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Biomedical subjects

L L Brown

Publications and source records attributed to L L Brown.

At least 19 recordsLinked to original sources
PubMed1992

Somatotopic organization in rat striatum: evidence for a combinational map.

2-Deoxy-D-[14C]glucose autoradiography was used in awake rats to map neural activity in the sensorimotor sector of striatum. Stimulation of hindlimb, trunk, or forelimb activated primary sensory cortex in a localized columnar pattern, indicating activation of somatosensory receptors and a discrete cortical functional unit. In sensorimotor striatum, an image analysis detection technique revealed regions of maximal activity, or features, that formed a patchy pattern of activation reminiscent of the known anatomic patterns of cortico-striate terminals. Ipsilateral as well as contralateral activation was observed. The activated areas revealed a body map in striatum that was organized in a manner consistent with cortical topography (dorsoventrally: hindlimb, trunk, forelimb) at most anteroposterior levels, similar to that found in other species. However, at other levels, a different organization (e.g., trunk, hindlimb, forelimb) was observed. Furthermore, the arrangements of body region and side were also unique at different anteroposterior levels. Thus, functional activity showed multiple, different juxtapositions of body elements--i.e., a combinational map. The data suggest that striatum may provide an anatomic substrate for different combinations of inputs necessary to select and integrate movement.

Animals↗
PubMed1991

Rapid measurement of leucine-specific activity in biological fluids by ion-exchange chromatography and post-column ninhydrin detection.

Commonly used methods for the measurement of leucine-specific activity use either high-performance liquid chromatography (HPLC) and pre-column derivatization or conventional ion-exchange chromatography. These are time-consuming, labor-intensive, relatively costly procedures, requiring high concentrations of radioactivity for accuracy. The present paper describes a method for the measurement of plasma leucine-specific activity using HPLC equipment, a large-bore ion-exchange column and post-column ninhydrin detection. With this method, determination of leucine concentration and leucine radioactivity was found to be linear (r2 greater than 0.999) over physiological ranges for both standards and deproteinized plasma. The intra- and inter-assay coefficients of variation for leucine concentrations were 1.4 and 2.7%, respectively. The intra- and inter-assay coefficients of variation for leucine-specific activities were 1.5 and 1.9%, respectively. The automated method is relatively fast (injection to injection time approximately 45 min), economical and capable of accurately assessing relatively small amounts of radioactivity.

Chromatography, High Pressure Liquid↗
PubMed1991

Interaction of exercise and insulin action in humans.

To assess the interaction of exercise and insulin action, healthy males were studied with saline infusion (n = 5) or with a hyperinsulinemic euglycemic clamp (0.5, 1.0, 2.0, or 15.0 mU.kg-1.min-1; n = 5 at each dose) during rest (40 min), moderate-intensity cycle exercise (100 min), and recovery (100 min). Metabolism was assessed using isotopic methods and indirect calorimetry. During rest, exercise, and recovery with saline infusion, plasma glucose was unchanged, total glucose utilization (Rd) was 2.4 +/- 0.4, 4.9 +/- 0.2, and 2.6 +/- 0.2 mg.kg-1.min-1, and carbohydrate (CHO) oxidation (OX) was 1.4 +/- 0.3, 10.6 +/- 1.1, and 0.5 +/- 0.2 mg.kg-1.min-1. The glucose infusion, insulin-dependent Rd, and CHO OX increased synergistically when exercise and insulin clamps were combined. Exercise decreased (P less than 0.05) the half-maximal doses (ED50) and increased the maximal responses (Vmax) for insulin-dependent Rd and CHO OX. Estimates of insulin-independent Rd were 1.3 +/- 0.7, 4.1 +/- 1.3, and 1.9 +/- 0.7 mg.kg-1.min-1 and insulin-independent CHO OX were 1.2 +/- 0.9, 10.4 +/- 1.3, and 0.6 +/- 0.3 mg.kg-1.min-1 during rest, exercise, and recovery. Estimates during exercise were greater than those at rest (P less than 0.05). The total suppression of free fatty acids (FFA) and fat OX by insulin were elevated by exercise (P less than 0.05). In summary, exercise and insulin interact synergistically in stimulating Rd and CHO OX.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Instability of orthophthalaldehyde reagent for amino acid analysis.

