Ontogenèse du rythme nycthéméral des états de vigilance chez le Rat - Kangourou (Potorous apicalis)

The ontogenesis of nycthemeral rhythm of the states of sleep in the kangaroo rat was studied by polygraphic methods in the young, one month before it finally left the pouch. In the 12 hr light-dark cycle, the first nycthemeral variations of the percent time of sleep were observed fifteen days before the beginning of the weaning, whether at about the sixteenth week of life. Previously, the sleep cycle of the young potoroo seemed to be independent of the 12 hr light-dark cycle and of its mother's nycthemeral rhythm of sleep. In the young animal kept in a permanent light, the apparition of the circadian rhythm of sleep, fifteen days before the weaning, showed the innate origin of this rhythm. The importance of the synchronizer facts, light and food, was dicussed.     

Effect of pinealectomy and circadian rhythm on avoidance behavior in the male rat

Male adult albino rats were divided into six groups: two pinealectomized (Px); two sham-operated (Sh) and two serving as controls (C). Half of these groups were studied in daylight and the other half at night. The animals were open-field tested and then conditioned by the avoidance behavior test in the appropriate light period. No differences were observed among the groups when they were conditioned in the dark; however, the Px were conditioned significantly more rapidly than Sh or C in daylight. Intragroup comparisons between night/day conditioning showed them to be similar in Px but more rapid at night in both Sh and C. The Sh group is unique and not comparable to controls.     

The multiplicity of biological oscillators in the control of circadian running activity in the rat

The purpose of this experiment was to determine the degree to which a circadian running activity could be controlled by multiple biological oscillators within a single organism. Twelve male rats, housed in running wheels, had access to food from noon to 1 p.m. daily. In addition to this noon or fixed feeding, the rats received a moving feeding during which they had access to food for 1 hr every 25 hr. These two circadian feedings had a continually shifting phase relationship to each other. The animals responded to this regime by displaying separate bursts of running activity which were in relative coordination. Each animal's behavior shifted between the three following general patterns: (1) one cycle of activity, either before the fixed or the moving feed; (2) two bursts of activity, one before the fixed feeding and one preceding the moving feeding or (3) a burst of activity not entrained to either one of the feedings but rather free running between the two. When the animals were subsequently offered continuous access to food, 10 of the 12 rats maintained two bursts of activity.     

Entrainment of the circadian activity rhythm to the light cycle: Effective light intensity for a Zeitgeber in the retinal degenerate C3H mouse and the normal C57BL mouse

Effective light intensities for entrainment of activity rhythms were obtained in the retinal degenerated C3Hf/He mice and the normal C57BL/6J mice. The circadian activity rhythms of the mice were examined under LD 12:12 cycles with one of five different levels of light (L phase) and complete darkness (D phase). The thresholds of a Zeitgeber, defined as the light intensity effective for 50% entrainment, were estimated between 1 lux and 5 lux in the C3H and lower than 0.01 lux in the C57BL mice. These results suggest that at least two different kinds of photoreceptor including rods and cones participate in the photic entrainment of the circadian activity rhythms.     

Absence of formation of benzo[a]pyrene/DNA adducts in the cuttlefish (sepia officinalis,mollusca: Cephalopoda)

Benzo[a]pyrene (B[a]P) injected intramuscularly into the base of the arms of cuttlefish was released continuously from the injection site and removed from the organism. Only a portion of the compound accumulated in the body. Twenty-four hr after its injection, 75% of B[a]P applied in olive oil was removed from the cuttlefish, and 1.2% was found in the body outside the head, the site of injection. If the carcinogen was dissolved in dimethylformamide, the removal of B[a]P was slower, so that only 18% of the injected B[a]P was removed from the organism and 0.36% accumulated in the body outside the head 24 hr after injection. The high level of B[a]P in gills and hemolymph 4 hr after injection and the kinetics of the decrease of its concentration with time indicate that these two organs could be involved in the excretion of B[a]P from the body. The B[a]P/DNA adducts characteristic for vertebrates could not be demonstrated in gills, skin, brain, hepatopancreas, and lymphocytes of the cuttlefish 24 hr after injection of B[a]P. The dose of the carcinogen injected into the cuttlefish was 2—4 times higher than the dose resulting in the formation of a high level of B[a]P/DNA adducts in the vertebrates. A different metabolism of B[a]P in the tissue of cephalopods, compared to vertebrates, could be less favorable to the process leading to malignant transformation and could explain the absence from the literature of reports of tumors in cephalopods. © 1994 Wiley-Liss, Inc.