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Biomedical subjects

A R Morrison

Publications and source records attributed to A R Morrison.

At least 73 records · Page 4Linked to original sources
PubMed1994

Modulation of lens epithelial cell proliferation by enhanced prostaglandin synthesis after UVB exposure.

PURPOSE: The goals of this investigation were to examine the synthesis of prostaglandins after UVB exposure of lens epithelial cells and to investigate their role in cell proliferation. METHODS: Cultured rabbit lens epithelial cells (cell line N/N1003A) were exposed to low levels of UV radiation. Prostaglandins were assayed by radioimmunoassay; products of arachidonic acid metabolism were analyzed by thin-layer chromatography and mass spectroscopy. Cell proliferation was measured by [3H]thymidine incorporation and proliferative autoradiography. RESULTS: Cultured lens epithelial cells exposed to UVB radiation showed a dose-dependent increase in basal prostaglandin synthesis measured 24 hours after UV exposure. At an optimal dose (250 J/m2) of UVB, prostaglandin E2 (PGE2) synthesis was enhanced tenfold. Product identity was confirmed using thin-layer chromatography and mass spectroscopy with authentic standards. Incubation of irradiated cells with exogenous arachidonic acid followed by extraction and thin-layer chromatography revealed that the cultures produced PGE2, prostaglandin I2 (measured as 6-keto-prostaglandin F1 alpha), prostaglandin F2 alpha, and hydroxyeicosatetraenoic acid. The synthesis of all of these products was enhanced threefold in cells exposed to 250-J/m2 UVB. Indomethacin pretreatment eliminated the synthesis of prostaglandins, further confirming their identity. To discover the relationship between PGE2 synthesis and irradiation-induced cell proliferation, [3H]thymidine incorporation into DNA was determined 24 or 48 hours after exposure. These experiments revealed a fivefold increase in incorporation induced by UVB exposure. UVB-enhanced incorporation of thymidine was eliminated by pretreatment of cultures with indomethacin to eliminate PG synthesis. However, when 100 nM PGE2 was added to the indomethacin-treated irradiated cultures, incorporation of the label was restored toward the level detected in the UVB-stimulated cells. Addition of other prostaglandins to the cultures was ineffective. CONCLUSIONS: The results indicate that the synthesis of PGE2 is enhanced by exposure of lens epithelial cells to UVB radiation. PGE2 seems to play a specific role in cell proliferation after UV exposure. This increase in PGE2 synthesis may be important in posterior subcapsular cataract formation in humans and in animals exposed to UVB radiation in vivo.

Animals↗
PubMed1993

The amplitude of elicited PGO waves: a correlate of orienting.

Ponto-geniculo-occipital (PGO) waves spontaneously occur in the pons, lateral geniculate body (LGB), and occipital cortex during rapid eye movement sleep (REM), and PGO-like waves (PGOE) may be elicited in LGB during sleep and waking. Because REM has been hypothesized to be a state of continual "orienting" or "hyper-alertness," we tested whether the amplitudes of PGOE in "alerting" situations (the abrupt onset of a loud sound or presentation of a novel stimulus within a series of stimuli) that evoke orienting responses (OR) would be greater than those following stimuli without OR. We also compared PGOE accompanying OR to PGOE during REM and NREM when OR are absent. The amplitudes of PGOE in W were greatest when OR were observed, and the amplitudes of PGOE accompanying OR were not significantly different from PGOE amplitudes in REM. Likewise, the amplitudes of PGOE during REM were not significantly different from those of the highest amplitude spontaneous PGO waves. We propose that the presence of PGOE signals registration of stimuli and that stimuli of sufficient significance to induce behavioral OR in waking also elicit PGOE of significantly greater amplitudes in all behavioral states. These findings support the hypothesis that the presence of high-amplitude PGO waves in REM indicates that the brain is in a state of more-or-less continual orienting.

Acoustic Stimulation↗
PubMed1993

Amplification of the arachidonic acid cascade: implications for pharmacologic intervention.

