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Tickling increases dopamine release in the nucleus accumbens and 50 kHz ultrasonic vocalizations in adolescent rats

Hori, Miyoa,b; Shimoju, Ried,e; Tokunaga, Ryotad; Ohkubo, Masatof; Miyabe, Shigekic; Ohnishi, Junjia,g; Murakami, Kazuoa; Kurosawa, Miekod,e

doi: 10.1097/WNR.0b013e32835edbfa
MOTIVATION, EMOTION, FEEDING, DRINKING
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Adolescent rats emit 50 kHz ultrasonic vocalizations, a marker of positive emotion, during rough-and-tumble play or on tickling stimulation. The emission of 50 kHz ultrasonic vocalizations in response to tickling is suggested to be mediated by dopamine release in the nucleus accumbens; however, there is no direct evidence supporting this hypothesis. The present study aimed to elucidate whether play behavior (tickling) in adolescent rats can trigger dopamine release in the nucleus accumbens with hedonic 50 kHz ultrasonic vocalizations. The effect of tickling stimulation was compared with light-touch stimulation, as a discernible stimulus. We examined 35–40-day-old rats, which corresponds to the period of midadolescence. Tickling stimulation for 5 min significantly increased dopamine release in the nucleus accumbens (118±7% of the prestimulus control value). Conversely, light-touch stimulation for 5 min did not significantly change dopamine release. In addition, 50 kHz ultrasonic vocalizations were emitted during tickling stimulation but not during light-touch stimulation. Further, tickling-induced 50 kHz ultrasonic vocalizations were significantly blocked by the direct application of SCH23390 (D1 receptor antagonist) and raclopride (D2/D3 receptor antagonist) into the nucleus accumbens. Our study demonstrates that tickling stimulation in adolescent rats increases dopamine release in the nucleus accumbens, leading to the generation of 50 kHz ultrasonic vocalizations.

aFoundation for Advancement of International Science

bGraduate School of Life and Environmental Sciences

cLife Science Center, Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba, Ibaraki

dGraduate School

eCenter for Medical Science, International University of Health and Welfare, Otawara, Tochigi

fDepartment of Tokyo Judo Therapy, Teikyo University of Science, Adachi

gDepartment of Food and Nutrition, Tokyo Kasei University, Itabashi, Tokyo, Japan

Correspondence to Mieko Kurosawa, PhD, Center for Medical Science, International University of Health and Welfare, Otawara, Tochigi 324-8501, Japan Tel: +81 28 724 3000; fax: +81 28 724 3191; e-mail: mieko-ku@iuhw.ac.jp

Received November 23, 2012

Accepted January 9, 2013

© 2013 Lippincott Williams & Wilkins, Inc.