CROSSING INPUTS OF THE SUPERIOR LARYNGEAL NERVE AFFERENTS TO MEDULLARY SWALLOWING-RELATED NEURONS IN THE CAT

To understand the neural mechanism for generation of synchronous activ ity on both sides during swallowing, we examined the convergence of in puts from the bilateral superior laryngeal nerves (SLNs) in the uretha ne-anesthetized cat medulla and we also examined the changes in swallo wing outputs after a longitudinal brain-stem split in decerebrate cats . Twenty-six (31%) of 84 swallowing-related neurons (SRNs) that were o ligosynaptically activated by ipsilateral SLN stimulation and recorded mostly in the reticular formation received contralateral inputs, whic h were confirmed by orthodromic spike responses (n = 16) or were detec ted as subliminal facilitatory or inhibitory inputs (n = 10) using con ditioning-test stimuli. The rate of convergence of inputs from bilater al SLNs in these SRNs was significantly higher than that (4%) in the S RNs that were regarded as sensory-relay neurons in the nucleus tractus solitarius (NTS). The SRNs receiving signals from the contralateral S LN were located diffusely from the NTS and the adjacent reticular form ation to the nucleus ambiguus (NA) and the reticular formation dorso-m edial to the NA. A midsagittal split from 3 mm caudal to 6 mm rostral to the obex could change symmetrical swallowing to unilateral swallowi ng. Thus the crossing projections to the contralateral SRNs appear to contribute to symmetrical swallowing. (C) 1998 Elsevier Science Irelan d Ltd. All rights reserved.