Characterization, distribution and lateralization of baroreceptor-related neurons in the rat insular cortex

The insular cortex contains a site of cardiovascular representation. Stimulation experiments suggest a discrete localization within the rostral posterior insula. In 34 urethane-anesthetized male Sprague-Dawley rats, we investigated whether cells responsive to baroreceptor stimulation with phenylephrine and sodium nitroprusside were selectively clustered within the insula compared with the surrounding frontoparietal cortex, the extent of distribution of these responsive cells within the insula, and whether there was any lateralization of response. In addition, we characterized the cells as SE (sympathoexcitatory), SI (sympathoinhibitory) or null cells using the criteria of Barman. Of the 128 insular cells investigated with extracellular recording techniques, 70% responded to baroreceptor manipulations compared to 32% of the 57 cells investigated outside the insula (P < 0.0001). The majority of the responsive cells were SE units and were distributed widely throughout the insular cortex including anterior areas not previously thought to be involved in cardiovascular control. Within the rostral posterior insula from which cardiovascular effects are mainly obtained in stimulation experiments, lateralization was identified, with significantly more cells responding to blood pressure changes being found within the right posterior insula than the left (P < 0.003). These data confirm the importance of the right posterior insula in the rat as a site of cardiovascular representation; identify a more extensive distribution of cells responsive to blood pressure changes within the insula than previous studies and imply more widespread convergence of visceral afferent information within the insula.