Effects of micro‐iontophoretic administration of magnesium and calcium on neurones in the central nervous system of cats

SUMMARY1. Ba2+, applied by micro-iontophoresis, excites most cortical neurones that are excitable by ACh; other neurones tend to be depressed.2. The discharges evoked by Ba2+ resemble those evoked by ACh, but they have an even slower time course and are characterized by firing in high frequency bursts.3. The excitatory action of Ba2 , unlike that of ACh, is not abolished by muscarine antagonists; but it can be prevented with dinitrophenol.4. The depolarizing effect of Ba2+ is associated with a rise in membrane resistance and it has a reversal level 24 mV more negative than the resting potential.5. These observations suggest that, as in other tissues, Ba2+ reduced the K+ conductance by a direct action on the cell membrane. Some diminution in Na+ inactivation is indicated by the repetitive firing at high frequency.6. TEA has a predominantly depressant effect on all neurones tested. Like Ba2+, it often increases greatly the duration of spikes, but there is no regular change in resting membrane resistance and no tendency to repetitive firing. TEA probably reduces only the delayed K+ current.7. Even in large doses neither Ba2+ nor TEA interferes with the conductance increase that generates the typical prolonged JPSPs recorded in cortical neurones.

Section: Effects Of Ba2+mentioning

confidence: 99%

Section: Mechanism Of Actionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of Ba²⁺ and tetraethylammonium on cortical neurones

Krnjević¹,

Pumain²,

Renaud³

1971

“…In the initial experiments, double-barrelled micropipettes were used, one barrel containing 3 M-KC1 and the other 0-2 m-CaCl2 (according to previous experience (Kato & Somjen, 1969), this concentration is more satisfactory for microiontophoresis than 0 5 or 1 M). However, it soon became evident that substantial injections of Cat' were necessary and that any effect produced might not greatly outlast the period of injection.…”

Section: Introductionmentioning

confidence: 99%

Injections of calcium ions into spinal motoneurones

Krnjević¹,

Lisiewicz²

1972

272

SUMMARY1. In cats under Dial anaesthesia, Ca2+ was injected inside lumbosacral motoneurones, by passing currents between CaCl2-and KCl-containing barrels of compound micropipettes.2. There was a reduction in excitability and a fall in membrane resistance, both rapid in onset and quickly reversible. 4. The most common change in membrane potential was a hyperpolarization; but in nearly half the cases, there was no clear change or a small depolarization. A reversal level for the effect of Ca2+ could be measured in five cells: on the average, it was 10 mV more negative than the resting potential.5. Observations on i.p.s.p.s showed that Ca2+ probably does not alter gC: it was concluded that the fall in membrane resistance caused by intracellular Ca2+ is mainly due to an increase in gK.6. These results confirm previous suggestions that a steep transmembrane gradient of Ca2+ is essential for the maintenance of a low membrane conductivity, and that a rise in internal free Ca2+ -whether due to influx or release from internal stores -may play an important role in regulating neuronal activity.

“…This effect of Ca on transmitter release occurs also at synapses of frog motoneurones (Katz & Miledi, 1963;Grinnell, 1966). On the other G. E. DAMBACH AND S. D. ERULKAR hand, Krnjevi6 (1965), Kato & Somjen (1969) and Kelly, Krnjevid & Somjen (1969) have shown that Ca ions have a direct depressant action on the electrical excitability of neurones in the cerebral cortex as well as in other parts of the central nervous system, but they were unable to record any increase in transmitter release by the Ca. Thus, two separate effects of Ca on central neurones have been described: one effect on transmitter release and the other on neural excitability.…”

Section: Introductionmentioning

confidence: 99%

The action of calcium at spinal neurones of the frog

Dambach¹,

Erulkar²

1973

SUMMARY1. The action of Ca on membrane excitability and synaptic transmission at motoneurones of the isolated spinal cord of the frog has been studied.2. Impulse propagation along presynaptic fibres was unaffected by [Ca] in the range of 0-10 mm in the presence of 1 mM-Mg. 3. Motoneurone membrane excitability was within normal ranges when the cord was bathed in low or 0 Ca solutions containing 1 mM-Mg but was depressed in 5 or 10 mM-Ca solutions.4. Spontaneous miniature synaptic potentials were recorded in the presence of tetrodotoxin. The frequencies were reduced but not abolished in the absence of bath Ca, but were increased greater than twofold in 5 or 10 mM-Ca in comparison to those in normal Ringer solution (1 mM-Ca).5. Iontophoretic application of Ca both near to and remotely from the intracellular recording site (presumably in the soma) caused facilitation of elicited post-synaptic potentials.6. It is concluded that the action of Ca at these central synapses is identical to that described at the neuromuscular junction.