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We tested the hypothesis that peripheral vascular responses (in the lower and upper limbs) to application of lower body positive pressure (LBPP) are dependent on the posture of the subjects. We measured heart rate, stroke volume, mean arterial pressure, leg and forearm blood flow (using the Doppler ultrasound technique), and leg (LVC) and forearm (FVC) vascular conductance in 11 subjects (9 men, 2 women) without and with LBPP (25 and 50 mmHg) in supine and upright postures. Mean arterial pressure increased in proportion to increases in LBPP and was greater in supine than in upright subjects. Heart rate was unchanged when LBPP was applied to supine subjects but was reduced in upright ones. Leg blood flow and LVC were both reduced by LBPP in supine subjects [LVC: 4.8 (SD 4.0), 3.6 (SD 3.5), and 1.4 (SD 1.8) ml x [min.sup.-1] x [mmHg.sup.-1] before LBPP and during 25 and 50 mmHg LBPP, respectively; P < 0.05] but were increased in upright ones [LVC: 2.0 (SD 1.2), 3.4 (SD 3.4), and 3.0 (SD 2.0) ml x [min.sup.-1] x [mmHg.sup.-1], respectively; P < 0.05]. Forearm blood flow and FVC both declined when LBPP was applied to supine subjects [FVC: 1.3 (SD 0.6), 1.0 (SD 0.4), and 0.9 (SD 0.6) ml x [min.sup.-1] x [mmHg.sup.-1] respectively; P < 0.05] but remained unchanged in upright ones [FVC: 0.7 (SD 0.4), 0.7 (SD 0.4), and 0.6 (SD 0.5) ml x [min.sup.-1] x [mmHg.sup.-1], respectively]. Together, these findings indicate that the leg vascular response to application of LBPP is posture dependent and that the response differs in the lower and upper limbs when subjects assume an upright posture. head-up tilt; leg blood flow; forearm blood flow doi:10.1152/ajpheart.00462.2006

Systemic salt loading has been reported to facilitate operant heat-escape/cold-seeking behavior. In the present study, we hypothesized that the median preoptic nucleus (MnPO) would be involved in this mechanism. Rats were divided into two groups (n = 6 each): one group had the MnPO lesion with ibotenic acid (4.0 [micro]g) and the other was the vehicle control. After subcutaneous injection (10 ml/kg) of either isotonic- (154 mM) or hypertonic-saline (2,500 mM), each rat was placed in a behavior box, where the ambient temperature was changed to 26[degrees]C, 35[degrees]C, and 40[degrees]C every 1 h. The position of a rat in the box and the body core temperature ([T.sub.core]) were monitored. A rat could trigger 0[degrees]C air for 45 s in the 35[degrees]C and 40[degrees]C heat when moved in a specific area in the box (operant behavior). In the control group, counts of the operant behavior were greater (P < 0.05) in the hypertonic- than in the isotonic-saline injection (17 [+ or -] 2 and 10 [+ or -] 2 at 35[degrees]C, 24 [+ or -] 2 and 18 [+ or -] 1 at 40[degrees]C). [T.sub.core] remained unchanged throughout the exposure, although the level was lower (P < 0.05) in the hypertonic- than in the isotonic-saline trial (36.6 [+ or -] 0.2[degrees]C and 37.4 [+ or -] 0.1[degrees]C at 26[degrees]C and 36.9 [+ or -] 0.2[degrees]C and 37.4 [+ or -] 0.1[degrees]C at 40[degrees]C, respectively). However, in the MnPO-lesion group, counts of the behavior were similar between the hypertonic- and isotonic-saline injection trials (10 [+ or -] 2 and 8 [+ or -] 1 at 35[degrees]C, and 17 [+ or -] 1 and 16 [+ or -] 1 at 40[degrees]C, respectively). [T.sub.core] increased (P < 0.05) in the heat in both trials (36.8 [+ or -] 0.1[degrees]C and 37.4 [+ or -] 0.1[degrees]C at 26[degrees]C and 37.4 [+ or -] 0.2[degrees]C and 37.8 [+ or -] 0.2[degrees]C at 40[degrees]C in the hypertonicand isotonic-saline injection trials, respectively). These results may suggest that, at least in part, the MnPO is involved in the facilitation of heat-escape/cold-seeking behavior during osmotic stimulation. osmolality; body temperature; operant behavior; lesion

