Figure 7. Cardiac vagal tone persists after inhibition of the KF in sympathetically‐disabled preparations.

Isoguvacine injections were repeated in seven animals with intact cardiac vagal branches and whose cardiac sympathetic innervation was disabled by destruction of the thoracic spinal cord. Cardiac vagal tone was quantified by comparing the HR before and after isoguvacine injection with its final level after systemic atropine. Inhibition of the KF greatly reduced the magnitude of the RSA (ΔHR) (A). The addition of atropine to the perfusing solution removed any remaining HR fluctuations. On average, inhibition of the KF removed half of chronotropic vagal tone (B). Isoguvacine injection sites for each experiment (numbered circles) (C). Data are values from individual experiments (black lines) and are the mean ± SEM (red dashed lines). ^** P < 0.01 compared to control; ^*** P < 0.001 compared to control, ^†† P < 0.01 compared to KF isoguvacine pairwise t test (n = 7). il, internal lateral parabrachial nucleus; me5, mesencephalic trigeminal tract; Pr5, principal sensory trigeminal nucleus; scp, superior cerebellar peduncle m, medial parabrachial nucleus; s, superior lateral parabrachial nucleus; v, ventral lateral parabrachial nucleus. [Colour figure can be viewed at wileyonlinelibrary.com]