Simulations of hypercapnia control, saporin-substance P conjugate (SSP-SAP) and kynurenic acid (Kyn) conditions. Motoneuron output for the phrenic nerve (PN), the thoracic sympathetic nerve (tSN), and the abdominal nerve (AbN) are presented for the control simulation, the simulation of animals with SSP-SAP retrotrapezoid nucleus (RTN) lesions, and the simulation of parafacial respiratory group (pFRG) Kyn injections. Select neuronal populations included are the preinspiratory/inspiratory (pre-I/I) population of the pre-Bötzinger complex (pre-BötC), the postinspiratory and augmenting expiratory populations of the BötC, the presympathetic population of the rostral ventrolateral medulla (RVLM), and the late-expiratory (late-E) population of the parafacial respiratory group (pFRG).