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Core temperature (T C ) is a critical determinant of the severity of neural damage that results from focal or global ischemia. Former studies indicated that especially intra-ischemic but also post ischemic mild hypothermia significantly decreased necrotic neural damage of a focal or global insult, as assessed between 3-7 days post-insult. More recent work shows that prolonged post-ischemic hypothermia reduces neural damage and inhibits associated behavioral deficits for up to one year after the insult (i.e. true neuroprotection with behavioral preservation). Alternatively, increases in core temperature via external heating or with pyrogens resulting from bacterial infections, at the time of the global ischemia insult worsen the neural damage of ischemic animals from those of respective normothermic controls given the same insult. This is paralleled in the clinical setting whereby ~50% of ischemic patients develop fevers within 2 days of the insult and have worsened neurological outcomes than non-febrile patients. The review discusses the possible mechanisms of neuroprotection of hypothermic therapy from cerebral ischemia as well as mechanisms involved in the exacerbation of neural damage of hypoxic ischemia under hyperthermic conditions. Questions are raised as to whether the medical community has sufficient evidence to begin appropriate hypothermic therapy of acute stroke patients. The importance of accurate monitoring core temperatures of all suspected stroke patients is emphasized, noting the differences in temperature that can occur with age, sex, medication or lifestyle so that appropriate temperature treatment could be implemented, if required. A. Hypothermia and cerebral ischemiaBrain Pathology 10: 145-152(2000)

It has been reported that a horse's common carotid arteries are cooled 6 , presumably by heat loss from the pulmonary circulation and the proximity of the arteries to the trachea and skin. When the horse is resting, mid blood is warmed and f. lacerum blood cooled. Other surrounding tissues, notably the salivary glands and neck muscles, which are at core temperature, influence the warming of mid blood. Adjacent to f. lacerum is the extracranial ventral petrosal venous sinus, which is cooler than the resting core temperature 4 .During trotting and cantering, the temperature at trifur rises, whereas that at mid and f. lacerum increases little by comparison ( Fig. 1b-d). After prolonged cantering, the temperatures of guttural-pouch air and f. lacerum are similar. The rectal temperature differs from that of the ICA throughout, probably because of the lag phase between the horse's rectum and core 4 .Guttural-pouch air temperature varied little with exercise (37.65 0.03 °C at rest, 37.55 0.05 °C trotting and 37.65 0.08 °C cantering), as did rectal temperature (38.35 0.01 °C at rest, 38.45 0.04 °C trotting and 38.75 0.1 °C cantering). Environmental air temperatures (and relative humidity) were 18.55 3.5 °C (465 5%) at rest, 18.35 3.0 °C (455 4%) trotting and 18.15 2.7 °C (475 5%) cantering. Exercise trials without the guttural-pouch temperature probe followed the same significant trends of cooling of the ICA.Cool air in the guttural pouch would drive heat transfer from the passing ICA, and this is the only structure in this area 382 NATURE | VOL 403 | 27 JANUARY 2000 | www.nature.com surface and froze, instruments being developed by NASA (P. Grunthaner, personal communication) could detect signs of life in ' 10 litres of melted and filtered surface ice. Ice from melt-through blooms may contain more cells, reducing melting requirements.These calculations indicate that a particular radiation-driven ecosystem is plausible, quantifiable using our current knowledge of Europa: others are possible. Neither photosynthesis nor hydrothermal vents need be postulated. But only direct exploration will reveal whether life on Europa actually exists.

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