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A H Watson

Publications and source records attributed to A H Watson.

At least 37 records · Page 2Linked to original sources
PubMed1993

GABA-immunoreactivity in processes presynaptic to the terminals of afferents from a locust leg proprioceptor.

Individually labelled sensory neurons from the femoral chordotonal organ, a proprioceptor at the femoro-tibial joint of a locust hindleg, were analysed by intracellular recording, and by electron microscopical immunocytochemistry to reveal the arrangement of their input and output synapses and to determine whether the input synapses were GABAergic. Intracellular recordings from these sensory neurons show spikes superimposed on a barrage of synaptic potentials during movements of the femoro-tibial joint. These synaptic inputs can be mimicked by GABA. Input synapses are made onto the vesicle-containing terminals of afferents and are often closely associated with the output synapses. By contrast, the axons of the afferents in the neuropil have no vesicles and neither make nor receive synapses. The input synapses to the afferent terminals are made from processes typically a few microns in diameter, whereas the output synapses are made onto much smaller processes of only 0.1-0.2 micron. Input synapses at which an afferent terminal is the only postsynaptic element are common. Where the synapse is dyadic the second postsynaptic element does not usually appear to be a chordotonal afferent. The output synapses from the afferent terminals are usually dyadic. At 78% of the input synapses, the presynaptic neurite showed immunoreactivity to a GABA antibody, supporting the physiological evidence that the presynaptic effects can be mediated by the release of GABA. The remaining (22%) immunonegative synapses are intermingled with those showing GABA immunoreactivity, but their putative transmitter is unknown. These morphological observations suggest that the presynaptic control of the chordotonal afferents is largely mediated by GABAergic neurons, but because other types of neuron also appear to be involved, presynaptic modulation may be more complex than has yet been revealed by the physiology.

Action Potentials↗
PubMed1993

Neonatal cross-infection with Listeria monocytogenes.

Transmission of Listeria monocytogenes by food continues to cause concern. Even so, this is not the only means of transmission and neonatal hospital-acquired infection has been well recorded. We report here two cases of perinatal listeriosis one of which was likely to have been due to cross-contamination in a Special Care Baby Unit (SCBU) with equipment acting as the vehicle.

Cross Infection↗
PubMed1992

Presynaptic modulation of sensory afferents in the invertebrate and vertebrate nervous system.

1. Ultrastructural examination of the central terminals of sensory afferent neurons in both invertebrates and vertebrates demonstrates that the synapses that form the substrate for presynaptic inhibition and facilitation are almost universally present. 2. Presynaptic modulation of afferent input acts in many ways which tailor the inflow of sensory information to the behaviour of the animal, effectively providing a means of turning this on and off, or of combining information of the same or different modalities to refine responsiveness or clarify ambiguity. 3. Presynaptic modulation may act in several different roles on the same afferent. 4. A comparison of the mechanisms of presynaptic inhibition in different animals demonstrates the likelihood of a variety of common mechanisms, several of which may act simultaneously on the same terminal. These include changes in the conductance of the afferent membrane to Cl-, K+ and Ca2+ ions, in addition to less well understood mechanisms that directly affect transmitter release. 5. A single transmitter can produce several effects on a terminal through the same or different receptors. 6. Ultrastructural studies of afferent terminals reveal that only a proportion of boutons on a given afferent may receive presynaptic input and that this may depend on the region of the nervous system in which these are found or on the identity of the postsynaptic neurons contacted. 7. The synaptic relationships of afferent terminals can be complex. In invertebrates different types of presynaptic neuron may interact synaptically, as may postsynaptic dendrites in vertebrates. 8. Axons presynaptic to afferent terminals in vertebrates frequently synapse also with dendrites postsynaptic to the afferents. 9. In both invertebrates and vertebrates reciprocal interactions between afferents and postsynaptic neurons are seen. 10. Ultrastructural immunocytochemistry reveals the likely dominance of GABA as an agent of presynaptic inhibition but also demonstrates the possible presence of other transmitters some of whose roles are less completely understood.

Animals↗
PubMed1991

GABA and glutamate-like immunoreactivity in processes presynaptic to afferents from hair plates on the proximal joints of the locust leg.

