Circadian rhythm of hypothalamo-hypophyseal-adrenal activity in the chicken.

Corticosteroid production, ACTH content in the adenohypophysis and CRF content in the median eminence were studied in vitro and in vivo in the 3-weeks-old chicken according to SAFFRAN and SCHALLY in four different parts of the day: at 6 and 12 a.m., and 6 and 12 p.m. The chicken adrenals in vitro produced only corticosterone in fluorimetrically measurable amounts, with the maximum during the day and the minimum in the evening and at night. Sensitivity to ACTH of the adrenals in vitro was higher during the day than in the evening or at night. After paper-chromatographic separation, steroid hormones equivalent to corticosterone and cortisol could be detected fluorimetrically in the plasma. The "cortisol" level was about 2-2.5 times higher than the corticosterone level. Plasma "cortisol" level displayed the peak at 6 a.m. and the minimum at 12 p.m., while corticosterone at 12 a.m. and 12 p.m., respectively. ACTH content in the adenohypophysis was lowest at 6 a.m. then increased gradually until 12 p.m. CRF level in the median eminence fell during the forenoon, was lowest at noon, to rise up to 6 p.m. and persist at a high level between 6 p.m. and 6 a.m. Thus, in the 3-week-old chicken the functioning of the hypothalamo-hypophyseal-adrenal system displays a circadian rhythm characteristic of animals showing diurnal activity.     

Genetic control of tryptophan hydroxylase activity in the mouse brain

Interstrain differences in tryptophan hydroxylase activity have been studied in the brain stem of 12 inbred strains of mice. The Mendelian analysis has been performed using BALB/c and C57BL/6J mice. The activity of tryptophan hydroxylase was shown to be controlled by a single gene having two alleles with additive effect. It was suggested that this gene controls either the structure of enzyme's molecule, or its amount in a nervous tissue.     

Chronic amphetamine administration decreases brain tryptophan hydroxylase activity in cats

Chronic administration of d-amphetamine sulfate (7.5 mg/kg, i.p. every 12 hrs. for 6 days) to cats produced significant decreases in the Vmax of brain-stem and forebrain tryptophan hydroxylase when measured 1 day (?34 and ?46%) and 10 days (?17 and ?30%) after the final amphetamine injection. Serotonin and 5-hydroxyindoleacetic acid (5HIAA) levels were decreased by a similar magnitude. A single injection of amphetamine (7.5 mg/kg) produced no significant changes in tryptophan hydroxylase activity, serotonin, or 5HIAA when measured 1 day after the injection. Neither acute nor chronic amphetamine treatment produced any significant changes in the Km of tryptophan hydroxylase for either tryptophan or the natural co-factor, tetrahydrobiopterin. These data suggest that chronic amphetamine treatment decreases central serotonergic neurotransmission by an action on the rate-limiting enzyme in serotonin biosynthesis.     

Circadian rhythm of autophagy and light responses of autophagy and disk-shedding in the rat retina

Summary The rhythm of autophagic degradation (AV) in visual cell inner segments shows circadian characteristics: it persists under constant conditions of continuous darkness (DD) and continuous light (LL) and can be reentrained to phase-shifts of the light-dark (LD) cycle. However, unlike the rhythm of disk-shedding and many other circadian rhythms, the rhythm of AV persists with a distinct peak even after 3 days of LL and is rapidly abolished to almost baseline levels after 1.5 days of DD, confirming our previous observations of a strong light-dependence of AV. Since the rhythms of disk-shedding and AV reveal this inverse pattern in DD and LL, different regulative mechanisms may be involved.Light stimulation with increasing intensities at day-time and night-time evoked AV responses that increased and disk-shedding responses that decreased at higher intensities. Furthermore, both the AV and phagosome response was different according to day-time or night-time stimulation, pointing towards the possibility of a circadian phase of sensitivity to light.Abbreviations AV autophagic degradation, autophagic vacuole, autophay - LD light dark cycle - DD constant darkness - LL constant light - CNS central nervous system - SCN suprachiasmatic nucleus - DA dopamine - ftc footcandle - ANOVA analysis of variance     

Circadian rhythm of DNA synthesis and mitotic activity in tongue keratinocytes

Tongue keratinocytes have a high mitotic index (MI) with an evident circadian variation. Our study set out to compare and contrast two phases of the cell cycle: DNA synthesis (S-phase), with inmunocytochemical detection by bromodeoxyuridine (BrdU), and mitosis (M-phase), by the colchicine-arrest of metaphase method, exploring both the dorsal and ventral surfaces of the mouse tongue throughout a circadian period. Adult male mice standardized for light periodicity used for MI experiment were injected intraperitoneally with colchicine. Other animals were injected intraperitoneally with 5-BrdU for S-phase determination. Animals given both treatments were divided into six groups and killed at 4 h intervals until 20:00 h. Tongue samples were processed for histology and immuno-histochemistry. S and M indices were expressed as labelled nuclei or colchicine metaphases, respectively, per 1000 nuclei. Peak MI occurred at 12:00, with the minimum value at 20:00 on dorsal and ventral tongue surfaces. Peak S-phase was at 04:00, whereas the minimum value was at 16:00 for both surfaces. These results show that the proliferative activity of the tongue epithelium is of similar intensity and temporal distribution on both surfaces.     

Circadian rhythm in acetylcholinesterase activity during aging of the central nervous system

The circadian rhythm of acetylcholinesterase (AChE) activity was investigated in the cerebrum, cerebellum, medulla and optic lobes of rats aged 1 day and 3, 13, 44 and 87 weeks. The rhythm was found to be age-dependent. Animals aged 1 day exhibited a bimodal rhythm in all the four regions of the brain studied. At 3 and 13 weeks the activity was unimodal. The peak occurred during the light-on phase at 3 weeks and during the light-off phase at 13 weeks. At 87 weeks the rhythms in the medulla and cerebrum were similar to those of 44 week animals. By contrast the cerebellum had a bimodal rhythm with peaks at intervals of 12 h. In the optic lobes there was a shift from a bimodal pattern at 44 weeks to a unimodal one at 87 weeks. The times of onset of the light-on and light-off peaks in different regions of the brain differed with age.