NEURONS IN THE POSTERIOR INSULAR CORTEX ARE RESPONSIVE TO GUSTATORY STIMULATION OF THE PHARYNGOLARYNX, BARORECEPTOR AND CHEMORECEPTOR STIMULATION, AND TAIL PINCH IN RATS

Extracellular unit responses to gustatory stimulation of the pharyngol aryngeal region, baroreceptor and chemoreceptor stimulation, and tail pinch were recorded from the insular cortex of anesthetized and paraly zed rats. Of the 32 neurons identified, 28 responded to at least one o f the nine stimuli used in the present study. Of the 32 neurons, 11 sh owed an excitatory response to tail pinch, 13 showed an inhibitory res ponse, and the remaining eight had no response. Of the 32 neurons, eig ht responded to baroreceptor stimulation by an intravenous (i.v.) inje ction of methoxamine hydrochloride (Mex), four were excitatory and fou r were inhibitory. Thirteen neurons were excited and six neurons were inhibited by an arterial chemoreceptor stimulation by an i.v. injectio n of sodium cyanide (NaCN). Twenty-two neurons were responsive to at l east one of the gustatory stimuli (deionized water, 1.0 M NaCl, 30 mM HCl, 30 mM quinine HCl, and 1.0 M sucrose); five to 11 excitatory neur ons and three to seven inhibitory neurons for each stimulus. A large n umber of the neurons (25/32) received converging inputs from more than one stimulus among the nine stimuli used in the present study. Most n eurons (23/32) received converging inputs from different modalities (g ustatory, visceral, and tail pinch). The neurons responded were locate d in the insular cortex between 2.0 mm anterior and 0.2 mm posterior t o the anterior edge of the joining of the anterior commissure (AC); th e mean location was 1.2 mm (n = 28) anterior to the AC. This indicates that most of the neurons identified in the present study seem to be l ocated in the region posterior to the taste area and anterior to the v isceral area in the insular cortex. These results indicate that the in sular cortex neurons distributing between the taste area and the visce ral area receive convergent inputs from gustatory, baroreceptor, chemo receptor, and nociceptive organs. (C) 1998 Elsevier Science B.V.