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Biomedical subjects

D L Armstrong

Publications and source records attributed to D L Armstrong.

At least 55 records · Page 3Linked to original sources

Valproate-induced liver failure in one of two siblings with Alpers disease.

Alpers disease is a neurodegenerative disorder of childhood characterized by early developmental delay, intractable seizures, and death in childhood. Neuropathologic changes are most severe in the gray matter and consist of diffuse neuronal loss, spongiform changes, and astrocytosis. We report 2 siblings with Alpers disease who were discordant for exposure to valproate (VPA). Both had developmental delay, and a progressive seizure disorder beginning at 5 years of age. The proband died at age 8 years of complications of ongoing seizures, including epilepsia partialis continua, with only minimal liver abnormalities. Her younger brother was treated with VPA for new-onset seizures and developed fulminant liver failure 6 months later, which led to his death at 5 years of age. Neuropathologic abnormalities of both siblings were consistent with Alpers disease. These observations support classification of Alpers disease and Alpers disease with liver cirrhosis as a single disease. They also confirm previous reports indicating that VPA may accelerate fulminant liver failure in Alpers disease. We recommend that a diagnosis of Alpers disease be considered in children with unexplained early developmental delay, cerebellar signs, or partial seizures, especially epilepsia partialis continua. When Alpers disease is strongly suspected, use of VPA should be avoided.

Anticonvulsants↗

Social class and race disparities in premature stroke mortality among men in North Carolina.

The purpose of this work was to examine the association between social class and premature stroke mortality among blacks and whites. For black men and white men in North Carolina, aged 35-54 years, mortality data from vital statistics files and population data from Census Public Use Microdata Sample files were matched according to social class for the years 1984-1993. Four categories of social class were defined based upon a two-dimensional classification scheme of occupations. For each category of social class, race-specific age-adjusted stroke mortality rates were calculated, and race-specific prevalences of income, wealth, education, unemployment, and disability were estimated. Women were excluded because comparable information on social class was not available from the mortality and population data sources. For both black men and white men, the highest rates of premature stroke mortality were observed among the lowest social classes. The rate ratios (RR) between the lowest and highest social class were 2.8 for black men and 2.3 for white men. Within each social class, black men had substantially higher rates of premature stroke mortality than white men (black-to-white RR ranged from 4.0 to 4.9). Among both black men and white men, the highest social class consistently had the most favorable levels of income, wealth, education, and employment. The inverse association between social class and stroke mortality for both black men and white men supports the need for stroke prevention efforts that address the structural inequalities in economic and social conditions.

Adult↗

Seasonal effects on ovarian responsiveness to exogenous gonadotrophins and successful artificial insemination in the snow leopard (Uncia uncia).

Ovaries of the seasonally-breeding snow leopard (Uncia uncia) were examined to determine whether they were responsive to exogenous gonadotrophins throughout the year. The potential of laparoscopic artificial insemination (AI) also was assessed for producing offspring. During the non-breeding, pre-breeding, breeding and post-breeding seasons, females (n = 20) were treated with a standardized, dual-hormone regimen given intramuscularly (600 I.U. of equine chorionic gonadotrophin followed 80-84 h later with 300 I.U. of human chorionic gonadotrophin (hCG)). Laparoscopy was performed 45-50 h after administration of hCG, and all ovarian structures were described. Females with fresh corpora lutea (CL) were inseminated, and anovulatory females were subjected to follicular aspiration to examine oocyte quality. Snow leopards responded to exogenous gonadotrophins throughout the year. Mean number of total ovarian structures (distinct follicles mature in appearance plus CL) did not differ (P > or = 0.05) with season, but the proportion of CL: total ovarian structures was greater (P < 0.01) for the breeding season compared with all other seasons. The proportion of females ovulating was greater (P < 0.05) during the breeding and post-breeding seasons than during the pre-breeding and non-breeding seasons respectively. No Grade-1 quality oocytes were recovered from follicles of anovulatory females. Serum concentrations of oestradiol-17 beta appeared elevated in all females, and neither oestradiol-17 beta concentrations nor progesterone concentrations differed (P > or = 0.05) among seasons. Of 15 females artificially inseminated, the only one that was inseminated in the non-breeding season became pregnant and delivered a single cub. This is the first successful pregnancy resulting from AI in this endangered species.

