GABAB Receptor-Mediated Enhancement of Vasoactive Intestinal Peptide-Stimulated Cyclic AMP Production in Slices of Rat Cerebral Cortex

Basal and vasoactive intestinal peptide (VIP)-stimulated accumulations of cyclic AMP were measured in slices of rat cerebral cortex. Neither gamma-aminobutyric acid (GABA) nor the selective GABAB receptor agonist (-)-baclofen stimulated basal cyclic AMP accumulation, whereas VIP caused a large dose-dependent increase in cyclic AMP levels. However, in the presence of 100 microM (-)-baclofen, the effects of VIP on cyclic AMP accumulation were significantly enhanced, with the responses to 1 microM and 10 microM VIP being approximately doubled. The enhancing effects of (-)-baclofen was dose related (1-1,000 microM), but an enhancing effect was not observed with 100 microM (+)-baclofen. In the presence of the GABA uptake inhibitor nipecotic acid (1 mM), GABA caused a similar dose-related enhancement of the VIP response. The ability of either GABA or (-)-baclofen to augment VIP-stimulated production of cyclic AMP was not mimicked by the GABAA, agonists isoguvacine and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and was not antagonized by the GABAA antagonist bicuculline. The putative GABAB antagonist 5-aminovaleric acid (1 mM) significantly reduced the effect of (-)-baclofen. The ability of (-)-baclofen to enhance VIP-stimulated accumulation of cyclic AMP was observed in slices of rat cerebral cortex, hippocampus, and hypothalamus. These results indicate that GABA and (-)-baclofen can enhance VIP-stimulated accumulation of cyclic AMP in rat brain slices via an interaction with specific GABAB receptors.     

Physical and biotic determinants of space utilization by the Galapagos land iguana (Conolophus pallidus)

Summary Home ranges of the Galapagos land iguana (Conolophus pallidus) were examined with respect to food availability and the thermal environment. Activity patterns, the amount of space used per day, and time required to use the entire home range were also investigated. The effects of, and the relationships between, these factors vary seasonally, as do home range sizes and preferred body temperatures.Food supplementation experiments resulted in only temporary reductions in use of space. Home range sizes were not different between the seasons with the least (Fall) and the most (Hot) food availalble, but home ranges were significantly smaller in Garua when food supplies were low, but not as low as in Fall. Calculations of metabolic expenditures in each season suggests that food availability alone does not explain seasonal patterns of home range size in this species.The thermal environment within each home range was characterized by microclimatic measurements and measurements of the area of sun, shade, and semi-shade. An index with units of m²h was used to quantify the thermal quality of each home range. Iguanas exploited optimal (with respect to body temperature) conditions more than would be expected from random use of their home ranges. Thermal transients (due to large body size) and optimal conditions were exploited to the largest degree in Fall.During Garua, low metabolic rates and time constraints imposed by an abundance of stressful thermal environments may result in small home ranges. In Fall, increased temperatures cause higher metabolic rates and allow more time for exploitation of the cooler portions of the home range, hence, home range sizes increase. In the Hot season, there is abundant food and optimal thermal conditions, but home ranges remain large. Searching for preferred foods may cause the large home ranges in this season.     

Oxalate digestibility in Neotoma albigula and Neotoma mexicana

Summary The cactus specialist, Neotoma albigula, tolerates high concentrations of potentially harmful oxalate compounds in its diet. Previous research has shown that oxalate compounds are broken down by intestinal micro-organisms. Thus the ability of N. albigula to utilize a diet high in oxalates may be a consequence of the adaptation of the microflora rather than its own evolution. To test this hypothesis, the oxalate degradation ability of N. albigula was compared with that of N. mexicana, a generalist herbivore. Apparent oxalate digestibility was not significantly different in the two species, when tested using field-acclimated individuals. Analysis of scats recovered from traps indicated that both species were consuming oxalates in the wild. I conclude that the ability of these herbivores to tolerate oxalates is a natural consequence of the utilization of microbial fermentation to degrade the structural carbohydrates of plants coupled with the high adaptive and evolutionary potential of the microflora.     

Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism

Branched-chain amino acid metabolism in skeletal muscte promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation.     

Propagation in vitro of the apple rootstock M4: effect of phytohormones on shoot quality

The quality of shoots in cultures of the apple rootstock, M4, was used as a criterion for the selection of an optimum medium. The frequency of shoots in defined shoot clases was monitored for each of five media, which differed in the type and concentration of phytohormone. Media containing BA (1.15 mg l^-1) and IBA (either 0.15 or 0.20 mg l^-1) produced the maximum number of shoots that were desirable for transplantation and acclimatization.     

Queuosine modification of the wobble base in tRNAHis influences ''in vivo'' decoding properties.

The 'in vivo' decoding properties of four tRNAHis isoacceptors, two from Drosophila melanogaster and two from brewer's yeast, were studied after their microinjection, along with turnip yellow mosaic virus (TYMV) coat protein mRNA, into Xenopus laevis oocytes. The two Drosophila isoacceptors are identical besides containing either a guanosine (G) or the hypermodified nucleoside queuosine (Q) in the wobble position. The brewer's yeast isoacceptors differ by four bases in the anticodon stem, and by one base in the amino acceptor stem. Our results show that, under competing 'in vivo' conditions, the Drosophila tRNAHis with the anticodon GUG clearly prefers the histidine codon CAC to the codon CAU, whereas little preference is observed for the tRNAHis with the anticodon QUG for the codon CAU, and no preference for either codon by the two yeast isoacceptors. Hence, it can be concluded that the presence of the Q-base clearly affects the choice of the codon. This is the first demonstration of an 'in vivo' codon preference by tRNA isoacceptors differing in the modification of the wobble base during the elongation step of protein synthesis. These results imply that one function of the Q-base is at the translational level.     

Prevalence of helminths in a cyclic snowshoe hare population

Five species of helminths were monitored in a population of snowshoe hares (Lepus americanus) near Rochester, Alberta, during 1961-1977. Prevalence of both Obeliscoides cuniculi and Protostrongylus boughtoni among young hares averaged about 50% by age 2 mo, then tended to level off. Prevalence of Taenia pisiformis (cysticerci) and Dirofilaria scapiceps rose more slowly, but continued to increase steadily beyond their mean levels of 8% and 1% at age 2 mo. There were well defined seasonal (within-year) cycles in prevalence of O. cuniculi and P. boughtoni that were generated evidently to a major degree by arrested development of larvae in fall and renewed development in late winter. It was hypothesized that renewed larval development was triggered (in February) in O. cuniculi by the seasonal rise of circulating pituitary gonadotrophins, and (in April) in P. boughtoni by the seasonal rise of gonadal androgens and estrogens. Indices to gonadal hormone levels in hares indicated that these increased most rapidly among males, and may have accounted for the higher prevalences of P. boughtoni in males during April-May. Neither T. pisiformis nor D. scapiceps exhibited conspicuous seasonal changes in prevalence. Maximum prevalence of T. pisiformis was attained at about 1 yr of age, whereas D. scapiceps increased among adult snowshoes through age 2 yr before stabilizing. Long-term (between-year) changes in prevalence of O. cuniculi, T. pisiformis, and D. scapiceps were correlated significantly with the cyclic hare population which declined from a peak in fall 1961 to a low in 1965-1966, rose to another peak by fall 1970, and declined again to a low in 1975. There was no detectable time lage between this "10-yr" cycle in hare density and the cycles of parasite prevalence among juveniles (less than 1 yr of age). Among adult hares, the cycle of O. cuniculi prevalence was likewise synchronous with that of the hare population, but the cycles of D. scapiceps and T. pisiformis lagged by approximately 1 and 2 yr, respectively. This lag in T. pisiformis prevalence was largely inexplicable to us. Our data on P. boughtoni were not suitable for analyses of between-year trends; nor were those for the fifth helminth, Taenia serialis (coenuri), because mean prevalence was less than 1% among both juveniles and adults. An apparent decline in T. serialis after the early 1950's, and its continued scarcity thereafter, paralleled a major change in numbers of one important definitive host--the red fox (Vulpes vulpes).(ABSTRACT TRUNCATED AT 400 WORDS)     

