HT2A Receptor Subtypes

There are currently three members of the 5-HT2 receptor family (5-HT2A, 5-HT2B, 5-HT2C) all of which are coupled positively to phospholipase C and mobilize intra-cellular calcium. Investigation of the function of individual members of the 5-HT2 family has only proved possible quite recently with the development of selective 5-HT2A and 5-HT2C receptor antagonists (5-HT2A receptor antagonist: M100907, formerly MDL 1009907; 5-HT2C receptor antagonists: SB 242084 and RS 102221). However, there is still a need for more selective agonists, particularly at the 5-HT2A receptor. Receptor autoradiography studies using tritiated ligands demonstrate high levels of 5-HT2A receptors in many forebrain regions, and particularly in cortical areas, including frontal cortex, the nucleus accumbens, caudate nucleus, and HPC (Lopez-Gimenez et al. 1997; Pazos et al. 1985, 1987).

5-HT2A receptors are located postsynaptically to serotonergic neurons and have been found on both yaminobutyric acid (GABA)-ergic interneurons as well as glutamatergic cortical pyramidal cells (Burnet et al. 1995; Francis et al. 1992; Morilak et al. 1993, 1994; Wright et al. 1995). Activation of the 5-HT2A receptors depolarizes the cell membrane, potentially through a decrease in K+ currents (Marek and Aghajanian 1995; Aghajanian and Marek 1997; Araneda and Andrade 1991). Although it has generally been reported that none of the more selective 5-HT2 receptor agonists or antagonists alter levels of 5-HT (e.g., Gobert and Millan 1999; Gobert et al. 2000), it has been suggested that 5-HT2A receptors are involved in a glutamatergic feedback loop originating from the prefrontal cortex (PFC) and terminating in the dorsal raphe nucleus (DRN). Therefore stimulation of 5-HT2A receptors in this region may have the capacity to alter 5-HT release throughout the forebrain (Martin-Ruiz et al. 2001).

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