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R Porter

Publications and source records attributed to R Porter.

At least 55 records · Page 3Linked to original sources
PubMed1987

'Long-latency' responses occurring with startle in the conscious monkey.

A monkey was noted to have an intermittent startle response to tendon tapping and vibration of proximal arm muscles. The latency of the first phase of this response, averaging 34 ms in triceps (and of average duration 49 ms), was similar to that described for the long-latency reflex response to muscle stretch in the same muscles. Unrecognised startle responses could explain some of the reported differences in long-latency reflexes in proximal and distal muscles.

Animals↗
PubMed1987

A quantitative study of the distribution of neurons projecting to the precentral motor cortex in the monkey (M. fascicularis).

The relative numbers and locations of neurons projecting to the "forelimb" region of the precentral motor cortex were studied in three monkeys by using the retrograde transport of horseradish peroxidase. Within the forelimb area of the motor cortex itself, there are extensive and profuse interconnections. However, regions within this area receive afferents from very few neurons in other parts of the motor cortex representing hindlimb or head movements. Most of the motor cortical representation of the forelimb in the anterior bank of the central sulcus is devoid of callosal connections. In both the ipsilateral and contralateral hemispheres, the premotor (lateral area 6) and supplementary motor (medial area 6) areas dominate quantitatively the inputs to the motor cortical representation of the forelimb. The afferents from the premotor area are restricted and come from a region immediately behind the arcuate spur and adjacent parts of the superior and inferior limbs of the arcuate sulcus in the floor, caudal bank, and caudal lip of that sulcus. From the supplementary motor area (SMA), afferents originate from its whole rostrocaudal extent. Thalamic nuclear regions projecting to a restricted zone in the anterior bank of the central sulcus are recipients of cerebellar and somatosensory outputs. Involvement of more anterior parts of the motor cortex by the tracer labels thalamocortical cells, which are targets of pallidal output also. Within the first somatosensory cortex, cytoarchitectonic areas 1, 2, and 3a project to area 4. The projection from area 3a may provide one pathway by which short-latency peripheral inputs, especially from muscles, reach the motor cortex.

Afferent Pathways↗
PubMed1987

Functional studies of motor cortex.

Defining functions for neural elements becomes more difficult the more remote they are, in synaptic linkages, from motor neurons. The precentral motor cortex contains a corticomotoneuronal projection system, only one synapse removed from motor neurons. Corticomotoneuronal fibres produce monosynaptic excitation of spinal motor neurons, which is more powerful for those acting distally, innervating extensor muscles of the fingers and intrinsic hand muscles. Latencies and time-course of corticomotoneuronal excitation are defined. Amplitudes of unitary corticomotoneuronal excitatory postsynaptic potentials are very small. Many corticomotoneuronal cells converge on a given motor neuron. Some motor neurons innervating proximally acting muscles appear to receive no corticomotoneuronal excitation. Disynaptic inhibitory actions are produced by corticospinal volleys via the common Ia inhibitory interneuron--possibly reciprocal actions produced over collaterals of corticomotoneuronal fibres. Anatomical divergence of projections of collaterals of an identified corticomotoneuronal fibre is extensive enough to provide both for delivery of synapses to a large number of motor neurons and for the dispersion of specific projections to inhibitory interneurons, to fusimotor neurons and to other interneurons. Functions of corticomotoneuronal elements in motor cortex whose targets have been identified and whose excitatory or inhibitory actions have been specified by cross-correlation have been studied by Fetz & Cheney (J Neurophysiol 1980; 44:751-772).

Animals↗
PubMed1987

A controlled study of progabide in partial seizures: methodology and results.

The results of a multicenter, double-blind, placebo-controlled clinical trial of the efficacy and safety of progabide (PGB) in the treatment of partial seizures are presented. This study was performed with a number of rigorous controls not usually present in clinical trials. These included uniform co-medication in which all patients received only phenytoin and carbamazepine; concentrations of these two drugs were maintained within narrow, predefined concentration ranges. There was no statistically significant difference between PGB and placebo in seizure frequency and seizure duration for most of the analyses performed. One patient was withdrawn from the study because of hepatotoxicity. PGB was associated with a significant inhibition of phenytoin but not carbamazepine clearance. The results of this study indicate that PGB was not a potent antiepileptic drug in this population of persons with intractable epilepsy.

Adolescent↗
PubMed1986

Short latency inputs to phrenic motoneurones from the sensorimotor cortex in the cat.

