Spike potential

About: Spike potential is a research topic. Over the lifetime, 423 publications have been published within this topic receiving 16023 citations.

The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum.

Abstract: 1. A single climbing fibre makes an extraordinarily extensive synaptic contact with the dendrites of a Purkinje cell. Investigation of this synaptic mechanism in the cerebellum of the cat has been based on the discovery by Szentagothai & Rajkovits (1959) that the climbing fibres have their cells of origin in the contralateral inferior olive. 2. Stimulation in the accessory olive selectively excites fibres that have a powerful synaptic excitatory action on Purkinje cells in the contralateral vermis, evoking a repetitive spike discharge of 5-7 msec duration. Almost invariably this response had an all-or-nothing character. In every respect it corresponds with the synaptic action that is to be expected from climbing fibres. 3. Intracellular recording from Purkinje cells reveals that this climbing fibre stimulation evokes a large unitary depolarization with an initial spike and later partial spike responses superimposed on a sustained depolarization. 4. Typical climbing fibre responses can be excited, but in a much less selective manner, by stimulation of the olive-cerebellar pathway in the region of the fastigial nucleus, there being often a preceding antidromic spike potential of the Purkinje cell under observation. 5. Impaled Purkinje cells rapidly deteriorate with loss of all spike discharge, the climbing fibre response being then reduced to an excitatory post-synaptic potential. This potential shows that stimulation of the inferior olive may evoke two or more discharges at about 2 msec intervals in the same climbing fibre. The complexity of neuronal connexions in the inferior olive is also indicated by the considerable latency range in responses. 6. A further complication is that, with stimulation in the region of the fastigial nucleus, the initial direct climbing fibre response is often followed by a reflex discharge, presumably from the inferior olive, which resembles the responses produced by inferior olive stimulation in being often repetitive. 7. Typical climbing fibre responses have been evoked by peripheral nerve stimulation and frequently occur spontaneously. 8. An account is given of the way in which the responses evoked by climbing fibres in the individual Purkinje cells can account for the potential fields that an inferior olive stimulus evokes on the surface and through the depth of the cerebellar cortex. 9. By the application of currents through the recording intracellular electrode it has been possible to effect large changes in the excitatory post-synaptic potential produced by a climbing fibre, it being diminished and even reversed with depolarizing currents and greatly increased by hyperpolarizing currents.

Action potential initiation and propagation in rat neocortical pyramidal neurons

Abstract: 1. Initiation and propagation of action potentials evoked by extracellular synaptic stimulation was studied using simultaneous dual and triple patch pipette recordings from different locations on neocortical layer 5 pyramidal neurons in brain slices from 4-week-old rats (P26-30) at physiological temperatures. 2. Simultaneous cell-attached and whole-cell voltage recordings from the apical trunk (up to 700 microns distal to the soma) and the soma indicated that proximal synaptic stimulation (layer 4) initiated action potentials first at the soma, whereas distal stimulation (upper layer 2/3) could initiate dendritic regenerative potentials prior to somatic action potentials following stimulation at higher intensity. 3. Somatic action potentials, once initiated, propagated back into the apical dendrites in a decremented manner which was frequency dependent. The half-width of back propagating action potentials increased and their maximum rate of rise decreased with distance from the soma, with the peak of these action potentials propagating with a conduction velocity of approximately 0.5 m s-1. 4. Back-propagation of action potentials into the dendritic tree was associated with dendritic calcium electrogenesis, which was particularly prominent during bursts of somatic action potentials. 5. When dendritic regenerative potentials were evoked prior to somatic action potentials, the more distal the dendritic recording was made from the soma the longer the time between the onset of the dendritic regenerative potential relative to somatic action potential. This suggested that dendritic regenerative potentials were initiated in the distal apical dendrites, possibly in the apical tuft. 6. At any one stimulus intensity, the initiation of dendritic regenerative potentials prior to somatic action potentials could fluctuate, and was modulated by depolarizing somatic or hyperpolarizing dendritic current injection. 7. Dendritic regenerative potentials could be initiated prior to somatic action potentials by dendritic current injections used to simulate the membrane voltage change that occurs during an EPSP. Initiation of these dendritic potentials was not affected by cadmium (200 microM), but was blocked by TTX (1 microM). 8. Dendritic regenerative potentials in some experiments were initiated in isolated from somatic action potentials. The voltage change at the soma in response to these dendritic regenerative events was small and subthreshold, showing that dendritic regenerative events are strongly attenuated as they spread to the soma. 9. Simultaneous whole-cell recordings from the axon initial segment and the soma indicated that synaptic stimulation always initiated action potentials first in the axon. The further the axonal recording was made from the soma the greater the time delay between axonal and somatic action potentials, indicating a site of action potential initiation in the axon at least 30 microns distal to the soma. 10. Simultaneous whole-cell recordings from the apical dendrite, soma and axon initial segment showed that action potentials were always initiated in the axon prior to the soma, and with the same latency difference, independent of whether dendritic regenerative potentials were initiated or not. 11. It is concluded that both the apical dendrites and the axon of neocortical layer 5 pyramidal neurons in P26-30 animals are capable of initiating regenerative potentials. Regenerative potentials initiated in dendrites, however, are significantly attenuated as they spread to the soma and axon. As a consequence, action potentials are always initiated in the axon before the soma, even when synaptic activation is intense enough to initiate dendritic regenerative potentials. Once initiated, the axonal action potentials are conducted orthogradely into the axonal arbor and retrogradely into the dendritic tree.

