Changes in heart rate, blood pressure and renal sympathetic nerve activity induced by microinjection of capsaicin into area postrema in rats.

The effects of capsaicin microinjection into area postrema (AP) on mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were investigated in 36 anesthetized Sprague-Dawley rats. The results obtained are as follows. (1) Following microinjection of capsaicin (10 micromol/L, 50 nl) into the AP, MAP, HR and RSNA were significantly increased from 12.34+/-0.53 kPa, 328.52+/-7.54 bpm and 100+/-0% to 15.17+/-0.25 kPa (P<0.001), 354.81+/-8.54 bpm (P<0.001) and 156.95+/-7.57% (P<0.001), respectively. (2) Ruthenium red (RR, 100 mmol/L, 0.2 ml, iv), a capsaicin receptor antagonist, significantly inhibited these effects of capsaicin. (3) Pretreatment with a NMDA receptor antagonist MK-801 (500 microgram/kg, 0.2 ml, iv) also reduced these effects of capsaicin. The above results indicate that microinjection of capsaicin into AP induces excitatory effects on MAP, HR and RSNA, which are mediated by capsaicin receptors with glutamate involvement.