Maternal consumption of Lake Ontario salmon in rats produces behavioral changes in the offspring.

The current study assessed the effects of maternal, paternal, or combined parental consumption of Lake Ontario salmon in rats on the behavior of their offspring. Adult female Sprague-Dawley rats were put on a 30 day diet of either ground rat chow containing 30% Lake Ontario salmon (LAKE) or 30% Pacific Ocean salmon (OCEAN). These females were then mated with adult male rats similarly exposed (LAKE or OCEAN). An additional control group of males and females who were fed ground rat chow (MASH) only were also mated. These pairing combinations resulted in five offspring groups: LAKE-LAKE, LAKE-OCEAN, OCEAN-LAKE, OCEAN-OCEAN, MASH-MASH. When the offspring reached 80 days of age, they were tested for reactivity to frustrative nonreward using runway successive negative contrast, which has been repeatedly shown to be increased in adult rats fed Ontario salmon. Consistent with previous work, results showed that the behavior of the OCEAN-OCEAN rats did not differ from the MASH-MASH group, indicating that a salmon diet per se does not cause behavioral change. However, the offspring of dams who consumed Lake Ontario salmon (LAKE-LAKE and OCEAN-LAKE) showed an increased depression effect relative to controls. There was little evidence of a paternal effect. A follow-up experiment employed cross-fostering to determine the relative contribution of pre- and/or postnatal exposure to Lake Ontario salmon consumption on offspring behavior. Rat pups were cross-fostered to or from dams who consumed Lake Ontario salmon during gestation and parturition. Results from two separate replications indicated that prenatal (LAKE to OCEAN) exposure alone or postnatal (OCEAN to LAKE) exposure alone produced a large increase in successive negative contrast relative to controls (OCEAN to OCEAN). These data are strong evidence of behavioral changes produced by maternal consumption of Lake Ontario salmon in the offspring rat. Further, they indicate that either prenatal or postnatal exposure alone is sufficient to produce behavioral changes in the offspring.

Persistence and the importance of nonreward: Some applications of frustration theory and DMOD.

Unfortunately our world does not always reward us when we expect it, and we must learn to deal with nonreward. How do these experiences influence our behaviors and how can we use them to help us? InFrustration Theory: An Analysis of Dispositional Learning and Memory (1992), Abram Amsel has answered these questions; he has summarized over 40 years of exciting research and the development of an elegant theory. He has also reviewed recent applications of frustration theory in such areas as fetal alcohol syndrome and attention deficit-hyperactivity disorders. In this invited commentary, we briefly summarize a mathematical model of frustration theory (called DMOD) and review simulations of the model that highlight the importance of the assumptions based on frustration theory (e.g., aversiveness of unexpected nonreward, counterconditioning). We also review assumptions (e.g., unlearning, passive and active "inhibition," decline in aversiveness of expected nonreward) that are required if one is to simulate intuitive and counterintuitive phenomena.

Reward reductions found more aversive by rats fed environmentally contaminated salmon.

Pacific salmon stocked in Lake Ontario concentrate persistent toxic chemicals such as PCBs, DDT, DDE, mercury and dioxin. The present experiments support earlier findings that consumption of these salmon by laboratory rats increases their behavioral reactions to negative events. For 20 days rats were fed a diet consisting of 30% Lake Ontario salmon or a control diet of Pacific Ocean salmon or no salmon. They were then trained to run down an alley to receive a large 15-pellet or small 1-pellet food reward (6 trials/day). Following 72 trials the 15-pellet groups were shifted to 1 pellet for 90 trials, and showed a contrast (depression) effect: they ran more slowly than the groups always given 1 pellet. Rats previously fed Lake Ontario salmon showed a much larger contrast effect than the two control groups. These results were replicated in a second experiment, and a group fed a 10% diet of Lake Ontario salmon for 60 days showed the same size contrast effect as the group fed a 30% diet for 20 days.

Changes in learning about aversive nonreward accounts for ontogeny of paradoxical appetitive reward effects in the rat pup: a mathematical model (DMOD) integrates results.

