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Biomedical subjects

R A O'Brien

Publications and source records attributed to R A O'Brien.

14 recordsLinked to original sources
PubMed1978

Axonal transport of acetylcholine, choline acetyltransferase and cholinesterase in regenerating peripheral nerve.

1. The axonal transport of acetylcholine (ACh), choline acetyltransferase (ChAc) and cholinesterase (ChE) was estimated in the peroneal nerves of rabbits by measuring the accumulation of each against a nerve crush over a period of 20 hr. 2. Estimates were made of the amounts of these substances that were transported in nerves that had been regenerating for up to 111 days after being crushed or up to 13 days after being cut. 3. The initial response was the same whether the injury was a crush or a cut; the amount of ACh transported was increased, while ChAc and ChE transport was reduced. 4. The amounts of ACh, ChAc and ChE transported tended to return to normal levels when the nerves were allowed to reinnervate the denervated muscles. ChAc transport also showed an early recovery in the cut nerves. 5. The ACh content of the central nerve stump did not alter throughout regeneration but ChAc and ChE contents were reduced at the times when the transport of the enzymes was reduced. 6. These results are discussed in relation to the time course of nerve regeneration.

Acetylcholine↗
PubMed1978

Observations on the elimination of polyneuronal innervation in developing mammalian skeletal muscle.

1. The mechanism responsible for the elimination of polyneuronal innervation in developing rat soleus muscles was studied electrophysiologically and histologically. 2. Initially all the axons contacting a single end-plate have simple bulbous terminals. As elimination proceeds one axon develops terminal branches while the other terminals remain bulbous and may be seen in contact with, or a short distance away from, the end-plate. It is suggested that the branched terminal remains in contact with the muscle fibre while the other terminals withdraw. 3. At a time when polyneuronal innervation can no longer be detected electrophysiologically, the histological technique still shows the presence of end-plates contacted by more than one nerve terminal. 4. The effect of activity on the disappearance of polyneuronal innervation was examined. Activity was increased by electrical stimulation of the right sciatic nerve. This procedure also produced reflex activity in the contralateral limb. In both cases polyneuronal innervation was eliminated more rapidly in the active muscles. 5. The finding that proteolytic enzymes are released from muscles treated with acetylcholine (ACh), and the observation of the more rapid elimination of supernumerary terminals at the end-plates of active muscles, lead to the suggestion that superfluous nerve-muscle contacts are removed by the proteolytic enzymes in response to neuromuscular activity. The selective stabilization of only one of the terminals is discussed in the light of these results.

Acetylcholine↗
PubMed1975

Immunopharmacological studies using 5-hydroxytryptamine antibody.

An antibody to serotonin (5-HT) was tested on several preparations in which 5-HT is considered to be involved. The antibody was capable of effectively competing with 5-HT receptor sites for free molecules of 5-HT. It inhibited the uptake of 3H-5HT by blood platelets and may explain the reduced endogenous 5-HT concentration in blood platelets of immunized rabbits. The decreased platelet content of 5-HT was substantiated by electron microscopic studies which showed a reduction in the number of 5-HT-containing subcellular storage organelles in platelets from these animals. The 5-HT antibody inhibited the 5-HT-induced contraction of aortic strips in a tissue bath preparation. When given intraventricularly, it inhibited for a time the sedative actions of reserpine thus adding new evidence to the often postulated role of 5-HT in the actions of reserpine.

Adenylyl Cyclases↗
PubMed1975

Platelet monoamine oxidase in children with infantile autism.

Platelet monoamine oxidase activity was measured in 9 autistic subjects and 9 controls. There were no significant differences in the rates of metabolism of 5-hydroxytryptamine, dopamine or tyramine between the two groups, although the rate of metabolism of tyramine was more rapid than 5-hydroxytryptamine or dopamine within each group. It is concluded that the data presented do not support the view that measurement of platelet monoamine oxidase can be used as a biochemical index to aid in the clinical diagnosis of infantile autism.

Adolescent↗
PubMedDate not supplied

Catechol-O-methyltransferase activity in erythrocytes of children with autism.

1. The activity of the enzyme catechol-O-methyltransferase (COMT) was determined in the erythrocytes of normal and autistic children. 2. There was no difference in enzyme activity between the two groups, although in both the normal and autistic females the erythrocyte COMT activity showed considerable within-group variation. 3. When the erythrocyte homogenates were divided into particulate and soluble fractions, some differences were observed. The COMT activity in the soluble fraction was less in erythrocytes from autistic males than in those from control males, whereas that in autistic females was higher than in those from control females.

Autistic Disorder↗