Biomedical subjects

David J Anderson

Publications and source records attributed to David J Anderson.

At least 55 records · Page 3Linked to original sources

PubMed2003

Diel changes in plasma melatonin and corticosterone concentrations in tropical Nazca boobies (Sula granti) in relation to moon phase and age.

We investigated the effects of moon phases and age on diel rhythms of plasma melatonin and corticosterone in free-living Nazca boobies (Sula granti) on the Galápagos Islands, Ecuador. Melatonin and corticosterone secretion are regulated by the circadian system and the two hormones play a role in the control of locomotor activity and foraging, which can be influenced by moon phases. These seabirds have a long life span and in many vertebrates circadian function deteriorates with age. The functioning of the circadian system under different environmental conditions and changes related to age are poorly understood and hardly studied in wild birds. Nazca boobies had generally low plasma melatonin concentrations but showed a diel variation with higher concentrations at 00:00 and 16:00h. The diel variations in melatonin concentrations disappeared during full moon, suggesting that natural light levels at night can suppress melatonin secretion in Nazca boobies. Maximal melatonin concentrations tended to decline in older birds (10-19 years). Birds showed a clear diel variation in basal plasma corticosterone with a peak in the early morning, before the active period begins, and low concentrations throughout the day. As with melatonin, there were no diel variations in corticosterone at full moon, which may be due to different activity patterns in response to food availability or changes in the circadian system. While other studies have found a relationship between corticosterone and melatonin, we found no such correlation in Nazca boobies. The lunar cycle appears to affect the hormone titers of Nazca boobies both directly and indirectly. First, melatonin rhythms can be directly affected by the light intensity associated with full moon. Second, prey availability may change foraging patterns and can therefore indirectly alter corticosterone secretion in Nazca boobies.

Aging↗

PubMed2003

Atypical expansion in mice of the sensory neuron-specific Mrg G protein-coupled receptor family.

The Mas-related genes (Mrgs) comprise a family of >50 G protein-coupled receptors (GPCRs), many of which are expressed in specific subsets of nociceptive sensory neurons in mice. In contrast, humans contain a related but nonorthologous family of genes, called MrgXs or sensory neuron-specific receptors, of which many fewer appear to be expressed in sensory neurons. To determine whether the diversity of murine Mrgs is generic to rodents or is an atypical feature of mice, we characterized MrgA, MrgB, MrgC, and MrgD subfamilies in rat and gerbil. Surprisingly, although mice have approximately 22 MrgA and approximately 14 MrgC genes, rats and gerbils have just a single MrgA and MrgC gene. This murine-specific expansion likely reflects recent retrotransposon-mediated unequal crossover events. The expression of Mrgs in rat sensory ganglia suggests that the extensive cellular diversity in mice can be simplified to a core subset of approximately four different genes (MrgA, MrgB, MrgC, and MrgD), defining a similar number of neuronal subpopulations. Our results suggest more generally that mouse-human genomic comparisons may sometimes reveal differences atypical of rodents.

Animals↗

PubMed2003

Neural correlates of competing fear behaviors evoked by an innately aversive stimulus.

Environment and experience influence defensive behaviors, but the neural circuits mediating such effects are not well understood. We describe a new experimental model in which either flight or freezing reactions can be elicited from mice by innately aversive ultrasound. Flight and freezing are negatively correlated, suggesting a competition between fear motor systems. An unfamiliar environment or a previous aversive event, moreover, can alter the balance between these behaviors. To identify potential circuits controlling this competition, global activity patterns in the whole brain were surveyed in an unbiased manner by c-fos in situ hybridization, using novel experimental and analytical methods. Mice predominantly displaying freezing behavior had preferential neural activity in the lateral septum ventral and several medial and periventricular hypothalamic nuclei, whereas mice predominantly displaying flight had more activity in cortical, amygdalar, and striatal motor areas, the dorsolateral posterior zone of the hypothalamus, and the vertical limb of the diagonal band. These complementary patterns of c-fos induction, taken together with known connections between these structures, suggest ways in which the brain may mediate the balance between these opponent defensive behaviors.

