Abstract
The subfornical organ (SFO) plays important roles for drinking behavior and cardiovascular regulation. It is well known that excitation of SFO neurons by angiotensin II (ANG) induces the two behavioral responses, but that by nicotine (NIC) induces only cardiovascular responses. Therefore, there may be present subpopulations of SFO neurons showing different sensitivity between ANG and NIC. In the present study, we verified that intracerebroventricular (i.c.v.) injections of ANG at 400 ng induced large water intake in rats, but that of NIC at 50 μg induced small water intake. The i.c.v. injection of NIC induced cardiovascular responses increased c-Fos expression in the SFO. In slice preparation, we compared with the responses of ANG and NIC on 101 SFO neurons by using an extracellular recording system. ANG and NIC respectively increased spontaneous firing frequencies in 67 and 62 SFO neurons. Although 45 ANG-sensitive neurons had NIC-sensitivity, the remaining 22 neurons did not. Recently, we have reported cell classification of dissociated SFO neurons, F- and S-types, and that a half of F-type and all S-type neurons have ANG-sensitivity. A patch-clamp recording showed that although almost F-type had NIC-sensitivity (n = 19/21), S-type did not (n = 7/8). From these results, we hypothesize that classified S-type cells have ANG-sensitivity without NIC-sensitivity and are related to drinking behavior, but not to cardiovascular responses, and their function is different from that of F-type cells. [J Physiol Sci. 2006;56 Suppl:S140]
