Neuroscience Research 39 (2001) 11 – 19 Neuronal activity in the putamen and the globus pallidus of rabbit during mastication Yuji Masuda *, Takafumi Kato, Osamu Hidaka 1 , Ryuji Matsuo 2 , Tomio Inoue 3 , Koichi Iwata, Toshifumi Morimoto Department of Oral Physiology, Faculty of Dentistry, Osaka Uniersity, 1 -8 Yamadaoka, Suita, Osaka 565 -0871, Japan Received 6 July 2000; accepted 8 August 2000 Abstract The pattern of jaw movements is changed during a masticatory sequence from ingestion of food to its deglutition. The masticatory sequence is divided into three distinct stages in the rabbit. However, the neural mechanism involved in the alteration of the masticatory stages is still unknown. This study was designed to determine whether neuronal activity in the putamen and globus pallidus is related to the alteration of the masticatory stages. Fifty-three percent of the recorded neurons showed significant alterations of activity during mastication. Of these neurons, 16% changed their firing frequency throughout the masticatory sequence (sequence-related neurons) and 84% changed their firing frequency with the transition of the masticatory stages (stage-related neurons). The stage-related neurons were classified into two groups based on their neuronal activity patterns observed during mastication, i.e. simple type and complex type. The former are the neurons that were either facilitated or inhibited once during mastication, and the latter are those showing the facilitation or inhibition twice or more during mastication. Complex-type neurons were observed more frequently in the globus pallidus than in the putamen. These results suggest that the basal ganglia is involved in mastication and may related to the transition between the masticatory stages. © 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. All rights reserved. Keywords: Mastication; Jaw movement; Putamen; Globus pallidus; Neuronal activity; Sequence; Rabbit www.elsevier.com/locate/neures 1. Introduction The masticatory sequence is a whole set of move- ments from ingestion to swallowing. It is made up of masticatory cycles that change in movement pattern as the food is gathered, moved backward to the molar teeth, then broken down and prepared for swallowing (Lund, 1991). The masticatory sequence can be divided into three distinct stages (stage I, IIa, IIb) in the rabbit based on the form of the jaw movements (Morimoto et al., 1985; Schwartz et al., 1989). The food is transported back to the molar teeth during stage I and ground up during stage II. The transition from stage I to II occurs abruptly. It is now generally accepted that the motor command for the basic pattern of rhythmical oral-facial movements during chewing is generated by a neuronal population in the brain stem (central pattern generator) (Nakamura and Katakura, 1995 for review). Sensory input from a variety of intraoral, joint, and muscle receptors interact with the central control system in the brain stem to adapt the program of chewing move- ments to the characteristics of the food (Morimoto et al., 1989; Hidaka et al., 1997). Therefore, the jaw movements for chewing have been called semi-auto- matic movements. However, it is still unclear what neural mechanism is involved in the transition from stage I, in which the animal manipulates the food and leads to the semi-automatic chewing movements, to stage II. Many investigations have demonstrated that feeding deficits are caused by lesions of the striatum or globus * Corresponding author. Tel.: +81-6-6879-2882; fax: +81-6-6879- 2885. E-mail address: masuday@dent.osaka-u.ac.jp (Y. Masuda). 1 Department of Orthodontics and Dentofacial Orthopedics, Osaka University Faculty of Dentistry, Suita, Osaka 565-0871, Japan. 2 Department of Oral Physiology, Okayama University Dental School, Okayama, Okayama 700-8525, Japan. 3 Department of Oral Physiology, School of Dentistry, Showa University, Shinagawa, Tokyo 142-8555 Japan. 0168-0102/01/$ - see front matter © 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. All rights reserved. PII:S0168-0102(00)00186-3