In human cortex and hippocampus area, [
3H]5-HT (5 nM) labels 5-HT
1A, 5-HT
1D and 5-HT
1E sites. After masking 5-HT
1A receptors by 0.1 μM 8-OH-DPAT, the binding displaced by 0.1 μM 5-CT presumably represented 5-HT
1D sites and the remaining binding 5-HT
1E sites. In frontal cortex, 5-HT
1A receptors represented the main binding in layers II and VI and a lower fraction on other layers. 5-HT
1D and 5-HT
1E sites, were more homogeneously distributed in layers II to VI (21–34% of specific [
3H]5-HT binding). 5-HT
1E sites were of similar affinities (
KD close to 6–8 nM) in the cortical layers II to VI. In CA1 field of hippocampus, (pyramidal layer, stratum radiatum, molecular layer), CA2 and dentate gyrus, 5-HT
1A receptors represented the major fraction, 5-HT
1D sites a significant fraction and 5-HT
1E a minor fraction of the specific [
3H]5-HT binding. In CA3–CA4 fields, 5-HT
1A receptors were less densely present, 5-HT
1D sites were predominant and 5-HT
1E sites represented a significant fraction (27%). The highest densities of 5-HT
1E sites have been measured in subiculum, where 5-HT
1A, 5-HT
1D, and 5-HT
1E binding sites were equally represented and in entorhinal cortex where 5-HT
1E sites represented the major binding in layer III. They were also present in layers II and IV (29 and 24%) and, to a lesser extent, in layers V and VI. 5-HT
1A sites were predominant in layer VI, II and V and were less abundant in other layers. 5-HT
1D were homogeneously present in layers II, III, IV and were present in low amounts in other layers. No 5-HT
1E were detected in choroid plexus, where [
3H]5-HT was dramatically reduced by mesulergine (5-HT
2C receptors). No significant displacement of [
3H]5-HT by mesulergine was measured in other structures.
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