Animals↗

Disproportionate loss of CA4 parvalbumin-immunoreactive interneurons in patients with Ammon's horn sclerosis.

We studied differences in the number and morphology of parvalbumin-immunoreactive (PV-IR) interneurons in 43 hippocampal specimens from patients with classical Ammon's horn sclerosis (AHS) who underwent anterior temporal lobectomy, as compared with 14 autopsy and non-AHS surgical control specimens. PV-IR neuronal loss in the AHS specimens varied significantly from that expected based on overall AHS-associated pyramidal and granule neuron loss. Most striking was the loss of PV-IR interneurons in CA4 of the AHS specimens, which was 12 times greater than AHS-associated pyramidal neuron loss, and significantly exceeded the PV-IR interneuron loss observed in the other sectors of the hippocampus. In addition, the PV-IR interneurons in the AHS specimens had markedly smaller and less defined cell bodies and shortened and simplified dendritic arbors compared with the PV-IR interneurons in the control specimens. Other differences noted in the AHS specimens included prominent dendritic varicosities; the loss or interruption of a band formed by PV-IR terminals in the dentate gyrus; and the virtual absence of a small, intensely staining PV-IR interneuron with a short, exuberant dendritic arbor that was readily identified in the autopsy specimens. We discuss these findings in relationship to the development of classical AHS and complex partial seizures (CPS).

Adolescent↗

Social class and premature mortality among men: a method for state-based surveillance.

OBJECTIVES: This study examined trends in mortality by social class for Black and White men aged 35 through 54 years in North Carolina, for 1984 through 1993, using an inexpensive, newly developed state-based surveillance method. METHODS: Data from death certificates and census files permitted examination of four social classes, defined on the basis of occupation. RESULTS: Premature mortality was inversely associated with social class for both Blacks and Whites. Blacks were at least twice as likely to die as Whites within each social class. CONCLUSIONS: Adoption of state-specific surveillance of social class and premature mortality would provide data crucial for developing and evaluating public health programs to reduce social inequalities in health.

Adult↗

Activation of protein kinase C inhibits calcium-activated potassium channels in rat pituitary tumour cells.

1. The regulation of large-conductance, calcium- and voltage-dependent potassium (BK) channels by protein kinase C (PKC) was investigated in clonal rat anterior pituitary cells (GH4C1), which were voltage clamped at -40 mV in a physiological potassium gradient through amphotericin-perforated patches. 2. Maximal activation of PKC by 100 nM phorbol 12, 13-dibutyrate (PdBu) almost completely inhibited the voltage-activated outward current through BK channels. In contrast PdBu had no significant effect on the residual outward current after block of BK channels with 2 mM TEA or 30 nM charybdotoxin. In single-channel recordings from cell-attached patches, PdBu reduced the open probability of BK channels more than eightfold with no significant effect on mean open lifetime or unitary conductance. 3. The effects of PdBu on BK channels were not mimicked by the 4 alpha-isomer, which does not activate PKC, and were blocked almost completely by 25 microM chelerythrine, a specific, noncompetitive PKC inhibitor. 4. PdBu had no significant effect on the amplitude of the pharmacologically isolated, high voltage-activated calcium current. 5. Inhibition of BK channel activity by PKC provides the first molecular mechanism linking hormonal activation of phospholipase C to sustained excitability in pituitary cells.

Amphotericin B↗

Effects of hypernatraemia in the central nervous system and its therapy in rats and rabbits.

