Adrenocorticotropic regulations after bilateral lesions of the paraventricular or supraoptic nuclei and in Brattleboro rats.
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Adrenocorticotropic Hormone↗
Biomedical subjects
I Assenmacher
Publications and source records attributed to I Assenmacher.
Light- and electron-microscope differentiation of axons containing vasopressin and oxytocin in the neurohypophyseal lobe of the rat.
In neural lobes of Sprague-Dawley rats fixed with glutaraldehyde but without osmication, toluidine blue staining of semi-thin sections revealed two clear axon types: type I, highly stained, and type II, slightly stained. After uranyl acetate and lead citrate impregnation of adjacent ultrathin sections, electron microscopy showed that type I axons contained electron-dense granules whereas type II axons mostly contained pale granules. When adjacent semi-thin sections were stained with toluidine blue or treated for immunocytochemistry, type I axons were found to react with vasopressin antisera, and type II axons with oxytocin antisera. In neural lobes of Brattleboro rats, only type II axons were observed and contained pale granules. Both in light and electron microscopy, glutaraldehyde fixation without osmication, therefore provided a simple and reliable approach to distinguish between neurohypophyseal axons containing vasopressin and oxytocin, respectively.
Animals↗
Effects of raphe lesions on circadian ACTH, corticosterone and motor activity rhythms in free-running blinded rats.
Blinded female rats underwent additional midbrain raphe lesions, in order to explore the role of the raphe in the organization of endogenous circadian rhythms for ACTH, corticosterone (B) and motor activity (MA). Amplitudes and mean levels of rhythms were depressed for ACTH and MA, with persistent free-running circadian periodicity for MA and, in several rats, for ACTH and B as well. Other rats exhibited split circadian and ultradian rhythmicity for ACTH and B, whereas other again displayed no detectable ACTH rhythmicity. These results are discussed in the light of the structure of circadian pacemaker systems.
Adrenocorticotropic Hormone↗
Radioautographic studies on the neurohypophysial projections of the supraoptic and paraventricular nuclei in the rat.
The distribution of labelled axonal pathways was studied after unilateral stereotaxic injection of 3H-leucine into either supraoptic (SON) or paraventricular nuclei (PVN). In addition to extrahypothalamic projections of both nuclei, the main efferents appeared to run towards the neurohypophysis, yet with a strikingly different pattern. At the neurohypophysial levels, the SO-neurohypophysial tract crossed the inner layers of the median eminence (ME) before scattering in the neural lobe. The PV-neurohypophysial pathway, by contrast, provided an exclusive innervation to the external layer of the whole neurohypophysial organ, including the median eminence, infundibular stalk and neural lobe. The functional correlates of the clear-cut anatomical distinctness between the two magnocellular neurosecretory systems are discussed.
Animals↗
Ultrastructural organization of actin filaments in neurosecretory axons of the rat.
The ultrastructural organization of actin filaments was studied in the neurohypophysial system of the rat after heavy meromyosin (HMM) labeling. This structural pattern is characterized by (1) a straight arrangement of the filaments parallel to the axonal axis in the proximal nondilated parts of axons, (2) a central location within axonal dilatations, and (3) a higher concentration within axonal endings where the filaments form a complex three-dimensional network. The relationships of the filaments to other axonal structures and organelles was further studied by use of electron microscopic stereoscopy. The actin filaments frequently appear anchored to the axolemma with either polar arrangements of the arrowhead decoration (i) at structurally undifferentiated sites, and (ii) more particularly within perivascular endings, at sites with electron-dense thickenings. In all axonal divisions actin filaments are also found to bind to filamentous material surrounding the microtubules and to various organelles. Within the terminal portions of the axons actin filaments exhibit close relationships to neurosecretory granules and to the numerous smooth microvesicles found in this region. Such preferential relationships are particularly observed both in axon ;terminals and in pituicytes, with coated vesicles frequently binding actin filaments. In water-deprived rats, the concentration of actin filaments is conspicuously increased along the axons and more clearly in the axonal swellings and endings, where they form a more complex and interconnected network. These data are discussed in the light of a possible involvement of contractile proteins in the mechanisms of axonal transport and terminal release of neurosecretory products.
Actins↗
Evidence of a sex related difference of transcortin level in adult ducks.
Corticosteroid binding globulin (CBG) serum level as evaluated by either equilibrium dialysis or gel filtration was found to be higher in male than in female adult ducks during the reproductive period. Castration did not modify CBG concentrations in females, whereas in males it induced a significant decreased in CBG, to the level observed in intact or castrated females. Testosterone injections administrated to castrated females increased CBG to the level of adult intact males. Finally it was found that testosterone stimulated CBG production in ducks without altering thyroxine levels.
Animals↗
[Effects of the destruction of the suprachiasmatic nuclei on the circadian rhythms of ACTH corticosterone and the general activity of female rats exposed to a aperiodic environment].
The effects of bilateral destruction of suprachiasmatic nuclei (SCN) on the temporal patterns of plasma concentrations in ACTH and corticosterone (sequential blood samples from an aortic cannula, at 4 h intervals over 48 h) and of general activity (stabilimeter recordings) were studied in female rats under constant illumination (LL : 10 lx). Under this arrhythmic environment, the SCN lesions induced a syndrome similar to that previously described in a photoperiodic environment (12 L-12 D). This SCN syndrome included : 1) blockade of the ACTH rhythm at baseline levels ; 2) maintained fluctuations of corticosterone, with either circadian or ultradian profiles ; 3) persistent rhythmicity of general activity, with a circadian periodicity in addition to ultradian periods. The persistence of a circadian rhythmicity in the SCN syndrome under arrhythmic environmental conditions, clearly argues in favour of the occurrence of endogenous components of the circadian pacemaker outside the SCN.
