Background: Serotonin receptors can be divided into seven different families with various subtypes. The serotonin 1A (5-HT1A) receptor is one of the most abundant subtypes in animal brains. The expression of 5-HT1A receptors in the brain has been reported in various animals but has not been studied in horses. The 5-HT1A receptor functions related to emotions and behaviors, thus it is important to understand the functional effects and distribution of 5-HT1A receptors in horses to better understand horse behavior and its associated mechanism. Methods: Brain samples from seven different regions, which were the frontal, central, and posterior cerebral cortices, cerebellar cortex and medulla, thalamus, and hypothalamus, were collected from six horses. Western blot analysis was performed to validate the cross-reactivity of rabbit anti-5-HT1A receptor antibody in horse samples. Immunofluorescence was performed to evaluate the localization of 5-HT1A receptors in the brains. Results: The protein bands of 5-HT1A receptor appeared at approximately 50 kDa in the frontal, central, and posterior cerebral cortices, cerebellar cortex, thalamus, and hypothalamus. In contrast, no band was observed in the cerebellar medulla. Immunofluorescence analysis showed that the cytoplasm of neurons in the cerebral cortices, thalamus, and hypothalamus were immunostained for 5-HT1A receptors. In the cerebellar cortex, 5-HT1A was localized in the cytoplasm of Purkinje cells. Conclusions: In conclusion, the study suggests that 5-HT and 5-HT1A receptor systems may play important roles in the central nervous system of horses, based on the widespread distribution of the receptors in the horse brain.

A specific serotonin receptor (Se-5HTR) has been identified in the beet armyworm, Spodoptera exigua and classified into 5-HT7 type. Se-5HTR expression was up-regulated in hemocytes and fat body in response to immune challenge. As being a GPCR, this receptor is presumably coupled with intracellular trimeric Gαs protein activating cAMP-dependent protein kinase (PKA) pathway to regulate several cellular functions. RNA interference (RNAi) of Se-5HTR as well as its downstream signal proteins exhibited significant suppression in cellular immune responses including nodulation and phagocytosis. Application of inhibitors to the signaling cascade suppressed the immune responses as well. To validate the Se-5HTR involvement in mediating cellular immunity, 5-HTR knock-out mutants were developed using CRISPR-Cas9 technique and suffered significant developmental anomalies.

세로토닌(serotonin, 5-HT)은 아민류 가운데 카테콜아민과 더불어 중요한 체네 생리 및 행동 조절을 담당하는 신경 전달물질이다. 특히 'Prozac'으로 잘 알려진 항우울제는 5-HT의 세포내 재흡수를 선택적으로 억제하는 약물(selective serotonin reuptake inhibitor, SSRI)로써 광범위하게 사용중인 약물인데, 알려진 부작용으로 사정 능력의 변화가 관찰된다. 이는 5-HT에 의한 성 행동 또는 성 기능 조절기작이