Increase Of Activity In Response Research Articles

Nathusius’ bats, Pipistrellus nathusii, bypass mating opportunities of their own species, but respond to foraging heterospecifics on migratory transit flights

In late summer, migratory bats of the temperate zone face the challenge of accomplishing two energy-demanding tasks almost at the same time: migration and mating. Both require information and involve search efforts, such as localizing prey or finding potential mates. In non-migrating bat species, playback studies showed that listening to vocalizations of other bats, both con-and heterospecifics, may help a recipient bat to find foraging patches and mating sites. However, we are still unaware of the degree to which migrating bats depend on con-or heterospecific vocalizations for identifying potential feeding or mating opportunities during nightly transit flights. Here, we investigated the vocal responses of Nathusius’ pipistrelle bats, Pipistrellus nathusii, to simulated feeding and courtship aggregations at a coastal migration corridor. We presented migrating bats either feeding buzzes or courtship calls of their own or a heterospecific migratory species, the common noctule, Nyctalus noctula. We expected that during migratory transit flights, simulated feeding opportunities would be particularly attractive to bats, as well as simulated mating opportunities which may indicate suitable roosts for a stopover. However, we found that when compared to the natural silence of both pre-and post-playback phases, bats called indifferently during the playback of conspecific feeding sounds, whereas P. nathusii echolocation call activity increased during simulated feeding of N. noctula. In contrast, the call activity of P. nathusii decreased during the playback of conspecific courtship calls, while no response could be detected when heterospecific call types were broadcasted. Our results suggest that while on migratory transits, P. nathusii circumnavigate conspecific mating aggregations, possibly to save time or to reduce the risks associated with social interactions where aggression due to territoriality might be expected. This avoidance behavior could be a result of optimization strategies by P. nathusii when performing long-distance migratory flights, and it could also explain the lack of a response to simulated conspecific feeding. However, the observed increase of activity in response to simulated feeding of N. noctula, suggests that P. nathusii individuals may be eavesdropping on other aerial hawking insectivorous species during migration, especially if these occupy a slightly different foraging niche.

Dopamine-induced inhibition of action potentials in cultured frog pituitary melanotrophs is mediated through activation of potassium channels and inhibition of calcium and sodium channels

A patch-clamp study was conducted in order to investigate the effects of dopamine on the ionic currents in cultured frog melanotrophs. Brief applications of dopamine (1 μM) hyperpolarized the cell and inhibited the spontaneous action potentials. The hyperpolarization was accompanied by an increase in membrane conductance. Under voltage clamp, dopamine evoked a net outward current. The dopamine-induced outward current was negligible at the equilibrium potential for potassium ions. It was also observed that dopamine increased the intensity of a voltage-dependent outward potassium current monitored by constant depolarizing pulses. In addition, voltage-dependent L- and N-like calcium currents and sodium current were reduced. In the cell-attached configuration, two distinct channel types were activated and one channel type was blocked by dopamine exposure to the extrapatch membrane, which indicates the involvement of an intracellular factor in the signal transduction pathway. A higher conductance channel (100 pS) was characterized by a very low basal activity which rapidly increased upon dopamine application. A lower conductance channel (30 pS) displayed a basal activity with frequent opening events, and a delayed (30–40 s) increase of activity in response to dopamine. Both currents reversed at a deduced potential corresponding to the equilibrium potential for potassium ions. The channel type inhibited by dopamine had a low conductance of 15 pS. The inhibition of the electrical activity induced by dopamine was totally blocked by the D 2 receptor antagonist S(−)-sulpiride (1 μM) but was not affected by the D 1 receptor antagonist SKF-83566 (1 μM). It is concluded that dopamine activates potassium channels and inhibits calcium and sodium channels in frog melanotrophs. The results also indicate that stimulus-response coupling is mediated by intracellular messenger system(s).

Control of Ornithine δ-Transaminase in Rat Liver and Kidney

Abstract Ornithine δ-transaminase activity in the livers of rats, on a commercial diet from 21 days after birth, increased to a maximum at about 35 days of age and decreased thereafter, reaching the 21-day level by about 120 days after birth. Under the same conditions the activity in the kidneys also reached a maximum at about 35 days but did not decline thereafter. One reason for the difference in the shapes of the developmental curves for ornithine δ-transaminase activity for the two organs appeared to depend on different responses to dietary components. The activity in the livers of younger animals was increased by a high nitrogen intake and was decreased by restricting the nitrogen intake. In older animals, high nitrogen intake did not increase ornithine δ-transaminase activity. The activity in kidneys of either young or older rats did not decrease on a restricted nitrogen intake, and the changes in total and specific activities brought about by dietary protein depended on the total food intake. Fasting decreased total ornithine δ-transaminase activity in both liver and kidney, but did not change the specific activities. With carbohydrate as the sole food source, liver activity decreased but kidney activity increased. In experiments with amino acids added to the diet, liver ornithine δ-transaminase activity was decreased by added arginine and increased by arginine deficiency, or increased ingestion of glycine or serine. The activity in kidney was increased by dietary leucine, valine, and isoleucine, all of which are known to inhibit the ornithine δ-transaminase reaction per se and decreased by extra glutamate in the diet. The only response observed in regard to ornithine δ-transaminase which is common to liver and kidney was a significant increase of activity in response to dietary methionine. This methionine-induced increase of activity was apparently not decreased by arginine in the case of liver or by glutamate in the case of kidney. It is speculated that ornithine δ-transaminase may exist in liver and kidney in two different forms, the former functioning in the direction of arginine synthesis and the latter in the direction of arginine metabolism to glutamate.