The injections of virus (PRSx8-hChR2 (H134R)-mCherry or PRSx8-Allato-EGFP) were made while the rats (Sprague-Dawley, males, weight: 219–282gm) were anaesthetized with a mixture of ketamine (75mg/kg), xylazine (5mg/kg) and acepromazine (1mg/kg) administered i.m. Surgery used standard aseptic methods, and after surgery, the rats were treated with the antibiotic ampicillin (100mg/kg, i.m.) and the analgesic ketorolac (0.6mg/kg, i.p.). The lentivirus was delivered into the RTN by controlled pressure injection (60 PSI, 3–8 ms pulses) using glass pipettes pulled to an external tip diameter of 25μm. These pipettes (resistance: 6–12Ω) allowed the recording of antidromic field potentials that were elicited by stimulating the mandibular branch of the facial nerve and were used to direct the electrode tip to the desired sites under the caudal pole of the facial nucleus. Injections were made unilaterally at 2 and, more rarely 3 different rostro-caudally aligned sites separated by 200 (3 injections) or 300μm (2 injections) for a total volume of 400 nl. In a subset of animals (n=5), we also injected anti-dopamine-β-hydroxylase conjugated to saporin (antiDβH-sap; Advanced Targeting Systems, San Diego, CA) at 0.22 μg per μl bilaterally (4 sites total, 100nl per site) into the region of the lateral horn of the second thoracic segment (1.0–1.2mm lateral of midline, 1mm below lateral sulcus) in order to destroy the C1 neurons that project to the spinal cord. Animals were maintained for no less than 3 weeks before they were used in physiological experiments. The surgical procedures and virus injections produced no observable behavioral or respiratory effects and these rats gained weight normally.