22 The BRAC was considered to be clearly expressed clinically early after birth and then, within weeks or months, to become less evident during daytime and mostly seen during sleep, with the alternation between rapid eye movement (REM) and nonREM sleep. Apart from sleep, several physiological functions have an ultradian periodicity of approximately 90 min In man. The buy Crizotinib period of the BRAC might be species-specific since, for example, Inhibitors,research,lifescience,medical luteinizing hormone (LH) blood concentrations oscillate with periods of 20 minutes to 2 hours in different animal

species.23 In mice, there Is an ultradian rhythm for avoidance behavior that Is of 9 min in young mice, near the Inhibitors,research,lifescience,medical period of REM/nonREM sleep, while in adult mice it is of 20 mln.24 In humans, a mean period of the BRAC of

around 90 mln was found In endocrine studies or In studies on dreaming and sleep.25 For example, the secretory pulses of prolactin Into blood In humans have a mean period of 95 mln and are closely associated with the secretory pulses of LH.26 There Is an ultradian rhythm of nasal permeability, with a shift between nostrils that Inhibitors,research,lifescience,medical correlates with changes In controlateral electroencephalogram (EEG) wave amplitude.27 The BRAC has the hypothetical role of coordinating bodily functions, hormones, sleep phases, and perceptual and cognitive capacities. This hypothesis raises Inhibitors,research,lifescience,medical several questions, few of which have yet been solved. First, there have been subsequent negative findings, for example regarding the absence of ultradian rhythms in the cognitive task

of the sentence -verification test.28 Also, many variables show more than one Inhibitors,research,lifescience,medical ultradian period and have superimposed circadian components. Finally, the existence of groups of neurons that govern ultradian periodicities has been demonstrated for gonadotrophin-releasing hormone (GnRH, also called LHRH, for luteizining hormone-releasing hormone) in the preoptic area of the hypothalamus and for the sleep architecture, but not for other rhythms; moreover, a few authors have suggested that evidence for the existence of BRAC might those result from artifacts in protocols and calculations.28 Ultradian clocks have not yet been as clearly delineated, as is the case for the circadian clock in the SCN Reciprocal influences and conpling between biological clocks Many biological functions show more than one rhythm and have superimposed ultradian and circadian components. Moreover, many tissues express endogenous rhythms.