The type 3 serotonin (5-HT3) receptor is the only ligand-gated ion channel
receptor for serotonin (5-HT), Many pharmacological, behavioral, and electr
ophysiological studies indicate heterogeneous properties for this receptor.
Although the basis for this heterogeneity is unknown, one possible explana
tion for these findings resides in the subunit composition of the receptor,
Two 5-HT3-receptor subunits have been cloned: the 5-HT3-receptor subunit A
(5-HT3A) and the 5-HT3-receptor subunit B (5-HT3B). Recombinant co-express
ion of 5-HT3A and 5-HT3B subunits produces a functional heteromeric 5-HT3A/
3B receptor with pharmacological and electrophysiological properties differ
ent from those displayed by the 5-HT3A homomeric receptor. In the present r
eport, we used in situ hybridization histochemistry to demonstrate that the
5-HT3B subunit is expressed in rat dorsal root ganglion (DRG) neurons. We
determined with cellular resolution that 5-HT3B subunit mRNA was expressed
in 43.2 +/- 2.8% of the total population of DRG neurons. By comparison, the
5-HT3A subunit was more widely expressed, with 70.0 +/- 2.8% of the total
population of DRG neurons expressing this subunit. Further analyses showed
that most of the neurons containing mRNA for the 5-HT3B subunit (91.5 +/- 3
.4%) also expressed the 5-HT3A subunit. In contrast, nearly half the popula
tion of neurons expressing 5-HT3A subunit lacked (52.8 +/- 5.9%) transcript
s for the 5-HT3B subunit. These results provide the first evidence indicati
ng that the 5-HT3B subunit of the 5-HT3 receptor is expressed in DRG and su
ggest that sensory neurons have the capacity to synthesize at least two str
ucturally different 5-HT3 receptors: a heteromeric 5-HT3A/3B receptor and a
homomeric 5-HT3A receptor. Consequently, 5-HT3 receptors with different pr
operties might be present in peripheral and central axons of the DRG. These
findings open the possibility that distinct types of 5-HT3 receptors may b
e involved in perception and/or processing of sensory information. J. Comp.
Neurol. 438:163-172, 2001. Published 2001 Wiley-Liss, Inc.dagger.