Biomedical subjects

F Malaval

Publications and source records attributed to F Malaval.

42 records · Page 3Linked to original sources

PubMed1980

[Correlation between the circadian rhythms of plasma ACTH and corticosterone, and of motor activity, evolving freely after ocular enucleation in the rat].

21, 35 and 60 days after bilateral ocular enucleation a similar phase-shift vs an environmental 12 L-12 D photoperiod was observed in the circadian rhythms of plasma ACTH and corticosterone (B) and of motor activity. This phase-shift is indicative of free-running endogenous circadian rhythms whose period was estimated at 2492-24.3 h. The rhythms' amplitude (C) appeared decreased at 21 d for both hormones, and subsequently for ACTH only, whereas the rhythms' mean levels (Co) were reduced for ACTH and augmented for B. The amount of total motor activity per day decreased progressively down to 60% of controls at 60 d. Under otherwise non-fluctuating conditions the photoperiod appears, therefore as a main synchronizer to the endogenous pace-maker(s) driving those hormonal and behavioral rhythms.

Adrenocorticotropic Hormone↗

PubMed1980

Serotoninergic system and circadian rhythms of ACTH and corticosterone in rats.

The circadian rhythms of plasma ACTH and corticosterone and of locomotor activity were explored in chronically cannulated female rats, after elimination of serotoninergic (5HT) innervation of the SCN (suprachiasmatic nuclei) either by stereotaxic lesion of the median and dorsal midbrain raphe nuclei (RX) or by local injection of SCN with the neurotoxin 5,7-dihydroxytryptamine (5,7DHT). Completeness of 5HT denervation was checked on serial sections of the hypothalamus either by the Falk-Hillarp technique or by radioautography. Neither lesion eliminated the intrahypothalamic 5HT system, which, however does not take part in the 5HT innervation of the SCN. In both experimental series, the circadian rhythms of the three parameters investigated were maintained in unchanged phase relationships compared to the sham-lesioned controls, and with respect to the photoperiod (12 light-12 dark). However, the estimated amplitudes of the ACTH rhythms dropped by 43% (RX) to 47% (5,7DHT) and their mean levels by 44% (RX) to 60% (5,7DHT), whereas the corticosterone rhythm displayed normal amplitude and its mean level rose by 24% (RX) or 38% (5,7DHT). In regard to locomotor activity rhythm, the most noticeable alteration was a 25-55% increase in the light-phase activity of both experimental groups with a correlative increase in the L/D activity ratio. The essential role of 5HT innervation of the SCN therefore seems to be to facilitate circadian control of the ACTH rhythm.

Adrenocorticotropic Hormone↗

PubMed1980

[Effect of the time of administration of 5-hydroxytryptophan on the restoration of circadian stimulation of ACTH secretion in rats treated with p-chlorophenylalanine].

In female rats kept under a photoperiod of 12L-12D (50 lux from 07.00-19.00 h) the pharmacological blockade of serotonin synthesis by pCPA (2 X 300 mg/kg i.p.) obliterated the diel ACTH stimulation, which could, however be restored by an additionnal 5-HTP injection (60 mg/kg i.p.), provided that the serotonin precursor was administered at 11.00 h. If injected at 23.00 h the same dosage of 5-HTP failed to elicit any increase in plasma ACTH. The circadian ACTH rhythm appears, therefore to depend upon a daily activation of the serotoninergic system occurring 4 h after the onset of the light phase.

5-Hydroxytryptophan↗

PubMed1979

Effects of lesions of the suprachiasmatic nuclei and of p-chlorophenylalanine on the circadian rhythms of adrenocorticotrophic hormone and corticosterone in the plasma, and on locomotor activity of rats.

Adrenocorticotrophin (ACTH) and corticosterone in the plasma of adult female rats were measured sequentially at 4 h intervals for 24 h before and after lesions of the suprachiasmatic nuclei or treatment with p-chlorophenylalanine (to inhibit serotonin synthesis). After lesions or p-chlorophenylalanine treatment, the concentrations of ACTH were diminished relative to those in control animals and rhythmic changes could not be detected. However, injection of animals, pretreated with p-chlorophenylalanine, with 5-hydroxytryptophan (60 mg/kg) 8 h before the time when plasma ACTH is maximal in intact animals, stimulated ACTH secretion up to control values. Mean corticosterone concentrations in plasma remained unchanged (after lesions) or increased (after p-chlorophenylalanine). This increase was associated with an increased minimal concentration of corticosterone. After both treatments there was evidence of continued circadian or ultradian rhythms of corticosterone concentration. Locomotor activity of female rats given identical treatment, but without blood sampling, indicated that nocturnal activity was diminished after lesions whereas diurnal activity was enhanced after p-chlorophenylalanine treatment. Periodicity analysis detected the persistence of free-running circadian, and sometimes ultradian activity, rhythms. Adrenalectomy did not alter further the activity pattern observed in rats with lesions. These results therefore support the proposition that both the suprachiasmatic nuclei and the serotoninergic system play an irreplaceable role in the mechanism of ACTH secretory rhythms. The suprachiasmatic nuclei are also important for synchronization of locomotor activity and corticosterone rhythms, which may both persist after the suppression of ACTH rhythms.

