Development of thermoregulation in the kitten

In normal kittens thermoregulation developed over the first 45 days of age. This maturational sequence went from a mean rectal temperature (T_B) of 37.0°C at 5 days of age to adult levels (38.2 ± 0.2°C) at about 7 weeks of age. Up until about 14 days of age the predominant response to being removed from the nesting box and placed at an ambient temperature of 23 to 25°C was a decrease in T_B of about 0.02°C/min. In response to stronger thermal challenges (i.e., short periods at + 60°C or ? 15°C) all kittens showed, from the first day of life, the ability to detect and move along a thermal gradient as reflected in an approach to warmth and an avoidance of cool. At ?15°C the kittens showed a decrease in T_B of about 0.2°C/min at 10 days decreasing to about 0.1°C/min at 40 days of age. After 45 days of age shivering as well as piloerection appeared immediately with cold onset and for short periods (i.e. less than 2 hours) at this temperature combined behavioral and physiological regulation sufficed to maintain the temperature at approximately 37.5°C. In response to heating the kittens showed a mean T_B increase of about +0.05°C/min at 10 days decreasing to +0.02°C/min at 45 days of age, at which time panting was also fully developed. These data demonstrate that the development of normal thermoregulation in the cat follows a time course of up to seven weeks.     

CNS monoamine levels and motoric behaviors in the hotfoot ataxic mutant

Mice that were homozygous recessive for the single-gene mutation, hotfoot, showed profound and progressive motor disturbances in an open field after approximately the 4th postnatal week. Studies were undertaken to examine the role of the monoaminergic system in the behavioral and developmental expression of this neurological mutation. Relative to controls, 10- and 30-day-old hotfoot mice demonstrated a significantly attenuated response to the stimulating locomotor effects of amphetamine while adult hotfoot mice were motorically unaffected by amphetamine administration. 30-day-old and adult hotfoot mice also were hypothermic relative to phenotypically normal mice after amphetamine administration. Examination of monoamine levels and turnover revealed that hotfoot mice had significantly greater concentrations of norepinephrine associated with lower turnover in cerebellum and greater levels of serotonin in cerebellum and striatum, relative to phenotypic controls. In addition, mice born and raised by hotfoot dams demonstrated neurochemical alterations regardless of genotype. Both the neurochemical data and the developmental response to the general catecholamine agonist, amphetamine, suggest that the monaminergic neurotransmitter system may be altered as a consequence of the hotfoot mutation.     

The role of adrenergic mechanisms in thermoregulatory control of blood flow through capillaries and arteriovenous anastomoses in the sheep hind limb

The possible role of adrenergic mechanisms in thermoregulatory changes in the partition of femoral blood flow between nutrient (capillary) and non-nutrient (arteriovenous anastomoses, AVA) circuits in the hind limb of conscious sheep has been investigated employing radioactive microsphere and electromagnetic blood flow measurement techniques. Constriction of AVAs, normally induced by spinal cooling, could be inhibited by phentolamine, whereas dilatation of AVAs, noramally induced by spinal heating, could be inhibited by noradrenaline or methoxamine. AVA constriction could be induced by noradrenaline or methoxamine, or dialation by phentolamine. Isoprenaline had a small dilator and propranolol a small constrictor effect on AVAs. It is concluded that adrenergic pathways involving predominantly -receptors play a role in thermoregulatory changes in skin blood flow (through AVAs) elicited by manipulation of CNS temperature; under these conditions, -receptors do not play any role, although manipulation of their activity will influence AVAs under non-thermoregulatory conditions. Capillary blood flows in skin, bone and fat were sensitive, at different ambient temperatures and to varying degrees, to some -and -adrenergic agents.     

Convergence of hepatoportal osmotic and cardiovascular signals on preoptic thermosensitive neurons

Effects of hepatoportal osmotic stimuli and changes in arterial blood pressure were studied on the neuronal activity of 24 thermosensitive and 47 thermally insensitive neurons of the preoptic and anterior hypothalamus (PO/AH) in the urethane-anesthetized rat. Infusion of hypertonic (3% NaCl, 9% mannitol) or hypotonic (water) solutions into the hepatic portal vein changes the activity in 59% of thermosensitive neurons and 13% of thermally insensitive neurons but the injection into the femoral vein did not. Changes in blood pressure induced by intravenous injection of vasoactive drugs altered the activity of thermosensitive neurons (75%) and thermally insensitive neurons (32%). Neurons having dual sensitivity to both osmotic and blood pressure were more frequently found among thermosensitive neurons (10/24) than among thermally insensitive neurons (4/47), chi 2(1) = 11.03, p less than 0.001. The convergence of osmotic and baro/volaemic information on thermosensitive neurons may provide explanations for thermoregulatory changes observed during dehydration and acute hypotension.     

Activation of central warm-sensitive neurons and the tail vasomotor response in rats during brain and scrotal thermal stimulation

The effects of preoptic and hypothalamic thermal stimulation on tail skin temperature were observed at different scrotal temperatures. The threshold hypothalamic temperature for tail vasodilation at a scrotal temperature of 40°C was significantly lower than that at a scrotal temperature of either 25°C or 33°C. The effects of scrotal thermal stimulation on tail skin vasodilated by higher hypothalamic temperatures were observed. Cooling the scrotum from 42 to 30°C invariably caused a rapid fall in tail temperature, whereas scrotal cooling from 30 to 25°C did not cause any significant change. Cooling of either the left or right half of the scrotum caused a similar fall in tail temperature. The temperature characteristics of the preoptic hypothalamic thermo-sensitive neurons were determined at scrotal temperatures of 32, 36 and 26°C. The firing rate of warm-sensitive neurons at a given hypothalamic temperature was highest at a scrotal temperature of 36°C, while that of cold-sensitive neurons was lowest at that temperature. The scrotal temperature range over which the number of neurons activated by scrotal warming increased rapidly was between 36 and 39°C when hypothalamic temperature was held at 36–37°C.     

