Effect Of Short-term Changes Research Articles

Effects of short-term changes in rain water supply on the ionic composition of acid moorland pools in the Campine of Antwerp (Belgium)

A study was made on the change of pH, corrected conductivity, Na, K, Ca, Mg, Cl and SO4 with time over a period of 3.5 years (autumn 1975-spring 1979) in 21 very acid shallow bogs in the Campine of Antwerp (North of Belgium). These moorland pools are subjected to severe changes in waterlevel due to the fact that they depend mostly on rainwater for their water supply. Subsequently the very hot and dry summer of 1976 made the waterlevel to decrease and some pools even became totally dry. The concomitant changes in the ionic concentrations and in the ionic composition have been studied in detail and are summarized in this paper.

Changes in unit responses to tones after food reinforcement in the auditory pathway of the rat: Intertrial arousal

Experiments were carried out to determine the effects of short-term changes in behavioral arousal on the responsiveness to auditory stimuli of medial geniculate and inferior colliculus neurons in the rat. The independent variable was the time of presentation of the signals after a food pellet, the assumption being that the animal's state of arousal might vary after a consummatory act, and that this fact in turn might modify unit activity. Eight different periods were tested in a random order of presentation, the periods varying between 20 and 180 s from the time of presentation of a food reward. The findings indicate increased responsiveness after long intervals, as measured in peak response firing rate, together with decreased spontaneous rate in a 200-ms period before the auditory signals (background rate). The results demonstrate that variations in arousal during the short periods between food rewards in the paradigm tested influence both the spontaneous rate of discharge and the responsiveness of auditory neurons to sensory input, but that the pattern of changes is different in the medial geniculate and in the inferior colliculus. These variations are of a short-term nature compared with the long-term variations that have come to be expected with changes in the motivational or sleep-wake state of the animal. Recognition of this type of modulating influence is of great importance to neurophysiological studies of learning, in view of the fact that associative neural changes have to be extracted from the nonassociative changes that occur simultaneously.

The effect of short-term changes in the external salinity on the levels of the non-protein nitrogenous compounds and the ornithine-urea cycle enzymes in Rana cancrivora

1. 1. Short-term changes in tissue osmolytes were examined in Rana cancrivora which had been exposed to media containing diluted sea water, saline, choline chloride, sucrose or mannitol. Estimations of the levels of the onithine-urea cycle enzymes were also made in some experiments. 2. 2. Progressive water depletion in muscle and live was observed on exposure to increasingly hyperosmotic environmental media, but the changes in tissue urea and non-essential amino acids were markedly greater than expected on the grounds of the change in water content alone. 3. 3. Lysine was notable in being decreased in hyperosmotic media compared to fresh water. 4. 4. An alteration in the activity of argininosuccinate synthetase was observed after 2 days' exposure to hyperosmotic media, but no significant concomitant change in carbamoyl phosphate synthetase could be detected. 5. 5. It is concluded that the initial elevation of the tissue urea concentration does not result simply from a generalized increase in biosynthesis of the enzymes of the ornithine-urea cycle.