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Biomedical subjects

R J Walker

Publications and source records attributed to R J Walker.

At least 235 records · Page 13Linked to original sources
PubMed1980

Effect of cyproheptadine on the octopamine-induced responses in the mammalian central nervous system.

Extracellular recordings have been made from rat thalamic neurones anaesthetized with urethane, 1.5--2 g/kg i.p. Iontophoretically applied octopamine excited certain thalamic neurones in the ventral basal complex while inhibiting others. Both effects were reversibly antagonized by iontophoretically applied cyproheptadine without affecting responses to noradrenaline and dopamine.

Animals↗
PubMed1980

Actions of glutamate, kainate, dihydrokainate and analogues on leech neurone acidic amino acid receptors.

Intracellular recordings have been made from leech Retzius cells. L-Glutamate and kainate both excite these cells, kainate being about 100 times more potent than glutamate. Cross desensitization was observed between glutamate and kainate. Dihydrokainate was found to be equipotent with kainate on these neurones. Esterification of either kainate or dihydrokainate rendered the compounds inactive as did the addition of a benzyloxycarbonyl group on the nitrogen of both compounds. These results suggest that the double bond in the side chain of kainate is not necessary for its potent activity on leech Retzius neurones. But, that free carboxyl groups and an unsubstituted nitrogen are essential for glutamate-like activity.

Amino Acids↗
PubMed1980

Antral vascular lesion, achlorhydria, and chronic gastrointestinal blood loss: response to steroids.

A 72-year-old female gave a history of chronic gastrointestinal blood loss necessitating transfusion with over 90 units of blood despite continuous oral iron therapy over a period of 24 years. Gastroscopic appearances were very similar to those recently described by Lewis and by Wheeler in patients with submucosal angiomatous lesions and chronic gastrointestinal blood loss. Striking erythematous streaks radiated from the pylorus and were confined to the antrum. In our case complete achlorhydria to pentagastrin was associated with low serum and antral gastrin concentrations. The introduction of oral prednisolone was followed by a marked fall in the rate of gastrointestinal blood loss, removing the need for transfusion during the following year. Complete achlorhydria persisted and endoscopic appearances remained unchanged, but there was a marked rise in antral and serum gastrin concentrations. The possible modes of action of prednisolone in this case are discussed. The patient remains well in November 1979. The dose of prednisolone was reduced to 10 mg on alternate days in May 1979. Iron supplements have been continued but no transfusion has been required since the start of steroid therapy. The hemoglobin has gradually risen to 14.9 g/dl.

Achlorhydria↗
PubMed1980

Structure-activity studies on an excitatory receptor for glutamate on leech Retzius neurones.

1 Intracellular recordings were made from Retzius cells from the segmental ganglia of Hirudo medicinalis and Haemopis sanguisuga. Glutamate had a direct excitatory effect on the leech Retzius cells. 2 L-Glutamate was 25 times more potent than D-glutamate. 3 L-Glutamate was approximately equipotent with ibotenic acid and 11.2 times more potent than L-aspartic acid. 4 Quisqualic acid and kainic acid were both approximately 100 times more potent than L-glutamate. DL-1-Amino-cis-1-3-dicarboxyclyclopentane was approximately 5 times more potent than L-glutamate, while the trans isomer was 105 times less potent. 5 alpha-NH2-pimelic acid and beta-CH3-glutamic acid reduced the response to L-glutamate. 6 It is suggested that glutamic acid may interact with the Retzius cell glutamate receptor in an extended conformation.

Animals↗
PubMed1979

Big and little gastrin responses to food in normal and ulcer subjects.

In normal, duodenal ulcer, and gastric ulcer subjects the two main forms of gastrin, G17 and G34, were estimated by radioimmunoassay in fasting serum and after feeding. Two antisera were used: one showing high specificity for G17, the other specific for the common COOH-terminus of G17 and G34 and so allowing estimation of G34 by difference. Basal G17 was similar in gastric ulcer, duodenal ulcer, and normal subjects and the increases of G17 after feeding were also similar in these groups. In contrast, basal G34 was similar in normal and duodenal ulcer subjects but raised in gastric ulcer subjects. After a meal the G34 concentration in both gastric and duodenal ulcer patients was significantly higher than normal. It is concluded that the higher post-prandial gastrin responses in peptic ulcer that have been previously described are due largely to increased G34.

Adult↗
PubMed1978

The action of conformationally restricted analogues of GABA on Limulus and Helix central neurones.

Intracellular recordings have been made from GABA sensitive neurones in the central nervous system of Limulus and Helix. The following conformationally restricted analogues of GABA all possessed GABA-like activity on Limulus neurones and Helix excitatory GABA receptors: muscimol, thiomuscimol, THIP, isoguvacine and piperidine-4- carboxylic acid. It is suggested that GABA interacts with these receptors in a partially extended and almost planar conformation.

Action Potentials↗