Lysyl oxidase-mediated crosslinking in granulation tissue collagen in two models of hyperglycemia.

Enzymatically mediated crosslinks and nonenzymatic glycation were quantified in granulation tissue collagen in two models of hyperglycemia, diabetes and galactosemia, that have opposite effects on collagen solubility. The effects of castration, which alters collagen solubility, was also investigated. Collagen from both diabetic and galactosemic rats had significantly increased levels of dihydroxylysinonorleucine (DHLNL), a difunctional reducible crosslink. Galactosemic rats had significantly decreased levels of hydroxypyridinium, a trifunctional product of DHLNL and hydroxylysine, relative to control values, while diabetic rats had normal levels. Values for all other detectable crosslinks in collagen from hyperglycemic rats were indistinguishable from control values. Nonenzymatic glycation was increased in both groups of hyperglycemic rats. In diabetic rats, but not in galactosemic rats, nonenzymatic glycation was strongly correlated with DHLNL content. Castration had no effect on crosslink content of collagen from diabetic or galactosemic rats. This study demonstrates that (1) collagen crosslinking is abnormal in granulation tissue collagen in both experimental diabetes and galactosemia, (2) these changes are similar to those observed in skin collagen from insulin-dependent diabetic subjects and (3) the crosslinking abnormalities are not correlated with alterations in collagen solubility. We conclude that hyperglycemia-associated increases in immature crosslinks cannot account for altered collagen solubility, although impaired maturation of such crosslinks may be partially responsible for the lathyrogenic effect of galactosemia.     

Characterization of Oxidative Stress in Various Tissues of Diabetic and Galactose-fed Rats

Rats fed a galactose-rich diet have been used for several years as a model for diabetes to study, particularly in the eye, the effects of excess blood hexoses. This study sought to determine the utility of galactosemia as a model for oxidative stress in extraocular tissues by examining biomarkers of oxidative stress in galactose-fed rats and experimentally-induced diabetic rats. Sprague-Dawley rats were divided into four groups: experimental control; streptozotocin-induced diabetic; insulin-treated diabetic; and galactose-fed. The rats were maintained on these regimens for 30 days, at which point the activities of catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase, as well as levels of lipid peroxidation and reduced and oxidized glutathione were determined in heart, liver, and kidney. This study indicates that while there are some similarities between galactosemic and diabetic rats in these measured indices of oxidative stress (hepatic catalase activity levels and hepatic and renal levels of oxidized glutathione in both diabetic and galactosemic rats were significantly decreased when compared to normal), overall the galactosemic rat model is not closely parallel to the diabetic rat model in extra-ocular tissues. In addition, several effects of diabetes (increased hepatic glutathione peroxidase activity, increased superoxide dismutase activity in kidney and heart, decreased renal and increased cardiac catalase activity) were not mimicked in galactosemic rats, and glutathione concentration in both liver and heart was affected in opposite ways in diabetic rats and galactose- fed rats. Insulin treatment reversed/prevented the activity changes in renal and cardiac superoxide dismutase, renal and cardiac catalase, and hepatic glutathione peroxidase as well as the hepatic changes in lipid peroxidation and reduced and oxidized glutathione, and the increase in cardiac glutathione. Thus, prudence should be exercised in the use of experimentally galactosemic rats as a model for diabetes until the correspondence of the models has been more fully characterized.     

