Evaluation of an Advanced Fault Management System Display for Next Generation Crewed Space Vehicles

The next generation Crew Exploration Vehicle is planned to employ Integrated Systems Health Management (ISHM) technology to enhance crew safety and improve onboard operations. For example, the ISHM could assist crewmembers with real-time fault management operations by automatically identifying the root cause of complex system malfunctions. However, to implement such a system, several human-factors issues have to be addressed. For instance, human-machine functional allocations have to be made and supporting crew interfaces designed and evaluated. The paper describes a concept for crew-ISHM interactions called the Fault Management Support System (FAMSS) that addresses these human-factors issues. Simulator experiment results showed that a simulated FAMSS interface improved operators' situation awareness and fault-management performance while decreasing fault-management workload.

Shared decision signal explains performance and timing of pursuit and saccadic eye movements

Each voluntary eye movement provides physical evidence of a visuomotor choice about where and when to look. Primates choose visual targets with two types of voluntary eye movements, pursuit and saccades, although the exact mechanism underlying their coordination remains unknown. Are pursuit and saccades guided by the same decision signal? The present study compares pursuit and saccadic choices using techniques borrowed from psychophysics and models of response time. Human observers performed a luminance discrimination task and indicated their choices with eye movements. Because the stimuli moved horizontally and were offset vertically, subjects' tracking responses consisted of combinations of both pursuit and saccadic eye movements. For each of two signal strengths, we constructed speed-accuracy curves for pursuit and saccades. We found that speed-accuracy curves for pursuit and saccades have the same shape, but are time-shifted with respect to one another. We argue that this pattern occurs because pursuit and saccades share a decision signal, but utilize different response thresholds and are subject to different motor processing delays.

Target selection and the superior colliculus: goals, choices and hypotheses

The intermediate and deep layers of the superior colliculus (SC) compose a retinotopically organized motor map and are known to be important for the control of saccadic eye movements. However, recent studies have shown that the functions of the SC are not restricted to the motor control of saccades. The pattern of activity observed during multi-saccade movements, combined eye-head movements, and pursuit eye movements argue that activity in the SC indicates the location of the goal, but does not specify the particular movements that will be used to acquire the goal. Prior to the onset of a movement, the SC is involved in representing possible targets, as has been shown by the effects of manipulating target probability and the changes in pre-motor activity found during visual search tasks. A major unresolved issue is how target-related activity in the SC is transformed into the signal that triggers the movement. One possibility is that the levels of activity across the SC motor map correspond to the likelihood of the possible targets, and that the movement decision is based on the neural equivalent of hypothesis testing. In one version of this mechanism, the decision to select a new goal would occur each time the null hypothesis, represented by neurons in the rostral SC, was rejected in favor of an alternative represented elsewhere in the SC.

Shared response preparation for pursuit and saccadic eye movements

Tracking a single target in the visual world requires coordination between pursuit and saccadic eye movements. The constraints imposed on pursuit and saccade decisions by visual processing and response preparation are difficult to compare because latency differences between the two movements provide different amounts of visual sampling time. The present study compares pursuit and saccade decisions when visual processing was directly manipulated. Human observers were asked to select between two stationary stimuli presented simultaneously at two different locations based on which had the higher contrast. The stimuli were presented for a brief, variable interval and then occluded by masks. Because the masks moved horizontally and were offset vertically, subjects were obliged to make both pursuit and saccadic eye movements to track the mask covering the target stimulus. For each of the exposure durations, we constructed oculometric curves for pursuit and saccades. We found that both systems had similar oculometric thresholds and response biases. The initial pursuit decisions differed from the subsequent saccade decisions on 1-13% of the trials but were the same more often than predicted by independent mechanisms. Moreover, pursuit reversed direction on discordant trials, so that the pursuit decision always matched that of the saccade by the time the saccade was started. These results support the view that, in addition to overlap in early visual areas and the final motor pathways, the pursuit and saccadic systems share processing at the level of response preparation. This shared processing may help ensure the coordination of pursuit and saccadic eye movements in selecting a single target.