1. We studied the effects of acute (1 or 4 h) and chronic (1 week) hypernatraemia (plasma [Na+], 170-190 mM) on brain histology, and brain water and solute contents in rats and rabbits. 2. In rabbits with acute hypernatraemia, there was significant loss of intracellular brain water, with increases in brain [Na+ + K+], amino acid concentration, and undetermined solute (idiogenic osmole). After 1 week of recovery, brain intracellular water content had returned to normal. 3. In hypernatraemic rats there was myelinolysis of brain white matter, with karyorrhexis and necrosis of neurons. 4. Hypernatraemic rabbits were treated with 77 mM NaCl (i.v.) to normalize plasma [Na+] over 4-24 h intervals. Therapy of either acute or chronic hypernatraemia resulted in significant brain oedema because brain osmolality failed to decrease at the same rate as plasma osmolality. 5. It is concluded that: (a) untreated hypernatraemia results in brain lesions demonstrating myelinolysis and cellular necrosis; (b) normalization of hypernatraemia over 4-24 h results in cerebral oedema, due primarily to failure of brain amino acids and idiogenic osmoles to dissipate as plasma [Na+] is decreased to normal.

Amino Acids↗

Somatostatin stimulates BKCa channels in rat pituitary tumor cells through lipoxygenase metabolites of arachidonic acid.

The stimulation of large-conductance, calcium-activated (BK) potassium channels by somatostatin through protein dephosphorylation in rat pituitary tumor cells (White et al., Nature 351, 570-573, 1991) is blocked by drugs that interfere with arachidonic acid release by phospholipase A2 and metabolism by 5-lip-oxygenase. In contrast, higher concentrations of the same drugs had no effect on BK channel gating in cell-free patches, on the inhibition of adenylyl cyclase by somatostatin, or on the stimulation of BK channels by protein dephosphorylation through a cGMP-dependent pathway (White et al., Nature 361, 263-266, 1993). Exogenous arachidonic acid (1-20 muM) stimulated BK channel activity through protein dephosphorylation as effectively as somatostatin and was also blocked by inhibitors of lipoxygenases but not by inhibitors of phospholipase A2. These results support the hypothesis that lipoxygenase metabolites of arachidonic acid are second messengers linking pertussis toxin sensitive G-proteins to protein phosphatases regulating potassium channel activity (Armstrong and White, Trends Neurosci. 15, 403-408, 1992).

Adenosine Triphosphate↗

Angiotensin II blockade of long-term potentiation at the perforant path--granule cell synapse in vitro.

Field recordings of evoked excitatory postsynaptic potentials (pEPSPs) were carried out in the granule cell stratum moleculare following stimulation of the perforant path in rat hippocampal slices. Under control conditions tetanic stimulation produced long-term potentiation (LTP) as measured by an increase in the initial slope of the pEPSPs that lasted for at least 1 h. LTP experiments were repeated with 0.5, 5.0, 50, or 500 nM angiotensin II (AII) present in the bath at the time of tetanization. Induction of LTP was blocked by 50 nM AII; however, normal baseline responses were not affected. At the highest dose tested, 500 nM, a decrease in the amplitude and slope of baseline pEPSPs was observed. When the AII AT1 receptor antagonist losartan was present in the bath AII inhibition of LTP was blocked. The application of losartan alone had no effect on LTP expression. These findings support previous results from in vivo studies demonstrating that activation of AT1 receptors in the dentate gyrus blocks the induction of LTP at the perforant path-granule cell synapse.

Analysis of Variance↗

Nicotine blocks angiotensin II inhibition of LTP in the dentate gyrus.

