Laryngeal afferent inputs to the nucleus of the solitary tract.

The following study was undertaken to examine the integration of laryngeal afferent inputs within the nucleus of the solitary tract (NTS), the primary site of termination of laryngeal afferent fibers. Intracellular recordings were obtained from 63 cells that responded to electrical stimulation of the superior laryngeal nerve (SLN) with an excitatory postsynaptic potential (EPSP; n = 49), an excitatory-inhibitory postsynaptic potential (EPSP-IPSP) sequence (n = 13), or an IPSP (n = 1). Mechanical stimulation of laryngeal mechanoreceptors revealed a variety of response patterns (e.g., slowly and rapidly adapting depolarizations or hyperpolarizations). Two types of response to increasing SLN stimulus frequency were observed. In 11 cells SLN-evoked EPSP amplitude at 10 Hz was only 47 +/- 4% of the amplitude at 1 Hz, while in 6 cells EPSP amplitude at 10 Hz was virtually identical (93 +/- 3%) to that at 1 Hz. Time-dependent inhibitory interactions occurred between SLN inputs to NTS neurons at intervals between 50 and 400 ms and in the absence of any change in membrane potential. NTS neuronal responses to brief activation of laryngeal mechanoreceptors correspond well to discharge patterns described for individual laryngeal mechanoreceptors. Frequency-dependent filtering and time-dependent inhibitory interactions might modify NTS neuronal responses during more intense stimulation of laryngeal afferents.