The criptochrome genes (Cry1 and Cry2) are involved in the molecular mechanism that controls the circadian clock, and mice lacking these genes ([Cry1.sup.-/-]/ [Cry2.sup.-/-]) are behaviorally arrhythmic. It has been speculated that the circadian clock modulates the characteristics of thermoregulation, resulting in body temperature ([T.sub.b]) rhythm. However, there is no direct evidence proving this speculation. We show here that Tb and heat production in [Cry1.sup.-/-]/[Cry2.sup.-/-] mice are arrhythmic under constant darkness. In contrast, both rhythms occur under a light-dark cycle and/or periodical food restriction linked with spontaneous activity and/or eating, although they are not robust as those in wild-type mice. The relationship between heat production and [T.sub.b] in [Cry1.sup.-/-]/[Cry2.sup.-/-] mice is linear and identical under any conditions, indicating that their [T.sub.b] rhythm is determined by heat production rhythm associated with activity and eating. However, [T.sub.b] in wild-type mice is maintained at a relatively higher level in the active phase than the inactive phase regardless of the heat production level. These results indicate that the thermoregulatory responses are modulated according to the circadian phase, and the Cry genes are involved in this mechanism. circadian clock; thermoregulation; metabolism

Maruyama, Megumi, Maiko Nishi, Masahiro Konishi, Yuko Takashige, Kei Nagashima, Toshikazu Kiyohara, and Kazuyuki Kanosue. Brain regions expressing Fos during thermoregulatory behavior in rats. Am J Physiol Regul Integr Comp Physiol 285: R1116-R1123, 2003. First published July 31, 2003; 10.1152/ajpregu.00166.2002.--We surveyed the neural substrata for behavioral thermoregulation with immunohistochemical analysis of the expression of Fos protein in the rat brain. We used an operant system in which a rat exposed to heat (40[degrees]C) could get cold air (0[degrees]C) for 30 s when it moved into the reward area. Rats moved in and out of the reward area of the system periodically and thus maintained their body temperature at a normal level. In the rats performing heat escape behavior (active group), strong Fos immunoreactivity (Fos-IR) was found in the median preoptic nucleus (MnPO), parastrial nucleus (PS), and dorsomedial hypothalamus (DMH) compared with the controls. Another group of rats (passive group) were given the same temperature changes, regardless of the rat's movement, as those obtained by rats of the active group. Fos-IR in the MnPO was also seen in this group. The present results suggest that the PS and DMH play an important role in the genesis of thermoregulatory behavior, whereas the MnPO may be important for detecting changes in ambient and/or body temperatures. preoptic area; dorsomedial hypothalamus; operant behavior

To investigate the mechanism involved in the reduction of body core temperature ([T.sub.core]) during fasting in rats, which is selective in the light phase, we measured [T.sub.core], surface temperature, and oxygen consumption rate in fed control animals and in fasted animals on day 3 of fasting and day 4 of recovery at an ambient temperature ([T.sub.a]) of 23[degrees]C by biotelemetry, infrared thermography, and indirect calorimetry, respectively. On the fasting day, 1) [T.sub.core] in the light phase decreased (P < 0.05) from the control; however, [T.sub.core] in the dark phase was unchanged, 2) tail temperature fell from the control (P < 0.05, from 30.7 [+ or -] 0.1 to 23.9 [+ or -] 0.1[degrees]C in the dark phase and from 29.4 [+ or -] 0.1 to 25.2 [+ or -] 0.2[degrees]C in the light phase), 3) oxygen consumption rate decreased from the control (P < 0.05, from 24.37 [+ or -] 1.06 to 16.24 [+ or -] 0.69 ml*[min.sup.-1]* kg body [wt.sup.-0.75] in the dark phase and from 18.91 [+ or -] 0.64 to 14.00 [+ or -] 0.41 ml*[min.sup.-1]*kg body [wt.sup.-0.75] in the light phase). All these values returned to the control levels on the recovery day. The results suggest that, in the fasting condition, [T. sub.core] in the dark phase was maintained by suppression of the heat loss mechanism, despite the reduction of metabolic heat production. In contrast, the response was weakened in the light phase, decreasing [T.sub.core] greatly. Moreover, the change in the regulation of tail blood flow was a likely mechanism to suppress heat loss. core temperature; oxygen consumption; heat loss mechanism

The contribution of plasma osmolality to the vasodilation of cutaneous vessels during exercise was investigated by correlating core body temperature and cutaneous vasodilation (CVD) during various levels of physical activities that alter plasma osmolality. Results reveal that there is similar correlation between CVD and body temperature in activity-induced and passive heating-induced CVD. The influence of plasma osmolality on core body temperature is discussed.

Researchers have investigated the effect of hyperosmolality on body core temperature thresholds for cutaneous vasodilation and sweating at a number of levels of plasma osmolality (Posm). The impact of hyperosmolality on these thresholds was calculated as functions of Posm. It was found that increased Posm linearly boosts the increased esophageal temperature (delta-Tes) threshold for cutaneous vasodilation, and also for sweating. Hyperosmolality has a similar impact on thermally induced cutaneous vasodilation and sweating.