Dorsal root ganglion neurons and tyrosine hydroxylase--an intriguing association with implications for sensation and pain.

Abstract

Tyrosine hydroxylase (TH) is a rate-limiting enzyme broadly expressed in noradrenergic and dopaminergic neurons in the central nervous system [57,70]. TH is also expressed by peripheral sympathetic neurons [98] as well as by enteric neurons within the gut [81,84]. Over 30 years ago, TH was unexpectedly discovered in developing and adult rodent cranial and dorsal root ganglion (DRG) neurons. Today, TH-expressing DRG neurons are being re-discovered as a relevant subpopulation. This review addresses the emerging importance of TH-expressing DRG neurons in sensation and pain mechanisms, focusing specifically on: 1) their nature as C-low threshold mechanoreceptors (C-LTMRs); 2) their involvement in nociception/pain; and 3) their catecholaminergic phenotype.