Characterization of new enkephalin-containing peptides in the adrenal medulla by immunoblotting

Immunoblotting combined with radioimmunoassays (RIAs) directed specifically towards certain sequences of the proenkephalin molecule has been used to characterize the enkephalin-containing peptides (ECPs) present in the bovine adrenal medulla. Immunoblotting allowed the simultaneous visualization of all ECPs present in a crude extract of this gland. Combining this technique with RIAs we have been able to characterize a new high molecular mass ECP, a 23.3-kDa protein which contains the amino-terminal part of proenkephalin and ends with the sequence of Leu-enkephalin at its carboxy-terminus.

A new class of selective and potent inhibitors of neuronal nitric oxide synthase

The synthesis and SAR of a series of 6-(4-(substituted)phenyl)-2-aminopyridines as inhibitors of nitric oxide synthase are described. Compound 3a from this series shows potent and selective inhibition of the human nNOS isoform, with pharmacokinetics sufficient to provide in vivo inhibition of nNOS activity.

Syntheses and anticholinesterase activity of tetrahydrobenzazepine carbamates

The synthesis of a series of alkylcarbamates of 1,5-methano-2,3,4,5-tetrahydro-1H-2-benzazepin-7-ol is reported. Many of these compounds are potent acetylcholinesterase (AChE) inhibitors. The in vitro AChE inhibition, cholinergic effects, acute toxicity, and elevation of brain acetylcholine levels in vivo of this series of compounds are described. A representative compound, 1d (5.6 mg/kg, po), was able to reverse hemicolinium-3-induced amnesia in the mouse passive avoidance assay.

The health insurance picture in 1993: some rare good news

Based on a national survey conducted in spring 1993 of 1,953 private and public employers, this DataWatch examines the design of employer-sponsored health benefits and how they have changed during the past five years. We contrast cost of coverage, employee cost sharing, and premium increases among small, mid-size, and large firms. Premiums increased 8.5 percent from 1992 to 1993, the lowest rate of increase since 1986-1987. Future premium increases should be modest by historical standards. Small firms and conventional plans experienced larger premium increases last year. Managed care plans now constitute 51 percent of enrollment, up from 29 percent in 1988. If current trends continue, even without health care reform legislation, the health care system of the future will contrast strikingly with the system most Americans remember from past decades.

Deletions of the synenkephalin domain which do not alter cell-specific proteolytic processing or secretory targeting of human proenkephalin

To identify signals that direct the proteolytic processing and regulated secretion of human proenkephalin (hPE), we have transfected the hPE gene or minigene constructs into pituitary tumor cells, either rat GH4Cl cells or mouse AtT-20 cells. Cells transfected with either the hPE gene or minigene contained similar levels of methionine-enkephalin (ME)-containing peptides and hPE mRNA. In the GH4Cl clones, ME was present predominantly in high-molecular-mass forms (5-25 kDa). In contrast, the AtT-20 clones contained almost exclusively free ME and low-molecular-mass forms (< 5 kDa), with very little high-molecular-mass species present. Thus, among pituitary cells, corticotroph-derived cells appear better equipped to process hPE than lactotroph-derived cells. Despite limited proteolytic processing, GH4Cl clones secreted large amounts of unprocessed (> 20 kDa) hPE into the medium, making up to 10% of endogenous rat prolactin secretion. Both precursor and processed forms of ME were cosecreted acutely (< 1 h) with rat prolactin, and release of both polypeptides was stimulated up to 12-fold by secretagogues. Thus, complete proteolytic processing was not required for accurate targeting of hPE to the regulated secretory pathway. When transfected with constructs bearing deletions of amino-terminal amino acids 2-43 or 2-67, i.e., part or nearly all of the synenkephalin moiety, GH4Cl cells handled the modified protein much like cells expressing the complete protein. They did not process the modified hPE extensively, but the protein was correctly targeted to the regulated secretory pathway. AtT-20 cells transfected with truncated hPE cDNA constructs expressed and processed the protein as efficiently as cells expressing unmodified hPE and expressed predominantly low-molecular-mass forms of ME. Therefore, the structural features required for correct targeting and processing are not present in the cysteine-rich amino-terminal third of the prohormone. It is interesting that the deletions did not include the SHLL peptide motif in synenkephalin, a motif that has been proposed as a sorting signal.

