Timothy O. Neild

Computerised colour: a technique for the assessment of burn scar hypertrophy. A preliminary report

A technique for the objective measurement of one parameter of burn scar hypertrophy is described. The technique involves capturing a video camera image on a computer and subsequent quantitative analysis of the colour of the scar using a custom-written computer programme. By analysing multiple areas and comparing the identical areas over the course of treatment, it is theoretically possible to measure the progress and compare differing modes of therapy.

Electrophysiological basis of arteriolar vasomotion in vivo.

We tested the hypothesis that cyclic changes in membrane potential (Em) underlie spontaneous vasomotion in cheek pouch arterioles of anesthetized hamsters. Diameter oscillations (∼3 min–1) were preceded (∼3 s) by oscillations in Em of smooth muscle cells (SMC) and endothelial cells (EC). Oscillations in Em were resolved into six phases: (1) a period (6 ± 2 s) at the most negative Em observed during vasomotion (–46 ± 2 mV) correlating (r = 0.87, p < 0.01) with time (8 ± 2 s) at the largest diameter observed during vasomotion (41 ± 2 µm); (2) a slow depolarization (1.8 ± 0.2 mV s–1) with no diameter change; (3) a fast (9.1 ± 0.8 mV s–1) depolarization (to –28 ± 2 mV) and constriction; (4) a transient partial repolarization (3–4 mV); (5) a sustained (5 ± 1 s) depolarization (–28 ± 2 mV) correlating (r = 0.78, p < 0.01) with time (3 ± 1 s) at the smallest diameter (27 ± 2 µm) during vasomotion; (6) a slow repolarization (2.5 ± 0.2 mV s–1) and relaxation. The absolute change in Em correlated (r = 0.60, p < 0.01) with the most negative Em. Sodium nitroprusside or nifedipine caused sustained hyperpolarization and dilation, whereas tetraethylammonium or elevated PO2 caused sustained depolarization and constriction. We suggest that vasomotion in vivo reflects spontaneous, cyclic changes in Em of SMC and EC corresponding with cation fluxes across plasma membranes.

Contribution of Active Membrane Processes to Conducted Hyperpolarization in Arterioles of Hamster Cheek Pouch

Objective: Conduction of vasodilation triggered by acetylcholine (ACh) in arteriolar networks reflects hyperpolarization and its spread from cell to cell along the vessel wall. The amplitude and distance of the vasomotor response appear greater than can be explained by simple passive decay of the electrical signal. The authors tested the hypothesis that the conduction of hyperpolarization involves active membrane processes as the signal travels along the arteriolar wall.

Noncultured keratinocyte/melanocyte cosuspension: effect on reepithelialization and repigmentation--a randomized, placebo-controlled study.

Randomized controlled trials in the literature investigating the efficacy of noncultured keratinocyte/melanocyte suspensions are scarce; however, the advocates of such techniques press the value of their application based largely on case studies and anecdote. Caucasian patients with burn hypopigmentation seldom request cosmetic revision making worthwhile clinical trials difficult so that informal case treatments with new therapies generate anecdotal results. A randomized, placebo-controlled trial was carried out to evaluate whether cosuspensions of noncultured skin cells are capable of (1) decreasing the time to reepithelialization and (2) reestablishing pigmentation in vitiligo leukoderma following epidermal/superficial dermal ablation (in the knowledge that a positive result would make the technique likely to be successful in burn hypopigmentation). Vitiligo is common and is socially more debilitating such that suitable trial subjects for new therapies from this pool are more forthcoming. This study demonstrated that suspensions of noncultured keratinocytes and melanocytes do not decrease the time to epithelialization of superficial partial thickness wounds compared with controls. It also suggested that the achievement, quality, and duration of any pigmentation were unpredictable and largely disappointing. Some pigmentation was recorded in placebo-treated areas indicating an effect of the method of epidermal ablation in these patients. These findings have mandated a complete review of the use of these techniques in burn care at the Royal Adelaide Hospital; they have been omitted from surgical protocols where the aim of use was to speed reepithelialization. Their infrequent use in burns hypopigmentation will continue contingent on the successful repigmentation of a test patch.

Simulating the spread of membrane potential changes in arteriolar networks.