Angiotensin (ANG)-containing axons, terminals, and receptors have been found in the hippocampus. When angiotensin II (ANG II) is administered to the dentate gyrus, long-term potentiation (LTP) induction, in response to medial perforant path stimulation, is inhibited and it can be blocked by losartan, an ANG II AT1 receptor antagonist. ANG II has been shown to mediate impairment of the retention of an inhibitory shock avoidance response and to be involved in ethanol and diazepam inhibition of dentate gyrus LTP, all of which can be blocked by losartan. Nicotine acetylcholine receptors are found in the hippocampus and nicotine is involved in the enhancement of complex and important psychological functions that are mediated by the hippocampus; therefore, the possibility that nicotine prevents the ANG II inhibition of dentate granule cell LTP was examined. Nicotine pretreatment reduced ANG II inhibition of LTP induction in a dose-dependent manner. Mecamylamine blocked the nicotine antagonism of ANG II-induced LTP inhibition and normal LTP occurred, whereas hexamethonium was ineffective in blocking these central effects of nicotine. Nicotine by itself did not affect normal LTP under these conditions. Nicotinic blocking of the ANG II inhibition of a frequency dependent type of synaptic plasticity provides a function for central nicotinic receptors and a possible mechanism of action a) to explain the enhancement of learning and memory by nicotine, b) an explanation for tobacco smoking while drinking alcohol, and c) a possible basis for the excessive use of tobacco in depression and schizophrenia that supports a possible therapeutic use of nicotine in some mental disorders.

Angiotensin II↗

The clinical significance of extracellular matrix in gangliogliomas.

Based on in vitro studies which demonstrate that collagen IV and laminin inhibit the proliferation and invasiveness of glioma cells, we investigated the clinical significance of these extracellular matrix proteins (ECM) in patients with gangliogliomas, tumors in which ECM is often a prominent feature. Our study compared the relative presence and deposition pattern of collagen IV and laminin in 19 gangliogliomas and in 18 gliomas without ganglion cell differentiation (8 low-grade astrocytomas, 7 anaplastic astrocytomas, and 3 anaplastic mixed gliomas). We also examined whether the presence of collagen IV and laminin correlated with other features often observed in gangliogliomas, including perivascular lymphocytic inflammation, granular bodies, microcalcification, and subarachnoid extension, and whether any of these features were associated with the patient's clinical course. Significant deposition of collagen IV and laminin was found in 9 gangliogliomas (47%), but in none of the other gliomas. The presence of these extracellular proteins in gangliogliomas correlated with both perivascular inflammation (P = 0.003), and involvement of the leptomeninges by tumor (P = 0.008). The duration of symptoms prior to surgical resection was significantly longer for patients whose tumors showed extracellular deposition of collagen IV and laminin than for patients whose tumors lacked deposition of these proteins (mean 13.7 vs 5.1 years; P = 0.02). In addition, the duration of symptoms was significantly longer for patients whose tumors exhibited perivascular inflammation than for patients whose tumors displayed little or no perivascular inflammation (mean 14.8 vs 4.8 years; P = 0.01). These findings suggests that collagen IV and laminin and perivascular inflammation are related to the indolent behavior of gangliogliomas.

Adolescent↗

Timing of ovulation after gonadotrophin induction and its importance to successful intrauterine insemination in the tiger (Panthera tigris).

