Effect of starvation and pesticide exposure on neutral lipid composition of the digestive gland of males of the apple snails Pomacea canaliculata.

Pollutants as well as starvation usually modify homeostasis of neutral lipids in aquatic organisms. However, studies on the simultaneous effects of both stressors are scarce. The aim of this study was to evaluate the effect of toxicant exposure under starvation conditions on neutral lipids of the freshwater snail Pomacea canaliculata, selected as the model organism. Starved adult male snails were exposed to sublethal concentration of the pesticide cypermethrin (100 µg/L) during 4 and 10 days. Fed snails were sacrificed at the onset of the experiment (T0), along with starved snails exposed to the pesticide vehicle (ethanol) and another group without solvent served as controls. Total lipid content, neutral lipid classes, fatty acid composition, and pesticide accumulation were determined in the digestive gland of snails. The ethanol concentration used was not an additional stressful agent. As expected, starvation caused a decrease in neutral lipid content in the digestive gland of snails with respect to T0 snails. Pesticide exposure caused, on the other hand, an increase in triacylglycerol content compared to ethanol exposure at day 10 of the bioassay. This increment correlated with the bioconcentration of cypermethrin, which was 47% higher by day 10 than by day 4. The fatty acid profile of triacylglycerols in the digestive gland was significantly altered under starvation and pesticide exposure. Stressed male snails showed the ability to preserve polyunsaturated fatty acids, as evidenced by their significant increase with respect to T0 snails. These results suggest that the alteration of lipid homeostasis could be involved in an adaptive mechanism of aquatic organisms to lipophilic and obesogenic pollutants.

Conditioned Approach and Contact Behavior toward Signals for Food or Brain-Stimulation Reinforcement.

When presentation of a retractable lever always preceded food delivery, rats licked or gnawed the lever. They also approached but seldom orally contacted a lever signaling brain-stimulation reinforcement; instead, subjects sniffed, pawed, or "explored" the lever. Therefore, a Pavlovian conditioned stimulus evoked directed skeletal responses whose specific form depended on the forthcoming unconditioned stimulus.

Response selection properties of food and brain-stimulation reinforcers in rats.

Rats were exposed to a differential conditioning procedure in which one lever-stimulus predicted a food UCS (for one group) or a brain-stimulation UCS (for 2 other groups) while a second lever-stimulus was explicitly unpaired with the UCS. A fourth group received differential training where one lever-stimulus signalled food and the other brain-stimulation. The animals reliably approached and contracted the predictive stimuli with there being no significant difference in this tendency between groups. There was, however, a significant difference in the form of the stimulus contact behavior as a function of the quality of the UCS. Rats gnawed the stimulus when the UCS was food but sniffed it when the UCS was brain-stimulation. This difference was independent of the level of food deprivation and occurred within animals in the group which received both kinds of UCS. The results indicate that properties specific to the reinforcer are important in response performance. Such effects should be considered in the analysis of performance on instrumental tasks, especially when concern is focussed on performance differences which are correlated with qualitatively different rewards.

Expectancy mediation of concurrent conditional discriminations.

Pigeons learned a pair of two-choice conditional discriminations concurrently. One was red/green identity matching. The other also employed red and green sample stimuli, but the choice alternatives were vertical vs. horizontal lines, with vertical being correct following red samples and horizontal being correct following green. Correct choices produced either food reward or a brief feedback tone. For the "congruent" group, a given sample reliably predicted a particular outcome (e.g., red-food, green-tone), regardless of whether the animal chose between colors or lines. For the "incongruent" group, the outcome that followed a particular sample was one thing on color-choice trials and the other thing on line-choice trials. For example, if a subject in the incongruent group received food for red matches and tone for green matches, then it received tone for correct vertical choices and food for correct horizontal choices. The congruent group reached significantly higher levels of correct performance on both problems than did the incongruent group. Moreover, these relative levels of performance were reversed when birds trained on the congruent procedure were switched to the incongruent procedure and vice versa, even though the stimulus-response requirements of both problems remained unchanged. The experiment provides further evidence that the outcome expectancies acquired in learning situations can be significant sources of stimulus control of instrumental behavior.

Interaction of memories and expectancies as mediators of choice behavior.

The interaction of food-based memories and food-event outcome expectancies in pigeons was assessed using a simultaneous, delayed-symbolic-matching-to-sample procedure. The components of the compound sample were presented in sequence, and consisted of a food-based event (food or no-food) followed by a color cue (red or green). Choice of a pattern of horizontal lines was "correct" following presentation of the red cue, while choice of a vertical line pattern was "correct" after green. In all but a control condition, the food-based event with which a trial began, or the food-event outcome with which a trial concluded, or both, were also correlated with the correct pattern. Of particular interest was the relative accuracy of two groups for whom both memories and expectancies were correlated with the correct choice-pattern. For one group, the memories and expectancies corresponding to the pre- and postchoice food-related events were similar, whereas for the other they were dissimilar. Outcome expectancies supported a higher level of performance than food-based memories, and subjects with both outcome expectancies and food-based memories chose more accurately than those with memories or expectancies only. In addition, subjects with dissimilar food-based memories and outcome expectancies chose more accurately than those with similar memories and expectancies. The implications of the above findings for the nature of event representation in pigeons are discussed.

Two housing systems for calves.

Thirty-six male Holstein calves were in an experiment with 2 X 2 factorial design with the objective of comparing management systems and milk feeding. Housing systems were similar except calves on A system were housed in pens .66 m wide with grated floors whereas calves on B system were in pens that were 1.36 m wide with solid floors bedded with straw. Within each management system nine calves were fed milk at 8% of body weight and nine calves at 12% of body weight. There was no interaction between management system and feeding percent. Preweaning calves fed more milk gained faster (.64 versus .50 kg/day) compared with calves fed less. Management system did not influence body weight gain or feed conversion prior to weaning, but postweaning A system resulted in slower gains (.74 versus .90 kg/day) and less favorable feed conversion (2.00 versus 1.77 kg dry matter intake/kg body weight gain) than calves housed under the B system. Eosinophil count was higher during 5th and 7th wk of the experiment for calves housed in A compared with B system. Measurements of body weight gain and feed conversion were effective in differentiating between two housing systems for calves.