Chronic Exposure to Adenosine Receptor Agonists and Antagonists Reciprocally Regulates the A1 Adenosine Receptor-Adenylyl Cyclase System in Cerebellar Granule Cells

Abstract: Chronic treatment with the adenosine receptor antagonist caffeine evokes an up-regulation of A₁ adenosine receptors and increased coupling of the receptor to G proteins in rat brain membranes. However, chronic agonist exposure has not been explored. Primary cultures of cerebellar granule cells were exposed chronically to A₁ adenosine receptor agonists and antagonists. Exposure to the A₁ adenosine receptor agonist N ⁶-cyclopentyladenosine resulted in (1) a time- and concentration-dependent reduction in the density of receptors labeled by 1,3-[³H]dipropyl-8-cyclopentylxanthine, (2) an enhanced ability of guanyl nucleotides to decrease the fraction of A₁ adenosine receptor sites displaying high affinity for 2-chloroadenosine, and (3) a functional uncoupling of receptors from adenylyl cyclase (EC 4.6.1.1). The adenosine antagonists caffeine and 8- p -sulfophenyltheophylline produced alterations in A₁ adenosine receptor homeostasis that were antipodal to those associated with agonist treatment. Antagonist exposure (1) increased the density of A₁ adenosine receptors in cerebellar granule cell membranes, (2) blunted the effect of guanyl nucleotides on receptor coupling to G proteins, and (3) increased the functional coupling of receptors to adenylyl cyclase inhibition. Forskolin treatment of cerebellar granule cells did not affect receptor density, suggesting that cyclic AMP is not involved in the regulation of A₁ adenosine receptor expression.     

NMR Studies of Pi-Containing Extracellular and Cytoplasmic Compartments in Brain

Abstract: The inorganic phosphate (P_i) NMR peak in brain has an irregular shape, which suggests that it represents more than a single homogeneous pool of P_i. To test the ability of the Marquardt-Levenberg (M-L) nonlinear curve fit algorithm software (Peak-Fit) to separate multiple peaks, locate peak centers, and estimate peak heights, we studied simulated P_i spectra with defined peak centers, areas, and signal-to-noise (S/N) ratios ranging from ∞ to 5.8. As the S/N ratio decreased below 15, the M-L algorithm located peak centers accurately when they were detected; however, small peaks tended to grow smaller and disappear, whereas the amplitudes of larger peaks increased. We developed an in vitro three-compartment model containing a mixture of P_i buffer, phosphocreatine, phosphate diester, and phosphate monoester (PME), portions of which were adjusted to three different pHs before addition of agar. Weighed samples of each buffered gel together with phospholipid extract and bone chips were placed in an NMR tube and covered with mineral oil. Following baseline correction, it was possible to separate the P_i peaks arising from the three compartments with different pH values if each peak made up 10–35% of total P_i area. In vivo, we identified the plasma compartment by intraarterial infusion of P_i. It was assumed that intracellular compartments contained high-energy phosphates and took up glucose. Based on these assumptions we subjected the brains to complete ischemia and observed that P_i compartments at pH 6.82, 6.92, 7.03, and 7.13 increased markedly in amplitude. If the brain cells took up and phosphorylated 2-deoxyglucose (2-DG), 2-DG-6-phosphate (2-DG-6-P) would appear in the PME portion of the spectrum ionized according to pH_i. Four 2-DG-6-P peaks with calculated pH values of 6.86, 6.94, 7.04, and 7.15 did appear in the spectrum, thereby confirming that the four larger P_i peaks represented intracellular spaces.     

Two amino acid residues confer type specificity to a neutralizing, conformationally dependent epitope on human papillomavirus type 11.

Characterization of virus binding by neutralizing antibodies is important both in understanding early events in viral infectivity and in development of vaccines. Neutralizing monoclonal antibodies (MAbs) to human papillomavirus type 11 (HPV11) have been described, but mapping the binding site has been difficult because of the conformational nature of key type-specific neutralization epitopes on the L1 coat protein. We have determined those residues of the L1 protein of HPV11 which confer type specificity to the binding of HPV11-neutralizing MAbs. Binding of three HPV11-specific neutralizing MAbs could be redirected to HPV6 L1 virus-like particles in which as few as two substitutions of corresponding amino acid residues from HPV11 L1 have been made, thus demonstrating the importance of these residues to MAb binding through the transfer of a conformationally dependent epitope. In addition, a fourth neutralizing MAb could be distinguished from the other neutralizing MAbs in terms of the amino acid residues which affect binding, suggesting the possibility that it neutralizes HPV11 through a different mechanism.     

