William P. Ireland

Ultrastructural and secretory heterogeneity of fa/fa (Zucker) rat islets.

Many previous studies of obese rodents documented biochemical changes in pancreatic islets that contribute to hyperinsulinemia in vivo. Those studies used heterogeneous populations of islets, although the size of islets from obese rats ranges from < 100 to > 500 microm. Here, functional and morphological changes in size-sorted (< 125 and > 250 microm diameter) islets from obese Zucker (fa/fa) rats were correlated. Ultrastructural examination revealed that > 250 microm cultured islets had an increased number of immature secretory granules in the beta cells. The number of degranulated beta cells in > 250 and < 125 microm cultured islets from fa/fa rats was higher than in lean rat islets (33 vs 25%). The glucose EC50 values for cultured islets were 4.64 +/- 0.43, 7.9 +/- 0.70 and 7.29 +/- 1.64 mmol.l(-1) for > 250 microm, < 125 microm, and lean groups, respectively. Inhibition of insulin secretion by 10 mmol.l(-1) mannoheptulose was reduced by 50% in > 250 microm islets compared with small islets. Studies of individual beta cells by reverse hemolytic plaque assay revealed 3-fold more cells from > 250 microm islets were stimulated by 1.4 mmol.l(-1) glucose than cells from < 125 microm islets. We conclude that functional defects in mixed size populations of islets from fa/fa rats are mainly due to alterations in the large islets, whereas smaller islets have relatively normal function. Exposure to high glucose exacerbates morphological and functional differences of large islets, which could have important implications in the transition to noninsulin-dependent diabetes when beta cell insulin production is unable to compensate for hyperglycemia.

Synaptic density in chronic animals with experimental neurofibrillary changes

Synaptic density was quantitated in the cerebral cortex and subiculum of rabbits with experimental neurofibrillary changes. Animals were subjected to subcutaneous injection of aluminum tartrate for 90 days, and synapses stained with ethanolic phosphotungstic acid were analyzed in animals killed 100, 200, or 300 days postinjection with aluminum tartrate. A significant difference was found in synaptic density between animals injected with aluminum tartrate and their age-matched controls. This difference was a result of a low synaptic density present in animals killed 200 or 300 days postinjection of aluminum tartrate. In contrast, animals killed 100 days postinjection revealed the same synaptic density as their control. The data suggest that the synaptic depopulation associated with experimental neurofibrillary changes is a gradual process, and such changes are demonstrable only long after the initial appearance of neurofibrillary changes.

A mathematical model for the growth of dendritic trees

A theoretical model for calculating the total length of dendritic trees is presented. Predictions of velocity of dendritic growth, time when branching begins and mean maximal extent of dendritic tree derived from the model for apical dendrites in entorhinal cortex of the rat are presented.

Dendritic alterations in chronic animals with experimental neurofibrillary changes

Dendritic changes were quantitated in the cerebral cortex and subiculum of rabbits injected with aluminum tartrate for 90 days (5 days/week) at 100, 200, and 300 days after the last injection of aluminum. Both apical and basal dendrites of the cerebral cortex and subiculum responded similarly to aluminum tartrate. The dendrites were fewer and shorter in the animals examined at 200 and 300 days postinjection of aluminum tartrate. Such dendritic changes were more prominent at longer postinjection times and in dendrites that were more peripheral from the cell body. Aluminum-induced changes in apical dendrites were more prominent in the subiculum than in the cerebral cortex. Aluminum-induced changes in basal dendrites, however, were more prominent in the cerebral cortex than in the subiculum. The results suggest a time delay between the initial accumulation of neurofibrillary changes and the subsequent loss of peripheral dendritic branches, which appears to be long-lasting.

Effects of modulatory agents on neurally-mediated responses of trout intestinal smooth musclein vitro.

Mediators and mechanisms responsible for the inhibitory modulation of trout intestinal smooth muscle were examined using a series of putative mediators and substances known to modulate neurotransmission in mammalian systems. Frequency response relationships to transmural stimulation and concentration response relationships to 5-hydroxytryptamine, carbachol, and substance P were established on paired segments of rainbow trout intestinein vitro in the presence and absence of putative modulatory agents. Modulation of neurally-mediated contractions of trout intestine was achieved with dibutyryl cyclic AMP and forskolin, agents that increase intracellular levels of cyclic AMP. The effect appears to be at the level of the smooth muscle, since the adenylate cyclase activator, forskolin, inhibited muscarinic and serotoninergic contractions as well as transmurally stimulated contractions. Substance P-induced contractions were unaffected by forskolin. The endogenous agonists/neurotransmitters which would increase cyclic AMP levels in rainbow trout intestinal smooth muscle are as yet unknown. The effects do not appear to be modulated by vasoactive intestinal peptide (VIP), calcitonin, calcitonin gene-related peptide (CGRP), or agents that activate β-adrenoceptors. Prostaglandin E2 (PGE2) and α2-adrenergenic agonists are possible agents which will decrease contractility of the smooth muscle. They were only active in the proximal intestine and on transmurally stimulated contractions. The effects of both PGE2 and α2-agonists appear to be prejunctional, decreasing release of contractile neurotransmitters in the enteric nervous system.

