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Biomedical subjects

T J Biscoe

Publications and source records attributed to T J Biscoe.

At least 55 records · Page 3Linked to original sources
PubMed1977

Numbers and diameters of motoneurons and myelinated axons in the facial nucleus and nerve of the albino rat.

The number and diameter of the motoneurons in serial sections of the facial nucleus in the albino rat were estimated using a photograph-camera lucida technique for counting and measuring cells in conjunction with a systematic section method for sampling the population. The mean diameter of facial motoneuron nucleoli was also estimated. Total cell counts were estimated using two formulas, one a basic count and the other the basic count corrected for split nucleoli errors. The mean motoneuron diameter is 33-93 micronm (+/- 6-18 micronm S.D.). The number and diameter of myelinated axons in both the facial nerve and its cutaneous auricular branch at the level of the stylomastoid foramen were estimated. There are 5353 myelinated axons in the facial nerve, with a mean diameter of 2-74 micronm, and 627 myelinated axons in the cutaneous auricular branch with a mean diameter of 1-47 micronm. The accuracy and reproductibility of results using the photograph-camera lucida technique for counting and measuring cells and the systematic section method of sampling are compared with those of the methods used by previous investigators. The accuracy of results obtained for estimates of the total cell count using the formulas for the basic count and the basic count corrected for split nucleoli are also compared.

Animals↗
PubMed1976

The sensitivity of rat spinal interneurones and renshaw cells to L-glutamate and L-aspartate.

L-Glutamate and L-aspartate were administered electrophoretically near spinal interneurones and Renshaw cells of pentobarbitone-annaesthetized rats. Other spinal interneurones were consistently more sensitive to L-glutamate than to L-aspartate. Renshaw cells, however, showed no consistent difference in their sensitivity to these two amino acids. The results, which are compared with those reported previously in the cat, support the hypothesis that L-glutamate could be a transmitter at spinal primary afferent terminals.

Action Potentials↗
PubMed1976

Structure-activity relations of excitatory amino acids on frog and rat spinal neurones.

1 A series of compounds structurally related to glutamic acid has been tested on frog and rat spinal neurones. The substances were added to procaine-containing medium bathing the isolated hemiscected spinal cord of the frog, and their potencies in depolarizing motoneurones were assessed by the magnitude of the potential produced in the ventral root. The electrophoretic technique was used to administer the substances around single interneurones of the rat spinal cord and the relative potencies of the compounds as excitants assessed by the magnitude of the currents required to produce similar rates of neuronal firing. 2 Parallel structure-activity relations were observed in the two series of experiments, suggesting that the receptors for excitatory amino acids on frog and rat spinal neurones are similar. 3 Quisqualate, domoate and kainate were the strongest excitants in both animals, with potencies around two orders of magnitude higher than that of L-glutamate. 4 2,4,5-Trihydroxyphenylalanine (6-OH-DOPA) was a stronger excitant and L-3,4-dihydroxyphenylalanine (L-dopa) a weaker excotamt than L-glutamate on frog spinal motoneurones. The former compounds was also a more potent convulsant than L-glutamate on intraventricular injection into mouse brain. The lack of activity of 6-OH-DOPA on electrophoretic administration was attributed to oxidation. 5 Unlike the majority of amino acid excitants, several of the compounds shown in the present work to have moderate excitatory activity are not anionic at physiological pH. This indicates either that two negatively charged groups are not essential for interaction with a common excitatory receptor, or that more than one type of receptor is involved in the actions demonstrated.

Amino Acids↗
PubMed1975

An investigation of the foetal rat spinal cord. I. Ultrastructural observations on the onset of synaptogenesis.

Ultrastructural studies on the foetal rat spinal cord show that during synaptogeneis there is difficulty in recognizing true synaptic precursors. Symmetric densities are found at unusual sites forming, for example, somato-dendritic and somato-somatic junctions. They are also found between neurons and possible glial processes. Symmetric densities occur between nerve cells but may be confused with desmosomes. Profiles exhibiting membrane density, cleft material and 50 nm vesicles, which are the most reliable indicators of presumptive synapses, are found between neurones, but also at junctions between neurons and what may be glial processes. The picture is further confused by the presence of degeneration axodendritic synapses at early foetal stages. Caution must be exercised in defining an apparent synapse or precursor in foetal cord as that of a presumptive functional synapse because of the observed degenerating profiles and because of our knowledge, somato-somatic, somato-dendritic, and neurono-glial synapses have not been observed in adult cord. It is not known whether these structures are an unwanted consequence of development or play a role in guiding development.

Animals↗
PubMed1975

An investigation of the foetal rat spinal cord. II. An ultrastructural study on the development of synapses with the aid of observations on some electrophysiological properties.

Electrophysiological and ultrastructural studies were carried out on foetal rat spinal cord. The electrophysiological observations allowed certain identification of the site of second order sensory neurones, regions of the most functionally mature ventral horn cells and the adequacy of reflex conduction at 18 days. In the ultrastructural studies we made use of these identifications. No definitive synapses were found at 13-14.5 days in dorsal and ventral horn neuropil though some possible precursors were seen. Immature axodendritic synapses are found first in both dorsal and ventral marginal zones at 14.5 days and in both dorsal and ventral neuropil regions at 15-16 days. At 17 days there is an abrupt increase in frequency and maturity of synaptic profiles in all regions; synapses containing pleomorphic populations of vesicles are first seen in the ventral horn neuropil at this age as rare axo-somatic synapses. At 18 days the synapses population increases and multiple contacts involving axons or dendrites commonly occur. Furthermore, axo-somatic synapses are seen for the first time in the dorsal horn. From 20 days onwards mature synapses were commonplace and all earlier stages can be found. In addition axo-dendritic synapses with pleomorphic populations of vesicles were first seen in the dorsal horn. Axo-somatic synapses in the dorsal horn remained immature in appearance at this time. These findings are discussed particularly in relationship to previous studies by others on the development of motility in the rat. It appears that in the rat lumbar cord, onset of formation of different synapse types in specific locations precedes the onset of possible related functions by 1-2 days.

Age Factors↗
PubMed1975

Acetylcholine receptors on Renshaw cells of the rat.

Experiments have been performed on Renshaw cells of rats to investigate the receptors mediating both the responses to electrophoretically applied cholinergic excitants and the synaptic excitation following stimulation of the ventral roots. The effects of atropine and dihydro-beta-erythroidine, muscarinic and nicotinic antagonists respectively, have been tested on both types of excitation. Most importantly we found that in the rat the ventral root evoked response can be blocked by atropine as well as by DHbetaE. It was not possible to categorise the responses to the cholinergic agents in terms of muscarinic and nicotinic receptors. In addition we have failed the late (muscarinic) excitation seen in the cat.

Acetylcholine↗
PubMed1975

Investigation of cranial and other nerves in the mouse with muscular dystrophy.

In the muscular dystrophic mouse mutant there is an absence of Schwann cells over circumscribed lengths of all cranial nerves except for II (I was not examined) and the lesion involves the sympathetic system. Where present, Schwann cells do not produce myelin of normal thickness. The lesion is similar to that described for the spinal roots. Causation is discussed.

Abducens Nerve↗