Functional topography of cardiovascular regulation along the rostrocaudal axis of the rat posterior insular cortex

Cardiovascular (CV) representation has been identified within the insular cortex (IC) and a lateralization of function previously suggested. In order to further understand the role of IC on cardiovascular control, the present study compared the CV responses evoked by stimulation of N-metil-D-aspartate (NMDA) receptors in the right and left posterior IC at different rostrocaudal levels. Intracortical microinjections of NMDA were performed into the IC of male Wistar rats anaesthetized with urethane (1.4 g/kg) prepared for blood pressure, heart rate and renal sympathetic nerve activity. Gene expression of NMDA receptor subunits NR2A and NR2B in the IC was confirmed by RT-PCR. Immunofluorescence for the NMDA receptor NR1 subunit was demonstrated in the IC (coordinates anteroposterior (AP) +1.5, 0.0 and -1.5 mm). A cardiac sympathoinhibitory site was identified, more rostrally located than identified in previous studies. A site of sympathoexcitatory cardiac control was identified more caudal to this region in agreement with earlier work. Under the experimental conditions, no lateralization of cardiovascular function was identified with chemical stimulation eliciting the same responses from either left or right insular cortices. No tonic role of the insula on cardiovascular control was identified with the use of the NMDA antagonist, AP-5. Peri-insular microinjection of NMDA was without cardiovascular effect indicating the specificity of the insula as a cardiovascular regulatory site. The current study reveals a functional topography for autonomic cardiovascular control along the rostrocaudal axis of the posterior IC.