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Biomedical subjects

R J MacGregor

Publications and source records attributed to R J MacGregor.

At least 19 recordsLinked to original sources
PubMed2001

Neonatal catecholamine levels and neurodevelopmental outcome: a cohort study.

AIMS: To determine whether neonatal plasma catecholamine concentrations can be used to predict (a) death plus disability and (b) motor and cognitive impairment at 5 years of age. METHODS: A cohort comprised 136 preterm infants from two randomised controlled trials of neonatal sedation (1989-1992). Adrenaline (epinephrine) and noradrenaline (norepinephrine) were measured at baseline (first day) and 24 hours later. Intelligence and motor ability were assessed at 5-6 years. RESULTS: Infants who died or sustained disability had significantly higher plasma noradrenaline levels on the second day of life. Noradrenaline levels above 9.0 nmol/l were most predictive of death (likelihood ratio 3.27; 95% confidence interval 1.48 to 7.23) and death plus disability (likelihood ratio 3. 55; 95% confidence interval 1.77 to 7.10). There was no correlation between neonatal catecholamine levels and cognitive or motor impairment at 5-6 years. CONCLUSIONS: Elevated noradrenaline levels are associated with adverse outcome in preterm infants; however, the power to predict death or disability is limited and they are not predictive of later motor or cognitive impairment.

Biomarkers↗
PubMed1997

Prospective assessment of incontinence after radical retropubic prostatectomy: objective and subjective analysis.

OBJECTIVES: To assess prospectively-using pad test and questionnaire-the rate and degree of incontinence after radical retropubic prostatectomy, to analyze factors that may predispose individuals to postoperative incontinence, and to assess the impact of incontinence on patient lifestyle. METHODS: Fifty-one consecutive patients were assessed at 3-month intervals for 1 year after radical retropubic prostatectomy. Patients were objectively assessed using a 1-hour pad test and subjectively assessed by questionnaire. Incontinence was graded objectively according to the change in weight of the pad at 1 hour and subjectively by the number of pads used per day. Lifestyle modifications were assessed by questionnaire at 12 months. A number of variable factors were studied to assess risk factors for postoperative incontinence. RESULTS: Continence continued to improve up to 12 months. At 12 months, pad testing revealed 84% of patients were dry, 6% were mildly incontinent. 6% were moderately incontinent, and 4% were severely incontinent. Questionnaire assessment revealed 80% wore no pad, 14% had mild incontinence, 4% had moderate incontinence, and 2% had severe incontinence. Pad testing was not as sensitive as the questionnaire for the detection of minimal incontinence but was more reliable for moderate and severe levels. Patients made lifestyle changes proportional to the level of incontinence. No predisposing factor was identified for the development of incontinence after radical retropubic prostatectomy. CONCLUSIONS: Significant incontinence after radical prostatectomy occurs in as many as 10% of patients. Pad testing provides an inexpensive and simple form of objective assessment in patients with bothersome incontinence and allows documentation of improvement over time.

Aged↗
PubMed1996

Sensory gating in a computer model of the CA3 neural network of the hippocampus.

We have developed a unique computer model of the CA3 region of the hippocampus that simulates the P50 auditory evoked potential response to repeated stimuli in order to study the neuronal circuits involved in a sensory processing deficit associated with schizophrenia. Our computer model of the CA3 hippocampal network includes recurrent activation from within the CA3 region as well as input from the entorhinal cortex and the medial septal nucleus. We used the model to help us determine if the cortical and septal inputs to the CA3 hippocampus alone are responsible for the gating of auditory evoked activity, or if the strong recurrent activity within the CA3 region contributes to this phenomenon. The model suggests that the medial septal input is critical for normal gating; however, to a large extent the activity of the medial septal input can be replaced by simulated stimulation of the hippocampal neurons by a nicotinic agonist. The model is thus consistent with experimental data that show that nicotine restores gating of the N40 evoked potential in fimbria-fornix lesioned rats and of the P50 evoked potential in schizophrenic patients.

Animals↗
PubMed1995

Characterization, scaling, and partial representation of neural junctions and coordinated firing patterns by dynamic similarity.

