Further evidence for a central reorganisation of synaptic connectivity in patients with hypoglossal-facial anastomosis in man

In normal subjects, electrical stimulation of trigeminal mucosal afferents (lingual nerve - V3) can elicit a short latency (12.5+/-0.3 ms; mean+/-S.D. ) reflex response in the ipsilateral genioglossus muscle (Maisonobe et al., Reflexes elicited from cutaneous and mucosal trigeminal afferents in norma l human subjects. Brain Res. 1998;810:220-228). In the present study on pat ients with hypoglossal-facial (XII-VII) nerve anastomoses, we were able to record similar R1-type blink reflex responses in the orbicularis oculi musc les, following stimulation of either supraorbital nerve (V1) or lingual ner ve (V3) afferents. However, these responses were not present in normal cont rol subjects. Voluntary swallowing movements produced clear-cut facilitatio ns of the R1 blink reflex response elicited by stimulation of VI afferents. In a conditioning-test procedure with a variable inter-stimulus interval, the R1 blink reflex response elicited by supraorbital nerve stimulation was facilitated by an ipsilateral mucosal conditioning stimulus in the V3 regi on. This facilitatory effect was maximal when the two stimuli (conditioning and test) were applied simultaneously. This effect was not observed on the R1 component of the blink reflex in the normal control subjects. These dat a strongly suggest that in patients with XII-VII anastomoses, but not in no rmal subjects, both cutaneous (VI) and mucosal (V3) trigeminal afferents pr oject onto the same interneurones in the trigeminal principal sensory nucle us. This clearly supports the idea that peripheral manipulation of the VIIt h and the XIIth nerves induces a plastic change within this nucleus. (C) 20 00 Elsevier Science B.V. All rights reserved.