PBPK modeling/Monte Carlo simulation of methylene chloride kinetic changes in mice in relation to age and acute, subchronic, and chronic inhalation exposure

During a 2-year chronic inhalation study on methylene chloride (2000 or 0 ppm; 6 hr/day, 5 days/week), gas-uptake pharmacokinetic studies and tissue partition coefficient determinations were conducted on female B6C3F1, mice after 1 day, 1 month, 1 year, and 2 years of exposure. Using physiologically based pharmacokinetic (PBPK) modeling coupled with Monte Carlo simulation and bootstrap resampling for data analyses, a significant induction in the mixed function oxidase (MFO) rate constant (Vmaxc) was observed at the 1-day and 1-month exposure points when compared to concurrent control mice while decreases in glutathione S-transferase (GST) rate constant (Kfc) were observed in the 1-day and 1-month exposed mice. Within exposure groups, the apparent Vmaxc maintained significant increases in the 1-month and 2-year control groups. Although the same initial increase exists in the exposed group, the 2-year Vmaxc is significantly smaller than the 1-month group (p < 0.001). Within group differences in median Kfc values show a significant decrease in both 1-month and 2-year groups among control and exposed mice (p < 0.001). Although no changes in methylene chloride solubility as a result of prior exposure were observed in blood, muscle, liver, or lung, a marginal decrease in the fat:air partition coefficient was found in the exposed mice at p = 0.053. Age related solubility differences were found in muscle:air, liver:air, lung:air, and fat:air partition coefficients at p < 0.001, while the solubility of methylene chloride in blood was not affected by age (p = 0.461). As a result of this study, we conclude that age and prior exposure to methylene chloride can produce notable changes in disposition and metabolism and may represent important factors in the interpretation for toxicologic data and its application to risk assessment.

Reduced NPY induced feeding in diabetic but not steroid-treated rats: lack of evidence for changes in receptor number or affinity

Concentrations of the potent hypothalamic appetite stimulating peptide neuropeptide Y (NPY), and its mRNA, are increased in rats with experimental diabetes, suggesting a role in the hyperphagia of this disorder. The 2-h feeding responses to intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) (5, 10, and 15 mu g doses) were measured in male Wistar rats treated with streptozotocin (55 mg/kg) to induce diabetes. Streptozotocin-diabetic rats given i.c.v. NPY exhibited reduced feeding responses compared to controls (P < 0.05). Dexamethasone treated rats exhibit similar changes in NPY content and mRNA in the hypothalamus to those seen in diabetes, but are not hyperphagic. Feeding responses were also measured in this model, to assess whether high levels of endogenous NPY might account for the reduced response in diabetes. In contrast, the feeding response to NPY in comparison to controls was unaltered in dexamethasone treated rats. To investigate whether altered NPY receptor number or affinity, was the underlying mechanism for these divergent responses, receptor binding experiments were performed using (125)I-PYY and membranes prepared from rat hypothalamus. No significant difference was found in receptor number or affinity between the 2 groups (B(max): 114.7 +/- 18.9 vs 127.4 +/- 27.1 fmol/mg protein, K(d): 99.6 +/- 28.2 vs 135.1 +/- 32.4 pM). Similarly no difference was found between hypothalamic membranes prepared from dexamethasone-treated and control animals. NPY receptor subtypes in the hypothalamus were compared with that of cortex (predominantly Y1) and hippocampus (predominantly Y2) using the Y1-specific ligand [Leu(31)Pro(34)] NPY. These studies showed that the binding profile in the hypothalamus most closely matched that in the hippocampus, suggesting that the majority of hypothalamic receptors were of the Y2 subtype. Receptor autoradiography revealed low binding in the hypothalamus, and particularly in the paraventricular nucleus of the hypothalamus. Competition with [Leu(31)Pro(34)] NPY confirmed that only a low density of binding to Y1 like receptors was present in the hypothalamus. No difference was observed between control and streptozotocin treated animals. The feeding response to exogenous NPY is reduced in experimental diabetes, but not in dexamethasone treated rats. These differing responses do not appear to be due to altered NPY receptor number or affinity in the hypothalamus.

Distribution of three nicotinic receptor alpha 4 mRNA transcripts in rat brain: selective regulation by nicotine administration

Northern blot analysis determined whether multiple alpha 4 transcripts for neuronal nicotinic receptors in rat brain could be detected as distinct bands. When poly(A)+ RNA was isolated from brain regions and hybridized with a Hinfl fragment of alpha 4-1 cDNA containing a sequence shared by both alpha 4-1 and alpha 4-2, but little homology with other alpha or beta subunits, bands at 6.0, 4.6, and 2.6 kb were obtained. When a Taql fragment with selectivity for alpha 4-1 was used, a single band was present at 6.0 kb. The 6.0-kb band was least abundant in all brain regions; the 2.6-kb band was most abundant in frontal cortex, hippocampus, striatum, basal forebrain, and thalamus, whereas the 4.6-kb band was most abundant in midbrain and cerebellum. Nicotine (3.6 mumol/kg, a.c., twice daily) increased the abundance of the 4.6-kb transcript in frontal cortex significantly by 28% following 2.5 days of injections; the 6.0- and 2.6-kb transcripts were unchanged. Nicotine did not affect alpha 4 transcripts in other brain regions. Results suggest that increased mRNA levels may mediate the nicotine-induced up-regulation of receptors in cerebral cortex.

Image analysis of helical objects: the Brandeis Helical Package

Although the fundamental steps in Fourier-based image analysis of electron micrographs of helical structures have not changed significantly since the techniques were developed 30 years ago, there have been developments which aid both the analysis itself and the interpretation of results. Increases in computational resources have allowed the automation of many of the repetitive steps in image processing. We describe here a set of computer programs which have been developed at Brandeis University over the past 10 or more years. These programs, referred to as the Brandeis Helical Package, are designed to operate independently of each other with a simple and more uniform protocol for the flow of information between them. The programs are now easier to understand and to use and therefore represent a good tool for the analysis of helical structures.

