Navegando por Autor "Blessing, William W."
Agora exibindo 1 - 5 de 5
Resultados por página
Opções de Ordenação
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 Brown adipose tissue thermogenesis precedes food intake in genetically obese Zucker (fa/fa) rats.(2013) Kontos, Anna; Menezes, Rodrigo Cunha Alvim de; Ootsuka, Youichirou; Blessing, William W.In Sprague–Dawley rats, brown adipose tissue (BAT) thermogenesis occurs in an episodic ultradianmanner (BAT on-periods) as part of the basic rest–activity cycle (BRAC). Eating occurs approximately 15 min after the onset of BAT on-periods. Zucker obese (fa/fa) rats eat larger less frequent meals than control rats. In chronically instrumented conscious unrestrained Zucker obese rats we examined ultradian fluctuations in BAT, body and brain temperatures, and the relation between BAT temperature and eating. The interval between BAT temperature peaks for the 12 hour dark phase was 121 ± 3 (mean ± SE) min for Zucker obese rats and 91 ± 3 min for control lean rats (p b 0.01). Corresponding values for the light phase were 148 ± 6 and 118 ± 4 min (p b 0.01).Mean BAT and body temperatures were lower in Zucker obese rats, in comparison with lean controls, during both BAT on-periods and BAT off-periods. Mean brain temperatures were lower during BAT off-periods. Amplitudes of the BRAC-related increases in all 3 temperatures were greater in the Zucker obese rats. Meal onset in Zucker obese rats commenced 15 ± 1 min after the onset of a BAT on-period, not significantly different for the delay observed in lean control rats (18 ± 1 min, p > 0.05). Thus periods between eating are increased in the Zucker obese rats, but the action of leptin, absent in these animals, is not crucial for the timing of eating in relation to increases in BAT and body temperature. Lack of the normal excitatory action of leptin on brain-regulated BAT sympathetic discharge could also contribute to lower BAT thermogenesis in Zucker obese rats.Item Inactivation of neuronal function in the amygdaloid region reduces tail artery blood flow alerting responses in conscious rats.(2013) Mohammed, M.; Kulasekara, Keerthi; Menezes, Rodrigo Cunha Alvim de; Ootsuka, Youichirou; Blessing, William W.Few studies have investigated whether neuronal function in the amygdaloid complex is necessary for the occurrence of the cardiovascular response to natural (unconditioned) environmental threats. In the present investigation in conscious unrestrained Sprague–Dawley rats we inactivated neuronal function in the amygdaloid complex acutely (bilateral muscimol injections) or chronically (unilateral or bilateral ibotenic acid injections) and measured the effect on sudden falls in tail artery blood flow elicited by non-noxious salient stimuli (sympathetic cutaneous vasomotor alerting responses, SCVARs). After acute bilateral injection of vehicle (200 nl Ringer’s solution) the SCVAR index was 81± 2%, indicating that tail blood flow was reduced by 81% in response to the salient stimuli. After acute bilateral injection of muscimol (1 nmol in 200 nl of Ringer’s solution) into the amygdaloid complex the SCVAR index was 49± 5%, indicating that tail blood flow was reduced by 49% in response to the salient stimuli (p <0.01 versus vehicle, n= 7 rats for vehicle and 6 for muscimol). One week after unilateral ibotenic acid lesions, the SCVAR index was 68± 3%, significantly less than 90± 1%, the corresponding value after unilateral injection of vehicle (p < 0.01, n= 6 rats in each group). After bilateral ibotenic acid lesions the SCVAR index was 52± 4%, significantly less than 93± 1%, the corresponding value after bilateral injection of vehicle (p < 0.001, n= 6 rats in each group). Ibotenic acid caused extensive neuronal destruction of the whole amygdaloid complex, as well as lateral temporal lobe structures including the piriform cortex. Our results demonstrate that the amygdaloid complex plays an important role in mediating the tail artery vasoconstriction that occurs in rats in response to the animal’s perception of a salient stimulus, redirecting blood to areas of the body with more immediate metabolic requirements.Item SR59230A, a beta-3 adrenoceptor antagonist, inhibits ultradian brown adipose tissue thermogenesis and interrupts associated episodic brain and body heating.