Abstract
The characteristics of high affinity [3H]5-HT (5-hydroxytryptamine) binding to non 5-HT1A non 5-HT1C sites were examined in crude membranes prepared from different regions of guinea-pig and pigeon brains. The coupling of these sites to adenylate cyclase was examined, and its pharmacological profile investigated. In the presence of 100 nmol/l 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) and 100 nmol/l mesulergine, [3H]5-HT labelled with nanomolar affinity an apparently homogeneous population of recognition sites in guinea-pig and pigeon brain membranes. The rank order of affinities of agonists and antagonists (5-CT (5-carboxamidotryptamine) greater than 5-HT greater than RU 24969 (5-methoxy-3-(1,2,3,6-tetrahydro-4- pyridinyl)-1H indole succinate) greater than yohimbine greater than or equal to rauwolscine greater than DP-5-CT (N,N dipropyl-5-carboxamidotryptamine) greater than or equal to mianserin greater than 8-OH-DPAT greater than mesulergine greater than SDZ 21-009 ((+/-)-4(3-tert-butyl-amino-2-hydroxypropoxy)-indol-2 carbonic acid isopropyl ester) greater than (-)propranolol), as well as their individual pKD values, were very similar to those at porcine caudate 5-HT1D sites and clearly different from those at rat cortex 5-HT1B sites. In the substantia nigra of the guinea-pig the 5-HT receptor-mediated inhibition of forskolin-stimulated adenylate cyclase had a pharmacological profile fully comparable to that of 5-HT1D binding sites (5-CT greater than 5-HT greater than yohimbine greater than RU 24969 greater than 8-OH-DPAT greater than SDZ 21-009 = isamoltane greater than (-)pindolol greater than (-)propranolol).(ABSTRACT TRUNCATED AT 250 WORDS)
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