The expected central targets for pruritoceptors, a subset of C
fibers, are dorsal horn neurons located in the upper laminae of
the spinal cord. Studies have investigated their potential role
as second-order neurons in the itch circuit. Simone et al.
(2004) saw that most monkey spinothalamic tract (STT) neurons
were capsaicin sensitive and a subset of these also responded to
histamine. Work in rat (Jinks and Carstens 2002 ) found
capsaicin also activated dorsal horn neurons responding to the
itch mediator serotonin 5HT. Experiments in mouse showed that
itch-selective spinal neurons, activated by histamine and 5HT as
well as SLIGRL-NH2 , an agonist for the PAR2 receptor, responded
to nociceptive stimuli including heat and mustard oil (Akiyama
et al., 2009a ). The inhibition of itch by pain was shown in
monkey by Davidson et al. (2007a) , who observed that peripheral
scratching inhibited histamine- or cowhage-sensitive STT
neurons. They later found a group of histamine- and capsaicin-
responsive cells that were i