Expression of a novel receptor for the calcitonin peptide family and a salmon calcitonin-like peptide in the alpha-thyrotropin thyrotroph cell line

We have previously shown an increased incidence of alpha-subunit-producing thyrotroph tumors after salmon calcitonin (sCT) injection into rats. However, it is not clear whether the effects of CT are direct or indirect. Our hypothesis was that for sCT to act directly, it must have a binding site on thyrotrophs. The alpha TSH cell line was used as a model for thyrotrophs. Receptor binding studies using alpha TSH membranes revealed a high affinity binding site for sCT [IC50 = 0.97 +/- 0.18 nM (n = 4); Kd = 5.45 +/- 0.43 nM (n = 3); binding capacity = 6.6 pmol/mg protein (n = 3)]. Rat CT did not compete with binding at this site. Receptor screening for other CT peptide family members revealed high specific binding for CT gene-related peptide (CGRP; IC50 = 0.25 +/- 0.08 nM; n = 3) and islet amyloid polypeptide (IC50 = 4.36 +/- 1.1 nM; n = 3). This together with the absence of rat CT binding excluded a conventional CT-binding site, and we propose a site similar to the CGRP subtype III receptor described in the rat nucleus accumbens. Guanosine 5'O-(3-thiotriphosphate) (GTP gamma S) (20 microM), reduced [125I]CGRP binding to 38% of maximal, indicating that this site is G-protein coupled. Immunocytochemically, all of the cells displayed intense sCT-like immunoreactivity, which was totally abolished by preabsorption of the antibody with sCT. The presence of this receptor supports the hypothesis that sCT mediates tumorigenesis via a direct pituitary action and, together with the coexistence of a sCT-like peptide in these cells, provides evidence for a possible autocrine role of this peptide in the control of thyrotroph function.

Structure of bacterial flagellar filaments at 11 A resolution: packing of the alpha-helices

Recent advances in the analysis of electron micrographs of frozen, hydrated bacterial filaments have allowed us to average data from more than 150 images and to reconstruct the bacterial flagellar filament of Salmonella typhimurium at a resolution of approximately 11 A. In addition to the outermost features seen in earlier lower resolution maps of the filament, we find a pair of concentric tubes which surround a approximately A diameter channel at the center of the structure. The walls of these tubes are composed of rod-like features which we have interpreted as columns of individual alpha-helices stacked end-to-end. Each column runs approximately parallel to the helix axis. The wall of the innermost tube, at a radius of approximately 20 A, is formed from 11 such columns. The wall of the second tube is formed from 22 columns which occur alternately at radii of approximately 43 and approximately 47 A. The two concentric tubes are held apart by spacers. These are short, rod-like features, which run approximately parallel to the helix axis. We have interpreted these as additional alpha-helices. By symmetry, each flagellin monomer contributes an alpha-helix to the inner tube, two alpha-helices to the outer tube and a fourth alpha-helix to the spacer. We have tentatively assigned one type of alpha-helix in the outer tube to the approximately 30 C-terminal residues of flagellin while the remaining three alpha-helices are assigned to the approximately 70 N-terminal residues. This interpretation of the reconstruction is consistent with available biochemical, biophysical and amino acid sequence information. We also present details of improved methodology to extract and evaluate the original data and also to assess the statistical significance of features in the three-dimensional map.

An abundant and specific binding site for the novel vasodilator adrenomedullin in the rat

Rat adrenomedullin is a novel 50-amino acid peptide with structural similarities to the calcitonin family of peptides, calcitonin, calcitonin gene-related peptide (CGRP), and islet amyloid polypeptide (IAPP). Using rat [125I]adrenomedullin, specific binding sites were demonstrated in heart, lung, spleen, liver, soleus, diaphragm, gastrocnemius, and spinal cord membranes. The highest binding was present in heart and lung, which was further characterized. These sites exhibited saturation, dissociation, and competition. In rat lung, only rat (IC50 = 5.8 nM) and human (IC50 = 94 nM) adrenomedullin competed with [125I]adrenomedullin. However, in rat heart, rat (IC50 = 0.2 nM) and human (IC50 = 4.2 nM) adrenomedullin, IAPP (IC50 = 240 nM), and CGRP (IC50 = 1050 nM) all competed with [125I] adrenomedullin. Saturation analysis revealed binding capacities and dissociation constants of 2.8 +/- 0.3 pmol/mg protein and 1.3 +/- 0.3 nM, respectively, in lung and 0.47 +/- 0.11 pmol/mg protein and 0.41 +/- 0.14 nM in heart. Comparison with [125I]CGRP- and [125I]IAPP-binding sites in lung showed that rat adrenomedullin could potently inhibit at these sites (IC50 = 5 and 6 nM, respectively). Chemical cross-linking demonstrated a major band of 83,000 mol wt in lung, diaphragm, spleen, and liver and a band of 94,000 mol wt in heart, soleus, and gastrocnemius. Thus, [125I]adrenomedullin-binding sites in rat lung are abundant and can be differentiated from binding sites in rat heart, both pharmacologically and by mol wt.

Enhanced glial fibrillary acidic protein RNA response to fornix transection in aged mice

The effects of age on basal and lesion-induced changes in astrocyte RNA messages reported to respond to neurodegeneration were examined in the mouse brain. The first study found an age-related increase in glial fibrillary acidic protein RNA throughout the brain. Other astrocyte RNAs remained generally stable with age. We hypothesize this increase is due to astrocytes undergoing a mild reaction to the small amount of synaptic degeneration occurring with usual aging. To test this theory, we used an experimental model of modest synaptic loss in the hippocampus by transecting the fimbria/fornix bundle in mice and examined the same series of messages. In situ hybridization revealed the expected increase in glial fibrillary acidic protein RNA after the lesion; however, we unexpectedly found that aged mice showed a greater magnitude of this response, which appeared to develop more slowly. There was no significant change in the hippocampus for any of the other messages, although responses were observed at the site of transection. This study supports the idea that the age-related increase in glial fibrillary acidic protein may be secondary to modest synaptic degeneration. We also demonstrated an exaggerated reactive astrocytic response in aged mice, which may be associated with age-related deficits in reactive synaptogenesis and behavioral recovery in normal aging.

The presence of islet amyloid polypeptide/calcitonin gene-related peptide/salmon calcitonin binding sites in the rat nucleus accumbens

Receptor autoradiographic analysis of binding in rat brain sections for [125I]islet amyloid polypeptide (IAPP), [125I]calcitonin gene-related peptide (CGRP) and [125I]salmon calcitonin indicated dense binding for all three ligands in the nucleus accumbens. Membrane binding studies revealed the existence of high affinity sites for all three peptides. The order of potency of various related peptides at each binding site was investigated and found for [125I]IAPP to be salmon calcitonin > IAPP = alpha CGRP > salmon calcitonin-(8-32); for [125I]CGRP to be alpha CGRP > IAPP > salmon calcitonin; and for [125I]salmon calcitonin to be salmon calcitonin > alpha CGRP > rat calcitonin > salmon calcitonin-(8-32) > IAPP, suggesting that [125I]IAPP targets the CGRP3 receptor subtype. This study confirms the existence of two receptors in the rat nucleus accumbens binding salmon calcitonin, one of which binds alpha CGRP and IAPP with a high affinity.

