Single-dose 8-OH-DPAT pretreatment does not induce tachyphylaxis to the 5-HT release-reducing effect of 5-HT1A autoreceptor agonists.
It has recently been suggested that central 5-HT1A autoreceptors are already desensitised after single-dose 5-HT1A agonist treatment. In turn, this would lead to an attenuated feedback suppression of transmitter release from 5-HT neurones, and thus to enhanced 5-HT synaptic transmission. In the present study in vivo brain microdialysis techniques were used in an attempt to test this hypothesis. The results show that single-dose pretreatment with the reference 5-HT1A receptor agonist 8-hydroxy-2-(din-propylamino)tetralin, 8-OH-DPAT, (i) did not significantly alter the baseline output of 5-HT in the rat ventral hippocampus 24 h later, and (ii) did not alter the release-reducing response to 5-HT1A agonist (8-OH-DPAT, ipsapirone or BMY 7378) challenge under the same conditions. These observations indicate that the functional responsiveness of the 5-HT release-controlling 5-HT1A autoreceptors is maintained after bolus 8-OH-DPAT pretreatment. When related to the acute 8-OH-DPAT-induced reduction in raphe 5-HT1A radioligand binding density recently reported by others, the present results are consistent with a large functional overcapacity of this 5-HT1A receptor population. The mechanism by which 5-HT1A receptor-mediated hypothermia and hyperphagia are rapidly attenuated by a previous large single dose of a 5-HT1A receptor agonist remains to be explained.
Hjorth
S
S
Department of Pharmacology, University of Göteborg, Sweden.
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000818:Animals; D001665:Binding Sites; D005246:Feedback; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010879:Piperazines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D013618:Tachyphylaxis; D013764:Tetrahydronaphthalenes / Q000008:administration & dosage / Q000494:pharmacology*
D010879:Piperazines; D011743:Pyrimidines; D011985:Receptors, Serotonin; D013764:Tetrahydronaphthalenes; D012701:Serotonin; C043077:ipsapirone; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C053428:BMY 7378