Median raphe

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

Figure 9.3 Brain regions to which neurons in the dorsal and median Raphe nuclei project. Some areas are innervated by neurons from both nuclei (e.g. hypothalamus) whereas others are innervated predominantly by either the MRN (e.g. the hippocampus) or the DRN (e.g. the amydgala)...

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 median raphe (MR) nucleus (also designated central superior or B8)... 

Azmitia, E.C., and Segal, M. An autoradiographic analysis of the differential ascending projections of the dorsal and median raphe nuclei in the rat. J Comp Neurol 179 641-668, 1978. 

Kosofsky, B.E., and Molliver, M.E. The serotoninergic innervation of cerebral cortex Different classes of axon terminals arise from dorsal and median raphe nuclei. Synapse 1 153-168. 1987. 

Mamounas, L.A., and Molliver, M.E. Dual serotonergic projections to forebrain have separate origins in the dorsal and median raphe nuclei Retrograde transport after selective axonal ablation by p-chloroamphetamine (PCA). Abstr Soc Neurosci 13 907, 1987. 

Waterhouse, B.D. Mihailoff, G.A. Baack, J.C. and Woodward, DJ. Topographical distribution of dorsal and median raphe neurons projecting to motor, sensorimotor, and visual cortical areas in the rat. J Comp Neurol 249 460-476, 1986. 

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. 

Hillegaart, V. (1990). Effects of local application of 5-HT and 8-OH-DPAT into the dorsal and median raphe nuclei on motor activity in the rat. Physiol. Behav. 48, 143-8. 

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. 

McQuade, R. Sharp, T. (1997). Functional mapping of dorsal and median raphe 5-hydroxytryptamine pathways in forebrain of the rat using microdialysis. 

Morin, L. P. 8r Meyer-Bernstein, E. L. (1999). The ascending serotonergic system in the hamster Comparison with projections of the dorsal and median raphe nuclei. Neuroscience 91, 81-105. 

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... 

The acute CNS effects of MDMA administration are mediated by the release of monoamine transmitters, with the subsequent activation of presynaptic and postsynaptic receptor sites.40 As specific examples in rats, MDMA suppresses 5-HT cell firing, evokes neuroendocrine secretion, and stimulates locomotor activity. MDMA-induced suppression of 5-HT cell firing in the dorsal and median raphe involves activation of presynaptic 5-HT1A autoreceptors by endogenous 5-HT.4142 Neuroendocrine effects of MDMA include secretion of prolactin from the anterior pituitary and corticosterone from the adrenal glands 43 Evidence supports the notion that these MDMA-induced hormonal effects are mediated via postsynaptic 5-HT2 receptors in the hypothalamus, which are activated by released 5-HT. MDMA elicits a unique profile of locomotor effects characterized by forward locomotion and elements of the 5-HT behavioral syndrome such as flattened body posture, Straub tail, and forepaw treading.44 6 The complex motor effects of MDMA are dependent on monoamine release followed by activation of multiple postsynaptic 5-HT and DA receptor subtypes in the brain,47 but the precise role of specific receptor subtypes is still under investigation. 

Gartside, S.E., McQuade, R., and Sharp, T., Acute effects of 3,4-methylenedioxymethamphetamine (MDMA) on 5-HT cell firing and release comparison between dorsal and median raphe 5-HT systems, Neuropharmacology 36(11-12), 1697-703, 1997. 

These differences may be extremely important in understanding the role of these two distinct serotonergic systems, arising from the dorsal and median raphe nuclei, in normal brain function and in mental illness. 

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. 

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