Convergence of oropharyngolaryngeal, baroreceptor and chemoreceptor afferents onto insular cortex neurons in rats.

Forty-two neurons that responded to electrical stimulation of at least one of four nerves, the chorda tympani (CT), the lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, the pharyngeal branch of the glossopharyngeal (PH-IXth) nerve and the superior laryngeal (SL) nerve, were identified from the insular cortex by using glass microelectrodes in paralysed and anesthetized rats. Four, 42, 41 and 40 neurons responded to the CT, LT-IXth, PH-IXth and SL nerve stimulation respectively. Of these 42 neurons, most (37/42, 88.1%) responded to three nerves (the LT-IXth, PH-IXth and SL), two (4.8%) responded to two nerves and the remaining three (7.1%) responded to all four nerves. No neurons responded to one specific stimulus. The responsiveness of these 42 neurons to baroreceptor and chemoreceptor stimulation by an i.v. injection of three drugs was investigated. For baroreceptor stimulation, methoxamine hydrochloride (Mex) and sodium nitroprusside (SNP) were used; for chemoreceptor stimulation, sodium cyanide (NaCN) was used. Of the 42 neurons, 31 (73.8%) showed an excitatory or inhibitory response to baroreceptor and chemoreceptor stimulation with at least one of the three drugs, and the remaining 11 (26.2%) showed no response. Of these 31 baroreceptor and chemoreceptor-sensitive neurons, 19 (61.3%) responded to two or all three drugs, and the rest (12; 38.7%) responded to one. Most neurons recorded were distributed in the posterior insular cortex. These results indicate that the neurons in the posterior insular cortex receive convergent inputs from the oropharyngolaryngeal region, the baroreceptors and the chemoreceptors, suggesting that the posterior insular cortex may integrate various sensory information.