CORRELATED EVOLUTION OF SELF-FERTILIZATION AND INBREEDING DEPRESSION: AN EXPERIMENTAL STUDY OF NINE POPULATIONS OF AMSINCKIA (BORAGINACEAE)

The relation between inbreeding depression and rate of self-fertilization was studied in nine natural populations of the annual genus Amsinckia. The study included two clades (phylogenetic lineages) in which small-flowered, homostylous populations or species are believed to have evolved from large-flowered, heterostylous, self-compatible ones. In one lineage the small-flowered species is tetraploid with disomic inheritance. Rates of self-fertilization were 25% to 55% in the four large-flowered, heterostylous populations; 72% in a large-flowered but homostylous population; and greater than 99.5% in the four small-flowered, homostylous populations, which produce seed autonomously. When present, inbreeding depression occurred in the fertility but not the survival components of fitness. Using a cumulative fitness measure incorporating both survival and fertility (flower number), we found inbreeding depression to be lower in the four very highly self-fertilizing populations than in the five intermediate ones. The Spearman rank correlation between inbreeding depression and selfing rate for the nine populations was –0.50, but was not statistically significant (P = 0.12). Inbreeding depression was greater in the two tetraploid populations than in the very highly self-fertilizing, diploid ones. Phenotypic stability of progeny from self-fertilization tended to be higher in populations with lower inbreeding depression. We conclude that levels of self-fertilization and inbreeding depression in Amsinckia are determined more by other factors than by each other. Estimates of mutation rates and dominance coefficients of deleterious alleles, obtained from a companion study of the four highly self-fertilizing populations, suggest that a strong relationship may not be expected. We discuss the relationship of the present results to current theory of the coevolution of self-fertilization and inbreeding depression.     

GOOD GENES AND DIRECT SELECTION IN THE EVOLUTION OF MATING PREFERENCES

A model is used to study quantitatively the impact of a good genes process and direct natural selection on the evolution of a mating preference. The expression of a male display trait is proportional to genetic quality, which is determined by the number of deleterious mutations a male carries throughout his genome. Genetic variances and covariances, including the covariance between the preference and male trait that drives the good genes process, are allowed to evolve under an infinitesimal model. Results suggest that the good genes process generates only weak indirect selection on preferences, with an effective selection intensity of a few percent or less. If preferences are subject to direct natural selection of the intensity observed for other characters, the good genes process alone is not expected to exaggerate the male trait by more than a few phenotypic standard deviations, contrary to what is observed in highly sexually selected species. Good genes can, however, cause substantial exaggeration if preference genes are nearly selectively neutral. Alternatively, direct selection on preference genes, acting on mating behavior itself or on the genes' pleiotropic effects, can cause mating preferences and male display traits to be exaggerated by any degree. Direct selection of preference genes may therefore play an important role in species that show extreme sexual selection.     

Temporal changes in the level of infestation of Simulium ornatum Meigen (complex) (Simuliidae: Diptera) larvae by the endosymbiotic fungus Harpella melusinae Lichtwardt (Harpellales: Trichomycetes)

The fungus Harpella melusinae (Harpellales: Trichomycetes) is obligately associated with the midguts of larval Simuliidae (Diptera). The level of infestation of a population of Simulium ornatum by H. melusinae was monitored at a stream in Hampshire, England. Significant temporal changes in the level of infestation were recorded during monthly and weekly collections; a twenty-fold increase being recorded over a nine-day period. Possible mechanisms by which these changes occur are discussed.     

