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Biomedical subjects

B Ault

Publications and source records attributed to B Ault.

At least 19 recordsLinked to original sources
PubMed1998

Organic dust exposures from work in dairy barns.

Environmental surveys were conducted in 85 barns, predominantly dairy, in central Wisconsin to characterize exposures to organic dusts and dust constituents from routine barn work. Environmental analytes included airborne dusts (total, inhalable inlet, and respirable), particle size distributions, endotoxins, total spore and bacteria counts, viable bacteria and fungi, histamine, cow urine antigen, mite antigen, ammonia, carbon dioxide, and hydrogen sulfide. The geometric mean (GM) concentration of airborne dusts include area total, 0.74 mg/m3; personal inhalable inlet, 1.78 mg/m3, and area respirable, 0.07 mg/m3. Viable bacteria and fungi, spores, endotoxins, histamine, cow urine antigen, and mite antigen were quantifiable constituents of these organic dusts and potential respiratory exposure hazards from routine dairy barn work. Endotoxin concentrations from the inhalable inlet samples ranged from 25.4 endotoxin units per cubic meter of air (EU/m3) to 34,800 EU/m3. The GM endotoxin concentration from these samples, 647 EU/m3, exceeds estimated threshold exposure levels for respiratory health effects. Ammonia was a common irritant quantified in most dairy barns. There were significant correlations between the concentrations of organic dusts and certain dust constituents, although in most instances these correlations were not strong. These sampling results demonstrate the complex nature of organic dusts and provide quantitative description of the exposures to toxic and immunogenic dust constituents during routine barn work.

Air Microbiology↗
PubMed1995

Novel benzo[b]quinolizinium cations as uncompetitive N-methyl-D-aspartic acid (NMDA) antagonists: the relationship between log D and agonist independent (closed) NMDA channel block.

A series of permanently charged benzo[b]quinolizinium cations having lower lipophilicity than MK-801 or phencyclidine (PCP) were synthesized. Data relating agonist independent block of N-methyl-D-aspartic acid (NMDA) ion channels to log D are described. Closed channel access is predicted to result in a more noncompetitive profile of antagonism compared to selective open channel blockers, which are uncompetitive inhibitors. Reduced closed channel block may underlie the absence of PCP or MK-801-like behavioral side effects observed for benzo[b]-quinolizinium cations.

Animals↗
PubMed1995

Novel NMDA antagonists: replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with heteroisoquinolinium cations.

Replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with thiazolium (4a and 4b) and N-methylimidazolium (4c and 4d) resulted in equipotent compounds in the [3H]TCP binding assay. The corresponding N-methyl-1,2,4-triazolium analogs were less potent in this assay. The thiazolium derivative 4b, with a Ki = 2.9 nM, is being evaluated as a possible neuroprotective N-methyl-D-aspartic acid (NMDA) antagonist.

Animals↗
PubMed1995

Discovery of 6,11-ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations, a novel class of N-methyl-D-aspartate antagonists.

6,11-Ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations 8, a novel class of N-methyl-D-aspartate (NMDA) antagonists acting at the phencyclidine site, have been identified. Structure-activity relationship studies around the lead compound 8a led to the identification of 12g (WIN 67870-2), one of the most potent compounds in this series. Compound 12g has a Ki = 1.8 +/- 0.2 nM vs [3H]TCP binding, has 700-fold selectivity for binding to the open state of the NMDA receptor-ionophore, and was devoid of MK-801- and PCP-like behavioral effects in rats. Compound 12g was neuroprotective in cultured mouse cortical neurons and exhibited antiischemic activity in a rat middle cerebral artery occlusion/reperfusion model of focal ischemia.

Animals↗
PubMed1995

WIN 63480, a hydrophilic TCP-site ligand, has reduced agonist-independent NMDA ion channel access compared to MK-801 and phencyclidine.