The application of toxicokinetic data to dosage selection in toxicology studies

Appropriate dosage selection is a key element in the design of toxicology studies and, hence, is the first step in the process of evaluating the safety of a new chemical or pharmaceutical agent. This demands careful consideration of exposure to the drug or chemical under investigation in relation to the pharmacological or toxicological effects it evokes in an experimental animal. Toxicokinetic data provide this perspective, but they should not be considered exclusively of other data which reflect the specific activity, potency, or metabolism of the drug or chemical in each individual test species. It is equally inappropriate to base dosage selection in toxicology studies exclusively on functional or morphological endpoints that cause effects outside the range which can be accommodated by homeostatic mechanisms and repair processes. Finally, extrapolation of toxicokinetic data across species lines can lead to serious miscalculations with respect to both dosage selection and the process of risk assessment. In each case, decisions should be based on the integration of toxicokinetic data with other measures and endpoints of biological and toxicological effect.

An important role of heparan sulfate proteoglycan (Perlecan) in a model system for the deposition and persistence of fibrillar A beta-amyloid in rat brain

A consistent rat model for the study of the consequences of congophilic and fibrillar A beta-amyloid in brain has been developed. One hundred percent of animals receiving infusions of synthetic beta-amyloid protein (A beta 1-40) plus a specific heparan sulfate proteoglycan (HSPG) for 1 week or 7 weeks (following 2 week infusions) demonstrated Congo red and thioflavin S-positive deposits adjacent to the infusion site. Extracellular amyloid fibrils were identified by electron microscopy and were immunogold decorated with A beta antibody. Significant increases in Congo red staining were observed in animals infused with A beta plus HSPG versus those infused with only A beta. Infusion of A beta alone was variable with respect to congophilic amyloid persistence, which occurred in 50% of animals and only when endogenous HSPGs accumulated at A beta deposition sites. By 7 weeks, only animals infused with A beta plus HSPG demonstrated compaction of the Congo red material from amorphous, wispy deposits (at 1 week) to stellate deposits resembling a Maltese cross. These spherical amyloid deposits were very similar to Congo red-stained amyloid plaques in human Alzheimer's disease brain, and in vitro data suggest that they were probably formed in vivo following interactions with endogenous brain components.

Tandem mass spectral decompositions of protonated N-acyloligoalanines and N-acyloligoglycines as models for those of the protonated free oligopeptides

The intensities of the y-type and b-type ions in the tandem mass spectra of the [M + 1]+ ions of acylated oligomers of alanine and glycine give evidence that these ions are not structurally similar to the [M + 1]+ ions of the free oligomers. For example, the intensities do not follow statistical or linear free energy relationships as would be expected if they were homologous. Instead there are sharp differences in intensities: the y3 ions are considerably more intense than expected, and the b2 ions are less intense. The ions whose intensities differ sharply seem to involve cleavage where the amount of stabilization of a product of cyclization changes when the terminal nitrogen is acylated.

Astrocytic messenger RNA responses to striatal deafferentation in male rat

This investigation describes the schedule and regional distribution of astrocytic responses in striatum following deafferentation by unilateral frontal cortex ablation. In the ipsilateral deafferented striatum, glial fibrillary acidic protein and clusterin (sulfated glycoprotein-2) messengerRNA showed peak elevations by 10 days postlesioning (Northern blots). Vimentin messengerRNA responded faster, with a transient elevation by three days postlesioning. The messengerRNA for glial fibrillary acidic protein, clusterin and vimentin returned toward control levels by 27 days postlesioning. However, the neuronal marker growth-associated protein messengerRNA, was decreased at all postlesion times. By in situ hybridization, the increased glial fibrillary acidic protein messengerRNA and clusterin messengerRNA signals were localized mainly to the dorsal half of the ipsilateral deafferented striatum and followed the same schedule as found by Northern blots. Glial fibrillary acidic protein messengerRNA was widely diffused in the dorsal striatum and was excluded from fascicles of the internal capsule; a similar distribution was found for glial fibrillary acidic protein-immunopositive astrocytes. While clusterin messengerRNA signal showed a distinct clustering, its immunoreactivity appeared as deposits in the deafferented striatal neuropil; Western blots confirmed the immunocytochemical results. By in situ hybridization, vimentin messengerRNA was mostly localized to the cortical wound cavity dorsal to the deafferented striatum and overlapped the distribution of vimentin-immunopositive cells. These findings suggest a coordination of striatal astrocytic messengerRNA responses with the degeneration of corticostriatal afferents. We also compared these same parameters with those from published reports on the hippocampus after deafferenting lesions. Certain astrocyte molecular responses to deafferentation are detected about five days earlier in the hippocampus than in the striatum. This different schedule in response to decortication may pertain to differences in synaptic remodeling in the hippocampus vs striatum.

Size of the export channel in the flagellar filament of Salmonella typhimurium

The size of the putative export channel in the bacterial flagellar filament appears small (25 A) in studies done by electron microscopy but large (60 A) in studies done by X-ray diffraction. We have undertaken additional studies by electron microscopy to examine some of the possible causes of the difference. A comparison of three-dimensional image reconstructions of native and reconstituted filaments rules out the presence or absence of flagellin monomers in the export channel as the source of the variation in apparent channel size. The channel seen in reconstructions from both kinds of filaments is 25 A in diameter. The difference in the previous studies is more probably a result of artifacts introduced in either the X-ray or the electron microscopical methodology. Comparisons of three-dimensional reconstructions from images of filaments embedded in various stains (anionic, cationic and neutral) and in ice, taken at a range of defocuses, rule out the two most likely sources of artifact in electron microscopy (i.e., staining artifacts and defocus phase contrast). Based on these studies we suggest that the channel seen in the image reconstructions is free of exported flagellin monomers, that its true diameter is about 25 A, and, therefore, that the flagellin monomer must be unfolded to pass along it.

