An implantable medical system includes an implantable medical device (IMD) and an electrode coupleable to the IMD. The electrode is operative to deliver a first electrical signal from the IMD to a neural structure. The system includes a sensor coupleable to the IMD. The sensor is operative to sense a physiological parameter. The physiological parameter may include at least one of a neurotransmitter parameter, a neurotransmitter breakdown product parameter, a neuropeptide parameter, a norepinephrine parameter, a glucocorticoid (GC) parameter, a neuromodulator parameter, a neuromodulator breakdown product parameter, an amino acid parameter, and a hormone parameter. The IMD includes a controller operative to change a parameter of the first electrical signal based upon at least one sensed physiological parameter to generate a second electrical signal and to apply the second electrical signal to the neural structure.