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S J Bacon

Publications and source records attributed to S J Bacon.

28 records · Page 2Linked to original sources
PubMed1993

A monosynaptic pathway from an identified vasomotor centre in the medial prefrontal cortex to an autonomic area in the thoracic spinal cord.

Chemical microstimulation (1 mM L-glutamate or 25 mM KCl) of the medial prefrontal cortex of anaesthetized rats produced falls in systolic and diastolic blood pressure of similar magnitude, without a change in heart rate. Application of the lectin Phaseolus vulgaris leucoagglutinin by iontophoresis from an adjacent barrel of the same micropipette revealed a direct projection to the central autonomic area of the thoracic spinal cord from this vasomotor area, which is equivalent to the region called prelimbic cortex by Krettek and Price [J. comp. Neurol. (1977) 171, 157-192] or Cg3 by Paxinos and Watson [The Rat Brain in Stereotaxic Coordinates (1986)]. Labelled axons descended in the dorsal corticospinal tract in the cervical spinal cord, where they displayed a few varicosities. In the thoracic spinal cord, labelled fibres occurred bilaterally in the gray matter, predominantly in the central autonomic area, where they displayed many varicosities. Electron microscope studies revealed that the anterogradely labelled varicosities in the central autonomic area were vesicle-filled boutons that formed asymmetric synaptic contacts. The synaptic targets were small dendrites or dendritic protrusions that were characterized by a high incidence of multivesicular bodies and coated vesicles. We conclude that a monosynaptic pathway that originates from a physiologically-defined vasomotor area in the medial prefrontal cortex terminates on a characteristic type of neuron in the central autonomic area of the thoracic spinal cord.

Animals↗
PubMed1990

Electron microscopic evidence of a monosynaptic pathway between cells in the caudal raphé nuclei and sympathetic preganglionic neurons in the rat spinal cord.

Electrophysiological and anatomical studies have suggested the existence of a pathway between the caudal raphé nuclei and regions of the spinal cord containing the sympathetic preganglionic neurons. However synaptic connections between cells in the raphé nuclei and identified sympathetic preganglionic neurons have not yet been shown. We have used a combination of anterograde tracing using Phaseolus vulgaris leucoagglutinin (PHA-L), retrograde tracing using a conjugate of cholera B chain and HRP and electron microscopy to look for such a pathway in rats. When PHA-L had been injected into the regions mainly restricted to the raphé pallidus and raphé magnus, synaptic contacts were found between PHA-L containing terminals and preganglionic neurons retrogradely labelled from the adrenal medulla. Out of the 43 synaptic contacts analysed, 26 were onto somata and 14 onto dendrites. 75% of the total appeared to have symmetric membrane specialisations, 20% asymmetric and the remainder could not be classified. Synaptic contacts were not seen in an animal in which the PHA-L injection site involved cells in the ventral raphé obscurus and surrounding gigantocellular reticular formation. These findings provide evidence of the existence of a direct monosynaptic pathway between cells in the raphé pallidus and/or caudal raphé magnus, and identified sympathetic preganglionic neurons and give further support for a role for the caudal raphé nuclei in sympathetic autonomic regulation.

Adrenergic Fibers↗
PubMed1988

A simple and rapid method for the production of cholera B-chain coupled to horseradish peroxidase for neuronal tracing.

A simple and rapid method is described for the production of cholera B-chain coupled to horseradish peroxidase suitable for neuronal tracing. Horseradish peroxidase was activated with a mild sodium periodate oxidation followed by incubation with the cholera B-chain, to yield the conjugates, samples of which were fractionated further by size exclusion chromatography. Both fractionated material and unfractionated conjugates were tested in vitro by a binding assay on rat synaptic membranes, and in vivo by their ability to undergo retrograde transport following injection into the adrenal medulla of rats. These assays showed that the unfractionated conjugates were equivalent to the fractionated conjugates in binding to the rat synaptic membranes, and that they both provided good retrograde labelling of neurones in the spinal cord after injection into the adrenal medulla, with extensive labelling of the distal dendrites.

Animals↗
PubMed1988

Preganglionic sympathetic neurones innervating the rat adrenal medulla: immunocytochemical evidence of synaptic input from nerve terminals containing substance P, GABA or 5-hydroxytryptamine.