Acoustic Stimulation↗

PubMed2003

SOX10 maintains multipotency and inhibits neuronal differentiation of neural crest stem cells.

The mechanisms that establish and maintain the multipotency of stem cells are poorly understood. In neural crest stem cells (NCSCs), the HMG-box factor SOX10 preserves not only glial, but surprisingly, also neuronal potential from extinction by lineage commitment signals. The latter function is reflected in the requirement of SOX10 in vivo for induction of MASH1 and PHOX2B, two neurogenic transcription factors. Simultaneously, SOX10 inhibits or delays overt neuronal differentiation, both in vitro and in vivo. However, this activity requires a higher Sox10 gene dosage than does the maintenance of neurogenic potential. The opponent functions of SOX10 to maintain neural lineage potentials, while simultaneously serving to inhibit or delay neuronal differentiation, suggest that it functions in stem or progenitor cell maintenance, in addition to its established role in peripheral gliogenesis.

Animals↗

PubMed2003

Correlation between plasma steroids and chick visits by nonbreeding adult Nazca boobies.

Nonbreeding adult Nazca boobies (Sula granti) often approach unattended chicks and perform parental and/or aggressive behaviors toward the chicks. Earlier descriptions of these encounters included sexual behaviors as well. We studied hormonal correlates of chick visits by such nonbreeding boobies during the breeding season. We compared the hormonal status of chick-visiting adults with that of nonvisiting adults in the colony. We determined levels of corticosterone (CORT), testosterone (T), androstendione, dihydrotestosterone, and estradiol as potential candidate hormones controlling parental, aggressive, or sexual behavior. Only T and CORT differed between chick-visiting and nonvisiting adults. Chick-visiting adults had higher CORT levels after the interaction than nonvisiting adults randomly caught in the colony. To the contrary. T levels after interactions were lower in chick-visiting compared to random nonvisiting adults. T levels, however, did not vary with level of aggression among chick-visiting adults. We suggest that chick-visiting behavior may be permitted by low T levels and activated by, or resulting in, high CORT levels.

Aggression↗

PubMed2003

Prosthetic stimulation of the auditory system with intraneural electrodes.

Prosthetic electrical stimulation of the auditory system is presently accomplished either via scala tympani electrode arrays or via cochlear nucleus surface electrode arrays. Many of the early cochlear implant studies, however, used electrode arrays placed within the auditory nerve itself--either within the modiolus or within the trunk of the nerve. For many reasons, such intraneural electrode arrays were abandoned in favor of intrascalar arrays. There remain, however, several theoretical and practical reasons why intraneural arrays might be advantageous, and recent developments in electrode technology solve many of the problems posed by early attempts at intraneural stimulation. In this article, we review the history and current status of intraneural auditory stimulation, and present some preliminary results of this mode of stimulation in an animal model.

Animals↗

PubMed2003

Waved albatrosses can navigate with strong magnets attached to their head.

The foraging excursions of waved albatrosses Phoebastria irrorata during incubation are ideally suited for navigational studies because they navigate between their Galápagos breeding site and one specific foraging site in the upwelling zone of Peru along highly predictable, straight-line routes. We used satellite telemetry to follow free-flying albatrosses after manipulating magnetic orientation cues by attaching magnets to strategic places on the birds' heads. All experimental, sham-manipulated and control birds, were able to navigate back and forth from Galápagos to their normal foraging sites at the Peruvian coast over 1000 km away. Birds subjected to the three treatments did not differ in the routes flown or in the duration and speed of the trips. The interpretations and implications of this result depend on which of the current suggested magnetic sensory mechanisms is actually being used by the birds.

Animals↗

PubMed2002

Synthesis and biological evaluation of pyridine-modified analogues of 3-(2-aminoethoxy)pyridine as novel nicotinic receptor ligands.

