Figure 12. Block by high Ca²⁺/K⁺ (Mg²⁺) solution of cervical rhythm in brainstem–spinal cords without VII.

A, in a BSC[−0.28]SD–P3, elevating superfusate Ca²⁺ from 1.2 to 2.4 mm and Mg²⁺ from 1.0 to 1.3 mm (3rd trace from top) abolished the inspiratory rhythm which was previously stable in both 3 mm (top trace) and 6.2 mm K⁺ (2nd trace from top). Rhythm very similar to control was reactivated in 2.4 mm Ca²⁺ and 1.3 mm Mg²⁺ by raising K⁺ further, to 10 mm (5th trace from top), whereas 8 mm K⁺ was less effective (4th trace from top). Rhythm was blocked again after return to 6.2 mm K⁺, 2.4 mm Ca²⁺ and 1.3 mm Mg²⁺ solution (2nd trace from bottom) and recovered effectively in 6.2 mm K⁺, 1.2 mm Ca²⁺ and 1 mm Mg²⁺ (bottom trace). B and C, mean rates (B) and durations (C) of cervical bursts in two sets of preparations with different mean rostral boundaries, specifically BSC[−0.25] and BSC[−0.39]. Digits above bars indicate the number of preparations tested. Only a subset of preparations in B was used for the analysis in C. Bars represent means and s.e.m.