Axonal branching of medullary swallowing neurons projecting on the trigeminal and hypoglossal motor nuclei: demonstration by electrophysiological and fluorescent double labeling techniques

Abstract

The projections of ventral medullary reticular neurons on both trigeminal (Vth) and hypoglossal (XIIth) motor nucleus were studied in sheep anesthetized with halothane. In a first series of experiments, extracellular microelectrodes were used to record the activity of medullary swallowing interneurons (SINs) located in the ventral region (around the nucleus ambiguus) of the swallowing center. Antidromic activation after electrical stimulation of the Vth and XIIth nuclei was tested in 83 SINs. For 38 SINs a clear antidromic activation was observed and for 8 of them the response was triggered by stimulation of either nucleus. As confirmed by the reciprocal collision test, these 8 SINs had branched axons sending information to both nuclei tested. Average latencies for antidromic activation of branched SINs after stimulation of the XIIth and the Vth motor nucleus were 2.2 +/- 0.6 ms and 2.7 +/- 0.8 ms respectively. The axonal conduction velocity of these neurons was 4.4 +/- 1.3 m/s for the collateral to the Vth motor nucleus and 2.7 +/- 0.7 m/s for axons projecting to the XIith motor nucleus. In a second series of experiments the double retrograde labeling technique was used to confirm the existence of neurons with branched axons in the medullary regions corresponding to the swallowing center. Small and well localized injections of Fast Blue (FB) and Diamidino Yellow (DY) fluorescent tracers were made in the Vth and in the XIIth motor nucleus respectively. A relatively large number of double-labeled cells was found in the ventral region of swallowing center (reticular formation around the nucleus ambiguus, 2-4 mm in front of obex).(ABSTRACT TRUNCATED AT 250 WORDS)

Jaw‐muscle spindle afferent pathways to the trigeminal motor nucleus in the rat

“…The location of neurons retrogradely labeled from the trigeminal motor nucleus in this study is comparable to that reported in previous studies using neuroanatomical tracing methodologies (Mizuno et al, 1978(Mizuno et al, , 1983Panneton and Martin, 1979;Travers and Norgren, 1983;Vornov and Sutin, 1983;Landgren et al, 1986;Amri et al, 1990;Mogoseanu et al, 1993;Turman and Chandler, 1994;Li et al, 1995;Takahashi et al, 1995;Fay and Norgren, 1997). These studies also report the presence of abundant trigeminal premotor neurons in the reticular formation and the region surrounding the contralateral trigeminal motor nucleus.…”

“…These electrophysiological studies do not allow determination of the precise location of interneurons relaying muscle spindle afferent feedback to the trigeminal motor nucleus, nor do they shed light on whether jaw-muscle spindle sensory feedback is relayed to the trigeminal motor nucleus through a restricted region of the brainstem or through multiple regions. Related information is available from retrograde neuronal labeling studies (Mizuno et al, 1978(Mizuno et al, , 1983Travers and Norgren, 1983;Vornow and Sutin, 1983;Landgren et al, 1986;Amri et al, 1990;Turman and Chandler, 1994;Li et al, 1995;Takahashi et al, 1995;Fay and Norgren, 1997;Kolta et al, 2000), which have described the location of some trigeminal premotor neurons. Because these studies were not combined with physiological methodologies, however, they provide no insight into the neural inputs that these premotor neurons receive.…”

Dysphagia in Lateral Medullary Infarction (Wallenberg’s Syndrome)

“…28,30,39 Premotor neurons located in and around the NTS and the NA are connected with different cranial motor neuron pools associated with swallowing. 32,38,39,40 In LMI, primarily these premotor neurons and their connections appear to be affected. Consequently, an acute disconnection could occur between the ipsilateral dorsal swallowing center, ie, the NTS, and the contralateral side of the center of swallowing at the medulla oblongata.…”

Trigeminal projections to hypoglossal and facial motor nuclei in the rat

“…It would be important to determine whether each subdivision of the sensory trigeminal complex participates to the trigeminohypoglossal and trigeminofacial projection and, if so, which might be the specific connections of the 5P, 5o, 5i, and 5c with the various subdivisions of the XII and VII. In addition, as recent investigations showed premotor neurons innervating simultaneously two orofacial motor nuclei (Amri et al;1990;Li et al, 1993), it is important to determine whether individual neurons of the sensory trigeminal complex project by axonal branching on both the XII and the VII.…”