Different contributions of platelet-activating factor and nitric oxide in long-term potentiation of the rat medial vestibular nuclei.
In rat brainstem slices, we investigated the differential role of nitric oxide (NO) and platelet-activating factor (PAF) in long-term potentiation (LTP) induced in the ventral portion of the medial vestibular nuclei (MVN) by high-frequency stimulation (HFS) of the primary vestibular afferents. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) and the PAF receptor antagonist ginkgolide B (BN-52021) were administered before and after induction of potentiation. The effect of carboxy-PTIO was to completely prevent LTP. By contrast, BN-52021 only reduced the amplitude of HFS potentiation, which could develop fully at the drug washout or decline to zero, becoming a short-term phenomenon, in the case of long-lasting PAF receptor block. Both drugs, when given after HFS, had no effect on the already established potentiation, but whilst BN-52021 showed an influence within 5 min of the LTP induction, carboxy-PTIO did not affect the response once HFS was delivered. Moreover, we showed that the NO donor, sodium nitroprusside, and methylcarbamyl PAF (mc-PAF) induced LTP which was associated with an increase in glutamate release as shown by reduction in the paired-pulse facilitation ratio. The mc-PAF LTP was prevented by the NO scavenger, while NO LTP was only reduced by BN-52021. We suggest that NO and PAF are implicated as retrograde messengers in two different phases of vestibular LTP: NO in the induction phase; and PAF in the full expression phase.
Pettorossi
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Department of Internal Medicine, Section of Human Physiology, University of Perugia, Perugia, Italy.
Grassi
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S
D000818:Animals; D001933:Brain Stem / Q000378:metabolism*; D005260:Female; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology*; D010972:Platelet Activating Factor / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D014726:Vestibular Nuclei / Q000378:metabolism*
D010972:Platelet Activating Factor; D018094:Receptors, Metabotropic Glutamate; D009569:Nitric Oxide