5-Hydroxytriptamine (5-HT; serotonin) is widely involved in human physiology [13]. The actions of 5-HT are mediated both by nervous and humoral activities [47]. The function of 5-HT has been established as a neural transmitter for the central nervous system [8]. 5-HT may evoke excitation and inhibition, and some of the effects appear to be evoked by the release of other transmitters [9]. This special issue contains three articles that focus on the contribution of 5-HT on the lower urinary tract (LUT) function. A wide variety of 5-HT receptor subtypes are variably expressed in bladder urothelium [10], smooth muscle [11], autonomic excitatory nerve terminals [12], and central pathways controlling the micturition reflex [13]. 5-HT has both physiological and pathological functions in the LUT [14].

This issue begins with a review by Matsumoto-Miyai et al. of the regulatory effects of 5-HT receptors on LUT function. The function of the 5-HT varies in a species- and site-dependent manner. Numerous 5-HT receptor subtypes which present in the LUT have suitably specific expression and/or activity to represent promising drug targets for the treatment of LUT symptoms.

The second paper by Michishita et al. discusses mast cell accumulation in rat bladder with partial bladder outlet obstruction (BOO). They conclude that mast cells contain 5-HT and are more abundant locally in the subserosal layer of partial BOO rat bladders. 5-HT released from mast cells can stimulate 5-HT2 receptors on the detrusor muscle and may cause storage symptoms.

The third paper by Imamura et al. focuses on expression of 5-HT receptors in human bladders with benign prostatic hyperplasia (BPH). The expression levels of 5-HT2B and 5-HT4 mRNA are similar between the BPH group and the normal group. The expression of 5-HT2A mRNA is significantly lower, while the expression of 5-HT3A and 5-HT7 mRNA is significantly higher in the BPH group than the normal group. Targeting 5-HT3A and 5-HT7 receptors in patients with BPH might be useful therapies for BPH related LUT symptoms.

Finally, I would like to thank the authors of the three articles for accepting the invitation to write articles for this special issue, and for submitting and revising their manuscripts in a timely manner. I am also grateful to the Editorial board of Advances in Therapy for reviewing and approving the supplement.