Effects of some divalent cations on synaptic transmission in frog spinal neurones.

Álvarez-Leefmans, Francisco J.; Santis, A. De; Miledi, Ricardo

doi:10.1113/jphysiol.1979.sp012936

Cited by 41 publications

(18 citation statements)

References 51 publications

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“…In adult frogs, the first component occurs within a fraction of a millisecond (at 14 'C) of the sensory impulse and is mediated electrically, whereas the second phase occurs with an additional delay of 1-2 ms and is chemically mediated Alvarez-Leefmans et al 1979;Shapovalov & Shiriaev, 1980;Westerfield & Frank, 1982). Triceps e.p.s.p.s in stage XIX tadpoles showed similar characteristics (Fig.…”

Section: Mode Of Synaptic Transmission At Early Sensory-motor Synsupporting

confidence: 50%

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Development of sensory‐motor synapses in the spinal cord of the frog.

Frank¹,

Westerfield²

1983

The Journal of Physiology

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SUMMARY1. The development and specificity of monosynaptic sensory-motor synapses were studied in the brachial spinal cord of bullfrog tadpoles. Intracellular and extracellular recordings were made from motoneurones innervating several different muscles of the forelimb. Excitatory synaptic potentials (e.p.s.p.s) were elicited by stimulation of various peripheral muscle nerves.2. Sensory and motor axons in the triceps brachii muscle nerves were electrically excitable at stage XIII, the earliest stage studied. Their conduction velocities were 02-0)4 in/s. These velocities increased during subsequent development so that by stage XXII they were approximately 5 m/s.3. Before stage XVII, synaptic potentials evoked in motoneurones by stimulation of the triceps sensory fibres had a long central latency and fatigued easily. These potentials were probably mediated polysynaptically.4. At stage XVII, the first short-latency triceps synaptic potentials appeared. They had central latencies of less than 3 ms and represented the direct, monosynaptic input from muscle sensory cells on to motoneurones. During subsequent development the percentage of triceps motoneurones innervated by triceps sensory fibres increased, while the number of long-latency polysynaptic inputs decreased.5. Both the electrical and chemical components, characteristic ofthese monosynaptic e.p.s.p.s in adult frogs, were prominent from the time the e.p.s.p.s first appeared.6. The pattern of innervation of brachial motoneurones by triceps sensory afferents was specific from the beginning. Triceps sensory fibres innervated most triceps motoneurones but very few subscapular or pectoralis motoneurones, just as in adult frogs. At no time were there appreciable numbers of 'aberrant' connexions.7. The developmental time course of several different classes of sensory-motor connexions was similar. Thus the synaptic specificity of this system cannot be explained by a differential timing of synaptogenesis.

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Section: Mode Of Synaptic Transmission At Early Sensory-motor Synsupporting

confidence: 50%

“…In the adult frog, transmission at sensory-motor synapses is mediated both electrically and chemically ; Alvarez-Leefmans et al 1979;Shapovalov & Shiriaev, 1980;Westerfield & Frank, 1982). It was of interest to determine how transmission at these synapses is mediated when they are first formed.…”

Section: Mode Of Synaptic Transmission At Early Sensory-motor Synmentioning

confidence: 99%

Development of sensory‐motor synapses in the spinal cord of the frog.

Frank¹,

Westerfield²

1983

The Journal of Physiology

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“…Divalent cations block Ca2+ channels (Katz & Miledi, 1967;Alvarez-Leefmans et al, 1979), and can thereby prevent release of neurotransmitters (Barker et al, 1975a). Since the presence of TTX in the Ringer only prevents propagated action potentials and may therefore not prevent all types of neurotransmitter release, responses to NMDLA could be generated by the release of endogenous excitory neurotransmitters.…”

Section: Intoductionmentioning

confidence: 99%

The Use of Low Concentrations of Divalent Cations to Demonstrate a Role for N‐methyl‐d‐aspartate Receptors in Synaptic Transmission in Amphibian Spinal Cord

