Neurobiology of Aging 24 (2003) 259–266 Aged Fischer 344 rats exhibit altered orolingual motor function: relationships with nigrostriatal neurochemical measures John A. Stanford a,c,d,∗ , Elena Vorontsova e , Stewart P. Surgener a,c,d , Greg A. Gerhardt a,b,c,d , Stephen C. Fowler e a Department of Anatomy & Neurobiology, The University of Kentucky Chandler Medical Center, 312 Davis Mills Bldg., Lexington, KY 40536-0098, USA b Department of Neurology, The University of Kentucky Chandler Medical Center, 312 Davis Mills Bldg., Lexington, KY 40536-0098, USA c Center for Sensor Technology, The University of Kentucky Chandler Medical Center, 312 Davis Mills Bldg., Lexington, KY 40536-0098, USA d Morris K. Udall Parkinson’s Disease Research Center of Excellence, The University of Kentucky Chandler Medical Center, 312 Davis Mills Bldg., Lexington, KY 40536-0098, USA e Departments of Human Development, Pharmacology & Toxicology, The Schiefelbusch Institute for Life Span Studies, University of Kansas, Lawrence, KS, USA Received 13 December 2001; received in revised form 4 April 2002; accepted 8 May 2002 Abstract The present study utilized a novel behavioral preparation to measure differences in orolingual motor function between young (6 months) and aged (24 months) Fischer 344 (F344) rats. Rats were trained to lick an isometric force-sensing operandum for water reinforcement so that the number of licks per session, licking rhythm and lick force could be compared between the two groups. The aged rats exhibited a greater number of licks per session, but a slowed licking rhythm, compared to the young rats. Lick force did not differ significantly between the groups. The dopamine (DA) uptake inhibitor nomifensine decreased all three measures in both groups. Analyses of whole brain tissue content of DA, 3,4 dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in the substantia nigra and dorsal striatum revealed no significant differences between the two age groups. Differences were observed between the two groups with respect to relationships between behavioral and neurochemical tissue measures. Striatal DA content and the number of licks per session were positively correlated for the young rats but not for the aged rats. In the aged rats, but not the young rats, positive correlations were also observed between licking rhythm and the DOPAC + HVA/DA ratio in the substantia nigra. These findings suggest that age-related alterations in orolingual motor function may relate in part to functional changes in DA neuronal circuits. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Aging; Movement; Licking; Operant; Dopamine; Basal ganglia 1. Introduction In humans and in animals, normal aging is often associ- ated with a marked deterioration in both the quantity and quality of motor activity [4,24,26]. In addition to bradyki- nesia and gait disturbances, alterations in orolingual and pharyngeal motor function have been associated with hu- man aging [2,14,20,27,28,34–36], and have been found to contribute to increased mortality and morbidity in the el- derly [2,27]. The fact that these deficits are also prevalent in Parkinson’s disease [1,7,18] suggests that diminished nigrostriatal dopamine (DA) neurotransmission may play a role in their occurrence [23]. Although there is substantial evidence from animal studies supporting a DA hypothesis ∗ Corresponding author. Tel.: +1-859-323-1724; fax: +1-859-257-5310. E-mail address: jastan2@pop.uky.edu (J.A. Stanford). of bradykinesia (e.g. [24]), a role for altered DA func- tion in age-related orolingual motor deficits remains to be examined in animal models of normal aging. Because of its functional relevance, deterioration in orolingual motor capacity has been the focus of a number of studies in elderly human volunteers (e.g. [2,14,20,27, 28,34–36]). In contrast, very few studies have examined age-related orolingual motor function using animal models [25,29,31]. The goal of the current study was to exam- ine age-related differences in orolingual motor function in young versus aged Fischer 344 (F344) rats using a novel be- havioral task that has been shown to be sensitive to neuronal DA function. In this study, young and aged rats were trained to lick water from a disk that was attached to an isometric force transducer. Our prior studies have demonstrated that reduction of DA neurotransmission decreases the number of licks emitted per session, lick force and the lick rhythm (licks 0197-4580/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII:S0197-4580(02)00083-0