Sympathetic preganglionic neurones that innervate the adrenal medulla were identified for subsequent light and electron microscopic study by the retrograde transport of horseradish peroxidase (HRP) or a conjugate of HRP and cholera B-chain. Most labelled neurones were found in the intermediolateral column, but some occurred in the intercalated nucleus and in the lateral funiculus of the thoracic spinal cord. Three morphologically distinct types of neurone were retrogradely labelled, two of which had dendrites that extended medially towards the central canal and laterally across the entire lateral funiculus. A combination of retrograde labelling with pre-embedding immunocytochemistry allowed us to demonstrate synaptic contacts between boutons immunoreactive for substance P or 5-hydroxytryptamine (5-HT) and the cell bodies or proximal dendrites of sympathoadrenal neurones. The 5-HT-immunoreactive boutons appeared to be of two morphologically distinct types. Postembedding immunocytochemistry enabled us to show that sympathoadrenal neurones receive a heavy synaptic innervation from GABA-immunoreactive boutons: 32% of a random series of boutons in synaptic contact with cell bodies were GABA-immunoreactive. Proximal dendrites and also distal dendrites within the white matter were ensheathed in synaptic boutons, 37% of which were GABA-immunoreactive. It is concluded that sympathoadrenal neurones receive at least 4 distinct types of afferent synaptic input: from neurones containing substance P, or GABA and from two types of neurones containing 5-HT. The presence of synaptic inputs on distal dendrites that extend across the white matter adds further complexities to the control of the activity of sympathetic preganglionic neurones.

Adrenal Medulla↗
PubMed1988

Degeneration of serotonin-specific neurons in the brain in experimental Trypanosoma brucei infection.

ORMEROD and HUSSEIN (1986) have shown that an intracellular stage of Trypanosoma brucei rhodesiense causes the destruction of ependymal cells lining the ventricles of the brain. The ventricular ependymal cells are intimately associated with a plexus of nerves that react specifically with monoclonal antibody raised against serotonin. We have shown that in areas where the ependyma is damaged, the supraependymal plexus also undergoes destruction and that retrograde degeneration of the neuron as far as the dorsal raphe nucleus also occurs. Although the work is as yet unfinished, we suggest that some of the neuro-psychological changes, observed in clinical sleeping sickness, may be the result of this lesion.

Animals↗
PubMed1985

A modified histochemical technique to visualize acetylcholinesterase-containing axons.

An improved histochemical method for light microscopic demonstration of acetylcholinesterase (AChE) has been developed. Axonal, dendritic, and perikaryal staining are well delineated, both in areas of low AChE content, such as cerebral cortex, and in areas of high AChE content, such as neostriatum. Axonal staining, including arborizations, stands out against a clear background devoid of diffuse reaction product.

Acetylcholinesterase↗
PubMed1984

Acetylcholinesterase-immunoreactive axonal network in monkey visual cortex.

Immunocytochemistry with antibodies to human erythrocyte acetylcholinesterase (AChE) was used to demonstrate axons containing this enzyme in the visual cortex (area 17) of macaques. AChE-positive fibers were most dense in layers I, IIIB, IV, and VIB of Hassler and Wagner (I, IVA, IVC, and VIB of Brodmann) with three strata of more sparsely distributed fibers (layers II-IIIA, IIIC, and V-VIA of Hassler and Wagner [II-III, IVB, and V-VIA of Brodmann]). Layer I contained the most dense plexus of AChE-positive axons, oriented horizontally. Horizontally oriented axons were also located in layers IIIB, IIIC, IV, and V of Hassler and Wagner (IVA, IVB, IVC, and V of Brodmann). Layer VIB contained axons of variable orientation, apparently afferent to cortex. Moderately stained neuronal perikarya were occasionally encountered in layer VIB and superficial white matter, but no intensely stained neurons were seen.

Acetylcholine↗
PubMed1983

Immunocytochemical identification of cholinergic neurons in the monkey central nervous system using monoclonal antibodies against choline acetyltransferase.

A monoclonal antibody directed against rat brain choline acetyltransferase (ChAT) was used to stain cholinergic nerve cells within the brain and spinal cord of macaques. ChAT immunoreactivity was seen in motor neurons of the brainstem and spinal cord, in large neurons of the striatum, and in large neurons in the basal forebrain (medial septum--diagonal band--nucleus basalis complex); each of these groups of neurons is believed to be cholinergic. The ability to visualize cholinergic neurons in the nervous system of primates provides a new approach to the study of cholinergic systems in health and disease.

Animals↗
PubMed1983

Personality variables in coping with the stress of a spouse's chronic illness.

Identified systematically those spouses of male VA hemodialysis patients who are at risk for experiencing difficulties in adapting to their husband's chronic kidney failure and hemodialysis treatment. To this end, an exploration was made of personality variables that might enhance a spouse's ability to cope with the unique stress of living with chronic illness. Fifty-six wives of VA dialysis patients were administered the Rotter Internal-External Locus of Control Scale (I-E), the Multidimensional Locus of Control Scale (MLC), the Multidimensional Health Locus of Control Scale (MHLC), the State-Trait Anxiety Inventory (STAI), and the Beck Depression Inventory (BDI). Significant relationships were found between I-E scores and all measures of emotional adjustment (state anxiety, trait anxiety, and depression) for the entire sample of spouses in general, and also for a subgroup of home dialysis spouses who were analyzed separately. Results were discussed in terms of the role that locus of control orientation plays in mediating the stress of living with chronic illness, as well as the failure to find relationships between adjustment and the MLC or the area-specific MHLC.

Adaptation, Psychological↗