Characterization of [³H]CP‐96,501 as a Selective Radioligand for the Serotonin 5‐HT_1B Receptor: Binding Studies in Rat Brain Membranes

Abstract

3-(1,2,5,6-Tetrahydro-4-pyridyl)-5-n-propoxyindole (CP-96,501) was found to be more selective ligand at the serotonin 5-HT1B receptor than the commonly used 5-HT1B agonist, 3-(1,2,5,6-tetrahydro-4-pyridyl)-5-methoxyindole (RU 24969). In rat brain membranes, the tritiated derivative, [3H]CP-96,501, was found to bind with a high affinity (KD, 0.21 nM) to a single binding site (nH, 1.0). The receptor density of this site (Bmax, 72 fmol/mg of protein) matched that of the 5-HT1B receptor determined with [3H]5-HT. Competition curves of 16 serotonergic compounds in [3H]CP-96,501 binding also indicated a single binding site. The rank order of their binding affinities with this new radioligand showed a high degree of correlation with their affinities at the 5-HT1B receptor determined with [3H]5-HT or [125I]iodocyanopindolol. Serotonergic compounds displayed competitive inhibition of [3H]CP-96,501 binding. In the presence of 5'-guanylylimidodiphosphate [Gpp(NH)p], [3H]CP-96,501 to displace [125I]iodocyanopindolol binding was also decreased. These findings are consistent with the agonist nature of CP-96,501. The results of this study suggest that [3H]CP-96,501 is a useful agonist radioligand for the 5-HT1B receptor.

Biphasic alterations in Serotonin‐1B (5‐HT1B) receptor function during abstinence from extended cocaine self‐administration

“…CP 93, 129 is highly selective for 5‐HT 1B receptors over other 5‐HT receptor subtypes (Macor et al . 1990; Koe et al . 1992; Chopin et al .…”

“…Moreover, several lines of evidence indicate that the CP 93,129-induced increase in DA efflux is mediated through 5-HT 1B receptors. CP 93, 129 is highly selective for 5-HT 1B receptors over other 5-HT receptor subtypes (Macor et al 1990;Koe et al 1992;Chopin et al 1994) and has no appreciable interaction with DA, noradrenaline or opiate receptors (Macor et al 1990). The effect of this agonist on dialysate DA levels is blocked by coperfusion with either the 5-HT 1B/1D receptor antagonist GR 127 935 (Iyer and Bradberry 1996) or the selective and neutral 5-HT 1B antagonist GR 55562 (present results).…”

Autoradiographic studies of 5‐HT1A‐receptor‐stimulated [35S]GTPγS‐binding responses in the human and monkey brain

“…Stanton et al . (1997) reported enhanced [ 35 S]GTPγS binding by the selective rodent 5‐HT 1B agonist CP 93129 (Koe et al . 1992) in rat substantia nigra.…”

“…Waeber & Moskowitz (1997) restricted analogue CP 122288 (Lee & Moskowitz, 1993) in the substantia nigra of guinea-pig brain sections. reported enhanced [ 35 S]GTPγS binding by the selective rodent 5-HT 1B agonist CP 93129 (Koe et al, 1992) in rat substantia nigra. Scott & Bruinvels (1997) also observed an increase (45-109%) in [ 35 S]GTPγS binding with the 5-HT 1A/1B/1D agonist SKF 99101 in substantia nigra and caudate putamen of rat brain sections, but this effect remained unchanged in the presence of the selective 5-HT 1A antagonist WAY 100635 and the 5-HT 1B inverse agonist SB 224289.…”

Functional characterization of 5‐HT1D autoreceptors on the modulation of 5‐HT release in guinea‐pig mesencephalic raphe, hippocampus and frontal cortex

“…However, it was reported that sumatriptan binds with nanomolar affinity for 5-HTlD sites but only has a ten fold selectivity for 5-HTID with respect to 5-HTlB and 5-HTIA sites (Hoyer, 1991). The involvement of 5-HTlB receptors may be ruled out on the basis of the present results since the 5-HTIB receptor agonist, CP93129 (Koe et al, 1992), at a concentration (0.1 gM) which does not affect the basal outflow of tritium, had no effect on the electrically evoked release of [3H]-5-HT from mesencephalic raphe as well as hippocampus and frontal cortex (Figures 1, 2, 3). In identical experiments in rat mesencephalic raphe slices (Pifneyro et al, 1995), the inhibitory effect of sumatriptan was also prevented by mianserin, a drug which has high affinity for rat 5-HTID but not 5-HTlB receptors (Hamblin et al, 1992).…”