Biomedical subjects

G E Gibson

Publications and source records attributed to G E Gibson.

At least 73 records · Page 4Linked to original sources

PubMed1995

The role of signal transduction systems in mediating cell density dependent changes in tyrosine hydroxylase gene expression.

Cell density has been implicated in the regulation of neuronal gene phenotype. This study tested the interaction of signal transduction pathways and the expression of tyrosine hydroxylase (TH) mRNA with varying cell density. Increasing cell density in a parental, wild type PC12 cell line elevated steady state levels of TH mRNA. Three observations suggested that this induction is not related to the cyclic AMP dependent signalling pathway: (1) Forskolin stimulated the level of TH mRNA similarly at multiple densities. (2) PKA deficient mutant PC12 cell lines that have either one third (A123.7, AB11) or 3% (A126-1B2) of normal basal expression of TH mRNA still exhibit the same density induced elevation of TH mRNA levels as the wild type. (3) Different cell densities did not change cyclic AMP concentrations in the basal or in the receptor stimulated state. Increasing cell density did not change basal levels of inositol triphosphate (IP3) levels, which suggests that the phosphatidylinositol cascade (PI) is not responsible for density dependent changes in TH expression. Increasing confluence was highly correlated to [Ca2+]i in control (r = 0.70; P < 0.0001), A123.7 (r = 0.92; P < 0.001), AB11 (r = 0.72; P < 0.0001) and A126 (r = 0.42; P < 0.07). Taken together, the results show that neither cyclic AMP nor the PI cascade is involved in cell density induced changes in TH mRNA and suggest that altered [Ca2+]i may have a role.

Animals↗

PubMed1995

Increased inositol 1,4,5-trisphosphate accumulation correlates with an up-regulation of bradykinin receptors in Alzheimer's disease.

An alteration in signal transduction systems in Alzheimer's disease (AD) would likely be of pathophysiological significance, because these processes control normal brain functions. Previously, a diminished beta-adrenergic-mediated cyclic AMP response was found in cultured fibroblasts from AD patients. Because cross-talk between the phosphoinositide and cyclic AMP pathways exists, the phosphoinositide cascade was studied under conditions that were similar to those for studying the cyclic AMP response. Cells from AD patients and age-matched controls responded to bradykinin (BK) and released inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in a time- and dose-dependent manner. The level of Ins(1,4,5)P3 increased rapidly and transiently in response to BK, peaked at 5 s, but still remained 116-132% above the basal level by 30 s. Although the temporal patterns were similar in both groups, the Ins(1,4,5)P3 concentrations in AD fibroblasts were 73 and 89% above levels in the age-matched controls at 5 and 10 s, respectively. Prostaglandin E1 also increased Ins(1,4,5)P3 formation, but this response was not different between the two groups. Although KD (affinity) values for the BK receptor were similar in both control and AD cells, the number of BK receptors (Bmax) was significantly elevated in AD fibroblasts (186.8 +/- 0.8 fmol/mg of protein) as compared with control fibroblasts (57.2 +/- 15.3 fmol/mg of protein). These results indicate that the elevated Ins(1,4,5)P3 production in response to BK in AD fibroblasts is positively correlated with an increase in the receptor numbers.

Aged↗

PubMed1995

Heterogeneous expression of transketolase in rat brain.

Transketolase (TK; EC 2.2.1.1) is a key pentose phosphate shunt enzyme that plays an important role in the production of reducing equivalents and pentose sugars. TK activity declines in the brains of patients with Alzheimer's disease or Wernicke-Korsakoff syndrome, as well as in thiamine-deficient rats. Understanding the role of TK in the pathophysiology of these neurodegenerative conditions requires knowledge of its regional, cellular, and subcellular distribution within the brain. The current study employed in situ hybridization and immunocytochemistry to examine the distribution of TK mRNA and its encoded protein in adult rat brain. TK mRNA and protein were widely distributed throughout the brain. However, they were enriched in selective perikarya in the piriform cortex, nucleus of the diagonal band, red nucleus, dorsal raphe, pontine nucleus, locus coeruleus, trapezoid, inferior olive, and several cranial nerve nuclei. Lower expression of TK mRNA and protein occurred in layer V of cortex, olfactory tubercle, ventral pallidum, medial septal nucleus, hippocampus, thalamic and hypothalamic nuclei, mammillary body, central gray, and the substantia nigra. TK immunoreactivity also occurred in the nuclei of ubiquitously distributed glial cells, as well as ependymal cells. The heterogeneous distribution of TK may reflect a variety of metabolic activities among different brain regions but does not provide a simple molecular explanation for selective cell death in either thiamine deficiency or other conditions where TK is reduced.

