1. An implantable medical system comprising: an implantable medical device (IMD) operative to provide a first electrical signal; an electrode coupleable to the IMD, the electrode operative to deliver the first electrical signal from the IMD to a neural structure; and a sensor coupleable to the IMD, the sensor operative to sense a physiological parameter, wherein the physiological parameter includes 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; wherein the IMD comprises 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, wherein the parameter includes at least one of a pulse width, a frequency, a polarity, and an amplitude.