slow (shoulder) component and was followed by pronounced after-hyperpolarization. 5. Complete deciliation ofDidinium eliminated the regenerative depolarization of the membrane. The resting potential, input resistance and late current/voltage relationship were not modified by the removal of ciliary membranes. Under voltage-clamp deciliation removed the early inward current and the hump component of the late outward current. 6. Depolarizing voltage-clamp pulses of up to + 20 mV revealed a residual inward current following the early transient. The transient included two decay time constants (3.3 ms; 31.8 ms). An 0.8 nA persistent inward current was isolated using the difference current of ciliated and deciliated cells. A late outward current rose with depolarizations beyond 20 mV including an upward inflection (hump) about 50 ms after step onset. 7. A decreasing Ca/Ba mole-fraction increased the frequency and duration of spontaneous action potentials, and depressed the amplitudes of both, early inward and late outward current under voltage-clamp. In Ca-free Ba solution the unclamped membrane fired repetitively; the depolarizations included shoulders of 10 s or more. Inactivation of inward Ba currents was slow under depolarizing voltage-clamp; the late outward current was strongly depressed. In deciliated cells an early inward current was missing in Ca-free Ba solution, and the late I/V relation resembled that of deciliated cells in Ba-free Ca solution. 8. Tail currents following the late outward current of ciliated cells in Ca-solution and of deciliated cells in Ca- or Ba-solutions decayed with similar time constants. 9. In conclusion, the voltage-activated Ca conductance of the ciliary membrane ofDidinium compares well with data from ciliates so far studied. Unique is (i) a persistent inward current isolated using minor step depolarization or the difference current of ciliated and deciliated cells, (ii) a slow activating voltage-dependent K conductance, and (iii) a late, potentially Ca-dependent, outward current, which may be related to spatial separation of the cilia from the majority of the soma membrane. Ba interferes with the Ca channel which favours a previous two-binding site model. Ba can inhibit the K conductance from inside the cell after passing the ciliary Ca channel.

Presynaptic actions of cholinergic agents upon the hair cell-afferent fiber synapse in the vestibular labyrinth of the frog

Spontaneous activity of semicircular canal afferents in the isolated labyrinth of the frog is altered by bath application of cholinergic agonists. Muscarinic agonists can produce an increase in action potential frequency of individual afferents. This increase develops slowly and is prolonged in the time course of its action. Nicotinic agonists can either increase (most cases) or decrease afferent activity. These effects occur rapidly and decay during the period of activation, suggesting desensitization. Muscarinic effects are blocked by prior administration of atropine and nicotinic effects (both increases and decreases in action potential frequency) by curare. Intracellular recordings reveal that the nicotinic effects on afferent action potential frequency are the result of alterations in the frequency of spontaneous synaptic potentials, indicating a presynaptic site of action on the hair cells for these compounds. This conclusion is supported by the fact that in the presence of high Mg 2+/low Ca 2+, which blocks hair cell release of transmitter, cholinergic agonists do not affect the resting membrane potential of the vestibular afferent. Electrical stimulation of the VIIIth cranial nerve can result in either an increase or a decrease in spontaneous synaptic potential and action potential frequency of an afferent. These effects are blocked by prior administration of curare or of nicotinic agonists. Repetitive or continuous stimulation of the VIIIth nerve results in a reversible reduction of the evoked response, suggesting desensitization. Transection of the VIIIth cranial nerve two weeks prior to recording eliminates these actions of electrical stimulation, but not the responses to cholinergic agonists, indicating that the effects of electrical stimulation are mediated by centrally arising efferents. These findings confirm that acetylcholine is probably the transmitter released from centrally arising vestibular efferents, and, in addition, demonstrate that efferent-mediated effects are predominantly expressed through nicotinic receptors. Studies comparing the effects of isolation of the semicircular canal alone versus the intact labyrinth suggest that the method of isolation may be an important factor in determining whether efferent activity results in a predominant increase or decrease in afferent activity.