Hair plate afferents from coxal group 1 on the meso- and prothoracic legs of the locust were backfilled with cobalt salts or HRP for light and electron microscopy. The distribution of the terminal branches of the afferents is described from wholemount preparations and from 150 microns thick slices through the ganglion. Identified branches from the slices were sectioned for electron microscopy and examined for the presence of input and output synapses. Both were found in close proximity on small-diameter varicose branches in all parts of the arborization. Immunocytochemistry using antibodies against GABA and glutamate was used to try to identify putative transmitters in processes presynaptic to the afferents. Ninety-three percent of processes presynaptic to the hair plate afferents were clearly immunoreactive for GABA and only 7% appeared unlabelled. Most neuronal processes in the vicinity of afferent terminals were also immunoreactive for GABA, but a small number of glutamate-immunoreactive processes were found in intimate contact with afferents and one of these was demonstrated to be presynaptic. Processes postsynaptic to the afferents were of small diameter (mean = 0.28 micron) and were not found to be immunoreactive for GABA.

Animals↗
PubMed1991

Quantitative analysis of the ultrastructural distribution of GABA-like immunoreactivity in the intermediate and medial part of hyperstriatum ventrale of chick.

The intermediate and medial part of the hyperstriatum ventrale of the chick telencephalon plays a crucial role in the learning processes of imprinting. The distribution within the intermediate and medial part of the hyperstriatum ventrale of the neurotransmitter gamma-amino butyric acid was studied with light and electron microscopy using an antibody against this amino acid. The antibody labelled 18.4% of neuronal somata. GABA-labelled terminals made symmetrical synapses onto somata and dendrites of labelled and unlabelled neurons. Labelled somata received about three times as many synaptic boutons as unlabelled somata. Approximately 21% of synaptic terminals on labelled somata were themselves labelled; unlabelled somata received a higher proportion (37.6%) of such terminals. Most labelled terminals synapsing with dendrites were confined to the shafts; very few labelled terminals contributed to axospinous synapses. Synaptic contacts made on dendritic shafts by labelled boutons were intermingled with symmetrical and asymmetrical contacts from non-immunoreactive terminals. The proportion of labelled terminals received by labelled dendrites (33.1%) was approximately twice that received by unlabelled dendrites (15.9%). Labelled neurons therefore received a higher proportion of labelled terminals on their dendrites and a lower proportion on their somata compared with unlabelled neurons. No immunoreactivity was seen in glial cells or ependyma.

Animals↗
PubMed1990

GABA-like immunoreactivity in a population of locust intersegmental interneurones and their inputs.

Intracellular labelling of locust intersegmental interneurones with lucifer yellow or horseradish peroxidase was carried out in combination with light and electron microscope immunocytochemistry by using an antibody raised against gamma amino butyric acid (GABA). Fifteen percent (four out of 27) of intracellularly stained interneurones showed GABA-like immunoreactivity. This is in agreement with previous physiological observations that 20% of the interneurones in this population make inhibitory output connections in the metathoracic ganglion. GABA-like immunoreactivity was also found in processes presynaptic to the interneurones in the mesothoracic ganglion. The presence of such immunoreactive inputs onto the intersegmental interneurones correlates well with physiological evidence that their receptive fields are in part shaped by direct input from GABA-ergic spiking local interneurones.

Afferent Pathways↗
PubMed1990

Substance P antibody reveals homologous neurons with axon terminals among somata in the crayfish and crab brain.

In the search for particular neurons that stain selectively and can be identified, the cerebral ganglia (brains) of the crayfish Cherax destructor and the crab Leptograpsus variegatus were immunocytochemically treated with a monoclonal antibody raised against substance P. Four large neurons in the cerebral ganglion of the crayfish and crab label selectively with a monoclonal antibody raised against substance P. Two of the large neurons have their cell bodies in the protocerebrum and two in the deutocerebrum in both animals. Each protocerebral cell in both animals projects through the ipsilateral and contralateral olfactory lobes to end among the lateral cell somata of the olfactory lobe and not in the neuropile. Electron micrographs show the presence of synapses within the cell somata area and on the cell somata themselves. Each deutocerebral cell in both animals projects only ipsilaterally and ends within the neuropile of the olfactory lobes. The immunoreactivity to substance P antibody and the shapes and the unique projections of the four cells suggest that they are homologous in the two species. Synaptic connections between axons and cell somata are rare in the arthropods but have been found on the Kenyon cells of the mushroom bodies of Limulus. This raises questions about homologies between the crustacean olfactory lobe and the mushroom bodies of Limulus and insects.

Animals↗
PubMed1989

Regional specialisation for synaptic input and output on a locust intersegmental interneurone with multiple spike-initiating zones.