Animals↗

PubMed1995

Determination of local rates of 45Ca influx into rat brain by quantitative autoradiography: studies of aging.

Calcium homeostasis in brain is altered in many conditions, but there is no method to assay quantitatively local calcium flux into brain in vivo. 45Ca uptake into gross-dissected brain regions was measured and compared with results obtained with a quantitative autoradiographic procedure developed to assay influx of 45Ca into brain. Regional calcium contents, brain-to-plasma distribution ratios for calcium and 45Ca, apparent plasma-to-brain transfer coefficients, and net uptake of 45Ca into gross-dissected regions varied by as much as 80%. Local rates of net uptake of 45Ca into 34 structures determined by autoradiography varied by 12- to 14-fold, and rates of movement of 45Ca down concentrations gradients varied by a factor of 7. Previous studies with gross-dissected brain regions suggested changes in calcium uptake into brain during aging, but the values of all the variables assayed in the present study were similar in young adult, middle-aged, and old male rats. A quantitative autoradiographic procedure to assay levels of 45Ca in brain provides the anatomical resolution required to investigate local calcium flux in a variety of physiological and pathological conditions.

Aging↗

PubMed1994

Molecular mechanisms of memory and the pathophysiology of Alzheimer's disease.

Research on molecular and biophysical mechanisms of associative learning and memory storage identified a number of key elements that are phylogenetically conserved. In both vertebrates and invertebrates, K+ channels, PKC, Cp20, and intracellular Ca2+ regulation play a fundamental role in memory mechanisms. Because memory loss is the hallmark and perhaps the earliest sign of Alzheimer's disease, we hypothesized that these normal memory mechanisms might be altered in AD. With the use of a variety of experimental methodologies, our results revealed that one of the critical elements in memory storage, K+ channels, are dysfunctional in AD fibroblasts. Moreover, beta-amyloid induced the same K+ dysfunction in normal cells. Intracellular Ca2+ release, also associated with molecular memory mechanisms, was found altered in fibroblasts from patients with AD. The results therefore strongly suggest that biophysical and molecular mechanisms of associative learning could be altered in AD and that they may contribute to the memory loss observed early in the disease.

Adult↗

PubMed1994

Expression of intracellular calcium-binding proteins in cultured skin fibroblasts from Alzheimer and normal aged donors.

Disturbed calcium homeostasis may play a role in the etiology in Alzheimer's and other neurodegenerative diseases. A protective role against cellular degeneration has been postulated for Ca(2+)-binding proteins in certain neuron populations. Recent data suggest that intracellular free calcium regulation is also altered in several non-neuronal cells, including skin fibroblasts, from patients with Alzheimer's disease. In this study we analyzed the expression of several EF-hand Ca(2+)-binding proteins in cultured skin fibroblasts from Alzheimer patients and age-matched normal donors. We detected a strong expression of some members of the S100 Ca(2+)-binding protein family and of calcineurin A. However, no significant differences were found between both types of donors by Northern blot and Western blot analysis. In addition, similar signals were detected on 45Ca(2+)-blots of fibroblasts extracts of Alzheimer patients and control donors. The present findings indicate that the altered level of some intracellular calcium-binding proteins in certain brain areas of Alzheimer patients is not found in skin fibroblasts of these patients.

Aged↗

PubMed1994

Distribution of the alpha-ketoglutarate dehydrogenase complex in rat brain.

