Effect of sex steroid hormones on the number of serotonergic neurons in rat dorsal raphe nucleus

Yuyu Kunimura
Kinuyo Iwata
Norio Iijima
Makito Kobayashi
Hitoshi Ozawa

Disorders caused by the malfunction of the serotonergic system in the central nervous system show sex-specific prevalence. Many studies have reported a relationship between sex steroid hormones and the brain serotonergic system; however
 the interaction between sex steroid hormones and the number of brain neurons expressing serotonin has not yet been elucidated. In the present study
 we determined whether sex steroid hormones altered the number of serotonergic neurons in the dorsal raphe nucleus (DR) of adult rat brains. Animals were divided into five groups: ovariectomized (OVX)
 OVX+ low estradiol (E2)
 OVX+ high E2
 castrated males
 and intact males. Antibodies against 5-hydroxytryptamine (5-HT
 serotonin) and tryptophan hydroxylase (Tph)
 an enzyme for 5-HT synthesis
 were used as markers of 5-HT neurons
 and the number of 5-HT-immunoreactive (ir) or Tph-ir cells was counted. We detected no significant differences in the number of 5-HT-ir or Tph-ir cells in the DR among the five groups. By contrast
 the intensity of 5-HT-ir showed significant sex differences in specific subregions of the DR independent of sex steroid levels
 suggesting that the manipulation of sex steroid hormones after maturation does not affect the number and intensive immunostaining of serotonergic neurons in rat brain. Our results suggest that
 the sexual dimorphism observed in the serotonergic system is due to factors such as 5-HT synthesis
 transportation
 and degradation but not to the number of serotonergic neurons. (C) 2015 Elsevier Ireland Ltd. All rights reserved.

NEUROSCIENCE LETTERS

ELSEVIER IRELAND LTD

594

10.1016/j.neulet.2015.03.060

https://doi.org/10.1016/j.neulet.2015.03.060
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