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Biomedical subjects

M Burrows

Publications and source records attributed to M Burrows.

At least 91 records · Page 5Linked to original sources
PubMed1981

Input and output synapses on identified motor neurones of a locust revealed by the intracellular injection of horseradish peroxidase.

Physiologically characterised motor neurones in the thoracic ganglia of the locus were injected with horseradish peroxidase in order that the spatial relationship between their input and output synapses could be observed with the electron microscope. A modification in the development procedure for the peroxidase ensured that the internal fine structure of the stained neurones was not obscured by the diaminobenzidine reaction product. Input and output synapses may occur within 1 micrometer of each other on the neuropilar processes of the motor neurones. This supports physiological evidence that motor neurones may be involved in local circuit interactions within the thoracic ganglia.

Action Potentials↗
PubMed1981

The effects of topical and systemic glucocorticosteroids on DNA synthesis in different tissues of the hairless mouse.

Two topical corticosteroids, clobetasol propionate and clobetasone butyrate, have been studied in hairless mice for their effects on DNA synthesis in the epidermis, thymus and spleen. Following topical application, both clobetasol propionate and clobetasone butyrate showed significant activity at the site of application throughout the range of concentrations tested (20 microliters; 0.0001-0.1%; 20 ng to 20 micrograms). However, whereas 20 ng clobetasol propionate also elicited significant effects in the distal (untreated) epidermis and the thymus, more than 2 micrograms of clobetasone butyrate were required to produce similar effects in these tissues. This finding was supported by the results obtained following intravenous administration of equivalent doses (0.01 and 0.001%; 200 microliters dose) of the same two steroids. Only clobetasol propionate showed significant activity in the epidermis and thymus. Clobetasone butyrate showed slight, non-significant effects in the epidermis at the highest concentration (200 microliters; 0.01%), but not in the thymus or spleen. An unexpected finding was that the effects following intravenous injection were generally lower than those following topical application. In conclusion, these results establish that (a) effects on DNA synthesis in the epidermis at a site distal to the application site are indicative of systemic activity from topically applied corticosteroids, (b) the thymus is especially sensitive to corticosteroids eliciting systemic effects and (c) an equivalent dose of a topical corticosteroid administered intravenously produces less inhibition of thymic and epidermal DNA synthesis than the same dose applied topically.

Administration, Topical↗
PubMed1980

The control of sets of motoneurones by local interneurones in the locust.

1. A motoneurone innervating a muscle in a hind leg of a locust is controlled in a graded manner by many non-spiking, local interneurones. There is overlap and fractionation of control between these interneurones. Some interneurones depolarize the motoneurone over part of its range, others hyperpolarize it, whilst some do both. 2. The interneurones organize the small number of motoneurones that innervate one muscle into overlapping sets of various sizes. A motoneurone can therefore be activated individually or in particular combinations with its fellow motoneurones. 3. The motoneurones innervating two muscles of a joint are also organized into overlapping sets by many local interneurones. This permits the motoneurones to the two muscles to be activated reciprocally, together, or independently. 4. One interneurone can elicit a co-ordinated movement of one, two or even three joints in a hind leg that are components of the normal behaviour of the locust. 5. A single interneurone acting alone does not usually elicit the maximum output from one motoneurone, nor a complete piece of behaviour. A stronger contraction of a muscle and a more complete movement results from the action of groups of interneurones. 6. It is suggested that local interneurones, exerting graded control over motoneurones are a major element in the organization of motor patterns in the locust.

Animals↗
PubMed1979

Synaptic potentials effect the release of transmitter from locust nonspiking interneurons.

An excitatory synaptic potential in a local nonspiking interneuron of a locust is able to effect the release of chemical transmitter. The consequence is that a discrete inhibitory synaptic potential is evoked in an identified postsynaptic motoneuron. These local interactions between interneurons and motoneurons are of behavioral significance in that they ensure the correct operation of a resistance reflex.

Action Potentials↗
PubMed1979

The morphology of local non-spiking interneurones in the metathoracic ganglion of the locust.