The effects of acute temperature change on smooth muscle contractility of rainbow trout (Oncorhynchus mykiss Walbaum) intestine.

The effects of altered temperature in vivo on in vitro smooth muscle contractility of rainbow trout intestine were investigated. Initial analysis of the data revealed a seasonal variation in the maximal tension of intestinal smooth muscle attainable with 5-hydroxytryptamine (serotonin), carbachol, KCl, and transmural stimulation in vitro. Peaks occurred in spring and troughs in autumn. There was no seasonal cycling of the potency of the stimulants. All data regarding the efficacy of the stimulants were subsequently corrected for seasonal variation. The response of smooth muscle depends on the temperature of the water in which the fish are placed (2°C−20°C). There was a marked linear increase in efficacy and a slight increase in potency of the stimulants with increasing temperature. Changes in responsiveness of the intestinal smooth muscle occurred within 30 min of moving the fish between tanks. Smooth muscle reactivity returned to pretreatment values by 48h. Any changes in responsiveness with regards to time were unlikely to be as a consequence of water temperature, but may have been a result of handling stress.

A simple mathematical model to aid quantification of electrophoresis gels by image analysis

In many scientific disciplines, measurements are taken from films that have been exposed to energetic sources. Examples include radiographs where the source is an X‐ray tube, autoradiography where the source is a radioactive isotope and electrophoresis gels where the source is an enhanced chemiluminescence reaction. In these situations it is of interest to quantify the darkening of the film and compute the strength of the source which in the cases of autoradiography and electrophoresis can be used to compute unknown concentrations of biochemicals. We developed a simple mathematical model of the darkening of films in radiography, autoradiography and electrophoresis bands disclosed by enhanced chemiluminescence, and present formulae to calculate the strength of the source from measurement of film blackening by image analysis. A simple model is used in two examples to predict blackening of film exposed to electromagnetic radiation. This blackening is measured by image analysis. Results show reasonable agreement between predictions of the model and blackening of film for the examples chosen. This model is proposed as an aid to quantification of electrophoresis gels.

A method for finding stereotaxic coordinates from brain sections

A method for finding the stereotaxic coordinates of brain areas from actual brain sections is presented. It uses a digitizer connected to a computer to gather coordinates from photographs of brain sections. The coordinates are mathematically translated and rotated to yield stereotaxic atlas coordinates of the areas digitized.

Mathematical means to allow computer calculation of stereotaxic settings.

Stereotaxic instruments have wide use in neuroscience research. In certain of these machines the electrode can be introduced at an angle as well as perpendicularly. Computation of instrument settings to place the electrode in the desired location is the problem this paper addresses. Mathematical formulae are presented that allow a computer to calculate instrument settings given coordinates and angles read from a stereotaxic atlas.

Changes in smooth muscle contractility of rainbow trout (Oncorhynchus mykiss Walbaum) intestine during acclimation to altered temperature.

The effects of altered water temperature in vivo on in vitro smooth muscle contractility of rainbow trout intestine were investigated. Temperature has a significant effect on receptor-mediated intestinal smooth muscle contractility in the rainbow trout. The efficacy of 5-HT, carbachol, and transmural stimulation increased with temperatures above 10°C, with an optimal increase at 15°C. There was also a modest increase in the potency of 5-HT and carbachol within 2 days of establishing trout at 20°C. By day 8, most of these changes had either stabilized or were returning to control values, suggesting that acclimation changes in membranes and enzyme activities were taking effect. However, the contractile responses to carbachol and transmural stimulation were still increasing at this time. This may imply that the muscarinic receptors are more resistant to membrane acclimation changes and may take longer to adapt. Because these experiments were controlled for handling stress and seasonal changes that affect contractility, we have been able to demonstrate some early changes in smooth muscle contractility that occur during acclimation to altered temperature.