Hypothalamus description

The mRNA coding for 5-HT6 receptor has been localized in the rat brain by Northern blot, PCR, and in situ hybridization (206,207,213,214) (see also Fig. 10) and the protein by immunohistochemistry (213). The first and more detailed description on the localization of mRNA coding for 5-HT6 receptor was published by Ward and co-workers (215), reporting that the main rat brain regions where this receptor is expressed is the pyramidal layer of the olfactory tubercle, islands of Calleja, nucleus accumbens, striatum, hippocampus, and piriform cortex. At moderate levels, it is expressed in other cortical areas, the olfactory bulb, some nuclei of the hypothalamus and amygdale, the habenula, and the cerebellum. No mRNA expression is found in the raphe nucleus. These results were confirmed later (204). 

This data, coupled with numerous positive outcome studies of the effectiveness of antidepressants, has led to the development of the monoamine (or biogenic amine) hypothesis of depression. The theory holds that depressive symptoms are ushered in by a malfunction of either norepinephrine (NE) or serotonin (5-HT) neurons, which play critical roles in the functioning of the limbic system and the adjacent hypothalamus. The basic neuronal malfunction is felt to be identical for either NE or 5-HT neurons, thus what follows (a description of the pathophysiology of NE neurons) can also be seen to occur in individuals in whom 5-HT neurons are affected. For reasons that are not well understood, patients with major depression (with vegetative symptoms) appear to suffer from either NE or 5-HT dysfunction, but probably not both simultaneously (although some exceptions exist). 

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