• Matteo Bologna, Rocco Agostino, Bruno Gregori, Daniele Belvisi, Mario Manfredi, and Alfredo Berardelli.
• Neuromed Institute (IRCSS), Via Atinense, Pozzilli (IS), Italy.
• Eur. J. Neurosci. 2010 Nov 1; 32 (10): 1707-14.

AbstractAlthough synaptic plasticity in the human cerebral cortex is governed by metaplasticity, whether a similar mechanism operates at brainstem level is unknown. In this study in healthy humans we examined the effects and interactions induced by pairing supraorbital nerve high-frequency electrical stimulation (HFS) protocols on the R2 component of the trigeminal blink reflex [Mao, J.B. & Evinger, C (2001) J Neurosci., 21:RC151(1-4)]. Changes in the R2 component were tested by pairing three different priming stimulation protocols inducing long-term potentiation (LTP)-like or long-term depression (LTD)-like effects (LTP-HFS and LTD-HFS), or no change (CONTROL-HFS) with a subsequent test LTP-HFS. Additionally, to examine changes in the R2 component induced by nonspecific factors, two CONTROL-HFS sessions were paired. Priming LTP-, LTD- or CONTROL-HFS potentiated, inhibited or left unchanged the area of the R2 component. Regardless of the type of priming LTP-, LTD- or CONTROL-HFS, the test LTP-HFS induced negligible differences in the R2 component. When two CONTROL-HFS sessions were paired, the test CONTROL-HFS increased the latency and markedly reduced the duration and area of the R2 component. The analysis of the normalized data across the first three experimental sessions, corrected for the inhibitory effects found in the fourth experiment, showed that the test LTP-HFS potentiated the R2 component area of the trigeminal blink reflex only when preceded by a priming LTD-HFS. We propose that homosynaptic metaplasticity might operate in the brainstem circuitry of the blink reflex.© 2010 The Authors. European Journal of Neuroscience © 2010 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.

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