title: Relationship Between L-DOPA-Induced Reduction in Motor and Exploratory Activity and Striatal Dopamine D2 Receptor Binding in the Rat.
abstract: OBJECTIVE
  The present study assessed the influence of L-DOPA administration on neostriatal dopamine (DA) D2 receptor binding in relation to motor and exploratory behaviors in the rat.
  
  
  METHODS
  D2 receptor binding was measured in baseline, after challenge with the aromatic L-amino acid decarboxylase inhibitor benserazide, and after challenge with either 5 or 10 mg/kg L-DOPA plus benserazide. Additional rats received injections of saline. For baseline and challenges, striatal equilibrium ratios (V[Formula: see text]) were computed as estimation of the binding potential. Motor and exploratory behaviors were assessed for 30 min in an open field prior to administration of [(123)I]IBZM. D2 receptor binding was measured with small animal SPECT 2 h after radioligand administration for 60 min.
  
  
  RESULTS
  Both L-DOPA doses significantly reduced D2 receptor binding relative to baseline and led to significantly less ambulation, less head-shoulder motility, and more sitting relative to saline. Moreover, 10 mg/kg L-DOPA induced less head-shoulder motility, more sitting, and more grooming than 5 mg/kg L-DOPA. Analysis of time-behavior curves showed that L-DOPA-treated animals relative to saline exhibited a faster rate of decrease of ambulation frequency and a slower rate of decrease of both duration and frequency of head-shoulder motility from a lower maximum level.
  
  
  CONCLUSIONS
  The reductions of striatal D2 receptor binding after L-DOPA may be conceived to reflect elevated concentrations of synaptic DA. L-DOPA-treated animals showed less ambulation and less head-shoulder motility than saline-treated animals, indicating an association between less behavioral activity and increased availability of striatal DA. The faster rate of decrease of ambulation frequency and the lower maximum levels of both head-shoulder motility duration and frequency may be interpreted in terms of influence of increased DA availability on behavioral habituation to a novel environment.
authors.affiliation: Clinic of Nuclear Medicine, University Hospital Düsseldorf Düsseldorf, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Nikolaus
authors.affiliation: Clinic of Nuclear Medicine, University Hospital Düsseldorf Düsseldorf, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Beu
authors.affiliation: Center for Behavioural Neuroscience, Institute of Experimental Psychology, Heinrich-Heine University Düsseldorf, Germany.
authors.forename: Maria A
authors.initials: MA
authors.lastname: de Souza Silva
authors.affiliation: Center for Behavioural Neuroscience, Institute of Experimental Psychology, Heinrich-Heine University Düsseldorf, Germany.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Huston
authors.affiliation: Clinic of Nuclear Medicine, University Hospital Düsseldorf Düsseldorf, Germany.
authors.forename: Hubertus
authors.initials: H
authors.lastname: Hautzel
authors.affiliation: M et P Pharma AGEmmetten, Switzerland; Oceanographic Center, Nova Southeastern UniversityFort Lauderdale, FL, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Mattern
authors.affiliation: Clinic of Nuclear Medicine, University Hospital Düsseldorf Düsseldorf, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Antke
authors.affiliation: Clinic of Nuclear Medicine, University Hospital Düsseldorf Düsseldorf, Germany.
authors.forename: Hans-Wilhelm
authors.initials: HW
authors.lastname: Müller
keywords: D2 receptor; L-DOPA methylester; [123I]IBZM; exploratory behavior; habituation; motor behavior; small animal SPECT; time-behavior curves