Sleep regulation: interactions among cytokines and classical neurotransmitters

The role of classical neurotransmitters in sleep regulation is amply documented (Hobson and Steriade, 1986). In recent years evidence has been gathered that immunoactive molecules, infectious agents and their components, or cytokines play some part in sleep regulation (Krueger and Obál, 1994; Opp et al., 1992; Moldofsky, 1994). Different cytokines possess hypnogenic properties when injected centrally or systemically to different animal species and their role in physiological sleep regulation is currently under investigation. Little is known of how cytokines and classical neurotransmitters interact and of the relevance of this interaction in sleep induction and maintenance. The present paper (i) reviews data on this topic; (ii) proposes a unitary interpretation whenever possible; and (iii) raises questions that might be addressed by future studies.