Acute, specific transgenic ‘silencing’ of Phox2b-expressing neurons in the caudal nucleus tractus solitarius reduces arterial pressure and respiration at rest and in response to hypercapnia in conscious rats

The caudal nucleus tractus solitarius (cNTS): 1) receives direct afferent inputs from the peripheral baro- and chemo- receptors; 2) contains neurons directly responsive to CO₂ (central chemoreceptors); 3) provides excitatory drive to the neurons in the caudal ventrolateral medulla; 4) is a critical region regulating both baro- and chemo- reflexes, and the set-point of arterial pressure. We hypothesize that transgenic ‘silencing’ of Phox2b-expressing neurons in the cNTS will reduce both respiration and arterial pressure at rest and in response to hypercapnia. We acutely and specifically ‘silenced’ Phox2b-expressing neurons in the cNTS by using a lentiviral vector, PRSx8-AlstR-EGFP-LV, that includes the Drosophila allatostatin receptor under the control of a Phox2b specific promoter (PRSx8). We injected the vector into the cNTS of anesthetized male rats (60–90 g) bilaterally & allowed 3–4 weeks for the AlstR-eGFP expression. We then studied the changes of ventilation, arterial pressure, heart rate, and metabolic rate in air and steady-state 7% CO₂ before and after ‘silencing’ Phox2b-expressing neurons in the cNTS by i.c.v. injection of allatostatin (2 mM, 10ul) in conscious rats. Allatostatin-induced ‘silencing’ of transfected cNTS Phox2b-expressing neurons: 1) significantly reduced VE/VO₂ at rest in wakefulness (~6%; P<0.05; N=8) and in response to hypercapnia in both wakefulness and NREM sleep (~30% P<0.001); 2) decreased arterial pressure in both air and hypercapnia with significance at 7%CO₂ in wakefulness (~7%, P<0.05; N=5). We conclude that Phox2b-expressing neurons in the cNTS region have ongoing discharge and contribute to both the control of ventilation and arterial pressure at rest and in response to hypercapnia.