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Biomedical subjects

M J George

Publications and source records attributed to M J George.

29 records · Page 2Linked to original sources
PubMed1988

Influence of anesthesia on spontaneous activity and receptive field size of single units in rat Sm1 neocortex.

Spontaneous and cutaneously driven unit activity was recorded in the hindfoot region of rat Sm1 neocortex under controlled intravenous infusion, at three selected rates, of the steroid anesthetic agent Althesin. Increasing depth of anesthesia decreased average spontaneous firing rates of 67 single units from 2.5 to 11 Hz during light anesthesia to 0 to 2.5 Hz in deep anesthesia. Thresholds to cutaneous stimulation for 58 units were innocuous (from 15 to 190 micron) using a 5-ms ramp displacement of the skin in the center receptive field. Responses from 13 sites on the hindfoot were classified according to response probability for each of the 58 units in reply to stimuli at 1.5 times center receptive field threshold. Small receptive fields were seen only under conditions of deep anesthesia, considerable expansion of both center and excitatory surrounds occurring with lighter anesthesia. Mean values for total receptive field size (center plus surround excitatory receptive field) were 10.8, 7.8, and 3.4 sites, respectively, for light, moderate, and deep anesthesia. The size of the receptive field was also influenced by stimulus repetition rate; moderate increases of this and anesthetic depth could eliminate substantial receptive fields. Surround inhibition of evoked activity was more effective in deeper anesthesia with little effect in light anesthesia. We suggest that receptive field expansion in light anesthesia arises from a relative increase in excitability of afferent pathways and an accompanying increase in the preponderance of surround excitation vis à vis surround inhibition.

Alfaxalone Alfadolone Mixture↗
PubMed1981

Employee withdrawal and job satisfaction in community residential facilities for mentally retarded persons.

This study was conducted to provide information concerning employee stability in community residential facilities serving mentally retarded persons. Information was collected on turnover, length of service, absenteeism, job satisfaction, and increased overhead costs as a consequence of the turnover rate for 21 randomly selected small and large community residential facility organizations that operated a total of 47 living units in Tennessee. Subjects included all house managers (full-time and relief) and administrator/supervisors in the 21 organizations for fiscal year 1978-1979. The results revealed a significant problem of controllable turnover of direct-service employees. The major factors contributing to this problem appeared to be (a) a lack of effective methods to orient, integrate, and maintain new staff members, (b) low pay and wide variations for amount and kind of work to be accomplished, and (c) a lack of training and support systems to deal with behavior problems presented by some residents.

Absenteeism↗
PubMed1980

Carotid sinus baroreceptor reflex control of the circulation in medial sclerotic and renal hypertensive rabbits and its modification by the aortic baroreceptors.

We studied the reflex control of blood pressure, heart rate, and hindlimb vascular resistance by the carotid sinus baroreceptors in normal (N), experimental renal hypertensive (RH, one kidney renal wrap model), and medial sclerotic (MS) rabbits under urethane anaesthesia using an isolated perfused carotid sinus preparation and auto-perfused hindlimb. The contralateral carotid sinus was denervated. Compared to N rabbits, the blood pressure and hindlimb vascular resistance of RH and MS rabbits were significantly elevated at all carotid sinus pressures 15 weeks after inducing the disease process. The maximum gains of the curves relating carotid sinus pressure to vascular resistance were significantly elevated in the MS and RH rabbits, but those relating carotid sinus pressure to heart rate were significantly reduced. The changes were greatest in the RH group in which the responses also were set to a higher carotid sinus pressure. In the three groups, division of the aortic nerves produced different changes in the sigmoid curves relating carotid sinus pressure to heart rate, blood pressure, and vascular resistance. There was a linear relationship between blood pressure and basal vascular resistance (correlation coefficient 0.88).

Animals↗
PubMed1980

Baroreflex sensitivity in rabbits during the development of experimental renal hypertension and medial sclerosis.

Baroreflex sensitivity was assessed in 9 normotensive (N), 8 renal wrap (one kidney model, RH) and 16 medial sclerotic rabbits (MS, fed on calciferol 50,000 i.u. and calcium lactate 1g for 10 days) before (mean BP;N, 79 +/- 3.3 mm Hg; RH, 80 +/- 7.4 mm Hg; and MS, 83 +/- 1.0 mm Hg) and at monthly intervals for up to 16 weeks after the induction of the disease processes (mean BP;N, 87 +/- 3.9 mm Hg; RH, 127 +/- 7.2 mm Hg and MS, 99 +/- 3.8 mm Hg). Blood pressure was elevated by i.v. phenylephrine (5 and 10 micrograms.kg-1) or angiotensin (250 ng.kg-1) and baroreflex sensitivity assessed by the increase of pulse interval per unit rise of pressure. The pressor response was greater in the RH and MS than in the N rabbits. The baroreflex sensitivity showed a progressive reduction with time and with the elevation of blood pressure in both MS and RH rabbits. The difference was significantly greater (P < 0.01) than in the aged related control rabbits (P < 0.05). There was an inverse relationship between baroreflex sensitivity and the pressor response in MS rabbits. Results indicated progressive baroreceptors dysfunction in hypertensive and medial sclerotic rabbits.

Angiotensin II↗
PubMed1976

Time-course of the reduction of baroreceptor sensitivity in experimental hypertensive rabbits.

1. Hypertension was produced experimentally in three groups of rabbits by atherosclerosis, meical sclerosis and renal encapsulation. 2. The sensitivity of afferent baroreceptor fibre recordings, obtained from an isolated perfused aortic arch preparation, was reduced in all three treated groups. 3. The reduction of baroreceptor sensitivity was directly related to the increase in the lability of the blood pressure in the intact animal and to the reduction of the distensibility of the perfused region. 4. There was a closer relationship between the length of time of rabbits had been hypertensive and the reduction in the baroreceptor sensitivity, than to the level of their blood pressure. 5. The reduction of baroreflex sensitivity obtained by the infusion of phenylephrine was also directly correlated with the period of the hypertension. 6. Baroreceptor resetting occurred to a higher pressure in the renal hypertensive group.

Animals↗
PubMedDate not supplied

Modification of receptive fields of posteriomedial barrel subfield neocortical single units by known concentrations of iontophoresed noradrenaline in the rat.

Using quantitative electromechanical stimulation of vibrissae poststimulus time histograms were used to map the receptive fields of single units from laminae II/III (12 units), IV (24 units) and V (12 units) of the posteriomedial barrel subfield in urethane anaesthetized rats prior to, and during the iontophoresis of known concentrations of Noradrenaline. All units had multivibrissae receptive fields prior to noradrenaline iontophoresis with laminae II/III units having the smallest size of center and surround receptive field and laminae V the largest. Lamina IV showed the strongest center receptive field response probability magnitude (spikes/stimulus) and the shortest modal latency of evoked responses. Noradrenaline iontophoresis diminished the size of surround receptive fields in each lamina and additionally decreased the size of center receptive fields in laminae IV and V. In Lamina IV, in contrast to laminae II/III and V, response probability magnitude from center receptive field vibrissae was not significantly depressed whilst modal latency of the evoked response was significantly reduced.

Animals↗