Navegando por Autor "Zaretsky, Dmitry V."
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Item Brown adipose tissue thermogenesis heats brain and body as part of the brain-coordinated ultradian basic rest-activity cycle.(2009) Ootsuka, Youichirou; Menezes, Rodrigo Cunha Alvim de; Zaretsky, Dmitry V.; Alimoradian, Abbas; Hunt, Joseph; Stefanidis, Aneta; Oldfield, Brian J.; Blessing, William W.Brown adipose tissue (BAT), body and brain temperatures, as well as behavioral activity, arterial pressure and heart rate, increase episodically during the waking (dark) phase of the circadian cycle in rats. Phase-linking of combinations of these ultradian (<24 h) events has previously been noted, but no synthesis of their overall interrelationships has emerged. We hypothesized that they are coordinated by brain central command, and that BAT thermogenesis, itself controlled by the brain, contributes to increases in brain and body temperature. We used chronically implanted instruments to measure combinations of bat, brain and body temperatures, behavioral activity, tail artery blood flow, and arterial pressure and heart rate, in conscious freely moving Sprague–Dawley rats during the 12-h dark active period. Ambient temperature was kept constant for any particular 24-h day, varying between 22 and 27 °C on different days. Increases in BAT temperature (>0.5 °C) occurred in an irregular episodic manner every 94_43 min (mean_SD). Varying the temperature over a wider range (18–30 °C) on different days did not change the periodicity, and neither body nor brain temperature fell before BAT temperature episodic increases. These increases are thus unlikely to reflect thermoregulatory homeostasis. Episodic BAT thermogenesis still occurred in food-deprived rats. Behavioral activity, arterial pressure (18_5 mmHg every 98_49 min) and heart rate (86_31 beats/min) increased approximately 3 min before each increase in BAT temperature. Increases in BAT temperature (1.1_0.4 °C) were larger than corresponding increases in brain (0.8_0.4 °C) and body (0.6_0.3 °C) temperature and the BAT episodes commenced 2–3 min before body and brain episodes, suggesting that BAT thermogenesis warms body and brain. Hippocampal 5–8 Hz theta rhythm, indicating active engagement with the environment, increased before the behavioral and autonomic events, suggesting coordination by brain central command as part of the 1–2 h ultradian basic rest-activity cycle (BRAC) proposed by Kleitman.Item Cardiovascular and thermal responses evoked from the periaqueductal grey require neuronal activity in the hypothalamus.(2009) Menezes, Rodrigo Cunha Alvim de; Zaretsky, Dmitry V.; Fontes, Marco Antônio Peliky; DiMicco, Joseph A.Stimulation of neurons in the lateral/dorsolateral periaqueductal grey (l/dlPAG) produces increases in heart rate (HR) andmean arterial pressure (MAP) that are, according to traditional views, mediated through projections to medullary autonomic centres and independent of forebrain mechanisms. Recent studies in rats suggest that neurons in the l/dlPAG are downstream effectors responsible for responses evoked from the dorsomedial hypothalamus (DMH) from which similar cardiovascular changes and increase in core body temperature (Tco) can be elicited.We hypothesized that, instead, autonomic effects evoked from the l/dlPAG depend on neuronal activity in the DMH. Thus, we examined the effect of microinjection of the neuronal inhibitor muscimol into the DMH on increases in HR, MAP and Tco produced by microinjection of N-methyl-d-aspartate (NMDA) into the l/dlPAG in conscious rats. Microinjection of muscimol alone modestly decreased baseline HR and MAP but failed to alter Tco. Microinjection of NMDA into the l/dlPAG caused marked increases in all three variables, and these were virtually abolished by prior injection of muscimol into the DMH. Similar microinjection of glutamate receptor antagonists into theDMHalso suppressed increases inHR and abolished increases in Tco evoked from the PAG. In contrast, microinjection of muscimol into the hypothalamic paraventricular nucleus failed to reduce changes evoked from the PAG and actually enhanced the increase in Tco. Thus, our data suggest that increases in HR, MAP and Tco evoked from the l/dlPAG require neuronal activity in the DMH, challenging traditional views of the place of the PAG in central autonomic neural circuitry.