Domain organization of the subunit of the Salmonella typhimurium flagellar hook

The deduced amino acid sequences of the family of axial proteins of the bacterial flagellum possess N and C-terminal heptad repeats of hydrophobic amino acid residues, which suggests that these proteins all fold to form bundles of alpha-helices (e.g. coiled coils). There is evidence that flagellin, which is one of the axial proteins, has an axially oriented bundle of alpha-helices that gives rise to the inner, rod-shaped domains seen in electron density maps. We present evidence that a second member of the family, the hook subunit, also has such an axially oriented, rod-shaped domain. In three-dimensional reconstructions from electron micrographs of the helical hook of Salmonella typhimurium, the rod-shaped domain has a diameter of 18 A, which is that expected for a coiled coil. The corresponding domain in the flagellin subunit of the filament, however, is larger, having a diameter of 24 A suggesting a bundle of three or more alpha-helices. In addition to the rod-shaped domain, the hook has two other domains. At a radius of 55 A is the middle spheroidal domain about 25 A in diameter and at a radius of 75 A is the outer ellipsoidal domain about 20 A by 30 A by 40 A. The flagellin subunit also has a middle and an outer domain although they appear different from those of the hook. This is no doubt a result of the lack of any sequence similarity of the hook and flagellin subunits, apart from the N and C-terminal heptad repeats. Along the hook axis, there is a 25 A wide channel, which presumably serves in the export of hook and flagellin subunits in the assembly of the filament. There is a comparably sized channel in the filaments as deduced from electron micrographs. Thus, electron microscopy consistently finds a small channel, whereas in X-ray diffraction studies of the filament, the channel size appeared to be about 60 A. At a diameter of 60 A, the channel could pass the flagellin or hook subunit in its completely folded state, but if the channel is only 25 A in diameter, the subunit would have to be at least partially unfolded in order to pass through the channel.

Proteins antigenically related to methyl-accepting chemotaxis proteins of Escherichia coli detected in a wide range of bacterial species

The four methyl-accepting chemotaxis proteins of Escherichia coli, often called transducers, are transmembrane receptor proteins that exhibit substantial identity among the sequences of their cytoplasmic domains. Thus, antiserum raised to one of these proteins recognizes the others and might be expected to recognize related proteins in other bacteria. We used antiserum raised to the transducer Trg in immunoblot experiments to probe a wide range of bacterial species for the presence of antigenically related proteins. Such proteins were detected in over 20 different species, representing 6 of the 11 eubacterial phyla defined by analysis of rRNA sequences as well as one archaebacterial group. Species containing proteins antigenically related to the transducers of E. coli included members of all four subdivisions of the phylum in which E. coli is placed, members of four of the six subdivisions of spirochetes, and two gliding bacteria. These observations provide substantial support for the notion that methyl-accepting taxis proteins are widely distributed among the diversity of bacterial species.

Age-dependent increases of DNA adducts (I-compounds) in human and rat brain DNA

Brain DNA from 20 humans ranging in age from neonatal to 100 years was analyzed by the nuclease P1-enhanced version of the 32P-postlabeling assay for bulky covalently modified nucleotides. A reproducible pattern of three 32P-labeled spots was obtained by thin-layer chromatography followed by autoradiography. Two of these spots increased with age (Mann-Whitney U-test; P < 0.001; comparison of ages < or = 60 years and ages > 60 years). Thus, these spots met the definition of I-compounds. Rat brain DNA exhibited the same two I-spots, whose intensities also increased with animal age (1, 4, and 10 months). In humans, considerable individual variation of brain I-compound levels was observed, especially at ages > 60 years, presumably reflecting environmental, life-style, or genetic factors. This variation was not noted for brain DNA of laboratory rats. Thus, human brain DNA undergoes progressive covalent modifications with aging.

Complement C1qB and C4 mRNAs responses to lesioning in rat brain

These data show the presence of mRNAs for two complement components (C) in the adult rat brain and describe their responses to experimental lesions. Cortical deafferentation caused elevations in striatal C1qB and C4 mRNAs that coincided temporally and overlapped anatomically with the course of degeneration of corticostriatal afferent fibers. By in situ hybridization, C1qB mRNA in the lesioned striatum was colocalized to cells immunoreactive for CR3, a complement receptor found on microglia-macrophages. The mRNA for SGP-2, a putative C inhibitor in rat, showed parallel changes. Similarly, in hippocampus and other brain regions, kainic acid lesions increased C1qB mRNA. The data suggest that microglia-macrophages and possibly other cells in rat brain rapidly up-regulate C-mRNAs in response to deafferentation and local neuron injury. These experimental responses provide models to analyze changes in C components during Alzheimer's disease and other chronic neurodegenerative conditions.

Processing images of helical structures: a new twist

Helical macromolecular assemblies are particularly difficult to study by X-ray diffraction but are quite well suited to analysis by electron microscopy. Most of our information about helical macromolecular assemblies has come from the electron microscope but has been limited to about 25 A resolution. With the use of low-dose electron cryomicroscopy, one can obtain structural data to near atomic resolution on two-dimensional crystals, but the problem is to extract the information from the noise. In this paper we present methods to extract signal from low-dose electron cryomicrographs of helically symmetric structures. We apply these methods to extract 10 A data from the bacterial flagellar filament.

Aortic stenosis and bleeding gastrointestinal angiodysplasia: is acquired von Willebrand's disease the link?

An association between aortic stenosis and haemorrhage from gastrointestinal angiodysplasia has been recognised for many years, but no explanation for this link has been found. Remarkably, aortic valve replacement, rather than bowel resection, corrects the bleeding. Aortic stenosis can be complicated by acquired von Willebrand's disease type IIA (vWD-IIA), which is corrected after valve replacement, and gastrointestinal angiodysplasia is a common site of bleeding in older patients with acquired or congenital vWD. Could the stenotic aortic valve lead to an acquired, reversible deficiency of the largest multimers of plasma von Willebrand factor (equivalent to vWD-IIA) and thus explain the association with gastrointestinal haemorrhage?

Patch averaging of electron images of GP3*I crystals with variable thickness

The combination of Fourier and correlation averaging techniques with multivariate statistical analysis and classification, a method known as patch averaging, is used to analyze untilted and tilted images of negatively stained GP32*I crystals, which exhibit variable thicknesses in a single crystal. Within a single image, coherent areas of the same apparent thickness can be distinguished from areas of differing thicknesses. Analysis using the phase relationships among symmetry-related reflections from reconstituted images obtained from untilted micrographs confirms the ability of the method to classify these variable thicknesses properly. Furthermore, the phases from some of the reconstituted images obtained from both untilted and tilted micrographs were found to match well with the phases in a previously determined three-dimensional data set of this crystal with pg symmetry along the crystallographic b axis. These results indicate the utility of the patch averaging procedures in the structural determination of protein crystals with different thicknesses.