A4I1 is a long intersegmental interneurone whose soma lies in the fourth abdominal ganglion and whose axon ascends through, and branches in, the thoracic and suboesophageal ganglia and the brain. It receives sensory input in the prothoracic ganglion from wind-sensitive hairs on the head and prosternum and in the fourth abdominal ganglion from cercal afferents (Pflüger: J. Comp. Neurol. 222:343-357, '84). Spikes can be initiated from both of these ganglia. In the present study the neurone was stained by intracellular injection of cobalt salts for light microscopy and of horseradish peroxidase for electron microscopy. The morphology of its neurites in the thoracic and fourth abdominal ganglia and the distribution of synapses upon them could then be observed and correlated. In the fourth abdominal ganglion the neurone receives input synapses but makes no outputs. In each thoracic ganglion the neurone has fine, varicose ventral neurites and thicker dorsal neurites. The ventral neurites are most abundant in the prothoracic ganglion where they receive only input synapses. In the meso- and metathoracic ganglia the ventral neurites also receive inputs, but in addition they make output synapses. In all three thoracic ganglia output synapses are abundant on the dorsal branches, but in the meso- and metathoracic ganglia a small number of inputs are also received here. The possibility that the function of the interneurone may not be the same in all of the thoracic ganglia is discussed in the light of its known physiological properties.

Action Potentials↗
PubMed1988

Distribution and morphology of synapses on nonspiking local interneurones in the thoracic nervous system of the locust.

The structure and distribution of synapses on nonspiking local interneurones in the metathoracic ganglion of the locust was revealed by electron microscopy following intracellular injection of horseradish peroxidase (HRP). Before staining, each interneurone was characterized physiologically as nonspiking and its output effects on motor neurones innervating muscles in a hindleg were investigated. Three nonspiking interneurones of different morphologies, each typical of a previously described population, were selected for detailed study. The first has a dorsal soma and ipsilateral neuropilar branches, the second a ventral soma and ipsilateral branches, and the third a ventral soma and contralateral branches. The somata have few trophospongial invaginations, and most of their volume is occupied by the nucleus. The initial parts of the primary neurites are either wrapped in glia or isolated in tracts from the neuropile and thus do not participate in synaptic interactions. Some of the larger secondary neurites are also wrapped in glia, but others both make and receive synaptic contacts. Output synapses have an array of some 500-1,600 round, agranular vesicles (diameter 47.0 +/- 5.7 nm; mean +/- S.D., n = 97) associated with a bar-shaped presynaptic density up to 0.3 micron long. Two postsynaptic processes, whose diameter can vary greatly, are usually associated with each presynaptic density. Processes making input synapses onto nonspiking local interneurones typically contain round, agranular vesicles and often make several contacts within a few microns. Serial reconstructions from one of the interneurones revealed input and output synapses intermingled on the larger processes with outputs dominating by a factor of 3:1, whereas on some of the thinner processes only input synapses are present. In the other two interneurones, however, both input and output synapses are present on the fine branches. No feature of the structure or distribution of synapses observed here on the nonspiking local interneurones distinguishes them from spiking neurones in the same ganglia.

Animals↗
PubMed1988

Structure and distribution of dorsal unpaired median (DUM) neurones in the abdominal nerve cord of male and female locusts.

Dorsal unpaired median (DUM) neurones in insects have been shown to modulate the activity of both skeletal and visceral muscle. It has been suggested that as a population they carry out a role analogous to that of the sympathetic nervous system in vertebrates; however, the extent of their distribution throughout the ventral nerve cord has not been assessed. This paper aims to fill this gap by systematically describing the number and morphology of DUM neurones in each of the abdominal ganglia of male and female locusts. To achieve this, the lateral nerves of each abdominal ganglion were backfilled to reveal the position of the somata of DUM neurones. To confirm their identity and reveal their structure, DUM somata were then impaled with microelectrodes and, after physiological characterization, the neurones were stained by intracellular injection with cobalt ions. In each of the first six abdominal ganglia of both sexes, two DUM neurones, one with axons in the tergal nerve and one with axons in the sternal nerve, were found. In the seventh abdominal, and the terminal, ganglion (composed of the eighth to eleventh neuromeres), there was considerable sexual dimorphism in DUM neurone distribution, which was most marked in those associated with some of the nerves innervating the genitalia. In the male, four clusters of somata in the seventh, eighth, and tenth segments have axons in the genital nerve. In the female, which lacks a genital nerve, clusters of DUM neurones, absent in the male, have axons in the seventh and eighth sternal nerves and the cercal nerve.

Animals↗
PubMed1988

Antibodies against GABA and glutamate label neurons with morphologically distinct synaptic vesicles in the locust central nervous system.

