Figure 7.

Schematic diagram illustrating potential changes to inputs and outputs of VTT neurons caused by intrathecal (i.t.) application of morphine. A, Under normal conditions, nociceptive VTT neurons (red) receive painful and innocuous input while pruriceptive VTT neurons (green) receive painful, innocuous, and itchy input. B, During i.t. application of morphine, painful input is decreased to nociceptive VTT neurons and innocuous and itchy input is increased to pruriceptive neurons, resulting in reduced pain and increased itch sensations. Although inputs are denoted with a single arrow, these inputs could be either monosynaptic or polysynaptic. Changes in relative strength of inputs and outputs in presence of morphine are indicated by changes in thickness of lines.