Myeloma-like cast nephropathy caused by human recombinant soluble CD4 (sCD4) in monkeys

CD4 is the receptor for human immunodeficiency virus (HIV) on lymphocytes and macrophages. Soluble CD4 (sCD4), a recombinant truncated form of CD4, has been shown to inhibit HIV-1 in vitro and is being tested as a therapy for AIDS. Preclinical studies in cynomolgus monkeys revealed a protein cast nephropathy after four daily intravenous doses of 100 mg/kg/day. Renal lesions were not found in monkeys that received 10 mg/kg/day. The renal lesions consisted of proteinaceous tubular casts associated with multinucleate giant cells and neutrophils located in the tubules of the distal nephron. The affected tubules were surrounded by an interstitial mixed inflammatory cell infiltrate. By electron microscopy, the casts were composed of moderately electron dense, paracrystalline material. Immunostaining demonstrated that the casts contained sCD4-derived material and Tamm-Horsfall protein. Moreover, biochemical analysis of urine showed that a portion of sCD4 was excreted as intact protein. Because infection with HIV-1 can be associated with clinically significant nephropathy, these data suggest that renal function should be closely monitored in patients receiving soluble forms of CD4.

Slow changes of tyrosine hydroxylase gene expression in dopaminergic brain neurons after neurotoxin lesioning: a model for neuron aging

Slow neuron regression develops during the adult phase of life in select brain systems of mammals. We describe a model in adult rats that resolves several phases in a slow atrophic process that differentially influences levels of mRNA and protein for tyrosine hydroxylase (TH). Responses of striatal dopaminergic markers to 6-hydroxydopamine (6-OHDA) lesions in rats indicated that the striatal terminals maintained TH protein, despite greater than 3-fold loss of TH mRNA in the substantia nigra pars compacta (SNC) cell bodies whose axons project to the striatum. The loss of TH mRNA/cell was progressive up to 9 months, whereas SNC cell body shrinkage stabilized by 3 months post-lesioning. Consideration of possible mechanisms in protein turnover motivated a search for PEST motifs in the TH of rats and other vertebrates that could be a point of regulation by altering the rate of TH protein turnover.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Recombinant human soluble CD4 does not inhibit immune function in cynomolgus monkeys

Recombinant soluble CD4 (sT4) has been shown to inhibit infectivity of HIV. Because of the role CD4 plays in the interaction of T-helper lymphocytes and cells bearing MHC Class II antigens, a potential adverse effect of therapy with sT4 is interference with lymphocyte function. To address this issue, we studied the effects of sT4 on mitogen-mediated blastogenesis, mixed lymphocyte reactions, and delayed type hypersensitivity reactions (DTH) in cynomolgus monkeys. We found no evidence of sT4-mediated suppression on the in vitro response to concanavalin A, phytohemagglutinin or pokeweed mitogen in 2-way mixed lymphocyte reactions, either when sT4 was added to the cultures or when cells were obtained 3 hr after drug administration from animals that received up to 100 mg/kg as an intravenous bolus. Furthermore, we also found no effect of sT4 on lymphocyte subsets or on the ability of monkeys to respond to dinitrochlorobenzene (DNCB)-mediated DTH. Because of the high degree of conservation of CD4 and MHC Class II antigens across the macaque-human barrier, these data suggest that soluble CD4-like molecules are unlikely to be immunosuppressive in humans.

Disappearance of GAD-mRNA and tyrosine hydroxylase in substantia nigra following striatal ibotenic acid lesions: evidence for transneuronal regression

Transneuronal regression in substantia nigra reticulata (SNR) and substantia nigra compacta (SNC) neurons was studied in Fischer 344 male rats by immunocytochemistry and by in situ hybridization. Three months after striatal lesioning by ibotenic acid, there was a shrinkage (30%) of the SNR region cross-sectional area and a 50% disappearance of neurons that contain glutamic acid decarboxylase (GAD)-mRNA, but only in the ventromedial portion of this nucleus. Loss of dopaminergic neurons, as recognized by tyrosine hydroxylase immunoreactivity, occurred only in caudal portions of the SNC and SNR. These findings suggest that lesions in reciprocally connected pathways, like the nigrostriatal and striatonigral systems, may produce a vicious cycle (feedforward cascade) of neurodegeneration due to interference with retrograde ana anterograde influences.

Age-related changes in glial fibrillary acidic protein mRNA in the mouse brain

Several RNA sequences were tested for age-related changes in prevalence levels in the mouse cerebral cortex, hippocampus, and cerebellum. In all three regions, there were increased levels of RNA for glial fibrillary acidic protein, an astrocyte-specific protein, by RNA gel-blot analysis and by a solution hybridization assay. There was no change in glutamine synthetase mRNA level, another glial protein. The only other mRNA sequence which changed was Thy-1 antigen, a neuronal protein, which decreased slightly in the hippocampus. We conclude that with age there is an age-related increase in glial fibrillary acidic protein RNA prevalence potentially reflecting an increase in the size, number, and/or fibrous character of astrocytes.

Haloperidol treatment increases D2 dopamine receptor protein independently of RNA levels in mice

Haloperidol, administered to mice in their drinking water, produced a 21% increase in striatal D2 dopamine receptor density after seven days of continuous exposure. The steady-state D2 receptor RNA prevalence was unaffected by this treatment, yet the RNA coding for preproenkephalin was elevated, as expected. These data indicate that the homologous up-regulation of dopamine receptor density by antipsychotic drugs proceeds by mechanisms other than changes in RNA abundance.

Tyrosine hydroxylase mRNA concentration in midbrain dopaminergic neurons is differentially regulated by reserpine

Tyrosine hydroxylase (TH)-mRNA, assayed by in situ hybridization combined with TH immunocytochemistry, showed a selective increase in the ventral tegmental area (A-10) but not in the substantia nigra (A-9) midbrain dopaminergic (DAergic) neurons 3 days after reserpine treatment. TH-mRNA in locus ceruleus noradrenergic (A-4) neurons was increased by reserpine, as confirmed by RNA blot hybridization. These findings show that TH-mRNA is differentially regulated in midbrain DAergic neurons in response to reserpine.