Smith

1982

British J Pharmacology

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5 These results suggest that: (i) divalent cations do not antagonize NMDLA responses by blocking Ca2+ channels which may mediate the response; (ii) postsynaptic NMDA receptors are activated by a neurotransmitter involved in the DR-DRP and DR-VRP pathways but not by any neurotransmitters involved in the VR-DRP pathway; (iii) the neurotransmitter activating NMDA receptors in amphibian spinal cord may be an aspartate-like substance rather than aspartate itself or glutamate. IntoductionThe acidic amino acids, L-glutamate and L-aspartate, are putative excitatory neurotransmitters in the central nervous system (CNS) (Krnjevic, 1974;Puil, 1981 . Certain lines of evidence support a role for calcium ions in the electrogenesis of responses to acidic amino acids (Sonnhof & Btihrle, 1981;Padjen & Smith, 1981;Puil,1981;butseealso Shapavolov, Shiriaev &Velumain, 1978 and McDonald &Wojtowicz, 1980;. Calcium influx may be especially important for responses evoked by DL-homocysteic acid, an agonist thought to act on NMDA receptors (Heinemann & Pumain, 1981). Recently, Co2+ and Mg2+ have been shown to be selective and highly potent antagonists at NMDA receptors (Ault, Evans, Francis, Oakes & Watkins, 0007-1188/82/100363-11 $01.00 1981). Since these ions are known to block calcium channels (Katz & Miledi, 1967; Alvarez-Leefmans, DeSantis & Miledi, 1979) (Blackman, Ginsborg & Ray, 1963

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“…Thus it was important to determine how this coupling interfered with the measurement of sensory-motor synaptic potentials. In experiments described elsewhere (Westerfield & Frank, 1982) Miledi, 1979) and the time of active invasion of motoneuronal somata by the antidromic impulses (Shapovalov & Shiriaev, 1978). This component is produced both by electrical coupling between sensory afferents and this motoneurone and by electrical coupling between this neurone and some of its antidromically activated neighbours (Grinnell, 1966).…”

Section: Methodsmentioning

confidence: 99%

Synaptic organization of sensory and motor neurones innervating triceps brachii muscles in the bullfrog

Frank

Westerfield

1982

The Journal of Physiology

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SUMMARY1. The anatomy and physiology of sensory-motor pathways were studied in the brachial spinal cord of adult bullfrogs to characterize the properties and specificity of these connexions.2. Motoneurones innervating a given forelimb muscle are located in discrete and reproducible regions of the lateral motor column. Yet only a fraction of the motoneurones in a particular region innervates any one muscle.3. The central projections ofsensory afferent axons from the triceps muscles extend throughout the rostro-caudal length of the brachial spinal cord. Within this region these projections terminate in an area containing many motoneuronal dendrites.4. Within the triceps motor pool sensory neurones from the triceps muscles produce monosynaptic potentials only in triceps motoneurones even though these motoneurones are mingled with motoneurones innervating other muscles.5. Motoneurones innervating each of the three heads of the triceps muscles, medial, internal and external, receive monosynaptic input from their own, homonymous muscle head. Sensory fibres from the medial head also innervate 98% of the heteronymous motoneurones projecting to the internal or external heads, and nearly 90 % of the medial triceps motoneurones are innervated by sensory axons from the other two heads.6. Similarly, other brachial motoneurones receive monosynaptic input from sensory axons in their own muscle nerves. However, most of the synaptic potentials evoked in triceps motoneurones by stimulation of muscle nerves other than triceps are of longer latency and probably involve polysynaptic pathways.7. Thus, the pattern of synaptic connexions between muscle sensory afferents and motoneurones in the frog's spinal cord is specific. Furthermore, comparison with homologous pathways in the cat's spinal cord suggests that the strength and pattern of these connexions are similar.

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Effects of some divalent cations on synaptic transmission in frog spinal neurones.

Cited by 41 publications

References 51 publications

Development of sensory‐motor synapses in the spinal cord of the frog.

Development of sensory‐motor synapses in the spinal cord of the frog.

The Use of Low Concentrations of Divalent Cations to Demonstrate a Role for N‐methyl‐d‐aspartate Receptors in Synaptic Transmission in Amphibian Spinal Cord

Synaptic organization of sensory and motor neurones innervating triceps brachii muscles in the bullfrog

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