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Biomedical subjects

D K Nelson

Publications and source records attributed to D K Nelson.

At least 55 records · Page 3Linked to original sources
PubMed1993

Quantifying ear-canal geometry with multiple computer-assisted tomographic scans.

Several audiological tests require knowledge of the sound-pressure spectrum at the eardrum. However, microphone readings are typically made at another, more-accessible position in the auditory canal. Recordings are then "adjusted" to the plane of the eardrum via mathematical models of the ear canal and eardrum. As bandwidths of audiological instruments have increased, ear-canal models have, by necessity, become more precise geometrically. Reported herein is a noninvasive procedure for acquiring geometry of the ear canal in fine detail. The method employs a computer-assisted tomographic (CAT) scanner in two steps to make radiographic images of parasagittal cross sections at uniform intervals along the lateral length of the canal. Accuracy was evaluated by comparing areas of cross sections appearing in radiographic images of a cadaver ear canal to cross sectional areas of corresponding michrotome slices of an injection mold of the same canal. Percent differences between these two areas had a mean value of 9.65% for 26 different cross sections of the one ear canal studied. Ear canal volume estimated from the CAT images was 6.12% different from the estimated volume of the injection mold: an improvement over the reported 39% maximum error of conventional acoustic volume measurements.

Acoustic Stimulation↗
PubMed1993

Neuroanatomical differentiation in the brain of the spontaneously hypertensive rat (SHR). I. Volumetric comparisons with WKY control.

A series of measurements was made to assess the morphology of the brain of the spontaneously hypertensive rat (SHR). The SHR brain was smaller than that of age-matched normotensive Wistar-Kyoto (WKY) controls in a majority of measures of external surface landmarks. This reduction in size was evident in the youngest age group examined (94 days) and persisted in older groups (170, 240 and 350 days). The brain of the SHR was also smaller in terms of brain weight and brain weight:body weight ratios. Section-by-section digitized analyses of coronal histologic sections from 94-day-old rats revealed significant reductions in mean cross-sectional area and volume of midbrain/pons (10%) and hindbrain (11%) regions, but not of forebrain, in the SHR. Alterations in the mediolateral dimension, particularly within the pontomedullary brainstem, accounted for more of these volumetric changes than those in the dorsoventral dimension. Using the same coronal sections, it was found that surface areas and volumes of five individual nuclei/fiber tracts, selected for their involvement in central cardiovascular regulation, were significantly decreased in the SHR. The largest reduction in volume (30%) was found in the nucleus tractus solitarius, the primary site of termination of afferent baroreceptor fibers. No differences in surface area or volume were found in that portion of the cerebroventricular system (aqueduct of Sylvius) associated with the periventricular grey region, or in the inferior colliculus, which is not thought to be involved in cardiovascular control. These observations not only have practical implications, but suggest that the pathophysiological condition expressed as spontaneous hypertension in this widely-used model may be related to morphological alterations in the central nervous system.

Animals↗
PubMed1992

Guanethidine sympathectomy increases substance P concentration in the superior sympathetic ganglion of adult rats.

Adult rats received intraperitoneal injections of guanethidine or saline for 5 weeks. Six to 8 weeks following completion of treatment, concentrations of substance P and neuropeptide Y (NPY) were measured by radioimmunoassay in the superior cervical ganglion (SCG) and thoracic spinal cord. The SCG was also immunostained for NPY and substance P. No differences were observed in thoracic spinal cord content of either NPY or substance P. We observed depletion of NPY immunoreactive neurons and NPY levels in the SCG, and pharmacologic evidence of postganglionic denervation in guanethidine-treated rats. In guanethidine-treated rats, there was a marked increase of substance P levels in the SCG, where substance P was localized in fibers, but not cell bodies. Thus, sprouting of substance P-containing sensory fibers in the sympathetic ganglia occurs following postganglionic sympathectomy in adult rats.

Animals↗
PubMed1992

Interdigestive gastroduodenal motility and cycling of putative regulatory hormones in severe obesity.

