M. R. Opp, Ph.D., L. Imeri, M.D.
Sleep presents a conundrum for neurobiology: we do not know what function(s) sleep serves for the brain (or the body). We do know, however, that adequate sleep is essential for physical and mental health. In addition to effects on cognition and performance, lack of sleep, or sleep disruption due to sleep disorders may be a contributing factor to multiple pathologies, including but not limited to hypertension, coronary artery disease, cerebrovascular disease, and hyperglycemia. Numerous studies demonstrate that sleep loss impairs immune function and that immune activation from infection alters sleep. Responsiveness to infection varies widely: in the extreme, some will live and others will die in response to the same pathogen(s). Numerous systematic pre-clinical studies demonstrate infection-induced alterations in sleep. Most infections increase non-rapid eye movements sleep (NREMS) and decrease rapid eye movements sleep (REMS). Our functional hypothesis is that the manner in which sleep is altered during infection is a critical determinant of clinical outcome. Indeed, one retrospective study demonstrates that specific sleep patterns of rabbits are associated with survival from infection. To further our understanding of central nervous system responses that result in good clinical outcome, we focus on the cytokine interleukin (IL)-1 as one mediator of altered sleep during immune activation. Data indicate IL-1 increases NREMS and suppresses REMS. We propose in this application to focus effort on IL-1-induced suppression of REMS, an effect that has been universally ignored. IL-1 inhibits ACh synthesis and release. Cholinergic neurons of the laterodorsal tegmental (LDT) and pedunculopontine (PPT) nuclei are involved in EEG desynchronization and thalamocortical activation during REMS. REMS-generating structures are under GABAergic inhibition: IL-1 enhances GABA inhibitory effects at multiple levels. Studies proposed in this application will test the mechanistic hypothesis that IL-1 suppresses REMS by opposed, yet complementary actions on brainstem cholinergic and GABAergic systems. Our preliminary data indicate: IL-1 microinjected into the LDT reduces REMS of rats; IL-1 reduces firing rates of cholinergic neurons in LDT slice preparations; and IL-1 increases the number of c-Fos+ neurons in the ventrolateral periaqueductal grey (vlPAG), a GABA-rich area that projects to the pontine reticular formation and the LDT. In this application, we propose to determine: 1) the impact on sleep of IL-1 microinjection into brainstem cholinergic / cholinoceptive nuclei, 2) in vitro effects of IL-1 on electrophysiological properties of cholinergic neurons, and 3) the impact of IL-1 on REMS-relevant brainstem nuclei and neurotransmitter systems using immuno-fluorescence techniques. Successful completion of these aims will provide novel data critical for our understanding of mechanisms by which REMS is suppressed during infection. Determination of whether alterations in sleep contribute to good clinical outcome will only be possible when the neuroanatomic and neurochemical substrates targeted by immune responses to infection are clearly understood.