Pertussis toxin pretreatment discriminates between pre- and postsynaptic actions of baclofen in rat dorsal raphe nucleus in vitro.
Intracellular recordings were made from rat dorsal raphe neurons in vitro. Baclofen (30 microM) and 5-carboxamidotryptamine (5-CT, 300 nM to 1 microM) hyperpolarized these neurons by 10 and 13 mV, respectively. Depolarizing synaptic potentials (DSPs) were evoked by single shocks: baclofen reduced the amplitude of the DSP by 81%, but 5-CT reduced it by only 23%. The somatic response to iontophoretically applied glutamate pulses was reduced by 12% by baclofen, and 23% by 5-CT. In slices from rats pretreated with intracerebroventricular pertussis toxin (PTX), the ability of baclofen to reduce the DSP was almost unchanged, although the hyperpolarizing action of baclofen, and both actions of 5-CT were virtually eliminated. We conclude that it is possible to distinguish the pre- and postsynaptic actions of baclofen with PTX, and that the actions of 5-CT are both blocked.
Colmers
W F
WF
Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland 97201.
Williams
J T
JT
D000818:Animals; D001418:Baclofen / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005971:Glutamates / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D037342:Pertussis Toxin; D011903:Raphe Nuclei / Q000166:cytology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D013570:Synaptic Membranes / Q000187:drug effects*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D005971:Glutamates; D010566:Virulence Factors, Bordetella; D012701:Serotonin; C047087:5-carboxamidotryptamine; D037342:Pertussis Toxin; D001418:Baclofen