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Biomedical subjects

A H Watson

Publications and source records attributed to A H Watson.

44 records · Page 3Linked to original sources
PubMed1983

The morphology, ultrastructure, and distribution of synapses on an intersegmental interneuron of the locust.

The structure and synaptic relationships of an intersegmental interneurone in the mesothoracic ganglion of the locust were studied by intracellular labelling for light and electron microscopy. Before labelling, the interneurone was characterized physiologically. It is depolarized and produces spikes when either of the two forewings are elevated, and by sensory inputs from the tarsi of the middle legs. The gross morphology of the interneurone is quite distinctive. Its cell body is on the ventral surface of the ganglion near the midline and its primary neurite lies in the T-tract. Its axon performs a characteristic lateral loop around the lateral dorsal tract before entering an anterior connective and ascending at least as far as the prothoracic ganglion. Within the mesothoracic ganglion, the interneurone gives rise to a profusion of branches. Ultrastructural examination and reconstruction of three regions of the interneurone from serial sections shows that input and output synapses are present in approximately equal numbers, and often are close to each other. There is no evidence for separate input and output regions. Output synapses are characterized by the presence of a presynaptic bar and a population of 500-2,000 round, electron-lucent vesicles. Most of the estimated 10(5)-10(6) synapses occur on the smaller diameter processes or on spines. The spines are of uniform diameter along their lengths, and are pre- or postsynaptic or both, but the postsynaptic spines are of smaller diameter than the others.

Animals↗
PubMed1982

The ultrastructure of identified locust motor neurones and their synaptic relationships.

Motor neurones in the thoracic ganglia of the locust were impaled with microelectrodes and identified according to the muscle they innervated and their other physiological properties. They were then labeled by intracellular injection of horseradish peroxidase and processed for electron microscopy. The nature and distribution of synapses on each motor neurone was examined and, by the use of reconstruction from serial sections, their spatial relationships revealed. The metathoracic fast extensor tibiae and mesothoracic tergosternal flight motor neurones have both output and input synapses on their neuropilar branches. These synapses are involved in serial, reciprocal, and recurrent relationships showing that the structural equivalent of a physiological synapse may be complex. The metathoracic slow extensor tibiae and anterior fast flexor tibiae motor neurones apparently have only input synapses within the neuropile.

Animals↗
PubMed1981

The ultrastructure of the innervation of the intestinal wall in the teleosts Myoxocephalus scorpius and Pleuronectes platessa.

The innervation of the intestinal wall in the teleosts Myoxocephalus and Pleuronectes was examined electron microscopically. Two classes of axons can be identified. The first, which is in the majority, contains numerous 50-150 nm granular vesicles as well as some 40-50 nm agranular vesicles while the second contains predominantly the 40-50 nm agranular vesicles. Chromate/dichromate staining methods suggest that the first type is aminergic. Both types lie in close association with the perikarya of intrinsic myenteric neurons but only axons containing predominantly agranular vesicles have synaptic membrane specialisations. No axon bundles pass into the longitudinal muscle layer in Myoxocephalus gut and though some do in Pleuronectes, they do not closely approach the smooth muscle cells. Axons containing large granular vesicles lie in intimate contact with the myocytes of the circular muscle layer. Both axon types pass through the submucosa to form a plexus underneath the mucosal epithelium. Varicosities containing agranular or granular vesicles are separated from the epithelial cells by a gap of about 200 nm in which lies a basal lamina.

Animals↗
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↗
PubMed1980

The structure of the coeliac ganglion of a teleost fish Myoxocephalus scorpius.

In order to compare the structure of a teleost sympathetic ganglion with those of other vertebrates, light, fluorescence histochemical and electron microscopy were carried out on the coeliac ganglion of the scorpion fish, Myoxocephalus scorpius. In common with studies on other vertebrates, fluorescence h istochemistry distinguished two cell types: a) principal neurones which exhibited low levels of specific catecholamine fluorescence and comprise the majority of neurones in the ganglia, and b) smaller intensely fluorescent cells, some of which had processes tens of micrometers long. With the electron microscope, the principal cells were seen to make axodendritic and axosomatic synapses with axons containing mainly 30 nm agranular vesicles at the synaptic site while in other vertebrates usually only one or other synaptic association is present. Both the somata and the processes of intensely fluorescent cells contain 300-600 nm diameter vesicles many of which have electron dense cores. These cells are also innervated by axons containing 30 nm agranular vesicles.

Animals↗
PubMed1980

The distribution of aminergic neurones and their projections in the brain of the teleost, Myoxocephalus scorpius.

Fluorescent histochemistry was carried out on the brain of the teleost Myoxocephalus scorpius to show the distribution of monoaminergic neurones and their projections. Posterior to the obex of the fourth ventricle, at the junction of the spinal chord and medulla, there is an unpaired dorsal nucleus of catecholaminergic cells. A second group of catecholaminergic perikarya are scattered lateral to the vagal and glossopharyngeal motor nuclei. Both groups of aminergic cells contribute to a tract which crosses the fourth ventricle at the obex and runs along the lateral wall of the medulla towards the diencephalon. At the level of the isthmus there is a lateral nucleus composed of large catecholaminergic cells with prominent fluorescent axons and its possible homology with the locus coeruleus is considered. Medially, in the same region a nucleus of serotonergic neurones lies between the paired tracts of the fasciculus longitudinalis medialis. In the diencephalon there are three paraventricular nuclei, the nuclei recessus posterioris and lateralis and the paraventricular organ pars anterior. Ventral to the lateral recess there is a further nucleus less closely associated with the ependyma. The distribution of fluorescent fibres is described and the dispositions of the aminergic nuclei compared to those of other teleosts.

Animals↗
PubMed1979

Fluorescent histochemistry of the teleost gut: evidence for the presence of serotonergic neurones.

The guts of the teleosts Myoxocephalus scorpius, Pleuronectes platessa and Clupea harengus were examined using fluorescent histochemistry and the innervation compared to that in mammals and other lower vertebrates. In Myoxocephalus and Pleuronectes both greeen and yellow fast fading fluorescent nerves were found in the intestine. To test whether the yellow nerves might be serotonergic, an attempt was made to extract 5-HT from the intestine of these fish in a region where enterochromaffin cells were absent. Chromatography of extracts showed the presence of 5-HT, and, in Myoxocephalus, dopamine.

Adrenergic Fibers↗