Syntheses, resolution, and structure-activity relationships of potent acetylcholinesterase inhibitors: 8-carbaphysostigmine analogues

The synthesis of a series of 1,2,3,3a,8,8a-hexahydroindeno[2,1-b]pyrrole 5-alkylcarbamates and their resolution are reported. These compounds are structurally related to physostigmine with substitution of a methylene group in place of the NMe group at position 8 of physostigmine. Many of these 8-carbaphysostigmine analogues are more potent acetylcholinesterase inhibitors in vitro and less toxic in vivo than physostigmine. The (-)-enantiomer (e.g., 1d and 1g) possessing the same absolute configuration at C3a and C8a as that of physostigmine, is about 6 to 12-fold more potent at inhibiting acetylcholinesterase than the corresponding (+)-enantiomer (e.g., 1e and 1h).

Correlation of brain levels of 9-amino-1,2,3,4-tetrahydroacridine (THA) with neurochemical and behavioral changes

9-Amino-1,2,3,4-tetrahydroacridine (THA) has been reported to cause improvement in patients with senile dementia of the Alzheimer's type. We have examined some effects of THA in vitro and in vivo to define its mechanism of action. In vitro, THA inhibits acetylcholinesterase (AChE) (IC50 = 223 nM) and blocks [3H]AFDX-116 (M2) and [3H]telenzepine (M1) binding (IC50 s of 1.5 and 9.1 microM respectively). In vivo levels of THA were 10-fold higher in brain than plasma following 3.2 mg/kg i.p., a dose which was found to be active in reversing amnesia induced by scopolamine assessed in T-maze tests in rats and passive avoidance tests in mice. Additionally, these brain concentrations were above the IC50 of THA for AChE inhibition. THA (5.6-17.8 mg/kg i.p.) also elevated acetylcholine levels in the rat CNS. THA-induced side effects were blocked by the central muscarinic antagonist, scopolamine, but not by the peripheral antagonists methscopolamine and glycopyrrolate, nor by nicotinic antagonists. We conclude that brain AChE inhibition by THA is sufficient to explain its purported therapeutic activity in Alzheimer's disease and that its favorable brain/plasma distribution in vivo may account for its central cholinergic action without inducing the severe peripheral cholinergic effects typically seen with other AChE inhibitors.

Altered expression of genes for amyloid and cytoskeletal proteins in Alzheimer cortex

Recent studies have indicated a normal gene dose for the amyloid precursor protein (APP) in Alzheimer's disease (AD). These findings leave open the possibility that elevated levels of messenger RNA (mRNA) for this protein may contribute to the pathogenesis of AD. Using Northern analysis, we compared the levels of mRNA for the APP and 3 cytoskeletal proteins in parietal cortex of 6 brains having marked AD-type degeneration with the levels of these mRNAs in 6 control samples. The cytoskeletal mRNAs studied were those for the human neurofilament 68-kDa subunit (HNFL), for alpha-tubulin, and for glial fibrillary acidic protein (GFAP). A ribonuclease (RNase) protection assay was also used to compare AD and control HNFL mRNA levels. The mRNAs for APP, HNFL, and alpha-tubulin were diminished in AD cortex. The decrement for APP mRNA was less than that for HNFL or alpha-tubulin. The message for GFAP in AD cortex showed no loss. The findings support a general deficit in neuronal mRNAs, including that for APP. They do not exclude the possibility of elevated levels of the message for the APP in small neuronal subsets, in subcortical neurons projecting to cortex, or as a generalized phenomenon in earlier stages of the disease.

Chromosomal localization of the human proenkephalin and prodynorphin genes

DNA probes derived from rat and human proenkephalin and prodynorphin genes have been used to localize these two opiate neuropeptide genes on human chromosomes. Hybridization of probes to Southern blots made with DNAs from a rodent-human somatic-cell hybrid panel indicates localization of proenkephalin to human chromosome 8 and of prodynorphin to human chromosome 20. In situ hybridization to metaphase chromosomes confirms these assignments and indicates regional localizations of proenkephalin to 8q23-q24 and of prodynorphin to 20p12-pter. A human genomic prodynorphin clone reveals a frequent two-allele TaqI polymorphism.

Distribution of enkephalin-containing peptides within bovine chromaffin granules

The distribution of large enkephalin-containing peptides (ECP's) between soluble and membrane components of bovine chromaffin granules was examined by immunoblotting with synenkephalin antiserum which recognizes the NH2-terminus of proenkephalin. Immunoblots showed that the 23.3 and 18.2 kilodalton ECP's were present in both soluble and membrane granule compartments but the 12.6 kilodalton ECP was present only in the soluble fraction. These results suggest that the larger ECP's may be preferentially associated with the granule membrane and may be redistributed to the soluble granule compartment upon proteolytic processing.

