Blockade of NK-1 receptors in the lateral commissural nucleus tractus solitarii of awake rats had no effect on the cardiovascular responses to chemoreflex activation

The neurotransmission of the chemoreflex in the nucleus tractus solitarii ( NTS), particularly of the sympatho-excitatory component, is not completely understood, There is evidence that substance P may play a role in the neuro transmission of the chemoreflex in the NTS, Microinjection of substance P ( 50 pmol/50 nl, N = 12, and 5 nmol/50 nl, N = 8) into the commissural NTS of unanesthetized rats produced a significant increase in mean arterial press ure (101 +/- 1 vs 108 +/- 2 and 107 +/- 3 vs 115 +/- 4 mmHg, respectively) and no significant changes in heart rate (328 +/- 11 vs 347 +/- 15 and 332 +/- 7 vs 349 +/- 13 bpm, respectively) 2 min after microinjection, Previous treatment with WIN, an NK-1 receptor antagonist (2.5 nmol/50 nl), microinj ected into the NTS of a specific group of rats, blocked the presser (11 +/- 5 vs 1 +/- 2 mmHg) and tachycardic (31 +/- 6 vs 4 +/- 3 bpm) responses to substance P (50 pmol/50 nl, N = 5) observed 10 min after microinjection, Bi lateral microinjection of WIN into the lateral commissural NTS (N = 8) had no significant effect on the presser (50 +/- 4 vs 42 +/- 6 mmHg) or bradyca rdic (-230 +/- 16 vs -220 +/- 36 bpm) responses to chemoreflex activation w ith potassium cyanide (iv), These data indicate that the activation of NK-1 receptors by substance P in the NTS produces an increase in baseline mean arterial pressure and heart rate, However, the data obtained with WIN sugge st that substance P and NK-1 receptors do not play a major role in the neur otransmission of the chemoreflex in the lateral commissural NTS.