NMDA channel blockers are potentially advantageous therapeutic agents for the treatment of ischemia and head trauma, which greatly elevate extracellular glutamate, because they should most effectively inhibit high levels of receptor activation. A novel high affinity TCP site ligand, WIN 63480, does not produce MK-801- or PCP-like behavioral activation at anti-ischemic doses. While WIN 63480, MK-801 and PCP were all observed to be effective blockers of open NMDA channels, WIN 63480 had much less access to closed NMDA channels. This difference may be due to the fact that WIN 63480 is hydrophilic (logD = -4.1) while MK-801 and PCP are lipophilic (logD = +1.8). In vivo, closed channel access may result in a non-competitive profile of antagonism for MK-801 and PCP compared to a more uncompetitive profile for WIN 63480. Release of glutamate, and depolarization, are likely to produce a high level of NMDA receptor activation in ischemic areas compared to normal tissue. Consequently, at anti-ischemic doses, WIN 63480 may produce less inhibition of physiological NMDA-mediated processes in neural systems involved in behavioral regulation than MK-801 or PCP, leading to an improved side effect profile.

Animals↗
PubMed1995

AMPA (amino-3-hydroxy-5-methylisoxazole-4-propionic acid) receptors in human brain tissues.

AMPA receptors may play an important role in acute and chronic neurodegenerative diseases. An assay for the specific binding of [3H]-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) to receptors in membranes from post-mortem human brain is described, which can be used in screening for selective AMPA receptor antagonists. Membranes were prepared from frozen human adult hippocampus and whole fetal brain tissues. [3H]-AMPA binding to human hippocampus was saturable; Scatchard analysis of equilibrium binding data indicated high and low affinity sites with affinity binding constants (KD) of 3.4 +/- 0.5 nM and 65 +/- 9 nM (n = 7) respectively. Biphasic association and dissociation rate constants for [3H]-AMPA binding were consistent with the biphasic Scatchard analysis. Inhibition of [3H]-AMPA binding revealed a rank order of potency as quisqualate = AMPA > BOAA > L-glutamate = DNQX = CNQX > kainate > L-aspartate = NMDA. AMPA receptors in human fetal brain had a comparable pharmacology. AMPA/kainate receptors were expressed in frog oocytes following injection of RNA prepared from human fetal brain. Human brain tissues may therefore be utilized for screening and functional analysis of AMPA receptor antagonists.

Adult↗
PubMed1994

Identification, synthesis, and characterization of a unique class of N-methyl-D-aspartate antagonists. The 6,11-ethanobenzo[b]quinolizinium cation.

A series of novel N-methyl-D-aspartate antagonists acting at the phencyclidine site has been identified. Compound 2 has a Ki = 8 +/- 1 nM (vs [3H]thienylcyclidine, [3H]TCP) as a mixture of enantiomers. Resolution and further testing indicate that (-)-2, Ki = 4 +/- 0.7 nM, is a potent and selective TCP site ligand with neuroprotective activity in cultured neurons in the presence of excitotoxic concentrations of NMDA (IC50 = 26 nM). Compound (-)-2 is > 1000-fold selective for the TCP site vs a panel of receptor types including opiate, adrenergic, serotonergic, dopamine, adenosine, dihydropyridine, and benzodiazepine and displays increased selectivity for the activated (open) NMDA receptor-ion channel complex vs PCP and MK801 as measured by patch recordings in cultured, voltage-clamped neurons. Highly enhanced "open-channel" selectivity leads to tentative classification of these ligands as uncompetitive vs NMDA. Ligands with these characteristics may enable deconvolution of the pharmacologic effects associated with typical noncompetitive NMDA antagonists. We report here on the identification, synthesis, and activity of compounds of this structural class.

Animals↗
PubMed1994

GABAA receptor-mediated excitation of nociceptive afferents in the rat isolated spinal cord-tail preparation.