Baby rats do not show any paradoxical appetitive reward effects (e.g., faster extinction following partial than continuous reinforcement, contrast effects when large and small rewards are given) until they are at least 12-14 days old, but can learn to pattern when reward and nonreward are alternated (e.g., Amsel, 1986). These results have been puzzling, but are now successfully integrated by DMOD (Daly MODification of Rescorla and Wagner's [1972] mathematical model; Daly & Daly, 1982). It was assumed that young rats do not have the capacity to learn about aversive nonreward but slowly gain this ability between 12 and 26 days (1 parameter reflecting the rate of conditioning of aversive nonreward, beta 1 for Vav, is increased from 0 to .15 beginning at 12 days). This theoretical integration has implications for understanding behavioral and neurological development of altricial organisms, and effects of neurological damage and toxic substances.

Ingestion of environmentally contaminated Lake Ontario salmon by laboratory rats increases avoidance of unpredictable aversive nonreward and mild electric shock.

To determine what behavioral changes are caused by consumption of Lake Ontario salmon, a 30% diet of Lake Ontario or control Pacific Ocean salmon was fed to rats for 20 days. In Experiments 1 and 2 (preference-for-predictability E-maze test), rats fed Lake Ontario salmon developed a preference for predictable food rewards more quickly than did the control rats. In Experiments 3 (passive avoidance) and 4 (conditioned suppression), rats fed Lake Ontario salmon suppressed responding to food far more after the introduction of mild electric shocks than did control rats. All results supported the hypothesis that ingestion of Lake Ontario salmon, contaminated with polychlorinated biphenyls, mercury, lead, etc., increases the reactivity of rats to aversive events. The results were successfully simulated by DMOD, a mathematical model of learning, using the assumption that rats fed Lake Ontario salmon find unpredictable nonreward and mild shock more aversive.

Preference for unpredictable food rewards occurs with high proportion of reinforced trials or alcohol if rewards are not delayed.

Organisms typically prefer situations where reward and nonreward are predictable rather than unpredictable. Although many theories can account for this result (e.g., information theory and delay-reduction theory), a recently developed mathematical model (DMOD) also predicts that subjects prefer the unpredictable reward situation under conditions that substantially decrease aversiveness of unpredictable nonreward (Daly & Daly, 1982). Because a high proportion of reinforced trials (lenient schedule) and alcohol injections decrease aversive conditioning, these variables were tested with rats in five E-maze experiments. A choice to one side of the maze resulted in a stimulus uncorrelated with reward outcome (unpredictable situation). A choice to the other side resulted in stimuli correlated with reward and nonreward (predictable situation). The stimuli were not visible until after the choice was made. A lenient reinforcement schedule resulted in preference for the unpredictable reward situation if rewards were not delayed. Alcohol resulted in preference for the unpredictable reward situation if a medium five-pellet reward was given. A lenient reinforcement schedule combined with an alcohol injection resulted in faster acquisition of the preference for the unpredictable reward situation than did a lenient schedule combined with a saline control injection. These results pose a major challenge to most theories, yet were predicted by DMOD.

Observing response acquisition: preference for unpredictable appetitive rewards obtained under conditions predicted by DMOD.

In five E-maze experiments, rats were given a choice between receiving reward and nonreward in a situation where stimuli were correlated with reward outcome (predictable situation) versus one where the stimuli were uncorrelated with reward outcome (unpredictable situation). Preference for the unpredictable situation occurred under the following conditions: (a) small (one 37-mg pellet), immediate rewards; (b) small, delayed (15 s) rewards, if the cues correlated with reward outcome were absent during the delay interval; (c) large (15 pellets), immediate rewards if a difficult discrimination was required; and (d) if the stimulus predicting nonreward was present at the choice point. Preference for the predictable situation was strongest if reinforcement was delayed and large or the stimulus predicting reward was present at the choice point. A weaker preference for the predictable situation occurred if reinforcement was immediate and large and a simple discrimination was required or if reinforcement was large and delayed and the cues that correlated with reward outcome were absent during the delay interval. The results support the predictions of DMOD (Daly modification of the Rescorla-Wagner model), a mathematical model of appetitive learning (Daly & Daly, 1982).