Neuronal mechanisms underlying the laryngeal adductor reflex.
OBJECTIVE
Electromyographic studies of the laryngeal adductor reflex, glottal closure occurring in response to laryngeal stimulation, have demonstrated an early ipsilateral response (R1) and a late bilateral response (R2). To better define the physiologic properties of these responses, we recorded responses from expiratory laryngeal motoneurons (ELMs) in rats during stimulation of the superior laryngeal nerve (SLN).


METHODS
Single unit extracellular recordings were obtained from 5 ELMs, identified by their antidromic responses to recurrent laryngeal nerve stimulation and postinspiratory firing pattern, in 4 Sprague-Dawley rats.


RESULTS
Unilateral stimulation of the SLN (at 20 Hz) stopped both phrenic nerve inspiratory activity and ELM postinspiratory activity. However, the ELMs displayed robust tonic firing, consisting of non-respiratory burst activity and single action potentials. The single action potentials were identified as short-latency ones (5 to 10 ms) activated by ipsilateral SLN stimulation, with an occurrence rate of 90%, and long-latency ones (20 to 50 ms) activated by bilateral SLN stimulation, with occurrence rates of 47% on the ipsilateral side and 58% on the contralateral side.


CONCLUSIONS
The R1 response appears to be the result of the short-latency action potentials, orthodromically activated by ipsilateral stimulation of the SLN. The R2 response is likely to be a result of the long-latency action potentials that can be recorded from ELMs on both sides.
Australian School of Advanced Medicine, Macquarie University, Sydney, Australia.
Qi-Jian
QJ
Sun
Jia Min
JM
Chum
Tara G
TG
Bautista
Paul M
PM
Pilowsky
Robert G
RG
Berkowitz
D000200:Action Potentials; D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D005931:Glottis / Q000502:physiology; D007821:Laryngeal Muscles / Q000294:innervation* / Q000502:physiology*; D007823:Laryngeal Nerves / Q000502:physiology*; D023421:Models, Animal; D009046:Motor Neurons / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D012009:Recurrent Laryngeal Nerve / Q000502:physiology; D012018:Reflex / Q000502:physiology*