The morphology is described of a number of non-spiking interneurones in the metathoracic ganglion of the locust that control motor neurones innervating muscles in the coxa and femur of a hind leg. The non-spiking interneurones are penetrated with microelectrodes, physiologically characterized, injected with cobalt, and the stain subsequently intensified with silver. The interneurones have diverse shapes but all are local, intraganglionic interneurones. Their cell bodies are 10-20 micrometer in diameter and lie in either the ventral or dorsal layers of cell bodies that form a cortex around the ganglion. The branches of the interneurones are profuse and overlap those of the motor neurones that they affect. On interneurone may have branches in both the most ventral and the most dorsal areas of the neuropile. Most interneurones have branches only in one half of the ganglion, but one interneurone has extensive and asymmetrical regions of branches in both halves of the ganglion (fig. 4). Similar physiological effects can be mediated by interneurones with distinct morphologies. For example, the single slow extensor motor neurone is excited by six distinct morphological types of interneurones (figs. 10-13). It is suggested that as many as 65% of the neurones within a ganglion may be local interneurones, many of which in turn may be non-spiking.

Action Potentials↗
PubMed1979

Graded synaptic interactions between local premotor interneurons of the locust.

1. Graded synaptic interactions are revealed between pairs of nonspiking, local interneurons in the metathroracic ganglion of the locust. These interneurons drive motor neurons innervating muscles of a hindleg. 2. All the interactions found between the interneurons are inhibitory and one way. Synaptic transmission is effected by the graded release of chemical transmitter. Some of the connections are apparently direct. One local interneuron can, therefore, exert a graded control over the membrane potential of another local interneuron. 3. There are inhibitory connections between local interneurons that excite the same motor neuron, between local interneurons that excite antagonistic motor neurons, and between local interneurons that excite motor neurons to muscles moving different joints of a hindleg. 4. Other pairs of interneurons, which are not connected, may be driven by common synaptic inputs. Their outputs add together at the level of the motor neurons to produce effects that are greater than the sum of their individual effects. 5. It is proposed that graded interactions between these local interneurons are an essential element in the generation of motor patterns.

Electrophysiology↗
PubMed1978

Graded synaptic transmission between local interneurones and motor neurones in the metathoracic ganglion of the locust.

1. In the metathoracic ganglion of the locust some neurones can effect changes in the membrane potential of identified post-synaptic motor neurones without themselves spiking. 2. These 'non-spiking' neurones have processes only within the metathoracic ganglion, and therefore are local intraganglionic interneurones. 3. The absence of spikes in the interneurones reflects their normal physiological state and is not due to the experimental conditions. 4. When the interneurones are depolarized by the injection of current pulses lasting several hundred milliseconds, post-synaptic motor neurones are either depolarized, or hyperpolarized, for the duration of the pulse. 5. The magnitude of the change in post-synaptic voltage is graded according to the amount of presynaptic current. 6. A number of physiological tests indicate that the graded effects upon motor neurones are mediated by chemical synaptic transmission. For example, an evoked hyperpolarization of a motor neurone can be reversed in polarity by simultaneously hyperpolarizing the motor neurone with injected current. 7. At their resting potential some interneurones tonically release sufficient transmitter to have a measurable post-synaptic effect. The injection of depolarizing and hyperpolarizing currents into these interneurones effects opposite changes in post-synaptic potential. 8. Other interneurones must be depolarized from resting potential before a post-synaptic effect is observed, and hyperpolarizing currents have no post-synaptic effect. In these interneurones it is estimated that a depolarization of only 2 mV is sufficient to effect the release of transmitter. 9. The membrane potentials of non-spiking interneurones can fluctuate by as much as 15 mV during active movements of the hind legs and individual p.s.p.s as large as 5 mV can be recorded. Therefore, summed p.s.p.s or even single ones are expected to be the electrophysiological signals effecting transmitter release from these interneurones.

Action Potentials↗
PubMed1978

Sources of variation in the output of locust spiracular motoneurones receiving common synaptic driving.