Analogues of the potent nicotinic receptor agonist 3-(2-aminoethoxy)pyridine substituted at the 5' and 6'-positions of the pyridine ring were synthesized and tested in vitro for nicotinic receptor binding activity (displacement of [(3)H](-)cytisine from whole rat brain synaptic membranes). The substituted analogues exhibited K(i) values ranging from 0.076 to 319 nM compared to a K(i) value of 26 nM for compound 1. Among the compounds tested, 5'-vinyl-6'-chloro substituted 1 was the most potent.

Animals↗

PubMed2002

Gradient chromatofocusing. versatile pH gradient separation of proteins in ion-exchange HPLC: characterization studies.

A new chromatofocusing technique called gradient chromatofocusing is characterized. Gradient chromatofocusing generates linear pH gradients on anion-exchange columns with inexpensive low molecular mass buffer components via HPLC gradient mixing. Gradient chromatofocusing results are compared with that of conventional chromatofocusing in the chromatography of several proteins on a Mono P column, including beta-lactoglobulin A and B, ovalbumin, BSA, and conalbumin. Gradient chromatofocusing shows superior performance, with resolution increases greater than 3-fold being realized for the entire protein mixture and up to 25-fold for a particular protein pair. This performance superiority arises from inherent advantages in the gradient chromatofocusing technique in optimizing conditions pertinent to separation, including buffer concentration and pH gradient slope. These resolution gains arise from both increases in separation factor and decreases in peak width achieved with the pH gradient chromatofocusing technique through the manipulation of buffer concentration and the pH gradient profile. Gradient chromatofocusing is also compared with conventional NaCl gradient ion-exchange chromatography using the same Mono P column, demonstrating 3-fold resolution gains, resulting from a 3-fold decrease in peak width. The present work demonstrates the significantly improved performance that gradient chromatofocusing has in protein separations compared to other ion-exchange chromatographic techniques. Mechanisms for the various effects are discussed.

Animals↗

PubMed2002

Orphan G protein-coupled receptors MrgA1 and MrgC11 are distinctively activated by RF-amide-related peptides through the Galpha q/11 pathway.

MrgA1 and MrgC11 belong to a recently identified family of orphan G-protein coupled receptors, called mrgs (mas-related genes). They are only expressed in a specific subset of sensory neurons that are known to detect painful stimuli. However, the precise physiological function of Mrg receptors and their underlying mechanisms of signal transduction are not known. We therefore have screened a series of neuropeptides against human embryonic kidney (HEK) 293 cells that stably express either MrgA1 or MrgC11 to identify ligands and/or agonists. MrgA1- or MrgC11-specific agonists stimulated dose-dependent increases in intracellular free Ca(2+) in a pertussis toxin-insensitive manner, but failed to alter basal or forskolin-stimulated levels of intracellular cAMP. Furthermore, studies using embryonic fibroblasts derived from various Galpha protein knockout mice demonstrated that both the MrgA1 and MrgC11 receptors are coupled to the Galpha(q/11) signaling pathway. Screening of neuropeptides identified surrogate agonists, most of these peptides included a common C-terminal -RF(Y)G or -RF(Y) amide motif. Structure-function studies suggest that endogenous ligands of Mrg receptors are likely to be RF(Y)G and/or RF(Y) amide-related peptides and that postprocessing of these peptides may serve to determine Mrg receptor-ligand specificity. The differences in ligand specificity also suggest functional diversity amongst the Mrg receptors.

Amino Acid Sequence↗

PubMed2002

Selective electrical silencing of mammalian neurons in vitro by the use of invertebrate ligand-gated chloride channels.