The ovarian response to equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG), the effect of timing of ovulation relative to hCG injection and the use of laparoscopic intrauterine artificial insemination (AI) were examined in two subspecies of tiger (Panthera tigris). Adult female tigers were subjected to the same eCG/hCG treatment followed by laparoscopy under xylazine/diazapam/ketamine HCl anaesthesia at 39-42 h (Group I, n = 9), 46-49 h (Group II, n = 5) or 51-55 h (Group III, n = 5) after hCG. Six of these females, observed to be postovulatory at the time of laparoscopy (Group II, n = 3; Group III, n = 3), were subjected to intrauterine AI. The number of preovulatory follicles observed on the ovaries of Group I females was twofold greater (P < 0.05) than the number observed on ovaries of females in Group II and III. Fewer (P < 0.05) corpora lutea were observed on ovaries of Group I females (1.3 +/- 0.6) compared with the number of corpora lutea in Group II and III (combined average, 7.8 +/- 0.8 corpora lutea per female). Only one of ten females in Groups II and III failed to ovulate by the time of laparoscopy. Four Group I females never ovulated, based on a laparoscopic re-evaluation 4 weeks later. One female inseminated 46 h after hCG (Group II) became pregnant and delivered a healthy cub after a normal gestation. There were no apparent differences between subspecies in response to the same ovulation induction protocol. Results demonstrate the importance of the relationship between exogenous gonadotrophin treatment and onset of anaesthesia for laparoscopic examination and AI in tigers. Data clearly indicate that anaesthesia/laparoscopy conducted too early (39-42 h after hCG) compromises the number of females and proportion of follicles ovulating. In contrast, ovulation success is high if anaesthesia/laparoscopy is performed after this time, and intrauterine insemination can result in healthy young.

Animals↗

GABAergic modulation of optic nerve-evoked field potentials in the rat suprachiasmatic nucleus.

The suprachiasmatic nuclei (SCN) at the base of the hypothalamus are known to be the site of the endogenous circadian pacemaker in mammals. The SCN are innervated by the retinohypothalamic tract, which conveys photic information to the SCN. GABA is one of the most abundant neurotransmitters in the SCN, and has been implicated in the modulation of photic responses of the SCN circadian pacemaker. This study sought to examine the effect of GABAergic compounds on optic nerve-evoked SCN field potentials recorded in rat horizontal hypothalamic slices. The GABAA agonist muscimol (10 microM) potentiated SCN field potentials by 23%, while application of the GABAA antagonist bicuculline (10 microM) inhibited SCN field potentials by a similar amount, (22%). Conversely, the GABA, agonist baclofen (1.0 microM) inhibited SCN field potentials by 48%, while the GABAB antagonist phaclofen (0.5 mM) augmented SCN field potentials by 62%. Recordings performed at both day and night times indicate that there were no qualitative day-night differences in GABAergic activity on SCN field potentials. This study concludes that, in general, GABAA activity tends to increase, and GABAB activity tends to decrease the response of SCN neurons to optic nerve stimulation.

Animals↗

Impaired retention by angiotensin II mediated by the AT1 receptor.

We demonstrated previously that hippocampal dentate gyrus neurons were sensitive to angiotensin II (AII) and recently discovered that AII applied directly to the dentate gyrus inhibited granule cell long-term potentiation induction and that the inhibition is mediated by the AT1 receptor and can be blocked by losartan, a specific AT1 antagonist. The purpose of the present study was to examine the effects of AII administered directly to the dentate gyrus, 1, 5, 50, 150, and 300 ng, on the retention of an inhibitory shock avoidance response and to determine if the resultant impairment of retention can be blocked by losartan. A total of 12 groups of rats in three experiments were studied. Three independent repetitions of 5 ng AII administered bilaterally to the dentate gyrus demonstrate a clear impairment of retention under these experimental conditions and that the impairment can be effectively prevented by pretreatment with 20 mg/kg of losartan IP.

Angiotensin II↗

Dose and time dependency of angiotensin II inhibition of hippocampal long-term potentiation.

We previously reported that injection of 1.0 microliter of 4.78 microM angiotensin II (AII) above the hippocampus in rats inhibits long-term potentiation (LTP) induction in medial perforant path-stimulated dentate granule cells. The present experiments were conducted in urethane-anesthetized Sprague-Dawley rats. LTP was measured in terms of the relative change in slope of the population EPSP compared to baseline. Effects of 0.48, 0.956, 1.195, 2.39, and 4.78 microM AII and time delays of 30, 60, 90, and 150 min with the 4.78 microM dose were determined. Results were significant and demonstrate that AII inhibition of LTP in dentate granule cells is both dose and time dependent. The threshold is approximately 1.0 pmol of peptide. Inhibition due to the 4.78 microM AII begins slowly after 1 h and is complete over the next 30 min, continues for another 30 min, and then fully recovers by the end of the next 30 min. This time dependency could be due to the internalization of the AII, interaction with a cytosolic receptor, and eventual degradation.

