Presynaptic cyclic nucleotide-gated ion channels modulate neurotransmission in the mammalian olfactory bulb

Cyclic nucleotide-gated channels (CNGCs) on the dendritic cilia of olfactory receptor neurons (ORNs) are critical for sensory transduction in the olfactory system. Do CNGCs also play a role in the axons and/or nerve terminals of ORNs? We find that the cyclic nucleotides cAMP and cGMP can both facilitate and depress synaptic transmission between olfactory nerve fibers and their targets in olfactory bulb glomeruli. Cyclic nucleotides increase intracellular Ca(2+) in ORN terminals and enhance spontaneous transmitter release; at higher concentrations, cyclic nucleotides depress evoked transmission by altering olfactory nerve excitability. Cyclic nucleotides have no effect on transmission or nerve excitability, however, in mice lacking olfactory CNGCs. Taken together, our results identify a novel role for presynaptic CNGCs in modulating neurotransmission.     

Topochemical factors in potentiation of contraction by heavy metal cations

In addition to the previously studied Zn²⁺, low concentrations (about 0.5 mM) of Be²⁺, Ba²⁺, Cd²⁺, Ni²⁺, Cu²⁺, Pt⁴⁺ and, outstandingly, 0.5 µM of UO₂ ²⁺, potentiate the twitch of frog sartorius and toe muscles by prolonging the active state of contraction. The degree of potentiation is a roughly S-shaped function of p(metal²⁺), suggesting that each metal binds to a ligand of the muscle fiber, representative apparent affinity constants being: UO₂ ²⁺, 5 x 10⁶; Zn²⁺, 2.8 x 10⁵; and Cd²⁺, 2 x 10⁴. UO₂ ²⁺ potentiation effects are rapidly reversed by PO₄, and Zn²⁺ and Cd²⁺ effects by EDTA, PO₄, and cysteine. The rapidity of these reversals by the nonpenetrating EDTA and PO₄, and the fact that heavy metal ions evidently potentiate by prolonging the action potential, indicate that the metal potentiators exert their primary action at readily accessible (i.e. plasma and T tubular) membrane sites. The relatively slow kinetics of development of potentiation, and the even slower reversal of it in pure Ringer''s solution, indicate that the metal ions are bound to connective tissue, as well as to muscle fibers. The binding effects at the readily accessible membrane sites evidently impairs delayed rectification and thus modifies the action potential and excitation-contraction coupling so as to cause potentiation. SH is excluded, and PO₄ and imidazole are possibilities, as the membrane ligand binding the potentiating metal ions.     

Electron nuclear double resonance of semiquinones in reaction centers of Rhodopseudomonas sphaeroides

Replacement of Fe2+ by Zn2+ in reaction centers of Rhodopseudomonas sphaeroides enabled us to perform ENDOR (electron nuclear double resonance) experiments on the anion radicals of the primary and secondary ubiquinone acceptors (QA- and QB-. Differences between the QA and QB sites, hydrogen bonding to the oxygens, interactions with the protons of the proteins and some symmetry properties of the binding sites were deduced from an analysis of the ENDOR spectra.     

Cannibalistic Interactions Resulting from Indiscriminate Predatory Behavior in Tadpoles of Poison Frogs (Anura: Dendrobatidae)1

Poison frogs in the genus Dendrobates have very small clutch sizes (2–6 eggs among species for which there are data) and typically transport their tadpoles singly to small phytotelmata, such as bromeliad tanks, leaf axils, fallen fruit capsules, and treeholes. Tadpoles of many species are predaceous, consuming larvae of insects that use the same microhabitat for breeding, such as giant damselflies and mosquitoes. Previous studies and observations on the behavior of poison frog tadpoles led us to question whether tadpoles might be cannibalistic. We studied a population of Dendrobates castaneoticus in lowland rainforest in Pará, Brazil; additional data were collected on Dendrobates auratus in Nicaragua. At the study site in Brazil, we established a grid of 40 Brazil nut capsules, the microhabitat used by D. castaneoticus for tadpole deposition. Of 42 tadpoles deposited during the 55 days of the study, 20 were killed or died; 16 of these were presumably killed by conspecific tadpoles. Growth rate and time to metamorphosis was higher among tadpoles that consumed three or more tadpoles or relatively large larvae of the mosquito Trichoprosopon digitatum, a colonist of newly opened Brazil nut capsules. We propose that selection has favored the development of predatory behavior in poison frog tadpoles primarily as a mechanism to eliminate predators from the small phytotelmata in which they develop and that cannibalism is a secondary outcome of this behavior. Predatory behavior also provides tadpoles with a source of food, which is frequently limited in these microhabitats. Additional studies of the biology of tadpoles of other species of Dendrobates are needed to determine the evolution of predatory and cannibalistic behavior in the clade.     

