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Lookup NU author(s): Dr Sasha Gartside
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Acute systemic injection of selective serotonin reuptake inhibitors (SSRIs) decreases 5-HT neuronal firing in the dorsal raphe nucleus (DRN). Recent data, however, question whether these drugs also inhibit the firing of 5-HT neurones in the median raphe nucleus (MRN). Using in vivo extracellular electrophysiological recording techniques in the chloral hydrate anaesthetised rat, we have tested the effect of acute administration of the SSRI, paroxetine, on 5-HT neuronal activity in the MRN and DRN. Presumed 5-HT neurones in the MRN displayed the same electrophysiological characteristics as those in the DRN, the only detectable difference being that MRN neurones showed a significantly (p < 0.001) slower mean (+/- SEM(n)) spontaneous firing rate (MRN, 5.6 +/- 0.9 (14) spikes/10 s; DRN, 13.5 +/- 1.6 (24) spikes/10 s). Paroxetine caused a dose-related (0.1-0.8 mg/kg i.v.) inhibition of all MRN neurons tested (n = 8), producing a complete cessation of cell-firing at the highest doses. DRN neurones (n = 9) responded in a similar fashion. Furthermore, paroxetine inhibited MRN and DRN neurones with almost identical potency (MRN ED50 259 +/- 57 micrograms/kg i.v.: DRN ED50 243 +/- 49 micrograms/kg i.v.). In the majority of cells tested, the effect of paroxetine was reversed by the 5-HT1A receptor antagonists spiperone or (+)WAY100135, implicating the involvement of the 5-HT1A autoreceptor. The selective 5-HT1A receptor agonist 8-OH-DPAT also inhibited the firing of MRN (n = 5) and DRN (n = 12) neurones and with equal potency (MRN ED50, 1.32 +/- 0.40 microgram/kg i.v.: DRN ED50, 1.19 +/- 0.23 microgram/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)
Author(s): Hajós M, Gartside SE, Sharp T
Publication type: Article
Publication status: Published
Journal: Naunyn-Schmiedeberg's Archives of Pharmacology
Year: 1995
Volume: 351
Issue: 6
Pages: 624-629
Print publication date: 01/06/1995
ISSN (print): 0028-1298
ISSN (electronic): 1432-1912
Publisher: Springer Berlin
URL: http://dx.doi.org/10.1007/BF00170162
DOI: 10.1007/BF00170162
Notes: 0028-1298 (Print) Journal Article
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