Development of dendritic calcium currents in ganglion cells of the rat lower lumbar sympathetic chain.

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106

115

1. Intracellular recordings were made from the parasympathetic ganglion cells that lie in the epicardium of the left atrium of guinea-pig heart near the interatrial septum. 2. Three distinct types of neurone were identified on the basis of their electrophysiological properties. In one group of neurones, S cells, somatic action potentials were followed by brief after-hyperpolarizations. In the other two sets of neurones, somatic action potentials were followed by prolonged after-hyperpolarizations.

Section: Resultsmentioning

confidence: 99%

Different types of ganglion cell in the cardiac plexus of guinea‐pigs.

Edwards¹,

Hirst²,

Klemm³

et al. 1995

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106

115

“…When the action potentials were blocked, the peak amplitude of the synaptic response was usually > 40 mV. About 25% of phasic neurones received two Str inputs (2 Str); although these rarely caused firing of two action potentials, two distinct peaky components could be distinguished during graded stimulation when the membrane was hyperpolarized (see Hirst & McLachlan, 1986).…”

Section: Ca2+-activated Glsmentioning

confidence: 99%

“…When action potentials were blocked by hyperpolarizing the neurones by some 25-40 mV (by passing current via the recording microelectrode), neurones with Str SYNAPTIC INPUT TO COELIAC NE UR ONES inputs were found to have underlying synaptic responses with a fast peak and a decay phase which was not simply exponential (see Hirst & McLachlan, 1986).…”

Section: Ca2+-activated Glsmentioning

confidence: 99%

Characteristics of synaptic input to three classes of sympathetic neurone in the coeliac ganglion of the guinea‐pig.

McLachlan

Meckler

1989

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SUMMARY1. Intracellular recordings from sympathetic neurones in the isolated coeliac ganglion of guinea-pigs have been used to define the synaptic input to three subtypes of neurone, classified on the basis of their discharge during maintained depolarizing current as phasic neurones, neurones with prolonged after-hyperpolarizations (LAH), and tonic neurones.2. The three classes of neurone were distributed characteristically in different parts of the ganglion.3. Passive membrane properties differed between the three neurone types. Mean input resistance was highest in phasic neurones and was inversely related to the size of the prolonged calcium-activated potassium conductance in LAH neurones. Mean input time constant was highest in tonic neurones, because of significantly higher cell capacitance.4. Phasic and LAH neurones usually received one suprathreshold ('strong') as well as several subthreshold excitatory synaptic potentials (ESPs) from the ipsilateral splanchnic nerve. In general, the amplitude and number of splanchnic inputs were greater, and the occurrence of two strong inputs more common, in phasic than in LAH neurones. The input to tonic neurones was small and usually subthreshold, even with supramaximal splanchnic stimulation. In a few (mostly tonic) neurones lying close to the midline, small ESPs were evoked by contralateral splanchnic stimulation.5. Antidromic action potentials were evoked in more than half of all neurones by high voltage coeliac nerve stimulation. In addition, multiple small subthreshold ESPs were recorded in virtually all tonic neurones (99 %) on coeliac nerve stimulation. In contrast, coeliac stimulation rarely evoked a few very small ESPs in LAH neurones (9%), but no synaptic response in phasic neurones.6. In about half of the tonic neurones tested (but no phasic or LAH neurones), small ESPs were evoked by stimulation of the intermesenteric nerve.7. Slow depolarization elicited by repetitive activation of splanchnic and coeliac nerve trunks, at voltages supramaximal for the fast cholinergic responses, were * Present address: Department of Physiology and Pharmacology, University of Queensland, St Lucia, Queensland 4067, Australia. E. M. McLACHLAN AND R. L. MECKLERrecorded from about half of both phasic and tonic neurones, but only one of twentyfour LAH neurones. These responses commonly faded during subsequent trials, so that it was difficult to characterize them.8. The data indicate that the three broad groups of coeliac neurone, classified on the basis of their voltage-and calcium-dependent potassium conductances, receive different patterns of synaptic input. The differences may be related to the three major functions of vasoconstriction, motility and mucosal secretion in the small intestine.

“…The same was true Of both phases when substituting Co2+ for Ca2+ (n = 2 neurones of each kind). K+ conductances (see McLachlan, 1977;Hirst & McLachlan, 1986 Raising the Ca2+ ion concentration from 2 to 10 mM in two l.a.h. neurones approximately doubled the amplitude of both fast and slow outward currents, without affecting the time constant of decay of the slow tail current (Fig.…”

Section: Dependence Of Outward Tail Currents On K+ Ionsmentioning

confidence: 99%

Two calcium‐activated potassium conductances in a subpopulation of coeliac neurones of guinea‐pig and rabbit.

Cassell

McLachlan

1987

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SUMMARY1. Some of the sympathetic neurones in coeliac ganglia isolated from young guinea-pigs and rabbits were found to generate action potentials followed by afterhyperpolarizations with durations of 3-8 s, much longer than those ( -300-500 ms) observed in the majority of other mammalian sympathetic neurones.2. This type of ganglion cell discharged only once at the onset of a depolarizing step unless a very high intensity current was applied. Passive and voltage-dependent membrane conductances studied in detail in guinea-pig ganglia differed from those in the two other classes of sympathetic ganglion cell described previously (Cassell, Clark & McLachlan, 1986).3. By using a single microelectrode to voltage clamp the soma, it was possible to demonstrate that both fast and slow components of the tail current following initiation of an uncontrolled 'action current' in neurones with long afterhyperpolarizations (l.a.h.) were carried by K+ ions, as was the fast tail current (time constant, T-130 ms) present in other coeliac neurones.4. The amplitude of both components of the tail current in l.a.h. neurones was markedly reduced by the replacement of Ca2+ by Mn2+, Co2+ or Ba2+ ions. These manoeuvres had similar effects on the fast tail current in other coeliac neurones.5. Both time course and amplitude of the fast tail current were increased when Ca2+ concentration was raised, or when several 'action currents' were initiated, whereas only the amplitude of the slow tail current was affected.6. The time course of the slow tail current could be described by the sum of two exponentials with Ton = 285 ms and Toff = 1-3 s at 35°C occurring after a delay of 60 ms. This current had a Qlo of about 4 between 35 and 25 'C. In contrast, the Qlo of the fast component was about 2.7. Morphine (10-6 M) and vasoactive intestinal polypeptide (106 M) had no effect on the outward tail current in l.a.h. neurones, but 5-hydroxytryptamine (106 M) was found to abolish the slow component without affecting the fast component.8. The slow tail current was activated in the subthreshold range of membrane