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Biomedical subjects

T J Biscoe

Publications and source records attributed to T J Biscoe.

107 records · Page 6Linked to original sources
PubMed1967

Carotid body chemoreceptor activity in the new-born lamb.

1. Tidal volume, carotid artery oxygen tension (P(a,O2)) and blood pressure and chemoreceptor activity in the sinus nerve have been continuously measured and recorded in nine lambs anaesthetized with pentobarbitone sodium, and varying in age from some minutes after birth to 5 days after birth.2. Inhalation of 100% oxygen caused, after a delay of 3-4 sec, a rise in P(a,O2), a fall in minute ventilation (V) and chemoreceptor activity. The respiratory response was abolished after section of both sinus nerves.3. Inhalation of 10% oxygen in nitrogen caused a fall in carotid P(a,O2), a rise in respiration and in chemoreceptor activity. The respiratory response was abolished after both sinus nerves had been cut.4. Minute ventilation, carotid P(a,O2) and chemoreceptor activity increased on breathing 5% CO(2) in air. Section of both sinus nerves did not affect the maximum increase in ventilation but the lag of the respiratory response approximately doubled while respiration increased more slowly.5. From these results, it was calculated that the chemoreceptors had a latency of 0.25-0.5 sec and the time constant of the rate of change of chemoreceptor activity was 10-15 sec.6. The chemoreceptors responded to changes in P(a,O2) of +/-5-10 mm Hg.7. Comparison of these results with those reported in adult animals suggest that the peripheral chemoreceptors are fully mature at birth, that their response does not differ with the age of the lamb and that the carotid body chemoreceptors are concerned both in the mediation of the hypoxic drive to ventilation and in the respiratory response to inhaled CO(2).

Action Potentials↗
PubMed1966

Noradrenaline and inhibition of Renshaw cells.

Although postsynaptic inhibition of Renshaw cells in the spine is blocked by strychnine the depression of these neurons by electrophoretically administered noradrenaline is resistant to this alkaloid. This finding raises doubts as to whether noradrenaline is an inhibitory transmitter in the spinal cord of the cat.

Acetylcholine↗
PubMed1966

Ultrastructure of the carotid body.

An electron microscope investigation was made of the carotid body in the cat and the rabbit. In thin-walled blood vessels the endothelium was fenestrated. Larger vessels were surrounded by a layer of smooth muscle fibers. Among the numerous blood vessels lay groups of cells of two types covered by basement membranes. Aggregates of Type I cells were invested by Type II cells, though occasionally cytoplasmic extensions were covered by basement membrane only. Type I cells contained many electron-opaque cored vesicles (350 to 1900 A in diameter) resembling those in endocrine secretory cells. Type II cells covered nerve endings terminating on Type I cells and enclosed nerve fibers in much the same manner as Schwann cells. The nerve endings contained numerous microvesicles ( approximately 500 A in diameter), mitochondria, glycogen granules, and a few electron-opaque cored vesicles. Junctions between nerve endings and Type I cells were associated with regions of increased density in both intercellular spaces and the adjoining cytoplasm. Cilia of the 9 + 0 fibril pattern were observed in Type I and Type II cells and pericytes. Nonmyelinated nerve fibers, often containing microvesicles, mitochondria, and a few electron-opaque cored vesicles (650 to 1000 A in diameter) were present in Schwann cells, many of which were situated close to blood vessels Ganglion cells near the periphery of the gland, fibrocytes, and segments of unidentified cells were also seen. It was concluded that, according to present concepts of the structure of nerve endings, those endings related to Type I cells could be efferent or afferent.

Animals↗
PubMed1966

Micro-electrophoretic studies of neurones in the cat hippocampus.

1. Drugs have been applied micro-electrophoretically to units in the hippocampal cortex of the anaesthetized cat, and their effects on cell firing were recorded simultaneously.2. L-Glutamate rapidly and powerfully excited hippocampal units, an effect which was quickly reversed on stopping the expelling current. The local application of L-glutamate also excited a fast seizure discharge at 15-50/sec. Both these effects of L-glutamate were strongly depressed by fimbrial stimulation.3. gamma-Aminobutyric acid had a strong depressant action on all the units on which it was tested; the time course of this effect was rapid.4. ACh excited half the units to which it was applied. Characteristically this excitation developed slowly over many seconds and persisted after stopping the expelling current. Most cholinoceptive units were found to be concentrated in the superficial layer of the cortex corresponding to the hippocampal pyramidal cells and their main dendritic processes.5. Atropine selectively blocked the excitation of cholinoceptive units by ACh, but not the excitation by L-glutamate. No cholinoceptive units were blocked by dihydro-beta-erythroidine, though several were selectively blocked by dimethyl (+)-tubocurarine.6. The most usual effect seen with 5-HT was depression, though several units were found to be excited. Some of the units tested with 3-hydroxytyramine (dopamine) or noradrenaline were found to be depressed.

