Facilitatory effect of ventral cut of dorsal raphe nucleus on lordosis in female rats

Female Reproductive Behavior

Reproductive behavior is the behavior related to the production of offspring and includes all aspects from the establishment of mating systems, courtship, sexual behavior, and parturition to the care of young. In this chapter, I outline the hormonal regulation of the estrous cycle, followed by a description of the neural regulation of female sexual behavior. Ovarian hormones play an important role in the induction of ovulation and behavioral estrus, in which they interact closely with several neurotransmitters and neuropeptides to induce sexual behavior. This chapter discusses the latest research on the role of estrogen, progesterone, serotonin, dopamine, noradrenaline, oxytocin, and GABA in female mating behavior. In addition, the most relevant brain areas, such as the preoptic area and the ventromedial nucleus of the hypothalamus, in which these regulations take place, are discussed.

The Role of Estrogen Receptor β in the Dorsal Raphe Nucleus on the Expression of Female Sexual Behavior in C57BL/6J Mice

17β-Estradiol (E₂) regulates the expression of female sexual behavior by acting through estrogen receptor (ER) α and β. Previously, we have shown that ERβ knockout female mice maintain high level of lordosis expression on the day after behavioral estrus when wild-type mice show a clear decline of the behavior, suggesting ERβ may be involved in inhibitory regulation of lordosis. However, it is not identified yet in which brain region(s) ERβ may mediate an inhibitory action of E₂. In this study, we have focused on the dorsal raphe nucleus (DRN) that expresses ERβ in higher density than ERα. We site specifically knocked down ERβ in the DRN in ovariectomized mice with virally mediated RNA interference method. All mice were tested weekly for a total of 3 weeks for their lordosis expression against a stud male in two consecutive days: day 1 with the hormonal condition mimicking the day of behavioral estrus, and day 2 under the hormonal condition mimicking the day after behavioral estrus. We found that the level of lordosis expression in ERβ knockdown (βERKD) mice was not different from that of control mice on day 1. However, βERKD mice continuously showed elevated levels of lordosis behavior on day 2 tests, whereas control mice showed a clear decline of the behavior on day 2. These results suggest that the expression of ERβ in the DRN may be involved in the inhibitory regulation of sexual behavior on the day after behavioral estrus in cycling female mice.

Serotonergic activation during courtship and aggression in the brown anole, Anolis sagrei

The role of serotonin (5-hydroxytryptamine, 5-HT) in social behavior regulation is not fully understood. While 5-HT release in nuclei of the social behavior network has generally been associated with inhibition of aggressive behavior across multiple classes of vertebrates, less is known about its effects on sexual, especially non-copulatory courtship display behaviors. Furthermore, most research has examined effects at 5-HT release sites, while studies examining the behavioral relevance of source cell populations have generated contradictory findings. This study utilized immunohistochemistry to examine the colocalization of 5-HT with Fos, an immediate early gene product and marker of neural activity, in the raphe and superior reticular nuclei of male brown anoles (Anolis sagrei) exposed to either aggression, courtship, or control social interactions. Supporting previous research, copulation was associated with a decrease in 5-HT activity, while a novel link between 5-HT activity and latency to non-copulatory courtship was also found. Within the aggression group, intensity and frequency of behavior were both associated with decreased 5-HT activity. An effect of social context was also seen, with anoles exposed to either courtship or aggression encounters showing decreased 5-HT activity in certain raphe and superior reticular nuclei populations compared to controls. Interestingly, context effects and behavioral effects were seen at separate brain nuclei, suggesting the presence of separate systems with distinct functional roles.

Effects of 5-HT1A-Receptor Agonist, 8-OH-DPAT, and GABAB-Receptor Agonist, Baclofen, on Lordosis in Female Rats With Lesions in Either the Dorsal Raphe Nucleus or Septum

The inhibitory effects of 8-OH-DPAT, a 5-HT1A-receptor agonist, and baclofen, a GABAB-receptor agonist, on lordosis were examined in estrogen and progesterone-treated ovariectomized rats with lesions in either the dorsal raphe nucleus (DRN) or septum and in rats with either sham lesions or no lesions. The first behavior test series was carried out 6 days after implantation of the rats with silicon tubes containing estradiol. Four hours after injection with 0.5 mg progesterone, behavioral tests were performed before and 30 min after an injection with 1 mg/kg body weight 8-OH-DPAT. As a result, the mean lordosis quotient (LQ)s were changed from 100 to less than 20 before and after the injection in all groups. These results suggest that 8-OH-DPAT acts on areas other than the DRN and the septum, leading to a decrease in lordosis. Two weeks after implantation with estradiol, the next behavioral test series was carried out after injection with progesterone. Behavioral tests were performed before and after an injection with 10 mg baclofen. The results showed that the mean LQs decreased after the injection in all groups, but the mean LQ in the DRN lesion group was higher than that in the sham groups. These results indicate that baclofen may act partially on the DRN in inhibiting lordosis in female rats.

Decrease of serotonin and metabolite in the forebrain and facilitation of lordosis by dorsal raphe nucleus lesions in male rats

In castrated male rats, a radiofrequency lesion was made in the dorsal raphe nucleus (DRL) and lordosis behavior was observed following treatment with estrogen. After the behavioral test, brains were removed and the contents of 5-HT and 5-HIAA in the forebrain were measured by high pressure liquid chromatography (HPLC). In the results, only 2 of 16 control males without brain surgery showed lordosis, and the mean lordosis quotient (LQ) was extremely low when compared to that in control females. In contrast, all male rats with DRL displayed lordosis and the mean LQ was higher than that of control males without brain surgery but lower than that in control females (P < 0.001). In the DRL males, 5-HT and 5-HIAA contents in the septum (SPT), the preoptic area (POA), the ventromedial hypothalamus (VMH) and the striatum (STM) were lower than those in control male and female groups (P < 0.001). These results suggest that the dorsal raphe nucleus prevents male rats from showing lordosis by serotonergic influence in the forebrain. In addition, HPLC results showed that levels of the 5-HT in the SPT, the POA and the VMH in the female group were higher than those in the control male group (P < 0.05). In female rats, the POA (P < 0.01) and the VMH (P < 0.05) contained larger 5-HT than those in the SPT and the STM, but there were no difference of 5-HT contents in the male rat.