Search results for "Rhythm"
showing 10 items of 822 documents
24-hour-variation of pineal gland volume, pinealocyte nuclear volume and mitotic activity in male Sprague-Dawley rats
1983
In two experiments carried out on two alternate days, the 24-h-rhythmicity of pineal gland volume, pinealocyte nuclear size in cortex and medulla and mitotic activity were studied in male Sprague-Dawley rats, to assess to what extent morphological parameters reflect the pronounced day/night differences in pineal melatonin formation. Pineal volume exhibited statistically significant changes in the second experiment only, with a distinct trough at 6 p.m. Karyometry revealed highly variable patterns. In the first experiment, pinealocyte nuclear changes lacked parallelism in cortex and medulla. The cortex exhibited a bimodal curve with peaks at noon of the first day and at 6 a.m. of the second …
Tentative immunohistochemical demonstration of melatonin in the rat pineal gland
1977
In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anti-body used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.
Circadian and photoperiodic correlation between the number of pineal gland synaptic ribbons and serum melatonin levels in the rat.
1987
A study is made of the number of pineal gland synaptic ribbons in 35 maleWistar rats over a 24-hour period during the months of September and February, in correlation to the serum melatonin levels during the same periods and photophases.The results of the study confirm those reported by others authors and suggest that the synaptic ribbons may be the stimuli-transmitting organs facilitating pineal secretory function.
Atypical 24-hour rhythms of serotonin N-acetyltransferase activity in the rat pineal gland.
1988
Previous long-term studies have shown that in the pineal gland of rats melatonin synthesis is subject to infradian rhythms with periods between 4 and 7 days. Since in these studies melatonin-related parameters were measured at one timepoint of a 24-hr cycle only, the aim of the present investigation was to extend these experiments by more frequent sampling, to characterize the infradian rhythmicity in more detail. Male Sprague-Dawley rats kept under a light schedule of LD 12:12 (lights on at 0700) were killed at 6-hr intervals on 8 consecutive days. After decapitation the pineal gland was rapidly dissected out, followed by measurements of one of the melatonin-forming enzymes, serotonin N-ac…
Fos-related antigen 2 (Fra-2) memorizes photoperiod in the rat pineal gland
2004
As the physiological role of fos-related antigen-2 (Fra-2) is largely unknown and since the pineal plays an important role in the photoperiodic control of the body, we have tested the hypothesis that Fra-2 expression is photoperiod-dependent and may be involved in imprinting photoperiod on the pineal gland and the body as a whole. To this end, we have investigated Fra-2 mRNA expression and Fra-2 protein expression under various light/dark (LD) cycles. A clear nocturnal increase occurs for both monitored parameters under all photoperiodic conditions studied. The level of Fra-2 protein expression clearly depends on photoperiod, because the amount of protein at dark onset and during the night …
The photoperiod entrains the molecular clock of the rat pineal.
2005
The suprachiasmatic nucleus-pineal system acts as a neuroendocrine transducer of seasonal changes in the photoperiod by regulating melatonin formation. In the present study, we have investigated the extent to which the photoperiod entrains the nonself-cycling oscillator in the Sprague-Dawley rat pineal. For this purpose, the 24-h expression of nine clock genes (bmal1, clock, per1, per2, per3, cry1, cry2, dec1 and dec2) and the aa-nat gene was monitored under light-dark 8 : 16 and light-dark 16 : 8 in the rat pineal by using real-time RT-PCR. The 24-h pattern of the expression of only per1, dec2 and aa-nat genes was affected by photoperiod. In comparison with the short photoperiod, the durat…
Influence of photoperiodic history on clock genes and the circadian pacemaker in the rat retina
2006
The influence of seasonal lighting conditions on expression of clock genes and the circadian pacemaker was investigated in the rat retina. For this purpose, the 24-h profiles of nine clock genes (bmal1, clock, per1, per2, per3, dec1, dec2, cry1 and cry 2) and the arylalkylamine N-acetyltransferase gene as an indicator of the circadian pacemaker output were compared between light-dark periods of 8 : 16 and 16 : 8 h. The photoperiod influenced the daily patterns of the amount of transcript for per1, per3, dec2 and arylalkylamine N-acetyltransferase. This indicates that photoperiodic information modulates clock gene expression in addition to the circadian pacemaker of the retina. Under constan…
The role of the hypothalamic paraventricular nuclei for the regulation of pineal melatonin synthesis: New aspects derived from the vasopressin-defici…
1990
Abstract There is evidence for an involvement of the hypothalamic paraventricular nuclei (PVN) in the regulation of pineal melatonin synthesis in rats. Since electrical stimulation of the PVN or the systemic administration of arginine-vasopressin (AVP) result in a depression of the nocturnal melatonin surge, this neuropeptide appears to be pivotal for the transduction of PVN-efferent, pinealopetal signals. We therefore used an AVP-deficient animal model, the Brattleboro rat, to further investigate the mechanisms responsible for pineal regulation. Anesthetized adult male animals received 2 min of bilateral electrical stimulation of the PVN either during the day or at night. Thirty min later,…
The role of arginine-vasopressin for pineal melatonin synthesis in the rat: involvement of vasopressinergic receptors.
1991
Abstract The endogenously synthesized nonapeptide arginine vasopressin (AVP) is thought to be involved in transduction of photic information to the pineal gland. The enhancement of circulating AVP leads to a suppression of the nocturnal melatonin surge the mechanisms of which are unknown so far. We therefore studied the effect of dDAVP, an AVP analog with antidiuretic but without vasopressor activity, on pineal melatonin synthesis in Sprague-Dawley and AVP-deficient Brattleboro rats. The nocturnal intra-arterial application of dDAVP mimicked the inhibitory effect of AVP on the activity of the rate-limiting enzyme for pineal melatonin synthesis, N-acetyltransferase (NAT), in both rat strains…
The effects of sex hormones, prolactin, and chorionic gonadotropin on pineal electrical activity in guinea pigs.
1981
Microelectrophoretic application of sex hormones onto pineal cells in guinea pigs has shown different responses in pregnant females as compared to males. In pregnant females estrone caused excitation in 74% of the cells tested, while progesterone and testosterone, prolactin, and HCG were inhibitory in a majority of the cells tested, while progesterone and testosterone, prolactin, and HCG were inhibitory in a majority of the cells. In contrast, in males estrone caused excitation of only 19% but inhibition of 37%. A smaller percentage of cells was inhibited by progesterone, while the predominant response to testosterone was excitation. These results suggest that the pineal gland may be under …