Interaction of purinergic and nitrergic mechanisms in the caudal nucleus tractus solitarii of rats

The interaction of purinergic and nitrergic mechanisms was evaluated in the caudal nucleus tractus solitarii (cNTS) using awake animals and brainstem slices. In awake animals, ATP (1.25 nmol/50 nL) was microinjected into the cNTS before and after the microinjection of a selective neuronal nitric oxide synthase (nNOS) inhibitor N-propyl-l-arginine (NPLA, 3 pmoles/50 nL, n=8) or vehicle (saline, n=4), and cardiovascular and ventilatory parameters were recorded. In brainstem slices from a distinct group of rats, the effects of ATP on the NO concentration in the cNTS using the fluorescent dye DAF-2 DA were evaluated. For this purpose brainstem slices (150 µm) containing the cNTS were pre-incubated with ATP (500 µM; n=8) before and during DAF-2 DA loading. Microinjection of ATP into the cNTS increases the arterial pressure (AP), respiratory frequency (fR) and minute ventilation (VE), which were significantly reduced by pretreatment with N-PLA, a selective nNOS inhibitor (AP: 39±3 vs 16±14 mm Hg; fR: 75±14 vs 4±3 cpm; VE: 909±159 vs 77±39 mL kg−1 m−1). The effects of ATP in the cNTS were not affected by microinjection of saline. ATP significantly increased the NO fluorescence in the cNTS (62±7 vs 101±10 AU). The data show that in the cNTS: a) the NO production is increased by ATP; b) NO formation by nNOS is involved in the cardiovascular and ventilatory responses to microinjection of ATP. Taken together, these data suggest an interaction of purinergic and nitrergic mechanisms in the cNTS.