Biochemical correlates of selection for weight-for-age in chickens: twenty-fold higher muscle ornithine decarboxylase levels in modern broilers

Summary Little is known about the biochemical correlates of selection for growth in farm or laboratory animals, or the identity of the gene products affected or produced by trait-genes. Modern broiler chickens have about 8-fold greater breast muscle mass than layer chickens at 7 weeks of age and over 2-fold greater breast muscle mass than their 1972 counterparts. This increase in muscle mass is associated with over 20-fold higher levels of ornithine decarboxylase (ODC) in broiler chickens at 1 week of age as compared with layer strain chickens; there is a comparable increase in a relaxed-selection strain of broilers. The increase in ODC levels is larger than the differences in muscle or body weight between broilers and layers at 7 weeks of age, occurs at an age when there is no difference in weights between the strains and precedes the major growth spurt. Increases in ODC levels and hence polyamine synthesis have been associated with, and usually precede, rapid growth and cell proliferation in a wide range of cell types and organisms in response to many different stimuli. Therefore, the correlation of ODC levels with genetic differences in muscle growth make it worth investigating the control of ODC gene expression in these strains.     

Lactobionic acid as an iron chelator: a rationale for its effectiveness as an organ preservant

Lactobionic acid, a major constituent of a solution used to preserve organs prior to transplantation, can chelate ferric iron. This is evident by its ability to solubilize iron as well as changes that occur in the UV-VIS spectra of iron in its presence. Relative to iron (III) chelated to EDTA, the lactobionic acid-iron (III) complex is less able to participate in the Fenton reaction as measured by formaldehyde generation from DMSO and bleaching of p-N,N-dimethylnitrosoaniline. Similar effects are seen with citrate and ATP, two substances which also appear to be able to ameliorate ischemia/reperfusion injury. These findings present a rationale for the effectiveness of lactobionic acid as an organ preservant.     

Patterns of range use,range defense,and intergroup spacing in moustached tamarin monkeys (Saguinus mystax)

In this paper we examine patterns of group spacing and habitat utilization in neighboring groups of marked free-ranging moustached tamarin monkeys (Saguinus mystax) inhabiting Padre Isla, a small island in the Amazon Basin of northeastern Peru, and describe the set of behavioral mechanisms used by tamarins to maintain the spatial isolation and social integrity of individual groups. Specifically, we address a series of questions regarding the importance of resource defense, mate defense, and territorial defense in intergroup interactions. From June through November 1990, we recorded 67 intergroup interactions involving members of our two main study groups. These interactions occurred at a rate of .14/observation hour and were of two general types. Vocal battles averaged 18 min in duration and were characterized by a series of high frequency, short syllable, long calls that were exchanged between groups separated by distances of greater than 25 m. Aggressive encounters averaged 26 min in duration and involved visual contact, alarm calls, scent marking, and sequences of chases and retreats. Intergroup confrontations did not cluster around the perimeter of a group's home range, and there was no evidence that moustached tamarins patrolled range borders. Our data indicate that 35% of aggressive encounters occurred in the vicinity of major feeding trees. Priority access to these sites is likely to have an important influence on tamarin foraging success. Mate defense and the exploration of new breeding opportunities also appear to be important functions of intergroup conflicts. Not only did the frequency of aggressive encounters increase during breeding periods, but three-fourths of all observed copulations occurred during or within 30 min of an encounter. Given the high degree of reproductive competition reported among tamarin females and the time and energy group members devote to intergroup aggression, maintaining access to a stable home range and the resources contained within that range appear to be critical functions of moustached tamarin social interactions.     

Immunohistochemical differentiation between histiocytic and lymphoid neoplasms

Summary Lysozyme has, until recently, been accepted as the only reliable immunohistochemical marker of benign and malignant histiocytes. Using this marker, very few lymphoreticular neoplasms of histiocytic origin are recognized and more recently -1-anti-trypsin has been shown to be a better marker of malignant histiocytes. By immunizing rabbits with highly purified human blood monocytes we have obtained an antiserum (S22) which stains histiocytes and neutrophils in paraffin sections with a high degree of specificity. Using this antiserum and antisera to lysozyme and -1-anti-trypsin we have stained paraffin sections of tissues containing reactive histiocytes, histiocytic proliferations, leukaemic infiltrates and lymphoreticular tumours of histiocytic and T-cell origin. Our results show that -1-anti-trypsin is the most reliable marker of malignant histiocytes but that the as yet uncharacterized antigen defined by S22 may offer a promising alternative.