A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera

Levels of mitochondrial DNA (mtDNA) sequence divergence between species within each of several avian (Anas, Aythya, Dendroica, Melospiza, and Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were compared. An analysis of digestion profiles generated by 13-18 restriction endonucleases indicates little overlap in magnitude of mtDNA divergence for the avian versus nonavian taxa examined. In 55 interspecific comparisons among the avian congeners, the fraction of identical fragment lengths (F) ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these translate into estimates of nucleotide sequence divergence (p) ranging from 0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater than 0.070. The small mtDNA distances among avian congeners are associated with protein-electrophoretic distances (D values) less than approximately 0.2, while the mtDNA distances among assayed fish and amphibian congeners are associated with D values usually greater than 0.4. Since the conservative pattern of protein differentiation previously reported for many avian versus nonavian taxa now appears to be paralleled by a conservative pattern of mtDNA divergence, it seems increasingly likely that many avian species have shared more recent common ancestors than have their nonavian taxonomic counterparts. However, estimates of avian divergence times derived from mtDNA- and protein-calibrated clocks cannot readily be reconciled with some published dates based on limited fossil remains. If the earlier paleontological interpretations are valid, then protein and mtDNA evolution must be somewhat decelerated in birds. The empirical and conceptual issues raised by these findings are highly analogous to those in the long-standing debate about rates of molecular evolution and times of separation of ancestral hominids from African apes.      

Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes

Statistical methods for computing the standard errors of the branching points of an evolutionary tree are developed. These methods are for the unweighted pair-group method-determined (UPGMA) trees reconstructed from molecular data such as amino acid sequences, nucleotide sequences, restriction-sites data, and electrophoretic distances. They were applied to data for the human, chimpanzee, gorilla, orangutan, and gibbon species. Among the four different sets of data used, DNA sequences for an 895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979) gave the least reliable one. The DNA sequence data suggested that the chimpanzee is the closest and that the gorilla is the next closest to the human species. The orangutan and gibbon are more distantly related to man than is the gorilla. This topology of the tree is in agreement with that for the tree obtained from chromosomal studies and DNA-hybridization experiments. However, the difference between the branching point for the human and the chimpanzee species and that for the gorilla species and the human-chimpanzee group is not statistically significant. In addition to this analysis, various factors that affect the accuracy of an estimated tree are discussed.      

Evidence for presence of kynurenine in lung and brain of neonate hamsters

Summary Using immunocytochemical techniques, we report here direct evidence of kynurenine (Kyn) presence and localization in the lung and brain. Kyn is a metabolite of tryptophan and 5-hydroxytryptophan, produced by indoleamine 2, 3-dioxygenase (IDO). Whereas IDO has been quantitated in tissues from lung, brain, and other organs, Kyn has only been identified in brain (by HPLC), and its specific localization has not been determined.We reacted alternate serial paraffin sections with anti-sera raised in rabbits against a l-Kyn-albumin conjugate, and with anti-5HT (serotonin, 5-hydroxytryptamine), using the PAP method. Kyn-like immunoreactivity in the lung was specifically localized to cells of the bronchiolar epithelium resembling basal cells. Taller epithelial cells in the bronchi and dorsal trachea were likewise positive whereas neuroepithelial bodies were negative. Immunoreactivity in the brain was typically localized to cells localized in the ependyma of the walls of all ventricles, and to nerve fibers. The cellular Kyn-like reactivity was totally separate from that of anti-5HT, the latter uniquely staining argyrophil lung neuroendocrine cells and raphae neurons of the brain. Our findings suggest a route of tryptophan metabolism in the lung and brain alternate to the common pathway leading to 5-hydroxyindoleacetic acid via 5-HT. This route is of physiologic and pathologic significance as many metabolites are pharmacologically active.Supported by the College of Agriculture and Life Sciences, University of Wisconsin-Madison and the Council for Tobacco Research USA, Inc. Grant #1437