Negative Feedback Hypothesis Research Articles

Test of the negative feedback hypothesis of colony size sensing in social insects.

Social insects can sense colony size-even without visual information in a dark environment. How they achieve this is yet largely unknown. We empirically tested a hypothesis on the proximate mechanism using ant colonies. In Diacamma colonies, the monogynous queen is known to increase the effort devoted to queen pheromone transmission behaviour (patrolling) as the colony grows, as if she perceives colony size. The negative feedback hypothesis assumes that, through repeated physical contact with workers, the queen monitors the physiological state (fertility) of workers and increases her patrolling effort when she encounters more fertile workers. Supporting this hypothesis, we found that the queen increased her patrolling effort in response to a higher ratio of fertile workers under the experimental condition of constant colony size. Furthermore, chemical analyses and bioassays suggested that cuticular hydrocarbons have queen pheromone activity and can mediate the observed queen-worker communication of fertility state. Such a self-organizing mechanism of sensing colony size may also operate in other social insects living in small colonies.

Advancing the pH hypothesis of negative feedback to photoreceptors: sources of protons and a role for bicarbonate in feedback.

Advancing the pH hypothesis of negative feedback to photoreceptors: sources of protons and a role for bicarbonate in feedback.

The traditional energy-growth nexus: A comparison between sustainable development and economic growth approaches

Gross Domestic Product (GDP) is the indicator commonly used to measure economic growth and sustainable development. However, this indicator can be very inefficient for evaluating development. The most prominent alternative indicator is the Index of Sustainable Economic Welfare (ISEW). Indeed, this index can be used to control for the way that countries use available resources, balancing ecological development, damages caused to the environment and income distribution between citizens. This paper compares a sustainable development approach, using the ISEW, with the traditional economic growth approach using GDP, and its relationship with energy consumption. The traditional hypotheses of the energy-growth nexus are tested through Panel-Corrected Standard Errors estimators, for a panel constituted by twenty European countries, with an annual data frequency for the time span 1995–2014. The results indicate a new negative feedback hypothesis for the alternative measure of development and a conservative hypothesis for economic growth with energy consumption. This study also finds various other effects on sustainable development by economic growth factors, such as Terms-of-trade and Rents from natural resources. These findings indicate that the economic growth approach, widely studied using GDP, has been wrongly interpreted by policy makers trying to achieve increased sustainable development.

Chemical weathering and climate — a global experiment: A review

How has the Earth maintained a habitable environment while its closest neighbors, Venus and Mars, are currently too hot or too cold? This fortunate state has been attributed to a negative feedback hypothesis that has stood unchallenged for years. In this model, any increase in atmospheric CO2 production is balanced by increased CO2 uptake by silicate weathering under greenhouse conditions. A decrease in atmospheric CO2, then, is balanced by decreased silicate weathering rates under the colder climate. A global experiment utilizing published geochemical data from large rivers at different latitudes helps us test the climate dependence of weathering, central to this hypothesis. When rivers draining granitic shields and basaltic provinces are compared, there is no systematic latitudinal variation (temperature dependence) in the rates of chemical weathering. At global scale the physical mechanisms superimpose a threshold effect on the underlying climate-dependence of silicate weathering. On tropical cratons, the buildup of lateritic regolith suppresses weathering. In the arctic/ subarctic, frost action efficiently removes the regolith and generates physical exposure of silicate rocks to the weathering agents (water, CO2), thereby accelerating reaction. Available field observations do not support the currently standard Clausius-Clapeyron-Arrhenius model.

Gamma-Aminobutyric acid acts at axon terminals of turtle photoreceptors: difference in sensitivity among cell types.

It has been proposed that horizontal cells of the vertebrate retina have a negative feedback synapse with cone photoreceptors. gamma-Aminobutyric acid (GABA) has been suggested to be a neurotransmitter of monophasic horizontal cells (a subtype of horizontal cells), which have direct connections with red-sensitive and green-sensitive cones. We have examined the feedback hypothesis by measuring the GABA sensitivity of photoreceptors. To eliminate interaction with other cells, we dissociated photoreceptors from the turtle retina enzymatically. The subtype of photoreceptors was identified unequivocally on the bases of the shape of the cell and the color of the oil droplets, which are known to correlate with the spectral sensitivity. Cells were voltage-clamped using "Giga-ohm sealed" suction pipettes in the whole-cell recording configuration, and membrane currents were measured in response to GABA applied ionophoretically at various positions on the cell. It was found that red-sensitive and green-sensitive cones were highly sensitive to GABA and that the sensitivity was localized at the axon terminals. GABA-sensitivity in blue-sensitive cones and in rods was very low. GABA-induced current reversed its polarity near the equilibrium potential of chloride, suggesting that GABA increased chloride conductance. Thus, our findings are consistent with the negative feedback hypothesis.