The aim of the present study was to evaluate interdigestive gastrointestinal motility and its coordination with plasma concentrations of motilin and pancreatic polypeptide (PP) in 14 patients with severe obesity and in 10 control subjects with normal body weight. Motor activity of the stomach, duodenum, and proximal jejunum was recorded by using an eight-lumen catheter. Blood samples were drawn for determination of interdigestive motilin and PP plasma concentrations. We observed no difference in total duration of the migrating motor complex (MMC) or of phases I, II, or III of the MMC. Gastric phase-III activity occurred less frequently in severely obese patients (only 15% originating in the stomach) than in controls (65%; p less than 0.01). Plasma motilin concentrations were decreased in obese patients in phase I (127 +/- 17 pg/ml in controls versus 87 +/- 10 pg/ml in obese), in phase II (189 +/- 26 pg/ml controls versus 134 +/- 15 obese) and in phase III (195 +/- 29 pg/ml controls versus 153 +/- 28 pg/ml obese). Peak motilin release occurred in synchrony with phase-III activity and was greater in controls than in obese patients. Plasma PP concentrations did not differ from those of controls during any phase of the MMC. These results further suggest a potential role for motilin in regulating gastrointestinal motor activity and indicate a potential defect in this regulatory mechanism in severe obesity. Whether the relationship between disordered motor activity and motilin release is etiologic with regard to the pathophysiology of obesity remains to be determined.

Adolescent↗
PubMed1991

Decreased levels of [Met]enkephalin, neuropeptide Y, substance P, and vasoactive intestinal peptide in parkinsonian adrenal medulla.

Adrenal medullary tissue was collected from parkinsonian patients at autopsy and at the time of autologous transplantation of the adrenal medulla to the caudate nucleus, and from nonparkinsonian patients at autopsy and during nephrectomy. Levels of the following neuropeptides were measured by radioimmunoassay in samples of the medullary tissue: neuropeptide Y (NPY), substance P (SP), [Met]enkephalin ([Met]ENK), vasoactive intestinal peptide (VIP), peptide YY, and bombesin-like immunoreactivity. Regression analysis was used to establish a relationship between patient age, time to organ harvest, and peptide levels in nonparkinsonian tissue. Levels of [Met]ENK, VIP, NPY, and SP were significantly lower in parkinsonian adrenal medullae than that predicted from the control group. These results suggest that the adrenal medulla of a parkinsonian patient is severely compromised, either by the disease process itself or by the antiparkinsonian medications used to treat the symptoms of the disease.

Adrenal Medulla↗
PubMed1991

In vivo neural isolation of the canine jejunoileum: temporal adaptation of enteric neuropeptides.

This study was designed to assess temporal changes in concentrations of neuromodulatory peptides in plasma and gastrointestinal tissues after in vivo neural isolation of the entire canine jejunoileum. Fasting plasma and transmural biopsy specimens of stomach, duodenum, jejunum, ileum, and colon were obtained from the same dogs before and two, six, and 12 weeks after in situ neural isolation of the entire jejunoileum. Concentrations of vasoactive intestinal peptide, substance P, and neuropeptide Y were determined by quantitative radioimmunoassay. Tissue concentrations of vasoactive intestinal peptide and substance P in the neurally isolated regions increased progressively with time (198% and 217% average maximal increases, respectively), while fasting plasma concentrations changed little. Neuropeptide Y concentrations in plasma and in the jejunoileum were decreased (by 30% to 70%) at two weeks and remained decreased thereafter. Temporal changes in tissue neuropeptide concentrations occur in the neurally isolated jejunum and ileum. These adaptive changes in the neuropeptidergic innervation of the gut may play a role in the alterations in enteric function that occur after extrinsic denervation and after intestinal transplantation.

Adaptation, Physiological↗
PubMed1991

Neurohormonal factors in functional dyspepsia: insights on pathophysiological mechanisms.