Acetylcholine↗
PubMed1966

The distribution of cholinesterases in the cat carotid body.

1. The distribution of acetyl- and butyrylcholinesterase in the carotid body of the cat has been examined histochemically. Studies were made on normal carotid bodies and on carotid bodies from cats in which certain nerves had been cut some time previously. The nerves sectioned were the sinus nerve, the post-ganglionic sympathetic branch of the superior cervical ganglion or the preganglionic cervical sympathetic trunk.2. It was confirmed that more butyrylcholinesterase than acetylcholinesterase is present. Both enzymes are found in three sites: (i) as strands, (ii) as plexuses, (iii) inside a few cells.3. The distribution is unaffected by cutting the sinus nerve or preganglionic cervical sympathetic nerves. Disorganization and depletion of the cholinesterases in the strands and plexuses occurs when the post-ganglionic branch of the superior cervical ganglion is cut. The cholinesterase in cells is unaffected.4. In carotid bodies in which vessels were filled with red blood cells or in which the vascular bed was injected with carmine-gelatine, it was seen that strands and plexuses are associated with blood vessels, and with blood vessels and cells respectively.5. It is suggested that a cholinergic pathway controlling carotid body blood vessels runs in the post-ganglionic cervical sympathetic.

Acetylcholinesterase↗
PubMed1966

The effects of cyclopropane, halothane and ether on central baroreceptor pathways.

1. The reductions in arterial pressure and preganglionic sympathetic activity evoked by aortic nerve stimulation in the rabbit were studied before and during administration of constant inspired concentrations of the inhalation anaesthetics cyclopropane, halothane, and ether. The background anaesthetic was pentobarbitone, gallamine triethiodide was given, and pulmonary ventilation was with 100% oxygen.2. During light pentobarbitone anaesthesia, aortic nerve stimulation usually induced similar reductions in arterial pressure and preganglionic discharge, expressed as the maximum percentage reduction from prestimulation levels. There were two components in the sympathetic responses, attributable to A and C fibre excitation in the aortic nerve, which was also shown to contain a third fibre group with properties similar to those of B fibres.3. The arterial pressure, heart rate, and preganglionic sympathetic responses to aortic nerve stimulation were rapidly and profoundly inhibited by 50% cyclopropane, which also produced arterial hypertension.4. Halothane (3%) significantly inhibited the depressor responses, but even in the presence of severe hypotension the arterial pressure could usually be further reduced by aortic nerve stimulation. The inhibitory effects of 2% halothane were slow in onset and not pronounced. In the concentrations used, these actions of halothane were significantly less than those of cyclopropane.5. The inhibitory effects of ether on the depressor responses were roughly intermediate between those of cyclopropane and halothane; complete suppression of the responses occurred with high ether concentrations, which were also liable to cause circulatory collapse.6. It is concluded that the three anaesthetics significantly inhibit impulse transmission through central baroreceptor pathways; the implications of the findings are discussed in relation to the different circulatory actions of these anaesthetics.

Action Potentials↗
PubMedDate not supplied

Electrophysiological observations on the spinal cord of the normal and dystrophic mouse.

A method of carrying out electrophysiological experiments on the mouse spinal cord is described. The conduction velocity in the spinal dorsal roots (DR) of the normal mouse was in the range 10-100 m sec-1 and in the ventral roots (VR) 50-70 m sec-1. In the dystrophic mutant (129 ReJ dy/dy) the conduction velocity for both roots was usually in the range 0.1-2.0 m sec-1. Reflexes from DR to VR were recorded in both mutant and wild type animals and it was concluded that the delays in the mutant reflex were probably due to the slower conduction velocity in the roots. Postsynaptic inhibition and presynaptic inhibition were demonstrated and records were made from Renshaw cells and intracellularly from motoneurones. Delayed activity in spinal reflex paths, probably of supraspinal origin, was more pronounced in the dystrophic mutant. It is concluded that if the dystrophic mouse mutant were to be regarded as a model for human disease then similar reflex delays should be demonstrated in human subjects with muscular dystrophy.

Afferent Pathways↗