A hypothesis to explain the presynaptic effects of adrenoceptor antagonists.

The hypothesis of negative feedback regulation of transmitter release was examined in a range of tissues obtained from three species. Tissues were transmurally stimulated with 100 pulses at 2 Hz with pulse durations from 50 microseconds to 5,000 microseconds, and the efflux of [3H]-noradrenaline determined. The stimulation-induced efflux of tritium increased with increasing pulse duration, but yohimbine, a prototypal alpha 2-antagonist had an effect which was consistently contrary to expectations for a negative feedback system. Enhancement of efflux by the antagonist, supposedly correlated directly with the extent of ongoing auto-inhibition, became smaller rather than larger as the stimulation-induced efflux rose with increases in pulse duration, with all other parameters of stimulation maintained constant. Similar findings were obtained in rat spleen with the haloalkylamine antagonist, phenoxybenzamine. It is concluded that the presynaptic effects of adrenoceptor antagonists do not involve a negative feedback function nor do they relate, in any detectable way, to the extracellular concentration of transmitter. The effects on stimulation-induced tritium efflux of yohimbine, phenoxybenzamine and enlargment of the pulse duration, in a variety of tissues, support the previously described hypothesis of a common action to enhance efflux. The antagonists increased efflux to approximately the same value between 50 and 1,000 microseconds pulse durations and that value was equivalent to that obtained in each given tissue with pulses of 1,000-2,000 microseconds in the absence of the antagonist. Tetraethylammonium, an inhibitor of stimulation-induced potassium efflux from nerves had an effect on transmitter efflux in rat spleen essentially like that of the adrenoceptor antagonists. These findings provide further support for an alternative to the hypothesis of negative feedback. Yohimbine and other presynaptic antagonists may prolong the period of potassium efflux from nerve varicosities, and by this means prolong depolarization and the associated period of transmitter release, rather than act by disrupting an ongoing system sensing and responding to fluctuations in extracellular transmitter levels.

Yohimbine and prolongation of stimulation pulse duration alter similarly 3H-transmitter efflux in heart: an alternative to the negative feedback hypothesis.

The hypothesis of negative feedback regulation of noradrenaline release was studied in guinea-pig left atrial halves mounted in vitro. Tissues were transmurally stimulated with 30, 100 or 300 pulses at 2 Hz with pulse durations ranging from 50 mus to 2,000 mus, and the efflux of 3H-transmitter determined. The efflux of tritium increased with increasing pulse duration as was anticipated, but the effects of supposed presynaptic antagonism by yohimbine were opposite to expectations for a negative feedback system. The magnification of efflux by yohimbine, compared to untreated controls was less rather than more as stimulation-induced transmitter efflux climbed with increases in pulse duration, and with all other parameters of stimulation held constant. It is concluded that the neuronal effect of yohimbine is not linked to negative feedback or to any other system sensing the perineuronal concentration of previously released transmitter. Analysis of the effects on tritium efflux of yohimbine and of prolongation of the stimulation pulse duration, reveals a similarity in the way that they promote transmitter release. Yohimbine increased efflux to approximately the same value at all pulse durations between 50 and 1,000 mus and the value reached was equivalent to that obtained in untreated atria during stimulation with very long pulses (2,000 mus duration). It is suggested that yohimbine prolongs the outward current attributable to the efflux of potassium from axon terminals, and by this means prolongs depolarization and the period of transmitter release. Tetraethylammonium (TEA), a quaternary ion known to plug potassium efflux channels, had an effect on transmitter efflux that was, in some ways, similar to that of yohimbine but of greater magnitude. The present findings provide, for the first time, an alternative to the hypothesis of negative feedback, that might explain the presynaptic effects of adrenoceptor antagonists and possibly other compounds.