A comparison of slopes of the full baroreflex analysis (including reductions and increases in MAP and reflex get EPZ004777 changes in HR; not shown) did show that responses in the PBS (r = -1.27), eGFP (r = -1.21), and cDNA nNOS (r = -1.20) groups did not differ from each other but responses in the shRNA group (r = -0.73) differed significantly (P = 0.002; 0.004; and 0.007 respectively) from responses in each of the other groups. Basal MAP and HR did not significantly differ between groups (see Table 3).2012 The Authors. The Journal of Physiology 2012 The Physiological SocietyCCJ Physiol 590.nNOS and the baroreflexNTS led to reduced blood pressure in hypertensive animals (Waki et al. 2006). However, the inhibitory action of NO?in NTS as shown in the aforementioned studies had itself been questioned given findings that local overexpression of eNOS in NTS led to hypotension and bradycardia, responses that suggest a positive baroreflex effect of NO?(Sakai et al. 2000; Hirooka et al. 2001). Both of the latter studies used adenovirus as a vector and therefore likely targeted glia as well as neurons (Allen et al. 2006). Others, however, have used pharmacological methods to study the question and have found that NO?positively modulates the baroreflex at the NTS level (Talman Nitschke Dragon, 2004; Dias et al. 2005). In our own previously published work in which we used AR-R 17477 to block, somewhat selectively, nNOS, we found attenuation of baroreflex responses with acute inhibition of nNOS. However, AR-R 17477, while trans-4-Hydroxytamoxifen clinical trials 100-fold more effective an antagonist of nNOS than of eNOS, is not completely devoid of activity on eNOS (Johansson et al. 1999). Thus, interpretation of published studies is somewhat limited with respect to the role of NO?as a neurotransmitter or neuromodulator in cardiovascular signal transduction in NTS, and methods that would avoid pharmacological effects on the enzyme were needed. It is relevant that acute blockade of nNOS with pharmacological agents led to reduced baroreflex function as we report here with a method that led to altered nNOS over the course of several weeks during which transduction occurred. The two approaches, then, were complementary. However, to avoid pharmacological manipulation of the NTS, we developed an shRNA that decreased expression of nNOS in NTS but did not affect expression of eNOS. Similar methodology, though with a different shRNA, has been used by others in the basal forebrain (Mahairaki et al. 2009); but, to our knowledge, the use of nNOS shRNA in the current paper is the first application of thattechnology in assessing physiological reflex function at a central level in vivo in a mammalian species. In contrasting experiments we used an nNOS cDNA (Silvagno et al. 1996) (provided by Dr David Bredt), which we have shown (Lin et al. 2011) produces an 11-fold increase in nNOS seen when punches of tissue from NTS were analysed by RT-PCR. Both the nNOS shRNA and nNOS cDNA were introduced into the NTS via AAV2, which has been shown to selectively transfect neurons (Nomoto et al. 2003; Lin et al. 2011). In this paper we report for the first time the use of a shRNA that we developed to downregulate expression of nNOS in central neurons of the NTS. We show that loss of nNOS expression in NTS is associated with selective loss of largely sympathetically mediated reflex tachycardia induced by acute depressor effects of sodium nitroprusside without loss or attenuation of largely parasympathetically mediated reflex br.A comparison of slopes of the full baroreflex analysis (including reductions and increases in MAP and reflex changes in HR; not shown) did show that responses in the PBS (r = -1.27), eGFP (r = -1.21), and cDNA nNOS (r = -1.20) groups did not differ from each other but responses in the shRNA group (r = -0.73) differed significantly (P = 0.002; 0.004; and 0.007 respectively) from responses in each of the other groups. Basal MAP and HR did not significantly differ between groups (see Table 3).2012 The Authors. The Journal of Physiology 2012 The Physiological SocietyCCJ Physiol 590.nNOS and the baroreflexNTS led to reduced blood pressure in hypertensive animals (Waki et al. 2006). However, the inhibitory action of NO?in NTS as shown in the aforementioned studies had itself been questioned given findings that local overexpression of eNOS in NTS led to hypotension and bradycardia, responses that suggest a positive baroreflex effect of NO?(Sakai et al. 2000; Hirooka et al. 2001). Both of the latter studies used adenovirus as a vector and therefore likely targeted glia as well as neurons (Allen et al. 2006). Others, however, have used pharmacological methods to study the question and have found that NO?positively modulates the baroreflex at the NTS level (Talman Nitschke Dragon, 2004; Dias et al. 2005). In our own previously published work in which we used AR-R 17477 to block, somewhat selectively, nNOS, we found attenuation of baroreflex responses with acute inhibition of nNOS. However, AR-R 17477, while 100-fold more effective an antagonist of nNOS than of eNOS, is not completely devoid of activity on eNOS (Johansson et al. 1999). Thus, interpretation of published studies is somewhat limited with respect to the role of NO?as a neurotransmitter or neuromodulator in cardiovascular signal transduction in NTS, and methods that would avoid pharmacological effects on the enzyme were needed. It is relevant that acute blockade of nNOS with pharmacological agents led to reduced baroreflex function as we report here with a method that led to altered nNOS over the course of several weeks during which transduction occurred. The two approaches, then, were complementary. However, to avoid pharmacological manipulation of the NTS, we developed an shRNA that decreased expression of nNOS in NTS but did not affect expression of eNOS. Similar methodology, though with a different shRNA, has been used by others in the basal forebrain (Mahairaki et al. 2009); but, to our knowledge, the use of nNOS shRNA in the current paper is the first application of thattechnology in assessing physiological reflex function at a central level in vivo in a mammalian species. In contrasting experiments we used an nNOS cDNA (Silvagno et al. 1996) (provided by Dr David Bredt), which we have shown (Lin et al. 2011) produces an 11-fold increase in nNOS seen when punches of tissue from NTS were analysed by RT-PCR. Both the nNOS shRNA and nNOS cDNA were introduced into the NTS via AAV2, which has been shown to selectively transfect neurons (Nomoto et al. 2003; Lin et al. 2011). In this paper we report for the first time the use of a shRNA that we developed to downregulate expression of nNOS in central neurons of the NTS. We show that loss of nNOS expression in NTS is associated with selective loss of largely sympathetically mediated reflex tachycardia induced by acute depressor effects of sodium nitroprusside without loss or attenuation of largely parasympathetically mediated reflex br.