5-Hydroxytryptophan↗

PubMedDate not supplied

Chronic orthostatic and antiorthostatic restraint induce neuroendocrine, immune and neurophysiologial disorders in rats.

The tail-cast suspension rat model has been developed in ground laboratories interested in space physiology for extensive study of mechanisms causing the pathophysiological syndrome associated with space flights. We used individually-caged male rats to explore the effects of acute and chronic (7d) orthostatic restraint (OR) and head-down anti-orthostatic restraint (AOR) on a series of physiological variables. The acute restraint study showed that (1) the installation of the OR device induced an acute reaction for 2 days, with a substantial rise in ACTH (x2) and CORT (x6), and that (2) the head-down tilt from OR to AOR induced (i) within 10 min and lasting 60 min a 2-fold rise in the intra-cerebro-ventricular pressure (Picv) monitored with an icv telemetric recording system, which receded to normal between 60 and 120 min; and (ii) within 30 min a short-lived 4-fold rise in plasma ACTH and CORT levels. Chronic OR induced (1) the suppression of the diurnal ACTH/CORT rhythm, with increased mean levels, especially for ACTH, (2) a degraded circadian locomotor activity rhythm manifested by a significant reduction in the spectral power of the 24h periodicity and a concomitant emergence of shorter (ultradian) periodicities, (3) an associated, but less pronounced alteration of the diurnal rhythm in body temperature; and (4) a marked increase in baseline plasma levels of IL-1 beta and an increased reactivity in cytokine release following an E. coli endotoxin (LPS) challenge. AOR induced (1) a similar obliteration of the circadian ACTH/CORT rhythm, (2) the loss of close correlation between ACTH and CORT, (3) a generalized increase in baseline plasma IL-1 beta levels and (4) more extensive degradation of the circadian periodicity for both locomotor activity and, to a lesser extent, body temperature, replaced by dominant spectral powers for ultradian periodicities (3 to 10h). In conclusion, both experimental paradigms--but AOR more than OR--caused a blockade of the circadian rhythmicity of major physiological variables, the loss of normal correlations between ACTH and CORT, and inflammatory-immune hyperreactivity. These pathophysiological disorders may all be parts of a complex chronic stress syndrome.

Adrenocorticotropic Hormone↗

PubMedDate not supplied

Chronic restraint enhances interleukin-1-beta release in the basal state and after an endotoxin challenge, independently of adrenocorticotropin and corticosterone release.

To explore the interactions between the hypothalamic-pituitary-adrenocortical axis and the immune system under stress conditions, we used an experimental rat model for chronic tail-restraint devised earlier for ground studies in space physiology. The system was used in two positions: (1) the orthostatic restraint position (OR) and (2) the antiorthostatic position (AOR) after the rat hind limbs had been raised by a head-down tilt. After 7 days of either restraint, sequential blood samples were taken via an indwelling aortic cannula, before and at various time intervals between 15 and 300 min after an intravascular infusion of 25 micrograms/kg lipopolysaccharide (LPS). The plasma titers of adrenocorticotropin (ACTH), corticosterone (CORT) and interleukin-1 beta (IL-1 beta) were assayed. Under basal conditions, both OR and AOR restraints induced a 5-fold increase in IL-1 beta with no significant changes in ACTH and CORT levels. A robust increase in all three variables was observed after LPS injection. However, the IL-1 beta response to LPS was significantly higher in both restrained groups than in controls. Both the amplitude and the percentage of individually restrained rats displaying elevated IL-1 beta levels were increased up to 5 h. In contrast, the ACTH and CORT post-LPS responses were normal in the OR group. They were unusually dissociated in the AOR rats, which displayed depressed ACTH levels associated with slightly increased CORT levels. Our results suggest that immune-neuroendocrine responses to chronic restraint stress may differ from those generally observed in acute stress.

Adrenocorticotropic Hormone↗