Effects of sensitization to dinitrochlorobenzene (DNCB) on clinical pathology parameters and mitogen-mediated blastogenesis in cynomolgus monkeys (Macaca fascicularis)

Immunotoxicologic testing of drug candidates and environmental contaminants is of growing importance. Cutaneous delayed type hypersensitivity (DTH) is a convenient way of testing immune function in vivo. However, DTH testing must not interfere with interpretation of other relevant parameters. We have evaluated the effects of sensitization and challenge with dinitrochlorobenzene (DNCB) on clinical parameters routinely evaluated in toxicity testing and on lectin-mediated blastogenesis. Female cynomolgus monkeys were sensitized to DNCB with 4 daily applications of DNCB in acetone to the skin of the axilla. Fifteen days later, the monkeys were challenged for DTH by applying DNCB to the antecubital skin. Skin fold thickness was measured and the macroscopic appearance of the challenge site was scored 24 and 48 hr after challenge. All 5 monkeys were successfully sensitized to DNCB. There was a significant increase in the mean skin fold thickness (compared to pre-challenge thickness) of 2 mm at 24 hr and 1 mm at 48 hr (p less than 0.001). The clinical score of the challenge site was also increased. Histologic examination of the sensitization and challenge sites from a second group of monkeys exposed to DNCB in an identical manner showed the perivascular inflammatory cell infiltrate typical of DTH. Evaluation of hematologic parameters at days 7, 14, and 21 revealed no change in the erythron at any interval and a mild decrease in total WBC, neutrophil and lymphocyte counts on day 7 in 4/5 monkeys. The WBC parameters remained within the normal range and returned to pre-sensitization values at the later intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

GFAP RNA increases during a wasting state in old mice

A prolonged wasting condition is often associated with morbidity in older humans. The effects that such a state has on the quality/quantity of RNA are not known. In initial attempts to develop an animal model for premortem wasting, we examined whole brain RNA from mice slowly approaching death from natural causes. Glial fibrillary acidic protein (GFAP) RNA showed a three-fold increase as detected by RNA gel-blot hybridization analysis. Five other RNA sequences were stable under these circumstances. We conclude that brain RNA changes are selective during a degenerating premortem state. Moreover, RNA sequence changes in conditions such as Alzheimer's disease should be considered in the context of the wasting condition of the individual and may not be due to a direct effect of the disease process.

RNA and protein metabolism in the aging brain

Much work in the molecular neurobiology of aging is still necessarily descriptive, pending more data on the relative contributions of neuron loss vs. neuron atrophy and glial hyperactivity during normal and neuropathological aging. Major loss of neuronal cells is not the rule, even in AD. A working hypothesis holds that increased astrocytic volumes and decreased neuronal volumes are a major factor in age-related neurochemical decreases. Resolution of these questions is needed to understand how regional RNA and protein synthesis change during aging. We have presented alternative mechanisms for changes in gene expression that may be cell specific. The literature, mainly from non-neural tissues, suggests derepression of normally silent genes, possibly in association with DNA demethylation; decreased synthesis of neuronal rRNA due to deletion of rRNA genes; epigenetic changes in hnRNA splicing; reduced turnover rates and the accumulation of nonfunctional proteins. Although global qualitative changes in the inventory of mRNA and proteins are not found in neural tissues at advanced ages, the synthesis and turnover of RNA and protein may be slowed. Impaired protein turnover or catabolism could contribute to the accumulation of NFT and brain amyloid. In sum, several different types of mechanisms appear to be important in RNA and protein metabolism of the brain during aging, but selectivity for brain region and cell type seems to prevail throughout these myriad changes.

Considerations in the treatment of neurological disorders with trophic factors

The rationale for the therapeutic administration of NGF in Alzheimer's disease cannot be based purely on the premise of replacement therapy, and must instead consider the general anabolic properties of this trophic substance. In addition, there are potentially deleterious side effects of such therapy which should be evaluated in clinical trials. The selectivity of NGF for cholinergic neurons (in CNS) compared to the more generalized degeneration found in Alzheimer's disease raises the possibility of using trophic factors supporting a broader variety of neuron classes (FGF, ILGF).

Role of dopaminergic and adrenergic receptors in the pathogenesis of arterial lesions induced by fenoldopam mesylate and dopamine in the rat

Fenoldopam mesylate (FM), a selective, postjunctional, dopaminergic (DA1) vasodilator, causes a novel lesion of large caliber splanchnic arteries (100 to 800 microns) in the rat characterized by necrosis of medial smooth muscle cells and hemorrhage. FM does not induce lesions in other vascular beds of the rat or in dogs or monkeys. Dopamine, like FM, causes hemorrhagic lesions of large caliber splanchnic arteries in the rat, as well as fibrinoid necrosis of small caliber arteries (less than 100 microns) of the splanchnic, cerebral, coronary, and renal vascular beds. Dopamine, an alpha- and beta-adrenoceptor and dopaminergic agonist, is used clinically, principally as a pressor agent. Because these arterial lesions were believed to result from the pharmacologic activity of these two compounds, the role of vascular receptor subtypes in their pathogenesis was investigated. Rats were coexposed to either FM or dopamine and a variety of receptor antagonists (alpha, beta, DA1, DA2, and 5HT2). In rats coexposed to the alpha-adrenoreceptor antagonist phenoxybenzamine (PBZ) and either FM or dopamine, the incidence and severity of hemorrhagic lesions of large caliber arteries were increased; PBZ, however, prevented the formation of dopamine-induced fibrinoid lesions in arteries of small caliber. SK&F 83566-C, a selective DA1 dopaminergic receptor antagonist, prevented the induction of FM and dopamine-induced hemorrhagic lesions of large caliber arteries. Rats exposed concurrently to dopamine, phenoxybenzamine, and SK&F 83566-C were free of all arterial lesions. The other receptor antagonists tested did not prevent arterial injury. Thus, the induction of splanchnic arterial lesions in the rat by dopamine and FM is caused by stimulation of, and interaction between, alpha-adrenoceptors and dopaminergic DA1 receptors. Activation of the postjunctional, dopaminergic (DA1) receptor is causally associated with the induction of novel hemorrhagic lesions of large caliber splanchnic arteries in the rat.

Combined in situ hybridization and immunocytochemistry in the assay of pharmacological effects on tyrosine hydroxylase mRNA concentration

An assay for tyrosine hydroxylase (TH) mRNA by in situ hybridization in combination with immunocytochemistry (ICC) for TH on the same section is described. The in situ hybridization protocol was optimized for [35S]cRNA (complementary RNA, i.e. anti-sense strand) probe concentration and time of hybridization. The specificity of hybridization was measured by several critera. The advantage of measuring grain density versus grains per cell is discussed for quantitation of in situ autoradiography. Finally, the reserpine-induced increase in adrenal TH mRNA was used to validate quantitative aspects of the in situ hybridization technique by comparison with blot hybridization. In contrast to the adrenal, reserpine did not increase TH mRNA in substantia nigra (s. nigra) neurons as measured by either technique.