The signal transduction pathway that results in prostaglandin production is thought to occur in a stepwise manner that involves agonist-stimulated action of a phospholipase that releases the second messenger arachidonic acid from membrane phospholipids. Prostaglandin endoperoxide synthase (PGH synthase) then converts arachidonic acid to the prostaglandin precursors. Further delineation of this cascade has recently occurred with the identification of two distinct prostaglandin endoperoxide synthases, PGH synthase-1 and PGH synthase-2. There is evidence that PGH synthase-1 may have broad cellular expression and may be constitutively expressed in most cells. In contrast, PGH synthase-2 expression may be more limited and has been shown to be stimulated by a variety of cytokines and growth factors. Dexamethasone inhibits the expression of an early response gene, TIS10, which is homologous to PGH synthase-2. The exact mechanism of PGH synthase-2 gene regulation in mesangial cells is unknown; however, it may be a potential site for pharmacologic intervention. Regulation of PGH synthase-2 could in turn modulate prostaglandin production and temper the production of extracellular matrix and thus scar formation that occurs in a wide variety of inflammatory renal diseases.

Arachidonic Acid↗
PubMed1993

Enhanced keratinocyte prostaglandin synthesis after UV injury is due to increased phospholipase activity.

The possibility that increased eicosanoid synthesis in skin after ultraviolet light irradiation is due to enhanced phospholipase activity was examined. [3H]arachidonic acid-labeled human keratinocyte cultures exposed to 30 mJ/cm2 ultraviolet (UV) B were studied 6 h after injury. Bradykinin-stimulated release of [3H]arachidonic acid was increased 1.8-fold over release from control cultures by prior irradiation. In unlabeled cultures, prior irradiation produced a threefold increase in bradykinin-stimulated prostaglandin (PG) E2 synthesis as measured by immunoassay. The relative contribution of increased phospholipase vs. cyclooxygenase activity was therefore examined using stable isotope mass measurements of PGE2. By this method, prior irradiation increased bradykinin-stimulated phospholipase activity 3.5-fold, while no change in total cellular cyclooxygenase activity was observed. The effects of irradiation on phospholipase activity were then assessed in more detail. The activities of phospholipase A2, arachidonoyl-CoA synthetase, and arachidonoyl-CoA lysophosphatide acyltransferase in cell homogenates were determined. No effect of UV exposure on the activity of these enzymes was observed. These results suggest that the increase in prostaglandin synthesis produced after UV irradiation is due to increased phospholipase activity, thus enhancing arachidonate release.

Acylation↗
PubMed1992

Phospholipase activation during monocyte adherence and spreading.

Phospholipase activation is an important element in cellular signal transduction. In our study we investigated the role and regulation of phospholipase activation during human monocyte adherence and spreading. In human monocytes, phospholipase inhibition (with bromophenacyl bromide (BPB) or manoalide) impaired cell adherence and spreading. In contrast, neither cyclooxygenase/lipoxygenase inhibition nor platelet activating factor receptor blockade affected these responses. The impaired adherence and spreading induced by phospholipase inhibition with BPB could be partially reversed by the addition of nM levels of arachidonate (20:4(n - 6)). Dihomogammalinolenic acid (20:3(n - 6)) could substitute for arachidonate, but other polyunsaturated fatty acids were ineffective in this regard. The phospholipase inhibitor, BPB was selective in its effects on cellular phospholipase activities. BPB inhibited adherence/spreading-related and PMA-stimulated phospholipase activities, but not Ca2+ ionophore-stimulated phospholipase activity. To further probe for the role of Ca2+ in monocyte adherence and spreading, monocytes were loaded with MAPTAM (bis-(2-amino-5-methylphenoxy)-ethane-N,N,N',N', tetraacetic acid tetraacetoxymethyl ester), an EGTA analog. In contrast to phospholipase inhibition, intracellular Ca2+ chelation with MAPTAM did not affect monocyte adherence but did inhibit monocyte spreading. MAPTAM partially inhibited adherence/spreading-stimulated phospholipase activity, but did not inhibit PMA-stimulated phospholipase activity. These data suggest that human monocyte adherence and spreading may sequentially activate Ca(2+)-independent and then Ca(2+)-dependent phospholipases to release arachidonate. The activation of phospholipase and the release of arachidonate appear to be integral parts of the adhesion process.