Short latency responses were recorded from C5 phrenic roots and intracellularly from phrenic motoneurones following stimulation of the pericruciate cortex or medullary pyramids in cats anaesthetized with Nembutal or chloralose-urethane. Focal stimulation of the cortical surface (single pulses, 0.5-2 ms, 0.3-8 mA) during inspiration evoked EPSPs (latency 4.7 +/- 1.7 ms, rise time 1.9 +/- 1.1 ms, amplitude 0.22 to 3.94 mV) in 42% of motoneurones studied (n = 107). The EPSPs were absent, or on average 60% smaller, following stimulation during expiration. In all but two motoneurones, during both inspiration and expiration, hyperpolarizing potentials were observed either following the initial depolarization or alone. They could be reversed by hyperpolarizing current or chloride injection. Stimulation of the pyramidal tract at mid medullary level (1 to 3 pulses, 0.2 ms) evoked short latency excitation in phrenic motoneurones only with currents of more than 200 microA. Smaller stimuli applied to the medial reticular formation above the pyramidal tract evoked excitation (onset latency 1.5-3.2 ms) in which the earliest part was probably monosynaptic. These results show that the corticospinal responses in phrenic motoneurones are both excitatory and inhibitory. They are not transmitted through the pyramidal tract and are at least disynaptic. Excitation evoked from the medullary pyramidal tract can be explained by current spread beyond the pyramidal tract fibres.

Animals↗
PubMed1986

Potential of human polymorphonuclear leukocytes to synthesize and secrete sulfated proteoglycans.

To analyze the function of proteoglycans (PG) in different types of leukocytes, both the relative amounts and specific types of proteoglycans produced by cultured human peripheral blood polymorphonuclear leukocytes (PMN) were were determined and compared to mononuclear leukocytes (PBMC). Media from 3-day cultured PMN contained significantly less (less than 10%) 35SO2-4-labeled PG than media from PBMC cultures. Incorporation of 35SO2-4 into cell-associated material was comparable for both types of white blood cells. In contrast to PBMC, PMN could not increase their synthesis or secretion of PG after exposure to concanavalin A or phorbol-12-myristate-13-acetate. Various inducers of leukocyte chemotaxis also failed to enhance PG production by PMNs. Release of prelabeled PG from PMNs could be induced by exposure to either opsonized or unopsonized zymosan (yeast) as well as the bacteria S. aureus, suggesting that particle ingestion may be accompanied by PG exocytosis. Both chondroitinase ABC and AC digested greater than 90% of PMN 35S-labeled material in media and 75% in cell lysates; HNO3 treatment removed less than 5% of N-linked 35SO4 from radiolabeled media and 25% from cells. Treatment with 0.5 N NaOH released shortened glycosaminoglycan chains from 35S-labeled PMN cell lysates. beta-D-xylosides did not stimulate an increase in polysaccharide chain production by cultured PMNs. These data suggest that PMNs can produce chondroitin 4-sulfate PG whose synthesis is not affected by treatments that alter PMN functions; in contrast to PBMCs, PMNs will actively release these molecules when exposed to micro-organisms that stimulate phagocytosis.

Cells, Cultured↗
PubMed1986

The diary of a madman, seventeenth-century style: Goodwin Wharton, MP and communer with the fairy world.

Goodwin Wharton (1653-1704) was a nobleman's son and a Whig MP who played no small part in English public life. His manuscript journal shows, however, that he also lived a bizarre secret life of the mind of a kind which, in later generations, would have led to his confinement as suffering from mental illness. Above all, through the offices of his medium and lover, Mary Parish, he entered into elaborate relations both with the fairy world and with God and His Angels. This paper examines our records of Wharton's consciousness.

England↗
PubMed1986

Isolation of smooth muscle cells from swine carotid artery by digestion with papain.

A new method is described for the preparation of viable, elongated smooth muscle cells from the swine carotid artery. Cells were prepared by papain digestion of pressurized arteries in calcium-free solution. After digestion, the arteries were everted, and fine strips were teased from the intimal surface of the media in calcium-free solution, releasing single cells. Viability was assessed by exclusion of trypan blue and by appearance under phase-contrast microscopy. By these criteria, approximately 20% of the isolated cells were viable. The most distinguishing and unexpected characteristic of these cells was their length. Mean length of the relaxed viable cells was 240.4 +/- 47.4 microns (SD, n = 76), which is much longer than previously reported for arterial smooth muscle cells. Calcium (1.6 mM) caused most of the viable cells to contract slightly, and the mean cell length in calcium was 194.4 +/- 57.7 microns. Cells in 1.6 mM calcium contracted substantially in response to 10 microM histamine or the calcium ionophore A23187 (10 microM), demonstrating that histamine receptors and the contractile apparatus were still functional.

Animals↗
PubMed1985

International scientific meetings: relation between structure and function.

Increasing pressure is being placed on the scientific community to evaluate research activities. Scientific meetings consume a small but important fraction of the research budget. Audit of a well established series of scientific meetings showed that they met their immediate objectives in that they were international and multidisciplinary and provided a forum in which all participants actively contributed to discussion. The meetings had a positive outcome for the participants, leading in many cases to the subsequent exchange of research material (60% of participants) and to the establishment of collaborative research projects (31%). The impact of the meetings on the scientific community at large was assessed by citation analysis, which showed that the proceedings were cited early, often, and over a substantial period.

Australia↗
PubMed1985

Corticomotoneuronal synapses in the monkey: light microscopic localization upon motoneurons of intrinsic muscles of the hand.

