Low ambient temperature accelerates short-day responses in Siberian hamsters by altering responsiveness to melatonin.

Exposure to low ambient temperatures (Ta) accelerates appearance of the winter phenotype in Siberian hamsters transferred from long to short day lengths. Because melatonin transduces the effects of day length on the neuroendocrine axis, the authors assessed whether low Ta promotes the transition to winterlike traits by accelerating the onset of increased nocturnal melatonin secretion or by enhancing responsiveness to melatonin in short day lengths. Male hamsters were transferred from 16L (16 h light/day) to 8L (8 h light/day) photoperiods and held at 5 degrees C or 22 degrees C. Locomotor activity was recorded continuously, and body mass, testis size, and pelage color were determined biweekly for 8 weeks. The duration of nocturnal locomotion (alpha), a reliable indicator of the duration of nocturnal melatonin secretion, lengthened significantly earlier in hamsters exposed to a Ta of 5 degrees C than 22 degrees C. Cold exposure increased the proportion of hamsters that were photoresponsive: gonadal regression in short days increased from 44% at 22 degrees C to 81% at 5 degrees C (p < 0.05); low Ta did not, however, accelerate testicular regression in animals that were photoresponsive. Nonphotoresponsive animals at 5 degrees C temporarily had longer alphas during the first 4 weeks in short days and significant decreases in body mass and testicular size that were reversed during the ensuing weeks when alpha decreased. In a 2nd experiment, pinealectomized male hamsters infused for 10 h/day with melatonin for 2 weeks had significantly lower body and testes masses when maintained at 5 degrees C but not 22 degrees C. Low-ambient temperature appears to accelerate the appearance of the winter phenotype primarily by increasing target tissue responsiveness to melatonin and to a lesser extent by augmenting the rate at which the duration of nocturnal melatonin secretion increases in short day lengths.

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager.

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10(-6) and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.

Testicular and somatic growth in Siberian hamsters depend on the melatonin-free interval between twice daily melatonin signals.

In Siberian hamsters, day length is encoded by the duration of the nocturnal melatonin signal; short and long melatonin signals over the course of several weeks stimulate and inhibit somatic and gonadal development, respectively, in prepubertal males. We sought to determine whether juvenile male Siberian hamsters respond to multiple melatonin signals each day and the manner in which the sequence of melatonin signals and the duration of the melatonin-free interval between signals affects development. Twenty-one day old male Siberian hamsters, gestated and maintained in a short-day photoperiod of 10 h light/day (10 L), were transferred to constant light to suppress endogenous melatonin secretion and received s.c. infusions of melatonin or saline for 12 days. Hamsters infused with saline retained small testes, whereas one short melatonin infusion each day resulted in significant testicular growth. Other hamsters were provided with two melatonin signals each day, one long (9 h) and one short (4 or 5 h); the order in which these signals was administered and the duration of the melatonin-free interval after each signal varied between groups. In asymmetrical melatonin infusions, the first and second daily infusions were followed by 3-h and 7-h melatonin-free intervals, respectively, whereas in symmetrical infusions, each melatonin signal was followed by a 5-h melatonin-free interval. In the asymmetrical sequence, the melatonin signal that immediately preceded the longer melatonin-free interval determined the rate gonadal growth. Equal melatonin-free intervals after each of the long and short daily melatonin infusions produced intermediate increases in gonadal and somatic development. The hypothalamic-pituitary-gonadal axis of Siberian hamsters can respond to multiple melatonin signals each day, with the rate of testicular growth determined primarily by the duration of the melatonin-free interval following each infusion.

Appropriate thermal manipulations eliminate tremors in rats recovering from halothane anesthesia.

Tremors are common in mammals emerging from anesthesia. To determine whether appropriate thermal manipulations immediately before emergence from anesthesia are sufficient to eliminate these tremors, electroencephalographic (EEG) and electromyographic (EMG) activities, hypothalamic temperature (Thy), and O2 consumption were monitored in 12 rats recovering from halothane anesthesia under three thermal regimes. EEG and EMG activities were recorded throughout anesthesia and served as feedback signals for controlling anesthetic depth. During anesthesia, Thy was either 1) allowed to fall to 32-34 degrees C, 2) maintained at 37-39 degrees C, or 3) allowed to fall to 32-34 degrees C and then raised to 37-39 degrees C. When hypothermic on emergence from anesthesia, all of the animals exhibited postanesthetic tremors that persisted until Thy values returned to normothermia. None of the animals expressed postanesthetic tremors when normothermic on emergence from anesthesia. In addition, the time between emergence from anesthesia (as determined by EEG/EMG parameters) and the initiation of coordinated motor activities was significantly decreased in the normothermic animals.

