Sexual excitation induces courtship ultrasonic vocalizations and cataplexy-like behavior in orexin neuron-ablated male mice

Tomoyuki Kuwaki,Kouta Kanno

doi:10.1038/s42003-021-01696-z

Abstract

Cataplexy is triggered by laughter in humans and palatable food in mice. To further evaluate mice’s cataplexy, we examined courtship behavior in orexin neuron-ablated mice (ORX-AB), one of the animal models of narcolepsy/cataplexy. Wild-type female mice were placed into the home cage of male ORX-AB and cataplexy-like behavior was observed along with ultrasonic vocalizations (USVs), also known as the “love song”. ORX-AB with a female encounter showed cataplexy-like behavior both during the dark and light periods, whereas ORX-AB with chocolate predominantly showed it during the dark period. During the light period observation, more than 85% of cataplexy-like bouts were preceded by USVs. A strong positive correlation was observed between the number of USVs and cataplexy-like bouts. Cataplexy-like behavior in narcoleptic mice is a good behavioral measure to study the brain mechanisms behind positive emotion because they can be induced by different kinds of positive stimuli, including chocolate and female courtship.

Highlights

Cataplexy is triggered by laughter in humans and palatable food in mice
Since we found a high incidence of cataplexy in orexin neuron-ablated mice (ORX-AB) mice during the light period as a result of a female encounter, we examined whether melanin concentrating hormone (MCH) neurons were preserved by utilizing immunohistochemistry
We examined the frequency of cataplexy-like behavior during the dark and light periods

Summary

Introduction

Cataplexy is triggered by laughter in humans and palatable food in mice. To further evaluate mice’s cataplexy, we examined courtship behavior in orexin neuron-ablated mice (ORX-AB), one of the animal models of narcolepsy/cataplexy. In order to expand on these findings, we decided to characterize the positive emotion-related nature of cataplexy through experiments utilizing orexin neuron-ablated (ORX-AB) mice, an animal model of narcolepsy/cataplexy[14]. Sexual excitation in response to a female mouse can be quantified by measuring courtship ultrasound vocalizations (USVs), one of the precopulatory behaviors in male mice[15,16] and thought of as a “love song”[17]. Replacement of testosterone into the ventral tegmental area of castrated male mice, one of the main dopaminergic sources, restored the number of courtship vocalizations back to precastration levels[20] These findings suggest that male to female USVs can be a measure of positive excitation. Since we found a high incidence of cataplexy in ORX-AB mice during the light period as a result of a female encounter (see Fig. 1 and related “Results” section), we examined whether MCH neurons were preserved by utilizing immunohistochemistry

Methods

Results

Conclusion