Neurohormonal factors were investigated in 10 patients with functional dyspepsia who had normal or slow upper gut transit and 10 age- and sex-matched healthy controls. Gastric and small bowel motility and transit, jejunal responses to luminal distention and IM neostigmine, gut hormones, and vagal and sympathetic functions were studied. Slow upper gut transit was defined by a gastric emptying slope less than 0.3%/min or 10% small bowel transit time greater than 300 minutes. Four patients with slow transit had reduced postprandial antral motility and gut hormone responses. Two of the four patients had vagal and sympathetic dysfunction. In 6 patients with normal transit, balloon distention in the jejunum was perceived at a lower volume (32.7 +/- 5.9 mL) than in controls (46.6 +/- 3.0 mL). Pressure responses to balloon distention were reduced in 5 and exaggerated in 1 patient; abnormal efferent vagal (2 patients) and sympathetic (1 patient) function were also documented. In view of the normal transit, motility, and jejunal pressure responses to neostigmine in all 6 patients, the abnormal response to distention suggests afferent dysfunction. Functional dyspepsia is a heterogenous disorder. Abnormal transit is sometimes associated with disorders of extrinsic neural control, but the latter are also found in patients with normal transit. Increased perception of intraluminal stimuli in those with normal transit suggests a disturbance in afferent function.

Adult↗
PubMed1990

Noradrenergic and neuropeptide Y mechanisms in guanethidine-sympathectomized rats.

The cardiovascular responses to sympathomimetic agents, the norepinephrine (NE) content in peripheral tissues, and the tissue content and cardiovascular effects of neuropeptide Y (NPY) were examined in anesthetized adult rats with guanethidine-induced sympathectomy (GuSx). We observed blunted pressor responses to tyramine, exaggerated pressor responses to phenylephrine, and markedly reduced NE contents in the atrium, femoral artery, superior cervical ganglion (SCG), and sciatic and vagus nerves. When tyramine responses were corrected for the NE content in the SCG, GuSx rats were similar to controls. A depletion of NPY levels in tissue resulted in an increased sensitivity to the pressor effects of intravenous NPY administration. GuSx, therefore, reproduces findings of postganglionic adrenergic failure in humans. Responses to the administration of sympathomimetic agents may reflect the degree of noradrenergic denervation. NPY may be a potential marker of chronic postganglionic sympathetic denervation in cardiovascular tissue.

Animals↗
PubMed1990

Interdigestive cycling and post-prandial release of pancreatic polypeptide in severe obesity.

Changes in pancreatic polypeptide plasma concentrations have been reported in obesity. It has been suggested that altered PP plasma levels may play a role in the abnormal food intake observed in obesity. Earlier studies, however, have not considered the physiological fluctuations of PP during fasting. We examined PP plasma concentrations in 12 subjects with severe obesity and in 10 normal subjects during the entire cycle of interdigestive motility and after the administration of a standard mixed meal. Obese patients and healthy controls showed similar fluctuations of PP during individual phases of the migrating motor complex (MMC) and reached their peak PP plasma levels (134 +/- 35 (s.e.m.) pg/ml in controls vs 113 +/- 17 pg/ml in obese subjects) during phase III activity. Following the test meal, prompt release of PP occurred which was significantly higher than basal values at each 15 min interval during the first postprandial hour in both controls and obese patients. The integrated PP postprandial response at 60 min did not differ between obese patients (163 +/- 15 pg/ml.h) and controls (198 +/- 37 pg/ml.h; n.s.). A putative causal role for PP in obesity thus seems very unlikely.

Adult↗
PubMed1988

Gastrointestinal neuropeptide concentrations following guanethidine sympathectomy.