This paper presents a dynamic-similarity-based system for mathematically characterizing the functional connectivity and information flow of neural junctions. This approach allows for quantitative comparison of operations of neural junctions across systems, and an interpretation of their connectivity parameters in terms of the flow of multiunit firing patterns. The paper further uses this characterization to show how to rationally construct reduced operational models of neural junctions. Both uniformly proportional scaling and partial fragmentary representations are developed. The uniformly scaled models are better adapted to overall capacities and broader theoretical conceptualizations; the partial representations are better adapted to direct comparison with microelectrode experimentation. The characterization of information flow is based on coordinated multiunit patterns such as synfire chains or sequential configurations. The system can be applied to component parts of large composite networks including junctions with topographical patchiness and other irregularities. The characterization should be of use to anatomists, physiologists, modelers, and theorists. The theory predicts that the necessity for cooperative confluence of synaptic potentials in sending and receiving sequential configurations across topographically constrained projection fields requires the existence of functional 'pattern modules' within the topographical synaptology of the junction.

Animals↗
PubMed1995

Characterization, scaling, and partial representation of diffuse and discrete input junctions to CA3 hippocampus.

This paper applies a general mathematical system for characterizing and scaling functional connectivity and information flow across the diffuse (EC) and discrete (DG) input junctions to the CA3 hippocampus. Both gross connectivity and coordinated multiunit informational firing patterns are quantitatively characterized in terms of 32 defining parameters interrelated by 17 equations, and then scaled down according to rules for uniformly proportional scaling and for partial representation. The diffuse EC-CA3 junction is shown to be uniformly scalable with realistic representation of both essential spatiotemporal cooperativity and coordinated firing patterns down to populations of a few hundred neurons. Scaling of the discrete DG-CA3 junction can be effected with a two-step process, which necessarily deviates from uniform proportionality but nonetheless produces a valuable and readily interpretable reduced model, also utilizing a few hundred neurons in the receiving population. Partial representation produces a reduced model of only a portion of the full network where each model neuron corresponds directly to a biological neuron. The mathematical analysis illustrated here shows that although omissions and distortions are inescapable in such an application, satisfactorily complete and accurate models the size of pattern modules are possible. Finally, the mathematical characterization of these junctions generates a theory which sees the DG as a definer of the fine structure of embedded traces in the hippocampus and entire coordinated patterns of sequences of 14-cell links in CA3 as triggered by the firing of sequences of individual neurons in DG.

Animals↗
PubMed1991

Sequential configuration model for firing patterns in local neural networks.

This paper presents a sequential configuration model to represent the coordinated firing patterns of memory traces in groups of neurons in local networks. Computer simulations are used to study the dynamic properties of memory traces selectively retrieved from networks in which multiple memory traces have been embedded according to the sequential configuration model. Distinct memory traces which utilize the same neurons, but differ only in temporal sequencing are selectively retrievable. Firing patterns of constituent neurons of retrieved memory traces exhibit the main properties of neurons observed in multi microelectrode recordings. The paper shows how to adjust relative synaptic weightings so as to control the disruptive influences of cross-talk in multipy-embedded networks. The theoretical distinction between (primarily anatomical) beds and (primarily physiological) realizations underlines the fundamentally stochastic nature of network firing patterns, and allows the definition of 4 degrees of clarity of retrieved memory traces.

Animals↗
PubMed1991

Cross-talk theory of memory capacity in neural networks.

The present paper presents a theory for the mechanics of cross-talk among constituent neurons in networks in which multiple memory traces have been embedded, and develops criteria for memory capacity based on the disruptive influences of this cross-talk. The theory is based on interconnection patterns defined by the sequential configuration model of dynamic firing patterns. The theory accurately predicts the memory capacities observed in computer simulated nets, and predicts that cortical-like modules should be able to store up to about 300-900 selectively retrievable memory traces before disruption by cross-talk is likely. It also predicts that the cortex may has designed itself for modules of 30,000 neurons to at least in part to optimize memory capacity.

Animals↗
PubMed1988

Theory of dynamic similarity in neuronal systems.