Objective: Our aim was to simulate the spread of membrane potential changes in microvascular trees and then make the simulation programs accessible to other researchers. We have applied our simulations to demonstrate the implications of electrical coupling between arteriolar smooth muscle and endothelium.

An equation describing spread of membrane potential changes in a short segment of blood vessel

The spread of membrane potential changes throughout certain cells and tissues plays an important role in their physiology. The attenuation of such changes in any tissue is usually characterized by the cable length constant lambda, which can be determined experimentally if the equations describing membrane potential spread in the tissue are known. Here we derive an equation describing spread of membrane potential changes in a short cable, which is an appropriate model for short segments of blood vessels. This equation is more general than those already published in that the positions of both the current source that gives rise to a potential change, and the point at which the change is measured, can be anywhere along the cable.

Immunohistochemical and electrophysiological characterization of submucous neurons from the guinea-pig small intestine in organ culture

Immunohistochemical and electrophysiological properties of submucous neurons were investigated in organ cultures of the guinea-pig small intestine. Preparations of submucosa, with or without the myenteric plexus attached, were maintained in vitro for 3 to 5 days. Immunohistochemical labelling for peptides revealed that the cultured submucous plexus remained substantially intact and the immunoreactivity of cell bodies was well preserved. Substantial sprouting of nerve fibers immunoreactive for vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) was evident in submucous ganglia after 5 days in organ culture. Nerve fibers immunoreactive for substance P. somatostatin, 5-hydroxytryptamine or tyrosine hydroxylase were substantially depleted in submucous ganglia or perivascular nerves at 3 days and had virtually disappeared after 5 days in cultures of isolated submucosa. During intracellular recording from submucous neurons, action potentials were initiated by depolarizing current pulses in all neurons cultured with or without the myenteric plexus and muscle layers. Electrical stimulation of internodal strands evoked fast excitatory synaptic potentials (fast EPSPs) in nearly all neurons whether or not the myenteric plexus was present during the culture period up to 5 days. The removal of myenteric plexus and extrinsic nerves did not abolish fast EPSPs from submucous neurons, suggesting that some fast EPSPs may originate from neurons in the submucous plexus, although the possibility that new synapses formed by sprouting, or surviving axons severed from myenteric or sympathetic ganglia may have been functional, cannot be entirely excluded. This work demonstrates that the immunohistochemical and electrophysiological characteristics of submucous neurons are largely maintained in organ cultures of the submucosa.

Electrical coupling between smooth muscle and endothelium in arterioles of the guinea-pig small intestine

Equations describing the steady-state passive electrical properties of arterioles have been derived. The arteriole was modelled as having two thin layers of cells (muscle and endothelium) with strong electrical coupling between cells within a layer and variable coupling between the layers. The model indicated that spread of membrane potential changes was highly dependent on the thickness of cells within the layers. The model was also used to identify the optimal experimental strategy for detecting coupling between the two layers, and experiments were carried out on arterioles from the guinea-pig small intestine. Thickness of the endothelial layer was measured using electron microscopy and was found to be around 0.5 microm. Electrical input resistance was measured in intact arterioles and compared to input resistance of arterioles from which the endothelium had been removed. The experiments confirmed that there was a strong electrical coupling between the muscle and endothelium in these vessels.

Design concepts for adult learning with computers, based on student use of computers in a medical course

SUMMARY Many Computer‐Assisted Learning (CAL) programs have a structure very similar to small conventional text books. They differ from books in their use of sound or animation, but they often contain less material and provide less flexibility of access at a higher cost. They offer no special advantages to the adult learner, despite their advanced technology. A survey of medical students at Flinders University revealed that they largely ignored comprehensive book‐like programs. They favoured smaller programs that gave a specialized approach to one topic, and that took advantage of the graphic and sound capabilities of a computer. It appeared that if CAL programs are to be useful, especially for adult learners, they will need to exploit the features unique to computers. If we see adult learning as a process of exploration with encouragement to expand knowledge freely in the learners’ chosen direction, CAL programs with connections to appropriate starting points on the Internet would be a valuable resource.

Cellular coupling and conducted vasomotor responses.

1. The present brief review examines the concept of spreading vasodilator responses in arteriolar trees, its physiological relevance and possible mechanisms.