Determination of amino acids by reversed-phase chromatography of the adduct with orthophthalaldehyde and a thiol is rapid and sensitive. The major recognized adverse feature of this method is the instability of the reaction product, which requires precise control of reaction timing and chromatographic parameters for reliable quantitative application. We report another source of major variability: reagent instability. Deterioration of reagent was noted as low peak heights and peak broadening and was predictable if the premixed reagent was left at room temperature. Restoration of sharp chromatograms was accomplished by addition of mercaptoethanol or sodium metabisulfite. Reagent which was chromatographically inert contained minimal free thiol by direct assay. Free thiol disappearance was markedly slowed by addition of a chelating agent. Excess mercaptoethanol was deleterious. We conclude that reagent deterioration represents oxidation of the thiol, may be reversed by rereduction with minimal thiol or bisulfite, and may be minimized by inclusion of a metal chelator in the reagent.

Aldehydes↗
PubMed1989

The nucleus locus coeruleus modulates local cerebral glucose utilization during noise stress in rats.

Local cerebral glucose utilization (LCGU), estimated by the quantitative autoradiographic 2-deoxyglucose technique, was studied in rats with bilateral 6-hydroxydopamine lesions of the locus coeruleus (LC) and in vehicle-injected controls. Unanesthetized animals were studied during exposure to stressful levels of white noise (95 dB) or in relative silence (50 dB). Results indicated that noise caused greater and more widespread increases in LCGU in animals with LC lesions than in vehicle-injected controls. Lesions alone had little or no effect in animals not subjected to noise. Analyses of variance revealed significant treatment interaction effects (intact/lesion x silence/noise) for 37 of 109 regions measured. The pattern of results suggests that the LC acts during stress to limit unnecessary cerebral activity that might interfere with efficient sensory processing and/or the organization of appropriate behavioral responses. In this respect LC function may be similar to those actions of the peripheral sympathetic nervous system that suppress vegetative functions during stress to allow for the performance of coping responses.

Animals↗
PubMed1989

Intraperitoneal transplantation of microcarrier-attached enterocytes in rats.

The purpose of this study was to determine whether enterocyte transplantation could be used to correct a specific genetic metabolic defect. Bilirubin uridine diphosphoglucuronyl transferase (UDPGT) activity has been demonstrated in normal rat intestinal mucosa. We hypothesized that normal rat enterocyte transplantation may restore the ability of Gunn rats, which lack bilirubin UDPGT, to conjugate bilirubin. Small intestine was resected from normal Wistar rat donors. Enterocytes were harvested and suspended in Dulbecco's modified Eagle's medium with 10 percent fetal calf serum. Isolated enterocytes were attached to collagen-coated dextran microcarriers and transplanted into congeneic Gunn rat recipients. Recipient rats underwent bile duct cannulation after transplantation, and bile was analyzed for bilirubin glucuronides by high-pressure liquid chromatography. Fifty percent of the transplanted rats showed a significant increase in the concentration of bilirubin monoglucuronide and diglucuronide in their bile 4 and 7 days posttransplantation. Recipient rats had well vascularized microcarrier-enterocyte aggregates in the peritoneal cavity. Our method for intraperitoneal transplantation of isolated enterocytes in rats could potentially be used to correct specific enzymatic and metabolic defects.

Animals↗
PubMed1989

Central effects of beta-endorphins on glucose homeostasis in the conscious dog.

The effects of centrally administered beta-endorphins on glucose homeostasis in the conscious dog were studied. Intracerebroventricular administration of beta-endorphin (0.2 mg/h) caused a 70% increase in plasma glucose. The mechanism of the hyperglycemia was twofold: there was an early increase in glucose production and a late inhibition of glucose clearance. These changes are explained by marked increases in plasma epinephrine (30-fold) and norepinephrine (6-fold) that occurred during infusion of beta-endorphin. Central administration of beta-endorphin also resulted in increased levels of adrenocorticotropic hormone and cortisol. In addition there was an increase in plasma insulin but no increase in plasma glucagon. Intravenous administration of beta-endorphin did not alter glucose homeostasis. Intracerebroventricular administration of acetylated beta-endorphin did not perturb glucose kinetics or any of the hormones that changed during infusion of the unacetylated peptide. We conclude that beta-endorphin acts centrally to cause hyperglycemia by stimulating sympathetic outflow and the pituitary-adrenal axis. Acetylation of beta-endorphin abolishes the in vivo activity of the peptide.