Foraging ecology of Gentoo Penguins Pygoscelis papua at Macquarie Island during the period of chick care

The diet, diving behaviour, swimming velocity and foraging range of Gentoo Penguins Pygoscelis papua were studied at Macquarie Island during the breeding season in the 1993–1994 austral summer. Gentoo Penguins are considered to be inshore feeders, and at Macquarie Island the diet and estimated foraging ranges supported this. The diet consisted of 91.6% fish and 8.3% squid, by mass. The dominant prey taxa were the fish Gymnoscopelus sp. and Paranotothenia magellanica. A mixture of pelagic and benthic prey was consumed, with a greater proportion of benthic species occurring later in the season. The penguins exhibited a strong diurnal pattern in their diving behaviour. Deep diving (≥30 m) began near sunrise (03.00 h) and finished close to sunset (21.00 h). Diving at night was less common and very shallow (<10 m). Early in the breeding season, dive profiles indicated that birds were probably following vertically migrating pelagic prey through the water column and were foraging in waters over 100 m deep. Later in the season, more uniform, shallower depths were used, suggesting an increase in benthic foraging activity. These changes in dive pattern and depth were consistent with the habitat preferences of prey species found in the diet. Gentoo Penguins swam at 1.04 m per s and had a maximum potential foraging range of about 26 km for single-day trips. They tended to forage within 14 km of the colony, with a mean range of 5.4 km. This range encompassed the deep ocean habitat to the west and east of the island and a shallow area to the north.     

Facultative mutualism between an herbivorous crab and a coralline alga: advantages of eating noxious seaweeds

Because encrusting coralline algae rely on herbivory or low light levels to prevent being overgrown by competitively superior fleshy algae, corallines are relatively rare in shallow areas with low rates of herbivory. In contrast to this general trend, the branching coralline alga Neogoniolithon strictum occurs primarily in shallow seagrass beds and along the margins of shallow reef flats where herbivory on macrophytes is low. This alga apparently persists in these habitats by providing refuge to the herbivorous crab Mithrax sculptus at mean densities of 1 crab per 75 g of algal wet mass. When crabs were removed from some host corallines, hosts without crabs supported 9 times the epiphytic growth of hosts with crabs after only 30 days. Crabs without access to a coralline alga were rapidly consumed by reef fishes, while most of those tethered near a host alga survived. These results suggest that the crabs clean their algal host of fouling seaweeds and associate with the host to minimize predation. However, to effectively clean the host, the crab must consume the wide array of macroalgae that commonly co-occur with coralline algae in these habitats, including chemically defended species in the genera Halimeda, Dictyota, and Laurencia. Crabs did readily consume these seaweeds, which were avoided by, and are chemically defended from, herbivorous fishes. Even though crabs readily consumed both Halimeda and Dictyota in whole-plant feeding assays, chemical extracts from these species significantly reduced crab feeding, suggesting that factors other than secondary chemistry (e.g., food value, protein, energy content), may determine whole-plant palatability. Having the ability to use a wide variety of foods, and choosing the most profitable rather than the least defended foods, would diminish foraging time, increase site fidelity, and allow the crab to function mutualistically with the host alga. Despite the obvious benefit of associating with N. strictum, M. sculptus did not prefer it over other habitats offering a structurally similar refuge, suggesting that these crabs are not N. strictum specialists, but rather occupy multiple habitats that provide protection from predators. Structurally complex organisms like N. strictum may commonly suppress competitors by harboring protective symbionts like M. sculptus. It is possible that diffuse coevolution has occurred between these two groups; however, this seems unlikely because both herbivore and host appear to respond most strongly to selective pressures from predators and competitors outside this association.     

Duplication of the PMP22 gene in 17p partial trisomy patients with Charcot-Marie-Tooth type-1A neuropathy

Autosomal dominant Charcot-Marie-Tooth type-1A neuropathy (CMT1A) is a demyelinating peripheral nerve disorder that is commonly associated with a submicroscopic tandem DNA duplication of a 1.5-Mb region of 17p11.2p12 that contains the peripheral myelin gene PMP22. Clinical features of CMT1A include progressive distal muscle atrophy and weakness, foot and hand deformities, gait abnormalities, absent reflexes, and the completely penetrant electrophysiologic phenotype of symmetric reductions in motor nerve conduction velocities (NCVs). Molecular and fluorescence in situ hybridization (FISH) analyses were performed to determine the duplication status of the PMP22 gene in four patients with rare cytogenetic duplications of 17p. Neuropathologic features of CMT1A were seen in two of these four patients, in addition to the complex phenotype associated with 17p partial trisomy. Our findings show that the CMT1A phenotype of reduced NCV is specifically associated with PMP22 gene duplication, thus providing further support for the PMP22 gene dosage mechanism for CMT1A. Received: 3 May 1995 / Revised: 1 August 1995