The raphe nuclei are a moderate-size cluster of nuclei found in the brain stem. They have 5-HT1 receptors which are coupled with Gi/Go protein inhibiting adenyl cyclase. They function as autoreceptors in brain and decreases release of serotonin. The antianxiety drug Buspirone act as partial agonist. Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets.
The ventral tegmental area (VTA), also known as the ventral tegmental area of Tsai, or simply ventral tegmentum, is a group of neurons located close to the midline on the floor of the midbrain. The VTA is the origin of the dopaminergic cell bodies of the mesocorticolimbic dopamine system and other dopamine pathways; it is widely implicated in the drug and natural reward circuitry of the brain. The VTA plays an important role in a number of processes, including cognition, motivation, orgasm, and intense emotions relating to love, as well as several psychiatric disorders. Neurons in the VTA project to numerous areas of the brain, ranging from the prefrontal cortex to the caudal brainstem and several regions in between.
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. The reticular formation is not anatomically well defined because it includes neurons located in different parts of the brain. The neurons of the reticular formation make up a complex set of networks in the core of the brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata. The reticular formation includes ascending pathways to the cortex in the ascending reticular activating system (ARAS) and descending pathways to the spinal cord via the reticulospinal tracts of the descending reticular formation.
The ventrolateral preoptic nucleus (VLPO), also known as the intermediate nucleus of the preoptic area (IPA), is a small cluster of neurons situated in the anterior hypothalamus, sitting just above and to the side of the optic chiasm in the brain of humans and other animals. The brain's sleep-promoting nuclei, together with the ascending reticular activating system and the widely-projecting system of orexin neurons in the lateral hypothalamus, are the interconnected neural systems which control states of arousal, sleep, and transitions between these two states. The VLPO is active during sleep, primarily during non-rapid eye movement sleep, and releases inhibitory neurotransmitters, mainly GABA and galanin, which inhibit neurons of the ascending reticular activating system that are involved in wakefulness and arousal. The VLPO is in turn innervated by neurons from the aforementioned neural systems. The VLPO is activated by the sleep-inducing neurotransmitters serotonin and adenosine and endosomnogen Prostaglandin D2. The VLPO is inhibited during wakefulness by the arousal-inducing neurotransmitters norepinephrine and acetylcholine. The role of the VLPO in sleep and wakefulness, and its association with sleep disorders – particularly insomnia and narcolepsy – is a growing area of neuroscience research.
In neuroanatomy, habenula originally denoted the stalk of the pineal gland, but gradually came to refer to a neighboring group of nerve cells with which the pineal gland was believed to be associated, the habenular nucleus. The habenular nucleus is a set of well-conserved structures in all vertebrate animals.
The septal nuclei are a set of structures that lie below the rostrum of the corpus callosum, anterior to the lamina terminalis. The septal nuclei are composed of medium-size neurons which are classified into medial, lateral, and posterior groups. The septal nuclei receive reciprocal connections from the olfactory bulb, hippocampus, amygdala, hypothalamus, midbrain, habenula, cingulate gyrus, and thalamus.
The zona incerta is a horizontally elongated region of gray matter in the subthalamus below the thalamus. Its connections project extensively over the brain from the cerebral cortex down into the spinal cord.
The dorsal raphe nucleus is located on the midline of the brainstem and is one of the raphe nuclei. It has rostral and caudal subdivisions.
The nucleus raphe magnus, is located directly rostral to the nucleus raphe obscurus, and receives input from the spinal cord and cerebellum.
The lateral hypothalamus(LH), also called the lateral hypothalamic area, contains the primary orexinergic nucleus within the hypothalamus that widely projects throughout the nervous system; this system of neurons mediates an array of cognitive and physical processes, such as promoting feeding behavior and arousal, reducing pain perception, and regulating body temperature, digestive functions, and blood pressure, among many others. Clinically significant disorders that involve dysfunctions of the orexinergic projection system include narcolepsy, motility disorders or functional gastrointestinal disorders involving visceral hypersensitivity, and eating disorders.
The ventral reticular nucleus is a continuation of the parvocellular nucleus in the brainstem.
The gigantocellular nucleus is a subregion of the medullary reticular formation. As the name indicates, is mainly composed of the so-called giant neuronal cells.
The paramedian reticular nucleus sends its connections to the spinal cord in a mostly ipsilateral manner, although there is some decussation.
The median preoptic nucleus is located dorsal to the other three nuclei of the preoptic area of the anterior hypothalamus. The hypothalamus is located just beneath the thalamus, the main sensory relay station of the nervous system, and is considered part of the limbic system, which also includes structures such as the hippocampus and the amygdala. The hypothalamus is highly involved in maintaining homeostasis of the body, and the median preoptic nucleus is no exception, contributing to regulation of blood composition, body temperature, and non-REM sleep.
Sleep onset is the transition from wakefulness into sleep. Sleep onset usually transmits into non-rapid eye movement sleep but under certain circumstances it is possible to transit from wakefulness directly into rapid eye movement sleep.
The rostral ventromedial medulla (RVM), or ventromedial nucleus of the spinal cord, is a group of neurons located close to the midline on the floor of the medulla oblongata (myelencephalon). The rostral ventromedial medulla sends descending inhibitory and excitatory fibers to the dorsal horn spinal cord neurons. There are 3 categories of neurons in the RVM: on-cells, off-cells, and neutral cells. They are characterized by their response to nociceptive input. Off-cells show a transitory decrease in firing rate right before a nociceptive reflex, and are theorized to be inhibitory. Activation of off-cells, either by morphine or by any other means, results in antinociception. On-cells show a burst of activity immediately preceding nociceptive input, and are theorized to be contributing to the excitatory drive. Neutral cells show no response to nociceptive input.
The parabrachial nuclei, also known as the parabrachial complex, are a group of nuclei in the dorsolateral pons that surrounds the superior cerebellar peduncle as it enters the brainstem from the cerebellum. They are named from the Latin term for the superior cerebellar peduncle, the brachium conjunctivum. In the human brain, the expansion of the superior cerebellar peduncle expands the parabrachial nuclei, which form a thin strip of grey matter over most of the peduncle. The parabrachial nuclei are typically divided along the lines suggested by Baxter and Olszewski in humans, into a medial parabrachial nucleus and lateral parabrachial nucleus. These have in turn been subdivided into a dozen subnuclei: the superior, dorsal, ventral, internal, external and extreme lateral subnuclei; the lateral crescent and subparabrachial nucleus along the ventrolateral margin of the lateral parabrachial complex; and the medial and external medial subnuclei
The rostromedial tegmental nucleus (RMTg), also known as the tail of the ventral tegmental area (tVTA), is a GABAergic nucleus which functions as a "master brake" for the midbrain dopamine system. It is poorly differentiated from the rest of the ventral tegmental area (VTA) and possesses robust functional and structural links to the dopamine pathways. Notably, both acute and chronic exposure to psychostimulants have been shown to induce FosB and ΔFosB expression in the RMTg; no other drug type has been shown to induce these proteins in the RMTg.
The parafacial zone (PZ) is a brain structure located in the brain stem within the medulla oblongata. Due to a high presence of GABAergic neurons, as well as its involvement in slow-wave sleep, the parafacial zone is believed to be heavily responsible for non-rapid eye movement (non-REM) sleep regulation.
