Frequency-dependent LTP/LTD in guinea pig Deiters' nucleus

Synaptic plasticity was studied in the lateral vestibular nuclei (LVN) of the guinea pig in vivo. High frequency stimulation (HFS) of increasing or decreasing frequencies was applied to the ipsilateral vestibular nerve. Vestibular field potentials (VFPs) and extracellular single unit activity evoked in the LVN by electrical stimulation of the ipsilateral vestibular nerve, were analyzed before and after the application of different protocols of HFS. Results show that the monosynaptic component of the VFPs undergo long-term potentiation (LTP) with stimulation of 100 Hz applied for 20 s lower frequencies, applied for shorter periods, induce only a transient post-tetanic potentiation. This potentiation, although long lasting, is not permanent since it is susceptible of a reversal or cancellation by opposite patterns of HFS that determine a depression or depotentiation of the previously acquired potentiation. The results demonstrate that the plasticity phenomena that take place at the level of the LVN neurons are not steady but undergo continuous adjustment of their sign and gain depending on the variable flow of vestibular information that reach the nuclei from the labyrinthine receptors.