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G Hoyle

Publications and source records attributed to G Hoyle.

18 recordsLinked to original sources
PubMed1986

Glial cells of an insect ganglion.

The rapid development of the study of insect neurobiology, which is currently occurring principally because individual neurons can be re-identified and because their activities can be recorded in situ and related to behavior, is generating a demand for more knowledge concerning insect glial cells and their functional relationships with neurons. This study examines the ultrastructure of glial cells in locust metathoracic ganglia in relation to general locale within the ganglion and also to specific identified neurons and neuron types. Seven major types of glial cell form are recognized, with subdivisions, requiring a new scheme for classification. Glial invaginations into neurons are of four different kinds: regular, chunky, filigree, and ridge (found only at axon hillocks). They also range from only intrusive to fully reciprocal. In addition, some neurons make projections of various lengths into surrounding glia and between neighboring neuron somata, and some glia make long, branched projections into other glial cells. The differences show that insect glial cells develop highly specific functional specializations; they may not be interchangeable. The complexity and intimacy of relationships of glia with neurons suggest that some glial cells may have roles other than that of nursemaids, possibly in modulation of behavior-determining neural activity, and in learning and other adaptive acts.

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PubMed1986

Functional morphology of insect neuronal cell-surface/glial contacts: the trophospongium.

Ultrastructural studies were carried out on the surfaces of insect nerve cell bodies. Some of the neurons were identified, by using physiological criteria, before filling with dye. Their surface patterns were compared, to provide data needed for understanding dynamic relationships with glial cells, in the trophospongium. The data are also needed in connection with interpretation of electrical signals recorded from the somata and of their roles in integration and in learning and memory. The surfaces were found to be extremely complex and also varied, even for neurons of comparable size and function, as well as for different regions of the same neuron, suggesting that the surface is constantly changing as the neuron receives food and loses waste. There is a variety of cytoplasmic types of invagination of neuron somata by glial processes. The invaginations were classified into four easily recognized types: regular, chunky, filigree, and ridge (present only in axon hillock regions). Motor neurons also make reciprocal invaginations into the glial cells that surround them. Some of these extend for distances up to 40 microns from the surface. The effective surface area is increased, compared with that calculated for a smooth surface, as a result of the invaginations, by from as little as 5% for a small interneuron to as much as 12-fold for a large motor neuron. The axon hillock region of all types of neurons is heavily invaginated.

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PubMed1979

Neuromuscular transmission in Peripatus.

The electrical and mechanical responses of body, leg and jaw muscle of Peripatus to electrical excitation of their motor-nerves were examined. A small twitch was obtained from each muscle, whose strength increased stepwise with increasing stimulus strength. In jaw and body muscles as many as ten increments in height were obtained with increasing stimulus strength. Only a single twitch height was obtained from the claw retractor muscle. Tetanus:twitch ratio under supraminal stimulation was less than 2:1 for jaw muscles, about 50:1 for the claw retractor and about 6:1 for muscles moving the legs. The jaw-muscle twitch duration was 0.6 s, that for the leg muscles 1.2 s and for body muscles about 3.0 s. Large miniature junctional potentials were frequently recorded regardless of electrode location. Responses to neural stimulation consing stimulus strength, generally with three steps. With repetitive stimulation, facilitation of the second and third junctional potentials occurred, plus summation. A few fibres gave spikes to a single shock: most gave a few spikes sporadically, during repetitive stimulation only. No abrupt tension increments occurred in whole muscles when individual fibres spiked. We saw no evidence for peripheral inhibitory axons. The excitation of Peripatus muscle is by local graded junctional potentials at distributed nerve-on-muscle fibre synapses, together with action potentials. The latter are initiated only by larger junctional potentials compounded of multiple smaller ones summated and/or facilitated. The details of neuromuscular physiology are not compatible with the phylogenetic status commonly proposed for Peripatus.

Action Potentials↗
PubMed1978

The dorsal, unpaired, median neurons of the locust metathoracic ganglion.

Neurons having large cell bodies in the anterior dorsal median cluster in the metathoracic ganglion of the locust Schistocerca gregaria and the grasshopper Romalea microptera were studied by direct dye injection and reverse filling combined with elyctrical stimulation and recording. Eight, possibly nine, are of the unpaired type, with a T branch leading into left and right axons that leave the ganglion to terminate in muscles. Another six are probably paired, and may be interneurons. Five of the 8 or 9 unpaired neurons have one axonal branch in both N4 and N5, on both sides: the others have but a single branch. One of the nine, DUMETi, has left and right axons exclusively innervating the jumping muscles, and another, DUMDL, has left and right axons exclusively innervating the dorsal longitudinal flight muscles. Neither the locations, sizes or numbers of somata, nor their locations were as constant as is the case for ordinary ventral motoneurons.

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PubMed1978

Intrinsic rhythm and basic tonus in insect skeletal muscle.

