title: Individual differences in novelty-seeking behavior in spontaneously hypertensive rats: Enhanced sensitivity to the reinforcing effect of methylphenidate in the high novelty-preferring subpopulation.
abstract: BACKGROUND
  High novelty seeking has been assumed to predict vulnerability to use addictive drugs. Notably, it is also a symptom associated with attention-deficit/hyperactivity disorder (ADHD). The aim of this study was to identify whether spontaneously hypertensive rats (SHRs), putative animal models of ADHD, display individual differences in novelty-seeking behavior, and whether high novelty-seeking SHRs show enhanced sensitivity to the reinforcing effect of methylphenidate, the most commonly prescribed stimulant ADHD medication.
  
  
  METHODS
  First, we established that SHRs show higher levels of novelty-seeking behavior than their normotensive control strain, Wistar Kyoto (WKY) rats. Novelty seeking was measured in two tests: open field test in a novel test arena, and novel object preference tests. Thereafter, SHRs were classified into high responders (HR) or low responders (LR), high novelty-preferring (HNP) or low novelty-preferring (LNP) rats, based on individual scores in the two behavioral assays. Methylphenidate self-administration was assessed thereafter.
  
  
  RESULTS
  SHRs showed higher levels of novelty-seeking behavior than WKY rats. HR/LR and HNP/LNP subgroups were identified. HR and LR rats showed comparable rates of methylphenidate self-administration. However, HNP SHRs worked more for methylphenidate infusions than their LNP counterparts.
  
  
  CONCLUSIONS
  We showed some evidence on inter-individual variations in novelty seeking in SHRs. Importantly, we demonstrated enhanced sensitivity of HNP SHRs to the reinforcing effect of methylphenidate, indicating a "drug-vulnerable" SHR subpopulation. These findings are important as they may provide basis for a potential screening tool to identify a subset of ADHD patients (i.e. high novelty seekers) who may be at risk for misusing/abusing methylphenidate.
authors.affiliation: Uimyung Research Institute for Neuroscience, Sahmyook University, 26-21 Kongreung-2-dong, Hwarangro-815 Nowon-gu, Seoul 139-742, Republic of Korea.
authors.forename: Ike
authors.initials: I
authors.lastname: dela Peña
authors.affiliation: Department of Neuroscience, School of Medicine, Konkuk University, Seoul 143-701, Republic of Korea.
authors.forename: Edson Luck
authors.initials: EL
authors.lastname: Gonzales
authors.affiliation: Uimyung Research Institute for Neuroscience, Sahmyook University, 26-21 Kongreung-2-dong, Hwarangro-815 Nowon-gu, Seoul 139-742, Republic of Korea.
authors.forename: June Bryan
authors.initials: JB
authors.lastname: de la Peña
authors.affiliation: Division of Child and Adolescent Psychiatry, Clinical Research Institute, Seoul National University Hospital, 28 Yungundong, Chongrogu, Seoul 110-744, Republic of Korea.
authors.forename: Bung-Nyun
authors.initials: BN
authors.lastname: Kim
authors.affiliation: Department of Psychiatry, Chung-Ang University Medical School, 102 Heukseok-ro, Dongjak-gu, Seoul 156-755, Republic of Korea.
authors.forename: Doug Hyun
authors.initials: DH
authors.lastname: Han
authors.affiliation: Department of Neuroscience, School of Medicine, Konkuk University, Seoul 143-701, Republic of Korea.
authors.forename: Chan Young
authors.initials: CY
authors.lastname: Shin
authors.affiliation: Uimyung Research Institute for Neuroscience, Sahmyook University, 26-21 Kongreung-2-dong, Hwarangro-815 Nowon-gu, Seoul 139-742, Republic of Korea. Electronic address: cheongjh@syu.ac.kr.
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Cheong
mesh_terms: D000818:Animals; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D003216:Conditioning, Operant / Q000187:drug effects; D004195:Disease Models, Animal; D005106:Exploratory Behavior / Q000187:drug effects*; D007206:Individuality; D008297:Male; D008774:Methylphenidate / Q000008:administration & dosage*; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012054:Reinforcement, Psychology; D012646:Self Administration
chemical_list: D000697:Central Nervous System Stimulants; D008774:Methylphenidate
keywords: ADHD; Addiction; Methylphenidate; Novelty-seeking; SHR