Chronic lesions differentially decrease tyrosine hydroxylase messenger RNA in dopaminergic neurons of the substantia nigra

Long-term effects of lesions were analyzed in terms of gene expression. Nine months after unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (s. nigra), the remaining dopaminergic (DAergic) neurons (tyrosine hydroxylase (TH) cells determined by immunocytochemistry (ICC] on the lesioned side were atrophic with smaller nucleoli. By in situ hybridization, the DAergic neurons on the lesioned side had a 50% smaller TH-mRNA concentration than on the contralateral non-lesioned side. However, beta-tubulin mRNA concentration in DAergic neurons was unaffected by the lesion. The lesions did not alter TH-mRNA concentration in the contralateral non-lesioned side by comparison with unoperated controls. We propose that chronic lesions have long-term effects on gene expression because of damage sustained during compensatory hyperactivity after the lesion, or because of decreased trophic support from other neurons.

Ultrastructure of an arterial lesion induced in rats by fenoldopam mesylate, a dopaminergic vasodilator

Fenoldopam mesylate (FM) is a dopaminergic vasodilator with demonstrated efficacy and a favourable safety profile in hypertensive and congestive heart failure patients. FM produced a novel arterial lesion in renal and splanchnic arteries of rats, but not dogs or monkeys. The studies reported here were undertaken to investigate the ultrastructure of the arterial lesion induced in rats by FM in an attempt to shed light on its pathogenesis. Rats were infused intravenously with FM, either 50 micrograms/kg/min for 1 or 4 h, or 5 or 100 micrograms/kg/min for 24 h. Control rats were infused for 4 or 24 h with vehicle alone. Perfusion-fixed tissue from the stomach and pancreas of control and drug-treated rats was examined by transmission electron microscopy. No arterial lesions were seen in rats infused with the drug for 1 or 4 h, or in control rats. All drug-treated rats infused with 5 or 100 micrograms/kg/min of FM for 24 h had lesions in subserosal gastric arteries and interlobular pancreatic arteries. In areas of mild arterial damage, medial smooth muscle cells contained intracytoplasmic pseudovacuoles, autophagic vacuoles, and electron-dense, myofilamentous inclusions. More severe lesions were characterized by overt medial necrosis and haemorrhage. The endothelium of affected arteries was invariably intact, except in areas of severe medial damage. The internal elastic lamina and connective tissue elements within the arterial wall were unaffected. These findings suggest that medial smooth muscle cells are the primary site of damage caused by fenoldopam mesylate in splanchnic arteries of the rat. This iatrogenic arterial lesion could provide an interesting model to study the response of medial smooth muscle to pharmacologically mediated injury.

Uptake of human recombinant tissue-type plasminogen activator by rat hepatocytes in vivo: an electron microscope autoradiographic study

The hepatic uptake of recombinant human tissue-type plasminogen activator (tPA) has been studied by electron microscope autoradiography (EMARG) of serial hepatic biopsies taken from anaesthetized, laparotomized rats following intravenous injection of 125I labeled tPA. Serial blood samples showed both radiolabel and biologic activity to be eliminated from circulation with an initial half-life of approximately two minutes. Grain half-distance distribution profiles and grain density analysis showed that the para-sinusoidal region of the hepatic parenchymal cell is the only site in the liver to concentrate radiolabeled tPA after intravenous injection. These data support the hypothesis that the parenchymal cell is the principal cell responsible for hepatic clearance of tPA from circulation and suggest that receptor mediated endocytosis may be the mechanism of cellular uptake.

Pathogenesis of arterial lesions induced by dopaminergic compounds in the rat

Fenoldopam mesylate (FM), a selective post-junctional dopaminergic (DA1) vasodilator, causes lesions of large caliber splanchnic arteries (100-800 microns) in the rat characterized by necrosis of medial smooth muscle cells and hemorrhage. FM does not induce lesions in other vascular beds of the rat, or in dogs or monkeys. Dopamine, like FM, causes hemorrhagic lesions of large caliber splanchnic arteries in the rat, as well as fibrinoid necrosis of small caliber arteries (less than 100 microns) of the splanchnic, cerebral, coronary and renal vascular beds. Dopamine is an alpha- and beta-adrenoceptor and a dopaminergic receptor agonist. Because these arterial lesions are thought to result from the pharmacologic activity of these 2 compounds, we sought to ascertain the presence of DA1 receptors in mesenteric arteries of the rat and to determine the role of these or other vascular receptor subtypes in lesion induction. We also studied the process of repair after arterial injury caused by FM or dopamine. The presence of DA1 receptors was confirmed in isolated perfused mesenteric arteries by standard pharmacologic techniques; stimulation by FM resulted in vasodilation which was inhibited by the DA1 receptor antagonist SK&F 83566-C. Likewise, SK&F 83566-C prevented the induction of hemorrhagic lesions of large caliber arteries in rats upon infusion of FM or dopamine. In rats co-exposed to the alpha-adrenoreceptor antagonist phenoxybenzamine (PBZ) and either FM or dopamine, the incidence and severity of hemorrhagic lesions of large caliber arteries were increased, but PBZ prevented the formation of dopamine-induced fibrinoid lesions in arteries of small caliber. Rats exposed concurrently to dopamine, phenoxybenzamine, and SK&F 83566-C were free of all arterial lesions. Thus, the induction of splanchnic arterial lesions in the rat by dopamine and FM is caused by stimulation of, and interaction between, alpha-adrenoceptors and dopaminergic DA1 receptors. Fibrinoid lesions of small arteries (alpha-adrenoceptor-mediated) were repaired, as observed morphologically by 14 d after exposure to dopamine. Hemorrhagic lesions of large caliber arteries (DA1 receptor-mediated) had undergone significant repair by 28 d after exposure to FM but these arteries possessed a thicker media surrounded by adventitial fibrosis. Thus, morphologically distinct receptor-mediated splanchnic arterial lesions induced by dopaminergic and alpha-adrenoceptor agonists follow a markedly different course of repair. Arterial lesions induced by FM or dopamine by activation of post-junctional dopaminergic DA1 receptors may represent a model of polyarteritis nodosa.