Antibodies raised against GABA and glutamate were used to stain sections through locust thoracic ganglia for light and electron microscopy. Using a peroxidase-antiperoxidase method for light microscopy, the GABA antibody was shown to label inhibitory motor neurons thought to use GABA as their neurotransmitter, and the glutamate antibody to label excitatory motor neurons thought to use glutamate. An immunogold method was used to reveal labelled neuropilar processes in the electron microscope. Each antibody specifically labels a particular population of processes. With the GABA antibody, labelling is equally clear whether the processes concerned contain synaptic vesicles or not and is strongly contrasted against very low background levels. With the glutamate antibody, most processes show some affinity for the antibody, probably reflecting the presence of metabolic glutamate, however one population can be clearly distinguished by the presence of a much greater density of gold particles over synaptic vesicles. In the locust it appears, therefore, that the antibody can distinguish clearly between the metabolic and neurotransmitter pools of glutamate. It has been proposed that synaptic vesicles in GABAergic neurons have a different shape to those in glutamatergic neurons. This was supported by the electron microscope immunocytochemistry. Those showing GABA-like immunoreactivity contain predominantly pleomorphic agranular vesicles approximately 21 x 30 nm in diameter. Those showing glutamate-like immunoreactivity contain round agranular vesicles of about 38 nm in diameter. The GABA antibody appears to label all processes containing pleomorphic agranular vesicles. By contrast, some processes containing round agranular vesicles are not labelled by the glutamate antibody, even though the vesicles they contain are statistically identical in size to those in labelled profiles. With neither antibody was the labelling of glial cells greater than the background level.

Animals↗
PubMed1987

Immunocytochemical and pharmacological evidence for GABAergic spiking local interneurons in the locust.

In the locust thoracic nervous system, spiking local interneurons within a ventral midline population are stained by a polyclonal antibody raised against GABA. Their cell bodies, their primary neurites in ventral commissure II, and their prominent neurites in the perpendicular tract linking ventral and dorsal fields of fine branches are all stained. Individual interneurons in this population were labeled with Lucifer yellow after their receptive fields had been determined physiologically. Alternate sections were stained with the antibody. Some, but not all, of the spiking local interneurons labeled with Lucifer yellow are also stained with the antibody. Apart from having somata that lie more posteriorly within the midline population, the antibody-stained interneurons cannot be distinguished on morphological or physiological grounds from those that are unstained. The way in which this cytochemical heterogeneity within an otherwise homogenous population might arise during development is discussed. A second group of spiking local interneurons with similar sensory input to that of the ventral midline population, but with cell bodies in the anterior lateral region of the ganglion and primary neurites in ventral commissure I, are not stained. Interneurons in the midline group receive direct inputs from sensory neurons and some directly inhibit particular leg motor neurons that mediate interjoint and tactile reflexes. Picrotoxin reversibly blocks the inhibition of the motor neurons and therefore abolishes these reflexes. Immunocytochemical and pharmacological experiments thus suggest that inhibition by some spiking local interneurons may be mediated by GABA.

Action Potentials↗
PubMed1986

Team approach to treatment of the posttraumatic stiff hand. A case report.

Posttraumatic hand stiffness is a common but complex problem treated in many general clinics and in hand treatment centers. Although much information is available regarding various treatment procedures, the use of a team approach to evaluate and treat hand stiffness has not been examined thoroughly in the Journal. The problems of the patient with a stiff hand include both physical and psychological components that must be addressed in a structured manner. The clinical picture of posttraumatic hand stiffness involves edema, immobility, pain, and the inability to incorporate the affected extremity into daily activities. In this case report, we review the purpose and philosophy of the team approach to hand therapy and the clarification of responsibilities for physical therapy and occupational therapy intervention.

Aged↗
PubMed1985

The distribution of synapses on the two fields of neurites of spiking local interneurones in the locust.

Spiking local interneurones in the metathoracic ganglion of the locust have two fields of neuropilar branches linked by a single process. One, with numerous fine neurites of relatively uniform diameter, is in a ventral area of neuropile where the afferents from hairs on a hind leg also terminate. The other, with sparser and varicose neurites, is in a more dorsal area of neuropile where the motor neurones of the leg muscles have many neurites. Physiological studies have shown that these interneurones receive direct inputs from some hair afferents and in turn synapse directly upon some leg motor neurones (Burrows and Siegler, '82; Siegler and Burrows, '83). The distribution of synapses in these two fields was revealed by injecting HRP intracellularly into an interneurone following its physiological characterization. In the ventral field, the majority of synapses are input synapses. Many are from profiles with round agranular vesicles of similar diameter to those of known afferents. Other presynaptic profiles contain pleomorphic agranular, or large round granular, vesicles. There are also some output synapses, each with only a small population of vesicles. Most input synapses are made onto small-diameter neurites, whereas the majority of outputs are made from the larger-diameter neurites. In the dorsal field, the majority of synapses are output synapses. They are made from vesicle-filled varicosities onto postsynaptic profiles of small diameter. A single varicosity can be the site of many output synapses. Input synapses are few in number, but occur close to the output synapses. The absence of varicosities in the ventral field cannot therefore be correlated with a lack of output synapses and while the dorsal varicosities can be the sites of output, they can also receive input synapses.

