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

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.

Hypothalamic orexinergic neurons modulate pain and itch in an opposite way: pain relief and itch exacerbation

“…We backcrossed the mutant mice with C57BL/6 mice (Clea Japan Inc., Tokyo, Japan) for more than 10 generations. We have confirmed that the expression of orexin peptide disappeared in ORX-KO and ORX-abl mice [31,33]. cFos-tTA; TetO-GCaMP6 mice were generated by crossing Tg(Fos-tTA, Fos-EGFP*)1Mmay mice (obtained from The Jackson Laboratory, Stock No: 018306) with TetO-GCaMP6 knock-in mice (B6;129-Actb<tm3.1(tetO-GCaMP6)Kftnk >, obtained from the RIKEN Bio Resource Research Center, RBRC09552).…”

“…All animals were 8-16 weeks old at the start of each experiment. The generation of mutant mice has been described in detail elsewhere [28][29][30][31][32]. Regarding the method for selective ablation of orexin neurons (ORX-abl), orexintetracycline transactivator (tTA) mice, which express tTA exclusively in orexin neurons under the control of the human prepro-orexin promoter, were bred with tetO diphtheria toxin A fragment (DTA) mice (B6.Cg-Tg (tetO DTA) 1Gfi/J, The Jackson Laboratory) to generate orexin-tTA; tetO DTA mice.…”

Activity of putative orexin neurons during cataplexy

“…We do not know whether such excitation, if any, might be enough to overcome succeeding inhibitory inputs to the orexin neurons. The second interpretation of the current results may be that the reduction of heart rate and GCaMP6 signals may indicate a transient slow-down of hyper arousal state with high sympathetic tones, because cataplexy often occurs in the middle of highly active behavior in ORX-deficient mice [ 2 , 20 , 21 ]. The lowered signals, especially the heart rate (~ 550 bpm, Fig.…”

“…Orexin neurons express opioid receptors, and activation of the receptor inhibits orexin neuronal activity at least in vitro [ 28 ]. Positive emotions induce both cataplexy [ 21 , 29 ] and opioid release [ 30 ]. Sympathetic activation, a role of orexin neurons [ 31 ], is not as strong during negative emotions as during positive emotions [ 32 ].…”

“…On the experimental day, mice were individually placed into a recording chamber in a soundproof box with a 12-h:12-h reversed light/dark cycle for 10 h, from 8:00 (lights off at 7:00) to 18:00. The chamber was illuminated with a far infrared lamp (940 nm, SA2-IR, World Musen, Hong Kong), and a piece of chocolate was placed in the chamber at the start of observation to increase the episodes of cataplexy [ 21 ]. Mouse behavior was continuously recorded with a video camera (CBK21AF04, The Imaging Source Asia, Taipei, Taiwan) and was monitored on a personal computer located outside the soundproof box using the video capture function in LabChart.…”