1. The techniques of dynamic similarity from the engineering science of fluid mechanics are applied to neuronal systems to suggest how to scale down critical parameters (such as numbers of constituent cells and synapses, synaptic strengths, thresholds, etc.) from naturally occurring systems to computer models. 2. The interconnectivity of a prototypical neuronal junction is defined in terms of the total number of projecting fibers, receiving cells, synapses, and directly connected cell fiber pairs. Critical derivative parameters are defined in terms of these, including: a global convergence factor, alpha ij, which is the ratio of the numbers of projecting fibers to receiving cells; and an interconnectivity completeness parameter or microscopic convergence/divergence parameter, gamma ij, which measures both the percentage of cells to which a given sending fiber projects (and the percentage of fibers from which a given cell receives) and the percentage of cell fiber combinations which are directly connected. 3. Analysis of the differential equations governing neuroelectric activity in constituent neurons suggests the definition of a sensitivity parameter complex, sigma ij (with components eta ij and mu ij) for each ij junction. These numbers represent the ratio of synaptic drive to current leakage in nonactive neurons. 4. A model for quasi-steady firing suggests the definition of a parameter, rho *j, which may be used to characterize the level of activity in a given neuronal population in terms of its synaptic drive and system parameters. It may be considered as the neuronal analog of the Reynolds number in fluid mechanics. 5. The analysis implies that computer models of neuronal systems should be scaled so as to keep the parameters alpha ij, gamma ij, and sigma ij for every junction at the same values as in the corresponding junctions of naturally occurring system being modeled. Equations for a scaling factor, chi, numbers of constituent synapses, thresholds, etc., are provided. The scaling method is illustrated by a computer simulation example and by application to the junction of the perforant path fibers to the granule cells of the hippocampus. 6. The analysis shows that there is a fundamental trade-off in scaled down computer models between verisimilitude at the level of network interconnectivity and verisimilitude at the level of individual neuronal dynamics. 7. The approach of dynamic similarity is discussed with respect to compression of free parameters and predictive comparison of naturally occurring systems.

Action Potentials↗
PubMed1984

Incidental adenocarcinoma of the prostate: the role of repeat transurethral resection in staging.

Accurate staging of patients with incidental prostatic adenocarcinoma (A1 vs A2) is crucial to the selection of appropriate treatment. To evaluate the potential sampling error in specimens obtained by transurethral resection, repeat resection was performed on 31 patients pathologically staged as A1 (five or less chips with tumor). Second specimens showed no tumor in 22 (71%), stage A1 in six (20%), and stage A2 in three (9%). The weight of tissue removed at reresection was greater in patients found to have more extensive involvement (P less than 0.005). No patient with initial Gleason score 2, 3, or 4 had stage A2 at reresection. Repeat resection is not routinely necessary, but may be helpful when the tumor is high grade but of minimal extent, in an anxious younger patient who may wish therapy if disease persists, or where some suspicion of an incomplete resection exists.

Adenocarcinoma↗
PubMed1984

Long-term followup of the artificial urinary sphincter.

The artificial urinary sphincter with a pressure regulating balloon was implanted in 30 patients. All implantations were done before September 1982, for a minimum followup of 1 year and an average followup of 3.7 years. Of the patients 21 (70 per cent) have a functioning sphincter: 17 are continent and 4 are slightly incontinent, requiring 1 pad per day. Failure was owing to erosion in 6 patients and infection of the device in 3. Critical factors for successful implantation include preoperative evaluation, cuff location and pressure, primary deactivation and postoperative care. Our experience supports the further use of this device in appropriate cases.

Adult↗
PubMed1983

Diuretic radionuclide urography in the diagnosis of suspected ureteral obstruction following renal transplantation.

The diuretic radionuclide urogram has been shown to be an effective method to discriminate obstructive from nonobstructive hydronephrosis in nontransplanted renal units. This test was evaluated in 9 renal transplant patients with suspected partial ureteral obstruction. An obstructed pattern in 2 patients was confirmed and relieved by an operation. Nonobstructed patterns in 7 patients were verified by long-term clinical followup and subsequent ancillary testing. Accurate in all 9 cases, this investigation appears to provide a safe, noninvasive method to diagnose suspected post-transplantation ureteral obstruction.

Adult↗
PubMed1982

Treatment of vasculogenic erectile dysfunction by direct anastomosis of the inferior epigastric artery to the central artery to the corpus cavernosum.

We present a case of vasculogenic erectile dysfunction following trauma, which was treated successfully by direct anastomosis of the inferior epigastric artery to the central artery of the corpus cavernosum. This is the first report of this operative technique. Its theoretical advantages over previously described revascularization techniques include an end-to-side vascular anastomosis, possibly decreasing perianastomotic fibrosis, and regulation of new blood flow into the corporeal bodies by the neurovascular mechanism of the central artery.

Abdominal Muscles↗
PubMed1981

The alpha-adrenergic blocking action of prazosin hydrochloride on the canine urethra.

We studied the action of prazosin hydrochloride on the canine urethra by measuring urethral pressure profiles, employing both oral and intravenous preparations. Its interaction with intravenous ephedrine sulfate was determined. Prazosin hydrochloride produced a marked depressant effect on the maximum urethral pressure and the urethral pressure profile. It antagonized the effect of intravenous ephedrine sulfate. We believe that the effects of prazosin hydrochloride are caused by alpha-adrenergic blockade and that application of this drug to human voiding dysfunction should be considered.

Adrenergic alpha-Antagonists↗