Synenkephalin in bovine and human spinal cord

Synenkephalin, which comprises 70 residues at the aminoterminal of proenkephalin, was studied with immunocytochemical methods in the human and bovine spinal cord. Immunoreactive fibers had the same general distribution as methionine-enkephalin, but not as leucine-enkephalin fibers. They were found in all spinal layers and were most numerous in lamina II (outer zone) and V-VI (lateral portion). Synenkephalin immunoreactivity was overall less dense than that of the enkephalins. These results suggest that proenkephalin is the precursor protein also in enkephalinergic neurons of the human spinal cord.

Expression of the human proenkephalin gene in mouse pituitary cells: accurate and efficient mRNA production and proteolytic processing

A recombinant plasmid containing the human proenkephalin gene ligated to pBR322 was introduced into a mouse pituitary cell line (AtT-20D16v) that normally expresses pro-opiomelanocortin but not proenkephalin. The plasmid was introduced by co-transformation with the G418-selectable plasmid, pRSVneo. Stable transformants were isolated and analyzed for the presence of the human proenkephalin gene. AtT-20 transformants which had one or more copies of the human proenkephalin gene integrated stably into the mouse chromosomal DNA expressed a 1.45 kb mRNA identical in size to human proenkephalin mRNA. Primer extension analysis indicated that the human proenkephalin gene was accurately and efficiently transcribed from its own promoter. AtT-20 transformants that expressed the 1.45 kb human proenkephalin mRNA also expressed proenkephalin protein and cleaved the protein to form free Met-enkephalin. This is of particular interest because these cells do not cleave all of the available pairs of basic amino acids in the endogenous protein, pro-opiomelanocortin, the precursor to ACTH, beta-endorphin and melanocyte stimulating hormones. The release of both ACTH and Met-enkephalin from these cells is stimulated by corticotropin releasing factor, a natural secretagogue for ACTH, indicating that the two classes of peptide share a related secretory pathway.

Characterization of a new 23 kDalton enkephalin-containing protein in the bovine adrenal medulla

Immunoblots combined with specific radioimmunoassays (RIAs) have been used to visualize simultaneously all the enkephalin-containing peptides (ECPs) present in a crude extract of bovine adrenal medulla. They have allowed the characterization of a new high molecular weight ECP which has a molecular weight of 23.3 kDalton, contains the amino-terminal part of proenkephalin and ends with the sequence of Leu-enkephalin at its carboxy-terminus.

Release of synenkephalin from neuronal terminals in vitro

Synenkephalin, the amino-terminal 1-70 residues of proenkephalin is released intact from bovine globus pallidus following potassium-induced depolarization in vitro via a Ca++ dependent mechanism. The release of synenkephalin accompanies that of Met-enkephalin in a molar ratio of 1/4. In contrast to Met-enkephalin which is readily destroyed when released, synenkephalin is not destroyed.

Processing of proenkephalin is tissue-specific

Most neuropeptides are synthesized as large precursor proteins. These precursors undergo a maturation process involving several proteolytic events that generate the biologically active peptides. The enzymatic mechanisms underlying this processing are still largely unknown. The processing of the precursor protein proenkephalin was studied in two different bovine tissues, the hypothalamus and adrenal medulla. The high molecular weight enkephalin-containing peptides that accumulate in these two tissues were found to be different, indicating the existence of two processing pathways for this neuropeptide precursor.

Purification from brain of synenkephalin, the N-terminal fragment of proenkephalin

The primary sequence of adrenal proenkephalin was recently deduced from the structure of the cloned cDNA that codes for this protein. Several enkephalin-containing proteins with molecular weights between 8,000 and 20,000 daltons were purified from the bovine adrenal medulla. These proteins appear to represent intermediates in the processing of proenkephalin into physiologically active opioid peptides. While the concentrations of these large processing intermediates in the adrenal medulla are quite high, similar proteins have not yet been shown to be present in brain, and there is some question as to whether the brain synthesizes an enkephalin precursor similar to adrenal proenkephalin. We report here the purification from bovine caudate nucleus of synenkephalin, the N-terminal fragment of adrenal proenkephalin. The amino acid composition of synenkephalin indicates that the protein represents residues 1-70 of adrenal proenkephalin. Thus the brain and adrenal glands appear to utilize a similar precursor for enkephalin biosynthesis.

