The dual orexin receptor antagonist, DORA-22, lowers histamine levels in the lateral hypothalamus and prefrontal cortex without lowering hippocampal acetylcholine.

Chronic insomnia is defined as a persistent difficulty with sleep initiation maintenance or non-restorative sleep. The therapeutic standard of care for this condition is treatment with gamma-aminobutyric acid (GABA)A receptor modulators, which promote sleep but are associated with a panoply of side effects, including cognitive and memory impairment. Dual orexin receptor antagonists (DORAs) have recently emerged as an alternative therapeutic approach that acts via a distinct and more selective wake-attenuating mechanism with the potential to be associated with milder side effects. Given their distinct mechanism of action, the current work tested the hypothesis that DORAs and GABAA receptor modulators differentially regulate neurochemical pathways associated with differences in sleep architecture and cognitive performance induced by these pharmacological mechanisms. Our findings showed that DORA-22 suppresses the release of the wake neurotransmitter histamine in the lateral hypothalamus, prefrontal cortex, and hippocampus with no significant alterations in acetylcholine levels. In contrast, eszopiclone, commonly used as a GABAA modulator, inhibited acetylcholine secretion across brain regions with variable effects on histamine release depending on the extent of wakefulness induction. In normal waking rats, eszopiclone only transiently suppressed histamine secretion, whereas this suppression was more obvious under caffeine-induced wakefulness. Compared with the GABAA modulator eszopiclone, DORA-22 elicits a neurotransmitter profile consistent with wake reduction that does not impinge on neurotransmitter levels associated with cognition and rapid eye movement sleep.