Relationship between cell turgor pressure, electrical membrane potential, and chloride efflux inAcetabularia mediterranea

Turgor pressureP, electrical membrane potentialVm and release of36Cl− have been measured on individual cells of the marine green algaAcetabularia mediterranea. In contrast to other marine and pond water algal cells a continuous turgor pressure increase is observed in many cells ofA. mediterranea (0.8 to 5×10−4 bar sec−1), even though the osmolarity of the external seawater is kept constant. Above a critical pressure value of 2.26±0.22 bar (n=25,T=18 and 23 °C), the turgor pressure exhibits continuous decreases and increases in a range of 0.22±0.13 bar (n=23). At lower temperatures (6 to 10 °C) the threshold for pressure regulation is shifted towards higher values. Pressure regulations in the critical range are accompanied by bursts of36Cl-efflux and in most cases by action potentials, but not every action potential is associated with a decrease in turgor pressure. The frequency of spontaneous action potentials increases with rising cell turgor. The amount of36Cl-released, i.e. about 4% of the cellular Cl− content (H. Mummert, Ph.D. Thesis, University of Tubingen, Germany, 1979), compares well with the observed reduction in turgor pressure after the burst. The kinetics of turgor reduction, however, are not compatible with a release of chloride by vesicular transport as suggested by H. Mummert and D. Gradmann (In: Plant Membrane Transport: Current Conceptual Issues. Elsevier/ North-Holland, Amsterdam, 1980). It is concluded that the steady turgor increase is generated by a net influx consisting largely of KCl due to the electrogenic chloride import pump and the strong inward driving force for K+ whereas the subsequent occurring regulations of turgor pressure can be understood on the basis of a passive chloride channel in the plasmalemma which is controlled by turgor.

Spontaneous Electrical Activity in Pressurized Small Mesenteric Arteries

Spontaneous electrical activity was recorded intracellularly in vitro from smooth muscle cells of guinea pig small pressurized mesenteric arteries. Spontaneous action potentials were recorded at 37 degrees C at frequencies of 30-55/min. Each action potential consisted of a prepotential (pacemaker potential) followed by a spike of variable amplitude (10-35 mV). This activity was not blocked by tetrodotoxin (TTX) or guanethidine, indicating it was myogenic in origin. Sympathetic nerve stimulation (single 0.5-ms field stimuli) could evoke action potentials in between the spontaneous action potentials and could drive the activity, this effect was blocked by TTX. Addition of the vasodilator adenosine (10(-6) to 10(-4) M) reversibly decreased action potential amplitude and frequency. Lowering the temperature to 35 degrees C for 1-3 min during a single impalement decreased spontaneous action potential frequency. Spontaneous activity was abolished after longer periods at 35 degrees C. The spontaneous activity recorded in vitro at 37 degrees C and 5 or 40 mm Hg inflation pressure was similar to that previously reported from guinea pig and rat mesenteric arteries in vivo. Such activity might be important in the normal physiological control of arterial tone.

Effects of barium on cat spinal motoneurons studied by voltage clamp.