Lysyl oxidase-mediated crosslinking in granulation tissue collagen in two models of hyperglycemia

Enzymatically mediated crosslinks and nonenzymatic glycation were quantified in granulation tissue collagen in two models of hyperglycemia, diabetes and galactosemia, that have opposite effects on collagen solubility. The effects of castration, which alters collagen solubility, was also investigated. Collagen from both diabetic and galactosenic rats had significantly increased levels of dihydroxylysinonorleucine (DHLNL), a difunctional reducible crosslink. Galactosemic rats had significantly decreased levels of hydroxypyridinium, a trifunctional product of DHLNL and hydroxylyse, relative to control values, while diabetic rats had normal levels. Values for all other detectable crosslinks in collagen from hyperglycemic rats were indistinguishable from control values. Nonezymatic glycation was increased in both groups of hyperglycemic rats. In diabetic rats, but not in galactosemic rats, nonenzymatic glycation was strongly correlated DHLNL content. Castration had no effect on crosslink content of collagen from diabetic or galactosemic rats. This study demonstrates that (1) collagen crosslinking is abnormal in granulation tissue collagen in both experimental diabetes and galactosemia, (2) these changes are similar to those observed in skin collagen from insulin-dependent diabetic subjects and (3) the crosslinking abnormalities are not correlated with alterations in collagen solubility. We conclude that hyperglycemia-associated increases in immature crosslinks cannot acount for altered collagen solubility, although impaired maturation of such crosslinks may be partially responsible for the lathyrogenic effect of galactosemia.     

Ultrastructural localization of blood-retinal barrier breakdown in diabetic and galactosemic rats

Breakdown of the blood-retinal barrier (BRB) is an early event in diabetic and galactosemic rats, but the location and nature of the specific defect(s) are controversial. Using an electron microscopic immunocytochemical technique, the retinas of normal, diabetic, and galactosemic rats were immunostained for endogenous albumin. Normal rats showed little evidence of BRB breakdown at either the inner barrier (retinal vasculature) or the outer barrier (retinal pigment epithelium) (RPE). In diabetic and galactosemic rats, as was true in human diabetics, BRB breakdown occurred predominantly at the inner BRB, but in some cases at the outer barrier as well. Treatment with the aldose reductase inhibitor sorbinil largely prevented BRB failure in galactosemic rats. In the inner retina of diabetic and galactosemic rats, albumin was frequently demonstrated on the abluminal side of the retinal capillary endothelium (RCE) in intercellular spaces, basal laminae, pericytes, ganglion cells, astrocytes, and the perinuclear cytoplasm of cells in the inner nuclear layer. Albumin did not appear to cross RCE cell junctions; however, it was occasionally seen in RCE cytoplasm of galactosemic rats. In the outer retina, albumin was frequently detected in the subretinal space, in the intercellular space between photoreceptors, and in the perinuclear cytoplasm of photoreceptor cells, but was only infrequently found in the RPE cells constituting the barrier. Albumin derived from the choroidal vasculature did not appear to cross the tight junctions of the RPE. These findings suggest that specific sites of BRB compromise are infrequent but that once albumin has crossed the RCE or RPE it freely permeates the retinal tissue by filling intercellular spaces and permeating the membranes of cells not implicated in BRB formation. The diffuse cytoplasmic staining of some RCE and RPE cells suggests that the predominant means of BRB breakdown in diabetes and galactosemia involves increased focal permeability of the surface membranes of the RCE and RPE cells rather than defective tight junctions or vesicular transport.     

Dopaminergic modulation of the P50 auditory-evoked potential in a computer model of the CA3 region of the hippocampus: its relationship to sensory gating in schizophrenia

