Median raph nucleus

B5 and B8 Median Raphe nucleus B2 Nucleus Raphe obscurus... 

Figure 22.8 The distribution of brainstem Raphe nuclei. Neurons that release 5-HT are clustered in two groups of nuclei in the pons and upper brainstem. The superior group, which projects to forebrain areas, includes the dorsal Raphe nucleus (DRN) and the median Raphe nucleus (MRN). The inferior group projects to the medulla and spinal cord and includes the nucleus Raphe pallidus (NRP), the nucleus Raphe obscurus (NRO) and the nucleus Raphe magnus (NRM)...

The neural structures involved in the promotion of the waking (W) state are located in the (1) brainstem [dorsal raphe nucleus (DRN), median raphe nucleus (MRN), locus coeruleus (LC), laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT), and medial-pontine reticular formation (mPRF)] (2) hypothalamus [tuberomammillary nucleus (TMN) and lateral hypothalamus (LH)[ (3) basal forebrain (BFB) (medial septal area, nucleus basalis of Meynert) and (4) midbrain ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) (Pace-Schott Hobson, 2002 Jones, 2003). The following neurotransmitters function to promote W (1) acetylcholine (ACh LDT/PPT, BFB) (2) noradrenaline (NA LC) (3) serotonin (5-HT DRN, MRN) (4) histamine (HA TMN) (5) glutamate (GLU mPRF, BFB, thalamus) (6) orexin (OX LH) and (7) dopamine (DA VTA, SNc) (Zoltoski et al, 1999 Monti, 2004). 

Table 9.1 Efferent connections of the dorsal raphe nucleus and the median raphe nucleus of the rat...

Dorsal raphe nucleus Median raphe nucleus... 

Dorsal raphe nucleus, median raphe nucleus, locus coeruleus From To et at (1995), Gustafson et al. (1996), and Neumaier et al. (2001). 

Behzadi, G., Kalen, P., Parvopassu, R Wiklund, L. (1990). Afferents to the median raphe nucleus of the rat retrograde cholera toxin and wheat germ conjugated horseradish peroxidase tracing, and selective D-[3H]aspartate labelling of possible excitatory amino acid inputs. Neuroscience 37, 77-100. 

Marcinkiewicz, M., Morcos, R. Chretien, M. (1989). CNS connections with the median raphe nucleus retrograde tracing with WGA-apoHRP-gold complex in the rat. J. Comp. Neurol. 289, 11-35. 

Varga V., Sik A., Freund T. F Kocsis B. (2002). GABA(B) receptors in the median raphe nucleus distribution and role in the serotonergic control of hippocampal... 

Lesions of serotonergic neurons in laboratory animals have been reported by some, but not all, investigators to disrupt locomotor rhythms or to result in the loss of the daily rhythm of corticosterone. There is evidence that, in the hamster, the median raphe nucleus projects to the SCN whereas the dorsal raphe nucleus innervates the IGL furthermore, the serotonergic innervation to the SCN and not the IGL is necessary for the photic entrainment of locomotor activity [22]. It appears then, that the SCN circadian pacemaker or clock is modulated by stimulation of serotonergic receptors in the SCN and that serotonergic projections to the SCN may modulate the phase of the SCN in intact animals. 

Figure 5. Serotonergic systems in the human brain with projections to the cerebral cortex from the dorsal raphe nucleus (continuous line) and from the median raph nucleus (dotted line). Projections from more posterior nuclei also as continuous lines.

Bosker F, Klompmakers A, Westenberg H. Extracellular 5-hydroxytryptamine in median raphe nucleus of the conscious rat is decreased by nanomolar concentrations... 

The injection of histamine into the dorsal raphe nucleus and PAG region produces an antinociception, whereas its injection into the median raphe nucleus causes hyperalgesia (Glick and Crane, 1978 Thoburn et al., 1994). Some data suggest that activation of opioid receptors can increase histamine release in PAG (Barke and Hough, 1993). 

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