Animals↗
PubMed1989

Amino acids augment insulin's suppression of whole body proteolysis.

Leucine (LEU) kinetics were assessed using a primed-continuous infusion of L-[1-14C]LEU in normal overnight-fasted male volunteers during a basal period and an experimental period where insulin (INS) was infused at either 0.6, 1.2, 2.5, 5.0, 10, or 20 mU.kg-1.min-1 with euglycemia maintained. Two protocols were used: 1) subjects were allowed to develop hypoaminoacidemia or 2) plasma essential amino acids (AA) were maintained near basal levels by frequently monitoring plasma LEU in conjunction with variable infusions of an AA solution (LEU infused = 0.41, 0.72, 0.93, 1.03, 1.31, and 1.35 mumol.kg-1.min-1 at escalating INS doses, respectively). Basal rates of LEU appearance (Ra), nonoxidative disappearance (NORd) and oxidative disappearance (OXRd) were similar in both protocols (means = 1.74, 1.40, and 0.36 mumol.kg-1.min-1, respectively). INS infusions without AA resulted in a progressive decrement in LEU Ra (14 to 45%), NORd (16-41%), and OXRd (3-56%) compared with basal values. The infusion of AA resulted in an additional reduction in endogenous Ra (P less than 0.01; approximately 100% suppression achieved at plasma INS greater than 1,000 microU/ml) and a blunting of NORd reduction (P less than 0.05) at each dose of INS. Observed differences in INS's suppression of LEU Ra between the two protocols suggests the existence of a component of whole body proteolysis that is highly dependent on circulating plasma AA. Therefore, hypoaminoacidemia associated with INS treatment would appear to blunt the responsiveness of INS's suppression of protein breakdown and in the presence of near basal plasma AA, proteolytic suppression by INS is enhanced.

Adult↗
PubMed1989

Regional cerebral glucose utilization reveals widespread abnormalities in the motor system of the rat mutant dystonic.

Rats with an inherited movement disorder (dystonic, dt), their phenotypically normal littermates, and normal unrelated controls were studied using a metabolic mapping technique, 2-deoxyglucose autoradiography. This approach was used to identify potential sites of abnormality underlying the movement disorder, as no morphological abnormalities using light and electron microscopic techniques have been identified in this mutation. There was a significant overall glucose utilization (GU) reduction in the dt rats and their littermate controls when they were at rest and not displaying abnormal movements. Conversion of GU values to standard scores showed abnormalities in dt compared with both control groups in the following areas: deep cerebellar nuclei, locus coeruleus, pontine gray, ventrolateral-ventromedial thalamic complex, nucleus of the third nerve, lateral habenula, and basolateral amygdala. Littermates were different from nonlittermates in several regions, including the dentate and red nuclei. A study of relative GU performed in animals displaying dystonic movements also showed abnormalities in the deep cerebellar nuclei and locus coeruleus, and in the red nucleus, external cuneate, and medial septum. Correlations computed for GU in pairs of regions with known anatomical connections suggested that cerebellar, substantia nigra, and basal ganglia efferents may be abnormal. These studies complement existing biochemical and neuropharmacological data which show abnormalities in the cerebellum of the dt rat. Additionally, the function of brain stem and even basal ganglia nuclei is affected in this mutant, perhaps as a consequence of abnormal cerebellar activity. The partial effects in the littermates suggest that abnormalities in only a few regions are not sufficient to produce the movement disorder, and a gene dose effect may exist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Human liver cell transplantation. Prolonged function in athymic-Gunn and athymic-analbuminemic hybrid rats.

Isolated cryopreserved human liver cells, attached to collagen-coated microcarriers, were injected intraperitoneally into mutant rat recipients genetically deficient in either bilirubin uridine diphosphoglucuronosyltransferase activity (Gunn rats) or albumin synthesis (Nagase analbuminemic rats). One group of the recipient Gunn and analbuminemic rats were made genetically immunodeficient by interbreeding with athymic rats with inherited T-cell deficiency. Injected microcarriers and cells formed aggregates on the surface of the pancreas. There was no morphologic evidence of rejection in athymic recipients, whereas immunocompetent recipients demonstrated rejection within 5 days of transplantation. Athymic-Gunn rat recipients demonstrated excretion of bilirubin glucuronides in bile for 30 days and reduction in their serum bilirubin levels. In recipient athymic-analbuminemic rats, plasma albumin levels increased from pretransplantation levels of 0.025-0.05 mg/ml to 3.9-4.8 mg/ml 8 days posttransplantation and remained nearly at that level throughout the 30 days of the study. A method of harvesting, attaching to microcarriers, cryopreserving, and in vivo testing of human hepatocytes with prolonged survival and function in athymic-Gunn and athymic-analbuminemic hybrid rats is reported. These rats are excellent animal models for testing xenograft function.

