A, absence of appreciable respiratory effects ∼3 min after bilateral microinjections of 1 mm strychnine (Stryc) into the pTRG in one preparation. B, marked increases in respiratory frequency ∼3 min after a unilateral microinjection of 1 mm Stryc into the region of vagal motoneurons (MN region) in a different preparation. The sites (pink area, pTRG; blue area, vagal MN region) where Stryc was microinjected are shown on a schematic illustration of a dorsal view of the lamprey mesencephalon–rhombencephalon. pTRG, paratrigeminal respiratory group; V, trigeminal motor nucleus; VII, facial motor nucleus; IX, glossopharyngeal motor nucleus; X, vagal motor nucleus; VA, raw vagal nerve activity; IVA, integrated vagal nerve activity.