 We modeled the neuronal circuits that may underlie a sensory-processing deficit associated with schizophrenia. Schizophrenic patients have small P50 auditory-evoked responses to click stimuli compared to normal subjects. The P50 auditory-evoked response is a positive waveform recorded in the EEG approximately 50 ms after the auditory click stimulus. In addition to relatively small amplitudes, schizophrenic patients do not gate or suppress the P50 auditory-evoked response to the second of two paired-click stimuli spaced 0.5 s apart. Neuropleptic medication, which decreases dopaminergic neuronal transmission, increases the amplitude of the P50 auditory-evoked response but does not improve gating. Normal subjects have large P50 auditory-evoked responses to click stimuli when compared to unmedicated schizophrenic patients, and they gate their response to paired click stimuli or have smaller P50 auditory-evoked response amplitudes to the second of two click stimuli spaced 0.5 s apart. Schizophrenic patients do not gate and have similar response amplitudes to both clicks. We hypothesized that the small amplitudes of unmedicated schizophrenic subjects were due to a state of occlusion whereby excessive background noise in local circuits reduced the ability of cells to respond synchronously to sensory input, thereby reducing the amplitude of the P50 waveform in the EEG. Because the P50 auditory-evoked potential amplitudes increased with neuroleptic medication, which reduces dopaminergic neuronal transmission, we hypothesized a role for dopamine in modulating the signal-to-noise (S/N) in the local circuits responsible for sensory gating. To test the hypothesis that modulation of the S/N ratio reduces sensory gating, we developed a model of the effects of dopaminergic neuronal transmission that modulates the S/N in neuronal circuits. The model uses the biologically relevant computer model of the CA3 region of the hippocampus developed in the companion paper [Moxon et al. (2003) Biol Cybern, this volume]. Modified Hebb cell assemblies represented the response of the network to the click stimulus. The results of our model showed that excessive dopaminergic input impaired the ability of cells to respond synchronously to sensory input, which reduced the amplitudes of the P50 evoked responses. Received: 3 December 2001 / Accepted: 23 October 2002 / Published online: 28 February 2003 Correspondence to: K.A. Moxon (e-mail: karen.moxon@drexel.edu, Tel.: +1-215-8951959, Fax: +1-215-8954983) Supported by USPHS, MH01245 & MH58414, MH-01121, and research grants from the Department of Veterans Affairs and the National Alliance for Research on Schizophrenia and Depression.     

Auditory neuropathy: a report on three cases with early onsets and major neonatal illnesses

We report 3 children without any brainstem auditory evoked potential (BAEP) neural component who all retained isolated cochlear microphonic potentials as well as click-evoked otoacoustic emissions. Two of them demonstrated only moderately impaired audiometric thresholds. These features correspond to a peculiar pattern of auditory dysfunction recently coined `auditory neuropathy'. In contrast with the published previous cases of auditory neuropathy presenting with an acquired hearing deficit as children or young adults, all 3 children had a history of major neonatal illness and the auditory neuropathy was already demonstrated in the first months of their lives.     

Vasopressin and oxytocin do not influence early sensory processing but affect mood and activation in man

Effects of arginine-vasopressin (AVP) and oxytocin (OX) on brainstem and middle latency auditory-evoked potentials (BAEP and MAEP), reflecting early sensory processing within the specific auditory pathways and primary auditory cortex, were investigated. Additionally, subjects rated their feelings of activation and mood on an adjective check list (EWL). The experiments were undertaken in 12 healthy male volunteers, receiving either placebo, 0.15 IU AVP, 0.5 IU AVP or 0.5 IU OX as IV bolus injection according to a within-subject double-blind design. There were no consistent effects of AVP and OX on BAEPs and MAEPs. AVP decreased self-perceived deactivation, fatigue and arousal. Results do not suggest an effect of AVP and OX on early stages of sensory processing, but, consistent with previous studies, demonstrate changes towards increased (self-perceived) general activation following administration of these hormones.     

The antidiabetic effects of cysteinyl metformin, a newly synthesized agent, in alloxan- and streptozocin-induced diabetic rats