The jumping muscle of orthopterous insects contains fibres that possess an intrinsic rhythm (IR) of slow contraction. The contributing fibres are generally synchronized, but as many as three or four pacemakers are present. The frequency, amplitude and duration of IR contractions fluctuate erratically over a 24 h period. Metathoracic DUM neurone bursts suppress IR for a few minutes. Other, unidentified dorsal neurones enhance its amplitude. In addition to IR, the extensor tibiae shows intrinsic basic tonus (BT). BT is relaxed for several s by low-frequency burst output from unidentified metathoracic dorsal neurones. DUM neurone bursts may enhance extensor BT, relax it, or leave it unaffected. The effects on IR of various regimes of activity in the slow extensor tibiae (SETi) and the common inhibitor (CI) axons were examined. CI affects IR when stimulated at frequencies above 2 Hz. It causes amplitude depression and reduced duration of individual IR contractions as well as increased frequency. At 30 Hz and above, CI completely suppresses IR. An enhanced IR contraction starts within a few milliseconds of the termination of a CI train. At low frequencies (below 10 Hz) SETi causes increased frequency and decreased amplitude of IR, with a depressed IR contraction following cessation of the SETi burst. At frequencies above 15 Hz the SETi-evoked contraction dominates tension development, though IR summates with it during the rising phase. In quiescent preparations not showing IR, SETi stimulation at 10 Hz often started up IR. Single SETi or FETi impulses can initiate an IR contraction, and cause altered phasing, with up to a quintupling of frequency. After a critical period has elapsed following the onset of an IR contraction, a single single impulse in any one of the three axons will terminate it abruptly. The early termination is followed by a reduced interval which is proportional to the reduced IR contraction time. The rhythm of accumulated readiness to go into an IR contraction is independent of the pacemaker rhythm that initiates the contraction.

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PubMed1978

Distributions of nerve and muscle fibre types in locust jumping muscle.

Muscle fibres of the locust extensor tibiae (jumping muscle) were examined by interference microscopy and by electron microscopy. The electrical responses of single fibres and the mechanical responses of bundles or selected regions to the nerve fibres were examined. Four axons innervate the muscle: fast (FETi), slow (SETi), common inhibitor (CI) and dorsal unpaired median (DUMETi). Their distributions were examined by combined electrophysiological tracing and EM sectioning. The mean diameter of muscle fibres in different regions varies from 40 to 140 micrometer and is related to the local leg thickness rather than muscle fibre type. The fine structure of a fibre is related to its innervation. Fibres innervated by FETi but not SETi are of fast type ultrastructurally. Fibres innervated by SETi but not by FETi are of slow type ultrastructurally. Fibres innervated by both axons are generally intermediate between the extremes though more nearly of fast type than slow. Distal slow muscle fibres have much slower relaxation rates than do proximal ones. The most proximal bundles are of mixed muscle fibre type. There is an abrupt transition from a mixed population to homogeneous fast type, in the muscle units immediately distal to the most proximal bundles. This transition is associated with the presence of DUMETi terminals on some of the fibres distal to the transition point. There are no SETi endings on these same fibres. Fibres innervated by both SETi and FETi are scattered throughout the leg, but are commonest in the dorsal bundles. The percentage of these increases progressively passing distally. The most distal muscle fibres are innervated by SETi but not by FETi. It is concluded that different regions of the muscle will play different roles functionally since they are differentially sensitive to the pattern of SETi discharge.

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PubMed1975

Evidence that insect dorsal unpaired medican (DUM) neurons are octopaminergic.

The dorsal unpaired median neuron innervating the extensor tibiae (DUMETi) of locusts and grasshoppers, as well as some other DUM neurons, cause long-term inhibition of the slow intrinsic rhythm of contraction of the muscle by releasing a neurohumoral agent. Large, (600 - 1900 A), dense-core vesicles are present in the nerve terminals. The inhibitory action is mimicked by infusioninto the leg of a minute (0.01 ml.) drop of locust saline containing a very low concentration (10(-6)M) of dopamine or noradrenaline, or an extraordinarily low concentration of octopamine (2.5 x 10(-9) M). The amplitude and frequency of the contractions slowly return to normal. Neither the cell body nor the neuron fluoresces with the Falck-Hillarp treatment, even after a period of ligature has caused an accumulation of vesicles. Octopamine does not fluoresce with this treatment. Accordingly, it is suggested that this neuron, and the other efferent DUM neurons, are octopaminergic.?23Author

Action Potentials↗
PubMed1975

Synthesis of octopamine by insect dorsal median unpaired neurons.

Dorsal unpaired median (DUM) neurons of locusts and grasshoppers inhibit the instrinsic rhythm of contraction of metathoracic extensor tibia muscle fibers. This physiological action is mimicked by very low concentrations of octopamine and by higher concentrations of dopamine and noradrenaline. We have examined the synthesis of biogenic amines from tritiated tyrosine by these neurons. DUM cell bodies and a peripheral nerve containing the DUM axon which terminates in the extensor tibia both produced octopamine, but neither noradrenaline nor dopamine synthesis was detected. The observations support the suggestion that the dorsal unpaired median neurons are octopaminergic.

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PubMed1973

Ultrastructure of barnacle giant muscle fibers.

Increasing use of barnacle giant muscle fibers for physiological research has prompted this investigation of their fine structure. The fibers are invaginated by a multibranched system of clefts connecting to the exterior and filled with material similar to that of the basement material of the sarcolemmal complex. Tubules originate from the surface plasma membrane at irregular sites, and also from the clefts They run transversely, spirally, and longitudinally, making many diadic and some triadic contacts with cisternal sacs of the longitudinal sarcoplasmic reticulum. The contacts are not confined to any particular region of the sarcomere. The tubules are wider and their walls are thicker at points of contact with Z material. Some linking of the Z regions occurs across spaces within the fiber which contain large numbers of glycogen particles. A-band lengths are extremely variable, in the range 2.2 microm-20.3 microm (average 5.2 microm) Individual thick filaments have thin (110 A) hollow regions alternating with thick (340 A) solid ones. Bridges between thick filaments occur at random points and are not concentrated into an M band The thin:thick filament ratio is variable in different parts of a fiber, from 3:1 to 6:1. Z bands are basically perforated, but the number of perforations may increase during contraction.

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