Changes in sleep on chronic exposure to warm and cold ambient temperatures

Alterations in sleep induced by chronic exposure to mild changes in ambient temperature (Ta) were studied in male Wistar rats with chronically implanted electrodes for recording electrooculogram (EOG), electroencephalogram (EEG) and electromyogram (EMG), and a thermocouple to record the brain temperature (Tbr). Changes in sleep-wakefulness (S-W) and Tbr on exposure to warm (30+/-1 degrees C) and cold (18+/-1 degrees C) Ta for 4 weeks were studied in two groups of five rats each. Chronic heat exposure produced a persistent increase in sleep, primarily due to an increase in the durations of sleep episodes. A disproportionate increase in sleep during the dark period resulted in reduced circadian variation. The paradoxical sleep (PS)/total sleep time (TST) ratio also remained increased, during heat exposure. On chronic cold exposure, the sleep was decreased initially, but it recovered after 3 weeks, due to an increase in the frequency of slow wave sleep (SWS) episodes. The Tbr was not altered on exposure to warm Ta, but it remained high throughout the 4 weeks of cold exposure. The increase in the amount of sleep, especially the PS with enhanced ambient temperature, may be considered as an adaptation to thermal load aimed at energy conservation. Though the increased wakefulness is suggested to enable the organism to optimize thermoregulation during acute cold stress, thermoregulation itself may be readjusted to ensure homeostatic restoration of sleep during chronic cold exposure.     

Determinants of mother-young contact in Norway rats

Rat dams choose to care for their pups in a relatively warm area, apparently because they have an elevated thermal set point for the regulation of their body temperature. Since the duration of their contact bouts with their pups is limited by an acute hyperthermia that they experience while on the pups, their choice limits the time that they can spend with their pups. When dams could choose the temperature at which they cared for their young they spent only about half the time in contact with their offspring as did dams caring for their pups at the ambient temperature of the laboratory. We conclude that rat dams do not attempt to maximize the duration of their contact bouts with their offspring. Dams also do not attempt to minimize the amount of time that they spend away from their offspring. The duration of the intervals between contact bouts was influenced by the ability of the dams to dissipiate the heat gained during the contact bout with the pups. Again, dams did not seek out a cool area in which to spend their interbout intervals, preferring to remain in relatively warm areas. Their thermal preference facilitated the retention of their body heat and prolongation of the interbout intervals. Dams may return to the nest periodically for brief bouts during which the state of the pups is monitored. Pups were found to play both passive and active roles in modulating the overall pattern of maternal contact, for dams maintained contact with pups if the pups were cool, but failure to attach to the nipples soon after contact was established frequently led to rapid bout termination, particularly with warm pups. Contact is maintained if the pups are cool or if they attach to the nipples. Finally, it was found that pups could actively curtail interbout intervals by emitting ultrasonic vocalizations.     

Effects of circadian regulation and rest-activity state on spontaneous seizures in a rat model of limbic epilepsy

PURPOSE: Circadian regulation via the suprachiasmatic nuclei and rest-activity state may influence expression of limbic seizures. METHODS: Male rats (n = 14) were made epileptic by electrical stimulation of the hippocampus, causing limbic status epilepticus and subsequent seizures. We monitored seizures with intrahippocampal electrodes in 12-12-h light/dark (LD) cycles and in continuous dark (DD). We used radiotelemetry monitoring of activity to measure state and body temperature to determine circadian phase. Cosinor analysis and chi2 tests determined whether seizures occurred rhythmically when plotted by phase. State was defined as inactive or active in 10-min epochs based on whether activity count was below or above a cut-off value validated from video observation. RESULTS: In LD, the peak seizure occurrence was 14:59 h after circadian temperature peak (95% confidence limit, 13:37-16:19). Phasic seizure occurrence persisted in DD for 14:05 (12:31-15:38), p < 0.0001, against uniform mean distribution. In LD, 14,787 epochs contained 1, 268 seizures; seizures preferentially occurred during inactive epochs (965 observed, 878 expected in proportion to the overall distribution of inactive versus active epochs; p < 0.001). In DD, 20, 664 epochs contained 1,609 seizures; seizures had no preferential occurrence by state (999 observed, 1,025 expected; p = 0.16). CONCLUSIONS: Limbic seizures occurred with an endogenous circadian rhythm. Seizures preferentially struck during inactivity during entrainment to the light-dark cycle.     

桂枝汤提取物体温双向调节的研究进展

目的：综述近年来桂枝汤提取物体温双向调节的研究进展。方法：主要对近十年来有关于桂枝汤双向调节体温的文献进行综述。结果：桂枝汤及其提取物对体温调节多条信号转导通路有影响，能促进异常体温向正常方向转化。结论：桂枝汤及其提取物对体温具有双向调节作用。但其作用机制、物质基础还有待于更进一步研究。