Temperature sensitivity of sleep homeostasis during hibernation in the golden-mantled ground squirrel.

Brain temperature (Tbr), vigilance state, and electroencephalograph slow-wave activity (EEG SWA, 1.0-4.0 Hz) were measured during hibernation and spontaneous arousals to euthermia in seven golden-mantled ground squirrels (Spermophilus lateralis). Animals were held at air temperatures (Ta) ranging from 6 to 21 degrees C. SWA was used as a measure of the intensity of non-rapid eye movement (NREM) sleep. Squirrels that had hibernated at high Ta had lower SWA in NREM sleep in the hours following arousal than when they hibernated at low Ta. SWA in NREM sleep during euthermia immediately following arousal was significantly correlated to minimum Tbr and SWA during hibernation. The duration of the preceding hibernation bout had no significant effect on SWA during euthermia. We hypothesize that the restorative process of sleep, reflected by SWA, is temperature sensitive and is compromised by the low temperatures in hibernation. The accumulation of a SWA debt during hibernation may be related to the temperature-dependent depression of SWA during hibernation.

Sleep after arousal from hibernation is not homeostatically regulated.

Electroencephalographic slow-wave activity (SWA) in non-rapid eye movement (NREM) sleep is directly related to prior sleep/wake history, with high levels of SWA following extended periods of wake. Therefore, SWA has been thought to reflect the level of accumulated sleep need. The discovery that euthermic intervals between hibernation bouts are spent primarily in sleep and that this sleep is characterized by high and monotonically declining SWA has led to speculation that sleep homeostasis may play a fundamental role in the regulation of the timing of bouts of hibernation and periodic arousals to euthermia. It was proposed that because the SWA profile seen after arousal from hibernation is strikingly similar to what is seen in nonhibernating mammals after extended periods of wakefulness, that hibernating mammals may arouse from hibernation with significant accumulated sleep need. This sleep need may accumulate during hibernation because the low brain temperatures during hibernation may not be compatible with sleep restorative processes. In the present study, golden-mantled ground squirrels were sleep deprived during the first 4 h of interbout euthermia by injection of caffeine (20 mg/kg ip). We predicted that if the SWA peaks after bouts of hibernation reflected a homeostatic response to an accumulated sleep need, sleep deprivation should simply have displaced and possibly augmented the SWA to subsequent recovery sleep. Instead we found that after caffeine-induced sleep deprivation of animals just aroused from hibernation, the anticipated high SWA typical of recovery sleep did not occur. Similar results were found in a study that induced sleep deprivation by gentle handling (19). These findings indicate that the SWA peak immediately after hibernation does not represent homeostatic regulation of NREM sleep, as it normally does after prolonged wakefulness during euthermia, but instead may reflect some other neurological process in the recovery of brain function from an extended period at low temperature.

The disappearing slow wave activity of hibernators.

High and monotonically declining levels of EEG slow wave activity (SWA) occur following arousal from hibernation. Similar profiles of SWA occur in mammals including humans during sleep following periods of prolonged wakefulness, and have been interpreted as reflecting a homeostatic process regulating NREM sleep. It was proposed that even though hibernation appears to be an evolutionary extension of NREM sleep, the low brain temperatures during hibernation are not compatible with sleep restorative processes, and therefore sleep debt accumulates during hibernation and may be a factor triggering periodic arousal. In the present study, golden-mantled ground squirrels were sleep deprived by gentle handling following arousal from hibernation. If the SWA peaks following bouts of hibernation reflect a homeostatic response to an accumulated sleep debt, sleep deprivation should simply displace the SWA which would then occur, and be augmented, during subsequent sleep. In contrast, when animals were sleep deprived following arousal from hibernation, the anticipated SWA peak did not occur during subsequent sleep. It is suggested that the SWA following arousal from hibernation does not represent homeostatic regulation of NREM sleep, but instead some other neurological process involved in the recovery of brain function from an extended period at low temperature.

An extragalactic supernebula confined by gravity.

Little is known about the origins of globular clusters, which contain hundreds of thousands of stars in a volume only a few light years across. Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy NGC5253. The lines arise in gas heated by a cluster of about one million stars, including 4,000-6,000 massive, hot 'O' stars. It is so young that it is still enshrouded in gas and dust, hidden from optical view. The gases within the cluster seem bound by gravity, which may explain why the windy and luminous O stars have not yet blown away those gases. Young clusters in 'starbursting' galaxies in the local and distant Universe may also be gravitationally confined and cloaked from view.