Angiotensin II↗

United States mortality from ill-defined causes, 1968-1988: potential effects on heart disease mortality trends.

BACKGROUND: Deaths are coded to the International Classification of Diseases (ICD) category, 'Symptoms, Signs, and ill-defined Conditions' when there is insufficient information for cause of death determination. Due to difficulties of diagnosis of coronary heart disease (CHD) death and since CHD is the leading cause of death among US adults, CHD is the most likely cause of ill-defined deaths. METHODS: Vital statistics and census data were used to create annual age-adjusted ill-defined rates, unrevised CHD rates, and CHD rates revised to include ill-defined deaths for US African Americans and whites, ages 35-74 years, during 1968-1988. Ill-defined and CHD mortality trend analyses were conducted. RESULTS: In 1968, African American/white ratios of ill-defined mortality were 5 among men and 7 among women; following steep declines in ill-defined mortality among African Americans, ratios were 3 among men and 2 among women in 1988. In 1968, approximately 3% and 1% of all deaths among African Americans and whites, respectively, were certified to ill-defined causes; in 1988, approximately 1.5% of deaths among African Americans were coded ill-defined, with no change among whites. Revised CHD rates showed substantially higher excess CHD mortality among African Americans than whites compared to unrevised CHD rates. Declines in revised CHD mortality steepened throughout the study period among men, and among women began to decelerate after 1978. CONCLUSIONS: Ill-defined mortality was of sufficient magnitude to potentially contribute to substantial underestimation of racial disparities in CHD mortality. Also, temporal changes in ill-defined mortality may have affected CHD trends which are used to evaluate the efficacy of public health interventions.

Adult↗

Pathology and immunohistochemistry of callitrichid hepatitis, an emerging disease of captive New World primates caused by lymphocytic choriomeningitis virus.

Callitrichid hepatitis is an arenavirus infection that recently emerged as a highly fatal disease of New World primates in the Callitrichidae family. As we previously reported, these primates develop hepatitis after contact with mice that are infected with variants of LCMV (LVMCCH), recently determined to have 86% identity with GC-P gene of the Armstrong and Western strains of LCMV. Here, we describe the histopathological lesions and tissue localization of viral antigens in confirmed cases of callitrichid hepatitis from recent outbreaks in two U.S. zoos. The liver in marmosets and tamarins with fatal infections consistently showed degeneration, necrosis, and inflammation, with variable involvement of the spleen, lymph nodes, adrenal glands, intestine, pancreas, and central nervous system. Lymphocytic choriomeningitis virus antigens were identified immunohistochemically in necrotic foci in these organs as well as in nondegenerating areas in lungs, kidney, urinary bladder, brain, and testes. The multi-organ tropism and histological pattern of LCMV infection in marmosets and tamarins are similar to those reported for the highly virulent arenavirus that causes Lassa fever in humans. Comparative studies of callitrichid hepatitis and Lassa fever would therefore be mutually beneficial for human and nonhuman primate medicine.

Animals↗

Prenatal sonographic detection of basilar aneurysm.

Retrospective reviews document the infrequency of intracranial aneurysms in the first decade of life, with an even greater rarity in the first 2 years. Intracranial aneurysms are not known to be associated with trisomy 18. An infant is reported who was diagnosed at 32 weeks gestation as having trisomy 18. Prenatal ultrasonography identified a large cystic lesion in the posterior cerebral circulation. This small-for-gestational-age infant was born at term by dates, but renal maturation suggested a gestational age of 35-36 weeks. He survived 5 days. This is the first report of prenatal sonographic imaging of a basilar artery aneurysm confirmed by autopsy.

Adult↗