ArticlesEffects of barium on cat spinal motoneurons studied by voltage clampP. C. Schwindt, and W. E. CrillP. C. Schwindt, and W. E. CrillPublished Online:01 Oct 1980https://doi.org/10.1152/jn.1980.44.4.827MoreSectionsPDF (4 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Download PDF FiguresReferencesRelatedInformation Cited ByTake Your PIC: Motoneuronal Persistent Inward Currents May Be Somatic as Well as Dendritic. Focus on “Facilitation of Somatic Calcium Channels Can Evoke Prolonged Tail Currents in Rat Hypoglossal Motoneurons”Robert M. Brownstone1 August 2007 | Journal of Neurophysiology, Vol. 98, No. 2Key mechanisms for setting the input–output gain across the motoneuron poolIntegration of synaptic and intrinsic dendritic currents in cat spinal motoneuronsBrain Research Reviews, Vol. 40, No. 1-3Effects of Excitatory Modulation on Intrinsic Properties of Turtle MotoneuronsT. George Hornby, Jennifer C. McDonagh, Robert M. Reinking, and Douglas G. Stuart1 July 2002 | Journal of Neurophysiology, Vol. 88, No. 1Role of Potassium Conductances in Determining Input Resistance of Developing Brain Stem MotoneuronsWilliam E. Cameron, Pedro A. Núñez-Abades, Ilan A. Kerman, and Tracy M. Hodgson1 November 2000 | Journal of Neurophysiology, Vol. 84, No. 5Synaptic Control of Motoneuronal ExcitabilityJens C. Rekling*, Gregory D. Funk*, Douglas A. Bayliss, Xiao-Wei Dong, and Jack L. Feldman4 January 2000 | Physiological Reviews, Vol. 80, No. 2Summation of Effective Synaptic Currents and Firing Rate Modulation in Cat Spinal MotoneuronsRandall K. Powers, and Marc D. Binder1 January 2000 | Journal of Neurophysiology, Vol. 83, No. 1Synaptic Activation of Plateaus in Hindlimb Motoneurons of Decerebrate CatsDavid J. Bennett, Hans Hultborn, Brent Fedirchuk, and Monica Gorassini1 October 1998 | Journal of Neurophysiology, Vol. 80, No. 4Short-Term Plasticity in Hindlimb Motoneurons of Decerebrate CatsDavid J. Bennett, Hans Hultborn, Brent Fedirchuk, and Monica Gorassini1 October 1998 | Journal of Neurophysiology, Vol. 80, No. 4Prolonged Firing in Motor Units: Evidence of Plateau Potentials in Human Motoneurons?Ole Kiehn, and Torsten Eken1 December 1997 | Journal of Neurophysiology, Vol. 78, No. 6Compartmental Model of Vertebrate Motoneurons for Ca2+-Dependent Spiking and Plateau Potentials Under Pharmacological TreatmentVictoria Booth, John Rinzel, and Ole Kiehn1 December 1997 | Journal of Neurophysiology, Vol. 78, No. 6Barium-induced bistability in rat ocular motoneurones in vitroNeuroscience Letters, Vol. 170, No. 1Effects of divalent cations on the frequency of spontaneous action potentials from the lateral line organ ofXenopus laevisBrain Research, Vol. 508, No. 1The activity pattern of phrenic motoneurons during the aspiration reflex: an intracellular studyBrain Research, Vol. 505, No. 2An aminopyridine-sensitive, early outward current recorded in vivo in neurons of the precruciate cortex of cats using single-electrode voltage-clamp techniquesBrain Research, Vol. 480, No. 1-2Electrophysiological properties of hypoglossal motoneurons of guinea-pigs studied in vitroNeuroscience, Vol. 30, No. 3The physiology of excitatory amino acids in the vertebrate central nervous systemProgress in Neurobiology, Vol. 28, No. 3Ionic mechanisms underlying the firing properties of rat neonatal motoneurons studied in vitroNeuroscience, Vol. 19, No. 3Changes in free calcium ion concentration recorded inside hippocampal pyramidal cells in situBrain Research, Vol. 374, No. 1Effects of barium on isolated frog spinal cordComparative Biochemistry and Physiology Part C: Comparative Pharmacology, Vol. 85, No. 1Electrophysiological studies on the postnatal development of intracerebellar nuclei neurons in rat cerebellar slices maintained in vitro. II. Membrane conductancesDevelopmental Brain Research, Vol. 20, No. 1Changes in intracellular free ca ion concentration evoked by electrical activity in cat spinal neurons in situNeuroscience, Vol. 14, No. 2Electrophysiological properties of dentate granule cells in mouse hippocampslices maintained in vitroBrain Research, Vol. 311, No. 1Electrophysiological properties of in vitro hippocampal pyramidal cells from normal and staggerer mutant miceBrain Research, Vol. 311, No. 1Isolation and kinetic analysis of inward currents in neuroblastoma cellsNeuroscience, Vol. 13, No. 1Selective actions of barium on thec-wave and slow negative potential of the rabbit eyeVision Research, Vol. 24, No. 10Action potential mechanism of mammalian cortical neurons in cell cultureBrain Research, Vol. 289, No. 1-2Bioelectrical properties of cerebellar Purkinje cells in reeler mutant miceBrain Research, Vol. 274, No. 2Active currents in mammalian central neuronsTrends in Neurosciences, Vol. 6Cholinergic excitation of mammalian hippocampal pyramidal cellsBrain Research, Vol. 249, No. 2Negative slope conductance due to a persistent subthreshold sodium current in cat neocortical neurons in vitroBrain Research, Vol. 236, No. 1Calcium channels in the neuronal membraneBiochimica et Biophysica Acta (BBA) - Reviews on Biomembranes, Vol. 650, No. 2-3Negative slope conductance at large depolarization in cat spinal motoneuronsBrain Research, Vol. 207, No. 2 More from this issue > Volume 44Issue 4October 1980Pages 827-846 Copyright & PermissionsCopyright © 1980 the American Physiological Societyhttps://doi.org/10.1152/jn.1980.44.4.827PubMed6253606History Published online 1 October 1980 Published in print 1 October 1980 Metrics

Temperature acclimation: effects on membrane physiology of an identified snail neuron.