Selectively reducing the excitability of specific neurons will (1) allow for the creation of animal models of human neurological disorders and (2) provide insight into the global function of specific sets of neurons. We focus on a combined genetic and pharmacological approach to silence neurons electrically. We express invertebrate ivermectin (IVM)-sensitive chloride channels (Caenorhabditis elegans GluCl alpha and beta) with a Sindbis virus and then activate these channels with IVM to produce inhibition via a Cl- conductance. We constructed a three-cistron Sindbis virus that expresses the alpha and beta subunits of a glutamate-gated chloride channel (GluCl) along with the green fluorescent protein (EGFP) marker. Expression of the C. elegans channel does not affect the normal spike activity or GABA/glutamate postsynaptic currents of cultured embryonic day 18 hippocampal neurons. At concentrations as low as 5 nm, IVM activates a Cl- current large enough to silence infected neurons effectively. This conductance reverses in 8 hr. These low concentrations of IVM do not potentiate GABA responses. Comparable results are observed with plasmid transfection of yellow fluorescent protein-tagged (EYFP) GluCl alpha and cyan fluorescent protein-tagged (ECFP) GluCl beta. The present study provides an in vitro model mimicking conditions that can be obtained in transgenic mice and in viral-mediated gene therapy. These experiments demonstrate the feasibility of using invertebrate ligand-activated Cl- channels as an approach to modulate excitability.

Action Potentials↗

PubMed2002

6-Chloropyridazin-3-yl derivatives active as nicotinic agents: synthesis, binding, and modeling studies.

3,8-Diazabicyclo[3.2.1]octane (1), 2,5-diazabicyclo[2.2.1]heptane (2), piperazine (3), and homopiperazine (4) derivatives, substituted at one nitrogen atom with the 6-chloro-3-pyridazinyl group while the other nitrogen atom was either unsubstituted or mono- or dimethylated, were synthesized and tested for their affinity toward the neuronal nicotinic acetylcholine receptors (nAChRs). All of the compounds had K(i) values in the nanomolar range. A molecular modeling study allowed location of their preferred conformations, the energies of which were recalculated in water with a continuum solvent model. Some of the compounds showed, in their populated conformations, only pharmacophoric distances longer than the values taken into consideration by the Sheridan model for nAChRs receptors. Thus, this SAR study gives support to the hypothesis that these longer distances are still compatible with affinity for alpha4beta2 receptors in the nanomolar range.

Animals↗

PubMed2002

Conformationally constrained nicotines: polycyclic, bridged, and spiro-annulated analogues as novel ligands for the nicotinic acetylcholine receptor.

A set of novel nicotine-related, conformationally constrained compounds, including tetracyclic, bridged (4), and tricyclic, spiro-annulated (5) structures, were synthesized in a straightforward manner and optically resolved in a convenient fashion with (+)- and (-)-O,O'-di-p-toluoyltartaric acids. Absolute configurations were determined by X-ray crystallography. These compounds were evaluated for their ability to displace [(3)H]cytisine in a rat forebrain preparation and compared to (-)-nicotine. Three substances emerged with high affinity in the low nanomolar range. Moreover, one of these compounds ((+)-5b) showed not only high binding affinity (K(i) = 4.79 nM) but also significant enantioselectivity over its antipode (K(i) = 148 nM), supporting the hypothesis that conformational restraint can lead to high-affinity ligands, which are stereochemically discriminated by the nicotinic acetylcholine receptor and may feature optimum locations of the active sites of the pharmacophore.

Animals↗

PubMed2002

Global analysis of the Deinococcus radiodurans proteome by using accurate mass tags.

Understanding biological systems and the roles of their constituents is facilitated by the ability to make quantitative, sensitive, and comprehensive measurements of how their proteome changes, e.g., in response to environmental perturbations. To this end, we have developed a high-throughput methodology to characterize an organism's dynamic proteome based on the combination of global enzymatic digestion, high-resolution liquid chromatographic separations, and analysis by Fourier transform ion cyclotron resonance mass spectrometry. The peptides produced serve as accurate mass tags for the proteins and have been used to identify with high confidence >61% of the predicted proteome for the ionizing radiation-resistant bacterium Deinococcus radiodurans. This fraction represents the broadest proteome coverage for any organism to date and includes 715 proteins previously annotated as either hypothetical or conserved hypothetical.

