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Influence on 5‐[ 3 H]Hydroxytryptamine Binding Site Development in Chick Embryo by Serotonergic Compounds
Author(s) -
Soblosky Joseph S.,
Jeng Ingming
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb05447.x
Subject(s) - serotonergic , methysergide , binding site , serotonin , forebrain , chemistry , lysergic acid diethylamide , ligand (biochemistry) , embryo , medicine , endocrinology , population , stereochemistry , biology , biochemistry , receptor , central nervous system , microbiology and biotechnology , demography , sociology
Saturable and specific binding sites for 5‐[ 3 H]hydroxytryptamine (5‐HT, serotonin) characterized by a K D of 3.5–4.5 n M were detected in the chick embryo brain and were shown to develop linearly as a function of age, weight, and protein content. Saturation and displacement studies using unlabeled 5‐HT as the displacing ligand suggested a single population of binding sites. However, displacement studies using 5‐methoxytryptamine, lysergic acid diethylamide (LSD), 2‐bromo‐lysergic acid diethylamide (BOL), methysergide, and spiperone as competing ligands suggested the existence of subclasses of [ 3 H]5‐HT binding sites because the Hill coefficients were less than unity. When compared with the reported [ 3 H]5‐HT binding sites (5‐HT 1 ) in the rat forebrain, the IC 50 values of the competing ligands were similar. However, the Hill coefficients for LSD and methysergide were less than unity which suggested that the [ 3 H]5‐HT binding sites in the chick embryo brain may be more similar to those found in rat spinal cord than rat forebrain. To study [ 3 H]5‐HT binding site regulation and development, various serotonergic compounds were injected into the chorioallantoic fluid of the eggs at different times during embryonic development. Multiple pretreatments with d,l ‐5‐hydroxytryptophan, 5‐HT, or BOL were found to have no significant effects on either the affinity ( K D ) or number ( B max ) of specific [ 3 H]5‐HT binding sites. Multiple pretreatments with p ‐chlorophenylalanine were found to increase the B max of specific [ 3 H]5‐HT binding by 23% (p < 0.01) whereas multiple pretreatments with LSD were found to decrease the B max of specific binding by 45% (p < 0.01). Neither of these pretreatments affected K D values which indicated that only the number of specific [ 3 H]5‐HT binding sites was altered. Evidence was presented suggesting that these effects were probably not due to excess endogenous 5‐HT or LSD remaining in the tissue preparation. The overall evidence indicated that the chick embryo brain may have a functioning serotonergic system and that the chick embryo may be an ideal system for the study of [ 3 H]5‐HT binding site regulation and development.