Figure 5.

Scheme of the highly interconnected multiple ascending arousal systems, which are directly or indirectly involved in the homeostatic sleep function of adenosine. This homeostatic function depends mostly on the accumulation of extracellular adenosine in basal forebrain and cortex. BF: area of origin of the corticopetal basal forebrain system; LC: locus coeruleus; LDT and PPT: laterodorsal and pedunculopontine nuclei; TM: tuberomammillary nucleus; Orx: area of origin of the hypocretin/orexin system; Thal: thalamus. The brown broken lines indicate the existence of descending prefrontal corticofugal neurons that influence the pontomesencephalic tegmentum (see text). Reproduced and modified from Ferré 2010