Measures of phototaxis and movement detection in the larval salamander.

In this investigation, we describe two precise tests of visual function that integrate quasinatural situations with time-lapse video recording and infrared computerized monitoring of activity to assess movement detection and phototaxic tendencies, respectively. Four groups of larvae from A. punctatum, A. tigrinum, A. mexicanum, and a mutant albino axolotl were tested in an alley containing light and dark halves and lined with infrared sensors to monitor their phototaxic response. A. punctatum showed no phototaxic tendency, while the other three groups displayed a strong negative phototaxic response. Enucleation of the eyes in mutant albinos eliminated the negative phototaxis. Visual detection of motion was tested by videorecording the behavior of A. punctatum, A. mexicanum, and the mutant albino axolotl larvae while they explored a large bowl with 6 small vials on the perimeter, one of which contained white worms. A. punctatum rapidly approached the worm vial and engaged in intense predatory behavior. A. mexicanum responded to the presence of worms very slowly and rapidly lost interest. Albino axolotls displayed no visual recognition of the worms. The results indicate that visual function can be precisely determined in larval salamanders utilizing behavioral measures consistent with the animal's natural tendencies.

A longitudinal investigation of the effects of experience on the behavior of aging mice.

The effects of differential experience over most of the adult lifespan of mice were examined utilizing longitudinal designs. Repeated experience with nest building was contrasted with one-time only experience at various age levels from 4 to 24 months of age. The results suggest that the presence or absence of repeated exposure to nest building opportunities affects stability of nest building, while open field activity remains stable regardless of experience and vitality declines regardless of experience. Because nest building at maturation is not influenced by prior experience, the effect of differential experience during the course of aging is not interpreted as a reflection of differential initial acquisition of the behavior. Rather, performance differences are interpreted as providing evidence for the differential maintenance of neural integrity of the underlying mediator for the behavior. The discrepancy among the patterns of change for nest building, open field activity, and performance on the tightrope test is interpreted as reflecting differences in the relative importance of deterioration of the underlying neural mediators in comparison with decreases in muscular strength and flexibility. Implications for design issues in animal research in aging are discussed.

Age differences in the oxidation of and neural response to ethanol in mice.

Male mice (C57BL/6J) from three age groups, 4, 14, and 26 months, were tested to determine their oxidation rate of intragastrically infused ethanol and the response of the centrally mediated jaw-jerk reflex to ethanol challenge. There were no age-related differences in the rate of oxidation of ethanol. However, age differences in ethanol-induced decrement of the jaw-jerk amplitude were significant. The 26 month animals were the most affected, followed by the 4 month group. The middle aged mice (14 month) showed the greatest resistance to the depression induced by ethanol. The results were evaluated with regard to the current hypotheses.