Action Potentials↗
PubMed1985

The morphology and ultrastructure of common inhibitory motor neurones in the thorax of the locust.

The morphologies of three common inhibitory motor neurones which innervate muscles of a hind leg and the homologous three neurones which innervate muscles in a middle leg are described in relation to known commissures, tracts, and areas of neuropile in their ganglia. The neurones were stained individually by the intracellular injection of cobalt, and the ultrastructure of common inhibitor 1 (CI1) in the metathoracic ganglion was revealed by the intracellular injection of horseradish peroxidase. Homologous inhibitory motor neurones in the meso- and metathoracic ganglia have similar shapes. CI1 has axons in nerves 3, 4, and 5, but common inhibitors 2 and 3 (CI2, CI3) have only a single axon in nerve 5. They nevertheless all share many features in common. All have large (60 70 micron diameter) cell bodies in the ventral cortex near the midline, well separated from those of the excitatory leg motor neurones. Their primary neurites run dorsally and laterally and send many fine branches into the dorsal and lateral neuropile, and some fine branches medially. None enter the ventral neuropile. CI1 and CI2 have a small branch that arises close to the cell body and arborises on either side of the midline. When examined with the electron microscope, CI1 was not found to make any output synapses, even though some of its fine branches are varicose and end in bulbous swellings. These were seen to be packed with mitochondria but not vesicles. Input synapses tend to be grouped together on the secondary neurites and, more especially, on the finer branches and their spines. The majority of processes presynaptic to CI1 contain round agranular vesicles.

Animals↗
PubMed1984

The dorsal unpaired median neurons of the locust metathoracic ganglion: neuronal structure and diversity, and synapse distribution.

Dorsal unpaired median ( DUM ) neurons are bilaterally symmetrical. A single primary neurite arises from the soma and runs anteriorly through the neuropil before dividing into two lateral neurites which pass to the nerve roots on each side of the ganglion. The primary neurite runs in one of two tracts, one of which lies further from the surface of the ganglion than the other. The primary neurites in the deeper tract belong to DUM1 , DUM5 and DUM3 ,4,5 neurons, and those in the more superficial tract, to DUM3 , DUM3 ,4 and DUM3 ,4,5 neurons. Previous studies have shown that in the developing embryonic nervous system the primary neurites of DUM neurons can also be observed to lie in one of two tracts, but these do not appear to correspond to those seen in the adult. The results described here differ further from those of other investigations of adult and embryonic locusts in that no DUM4 ,5 neurons were seen, but DUM3 ,4 neurons, not found in previous studies, were frequently stained. The secondary neurites of DUM neurons characteristically give rise to fine 0.2-0.5 micron diameter processes which may run for hundreds of microns through the neuropil with very little branching. The problems this may pose for signal transmission along such processes is discussed. Presynaptic processes of several types make inputs on to spines on the lateral neurites of DUM neurons and on to branches from secondary neurites. Output synapses were rarely observed and were found only on lateral neurite spines. It therefore appears unlikely that the DUM neurons examined play a major central role within the metathoracic ganglion. A novel structure, with the appearance of a presynaptic density but which was not associated with synaptic vesicles, was found in certain regions of the neurons.

Animals↗
PubMed1984

The ultrastructure of prosternal sensory hair afferents within the locust central nervous system.

The sensory neurones innervating long prosternal hairs of Locusta migratorioides were backfilled with horseradish peroxidase through their dendrites. The neurones' central projections in and around the medial ventral tract were examined with electron microscopy. Most synapses occur on axon collaterals which ramify through the neuropile around the tract where both input and output synapses were observed. Serial sectioning methods were used to determine the relative distribution of inputs and outputs which often lie in close proximity to one another on the axon terminals. The prosternal hair terminals contain agranular synaptic vesicles approximately 37 nm in diameter. Surrounding unidentified neuropilar profiles contain vesicles which are either statistically indistinguishable in size, or are larger, 45 nm diameter agranular vesicles. Neurones which are pre- or postsynaptic to labelled terminals generally contain vesicles of the second type. Input synapses onto the central terminals of primary afferent neurones can be recognised as a widespread phenomenon in the nervous systems of both invertebrates and vertebrates which will allow a fine degree of control of sensory inflow into the central nervous system.

Animals↗