Acetophenones↗
PubMed1992

Tocopherol analogs suppress arachidonic acid metabolism via phospholipase inhibition.

alpha-Tocopherol and three derivatives in which the phytol chain is modified or deleted were examined for their effect on cultured keratinocyte arachidonic acid metabolism. 2,2,5,7,8-Pentamethyl-6-hydroxychromane (PMC), in which the phytol chain is replaced by a methyl group, inhibited basal, bradykinin (BK)- and A23187-stimulated prostaglandin E2 (PGE2) synthesis with an apparent Ki of 1.3 microM. The Ki of the analogue with six carbon atoms in the side chain (C6) was 5 microM while that of the C11 analogue was 10 microM. No effect of alpha-tocopherol was observed. The mechanism of inhibition was studied using PMC. The effect of PMC on phospholipase and cyclooxygenase activity was assayed using stable isotope mass measurements of PGE2 formation, which assesses arachidonate release and cyclooxygenase metabolism simultaneously. BK-stimulated formation of PGE2, derived from endogenous phospholipid, was decreased 60% by 5 microM PMC and eliminated by 50 microM PMC, compared with controls. No difference in PGE2 formed from exogenous arachidonic acid was observed, indicating no effect of PMC on cyclooxygenase activity. In contrast, no effect of 5 microM PMC was observed on BK-stimulated [3H]arachidonic acid release from prelabeled cultures. The capacity of PMC to inhibit phospholipase activity in vitro was also assessed. PMC inhibited hydrolysis of phospholipid substrate by up to 60%. These results suggest that alpha-tocopherol analogues with alterations in the phytol chain inhibit eicosanoid synthesis by preferential inhibition of phospholipase.

Arachidonic Acids↗
PubMed1992

Raphespinal and reticulospinal axon collaterals to the hypoglossal nucleus in the rat.

Neurons in the medial tegmental field project directly to spinal somatic motoneurons and to cranial motoneuron pools such as the hypoglossal nucleus. The axons of these neurons may be highly collateralized, projecting to multiple levels of the spinal cord and to many diverse regions at different levels of the neuraxis. We employed a double fluorescent retrograde tracer technique to examine whether medial tegmental neurons that project to the spinal cord also project to the hypoglossal nucleus. Injections of Diamidino Yellow into the hypoglossal nucleus and Fast Blue into the spinal cord produced large numbers of double labeled neurons in the medial tegmental field, particularly in the caudal raphe nuclei and adjacent ventromedial reticular formation. In these structures the number of neurons projecting to both the hypoglossal nucleus and the spinal cord was equivalent to the number of neurons projecting to multiple levels of the spinal cord observed in control animals. Fewer neurons projecting to both the hypoglossal nucleus and the spinal cord were observed in several other nuclei and subregions of the medial tegmental field, while almost no such neurons were observed in the lateral tegmental field or other pontomedullary structures. These results demonstrate that neurons of the caudal raphe nuclei and adjacent ventromedial reticular formation project to both the spinal cord and the hypoglossal nucleus, and support the concept that the diffuse projections to motoneuron pools from the medial tegmental field globally modulate both spinal and cranial somatic motoneuron excitability.

Amidines↗
PubMed1992

Identification of a processed protein related to the human chaperonins (hsp 60) protein in mammalian kidney.

The chaperonin family of proteins, which includes GroEL protein of E. coli, yeast heat shock protein (hsp-60) and the ribulose-1-5-bisphosphate carboxylase (Rubis Co.) subunit binding protein of plant chloroplasts, shows strong sequence homology to the Chinese hamster ovary (CHO) mitochondrial P1 protein. We have identified a 60 kDa protein from bovine kidney which by N-terminal sequencing gives the amino acid sequence AKDVKFGADARALLMLQGVDLLADA. Bovine whole kidney membranes were delipidated, solubilized with octyl glucoside and fractionated over an affinity column using the amiloride analog 5-N pyrazine amiloride as the ligand. After extensive washing with 200 mM NaCl, the column was eluted with pH 4.0 buffer. Analysis of column fractions on a 7.5% polyacrylamide gel revealed 3-4 bands with a predominant band at 60,000 Da. Amino acid analysis after transfer to immobilon membranes demonstrated sequence identity to the human HSP (60), extending 24 amino acids from the N-terminus, but lacking the leader sequence. These data indicate that a processed form of a protein related to the human HSP (60) chaperonin is associated with a membrane fraction in the mammalian kidney, and that the processed form of the protein binds strongly to an amiloride affinity support.