Animals↗
PubMed1988

Effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid levels of ir-beta-endorphins, ACTH, cortisol, norepinephrine, insulin and glucose in the conscious dog.

This study was designed to assess effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid (CSF) levels of immunoreactive (ir) beta-endorphins, adrenocorticotropin (ACTH), cortisol, norepinephrine, insulin, and glucose in the conscious, overnight fasted dog. Dogs received either an intravenous infusion of saline or insulin (5 mU/kg/min) for 3 h. Infusion of saline alone in conjunction with acute sampling of CSF caused no measurable perturbations of glucose homeostasis. Insulin infusion caused a 60% drop in both plasma and CSF glucose. Plasma levels of ir-beta-endorphins, ACTH and cortisol rose markedly. CSF levels of ir-beta-endorphins and ACTH also increased. While the magnitude of the increase was smaller than that in the plasma, it was greater than would be expected if crossover of the peptides from the plasma were the sole source of the increase. Hypoglycemia also induced elevations in CSF cortisol and insulin. In addition, there was a 45% decrease in CSF norepinephrine in spite of large elevations of norepinephrine in the plasma. We conclude that hypoglycemia is associated with marked changes in central as well as peripheral levels of neuroendocrine factors. The importance of these changes in mediating acute and long-term responses to hypoglycemia remains to be established.

Adrenocorticotropic Hormone↗
PubMed1988

Stimulation of glucose production through hormone secretion and other mechanisms during insulin-induced hypoglycemia.

To assess the role of counterregulatory hormones per se in the response to continuous insulin infusion, overnight-fasted dogs were given 5 mU.kg-1.min-1 insulin intraportally either alone (INS, n = 5), with glucose to maintain euglycemia (INS + GLU, n = 5), or with glucose and hormone replacement [i.e., glucagon, epinephrine, norepinephrine, and cortisol infusions (INS + GLU + HR, n = 6)]. The increases in counterregulatory hormones that occurred during insulin-induced hypoglycemia were simulated in the latter group. In this way, it was possible to separate the effects of hypoglycemia per se from those due to the associated counterregulatory hormone response. Glycogenolysis and gluconeogenesis were measured with a combination of tracer ([ 3-3H]glucose and [U-14C]alanine) and hepatic arteriovenous (AV) difference techniques during a 40-min control and a 180-min experimental period. Insulin levels increased similarly in all groups (to congruent to 250 microU/ml), whereas plasma glucose levels decreased in INS (115 +/- 3 to 41 +/- 3 mg/dl; P less than .05) and rose slightly in both INS + GLU (108 +/- 2 to 115 +/- 4 mg/dl; P less than .05) and INS + GLU + HR (111 +/- 3 to 120 +/- 3 mg/dl; P less than .05) due to glucose infusion. Glucagon, epinephrine, norepinephrine, and cortisol were replaced in INS + GLU + HR so that the increments in their levels were 102 +/- 6, 106 +/- 14, 117 +/- 9, and 124 +/- 37%, respectively, of their increments in INS. At no time was there a significant difference between the hormone levels in INS and INS + GLU + HR. The rise in the counterregulatory hormones per se accounted for only half (53 +/- 9% by the AV difference method and 54 +/- 10% by tracer method) of the glucose production associated with hypoglycemia resulting from insulin infusion. The rate and efficiency of alanine conversion to glucose in the hormone-replacement studies were only 29 +/- 10 and 50 +/- 27% of what occurred during hypoglycemia induced by insulin infusion. In conclusion, the counterregulatory hormones alone (i.e., without accompanying hypoglycemia) can account for only 50% of the glucose production that is present during insulin-induced hypoglycemia. The remaining 50%, therefore, must result from effects of hypoglycemia other than its ability to trigger hormone release.

Alanine↗