In this paper, the antidiabetic effects of cysteinyl metformin (CM), a newly synthesized agent, were investigated to evaluate the hypoglycemic/hypolipidemic effects by measuring blood glucose, triglyceride and insulin levels in CM- and metformin-treated diabetic rats. Two diabetic models were used: (1) an alloxan-induced model in which diabetes was produced by alloxan (200 mg/kg, i.p.), then rats were treated with CM (300, 100 and 33 mg/kg) for 14 days; (2) a streptozocin-induced model in which diabetes was produced by streptozocin (30 mg/kg, i.p.) and a sustained high lipid diet, then rats were treated with CM for 8 weeks. The hypoglycemic effect of CM exceeded that of metformin while the hypolipidemic effect was similar. In addition, CM increased the blood insulin level of the alloxan-induced experimental animals (which had an insulin deficiency), but reduced the insulin level of the streptozocin-induced animals (which had an insulin excess), suggesting that CM improves pancreatic beta-cell function. The effects of CM, metformin and cysteine on the antioxidant defense system in alloxan-induced rats were also studied. The serum malondialdehyde (MDA) level was determined to provide evidence for lipid peroxidation, All the groups of animals given CM, metformin and cysteine exhibited less severe oxidative stress than the diabetic group. Then, several key antioxidants such as superoxide dismutase (SOD), reduced glutathione (GSH), catalase (CAT) and the pancreatic exocrine enzyme amylase (AMS) were measured. CM restored the activity of all these agents to nearly normal values while metformin and cysteine merely restored the activity of SOD. At the end of our study, the animals were sacrificed by decapitation and the liver, kidney and pancreas were weighed to allow investigation of organ edema. The results obtained showed that CM corrected the organ edema of the diabetic rats. All these findings suggested that CM has a protective effect on the antioxidant defense system and beta-cell dysfunction in alloxan-induced diabetic rats. All these results suggest that CM is a potential candidate for the future treatment of both type 1 and type 2 diabetes.     

Antidiabetic effects of quercetin in streptozocin-induced diabetic rats

Effects of the intraperitoneal injection of quercetin in streptozocin-induced diabetic and normal rats were investigated and compared. Although quercetin had no effect on plasma glucose level of normal animals, it significantly and dose-dependently decreased the plasma glucose level of streptozocin-induced diabetic rats. Glucose tolerance tests of the diabetic animals approached those of normal rats, their plasma cholesterol and triglycerides were reduced significantly, while their hepatic glucokinase activity was significantly increased upon quercetin treatment. In normal rats, quercetin did not affect the glucose tolerance test, but resulted in an increase of plasma cholesterol and triglycerides and a decrease in hepatic glucokinase activity. No significant pathologic changes were noted in hepatocytes or kidney tubules and glomeruli, while the number of pancreatic islets significantly increased in both treated normal and diabetic groups. It is concluded that quercetin, a flavonoid with antioxidant properties brings about the regeneration of the pancreatic islets and probably increases insulin release in streptozocin-induced diabetic rats; thus exerting its beneficial antidiabetic effects. However, it may be of little value in normoglycemic animals.     

Inhibitory control of sensory gating in a computer model of the CA3 region of the hippocampus

 A model of the CA3 region of the hippocampus was used to simulate 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. Normal subjects have a reduced P50 auditory-evoked potential amplitude in response to the second of two paired auditory click stimuli spaced 0.5 s apart. However, schizophrenic patients do not gate or reduce their response to the second click. They have equal auditory-evoked response amplitudes to both clicks. When schizophrenic patients were medicated with traditional neuroleptics, the evoked potential amplitude to both clicks increased, but gating of the second response was not restored or improved. Animal studies suggest a role for septohippocampal cholinergic activity in sensory gating. We used a computational model of this system in order to study the relative contributions of local processing and afferent activity in sensory gating. We first compared the effect of information representation as average firing rate to information representation as cell assemblies in order to evaluate the best method to represent the response of hippocampal neurons to the auditory click. We then studied the effects of nicotinic cholinergic input on the response of the network and the effect of GABA_B receptor activation on the ability of the local network to suppress the test response. The results of our model showed that nicotinic cholinergic input from the septum to the hippocampus can control the flow of sensory information from the cortex into the hippocampus. In addition, postsynaptic GABA_B receptor activation was not sufficient to suppress the test response when the interstimulus interval was 500 ms. However, presynaptic GABA_B receptor activity may be responsible for the suppression of the test response at this interstimulus interval. Received: 3 December 2001 / Accepted: 23 October 2002 / Published online: 28 February 2003 Correspondence to: K. A. Moxon (e-mail: karen.moxon@drexel.edu, Tel.:+1-215-8951959, Fax: +1-215-8954983) Supported by USPHS, MH01245, MH58414, MH-50787, MH-01121, and research grants from the Department of Veterans Affairs and the National Alliance for Research on Schizophrenia and Depression.     