Algogens such as capsaicin, bradykinin, acetylcholine, 5-hydroxytryptamine and potassium ions applied to exposed tail skin of the rat isolated spinal cord-tail preparation evoke a ventral root response consisting of depolarization and spiking activity. L-glutamate and kainate also evoke similar reflexes. All these compounds evoke depolarization of afferent axons or dorsal root ganglion cells. Since GABA depolarizes unmyelinated afferent fibers, the ability of GABA receptor agonists to activate cutaneous nociceptive afferents has been examined. GABA superfused over exposed tail skin evoked a ventral root reflex essentially identical to that produced by capsaicin (3 microM). The EC50 was 27 microM. Muscimol, 3-aminopropane sulphonate, isoguvacine and beta-alanine had effects comparable to GABA, with EC50 values of 9.6, 26, 56 and 870 microM respectively. Baclofen (100 microM) or glycine (10 mM) had no effect. Bicuculline applied to the tail competitively antagonized GABA (Schild slope = -1.03) with a pA2 of 5.8. Spinal application of 1 microM morphine blocked the actions of GABA and capsaicin. These data indicate that GABAA receptors can depolarize and excite nociceptive afferents. GABA could be involved in nociception by contributing to firing of C-fibres, or by analogy to presynaptic inhibition in the spinal cord, may act to decrease neuropeptide transmitter release in cutaneous tissue.

Animals↗
PubMed1994

Glutamate receptor gene expression in spinal cord of arthritic rats.

Injury to peripheral tissue leads to hyperalgesia that appears to be partly mediated by functional changes at the level of the spinal cord. Glutamate receptors are thought to play a role in acute and short-term (minutes to hours) spinal cord nociceptive responses and may be involved in prolonged or chronic pain (hours to days). We used in situ hybridization to examine AMPA/kainate (GluR1, GluR2, and GluR3) and NMDA (NR1) receptor gene expression in spinal cord following induction of prolonged inflammation by a unilateral intraarticular injection of lipopolysaccharide (LPS; 10 micrograms) into the hindpaw. In control rats, GluR1 expression was prominent throughout the layers of the gray matter of the spinal cord. Microscopic examination revealed labeling of neuronal cell somata in all major nuclei. GluR2 was abundant in substantia gelatinosa and motor nuclei; emulsion-dipped sections exhibited intense labeling over densely packed neurons in the superficial laminae of dorsal horn and individual motoneurons of ventral horn. GluR3 and NR1 were expressed at low levels throughout spinal cord gray matter. One day after LPS injection, when joint swelling was maximal, GluR1 expression was bilaterally decreased by 25% in the substantia gelatinosa at the level of the lumbar cord. In contrast, no significant change was apparent in GluR2, GluR3, or NR1 expression in any nucleus of the cord. At 72 hr after injection, when joint diameter approached control values, all four transcripts were expressed at near control levels. These findings provide evidence for a specific decrease in GluR1 expression in the cord in response to joint inflammation.

Animals↗
PubMed1993

Long-term transplants of mouse trisomy 16 hippocampal neurons, a model for Down's syndrome, do not develop Alzheimer's disease neuropathology.

Hippocampal tissue from embryonic day 15-17 fetal mice, euploid or trisomic for chromosome 16, was transplanted into the striatum or the lateral ventricle of 6-8 week old female C57B1/6 mice. After 6-14 months of survival, host brains were sectioned and the grafts were examined by histochemical techniques and by immunocytochemistry for antigens present in pathological brain structures of Alzheimer's disease (AD) patients. Nissl-stained grafts contained aggregations of neurons similar to the pyramidal or the granule cell layers of the normal adult mouse hippocampus. No obvious morphological difference was detected between trisomic and control transplants. The monoclonal antibody Alz-50, which recognizes the paired helical filaments characteristic of AD, or an antibody raised to beta-amyloid peptide, did not reveal neurodegeneration in these grafts. Antibodies against ubiquitin, 200 kDa subunit of neurofilament, alpha 1-antichymotrypsin and tau also did not demonstrate AD-type immunoreactivity in the trisomic or control grafts. Thioflavin S- or silver stained-sections were also negative. We conclude that transplanted hippocampal tissue from the trisomy 16 mouse does not represent an animal model for AD-type neurodegeneration. These results differ from those of Richards et al., EMBO J. (10) (1991) 297-303, who reported AD-type degeneration in trisomy 16 hippocampal transplants.

Alzheimer Disease↗
PubMed1993

L-glutamate activates peripheral nociceptors.