The neuronal basis for thermal acclimation was examined by comparing the short- and long-term effects of temperature change on the physiological properties of an identified neuron in the isolated ganglion of Hexis aspersa. Using intracellular electrophysiological techniques, we found that the frequency of spontaneous action potentials and excitability of neurons from warm-acclimated animals was depressed by abruptly cooling from 20 to 5 degrees C. After a 2-wk period of acclimation to 5 degrees C, the levels of spontaneous activity and excitability were comparable to those of warm-acclimated neurons at 20 degrees C. Conversely, abrupt warming of neurons from cold-acclimated animals greatly increased the frequency of spontaneous activity, but after acclimation to 20 degrees C the frequency decreased. Although the duration of the action potential and the cell's electrogenic Na-K pump were temperature sensitive, thermal acclimation had no obvious effects on these parameters. Membrane permeability to Na and PNa/PK decreased with cooling, whereas PRb/PK and PCs/PK increased. Warming had the opposite effect on the relative alkali cation permeability (PX/PK). With acclimation PX/PK underwent compensatory changes.

Action potentials in gland cells of rat pituitary pars intermedia: inhibition by dopamine, an inhibitor of MSH secretion.

1. Cells were dissociated from rat pituitary pars intermedia, maintained in culture, and subjected to electrophysiological study.2. Recorded membrane potentials varied widely (range - 18 to about - 80 mV). They were relatively insensitive to changes in external Na but were rapidly and reversibly lowered by excess K.3. Action potentials were elicited by passing current through intracellular recording electrodes. They were reversibly blocked by tetrodotoxin (TTX, 2 x 10(-6)M) or by removal of Na from the recording solution and thus appeared to be Na spikes. Cells yielding action potentials in response to depolarization had relatively high membrane potentials (about - 65 mV) which may be representative of the true resting membrane potential of pars intermedia cells.4. Spontaneous action potentials were recorded extracellularly from nearly all the many isolated pars intermedia cells studied with a microsuction electrode. Their amplitude was reduced by TTX (0.1-2 x 10(-6)M). Electron microscopic examination of cells producing action potentials showed them to be hormone-containing parenchymal (gland) cells.5. Dopamine (10(-6)M), a presumed physiological inhibitor of secretion of melanocyte stimulating hormone (MSH) from pars intermedia cells, decreased the frequency of spontaneous action potentials but not their amplitude. Similar effects were seen with noradrenaline (10(-6)M), another inhibitor of MSH secretion, whereas isoprenaline and 5-hydroxytryptamine (5-HT), which do not inhibit MSH secretion, had no effect.6. Action potentials may be involved in stimulus-secretion coupling in pars intermedia cells.

Effects of pentagastrin, G17, and G34 on the electrical and mechanical activities of canine antral smooth muscle

Intracellular microelectrode technique and standard organ bath technique were used to investigate the effects of pentagastrin, G17, and G34 on the electrical and mechanical activities of canine antral circular muscle. All three molecular forms increased the amplitude and duration of the plateau of the gastric action potential and the frequency of spontaneous action potentials. They also increased the amplitude and frequency of spontaneous contractions. G17 was equal to or less potent than pentagastrin in all of its actions on this tissue. G34 had an equal or greater activity than G17. The electrical studies indicate that G17 is active in this tissue in a physiological range of concentrations. The ed50 for the effect of G17 to increase the amplitude of the plateau potential is less than that for the effect of G17 on gastric secretion, indicating that this is a physiological action of gastrin. Atropine studies indicate that only part of the in vitro inotropic action of gastrin is caused by the release of acetylcholine from nerve terminals, but that the chronotropic action is attributable to a direct effect on the smooth muscle membrane.

Effects of ammonium ions on spontaneous action potentials and on contents of sodium, potassium, ammonium and chloride ions in brain in vitro.