1. The closer muscles of the left and the right spiracles of a thoracic segment are both innervated by two motoneurones, which spike in a variety of patterns during expiration. This paper seeks to explain the origin of these patterns. 2. No direct coupling between the two motoneurones is revealed. In an isolated thoracic ganglion both motoneurones spike at different frequencies with no tendency for their spikes to become synchronized. 3. The two closer motoneurones in one segment receive common, patterned depolarizing synaptic potentials during expiration caused by interneurones relaying information from the metathoracic ganglion. 4. The closer motoneurones of all the thoracic segments receive the same pattern of synaptic potentials from these interneurones. Despite this, the spiracles of one segment may remain shut while those on other segments continue to open and close rhythmically. 5. The interplay between common synaptic driving, the threshold of the motoneurones for spike initiation, and the tendency for a motoneurone to spike at a particular frequency even in the absence of interneuronal driving, explains the various patterns of spikes during expiration. Common synaptic driving imposes the same basic pattern of commands on all the motoneurones, but the individual motoneurones determine the final pattern of motor spikes. 6. To be effective in producing a patterned output, an input pattern must operate within narrow limits on either side of the threshold of the motoneurone. If the depolarization is too large, a high frequency of unpatterned spikes will result; if too small, then either there will be no output or a low frequency of spikes will result whose patterning will be affected by other inputs.

Action Potentials↗
PubMed1977

The locust jump. I. The motor programme.

A motor programme is described for defensive kicking in the locust which is also probably the programme for jumping. The method of analysis has been to make intracellular recordings from the somata of identified motornuerones which control the metathoracic tibiae while defensive kicks are made in response to tactile stimuli. Three stages are recognized in the programme. (1) Initial flexion of the tibiae results from the low spike threshold of tibial flexor motorneurones to tactile stimulation of the body. (2) Co-contraction of flexor and extensor muscles followa in which flexor and extensor excitor motoneurones spike at high frequency for 300-600 ms. the tibia flexed while the extensor muscle develops tension isometrically to the level required for a kick or jump. (3) Trigger activity terminates the co-contraction by inhibiting the flexor excitor motorneurones and simultaneously exciting the flexor inhibitors. This causes relaxation of the flexor muscle and allows the tibiae to extend. If the trigger activity does not occur, the jump or kick is aborted, and the tibiae remain flexed.

Action Potentials↗
PubMed1977

The locust jump. II. Neural circuits of the motor programme.

1. Neural circuits which co-ordinate the motorneurones of the meta-thoracic tibiae of the locust in jumping and kicking have been investigated. 2. The fast extensor motorneurone is reflexly excited by the subgenual organ, by a network of cuticle strain receptors, and by Brunner's organ. The subgenual organ and the cuticle strain receptors are excited by tension in the extensor muscle and mediate a positive feedback which could help to produce the burst of fast extensor spikes which precedes a jump or kick. Brunner's organ is stimulated by pressure from the flexed tibia, and will be excited by the initial flexion and throughout the co-contraction phase of a kick. 3. A central excitatory connexion from the fast extensor to the slow extensor ensures that extensor muscle tension is as great as possible early in the co-contraction phase of a kick. 4. A central excitatory connexion from the fast extensor to flexor motorneurones is confirmed. This ensures that flexor muscle tension is great enough to keep the tibia flexed when the extensor muscle tension starts to develop before a jump or kick. 5. Reflex excitation of flexor motorneurones occurs in response to an extensor muscle twitch when the tibia is flexed. This helps to maintain the flexor connexion. 6. A receptor, the 'lump receptor', which is stimulated by flexor muscle tension only when the tibia is flexed, can inhibit the flexor motorneurones and may activate the trigger system which allows the extension of the tibia in a jump or kick. 7. Recptors in the suspensory ligaments of the joint inhibit the fast extensor when the tibia extends.

Action Potentials↗
PubMed1975

Monosynaptic connexions between wing stretch receptors and flight motoneurones of the locust.

