The American journal of physiology
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To investigate the adaptation of melatonin secretion to an abrupt time shift and the effects of sleep facilitation with a hypnotic, eight subjects were submitted to an 8-h advance shift achieved by advancing bedtimes from 2300-0700 to 1500-2300. Each subject participated in two studies (i.e., placebo and zolpidem). Each study included a baseline period with dim light during waking hours and 2300-0700 bedtimes in total darkness. ⋯ There was no relationship between sleep parameters and the magnitude of the melatonin shifts. Thus the overall advance of melatonin profiles was primarily achieved during the initial exposure to an 8-h period of darkness. The present data suggest that exposure to dark affects human circadian phase.
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Accumulating evidence demonstrates that genotoxic and oxidant stress can induce programmed cell death or apoptosis in cultured cells. However, little is known about whether oxidative stress resulting from the deleterious effects of hyperoxia can induce apoptosis in vivo and even less is known regarding the functional significance of apoptosis in vivo in response to hyperoxia. Using hyperoxia as a model of oxidant-induced lung injury in the rat, we show that hyperoxic stress results in marked apoptotic signals in the lung. ⋯ Furthermore, similar to the hyperoxia-tolerant LPS-pretreated young rats, the nontolerant LPS-pretreated aged rats also exhibited a significantly reduced apoptotic index compared with aged rats exposed to hyperoxia alone. Taken together, our data suggest that hyperoxia-induced apoptosis in vivo can be modulated by both aging and tolerance effects. We conclude that there is no overall relationship between apoptosis and tolerance.
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Although it is generally believed that circulating exogenous pyrogens [e.g., lipopolysaccharides (LPS)] induce fever via the mediation of endogenous pyrogens (EP) such as cytokines, the first of these, tumor necrosis factor-alpha, is usually not detectable in blood until at least 30 min after intravenous administration of LPS, whereas the febrile rise begins within 15 min after its administration. Moreover, although abundant evidence indicates that circulating LPS is cleared primarily by liver macrophages [Kupffer cells (KC)], these do not secrete EP in immediate response. This would imply that other factors, presumably evoked earlier than EP, may mediate the onset of the febrile response to intravenous LPS. ⋯ To test this postulated mechanism, we measured directly the levels of prostaglandin E2 (PGE2) in the interstitial fluid of the preoptic anterior hypothalamus (POA), the presumptive site of the fever-producing controller, of conscious guinea pigs over their entire febrile course, before and after C depletion by cobra venom factor (CVF) and before and after elimination of KC by gadolinium chloride (GdCl3). CVF and GdCl3 pretreatment each individually attenuated the first of the biphasic core temperature (Tc) rises after intravenous LPS, inverted the second into a Tc fall, and greatly reduced the usual fever-associated increase in POA PGE2. We conclude, therefore, that C activation may indeed be pivotal in the induction of fever by intravenous LPS and that substance(s) generated presumably by KC in almost immediate reaction to the presence of LPS and/or C may transmit pyrogenic signals via hepatic vagal afferents to the POA, where they rapidly induce the production of PGE2 and, hence, fever.
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We investigated the contribution of perivascular nerves and neurotransmitters to cortical spreading depression (CSD)-associated hyperperfusion in the rat. Chronic transection of the nasociliary nerve (NCN, 2 wk before) decreased ipsilateral CSD-associated hyperperfusion by 23 +/- 13% (mean +/- SD; n = 5, P < 0.05), whereas acute transection of the NCN or sham surgery had no effect (n = 8). When the NCN and parasympathetic nerve fibers (PSN) were both chronically transected, CSD hyperperfusion was attenuated by 55 +/- 19% (n = 5, P < 0.05). ⋯ Atropine (10(-4) M) afforded a decrease by 17 +/- 6% (n = 3). These reductions were not statistically significant. We conclude that CSD-associated hyperperfusion is mediated in part by a depolarization of trigeminal sensory and parasympathetic nerve fibers, resulting in a release of vasoactive trigeminal and parasympathetic neurotransmitters.
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The mathematical model presented in a previous work is used to simulate the time pattern of intracranial pressure (ICP) and of blood velocity in the middle cerebral artery (VMCA) in response to maneuvers simultaneously affecting mean systemic arterial pressure (SAP) and end-tidal CO2 pressure. In the first stage of this study, a sensitivity analysis was performed to clarify the role of some important model parameters [cerebrospinal fluid (CSF) outflow resistance, intracranial elastance coefficient, autoregulation gain, and the position of the regulation curve] during CO2 alteration maneuvers performed at different SAP levels. The results suggest that the dynamic "ICP-VMCA" relationship obtained during changes in CO2 pressure may contain important information on the main factors affecting intracranial dynamics. ⋯ Best fitting between model and clinical curves was achieved by minimizing a least-squares criterion function and adjusting certain parameters that characterize CSF circulation, intracranial compliance, and the strength of the regulation mechanisms. A satisfactory reproduction was achieved in all cases, with parameter numerical values in the ranges reported in clinical literature. It is concluded that the model may be used to give reliable estimations of the main factors affecting intracranial dynamics in individual patients, starting from routine measurements performed in neurosurgical intensive care units.