Anatomical and neurochemical bases accounting for the frequent association between headaches and sleep:: The hypnic headache paradigm

Introduction. The relationship between headache and sleep is complex and runs in two directions. Headache may, be the consequence of a (primary or secondary) sleep disorder or its cause (in chronic tension-type headache and/or chronic migraine with or without painkiller abuse). It can also be related to sleep ill an intrinsic way, as in the case of hypnic headache (which only appears during sleep) or other primary headaches, sitch as migraine and certain trigeminal-autonomic cephalgias (which can appear during the waking slate or during sleep): this type of headache occurs mostly during REM sleep. Development. The neural pathways that control sleep and pain are anatomically. physiologically and neurochemically cross-linked. These neural systems are located in the brain stem, the hypothalamus and the basal brain. Such cross-links are produced oil two different levels. On the one hand, they occur in the serotoninergic nuclei of the brain stem, whose activitv in physiologically diminished during REM sleep and which are involved in antinociceptive control. On the other hand, they are also to be found in the hypothalamus, where serotoninergic termials have been detected ill the suprachiasmatic nucleus (SCN). As cells in the SCN are lost with age. their circadian and homeostatic functioning Jails, the activity of the hypothalamus-pineal axis is reduced and the endogenous melatonin rhythm is altered. This results ill a disorder affecting the control of the sleep-waking cycle and antinociceptive control. Conclusions. Dysfunctions ill these neuronal networks ill the brain slein (especially ill the serotoninergic nuclei) or the hypothalamus (SCN) call account for headaches that begin in the REM phase of sleep and affect biologically predisposed subjects.