Differential modulation of extracellular levels of 5-hydroxytryptamine in the rat frontal cortex by (R)- and (S)-zacopride.
1. The ability of various anxiolytic and potential anxiolytic agents to modify 5-hydroxytryptamine (5-HT) release in the frontal cortex of the rat was assessed by the microdialysis technique. 2. The benzodiazepine receptor agonist, diazepam (2.5 mg kg-1, i.p.), the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.32 mg kg-1, s.c.) and the 5-HT1A receptor partial agonist buspirone (4.0 mg kg-1, i.p.) maximally reduced extracellular levels of 5-HT in the rat frontal cortex by approximately 50-60%, 70-80% and 30-40%, respectively. 3. (R)-zacopride (1.0-100 micrograms kg-1, i.p.) dose-dependently reduced extracellular levels of 5-HT in the rat frontal cortex (approximately 80% maximal reduction) whereas the other 5-HT3 receptor antagonists ondansetron (10 micrograms kg-1, i.p.) and (S)-zacopride (10-100 micrograms kg-1, i.p.) were ineffective. 4. In contrast to (S)-zacopride (100 nM; administered via the microdialysis probe), (R)-zacopride (1.0-100 nM; administered via the microdialysis probe) induced a concentration-dependent reduction in extracellular levels of 5-HT in the rat frontal cortex (approximately 70% maximal reduction). 5. In contrast to ondansetron (100 micrograms kg-1, i.p.), (S)-zacopride (10-100 micrograms kg-1, i.p.) dose-dependently reversed the (R)-zacopride (10 micrograms kg-1, i.p.) induced reduction in extracellular levels of 5-HT in the rat frontal cortex. The highest dose of (S)-zacopride (100 micrograms kg-1, i.p.) completely prevented the (R)-zacopride response.In addition, (S)-zacopride (100 nM; administered via the microdialysis probe) attenuated the inhibitory action of (R)-zacopride (10 nM; administered via the microdialysis probe) on extracellular levels of 5-HT in the rat frontal cortex.6. In conclusion, the present study provides further evidence of the ability of diazepam, 8-OH-DPAT and buspirone to reduce the activity of the central 5-hydroxytryptaminergic system in vivo. Furthermore,the results indicate that the ability of (R)-zacopride to reduce the in vivo release of 5-HT in the rat frontal cortex does not correlate with its 5-HT3 receptor antagonism. However, the differential affinity of (R)- and (S)-zacopride for a (S)-zacopride-insensitive (R)-zacopride site in rat cerebral cortex mirrors the relative activity of the two zacopride stereoisomers to modify the in vivo release of 5-HT in the frontal cortex of the rat and their ability to release suppressed behaviour in animal models of anxiety.
Barnes
N M
NM
Department of Pharmacology, Medical School, University of Birmingham.
Cheng
C H
CH
Costall
B
B
Ge
J
J
Naylor
R J
RJ
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002065:Buspirone / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005625:Frontal Lobe / Q000187:drug effects* / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D017294:Ondansetron / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013237:Stereoisomerism
D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D012702:Serotonin Antagonists; D012701:Serotonin; D017294:Ondansetron; D006897:Hydroxyindoleacetic Acid; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C055971:zacopride; D003975:Diazepam; D002065:Buspirone