The chemosensitivity of nociceptive afferents has been investigated using the isolated spinal-cord-tail preparation of the neonatal rat. L-glutamate applied to exposed rat tail skin stimulated nociceptive reflexes (ED50 = 136 microM). The action of L-glutamate was selective, since other constitutive L-amino acids or D-glutamate were inactive at a concentration of 10 mM. The known algogens bradykinin, acetylcholine, serotonin and potassium ions also stimulated nociceptive reflexes. Histamine (1 mM) and substance P (0.1 mM) had no observable effect. L-glutamate, which is released from macrophages, could therefore contribute to inflammation-related nociception by stimulation of cutaneous nociceptive nerve endings.

Acetylcholine↗
PubMed1993

Activation of nociceptive reflexes by peripheral kainate receptors.

The rat isolated spinal cord-tail preparation was used to examine the ability of peripherally applied excitatory amino acids to stimulate ventral root reflexes. Bolus applications (3 sec) of domoate (0.1-10 microM) or kainate (KA; 10-300 microM) to exposed skin of the rat tail stimulated ventral root responses comparably to those evoked by capsaicin (0.3-10 microM) or bradykinin (0.1-10 microM). The ventral root potential evoked by both capsaicin and KA is thought to be a nociceptive response because both compounds selectively activate peripheral C-fibers. L-Glutamate (0.01-10 mM), quisqualate (0.1-1 mM) and amino-5-methyl-4-isoxazole-propionic acid (0.1-1.0 mM) were of lower potency than KA, whereas N-methyl-D-aspartate (1 mM) and L-aspartate (10 mM) were inactive. Responses evoked by prolonged application of KA faded rapidly. Capsaicin-evoked responses partially faded during prolonged application, but residual spiking activity was recorded for at least 30 min. KA did not evoke any observable response during application of capsaicin. The effects of KA and capsaicin were blocked by spinal application of morphine (0.3-1.0 microM) in a naloxone-reversible manner, consistent with activation of peripheral nociceptive afferents. The action of KA, but not capsaicin, was competitively inhibited by the amino-5-methyl-4-isoxazole-propionic acid/KA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (10-100 microM) applied to the rat tail (pA2 = 5.9). Conversely, ruthenium red (1 microM) selectively blocked capsaicin-evoked nociceptive reflexes. The existence of functional KA receptors on nociceptive afferents suggests that peripherally released glutamate or other excitatory amino acids could be involved in nociception or neurogenic inflammation.

Amino Acids↗
PubMed1992

NMDA receptor-mediated depolarizing action of proline on CA1 pyramidal cells.

This study investigated the actions of proline on CA1 hippocampal pyramidal cells with use of slice preparations. Bath-applied L-proline first induced these cells to fire multiple orthodromic population spikes in response to a single stimulus and then blocked their response to both orthodromic and antidromic stimulation. These effects could be explained by postsynaptic depolarization followed by depolarization block. Grease-gap studies confirmed that L-proline depolarizes CA1 pyramidal cells. D-Proline was inactive in these tests. Excitatory amino acid antagonists reduced depolarizing responses to proline and N-methyl-D-aspartate (NMDA) in parallel. Mn2+ failed to attenuate proline-evoked depolarizations at concentrations that substantially inhibited synaptic transmission, but at a higher concentration it reduced responses to both proline and NMDA. These results suggest that proline depolarized CA1 pyramidal cells mainly by activating postsynaptic NMDA receptors. The neuroexcitatory and neurotoxic actions of proline in the hippocampus may contribute to the seizures and mental retardation associated with hyperprolinemia.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

cis and trans elements differ among mouse strains with high and low extrahepatic complement factor B gene expression.

Factor B (Bf), an enzyme of the alternative pathway of complement activation, is one of four major histocompatibility complex (MHC) class III genes. To ascertain the genetic mechanism for tissue-specific constitutive and regulated expression of Bf, we sequenced the regulatory regions 5' of the gene from mice of different H-2 MHC haplotypes and assessed trans-acting factors, specific DNA binding nucleoproteins, in liver and kidney. Striking tissue-specific differences in constitutive expression of Bf were demonstrated in mice of H-2f or H-2z haplotypes when compared with H-2d or H-2u (kidney and intestinal Bf in H-2d or H-2u much greater than H-2f or H-2z). These differences correlated with a point nucleotide substitution 3 bp downstream of the upstream Bf initiation site that affects interaction with a DNA binding protein. This and additional cis differences localize the sequence substitutions responsible for previously identified restriction fragment length polymorphisms among inbred mouse strains and also reveal two previously unrecognized polymorphisms generated by SmaI and HinfI digestion. Evidence for differences in trans was found in a comparison of DNA binding nucleoproteins from kidney, but not liver, of B10.PL when compared with B10.M. These data, together with the high degree of sequence homology between human and mouse Bf 5' flanking regions, should prompt a search for polymorphic restriction sites and cis binding elements in the Bf promoter that could serve as markers of human MHC-associated renal pathology and variants in local MHC class III gene expression.