1. The connexions between stretch receptors of the wings and motoneurones innervating flight muscles have been studied anatomically and physiologically. 2. Filling with cobaltous chloride shows that the single neurone of a forewing stretch receptor has a complex pattern of branches within the mesothoracic ganglion and branches which extend into the pro- and meta-thoracic ganglia. The single neurone of a hindwing stretch receptor has extensive branches in the metathoracic ganglion and branches in themesothoracic ganglion. The branches of both receptors are confined to the ipsilateral halves of the ganglia. 3. A stretch receptor gives information about the velocity and extent of elevation of a wing. 4. Each spike of a forewing stretch receptor casuses an EPSP in ipsilateral mesothoracic depressor motoneurones and an IPSP in elevators. The connexions are thought to be monosynaptic for the following reasons. The EPSPs in the first basalar (depressor) motoneurone follow each spike of the stretch receptor at a frequency of 125 Hz and with a constant latency of about 1 msec. In a Ringer solution containing 20 mM-Mg2+ the amplitude EPSP declines gradually. The IPSP'S upon elevators have similar properties but occur with a latency of 4-6 msec. 5. The connexions therefore comprise a monosynaptic negative feed-back loop; elevation of the wing excites the stretch receptor which then inhibits the elevator motoneurones and excites the depressors. 6. A hindwing stretch receptor synapses upon metathoracic flight motoneurones in the same way, causing EPSPs in depressor and IPSPs in elevator motoneurones. 7. No connexions of either fore- or hindwing stretch receptors have been found with contralateral flight motoneurones. 8. Interganglionic connexions are made by both receptors. For example, both fore- and hindwing stretch receptors cause EPSPs upon the meso- and metathoracic first basalar motoneurones. 9. Stimulation of the axon of a stretch receptor with groups of three stimuli repeated every 50-100 msec thus simulating the pattern which it shows during flight, causes subthreshold waves of depolarization in depressor motoneurones. When summed with an unpatterned input, the stretch receptor is able to influence the production of spikes in motoneurones on each cycle. During flight, it is expected that the stretch receptor will influence the time at which a motoneurone will spike and hence have an effect on the amplitude of the upstroke and upon the phase relationship between spikes of motoneurones.

Animals↗
PubMed1975

Co-ordinating interneurones of the locust which convey two patterns of motor commands: their connexions with flight motoneurones.

1. Some flight motoneurones receive two superimposed rhythms of depolarizing synaptic potentials when the locust is not flying; a slow rhythm which is invariably linked to the expiratory phase of ventilation, and a fast rhythm with a period of about 50 ms which is similar to the wingbeat period in flight. 2. By recording simultaneously from groups of motoneurones, the synaptic potentials which underly these rhythms have been revealed in 30 flight motoneurones in the three thoracic ganglia. The inputs occur in elevator motoneurones and some depressors but are of lower amplitude in the latter. The inputs have not been found in leg motoneurones. 3. The rhythmic depolarizations are usually subthreshold but sum with sensory inputs to evoke spikes in flight motoneurones at intervals equal to or multiples of the wingbeat period in flight. 4. Both rhythms originate in the metathoracic ganglion and are mediated by the same interneurones. They can be adequately explained by supposing that there are two symmetrical interneurones which each make widespread connexions with left and right flight motoneurones in the three ganglia. 5. The slow rhythm is coded in the overall burst of interneurone spikes during expiration and the fast rhythm in the interval between the spikes of a burst.

Action Potentials↗
PubMed1975

Co-ordinating interneurones of the locust which convey two patterns of motor commands: their connexions with ventilatory motoneurones.

1. The interneurones which make widespread connexions with flight motoneurones also synapse upon ventilatory motoneurones so that in all 50 motoneurones receive synapses. They influence three aspects of ventilation; (a) the closing and opening movements of the thoracic spiracles, (b) some aspects of abdominal pumping movements and (c) the recruitment of some motoneurones controlling head pumping. 2. The two closer motoneurones of a particular thoracic spiracle receive the same excitatory synaptic inputs (EPSPs) during expiration. The EPSPs match those in appropriate flight motoneurones. 3. The closer motoneurones of each thoracic spiracle whose somata are in the pro-, meso- or metathoracic ganglia all receive the same excitatory synaptic inputs. These inputs are an adequate explanation of the pattern of spikes in the closer motoneurones. Both the slow ventilatory and fast rhythms of synaptic potentials are expressed as spikes; the slow as the overall expiratory burst of spikes and the fast as the groups of spikes within that burst. This establishes a ventilatory function for the interneurones. All thoracic closer motoneurones therefore receive the same excitatory commands which will tend to synchronize the movements of each spiracle. 4. Spiracular opener motoneurones are inhibited during expiration, their IPSPs matching the EPSPs in flight or closer motoneurones. Therefore the interneurones have reciprocal effects on the antagonistic motoneurones of the spiracles. 5. The interneurones synapse upon some motoneurones which control the pumping movements of the abdomen and which have their somata in the metathoracic or first unfused abdominal ganglion. Motoneurones in four separate ganglia therefore receive inputs from these interneurones. 6. The interneurones also synapse upon motoneurones which control an auxiliary form of ventilation, head pumping.

Action Potentials↗