|Part of||Brainstem (Medulla oblongata)|
|Anatomical terms of neuroanatomy|
The parafacial zone (PZ) is a brain structure located within the medulla oblongata which contains GABAergic neurons and is involved in slow-wave sleep. It is one of several GABAergic sleep-promoting nuclei in the brain, which include the ventrolateral preoptic area of the hypothalamus, the nucleus accumbens core (specifically, the D2-type medium spiny neurons in the core which co-express adenosine A2A receptors), and a GABAergic nucleus in the lateral hypothalamus which co-release melanin-concentrating hormone.
The parafacial zone promotes slow-wave sleep by inhibiting the glutamatergic parabrachial nucleus, a component of the ascending reticular activating system that mediates wakefulness and arousal, via the release of the inhibitory neurotransmitter GABA onto those neurons.Optogenetic activation of GABAergic PZ neurons induces cortical slow-wave activity and slow-wave sleep in awake animals.
In the present study we show, for the first time, that activation of a delimited node of GABAergic neurons located in the medullary PZ can potently initiate SWS and cortical SWA in behaving animals. ... For now however it remains unclear if the PZ is interconnected with other sleep- and wake-promoting nodes beyond the wake-promoting PB. ... The intensity of cortical slow-wave-activity (SWA: 0.5-4Hz) during SWS is also widely accepted as a reliable indicator of sleep need ... In conclusion, in the present study we demonstrated that all polygraphic and neurobehavioral manifestation of SWS, including SWA, can be initiated in behaving animals by the selective activation of a delimited node of GABAergic medullary neurons.
This ascending reticular activating system (ARAS) is comprised of cholinergic laterodorsal and pedunculopontine tegmentum (LDT/PPT), noradrenergic locus coeruleus (LC), serotonergic (5-HT) Raphe nuclei and dopaminergic ventral tegmental area (VTA), substantia nigra (SN) and periaqueductal gray projections that stimulate the cortex directly and indirectly via the thalamus, hypothalamus and BF.6, 12-18 These aminergic and catecholaminergic populations have numerous interconnections and parallel projections which likely impart functional redundancy and resilience to the system.6, 13, 19 ... More recently, the medullary parafacial zone (PZ) adjacent to the facial nerve was identified as a sleep-promoting center on the basis of anatomical, electrophysiological and chemo- and optogenetic studies.23, 24 GABAergic PZ neurons inhibit glutamatergic parabrachial (PB) neurons that project to the BF,25 thereby promoting NREM sleep at the expense of wakefulness and REM sleep. ... Sleep is regulated by GABAergic populations in both the preoptic area and the brainstem; increasing evidence suggests a role for the melanin-concentrating hormone cells of the lateral hypothalamus and the parafacial zone of the brainstem
The sleep-promoting action of GABAergic neurons located in the preoptic hypothalamus (6-8) is now well-known and accepted (9). More recently, other groups of sleep-promoting GABAergic neurons in the lateral hypothalamus (melanin-concentrating hormone neurons) and brainstem [parafacial zone; (10)] have been identified.
More recently, Fuller's laboratory also discovered that sleep can be promoted by the activation of a gamma-aminobutyric acid-ergic (GABAergic) population of neurons located in the parafacial zone [11,12], while the role of the GABAergic A2AR-expressing neurons of the nucleus accumbens  and the striatum has just been revealed [14,15].
Here, we show that chemogenetic or optogenetic activation of excitatory adenosine A2A receptor-expressing indirect pathway neurons in the core region of the NAc strongly induces slow-wave sleep. Chemogenetic inhibition of the NAc indirect pathway neurons prevents the sleep induction, but does not affect the homoeostatic sleep rebound.