Abstract—The effects of ammonium ions on the frequency of spontaneous action potentials in guinea‐pig cerebellar slices, recorded with an extracellular microelectrode, and on the contents of sodium, potassium and chloride ions in incubated guinea‐pig cerebellar, and rat brain cortex, slices have been investigated. The frequencies of the spontaneous action potentials are partially suppressed by concentrations of NH4Cl less than 2 mm and completely abolished by concentrations exceeding 2 mm. The amplitudes of the spike discharges are unaffected. A lag period of at least 15 s precedes the inhibition. The suppressing action of NH on the spike frequency is reversible, as shown by complete recovery on removal of NH after short time intervals. Deficiency of Cl− in the superfusion medium causes conversion of inhibition by NH to excitation. Reduction of [K+], or of [Na+], causes increase of inhibition by NH in a normal [Cl1], and reduction of excitation in a low [Cl1], medium. The inhibitory effects of NH on spike frequency are unaffected by picrotoxin or strychnine. NH4Cl, even at 1 or 2 mm, causes a significant increase of aerobic glycolysis. It is suggested that the lag period preceding the suppression of the frequency of spike discharges by NH is partly due to a metabolic change induced by NH, perhaps a transient lowering of pH in the responsible neurons, causing changed permeability to Cl− and possibly to K+ and Na+, NH promotes, in guinea‐pig cerebellar slices, an inward flow of Na+ and an outward flow of K+, the latter being greater than that due to exchange of K+ for NH. NH4Cl at 1 or 2 mm causes an outward flow of K+ and an inward flow of Cl− in rat brain cortex slices. The movement of Cl− is biphasic, the first phase, seen with low [NH], consisting of an increase of tissue content of Cl− with little or no fluid uptake and a second phase, seen with high (> 5 mm) concentrations of NH, in which the uptake of Cl− is directly proportional to the fluid uptake. It is suggested that the first phase is largely neuronal in location whilst the second is largely glial. In infant rat brain cortex slices, there seems to be predominantly an equal exchange of NH for K+. There is little evidence of energy assisted concentrative uptake of NH by brain slices and this is thought to be due largely to the rapid diffusion of undissociated NH3 across cell membranes. It is suggested that some NH (amounting to about 2 mequiv/1) may be bound in the brain. It is concluded that changes in ionic permeabilities, particularly that of Cl−, partly due to a metabolic action, may be responsible for some of the acute cerebral effects of NH administration.

Spontaneous action potentials in isolated guinea-pig cerebellar slices: effects of amino acids and conditions affecting sodium and water uptake.

The effects of incubation conditions on the frequency of spontaneous action potentials exhibited by guinea-pig cerebellar slices, and recorded with an extracellular microelectrode, have been investigated. Various incubation conditions that lead to tetrodotoxin-sensitive uptakes of water and of sodium ions by the incubated cerebellar slices lead to enhanced frequencies of the spontaneous action potentials, e. g. the presence of protoveratrine or of ouabain, the absence of glucose or the onset of anoxia. The frequency of the spikes is also enhanced by acetylcholine (in presence of neostigmine) or by the presence of excitatory amino acids, such as L-glutamate, D-glutamate or L-aspartate. It is suppressed by tetrodotoxin, or by the inhibitory amino acids, e. g. γ -aminobutyrate, glycine or taurine, or by ammonium ions or by pentobarbital. It is concluded that guinea-pig cerebellar slices, incubated under specified conditions, may provide a suitable means for quantitative correlation of neurochemical data with data obtained by electrophysiological techniques in tissue incubated under similar conditions and also for quantitative assessment of the effects of amino acids on cerebellar electrical activity.

The circadian rhythm in the eye ofAplysia

1. The frequency of spontaneous compound action potentials (CAP) from the optic nerve of the eye ofAplysia is dramatically increased in zero calcium artificial sea water (ASW) but the circadian rhythm in this activity persists. 2. In high magnesium, >2.7 × normal, the spontaneous CAP activity is blocked. This effect is a result of decreased membrane responsiveness and not due to blocking chemical synapses. 3. In low calcium and high magnesium (at levels where molluscan chemical synapses are blocked) the spontaneous CAP activity and the circadian rhythm are clearly expressed. The average period for the rhythm is 23.3 hours, which is not different from the period in normal ASW. 4. These results suggest the neuronal oscillators that produce the circadian rhythm have axons directly in the optic nerve or they are electrontonically coupled to axons in the optic nerve, and that chemical synapses are not necessary for expression of the circadian rhythm.