Laryngeal protective reflex is a glottal closure reflex triggered by tactile receptors in the glottic and supraglottic mucosa, which evoke reflexive contraction of laryngeal musculature. Exaggeration of this normally protective reflexes is
thought
to be
responsible for several disorders, including the sudden infant death syndrome. Although the laryngeal brain stem evoked response (LBR) has been studied in several species of animals, the generator sources of each waves were not precisely
demonstrated
yet. The purposes of this study are to record the near-field brain stem activity as well as the far-field brain stem activity in the cat under the same experimental set-up and to search for the generator sources of the waves. Under general
anesthesia,
the LBR tracing were recorded adjacent and within the brain stem following direct electrical stimulation of the internal branch of the superior laryngeal nerve (SLN) and the following results were obtained:
1) Mean latency of laryngeal adductor reflex response was 8.61msec.
2) By far-field technique, a total of five reproducible positive and negative waves were detected, with mean latencies ranging 0.73-6.57msec.
3) After supranodosal vagotomy, only P1, N1, P2 waves showed reproducibility.
4) After sectioning the SLN, no waves were reproducible except triggering artifact.
5) By near-field technique, reproducible waves were recorded around the nucleus tractus solitarius region in the latency range of 1.59-4.49msec.
6) No reproducible waves were recorded around the nucleus ambiguus region.
These results suggest that P1, N1, P2 waves of far-field recording are originated from the vagus nerve. And P2, N2, P3 waves are thought to e originated from the nucleus tractus solitarius comparing the far- and near-field data in this study.
Through a
comparison of the far-field data in this study with prior near-field reports, nucleus ambiguus was speculated as the generator source of N3, P4, N4, P5 waves. (Korean J Otolaryngol 38:4, 1995)
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