(2011) Ootsuka, Youichirou; Kulasekara, Keerthi; Menezes, Rodrigo Cunha Alvim de; Blessing, William W.SR59230A, a beta-3 adrenoceptor antagonist, inhibits ultradian brown adipose tissue thermogenesis and interrupts associated episodic brain and body heating. Am J Physiol Regul Integr Comp Physiol 301: R987–R994, 2011. First published August 3, 2011; doi:10.1152/ajpregu.00085.2011.—Brown adipose tissue (BAT) thermogenesis occurs episodically in an ultradian manner approximately every 80–100 min during the waking phase of the circadian cycle, together with highly correlated increases in brain and body temperatures, suggesting that BAT thermogenesis contributes to brain and body temperature increases. We investigated this in conscious Sprague-Dawley rats by determining whether inhibition of BAT thermogenesis via blockade of beta-3 adrenoceptors with SR59230A interrupts ultradian episodic increases in brain and body temperatures and whether SR59230A acts on BAT itself or via sympathetic neural control of BAT. Interscapular BAT (iBAT), brain, and body temperatures, tail artery blood flow, and heart rate were measured in unrestrained rats. SR59230A (1, 5, or 10 mg/kg ip), but not vehicle, decreased iBAT, body, and brain temperatures in a dose-dependent fashion (log-linear regression P 0.01, R2 0.3, 0.4, and 0.4, respectively, n 10). Ultradian increases in BAT, brain, and body temperature were interrupted by administration of SR59230A (10 mg/kg ip) compared with vehicle, resuming after 162 24 min (means SE, n 10). SR59230A (10 mg/kg ip) caused a transient bradycardia without any increase in tail artery blood flow. In anesthetized rats, SR59230A reduced cooling-induced increases in iBAT temperature without affecting cooling-induced increases in iBAT sympathetic nerve discharge. Inhibition of BAT thermogenesis by SR59230A, thus, reflects direct blockade of beta-3 adrenoceptors in BAT. Interruption of episodic ultradian increases in body and brain temperature by SR59230A suggests that BAT thermogenesis makes a substantial contribution to these increases.Item Sympathetic cutaneous vasomotor alerting responses (SCVARs) are associated with hippocampal theta rhythm in non-moving conscious rats.(2009) Menezes, Rodrigo Cunha Alvim de; Ootsuka, Youichirou; Blessing, William W.Alerting stimuli that cause sympathetic cutaneous vasomotor alerting responses (“SCVARs”) in the thermoregulatory vascular bed of the rabbit ear pinna also induce theta (5–8 Hz) rhythm in the hippocampal EEG, a marker that the animal is engaged with the environment. The present study determines the relation between SCVARs in the thermoregulatory tail artery vascular bed and hippocampal EEG theta rhythm in Sprague- Dawley rats. A Doppler ultrasonic flow probe chronically implanted around the base of the tail artery was used to measure SCVARs. Unipolar electrodes were implanted in the hippocampus (CA1 region) to measure EEG. Six standard non-noxious brief alerting stimuli were administered during continuous recording of tail blood flow and EEG. The SCVAR index was calculated as the percentage fall from pre-alerting blood flow values. After stimuli the SCVAR index for the tail artery blood flow was 84±2% of the pre-alerting control. In contrast, the same stimuli caused little fall in blood flow within the superior mesenteric bed (SCVAR index=18±2%). The proportion of theta power in the total frequency range (0–20 Hz) increased significantly after alerting stimuli (46±2% vs. 29±1% before stimuli, p<0.05). Theta proportion began to increase approximately 0.5 s after the stimuli and preceded SCVARs by approximately 1 s. The SCVAR index was correlated with the magnitude of the increment in theta power. Our study demonstrates that alerting responses resulting in selective vasoconstriction of the tail vascular bed are associated with hippocampal theta rhythm in conscious rats.