Animals↗
PubMed1991

Effects of nerve growth factor on electrical membrane properties of cultured dorsal root ganglia neurons from normal and trisomy 21 human fetuses.

Trisomy 21 (Down syndrome) results in abnormalities of electrical membrane properties of cultured human fetal dorsal root ganglion (DRG) neurons; namely, faster rates of depolarization and repolarization of the action potential, and a shortened spike duration. A possible role of nerve growth factor (NGF) in the expression of abnormal electrical membrane properties fetal human DRG neurons from trisomy 21 subjects was examined. DRG neurons obtained from normal and trisomy 21 abortuses of 16-20 weeks gestation were cultured in the presence or absence of 40 nM 7S NGF. After 1 week in culture, action potentials were recorded using the whole cell patch-clamp technique, in current clamp mode. At the resting membrane potential, normal (diploid) neurons grown without NGF showed reduced maximal rates of depolarization (-41.3%) and of repolarization (-31.4%), a decreased spike amplitude (-14.2%) and a prolonged action potential (+49.2%), when compared to normal cells cultured with NGF. Trisomy 21 neurons showed similar changes, but had a greater relative decrease in the rates of action potential depolarization and repolarization. These changes were evident at different membrane potentials. Normal and trisomic DRG neurons cultured without NGF showed differences in action potential parameters similar to those previously described using NGF-supplemented culture medium. These data indicate that NGF can regulate electrical membrane properties in cultured human fetal DRG neurons, but apparently is not responsible for the abnormalities observed in trisomy 21 neurons.

Action Potentials↗
PubMed1991

Mouse trisomy 16 neurons, a model of human trisomy 21 (Down syndrome), can be maintained by intracerebral transplantation.

The trisomy 16 mouse is considered to be a model of human trisomy 21 (Down syndrome) due to genetic homology between parts of human chromosome 21 and mouse chromosome 16. Additionally, and because older Down syndrome individuals develop neuropathology indistinguishable from that of Alzheimer's disease, trisomy 16 tissue may provide a model of some pathological processes occurring in Alzheimer's disease. However, trisomy 16 fetuses die in utero or shortly after birth, preventing exploitation of this model. We therefore sought to examine trisomy 16 brain tissue over an extended period of time. We report that neural transplantation to normal hosts allows the maintenance of cortical and hippocampal neurons for at least 8 months, thus providing a model in which to examine pathological processes related to Down syndrome, and perhaps to Alzheimer's disease.

Animals↗
PubMed1990

Electrical membrane properties of cultured dorsal root ganglion neurons from trisomy 19 mouse fetuses: a comparison with the trisomy 16 mouse fetus, a model for Down syndrome.

Because of synteny between mouse chromosome 16 and human chromosome 21, murine trisomy 16 (Ts16) has been considered an animal model for Down syndrome. Indeed, previous investigations have demonstrated that action potentials of cultured dorsal root ganglion (DRG) neurons from human trisomy 21 (Down syndrome) or mouse Ts16 fetuses show increased depolarization and repolarization rates, and decreased spike duration, compared to control neurons. In order to determine the specificity of these changes, we studied the electrical membrane properties of DRG neurons in culture from trisomy 19 (Ts19) and control fetal mice, using the whole cell patch-pipette recording technique. We found no significant differences in action potential parameters and passive membrane properties between Ts19 and control neurons. These findings support the notion that the alterations previously reported in Ts16 DRG neurons are specific, and not a general consequence of genetic imbalance imposed by autosomal trisomies.

Action Potentials↗