The alpha-ketoglutarate dehydrogenase complex (KGDHC) is a key enzyme in mitochondrial oxidation that appears critical to neurodegenerative diseases. Its activity in the brain declines in thiamine-deficient animals, Alzheimer's disease, and Wernicke-Korsakoff syndrome. Since selective cell populations are affected in these disorders, understanding the cellular distribution of KGDHC is important in order to define its role in the pathophysiology of these diseases. We used antisera against both bovine KGDHC and its E1k component to determine the immunocytochemical distribution of the enzyme and compare it with that of another mitochondrial enzyme, pyruvate dehydrogenase complex (PDHC) and a cholinergic neuronal marker, choline acetyltransferase (ChAT) in rat brain. Although low levels of immunoreactivity occurred in neurons, glia, and neuropil throughout the brain, some regions displayed relatively high perikaryal KGDHC enrichment. In the cerebral cortex, high immunoreactivity occurred mostly in layers III, V, and VI. The hippocampal pyramidal layer in CA1 and CA2 exhibited more intense staining than CA3. In the mammillary body, intensely labeled cells occurred in the supramammillary and lateral nuclei, while moderately stained cells predominated in the medial nucleus. The basal forebrain, basal ganglia, reticular and midline thalamic nuclei, red nucleus, pons, cranial nerve nuclei, inferior and superior colliculi, and cerebellar nuclei also contained highly immunoreactive neurons. The distribution of KGDHC overlapped with that of PDHC and colocalized to a limited extent with ChAT. These data are the first to demonstrate KGDHC immunoreactivity in discrete areas of rat brain and are vital to our understanding of selective vulnerability to metabolic insults and disease.

Animals↗

PubMed1994

Selective enrichment of cholinergic neurons with the alpha-ketoglutarate dehydrogenase complex in rat brain.

Numerous reports suggest a close interaction between acetylcholine homeostasis and oxidative metabolism. However, the neuroanatomical basis of this relationship has not been established. A previous study showed that a key mitochondrial enzyme, alpha-ketoglutarate dehydrogenase complex (KGDHC) occurs at low levels in neurons, glia and neuropil throughout the rat brain. Some regions including those that are enriched with a cholinergic neuronal marker, choline acetyltransferase (ChAT) show relatively high perikaryal enrichment of KGDHC. The current study utilized double label immunofluorescence to determine whether cholinergic neurons are enriched with KGDHC in rat brain. In cranial nerve nuclei, trapezoid nucleus, nucleus ambiguous and inferior olive, virtually all cholinergic neurons were enriched with KGDHC. However, in basal forebrain nuclei, only a subpopulation of cholinergic cells were intensely immunoreactive for KGDHC. These data provide morphological evidence to support the hypothesized link between cholinergic function and oxidative metabolism in specific brain regions.

Acetylcholine↗

PubMed1994

Internal Ca2+ mobilization is altered in fibroblasts from patients with Alzheimer disease.

The recent demonstration of K+ channel dysfunction in fibroblasts from Alzheimer disease (AD) patients and past observations of Ca(2+)-mediated K+ channel modulation during memory storage suggested that AD, which is characterized by memory loss and other cognitive deficits, might also involve dysfunction of intracellular Ca2+ mobilization. Bombesin-induced Ca2+ release, which is inositol trisphosphate-mediated, is shown here to be greatly enhanced in AD fibroblasts compared with fibroblasts from control groups. Bradykinin, another activator of phospholipase C, elicits similar enhancement of Ca2+ signaling in AD fibroblasts. By contrast, thapsigargin, an agent that releases Ca2+ by direct action on the endoplasmic reticulum, produced no differences in Ca2+ increase between AD and control fibroblasts. Depolarization-induced Ca2+ influx data previously demonstrated the absence of between-group differences of Ca2+ pumping and/or buffering. There was no correlation between the number of passages in tissue culture and the observed Ca2+ responses. Furthermore, cells of all groups were seeded and analyzed at the same densities. Radioligand binding experiments indicated that the number and affinity of bombesin receptors cannot explain the observed differences. These and previous observations suggest that the differences in bombesin and bradykinin responses in fibroblasts and perhaps other cell types are likely to be due to alteration of inositol trisphosphate-mediated release of intracellular Ca2+.

Adult↗

PubMed1994

The role of cytosolic free calcium in the regulation of pyruvate dehydrogenase in synaptosomes.