Adrenocorticotropic Hormone↗
Neural control of circadian rhythms in plasma ACTH, plasma corticosterone and motor activity.
The circadian rhythms for plasma ACTH and corticosterone (B), as well as motor activity, were explored in female rats after ocular enucleation (O-X), stereotaxic lesion of the suprachiasmatic nuclei (SCN-X) or of midbrain raphe nuclei (R-X), or both O-X and R-X, pharmacological blockade of the serotoninergic (5HT) system by pCPA, sometimes bypassed by 5-HTP, or 5-HT denervation of the SCN by local injection of 5,7-DHT. The three circadian rhythms explored responded quite differently to the treatments. In particular, the ACTH and B rhythms lost their usual close correlations. The amplitude and mean level of ACTH fluctuations were depressed after all treatments, but remained normal or were enhanced for B rhythm. ACTH rhythmicity actually was undetectable after SCN-X, pCPA and, in several rats, combined O-X and R-X, whereas persisting circadian and/or ultradian B and locomotor activity rhythms were always measured. The participation of the suprachiasmatic nuclei, the midbrain raphe nuclei and other possible 5-HT components in a complex circadian pacemaker system is discussed.
Adrenocorticotropic Hormone↗
[Cécile Mialhe-Voloss (1917-1979)].
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Biochemistry↗
Serotonin and the regulation of pituitary hormone secretion and of neuroendocrine rhythms.
The importance of 5-HT synaptic transmission for induced or cyclic activation of pituitary secretion now seems widely agreed upon. Raphe structures, the suprachiasmatic nucleus, and, hypothetically, identified mesencephalic 5-HT containing neurons can be assumed to represent parts of the neuronal circuitry of a central clock which synchronizes neuroendocrine rhythms. Cyclic input from the pineal gland may also be involved, though the meaning of this has not yet been clearly established. The primary role of the transmitter may be to modulate transmission to neurosecretory neurons at the output of this clock. This modulation is not hormone-specific and affects, simultaneously, several endocrine functions. 5-HT has also been shown to facilitate the pituitary response to discrete neuroendocrine reflexes, such as the suckling-induced release of prolactin. 5-HT interactions with hormone control provide a good illustration of the neuromodulatory role of the amine.
Animals↗
[Stress responses of the ACTH-corticosterone and LH-testosterone systems in male rats given naloxone].
A single injection of naloxone (1 mg/kg s. c.) increased plasma baseline levels by 6 times for ACTH, 17 times for corticosterone, 3 times for LH and 2 times for testosterone. A concomitant ether-stress induced a further 6 fold increment in ACTH and an additional 2 fold increment in corticosterone, both hormones attaining their similar levels to those after ether-stress alone. On the other hand no further increment was observed for LH and testosterone, which actually were more stimulated by naloxone than by stress alone. The tonic inhibition exerted by endogenous opiates on ACTH and LH appears, therefore, to interfere with stress in a different way for the two neuroendocrine systems considered.
Adrenocorticotropic Hormone↗
[Effect of the equilibrium constant of steroid-transcortin binding on the metabolic clearance rate of cortisol and corticosterone in the rabbit].
In the Rabbit the metabolic clearance rate (MCR) was shown to be eightfold greater for corticosterone than for cortisol. This marked difference in the clearance kinetics of both glucocorticosteroids appears to result from a difference in the affinity of transcortin (CBG) towards both hormones, since the maximal association constant of CBG was twice as high for cortisol as for corticosterone.
Aldosterone↗
[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↗
Seasonal variations in the circulating concentrations of growth hormone in male Peking duck (Anas platyrhynchos) and teal (Anas crecca); correlations with thyroidal function.
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Animals↗
Postnatal development of estradiol receptor in female and male rats.
The concentration of available cytoplasmic estradiol receptor was quantified in the postnatal hypothalamus and pituitary of male and female rats, aged from 4 to 28 days. The uterine receptor was measured in female rats. The method used was designed to avoid non-specific contamination of cytosol from very young animals by plasma proteins, especially alpha-feto-protein (AFP). In the hypothalamus, the concentration of estradiol binding sites was maximal 6 days after birth, and declined until day 28 to low constant level. In the pituitary, the estradiol receptor concentration increased from day 4 and reached a plateau at 13--14 days, whereas in the uterus, the concentration of cytoplasmic binding sites rose up to day 10--12, and then markedly decreased.
Aging↗
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↗
Temporal relationships between the circadian rhythmicity in plasma levels of pituitary hormones and in hypothalamic concentrations of releasing factors.
Ovariectomized female rats were implanted with estradiol containing silastic implants to induce constant circulating levels of the steroid, and sacrificed every 2 h in order to determine neuroendocrine rhythms. Under these conditions, we observed very marked circadian fluctuations in the hypothalamic concentrations of corticotropin-releasing factor (CRF), luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH), and in plasma levels of adrenocorticotropin (ACTH), corticosterone, luteinizing hormone (LH) and prolactin; the amplitude of the prolactin cycle was in particular much higher than in non-chronically estrogenized animals. The daily variation in CRF, ACTH and corticosterone showed significant rank correlations. Changes in hypothalamic content of LHRH and TRH were biphasic; the increase observed during the light period was abruptly interrupted by a depletion episode, coincident with the period of maximal LH and prolactin secretion, respectively. The initial phase of ACTH, LH and prolactin increments occurred between 11.00 and 15.00 h, and was relatively well synchronized. The steepest rise in ACTH and prolactin occurred at the same time, and preceded that of LH by a constant lag of about 2 h. After that initial period, secretion kinetics of the three hormones followed an independent pattern. The data suggest that increased secretion of several hormones results from activation of neural mechanisms occurring within a limited period of the 24-hour cycle.
Adrenalectomy↗
[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↗