Figure 6. Model for the generation of the L1 activity after administration of opioids.

A, the diagram of the ventral aspect of the brainstem-spinal cord preparation showing a disynaptic pathway from the preinspiratory neurones to the L1 motoneurones. B, the activity of the preinspiratory neurones driving the twice-bursting bulbospinal neurones in the cVRG. Inside the dotted rectangular there are activities of the inspiratory neurones shaping the twice bursting pattern of the preinspiratory neurones (Onimaru et al. 1990; Ballanyi et al. 1999) and bulbospinal inspiratory neurones driving the C4 root. The plus and minus signs indicate synaptic excitation and inhibition, respectively. Arrows indicate the direction in which excitation/inhibition is transmitted.