Calcium homeostasis and mitochondrial oxidative metabolism interact closely in brain and both processes are impaired during hypoxia. Since the regulation of the pyruvate dehydrogenase complex (PDHC) may link these two processes, the relation of cytosolic free calcium ([Ca2+]i) to the activation state of PDHC (PDHa) was assessed in isolated nerve terminals (i.e. synaptosomes) under conditions that alter [Ca2+]i. K+ depolarization elevated [Ca2+]i and PDHa and both responses required external calcium. Treatment with KCN, an in vitro model of hypoxia decreased ATP and elevated [Ca2+]i and PDHa. Furthermore, in the presence of KCN, PDHa became more sensitive to K+ depolarization as indicated by larger changes in PDHa than in [Ca2+]i. The calcium ionophore Br-A23187 elevated [Ca2+]i, but did not affect PDHa. K+ depolarization elevated [Ca2+]i and PDHa even if [Ca2+]i was elevated by prior addition of ionophore or KCN. Previous in vivo studies by others show that PDHa is altered during and after ischemia. The current in vitro results suggest that hypoxia, only one component of ischemia, is sufficient to increase PDHa. These data also further support the notion that PDHa is regulated by [Ca2+]i as well as by other factors such as ATP. Our results are consistent with the concept that PDHa in nerve endings may be affected by [Ca2+]i and that these two processes are clearly linked.

Animals↗

PubMed1994

Aging and the brain.

This review considers some of the changes that occur during aging in the mammalian central nervous system. We focus particularly on neurotransmitter systems, calcium homeostasis, synaptic transmission, oxidative metabolism, amyloid deposition, and other neuropathological and anatomical features. Changes during aging in both humans and nonhuman mammals are discussed.

Aged↗

PubMed1993

Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer disease.

Since memory loss is characteristic of Alzheimer disease (AD), and since K+ channels change during acquisition of memory in both molluscs and mammals, we investigated K+ channel function as a possible site of AD pathology and, therefore, as a possible diagnostic index as well. A 113-pS tetraethylammonium (TEA)-sensitive K+ channel was consistently absent from AD fibroblasts, while it was often present in young and aged control fibroblasts. A second (166-pS) K+ channel was present in all three groups. Elevated external potassium raised intracellular Ca2+ in all cases. TEA depolarized and caused intracellular Ca2+ elevation in young and aged control fibroblasts but not AD fibroblasts. The invariable absence of a 113-pS TEA-sensitive K+ channel and TEA-induced Ca2+ signal indicate K+ channel dysfunction in AD fibroblasts. These results suggest the possibility of a laboratory method that would diagnostically distinguish AD patients, with or without a family history of AD, from normal age-matched controls and also from patients with non-AD neurological and psychiatric disorders.

Adult↗

PubMed1993

Altered beta-adrenergic receptor-stimulated cAMP formation in cultured skin fibroblasts from Alzheimer donors.

An alteration in signal transduction systems in Alzheimer's disease would likely be of pathophysiological significance, because these steps are critical to normal brain function. Since dynamic processes are difficult to study in autopsied brain, the current studies utilized cultured skin fibroblasts. The beta-adrenergic-stimulated increase in cAMP was reduced approximately 80% in fibroblasts from Alzheimer's disease compared with age-matched controls. The deficit in Alzheimer fibroblasts in response to various adrenergic agonists paralleled their beta-adrenergic potency, and enhancement of cAMP accumulation by a non-adrenergic agonist, such as prostaglandin E1, was similar in Alzheimer and control fibroblasts. Diminished adenylate cyclase activity did not underlie these abnormalities, since direct stimulation of adenylate cyclase by forskolin elevated cAMP production equally in Alzheimer and control fibroblasts. Cholera toxin equally stimulated cAMP formation in Alzheimer and control fibroblasts. Moreover, cholera toxin partially reduced isoproterenol-induced cAMP deficit in Alzheimer fibroblasts. Pertussis toxin, on the other hand, did not alter the Alzheimer deficits. The results suggest either that the coupling of the GTP-binding protein(s) to the beta-adrenergic receptor is abnormal or that the sensitivity of receptor is altered with Alzheimer's disease. Further, any hypothesis about Alzheimer's disease must explain why a reduced beta-adrenergic-stimulated cAMP formation persists in tissue culture.

Adenylate Cyclase Toxin↗

PubMed1993

Reversible bilateral ureteric obstruction due to a pancreatic pseudocyst.

An unusual case of bilateral ureteric obstruction and hydronephrosis due to pancreatic pseudocyst formation, after an episode of acute pancreatitis is reported. All abnormalities resolved with conservative management. Possible reasons for such ureteric obstruction include periureteric fat necrosis by pancreatic enzymes and compression by the inflammatory mass.