Synenkephalin is coreleased with met-enkephalin from neuronal terminals in vitro

Synenkephalin, the amino-terminal 1-70 residues of proenkephalin, is released intact from bovine globus pallidus and neurohypophysis following potassium-induced depolarization in vitro via a Ca2+-dependent mechanism. The release of synenkephalin accompanies that of Met-enkephalin in a molar ratio of 1/4. In contrast to Met-enkephalin, which is readily destroyed when released, synenkephalin is not destroyed.

Distribution and characterization of synenkephalin immunoreactivity in the bovine brain and pituitary

The distribution of synenkephalin, the N-terminal fragment of proenkephalin, was studied in various parts of the bovine brain (globus pallidus, caudate nucleus, hypothalamus) and in the posterior pituitary by the use of a radioimmunoassay. The distribution of synenkephalin-immunoreactivity (IR) was compared to the distribution of Met-enkephalin-IR. Gel exclusion chromatography was used to examine the molecular forms of the immunoreactivities present in the tissues. The distribution of synenkephalin-IR was similar to the distribution of Met-enkephalin-IR, with a molar ratio of Met-enkephalin/synenkephalin ranging between 2.7 and 5.9. In all regions tested except the hypothalamus the synenkephalin-IR was present as a single species. However, in the hypothalamus a small amount of IR material (3% of the total synenkephalin-IR) was detected in fractions where larger Met-enkephalin-containing peptides eluted. Based on the concordance between the molar ratio of Met-enkephalin to synenkephalin found in the tissues and the molar ratio present in the sequence of adrenal proenkephalin, it is concluded that the brain and adrenal glands utilize a similar precursor for enkephalin biosynthesis.

The enkephalinergic neuron: implications of a polyenkephalin precursor

The study of the biochemical and physiological functions of the enkephalinergic cell has greatly extended our understanding of peptidergic cells in general. In the adrenal gland, the major part of the proenkephalin-derived peptides is present as intermediates in the processing of the precursor. These peptides are contained within the adrenergic chromaffin granules, from which they are released in response to stimulation of the cell. The nature of the products released depends on the nature of the stimulus, but it appears that mature granules containing completely processed peptides are preferentially released under physiological conditions. In the brain, the presence and release of the heptapeptide that comprises the carboxyl terminus of adrenal proenkephalin suggest that similar mechanisms are operating centrally. The identity of brain and adrenal proenkephalin is further supported by the purification from brain of a large fragment of the proenkephalin molecule, synenkephalin , and the occurrence in brain of this and the other proenkephalin-derived peptides in a molar ratio close to that found in the sequence of the adrenal precursor. The processing of proenkephalin in brain appears to follow the classical models first proposed for peptide hormones (Steiner et al. 1980), which may thus be generalized to include peptide neurotransmitters/neuroregulators. In addition, the results presented in this paper indicate that enkephalins may be cotransmitters in at least two diverse systems. Enkephalins and catecholamines are colocalized in the adrenergic granules of the adrenal gland. In the brain, enkephalins and oxytocin are colocalized in the magnocellular neurons of the hypothalamo-neurohypophyseal oxytocinergic pathway. In both of these systems, the enkephalins are present in a molar concentration that is less than 1% of the concentration of the principal messenger. Such colocalization , coupled with the numerous active peptides that may arise from proenkephalin, suggests many elegant but complex schemes of neurotransmitter interactions. For example, release of enkephalins in the neurohypophysis may regulate oxytocin release through an action on autoreceptors of the oxytocinergic terminal. In the adrenal the coreleased enkephalins may act by regulating presynaptically the cholinergic output of the splanchnic nerve. However, further studies are needed to define clearly the physiological roles of such cotransmission . From the abundance of proenkephalin-derived peptides in the basal ganglia, it appears that enkephalins may represent the principal transmitter in some central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification of the N-terminal fragment of proenkephalin from bovine adrenal medulla

Two forms of the N-terminal fragment of proenkephalin have been purified from the bovine adrenal medulla and characterized. One of these proteins contains the sequence of Met-enkephalin and is composed of residues 1-77 of proenkephalin. The other protein does not contain Met-enkephalin and is composed of residues 1-72 of proenkephalin.