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Biomedical subjects

E Florey

Publications and source records attributed to E Florey.

At least 19 recordsLinked to original sources
PubMed1991

GABA: history and perspectives.

In 1957, factor I, a brain agent I had discovered earlier, was chemically identified as GABA in a collaboration between myself and Alva Bazemore at the Montréal Neurological Institute (MNI) in the Neurochemistry Laboratory then headed by K. A. C. Elliott. A personally biased excursion into the history of neurobiology illuminates the development of methods and concepts that led to this event, and recounts the early days at the MNI, when Hugh McLennan and I applied factor I to the exposed surface of the spinal cord and to sympathetic ganglia of cats and rabbits. It also tells of earlier studies at Graz, Naples, and elsewhere that prompted the experiments at the California Institute of Technology in which factor I was discovered as the agent in nerve extracts causing inhibition of isolated crayfish stretch receptor neurons, and in which it was found that this inhibition could be prevented by picrotoxin. There was justified doubt that GABA is indeed the transmitter substance of inhibitory neurones. Later studies, however, resolved the controversy. The functional role of GABA in brain and spinal cord and its mechanism of action are still far from being fully understood. Special problems are the extent and significance of spontaneous quantal and nonquantal release, the functional role and the mechanism of excitatory actions of GABA, its release from glial cells, and the energetics of its metabolic turnover.

Animals↗
PubMed1988

Reversible effect of depolarization by K-propionate on sub-miniature endplate potential to bell-miniature endplate potential ratios, on miniature endplate potential frequencies and amplitudes, and on synaptic vesicle diameters and densities in frog neuromuscular junctions.

Miniature endplate potentials were recorded from edge muscle fibers of frog sartorius muscles during high frequencies induced with K-propionate and during recovery. The identified neuromuscular junctions were studied with the electron microscope and their ultrastructure was correlated with amplitude and numbers of miniature endplate potentials generated. Miniature endplate potential amplitudes were maintained during the first 10 min of depolarization. They then decreased during the next 2-3 h until the mode was lost to the noise. Miniature endplate potential frequency was greatly increased during the first hour and there was initial depletion of vesicles. Miniature endplate potential frequencies remained high (5 x 10(5)/h) for 3 h but vesicle densities returned to nearly normal values during the second to third hour of treatment. The conspicuous infolding of the presynaptic membrane noted during the first hour of treatment suggests that recycling of vesicles is initially slower than fusion. Calculated recycling time is shorter than 25 min. During recovery after prolonged K-propionate treatment, the sub-miniature endplate potential class reappeared within minutes but about 20 min were required before it returned to control size. Subsequently, the bell-miniature endplate potentials reappeared and slowly increased in amplitude. The ultrastructure returned to a normal state. There was no change in vesicle diameters. No significant difference was found between the diameters of "touching vesicles" (vesicles touching the presynaptic membrane) and the non-touching vesicles. By comparison, lanthanum ions (1 mM) released a smaller number of quanta which did not exceed the number of vesicles present at the start of the experiment. Variations of the subunit hypothesis of the quantum of transmitter release are discussed.

Action Potentials↗
PubMed1987

New types of synaptic connections in crayfish stretch receptor organs: an electron microscopic study.

The synaptic input to crayfish (Orconectes limosus) stretch receptor neurons, and the synaptic interactions between the inhibitory and excitatory efferents were analysed by electron microscopy of serial sections. Several novel types of synaptic connections have been observed: (i) inhibitory synaptic input on the axon hillock and initial axon segment; (ii) serial synaptic terminals on the sensory cell body; (iii) simultaneous synaptic contacts of the same inhibitory terminal with sensory dendrites and muscle fibres; (iv) reciprocal synapses between the two types of inhibitory efferents; and (v) inhibitory synapses on the primary inhibitory axon. The possible functional significance of these synapses is discussed in the light of earlier electrophysiological and pharmacological findings.

Animals↗
PubMed1987

Immunocytochemical evidence for the GABAergic innervation of the stretch receptor neurons in crayfish.