Amiloride↗
PubMed1992

Neurons of the motor trigeminal nucleus project to the hypoglossal nucleus in the rat.

The hypoglossal nucleus (Mo12) contains motoneurons that innervate the tongue, while the motor trigeminal nucleus (Mo5) contains motoneurons that elevate or depress the mandible. Previous studies have revealed lateral and medial tegmental field neuronal afferents to the Mo12 adjacent to, but not within, the motor trigeminal nucleus (Mo5). The current studies demonstrate the presence of retrogradely labeled neuronal afferents to the Mo12 within the Mo5 produced by as little as 10 nl of Fast Blue (FB) injected into the Mo12. Retrograde labeling of Mo5 afferents to the Mo12 with injections of Diamidino Yellow (DY) combined with injections of FB into the lumbar spinal cord showed these neuronal afferents to the Mo12 are not part of the diffuse projections to motoneurons from the nucleus subcoeruleus. Retrograde labeling of Mo5 afferents to the Mo12 with DY combined with injections of FB into the masseter revealed these neuronal afferents to the Mo12 are not trigeminal motoneurons. These results indicate that Mo5 interneurons are part of the lateral tegmental field projections to the Mo12, and are likely to comprise part of the neural substrate coordinating the motor activity of the jaw and tongue.

Animals↗
PubMed1992

Varying expressions of alerting mechanisms in wakefulness and across sleep states.

Alerting stimuli, such as intense tones, presented to cats in wakefulness (W) elicit the orienting response (OR) and/or the acoustic startle reflex (ASR) in conjunction with elicited ponto-geniculo-occipital waves (PGOE) from the lateral geniculate body (LGB) and elicited waves from the thalamic central lateral nucleus (CLE). Alerting stimuli presented during rapid eye movement sleep (REM) and non-rapid eye movement sleep (NREM) also elicit PGOE. We presented tones in W, REM and NREM to determine whether CLE could be obtained in sleep and to examine the patterns of responsiveness of PGOE and CLE across behavioral states. Also, we recorded ASR and OR and compared the response patterns of behavioral and central correlates of alerting. The subjects were 7 cats; all exhibited spontaneously occurring waves in LGB and CL. All cats exhibited PGOE and 5 cats exhibited CLE in W, REM and NREM. PGOE and CLE showed less evidence of habituation than did ASR and OR. The pattern of responsiveness of CLE across behavioral states was different from that found for PGOE, and spontaneous CL waves were much rarer than the LGB waves. ASR was elicited in 5 cats during W trials, and in 3 cats during REM trials. OR habituated rapidly in W and did not occur in REM and NREM. The data indicate that central mechanisms of alerting function in sleep states as well as in W and suggest that CLE and PGOE reflect activity in mechanisms underlying cortical desynchronization and visual processes which may act in concert during alerting.

Acoustic Stimulation↗
PubMed1992

Peripheral and central components of alerting: habituation of acoustic startle, orienting responses, and elicited waveforms.

Behavioral orienting (OR), the acoustic startle reflex (ASR), pontogeniculooccipital (PGO) waves in the lateral geniculate body, and midlatency auditory evoked responses (MLR) represent components of alerting. The habituation rate for each was examined to test the hypothesis that OR, ASR, and PGO waves have related underlying neural mechanisms and determine the similarity in responsiveness between elicited PGO waves (PGOE) and elicited waves in the thalamic central lateral nucleus (CLE), a site that yields MLR. PGOE and CLE waves did not habituate in amplitude after 120 tones; however, the pattern of responses for each waveform was different. OR and ASR significantly decreased amplitude across trials with OR exhibiting a faster, more pronounced decrement. Some separation exists between the peripheral (OR and ASR) and central (PGOE and CLE) components of alerting. PGO and CL waves may have common underlying neural mechanisms.

Animals↗
PubMed1992

Regulation of mesangial cell cyclooxygenase synthesis by cytokines and glucocorticoids.

The cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF), potently induce prostaglandin formation in glomerular mesangial cells. Mechanisms by which these cytokines stimulate prostaglandin formation vary among cell types. We investigated whether alterations in phospholipase A2 (PLA2) or cyclooxygenase (COX) mass and activity contribute to the changes in mesangial cell prostaglandin production. These cytokines induced COX activity and mass in a time-dependent manner, which paralleled prostaglandin production. IL-1 increased COX mass approximately threefold by 24 h. TNF had a much smaller effect, although it appeared to be additive with IL-1. IL-1-induced COX mass was maintained at an increased level for at least 48 h. The glucocorticoid dexamethasone (DEX) virtually abolished prostaglandin production and blocked cytokine induction of COX activity and mass. DEX did not reduce COX activity or mass below the basal, serum-fed levels, however. By utilizing stable isotope methods, we could demonstrate that IL-1 increased free arachidonate levels, implying new PLA2 synthesis over a time course that was maximal at 6 h and was cycloheximide and actinomycin D sensitive. These data demonstrate that the cytokines IL-1 and TNF enhance synthesis of COX and PLA2, contributing to increased prostaglandin production. Cytokine-stimulated prostaglandin production ceases when cells are also treated with DEX, although control levels of COX activity and mass remain. This occurs because DEX inhibits the IL-1-induced enhanced arachidonate release.

Animals↗
PubMed1992

Different guanosine triphosphate-binding proteins couple vasopressin receptor to phospholipase C and phospholipase A2 in glomerular mesangial cells.

To evaluate the identity of the guanosine triphosphate--binding proteins coupling arginine vasopressin receptor occupancy with activation of phospholipase C, leading to Ca2+ mobilization, and activation of phospholipase A2, leading to arachidonate release and prostanoid formation, we used intact cells, saponin-permeabilized cells, and membranes of the rat mesangial cell. Arginine vasopressin 10(-7) mol/L produced a dose-dependent increase in cytosolic Ca2+ to maximal levels of 500 nmol/L with peak responses occurring within 10 seconds of addition of arginine vasopressin to cells in suspension. Arginine vasopressin 10(-7) mol/L elicited a maximal response. These increases were associated temporarily with a fourfold increase in tritiated D-myo-inositol 1,4,5-trisphosphate formation in prelabeled cells. Pertussis toxin (200 ng/ml) did not inhibit the Ca2+ increase nor did it inhibit the increase in tritiated D-myo-inositol 1,4,5-trisphosphate formation, suggesting a pertussis toxin--insensitive signaling pathway for phospholipase C hydrolysis in response to vasopressin. Membranes prepared from mesangial cells increased D-myo-inositol 1,4,5-trisphosphate formation in vitro in response to arginine vasopressin and guanosine-5'-0(3- thiotrisphosphate), and this stimulation was inhibited by guanosine-5'-0(2-thiodiphosphate), confirming the involvement of a guanosine triphosphate--binding protein. In contrast arginine vasopressin stimulated arachidonate release from intact mesangial cells, and this effect was blocked by pretreating cells with pertussis toxin. To demonstrate that this was through a pertussis toxin--sensitive guanosine triphosphate--binding protein, we permeabilized cells with saponin and determined that arginine vasopressin and guanosine-5'-0(3-thiotriphosphate) stimulated the release of arachidonic acid and the stimulation of guanosine-5'-0(3-thiotriphosphate) was inhibited by guanosine-5'-0(2-thiodiphosphate). Finally, pertussis toxin was able to stimulate adenosine diphosphate ribosylation in vivo of a substrate protein in mesangial cell membranes of 41 kd, and this ribosylation was inhibited by pretreating cells with pertussis toxin. These data suggest that the release of arachidonic acid by vasopressin in glomerular mesangial cells is linked to a pertussis toxin--sensitive guanosine triphosphate--binding protein and that this activation of phospholipase C in vasopressin is linked to a pertussis toxin--insensitive guanosine triphosphate--binding protein.

Adenosine Diphosphate Ribose↗
PubMed1991

Effects of stimulus intensity on elicited ponto-geniculo-occipital waves.