Electromechanical and pharmacomechanical coupling in vascular smooth muscle

Abstract: The electrical events accompanying contractions of helically cut vascular strips were studied by the sucrose gap method. Mechanical responses to drugs and caffeine were also determined in depolarized preparations. The isometric contractions of umbilical vein and pulmonary artery strips elicited by external electrical stimuli were observed. Norepinephrine, serotonin and histamine gradedly depolarized rabbit main pulmonary artery smooth muscle. There was some correlation between level of depolarization and drug concentrations. Drug-induced contractions were associated with lesser depolarization than the contractile response elicited by warming from room temperature to 35°C. Drugs or warming did not elicit repetitive action potentials in the rabbit main pulmonary artery preparations. Mesenteric vein strips of rabbits and dogs developed spontaneous action potentials associated with rhythmic contractions. Norepinephrine, serotonin, histamine and angiotensin produced depolarization and increased action potential frequency in these preparations. The absolute correlation between spike frequency and tension development was limited. Caffeine reversibly eliminated both the spontaneous and drug-induced action potentials of rabbit mesenteric veins without abolishing the resting membrane potential. The contractile response to drugs persisted, although it was diminished. The inequality of maximal mechanical responses to supramaximal concentrations of epinephrine, histamine and angiotensin was observed in preparations depolarized with potassium. The contractile response of electrically stimulated human umbilical veins was frequency-dependent. Graded, external electrical stimulation elicited graded contractions of rabbit main pulmonary artery strips. Caffeine had a diphasic mechanical effect on both polarized and depolarized vascular smooth muscle. We suggest the existence of two major electrophysiologic types of vascular smooth muscle, one gradedly responsive and the other producing repetitive action potentials. The mechanical response of the latter can be dissociated, with caffeine, from electrical spikes in the polarized state. Graded concentrations of drugs appear to elicit graded contractions through: 1) variable frequency spike electrogenesis; 2) graded depolarization; and 3) graded pharmacomechanical coupling. The inhibition-relaxation coupling mechanisms are also multiple and not solely dependent on inhibition of spike electrogenesis.

Temporal precision of spike trains in extrastriate cortex of the behaving macaque monkey

Abstract: How reliably do action potentials in cortical neurons encode information about a visual stimulus? Most physiological studies do not weigh the occurrences of particular action potentials as significant but treat them only as reflections of average neuronal excitation. We report that single neurons recorded in a previous study by Newsome et al. (1989; see also Britten et al. 1992) from cortical area MT in the behaving monkey respond to dynamic and unpredictable motion stimuli with a markedly reproducible temporal modulation that is precise to a few milliseconds. This temporal modulation is stimulus dependent, being present for highly dynamic random motion but absent when the stimulus translates rigidly.