The GABAergic innervation of the stretch receptor neurons of the crayfish Orconectes limosus has been investigated by means of light- and electron microscope immunocytochemistry using an antibody to GABA. Both whole-mount preparations and post-embedding semithin sections revealed a massive GABAergic innervation of both the slowly and the fast adapting receptor neurons. The stretch receptor organ is supplied by one principle GABA-immunoreactive axon, which gives off several branches that innervate the receptor neurons. Cell body, initial axon segment and dendritic region of the sensory neurons are covered by numerous GABA-immunoreactive varicose fibers. Electron microscopy revealed that the GABA-immunoreactive varicosities establish specialized synaptic contacts with the sensory neurons. The functional significance of the occurrence of GABA-immunoreactive varicosities on the different parts of the sensory neurons is discussed. The results support the physiological and pharmacological evidence that GABA is a transmitter substance of the efferent inhibitory neurons which innervate the crayfish stretch receptor neurons.

Animals↗
PubMed1987

Octopamine action on the contractile system of crustacean skeletal muscle.

1. In the opener muscle of walking legs of crayfish (Astacus leptodactylus) octopamine (OA) greatly enhances the contractions resulting from brief applications of L-glutamate or of elevated K-concentrations. Synephrine is as effective as OA. 2. In the case of potentiation of responses to high-K applications a presynaptic component of the OA action was excluded by first desensitising the muscle fibres to the action of the natural transmitter, using a high concentration (1 mM) of glutamate. 3. The Ca-antagonists Co, Ni and Mn (1 mM) reduced the effects of glutamate and of elevated K to about one-half. In preparations treated with OA, the same Ca-antagonists also depressed the potentiated contractural responses to glutamate and to elevated K, again to about one-half. 4. OA also enhanced contractions resulting from the application of caffeine. 5. With 5-hydroxytryptamine (5-HT) application, the same postsynaptic effects were obtained as described for OA, except that the 5-HT actions were much weaker. 6. With OA, maximal effects were obtained with concentrations of 5 x 10(-6)-10(-5) M; maximally effective concentrations of 5-HT were around 10(-5) M. 7. The lowest effective concentrations of OA were around 10(-8) M; those of 5-HT were around 10(-7) M. 8. In the same preparation, 5-HT is far more effective in enhancing transmitter release (presynaptic action) than OA, the lowest effective concentration being around 10(-11) M while no presynaptic effects of OA were seen at concentrations below 10(-8) M, in some cases even below 10(-5) M.

Animals↗
PubMed1985

Evidence for L-glutamate as a transmitter substance of motoneurons innervating squid chromatophore muscles.

Motor nerve branches were stimulated in the dermis layer prepared from isolated pieces of dorsal mantle skin of the squid Lolliguncula brevis and the contractions of chromatophore muscle fibers were recorded with the aid of a photo-electric transducer. L-Glutamate (L-Glu), kainate and quisqualate caused a contracture and often repetitive twitch-like contractions. These effects were readily reversible. In the case of L-Glu application, twitches induced by single stimuli applied to motor nerves were enhanced and prolonged. The glutamate antagonists glutamic acid gamma-methyl ester, glutamic acid diethyl ester, D,L-2-amino-4-phosphonobutyrate and gamma-D-glutamylglycine prevented both nerve induced and L-Glu induced contractions. The NMDA-receptor agonists N-methyl-D-aspartate, L-aspartate and D-glutamate, and their antagonists alpha-aminoadipate and D,L-2-amino-5-phosphonovalerate were found ineffective. With the aid of saline media of different Ca and Mg content, it was possible to selectively eliminate one or all components of the effect of L-Glu. Tetrodotoxin abolished nerve induced contractile responses but did not interfere with the contracture caused by L-Glu. Intracellular electrical recording indicated that nerve stimulation causes EPSPs which do not give rise to spike discharges. The results are compatible with the hypothesis that L-Glu is a transmitter substance of the motoneurons that innervate chromatophore muscle fibers.

Animals↗
PubMed1983

Effect of lanthanum ions on the amplitude distributions of miniature endplate potentials and on synaptic vesicles in frog neuromuscular junctions.

Miniature endplate potential (MEPP) amplitude distributions, MEPP frequencies and percentages of small MEPPs were determined as well as synaptic vesicle diameters and numbers in the frog neuromuscular junction during La3+ treatment. MEPP frequencies initially increased by two orders of magnitude and then fell to very low values. La3+ treatment had an initial postsynaptic effect making the MEPPs larger. Prolonged treatment had a variable effect on MEPP amplitudes. There were considerable variations in MEPP frequencies in adjacent junctions so single junctions on edge muscle fibers were recorded for the duration of many experiments and later identified in the electron microscope. Therefore, the physiological and morphological conditions of a given identified junction could be compared. There was a loss of synaptic vesicles and no change in mean diameter during depletion. During high MEPP frequencies infoldings occurred on the axolemma and these disappeared when MEPP frequencies decreased towards the end of the La3+ treatment. After 3-4 h of La3+ treatment, the overall frequency of MEPPs dropped and many were composed of a small class of MEPPs. It is suggested that the morphological correlate of small MEPPs, as well as the classical bell-MEPPs is likely to be synaptic vesicles.