Waves similar to spontaneous ponto-geniculo-occipital (PGO) waves of paradoxical sleep (PS) in cats are elicited by tones and can be considered a form of evoked potential termed PGOE. The aims of the present experiment were to determine: (1) the effects of tone intensity on the probability of producing PGOE; (2) the effects of intensity on the amplitude and latency of PGOE across slow-wave sleep (SWS) and PS; (3) whether the effects of intensity on PGOE are similar to those on a particular form of auditory evoked potential known as the mid-latency response (MLR). Increasing the intensity of the stimulus from 60 to 100 in 10 dB increments resulted in increased probability, increased amplitude, and decreased latency of PGOE in both SWS and PS. This pattern was similar to published findings with MLR, and latencies of PGOE (roughly 60-100 msec) fell within the range of 'C wave' type of MLR recorded in intralaminar nuclei of the thalamus of cats. The possibility that PGOE and MLR share underlying mechanisms and represent the same phenomenon is discussed with particular attention to the function of the mechanisms during alerting and orienting.

Acoustic Stimulation↗
PubMed1991

The effects of changing state on elicited ponto-geniculo-occipital (PGO) waves.

Waves similar to ponto-geniculo-occipital (PGO) waves occurring spontaneously in the lateral geniculate body (LGB), pons, and occipital cortex during rapid eye movement (REM) sleep can be elicited in the LGB and the cortex by tones in waking (W), non-rapid eye movement sleep (NREM), and REM. In W, the elicited waves (PGOE) sometimes accompany orienting responses (OR). We have hypothesized that REM is a state resembling exaggerated "orienting" in part because spontaneous PGO waves similar to PGOE accompanying OR are constantly observed in REM. The present experiment tested whether: (1) PGOE and OR were strongly correlated in W across a large number of tone presentations as might be predicted if PGOE were central wave form markers for a state of orienting; and (2) recovery of responsiveness of PGOE to tones would then be greater in REM than NREM, as might be expected if REM but not NREM were a state in which central mechanisms of orienting were highly active. Tones were presented in W and then in REM and NREM to six cats in order to measure the degree of habituation of OR and PGOE simultaneously. PGOE and OR exhibited a degree of independence: the former were readily produced in W despite the rapid decline in OR across trials. Recovery in the amplitude of PGOE occurred in both NREM and REM. The recovery tended to be greater in REM than NREM, although this was not statistically significant. Refinements of the theory that REM represents a state of exaggerated internal orienting are discussed.

Acoustic Stimulation↗
PubMed1991

Fatty acids are potential endogenous regulators of aldosterone secretion.

Adrenal glomerulosa cells washed with delipidated albumin produced increased amounts of aldosterone in response to angiotensin-II (AII) or (Bu)2cAMP. Albumin treatment also increased binding of 125I-labeled AII to high affinity binding sites on adrenal cells. Lipid extracts of albumin solutions that were used to wash cells inhibited AII binding and aldosterone responses by washed glomerulosa cells. Chromatographic fractionation and mass spectroscopic analysis indicated that the inhibitors removed from cells by albumin were long chain fatty acids. Exogenous fatty acids not only inhibited AII binding, but they inhibited basal aldosterone production and increments in aldosterone caused by AII or dbcAMP, suggesting an effect on postreceptor steps in aldosteronogenesis. The most potent and most abundant fatty acids removed from adrenal cells were oleic, linoleic, and arachidonic. These fatty acids inhibited at micromolar concentrations in the absence of albumin and at somewhat higher concentrations in its presence. Cells that had been washed, then inhibited by exogenous oleic acid in vitro, were restored to their enhanced responsiveness by a second albumin wash, making it unlikely that cell damage is the mechanism of inhibition by fatty acids. Responses of fasciculata cells were not potentiated by albumin washes, and cortisol production was less sensitive than aldosterone production to exogenous fatty acids. Binding of ANP to glomerulosa cells was not affected by albumin or fatty acids. These results combined with clinical correlations make it plausible that unesterified fatty acids are naturally occurring regulators of the adrenal glomerulosa. Insulin's ability to lower plasma levels of fatty acids may be one way that it causes sodium retention.

Aldosterone↗