Solitary tract

The large numbers of opioid receptors in areas of the brainstem such as the solitary tract and adjacent areas are probably related to respiratory effects of opiates, cough suppression and nausea and vomiting. Opiates acting in the brainstem reduce the sensitivity of the respiratory centres to pC02 and this is the most common cause of death from overdose with street use of opiates. 

Figure 7.4 Summary of some of the wide array of afferent and efferent connections of midbrain dopaminergic neurons (SN/A9, RRF/A8, and VTA/A10 in center of figure). This emphasizes their potential involvement in coordination of seemingly disparate behaviors inclusive of the sleep-wake state of the organism. Abbreviations BP, blood pressure BST, bed nucleus of the stria terminalis CEA, central nucleus of the amygdala MEA, midbrain extrapyramidal area NTS, nucleus of the solitary tract O2, oxygen tension PPN, pedunculopontine tegmental nucleus RRF, retrorubral field SN, substantia nigra VTA, ventral tegmental area.

A major side-effect of morphine is respiratory depression. Opiates are believed to cause this effect via actions in brainstem nuclei, fi receptor immunoreactivity and mRNA were detected in neurons of the nucleus of the solitary tract, nucleus ambiguous, and parabrachial nucleus. mRNA was detected in the bed nucleus of the stria terminalis which projects to the nucleus of the solitary tract, fi receptor immunoreactivity is found in the nucleus of the solitary tract and dorsal rhizotomy reduced receptor immunoreactivity in the nucleus suggesting a presynaptic localization of the receptor. 

Hippocampus, entorhinal cortex, amygdala, nucleus, accumbens, solitary tract nerve, trigeminal nerve, motor nucleus of the dorsal vagal nerve, area postrema, spinal cord... 

X3 NM 002559 Dorsal root ganglion, superficial dorsal horn of spinal cord, a subset of small-diameter sensory neurons, nucleus of the solitary tract, spinal trigeminal nucleus (important for peripheral pain)... 

Mosqueda-Garcia, R., Tseng, C.-J., Appalsamy, M., Beck, C. and Robertson, D. Cardiovascular excitatory effects of adenosine in the nucleus of the solitary tract. Hypertension 18 494-502,1991. 

Williams CL, Men D, Clayton EC, Gold PE. 1998. Norepinephrine release in the amygdala after systemic injection of epinephrine or escapable footshock contribution of the nucleus of the solitary tract. Behav Neurosci 112(6) 1414-1422. 

Neuropeptide Y [NPY] is a 36-amino acid peptide. The function of NPY, one of the most abundant peptide transmitters of the mammalian brain, remains unclear because of a lack of specific receptor antagonists. NPY meets many of the criteria of a neurotransmitter itself. NPY is costored and interacts with several monoaminergic neurons within the CNS [Lundberg et al. 1982], for example, noradrenergic afferents from the nucleus solitary tract to the amygdala. Both somatostatin and NPY colocalize at GABA interneurons within the amygdala, neocortex, and striatum. NPY also selectively modulates N-methyl-D-aspartate-induced hippocampal activation (pyramidal neurons] via oreceptors [Debonnel et al. 1994]. 

The vagus nerve terminates in the nucleus of the solitary tract with widespread projections, including the locus ceruleus. There are several lines of evidence that support the potential efficacy of vagus nerve stimulation (VNS) for depression, including the following ... 

Cumming, P., Gjedde, A. and Vincent, S. (1994). Histamine H3 binding sites in rat brain -localization in the nucleus of the solitary tract. Brain Res. 641, 198-202. 

Scislo TJ, O Leary DS. Purinergic mechanisms of the nucleus of the solitary tract and neural cardiovascular control. Neurol Res. 2005 27 182-194. 

Structures implicated in the production or maintenance of sleep include the nucleus of the solitary tract, dorsal medullary reticular formation, raphe nuclei, thalamus, anterior hypothalamus, preoptic area, basal forebrain, orbitofrontal cortex, caudate nucleus, basal ganglia, and cerebral cortex. None of these structures are individually necessary for sleep. No lesion has produced a long lasting total insomnia. After some sleep-reducing lesions, sleep returns toward normal if sufficient time is allowed for recovery. 

Glatzer NR, Smith BN (2005) Modulation of synaptic transmission in the rat nucleus of the solitary tract by endomorphin-1. J Neurophysiol 93 2530-40 Glaum SR, Miller RJ, Hammond DL (1994) Inhibitory actions of delta 1-, delta 2-, and mu-opioid receptor agonists on excitatory transmission in lamina II neurons of adult rat spinal cord. J Neurosci 14 4965-71... 

Prokineticins are also expressed in neurons of medial preoptic area, nucleus of solitary tract, trigeminal and facial nuclei, and DRG (Fig. 1). 

Fig. 1. Localization of prokineticin mRNAs in rat brain. PK1 and PK2 are both expressed in the olfactory bulb, island of Calleja, and SCN where they oscillate following the day—night cycle. PK2 mRNA is present also in the shell of nucleus accumbens, in nucleus arcuatus, and in nucleus of solitary tract.

Huang J, Pickel VM. Serotonin transporters (SERTs) within the rat nucleus of the solitary tract subcellular distribution and relation to 5-HT2A receptors. J Neurocytol 2002 31 667-679. 

The NAc receives brainstem information related to taste and visceral functions through direct input from the nucleus of the solitary tract to the medial shell as well as indirect input from the gustatory cortex to the lateral shell and core via parabrachial projections to the gustatory thalamus (Ricardo and Koh, 1978 Saper, 1982). Additonal taste information is relayed to the NAc from the basolateral amygdala, that integrates taste... 

Efferent projections from the NAc core and shell topographically terminate in the lateral and medial ventral pallidus respectively, but in addition the NAc shell targets the lateral hypothalamus, central grey and nucleus of the solitary tract (Heimer et al., 1991). 

Ricardo JA, Koh ET (1978) Anatomical evidence of direct projections from the nucleus of the solitary tract to the hypothalamus, amygdala, and other forebrain structures in the rat. Brain Res 755(1) 1—26. 

The physiological basis of the effects of cannabinoids on feeding behaviour is not known. A French group has reported that neurons in the solitary tract nucleus, which respond to increases in glucose concentrations, are sensitive to zl9-THC and have suggested that such neurons may mediate canna-binoid effects on feeding behaviour [129]. 

---