In an effort to investigate the interaction of the adrenergic and enteric components of the autonomic nervous system, gut neuropeptide concentrations were examined following chemical sympathectomy. Adult male rats were treated with guanethidine (40 mg/kg i.p., 5 days/week for 5 weeks), which selectively destroys peripheral sympathetic neurons. Controls received equal volumes of saline vehicle. Tissues from fundic and pyloric stomach, duodenum, jejunum, jejuno-ileum, ileum, caecum and colon were extracted and concentrations of selected neuropeptides determined by radioimmunoassay. Dopamine-beta-hydroxylase (DBH) in peripheral nerve, measured as an index of degree of sympathectomy, was depleted 80-90%. One week after cessation of treatment, vasoactive intestinal peptide (VIP) was elevated in jejunum (52%), ileum (53%), caecum (41%) and colon (59%), as was neurotensin (NT) in caecum (117%) and colon (261%). Methionine-enkephalin (MET) was lowered in duodenum by 28%. With the exception of MET in duodenum and NT in caecum, these alterations normalized by 5 weeks post-treatment, although DBH remained depressed. Statistically non-significant increases in substance P content were observed in upper gut regions. An inhibitory sympathetic input to VIPergic and NTergic systems is postulated.

Animals↗
PubMed1986

Modification of electroshock and pentylenetetrazol seizure patterns in rats after precollicular transections.

Rats with precollicular transections leaving the brain stem intact were subjected to electroshock or pentylenetetrazol-induced convulsions. Animals with transections failed to display the face and forelimb clonus (with or without rearing) typically seen in sham-operated rats subjected to pentylenetetrazol- or minimal electroshock-induced convulsions elicited with corneal electrodes. Moreover, rats with transections exhibited all other components of pentylenetetrazol- and electroshock-induced seizures. These findings support the hypothesis that tonic and some types of clonic convulsions can occur independently of seizure discharge in forebrain structures, whereas clonus restricted to the face and forelimbs depends on seizure discharge emanating from structures within the forebrain for expression.

Animals↗
PubMed1985

Variation in threshold and pattern of electroshock-induced seizures in rats depending on site of stimulation.

Although most laboratories employ transcorneal stimulation as a means of producing electroshock seizures, transauricular stimulation is also used by many investigators. The present study shows that seizures produced with transcorneal electroshock differ from those produced by transauricular electroshock in several ways: transauricular stimulation is more effective at eliciting tonic convulsions; the threshold for clonus is lower when transcorneal electrodes are used; and the face and forelimb clonus produced by transcorneal stimulation cannot be produced with transauricular stimulation at any current. The present findings are consistent with the hypothesis that tonic seizures are more easily triggered with transauricular stimulation because they originate in the brainstem and because this brain region is preferentially activated when ear-clip electrodes are used.

Animals↗
PubMed1985

Motor paralysis in rats after repeated electroconvulsive shock: comparison between aural and corneal stimulation.

Daily transaural electroshock treatment of rats results in a reversible hindlimb paralysis. Assuming there is a relationship between current pathway and the route of electroshock administration we compared both the type of convulsive behavior and the incidence of paralysis produced by transcorneal shock with that of transaural stimulation. Both transaural and transcorneal stimulation induced clonic and tonic convulsions, whereas, only transaural stimulation induced a body flexion (twisting and writhing). The use of transaural electrodes induced a higher incidence of paralysis than the use of corneal electrodes. These data demonstrate that both (1) the type of convulsive behavior produced and (2) the incidence of paralysis is related to electrode placement suggesting that paralysis is a function of current pathway.

Animals↗
PubMed1975

Evaluation of protein nutrition by metabolizable protein and urea fermentation potential.

Metabolizable protein and selected metabolizable amino acid requirements for lactating cows were described, and tentative values were established for differnt yields of milk.A new expression"urea fermentation potential of feeds," describes urea use in lactation rations for partial satisfaction of protein and amino acid requirements. Tentative urea fermentation values were established for the more common cattle feedstuffs. Four lactation rations were formulated with different fermentation values to illustrate the variable feeding value of urea in satisfying amino acid requirements at different yields of lactation. Urea had the highest feeding value in lower-protein rations when fed to cows with medium to low yields of milk.Conversely, urea, by the metabolizable protein system, had little or no feeding value in lactation rations having more than about12% protein on a dry matter basis or in rations supporting lactations in excess of 25 to 30 kg of milk per cow per day.

Amino Acids↗