Approche empirique pour déterminer les générateurs neurophysiologiques sous-jacents des potentiels évoqués auditifs engendrés par des sons de parole (Speech ABR)

Auditory evoked potentials to speech (Speech auditory brainstem response [Speech ABR]) are a non-invasive way to investigate neurophysiological activity, at the level of the brainstem. The Speech ABR precise neurophyiological generators remain poorly defined. However, latencies and low-pass spectrum both suggest that these generators might lie in the upper brainstem (roughly between the cochlear nucleus and the inferior colliculus). Having considered the particular functional pattern of cells along the auditory pathway, specific stimuli have been synthesized to make out the acoustic sensitivity of Speech ABR components. Accordingly, hypotheses have been made on the probable neurophysiological generators, most likely to have elicited both Speech ABR components: onset response and frequency following response. Speech ABR have been recorded to pure tones, harmonic complex tones, /ba/ and /pa/ syllables, and their analogues (calculated as a sum of five weighted sine waves at the formant frequencies and amplitudes, and modulated by the syllables temporal envelopes). In addition, the Auditory Image Model (Patterson et al., 1995 [17]), simulating the neural activity at the auditory periphery, i.e. inferior colliculus input, suggests that both analogues and syllables elicit the same amount of energy, in contrast to the recorded FFR. This contradiction means that the neurophysiological signal processing leading to FFR is made beyond auditory periphery. Indeed, FFR synchronisation on F0 seems to be the result of an overall processing of the whole stimulus spectrum. This behaviour reminds the functional characteristics of disc-shape cells in the inferior colliculus, as described in a previous study of physiological periodicity coding (Periodicity analysis network, Voutsas et al., 2005 [42]).     

Sensory perception and hypothyroidism

Subjective and objective changes in smell and taste perceptionwere evaluated in 16 patients with primary hypothyroidism beforeand after thyroxine (T4) replacement and in 17 control subjects.Visual evoked responses (VER) and brainstem auditory evokedresponses (BAER) were measured in 15 patients. Although 11 ofthe patients reported subjective alterations in smell and tasteand eight of these reported resolution or improvement with euthyroidism,no improvement was found using objective measures (mean follow-up6.4 months) in smell, taste or flavour perception or in visualand auditory brainstem evoked responses. However, on a ‘scratchand sniff’ encapsulated odour identification test, hypothyroidpatients had a significant deficit in detecting and identifyingodours when compared to controls. The possibility that the deficitwas due to age differences between the two groups is discussed.     

Comparison of amitriptyline metabolism in hepatocytes from streptozocin-induced diabetic rats and from non-diabetic rats

Biotransformation of amitriptyline (AMI) was studied at different intervals in freshly isolated hepatocytes from healthy or streptozocin-induced diabetic rats in order to investigate the influence of the diabetic state. Levels of free and conjugated AMI, demethylated and hydroxylated metabolites, were assessed by HPLC analysis. In hepatocytes isolated from diabetic rats, AMI was less completely metabolized and the demethylation reaction became more important than in non-diabetic rat hepatocytes. Although the proportions of hydroxylated metabolites decreased in diabetic rats, it always remained predominant. Furthermore, glucuronidation of metabolites was greater, especially for (Z)-10-hydroxynortriptyline in diabetic animals.     

