Temperature dependence of EEG frequencies during natural hypothermia

Effect of melatonin on sleep and brain temperature in the Djungarian hamster and the rat

The effect of a single dose of melatonin (3-5 mg/kg intraperitoneally) on sleep, electroencephalographic power density, and cortical temperature (TCRT) was investigated. Melatonin was administered to Djungarian hamsters 4 h or 12 h after lights on in a 16-h light:8-h dark cycle (LD 16:8) and to rats at dark onset in a LD 12:12. The effects in both species were short lasting and depended on the time of day. Sleep latency was prolonged in the late light period, sleep fragmentation was enhanced in the early light period, and TCRT was elevated in all three conditions. Rapid eye-movement sleep was reduced in the first postdrug hour after the late light period treatment in the hamsters and in postdrug hours 2 and 3 after dark onset treatment in the rat. Therefore, we have no evidence for a sleep inducing effect of 3-5 mg/kg of melatonin in the hamster or rat. In view of some data that indicate that melatonin may exert a sleep inducing effect in humans, it is suggested that melatonin induces changes that are typical for the dark period of each species, i.e., waking in the nocturnal Djungarian hamster and rat, and sleepiness in the diurnal human.

Altered circadian activity rhythms and sleep in mice devoid of prion protein

There is a wealth of data supporting a central role for the prion protein (PrP) in the neurodegenerative prion diseases of both humans and other species, yet the normal function of PrP, which is expressed at the cell surface of neurons and glial cells, is unknown. It has been speculated that neuropathology may be due to loss of normal function of PrP. Here we show that in mice devoid of PrP there is an alteration in both circadian activity rhythms and patterns. To our knowledge, this is the first null mutation that has been shown to affect sleep regulation and our results indicate that at least one of the inherited prion diseases, fatal familial insomnia, where there is a profound alteration in sleep and the daily rhythms of many hormones, may be related to the normal function of the prion protein.

Effects of N6-cyclopentyladenosine and caffeine on sleep regulation in the rat

To study the role of adenosine in sleep regulation, the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the antagonist caffeine were administered to rats. Intraperitoneal (i.p.) CPA 1 mg/kg but not 0.1 mg/kg, suppressed rapid-eye-movement (REM) sleep and enhanced electroencephalographic (EEG) slow-wave activity (power density 0.75-4.0 Hz) in non-REM sleep. The latter effect was remarkably similar to the response to 6-h sleep deprivation. The effects persisted when CPA-induced hypothermia was prevented. Caffeine (10 and 15 mg/kg i.p.) elicited a dose-dependent increase in waking followed by a prolonged increase of slow-wave activity in non-REM sleep. The combination of caffeine (15 mg/kg) and sleep deprivation caused less increase in slow-wave activity than sleep deprivation alone, indicating that caffeine may reduce the buildup of sleep pressure during waking. The results are consistent with the involvement of adenosine in the regulation of non-REM sleep.