Adult susceptibility induced by preweaning shifts of Zeitgeber in rats (II).

The exposure of young rats to atypical time indicators (Zeitgeber) between birth and weaning modifies the reactivity of adult rats. Rats treated in this way early in life are isolated at day 130 for 14 days and then put through a distributed trials learning in a Y maze. Day after day performances show a deficit of this group compared to controls in the evolution of daily success scores as well as in the number of negative reinforcements received. When the rats are left for 30 min or more in the test room before the beginning of the daily trials, the difference between control and experimental groups decreases, though it does not completely disappear. It is concluded, therefore, that the early alteration of the Zeitgeber modifies the later reactivity of the adult rat and affects its capacity to face a learning situation.

Adult susceptibility induced by preweaning shifts of zeitgeber in rats (I).

The exclusive manipulation of "time indicators" (Zeitgeber) early in development gives rise to a specific susceptibility observable in the course of experimental treatment in the adult. Independent groups of rats were submitted to equidistant shifts of the time indicators during three different periods of the postnatal development (days 1-18, 18-35 and 35-53). Apart from these specific episodes, each group remained in the same rearing conditions as the control groups (LD 12:12, temperature 12:12). The effects were evaluated at the adult stage. From day 130 until day 140, the animals were left in individual cages without any other modification in environmental conditions. They were then transported daily in a trolley in their individual cages, for five consecutive days (days 141-145 during three minutes at 15.00 hours). The results indicate that the rats belonging to the 1-18 group show a significant weight loss between the days 130 to 145. Moreover, they present a significant modification of the ultradian components of the circadian rhythms of their locomotor and feeding activity. The conclusion is that the early manipulation of the Zeitgeber before weaning may alone lead to a specific susceptibility which becomes apparent during the experimental treatment of the young adults.

Two apparatus for detection of motility and water consumption of rodents.

Two apparatus for time sequences data acquisition are described. The first is designed for detection of motility. It acts according to the principle of inertia. Movements of animal are transmitted to a plate supported by steel balls with a minimal resistance. Horizontal oscillations are detected using an electro-optical system. Very weak movements can be recorded. The second indirectly records feeding behavior (water intake) using also an optical detection of the air bubble passing through the glass-tube of the feeding-bottle. The long-term stability, accuracy and sensitivity of the apparatus are discussed. Examples of application are quoted.

Adult timing after preweaning shifts of Zeitgeber in rats: crossed sensitization to time?

Preweaning albino rats were exposed from days 1 to 18 of life to successive 6-h shifts in light and temperature Zeitgebers, (1-18 rats), whereas controls (C) were raised under constant 12:12 L:D and temperature cycles. Cyclic Peak Interval performance at adulthood (100 days) showed that 1-18 rats were more accurate and sensitive to time than C subjects. These effects, which were akin to a crossed senzitization to time, were interpreted within the framework of scalar timing theory and the temporal information-processing model. They seemed not to depend upon changes in the pacemaker rate (lambda) or the memory constant K*, but to a change at the level of the decision process: 1-18 rats used a smaller response threshold than controls.

Age-related differences for duration discrimination in rats.

The effects of age on duration discrimination were analysed with a symbolic matching-to-sample task, where a compound signal (light and sound) was presented at each trial for a duration of either 2 or 10 s. Four groups of rats (6, 12, 18, and 24 months old) were trained to press one lever if the signal was short and the other if it was long. Results show that, in comparison with younger rats (6 and 12 months), presenescent and senescent rats (18 and 24 months) were slower to reach the acquisition criterion. However, when the performance criterion was met, no age-related difference was found: the percentages of correct responses were equivalent, whatever the duration of the stimulus. These results are in accordance with other data, which have often shown that the cognitive impairment reported in old animals results more from a slowness to learn than from an incapacity to discriminate between different durations.

Maternal behaviour in the Wistar rat under atypical Zeitgeber.

In previous experiments, neonatal rats subjected to atypical Zeitgeber (light and temperature) produce adult animals that present a different reactivity in some test situations. On the other hand, a great body of evidence indicates that physiological and psychological processes, including the maturation of the circadian system, are regulated by maternal behaviour. In order to investigate in which manner the atypical Zeitgeber, mentioned above, influences maternal behaviour, mothers with their young were observed systematically. More precisely, the question was: is the changed reactivity due to the fact that the young experience a situation of classical early privation (e.g., a decrease in social or other sensory stimulation or in nutrition) or is it due to a situation in which only the temporal pattern of the maternal behaviour is modified and thus disturbs the proper development of the circadian system of the young. Results tend to show that the only difference between the experimental and the control group is a modification in the circadian rhythm of several behavioural items. Only one activity (licking of the young) shows a significant difference in the overall mean value but in favour of the experimental group. We would suggest that the modified temporal pattern of the maternal care could be a poor timegiver for the young, in such a way that the development of their circadian rhythms is disturbed. The unusual reactivity in adulthood could depend on this abnormal development of the circadian system and not on a care privation.