| Popis: |
The 5-hydroxytryptamine (5-HT) receptors involved in the function of the serotonergic system in the brain of mammalians are numerous and their knowledge is still not complete. A first classification was produced by Bradley et al. (1986) based on the existence of 3 classes of receptors 5-HT1, 5-HT2 and 5-HT3. The 5-HT1 class corresponded to the existence of 3 subtypes of sites called 5-HT1A/ 5-HT1B and 5-HT1C and 3 subtypes were also proposed for the 5-HT3 class. Recent results allowed to simplify the classification of these receptors on the basis of their transduction system. It is, indeed, possible to distinguish serotonergic receptors coupled directly to an ionic channel; they correspond to the 5-HT3 receptor class (Richardson and Buchheit, 1988). The existence of subtypes of 5-HT3 receptors proposed on the basis of pharmacological heterogeneities is not yet fully established (Richardson and Engel, 1986). The second main class of receptor consists of those coupled to G proteins; they are 5-HT1 and 5-HT2 sites. Moreover, a 5-HT4 receptor type has been proposed (Dumuis et al., 1988) and may correspond to a G protein related receptor, however, the corresponding recognition sites for 5-HT4 have not yet been identified. 5-HT1 receptors are subdivided into 4 subtypes 5-HT1A, 5-HT1B, 5-HT1C and 5-HT1D (Hoyer et al., 1987) and an additional 5-HT1E has been proposed by Leonhardt et al. (1989). |