Acute Disease↗

PubMed1992

Synaptosomal plasma and mitochondrial membrane potentials during anoxia.

The precise mechanism by which altered oxidative metabolism impairs neuronal function is unknown. Previous indirect studies suggest that anoxia's effects on the mitochondrial membrane potentials may underlie anoxia's actions. Twenty minutes of anoxia reduced the mitochondrial membrane potential of intact synaptosomes by 38-59 mV, but diminished the plasma membrane potential by only 4-10 mV. Anoxia did not alter the response of the plasma or mitochondrial membrane potentials to K+, nor did anoxia affect the reaction of the plasma membrane potential to valinomycin. However, anoxia diminished the response of the mitochondrial membrane potential to valinomycin by 50%. Thus, partial collapse of the mitochondrial membrane potential may be an important mediator of hypoxia-or anoxia-induced changes in neuronal function.

Anaerobiosis↗

PubMed1992

Cytosolic free calcium in lymphoblasts from young, aged and Alzheimer subjects.

Altered cellular calcium homeostasis may be important in the pathophysiology of aging and Alzheimer's disease. Calcium transport by freshly isolated lymphocytes declines with Alzheimer's disease compared with age-matched controls. To determine if these changes occur in the absence of complications due to drugs, diet or any of the other variables that are dependent upon the state of the patients, cytosolic free calcium ([Ca2+]i) was determined in cultured lymphoblasts from young and aged control subjects, as well as from Alzheimer patients. Lymphoblast [Ca2+]i was determined with the fluorescent probe fura-2 in either the presence or absence of serum. In cells that were grown in serum free medium, neither growth rates nor [Ca2+]i varied between groups. Growing cells in serum containing medium doubled growth rates and [Ca2+]i. However, [Ca2+]i from young, aged and Alzheimer groups were still similar. Thus, an age- or Alzheimer-related alteration in [Ca2+]i does not occur in cultured lymphoblasts.

Adult↗

PubMed1992

Nonneural markers in Alzheimer disease.

Nonneural tissues are now widely used to search for abnormalities in genes as well as for other markers of dementia of the Alzheimer type (DAT). Studies of nonneural tissues can experimentally circumvent problems inherent in the study of autopsy brain, but to be meaningful, abnormalities identified in the periphery must be correlated with abnormalities in the brain, which is the tissue of clinical interest. Among the topics in DAT research that can be readily studied in nonneural cells (including tissue cultures) are molecular genetics, amyloid precursor protein formation and metabolism, systemic manifestations of immunological and inflammatory mechanisms, proteolysis, membranes, signal transduction, and mitochondria and metabolism. Although phenomena suggesting the possibility of cytoskeletal abnormalities in nonneural DAT cells have been described, the tau molecules involved in paired helical filament formation are relatively brain-specific. Since the neuropathological diagnosis of DAT depends on recognizing a pattern of changes rather than any single abnormality, it seems unlikely that any one laboratory abnormality in peripheral tissues will correlate precisely with the clinicopathological entity of DAT. However, abnormalities found in nonneural DAT cells that correlate with the existence of similar abnormalities in the brain are likely to be informative about the disease process in the patients in whom they occur.

Aged↗

PubMed1992

Thiamin and Alzheimer's disease.

Because of clinical and neuropathological overlap between the characteristics of dementia of the Alzheimer type (DAT) and of a human thiamin deficiency syndrome (Wernicke-Korsakoff syndrome), thiamin pyrophosphate (TPP) dependent processes have been studied in DAT brain and other tissues. The activities of 3 TPP-dependent enzymes are reduced in DAT brain: transketolase (TK), the pyruvate dehydrogenase complex (PDHC), and the alpha-ketoglutarate dehydrogenase complex (KGDHC). Quantitatively, the most marked reductions are in KGDHC (to less than 20% of normal). In cultured skin fibroblasts, KGDHC activity is reduced to 50-60% of normal, TK activity to 80-90% of normal, and PDHC is normal. Structural and molecular studies of the DAT and non-DAT enzymes are in process. A lesion of KGDHC may be related to the pathogenesis of DAT. Treatment with large doses of thiamin has not been beneficial, but the data are not totally negative. Further studies of thiamin-dependent mechanisms in DAT seem justified.

Alzheimer Disease↗