Animals↗
PubMed1983

Changes in acetylcholine concentration, miniature end-plate potentials and synaptic vesicles in frog neuromuscular preparations during lanthanum treatment.

ACh content and synaptic ultrastructure were compared in neuromuscular preparations (sartorius muscle of Rana esculenta) incubated in control saline and in saline containing 1 mM LaCl3. ACh concentrations remained constant for 6 hr in control preparations. La3+ caused a 38% depletion of ACh within the first 30 min with subsequent recovery to 120% of control values within 3-4 hr. Recovery was prevented by hemicholinium-3. At 23 degrees C La3+ caused complete loss of synaptic vesicles: no depletion was seen at 4 degrees C. Initially MEPP frequency increased 300- to 700-fold (23 degrees C), then declined. Mean vesicle diameter did not change, but SD increased. As the frequency of MEPPs declined, the percentage of s-MEPPs greatly increased. La3+ had a postsynaptic effect which increased the amplitudes of both s-MEPPs and bell-MEPPs within a few seconds. The s-MEPP mean did not change during the course of La3+ treatment although the bell-MEPP mean usually decreased. How the decrease in synaptic vesicles, decrease in MEPP frequencies, and changes in ACh levels relate to changes in the percentage of different classes of quanta is discussed.

Acetylcholine↗
PubMed1983

Modulation of synaptic transmission and excitation-contraction coupling in the opener muscle of the crayfish, Astacus leptodactylus, by 5-hydroxytryptamine and octopamine.

The modulatory actions of 5-hydroxytryptamine (5-HT) and octopamine (OA) were investigated in the opener nerve-muscle preparation of the crayfish, Astacus leptodactylus. Membrane resistance and resting potential were unaltered by 5-HT and OA at concentrations up to 2.5 X 10(-5) M; but EPSP-amplitudes were increased, up to 3-fold by OA and up to 18-fold by 5-HT. The lowest effective concentration was 2.5 X 10(-9) M; a maximal effect was produced at 2.5 X 10(-6) M. The effect was reversible only after prolonged washing. The enhancement of EPSPs by 5-HT or OA is due to an increased amplitude of the synaptic current; the current duration is not altered. The facilitation ratio (ratio of amplitudes of a pair of EPSPs) is not significantly affected by 5-HT or OA despite the often enormous increase of the absolute EPSP-amplitudes. The modulatory action also affects the excitation-contraction (e-c) coupling process: the effectiveness of e-c coupling was increased 7.4-fold by 5-HT (2.5 X 10(-6) M) and 18.7-fold by OA (5 X 10(-6) M). The threshold potential of e-c coupling was not affected.

Animals↗
PubMed1982

The innervation pattern of crustacean skeletal muscle. Morphometry and ultrastructure of terminals and synapses.

The innervation pattern of distal muscle fibers of the opener muscle of walking legs of crayfish (Astacus leptodactylus) was investigated using methylene-blue staining, cobalt infiltration, and electron microscopy. A quantitative analysis of the entire innervation of single muscle fibers was attempted. It was found that instead of the generally assumed parallel array of numerous excitatory and inhibitory terminals, innervation consists of only a few branched terminals. The branches of excitatory and inhibitory terminals lie side-by-side. Both types are characterized by numerous varicosities (see Fig. 9B). The aggregate length of excitatory as well as inhibitory terminals on one muscle fiber is, on the average, about 1,500 micrometer with a total of 152 varicosities spaced about 10 micrometer apart. The average diameter of the varicosities is 4.26 micrometer, that of the connecting thin segments about 0.5 micrometer. Total terminal surface of motor or inhibitory terminals amounts to about 10,000 micrometers2 per muscle fiber. There are approximately 2,000 motor synapses on each muscle fiber, but their average total area is only about 6% of the terminal membrane area, or 0.06% of the (idealized) muscle fiber surface. There are conspicuous differences in the postsynaptic specializations associated with excitatory and inhibitory terminals; these are described in detail. The results are discussed in a functional context and with regard to design and results of electrophysiological experiments.