Previous Exercise Training Has a Beneficial Effect on Renal and Cardiovascular Function in a Model of Diabetes

Exercise training (ET) is an important intervention for chronic diseases such as diabetes mellitus (DM). However, it is not known whether previous exercise training intervention alters the physiological and medical complications of these diseases. We investigated the effects of previous ET on the progression of renal disease and cardiovascular autonomic control in rats with streptozotocin (STZ)-induced DM. Male Wistar rats were divided into five groups. All groups were followed for 15 weeks. Trained control and trained diabetic rats underwent 10 weeks of exercise training, whereas previously trained diabetic rats underwent 14 weeks of exercise training. Renal function, proteinuria, renal sympathetic nerve activity (RSNA) and the echocardiographic parameters autonomic modulation and baroreflex sensitivity (BRS) were evaluated. In the previously trained group, the urinary albumin/creatinine ratio was reduced compared with the sedentary diabetic and trained diabetic groups (p<0.05). Additionally, RSNA was normalized in the trained diabetic and previously trained diabetic animals (p<0.05). The ejection fraction was increased in the previously trained diabetic animals compared with the diabetic and trained diabetic groups (p<0.05), and the myocardial performance index was improved in the previously trained diabetic group compared with the diabetic and trained diabetic groups (p<0.05). In addition, the previously trained rats had improved heart rate variability and BRS in the tachycardic response and bradycardic response in relation to the diabetic group (p<0.05). This study demonstrates that previous ET improves the functional damage that affects DM. Additionally, our findings suggest that the development of renal and cardiac dysfunction can be minimized by 4 weeks of ET before the induction of DM by STZ.     

A comparative study of avian auditory brainstem responses: correlations with phylogeny and vocal complexity, and seasonal effects

We conducted a comparative study of the peripheral auditory system in six avian species (downy woodpeckers, Carolina chickadees, tufted titmice, white-breasted nuthatches, house sparrows, and European starlings). These species differ in the complexity and frequency characteristics of their vocal repertoires. Physiological measures of hearing were collected on anesthetized birds using the auditory brainstem response to broadband click stimuli. If auditory brainstem response patterns are phylogenetically conserved, we predicted woodpeckers, sparrows, and starlings to be outliers relative to the other species, because woodpeckers are in a different Order (Piciformes) and, within the Order Passeriformes, sparrows and starlings are in different Superfamilies than the nuthatches, chickadees, and titmice. However, nuthatches and woodpeckers have the simplest vocal repertoires at the lowest frequencies of these six species. If auditory brainstem responses correlate with vocal complexity, therefore, we would predict nuthatches and woodpeckers to be outliers relative to the other four species. Our results indicate that auditory brainstem responses measures in the spring broadly correlated with both vocal complexity and, in some cases, phylogeny. However, these auditory brainstem response patterns shift from spring to winter due to species-specific seasonal changes. These seasonal changes suggest plasticity at the auditory periphery in adult birds.     

Blood glucose control and glomerular capillary basement membrane thickening in experimental diabetes.

Glomerular capillary basement membrane thickness (BMT) was measured in 23 rats which had had streptozocin-induced diabetes for 14 months and in 12 age-matched controls. Diabetic rats were randomly allocated to different groups, either receiving no treatment or treated with a low carbohydrate diet or insulin, or both. Control rats were randomly allocated to a normal or low carbohydrate diet. Among the diabetic rats mean plasma glucose concentrations for the groups ranged from 27-4 mmol/l (494 mg/100 ml) in the untreated rats to 9-8 mmol/l (177 mg/100 ml) in those receiving both a low carbohydrate diet and insulin. A highly significant positive relation was found between BMT and plasma glucose concentration for individual rats. When BMT was corrected for body weight a similar relation was observed.     

Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats.