Bacteria↗

PubMed2002

Sensory nerves determine the pattern of arterial differentiation and blood vessel branching in the skin.

Nerves and blood vessels are branched structures, but whether their branching patterns are established independently or coordinately is not clear. Here we show that arteries, but not veins, are specifically aligned with peripheral nerves in embryonic mouse limb skin. Mutations that eliminate peripheral sensory nerves or Schwann cells prevent proper arteriogenesis, while those that disorganize the nerves maintain the alignment of arteries with misrouted axons. In vitro, sensory neurons or Schwann cells can induce arterial marker expression in isolated embryonic endothelial cells, and VEGF(164/120) is necessary and sufficient to mediate this induction. These data suggest that peripheral nerves provide a template that determines the organotypic pattern of blood vessel branching and arterial differentiation in the skin, via local secretion of VEGF.

Animals↗

PubMed2002

Transient expression of the bHLH factor neurogenin-2 marks a subpopulation of neural crest cells biased for a sensory but not a neuronal fate.

Lineage-tracing experiments have indicated that some premigratory neural crest cells (NCCs) are pleuripotent, generating sensory and sympathetic neurons and their associated glia. Using an inducible Cre recombinase-based fate mapping system, we have permanently marked a subpopulation of NCCs that expresses Ngn2, a bHLH transcription factor required for sensory neurogenesis, and compared its fate to the bulk NCC population marked by expression of Wnt1. Ngn2(+) progenitors were four times more likely than Wnt1(+) NCCs to contribute to sensory rather than sympathetic ganglia. Within dorsal root ganglia, however, both Ngn2- and Wnt1-expressing cells were equally likely to generate neurons or glia. These data suggest that Ngn2 marks an NCC subpopulation with a predictable fate bias, early in migration. Taken together with previous work, these data suggest that NCCs become restricted to sensory or autonomic sublineages before becoming committed to neuronal or glial fates.

Animals↗

PubMed2002

The bHLH transcription factors OLIG2 and OLIG1 couple neuronal and glial subtype specification.

OLIG1 and OLIG2 are basic-helix-loop-helix (bHLH) transcription factors expressed in the pMN domain of the spinal cord, which sequentially generates motoneurons and oligodendrocytes. In Olig1/2 double-mutant mice, motoneurons are largely eliminated, and oligodendrocyte differentiation is abolished. Lineage tracing data suggest that Olig1(-/-)2(-/-) pMN progenitors instead generate V2 interneurons and then astrocytes. This apparent conversion likely reflects independent roles for OLIG1/2 in specifying motoneuron and oligodendrocyte fates. Olig genes therefore couple neuronal and glial subtype specification, unlike proneural bHLH factors that control the neuron versus glia decision. Our results suggest that in the spinal cord, Olig and proneural genes comprise a combinatorial code for the specification of neurons, astrocytes, and oligodendrocytes, the three fundamental cell types of the central nervous system.

Animals↗

PubMed2002

Developmental changes in Notch1 and numb expression mediated by local cell-cell interactions underlie progressively increasing delta sensitivity in neural crest stem cells.

Neural stem cells become progressively less neurogenic and more gliogenic with development. Here, we show that between E10.5 and E14.5, neural crest stem cells (NCSCs) become increasingly sensitive to the Notch ligand Delta-Fc, a progliogenic and anti-neurogenic signal. This transition is correlated with a 20- to 30-fold increase in the relative ratio of expression of Notch and Numb (a putative inhibitor of Notch signaling). Misexpression experiments suggest that these changes contribute causally to increased Delta sensitivity. Moreover, such changes can occur in NCSCs cultured at clonal density in the absence of other cell types. However, they require local cell-cell interactions within developing clones. Delta-Fc mimics the effect of such cell-cell interactions to increase Notch and decrease Numb expression in isolated NCSCs. Thus, Delta-mediated feedback interactions between NCSCs, coupled with positive feedback control of Notch sensitivity within individual cells, may underlie developmental changes in the ligand-sensitivity of these cells.

Animals↗