Contribution of the lateral lemniscus to the control of swallowing in decerebrate cats

- Role of lemniscal area in the swallowing control was examined in decerebrate cats.
- Stimulation of LLD facilitated but that of LLV and PBN-KFN inhibited swallowing.
- Injections of glutamatergic and GABAergic agents into the LLD modulated swallowing.
- LLD, a relay nucleus of auditory sensation, may contribute to swallowing control.
- Lemniscal area may have functional topography in the control of swallowing.

Lateral lemniscus, a relay nucleus of auditory sensation, is involved in the control of phonatory movements such as human speech and vocalization of animals. The present study was designed to test whether neurons in the lateral lemniscus contributed to the control of swallowing, one of non-phonic oro-pharyngolaryngeal movements. In acutely decerebrated cats (n = 15), swallowing was induced by electrical stimulation (20-80 μA at 10 Hz for 20 s with rectangular pulses of 0.2 ms duration) delivered to the superior laryngeal nerve (SLN). Repetitive electrical stimulation (30-50 μA at 50 Hz for 10-20 s) applied to the dorsal nucleus of the lateral lemniscus (LLD) increased the number and reduced the latency to the onset of the SLN-induced swallowing. On the other hand, stimulation of the ventral nucleus of the lateral lemniscus and the paralemniscal area, corresponding to the ventrolateral part of the parabrachial nucleus and the Kölliker-Fuse nucleus, often suppressed the SLN-induced swallowing. Microinjection of NMDA (0.1-0.15 μl, 5.0-10 mM) into the LLD through a stereotaxically placed glass micropipette facilitated the SLN-induced swallowing, i.e., the number was increased and the latency of swallowing was reduced. We also injected muscimol (a gamma amino-butyric acid (GABA)A receptor agonist), bicuculline (a GABAA receptor antagonist) and baclofen (a GABAB receptor agonist) into the LLD (0.1-0.15 μl and 5.0 mM for each substance). It was observed that an injection of muscimol suppressed the SLN-induced swallowing. However, an injection of bicuculline facilitated the swallowing. An injection of baclofen did not alter the swallowing. These results suggest the presence of functional topography in the lateral lemniscus and the paralemniscal area in relation to the control of swallowing. The facilitatory LLD-effects on swallowing are modulated by glutamatergic and GABAergic receptors on neurons in the LLD.

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