Some corticospinal neurons give rise to axons which terminate directly upon motoneurons, thereby establishing corticomotoneuronal connections. The location of corticomotoneuronal synapses upon motoneurons innervating intrinsic muscles of the hand in the monkey was demonstrated by the use of intra-axonal and intracellular horseradish peroxidase (HRP). After a number of corticospinal axons originating from the "hand" area of the precentral gyrus had been injected with HRP in the lateral funiculus at C7-C8, a number of nearby identified intrinsic hand muscle motoneurons were also injected. Connections between corticomotoneuronal fibres and motoneurons were reconstructed from longitudinal parasagittal sections treated by the cobalt-enhanced diaminobenzidine method. Corticospinal axons in the lateral funiculus gave rise to main collaterals which provided an extensive arborization in lamina IX, where it was predominantly longitudinal, and in the adjacent intermediate zone. En passant and single or clustered groups of terminal boutons arose from preterminal branches of these arbors. Seven light-microscopically identified corticomotoneuronal synapses were found. They were located upon the dendrites of recipient motoneurons at 40 micron to 750 micron from the soma and ranged in size from 0.6 X 3.0 micron to 2.4 X 3.6 micron. The results suggest that each main collateral of a corticomotoneuronal axon establishes very few synaptic contacts, and possibly only one, with the dendrites of recipient motoneurons. This small number of contracts per motoneuron is consistent with the small amplitudes of minimal and unitary corticomotoneuronal EPSPs recorded from forelimb and hand motoneurons.

Animals↗
PubMed1985

The corticomotoneuronal component of the pyramidal tract: corticomotoneuronal connections and functions in primates.

Corticomotoneuronal fibers make up a functional component of the pyramidal tract-corticospinal system which is characteristic of primates. The corticomotoneuronal fibers include large, rapidly conducting axons. They arise from somatotopically arranged areas of precentral cortex and the largest concentration of pyramidal cells of origin in the deep part of lamina V is in area 4. Their influence is exerted contralaterally on the spinal cord, where monosynaptic excitation of spinal motoneurons occurs. Motoneurons innervating distally acting muscles are preferentially excited and marked convergence of corticomotoneuronal influences occurs on these. The excitatory post-synaptic potentials in these motoneurons are characterized by the property of temporal facilitation. Intraspinal divergence of the terminal arborizations of individual corticomotoneuronal fibers could permit the engagement of large populations of motoneurons and also the activation of excitatory and inhibitory interneurons and propriospinal neurons for that region of the spinal cord. Corticomotoneuronal synapses may be located more distally on the dendrites of motoneurons than are the monosynaptic connections from group Ia afferents. The corticomotoneuronal excitation has been demonstrated to be effective in natural functional states when the conscious animal is performing learned movement tasks. Abolition of corticomotoneuronal influences causes a permanent deficit in the fractionation of use of distal muscles and an inability to carry out independent movements of the fingers.

Animals↗
PubMed1985

Inappropriate emergency department visits.

Guidelines adopted in 1982 by the American College of Emergency Physicians were used to determine appropriate and inappropriate emergency department (ED) utilization patterns at three community hospitals during a two-week period in August 1983. In all, 3,130 visits were examined. There was an overall inappropriate visit rate of 10.8%, although considerable variation was observed among the three hospitals. Subgroups with the highest inappropriate visit rates included the following: 1) persons with Medicaid as the primary payment source (17.3%); 2) children aged 5 years or younger (15.2%); 3) those unable to identify a personal physician (14.1%); 4) unemployed persons (13.1%); 5) patients making visits during regular office hours (12.6%); and 6) those failing to attempt to contact their personal physicians (12.4%). These variations in inappropriate usage were all statistically significant at the P less than .05 level or better. Inability to identify a personal physician emerged as the most pervasive influence on inappropriate ED visit rates (P less than .001).

Adolescent↗
PubMed1985

Responses of precentral cells during cooling of post-central cortex in conscious monkeys.

A cooling plate was implanted over the forelimb representation in area 2 of the post-central region of cerebral cortex in two monkeys. Recordings were made of the discharges of thirty-seven movement-related neurones (thirty-four precentral and three post-central) in the forelimb motor representation of the cerebral cortex during active and passively imposed limb movements before, during and after cooling area 2 and local surrounding regions. Perfusion of the cooling plate with ice-cooled water for 3-5 min caused marked clumsiness of the conscious animal's forelimb movement and anaesthesia of the contralateral hand. Cooling of area 2 did not reduce the responses of area 4 cells to passive joint movements, nor did it alter the over-all pattern of activity of these cells during self-initiated lever pulling while that could still be performed. Cooling of area 2 did cause a significant increase in background cellular discharge in area 4 while the animal was at rest. Afferent impulses which are generated by passive joint movement and which have been shown to influence cells in area 4 of the conscious monkey at short latencies are probably not transmitted through cortico-cortical connexions from area 2.

Animals↗