Effects of age on behavioral responses to dopamine agonists in the rat |
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| Authors: | I Ushijima Y Mizuki K Soeda O Kishimoto T Hara M Yamada |
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| Affiliation: | 1. RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan;2. Institute of Psychiatry, King’s College London, London, SE5 8AF, UK;1. Department of Cognitive Biology, University of Vienna, Austria;2. Department of Behavioral and Social Sciences, SUNY Polytechnic Institute, USA;1. Department of Mechanical Engineering, Indian Institute of Technology Guwahati, 781039, Assam, India;2. Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, 721302, West Bengal, India;1. Mr. & Mrs. Ko Chi-Ming Centre for Parkinson''s Disease Research, School of Chinese Medicine, Hong Kong Baptist University, Hong Kong SAR, China;2. Institute for Research and Continuing Education, Hong Kong Baptist University, Shenzhen, 518057, China;3. Department of Chemistry, Hong Kong Baptist University, Hong Kong SAR, China;4. Centre for Trans-disciplinary Research, Department of Pharmacology, Saveetha Dental College and Hospitals, Chennai, Tamil Nadu, India;5. Division of Mycobiology and Neurodegenerative Disease Research, Department of Microbiology, School of Life Sciences, Central University of Tamil Nadu, Tiruvarur, India;6. Medical College of Acupuncture-Moxibustion and Rehabilitation, Guangzhou University of Chinese Medicine, Guangzhou, China;7. State Key Lab of Quality Research in Chinese Medicine, University of Macao, Macao;8. Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China;9. Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR, China |
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| Abstract: | This study served to examine the differential effects of age (rats aged 2 or 12 months) on behavioral responses induced by bromocriptine and apomorphine. Intraperitoneal (i.p.) injection of bromocriptine or apomorphine produced a lower frequency of yawning responses, in 12-month-old rats than in 2-month-old rats. Apomorphine produced a more pronounced stereotyped behavior in 12-month-old rats than in 2-month-old rats. Apomorphine, at 0.1 mg/kg administered after bromocriptine (1.0-20 mg/kg) potentiated yawning behavior. The frequency of yawning in 2-month-old rats was pronounced at 2.5 mg/kg of bromocriptine but only at 5 mg/kg 12-month-old rats. Apomorphine (0.1 mg/kg) did not produce perioral behavior in 2-month-old rats but did in 12-month-old rats. The apomorphine (1.0 mg/kg)-induced stereotypy was stimulated dose dependently by bromocriptine in 2-month-old-rats but not in 12-month-old rats. Bromocriptine did not produce this behavior when administered alone. Pretreatment of 2-month-old rats with reserpine, a catecholamine depletor, plus alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor, inhibited the yawning induced by bromocriptine but potentiated that induced by apomorphine. Such treatment did not significantly alter either bromocriptine or apomorphine-induced yawning responses in 12-month-old rats. The apomorphine-induced stereotypy in 2-month-old rats was markedly potentiated by catecholamine depletion but was not affected in 12-month-old rats. These results suggest that the increasing effect on stereotypy and decreasing effects on yawning in the 12-month-old rats seem to result in an alteration of potency and of the ratio of D-2 versus D-1 receptor activity. |
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