Acetaminophen and p-aminophenol nephrotoxicity in aging male Sprague-Dawley and Fischer 344 rats

Strain differences in susceptibility of rats to acetaminophen (APAP)-induced nephrotoxicity have been reported previously. Young adult male Fischer 344 (F344) rats are susceptible, whereas weight-matched Sprague-Dawley (SD) rats are not susceptible to APAP nephrotoxicity. Susceptibility to APAP nephrotoxicity is also age dependent, at least in F344 rats. Middle-aged (12-15 months old) male F344 rats are more susceptible to APAP-induced nephrotoxicity than are young adult (2-4 months old) males. APAP nephrotoxicity in aging SD rats has not been evaluated. The present studies were designed to define strain differences in the nephrotoxicity of APAP and p-aminophenol (PAP), a nephrotoxic metabolite of APAP, using 2-, 3-, and 9- to 12-month-old F344 and SD rats. At 2 months of age, F344, but not SD, rats were susceptible to APAP-induced nephrotoxicity. However, at 3 months of age, strain differences were less marked, as susceptibility to APAP nephrotoxicity appeared to increase between 2 and 3 months of age only in SD rats. By 9-12 months of age, susceptibility to APAP nephrotoxicity was comparable in F344 and SD rats. No age- or strain-related differences were observed in the excretory pattern of urinary APAP and metabolites that might explain the increased susceptibility of aging rats to APAP nephrotoxicity. Strain differences in age-matched rats were not marked for PAP-induced nephrotoxicity. Susceptibility of both 3- and 12-month-old F344 and SD rats to PAP-induced nephrotoxicity was greater compared to strain-matched 2-month-old rats. In both F344 and SD rats, PAP nephrotoxicity increased only modestly between 3 and 12 months of age, indicating that increased susceptibility to PAP probably does not play a major role in the age-dependent increase in APAP nephrotoxicity. Thus, strain differences in APAP nephrotoxicity decrease with advancing age. The mechanisms mediating the increased susceptibility to APAP nephrotoxicity in middle-aged rats are not known but may relate, at least in part, to age-dependent differences in pharmacokinetics. The present study highlights the importance of considering the age of rats when evaluating drug toxicity. Even in young adult rats, subtle maturational changes in drug metabolism and/or disposition may occur, making toxicological evaluation in weight-matched rats of different strains and ages inappropriate.

New approaches to the study of central nervous system function. Immune-nervous system interactions and cell culture

The paper by Lal and Forster is discussed with reference to future experiments which might provide insight into mechanisms regarding their exciting data that circulating brain reactive antibodies may cause learning deficits. The paper by Azmitia et al. on cell culture techniques is discussed with respect to the types of studies in which culture systems have proven most valuable in the past, and should continue to do so in the future.

Cryo electron microscopy of unstained, unfixed RecA-cssDNA complexes

Complexes of RecA protein with phi X174 circular single-stranded DNA (cssDNA) with and without ATP gamma S were rapidly frozen and embedded in a thin layer of vitreous ice. The electron micrographs of these frozen-hydrated complexes clearly show visible helicity. Quantitative image analyses of these micrographs reveal the helical pitch and the axial rise between DNA bases of these complexes. Both of these structural parameters of RecA-cssDNA complexes increase significantly when ATP gamma S is present. These observations agree qualitatively but not quantitatively with those from negative stained specimens and confirm the general model that the interactions among RecA molecules and between RecA and DNA could change according to the functional states of the RecA-cssDNA complex.

Crystallization and preliminary X-ray diffraction analysis of 11 S acetylcholinesterase

The 11 S form of acetylcholinesterase from Electrophorus electricus was purified by affinity chromatography. The protein was crystallized from polyethylene glycol solutions. One crystal form proved suitable for x-ray diffraction studies. Preliminary x-ray analysis demonstrates that the space group of this crystal is F222. The unit cell dimensions are a = 141.0 +/- 0.2, b = 202.4 +/- 0.2, and c = 237.4 +/- 0.1 A. The diffraction is anisotropic, extending to at least 3.5 A along the a* and b* axes, but becoming weak beyond about 6 A along the c* axis. Crystal density measurements suggest that one complete 11 S tetramer occupies the asymmetric unit of the crystal.

Effects of radioligand oxidation and ascorbate-induced lipid peroxidation on serotonin-1 receptor assay: use of ascorbate and ethylenediamine tetraacetic acid buffers to prevent (3H)-5-HT binding artifacts

The effects of ascorbic acid and ascorbate-induced lipid peroxidation upon (3H)-5-HT binding were examined in total membrane fractions prepared from mouse cortex and hippocampus. Low concentrations of ascorbic acid promoted lipid peroxidation of membranes as assessed by malondialdehyde production relative to intermediate concentrations of ascorbate. The actual concentration of ascorbate required for expression of pro-oxidative and antioxidative properties was dependent upon assay conditions such as temperature and ionic constituents. Ascorbate-induced lipid peroxidation was completely prevented by addition of 1 mM ethylenediamine tetraacetic acid (EDTA) and enhanced by GTP at concentrations typically used in binding assays. Marked lipid peroxidation was associated with loss of (3H)-5-HT binding sites with little effect upon affinity of the receptor for the ligand. In contrast, mild lipid peroxidation occurring during the binding assay with the ligand present was associated with a decreased affinity for (3H)-5-HT and the appearance of a curvilinear Scatchard plot. Under assay conditions that prevented ascorbate-induced lipid peroxidation, Scatchard analysis indicated only a single high-affinity binding site for (3H)-5-HT even when assayed with an expanded range of ligand concentrations. Preparation of ligand and assay of (3H)-5-HT binding in the absence of ascorbate resulted in shallow, markedly curvilinear Scatchard plots. These data support the continued use of ascorbate in (3H)-5-HT binding assays to prevent ligand degradation and the addition of 1 mM EDTA to prevent lipid peroxidation from occurring during the binding assay.

Three-dimensional structural analysis of tetanus toxin by electron crystallography

Two-dimensional crystalline arrays of native tetanus toxin have been formed at the interface between a solution of the toxin and a phospholipid monolayer containing a ganglioside. Electron crystallographic analysis has been used to study these periodic arrays. The arrays obey the symmetry of plane group p12(1), with a = 126 A and b = 84 A, and a thickness of 90 A (1 A = 0.1 nm). The three-dimensional structure of tetanus toxin in negative stain is reconstructed to a nominal resolution of 14 A from multiple tilt images. The molecule presents an asymmetric three-lobed structure and could interact with the monolayer in two possible orientations.

The effect of longterm treatment with auranofin and gold sodium thiomalate on immune function in the dog

Although gold compounds are recognized as effective immunomodulatory agents in the treatment of rheumatoid arthritis (RA), their mechanism of action is controversial. We examined the effect of longterm treatment with 0.6-3.6 mg/kg auranofin (AF) per os q24h, or intramuscular injections of 0.5-2.0 mg/kg gold sodium thiomalate (GSTM) q3d, on 13 variables of immune function in normal dogs. None of the changes in these variables previously attributed to treatment with AF or GSTM could be demonstrated after 6-7 years' dosing. As gold compounds are effective in treating spontaneous RA in dogs, these proposed actions may not be responsible for the remittive effects of chrysotherapy in this disease.