This study determined whether rates of protein synthesis increase after acute resistance exercise in skeletal muscle from severely diabetic rats. Previous studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabetic rats performed acute resistance exercise (n = 8) or remained sedentary (n = 8). A group of nondiabetic age-matched rats served as controls (n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucose concentrations were >500 mg/dl in the diabetic rats. Rates of protein synthesis (nmol phenylalanine incorporated. g muscle(-1). h(-1), means +/- SE) were not different between exercised (117 +/- 7) and sedentary (106 +/- 9) diabetic rats but were significantly (P < 0.05) lower than in sedentary nondiabetic rats (162 +/- 9) and in exercised nondiabetic rats (197 +/- 7). Circulating insulin concentrations were 442 +/- 65 pM in nondiabetic rats and 53 +/- 11 and 72 +/- 19 pM in sedentary and exercised diabetic rats, respectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no difference between exercised and sedentary diabetic rats. Muscle insulin-like growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below which rates of protein synthesis begin to decline in vivo. In contrast to previous studies using less diabetic rats, severely diabetic rats cannot increase rates of protein synthesis after acute resistance exercise.     

Electrically-Evoked Frequency-Following Response (EFFR) in the Auditory Brainstem of Guinea Pigs

It is still a difficult clinical issue to decide whether a patient is a suitable candidate for a cochlear implant and to plan postoperative rehabilitation, especially for some special cases, such as auditory neuropathy. A partial solution to these problems is to preoperatively evaluate the functional integrity of the auditory neural pathways. For evaluating the strength of phase-locking of auditory neurons, which was not reflected in previous methods using electrically evoked auditory brainstem response (EABR), a new method for recording phase-locking related auditory responses to electrical stimulation, called the electrically evoked frequency-following response (EFFR), was developed and evaluated using guinea pigs. The main objective was to assess feasibility of the method by testing whether the recorded signals reflected auditory neural responses or artifacts. The results showed the following: 1) the recorded signals were evoked by neuron responses rather than by artifact; 2) responses evoked by periodic signals were significantly higher than those evoked by the white noise; 3) the latency of the responses fell in the expected range; 4) the responses decreased significantly after death of the guinea pigs; and 5) the responses decreased significantly when the animal was replaced by an electrical resistance. All of these results suggest the method was valid. Recording obtained using complex tones with a missing fundamental component and using pure tones with various frequencies were consistent with those obtained using acoustic stimulation in previous studies.     

Role of ATP in specific binding of 125I-insulin to cytoplasmic receptors of the liver and muscle membranes of controls and diabetic rats

A study was made of the action of various concentrations of ATP on insulin ability to bind to the receptors of the liver and muscle membranes in control and streptozocin-induced diabetes animals. Specific binding of 125I-insulin to the receptors of the liver and muscle membranes was shown to rise in animals with streptozocin-induced diabetes as compared to control. This effect was most pronounced in the muscle membranes. Preincubation of the membranes with ATP did not affect insulin binding to the liver and muscle receptors of control animals. However, hormone binding to the liver receptors of diabetic rats was drastically suppressed by ATP (10(-3) M). Less ATP concentrations (10(12) M) produced an additional inhibitory action which was not marked. ATP led to decreased insulin binding to the muscle receptors of diabetic rats only at extremely low concentrations (10(-12) M). The data obtained may be of importance for regulation of membrane phosphorylation in the states characteristic of insulin resistance.     

Chronic implantation of transit-time flow probes on the ascending aorta of rodents

This study describes the implantation of transit-time flow probes on the ascending aorta of rats while minimizing the risk of postoperative complications. Special emphasis is placed on our new method of rat intubation as well as the production of materials necessary for the implantation procedure such as endotracheal tubes and heparin bonded vessel catheters. The effects of these devices on the response to acute hypoxia were studied in rats following a 5-7 day recovery from the implantation procedure. Systemic and microvascular measurements were made on instrumented rats (n = 5) and non-instrumented controls (n = 3) that were ventilated with 21%, 15%, 10%, 8% and 5% oxygen. Arterial pressure, PO(2), lactate, and base deficit were not different between the implanted and control animals at any inspired oxygen concentration. Microvascular flow in the primary arterioles of the spinotrapezius muscle was also similar between the two groups at all inspired oxygen concentrations. We conclude that this novel methodology facilitates the measurement of whole body oxygen delivery in resting and haemodynamically-stressed rats.