Capsaicin depletes corticotropin-releasing factor-like immunoreactive neurons in the rat spinal cord and medulla oblongata.

Treatment of newborn rats with capsaicin was shown to cause a disappearance of corticotropin-releasing factor immunoreactive nerve fibers in the dorsal horn of the spinal cord (laminae I and II), the spinal trigeminal nucleus and tract, and the nucleus tractus solitarius, but not in the median eminence and the nucleus amygdaloideus centralis. Since it is well known that capsaicin acts selectively on primary sensory neurons of the C-fiber type, it is suggested that corticotropin-releasing factor is also located in peripheral sensory neurons, representing a novel peptidergic neuronal system, possibly involved in the modulation or transmission of peripheral nociceptive impulses, which is different from the capsaicin-resistant hypothalamoinfundibular corticotropin-releasing factor system.