Nucleus accumbens subtype

Dopamine receptors include at least 4 subtypes which are concentrated in the striatum where D1 and D2 are evenly distributed and D3 is concentrated in the limbic portion, nucleus accumbens (Herroelen et al., 1994). D2 but not D1 receptors also occur throughout the cerebral cortex particularly temporal lobe, and D3 receptors are also present in lower densities in hippocampus and amygdala. D3 receptors are localised in several thalamic nuclei including the lateral geniculate, mediodorsal and anteroventral. 

Opioid binding at medullary sites is consistent with the respiratory depressant effects of the drugs. Binding in the nucleus accumbens and the resultant release of dopamine by the /x- and 8-opioids is linked to the development of physical dependence. However, the K-opioids, which also bind extensively in the nucleus accumbens, are linked to a decrease in dopamine release, possibly explaining their lower abuse liability. The localization of different receptor subtypes within different-size fiber pathways has been established. The x- and 8-receptors appear associated with the large-diameter fibers, while the K-receptors appear to be located in the small to medium-size fiber bundles of the dorsal root ganglia. Such differences may explain the modulation of specific types of nociceptive stimuli by the different opioid agonists and opioid peptides. 

Five subtypes of dopamine receptors have been described they are the Dj-like and Dj-like receptor groups. All have seven transmembrane domains and are G protein-coupled. The Dj-receptor increases cyclic adenosine monophosphate (cAMP) formation by stimulation of dopamine-sensitive adenylyl cyclase it is located mainly in the putamen, nucleus accumbens, and olfactory tubercle. The other member of this family is the D5-receptor, which also increases cAMP but has a 10-fold greater affinity for dopamine and is found primarily in limbic regions. The therapeutic potency of antipsychotic drugs does not correlate with their affinity for binding to the Dj-receptor. 

Fig. 7. Anatomical organization of dopamine Di mRNA expression in the adult human brain (whole hemisphere horizontal images) at a dorsal (A) and ventral (B) level. Notice strong cortical expression of this dopamine receptor subtype in addition to the intense expression levels in the striatum (CN, Pu and NAc). Adapted from Hurd et al. (2001). aCg, anterior cingulate Amy, amygdala Cb, cerebellum cc, corpus callosum CN, caudate nucleus Cun, cuneus F, frontal lobe Hip, hippocampus hyp, hypothalamus I, insular cortex mPFC, medial prefrontal cortex mm, medial mammillary nucleus NAc, nucleus accumbens O, occipital lobe Phg, parahippocampal gyrus Pu, putamen SN, substantia nigra T, temporal lobe U, uncal gyrus.

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