Animals↗
PubMed1982

Scanning electron microscopy of echinoid podia.

Tube feet of the sea urchin Strongylocentrotus franciscanus were studied with the scanning electron microscope (SEM). By use of fractured preparations it was possible to obtain views of all components of the layered tube-foot wall. The outer epithelium was found to bear tufts of cilia possibly belonging to sensory cells. The nerve plexus was clearly revealed as being composed of bundles of varicose axons. The basal lamina, which covers the outer and inner surfaces of the connective tissue layer, was found to be a mechanically resistant and elastic membrane. The connective tissue appears as dense bundles of (collagen) fibers. The luminal epithelium (coelothelium) is a single layer of flagellated collar cells. There is no indication that the muscle fibers, which insert on the inner basal lamina of the connective tissue layer are innervated by axons from the basi-epithelial nerve plexus. The results agree with previous conclusions concerning tube-foot structure based on transmission electron microscopy, and provide additional information, particularly with regard to the outer and inner epithelia.

Animals↗
PubMed1982

Postsynaptic potential and postsynaptic current in muscle fibres with large time-constant. EPSP amplitude is independent of membrane resistance.

1. Equations have been developed for a computer programmed calculation of synaptic current from synaptic potentials (epsps). 2. The method permits separation of presynaptic and postsynaptic effects in experiments involving drugs which affect synaptic transmission. It is particularly applicable where the postsynaptic cells are large as in the case of commonly employed crustacean muscle fibres. 3. Contrary to a widely held view the theoretical approach used predicts that epsp-amplitude is relatively independent of membrane resistance. 4. Confirmation is provided by experiments involving the application of barium which increases, and of GABA which decreases membrane resistance.

Animals↗
PubMed1980

Cholinergic motor control of sea urchin tube feet: evidence for chemical transmission without synapses.

Isolated tube feet of Strongylocentrotus franciscanus contract briefly when the outer epithelium is touched. Similar twitch-like contractions can be induced by electrical stimulation of the outer surface of the tube foot. These responses appear to be chemically mediated. The following evidence indicates that the transmitter substance may be acetylcholine (ACh): ACh causes muscle contraction. This effect and that of electrical stimuli is potentiated by anticholinesterase agents and is antagonized by cholinergic blocking agents. Anaesthesia with chloralhydrate or chloretone abolishes responsiveness to mechanical or electrical stimulation but not to ACh. Desensitization with carbachol prevents responses to ACh and to mechanical or electrical stimulation. There are no neuromuscular synapses and no axons can be detected which cross the connective tissue layer which separates the muscle fibres from the subepithelial nerve plexus. The latter is known to contain conspicuous amounts of ACh; nerve terminals containing clear vesicles invest the outer surface of the connective tissue layer. All evidence indicates that chemical transmission involves diffusion of ACh (released from activated nerve terminals) across this connective tissue layer which is around 5 micron thick in fully extended tube feet but may have a thickness of 20 or even 25 micron in less extended ones. Calculations based on equations describing transmitter diffusion prove the feasibility of such a mechanism.

Animals↗
PubMed1979

Is glutamate the transmitter of crustacean motoneurons?

1. Bath-application of L-glutamate to crayfish opener muscle causes depolarization and resistance changes which both increase with falling temperature. At temperatures above 15 degrees C there is usually a resistance increase, at lower temperatures the resistance is decreased. 2. Meso-gamma . gamma'-diaminosuberic acid-dihydrochloride (meso-di-GABA) and dl-diamino-nonanedicarboxylic acid dihydrochloride (C-9) were newly synthesized as potential glutamate blockers. 3. Meso-di-GABA (10(-4) to 10(-3)M) usually caused a significant increase (15 degrees C) or decrease (7 degrees C) of membrane resistance and slight depolarization. Excitatory junction potentials (ejps) were reversibly depressed or blocked while the effects of glutamate were potentiated. The depression or block of neuromuscular transmission was not prevented by picrotoxin or by concanavaline A. 4. C-9 (3 x 10(-4) M) depressed or blocked the effect of applied glutamate with little or no effect on ejps. 5. The results are best explained by assuming that bath-applied glutamate acts mainly on extrasynaptic receptors. Meso-di-GABA is assumed to block synaptic receptors and to activate non-synaptic receptors while C-9 seems to act mainly as a blocker of glutamate action on non-synaptic receptors.

Amino Acids, Diamino↗