title: Dopamine D2 receptors regulate unconditioned fear in deep layers of the superior colliculus and dorsal periaqueductal gray.
abstract: BACKGROUND
  Electrical and chemical stimulation of the dorsal periaqueductal gray (dPAG), deep layers of the superior colliculus (dlSC), and inferior colliculus (IC) causes freezing and escape behavior in rodents. Systemic injections of the selective dopamine D2 receptor antagonist sulpiride increased the number of switch-off responses (SORs) to light and auditory evoked potentials in response to loud sounds. Dopamine D2 receptor inhibition in the IC was shown to enhance unconditioned fear. Nevertheless, the role of dopamine receptors in the dlSC and dPAG in the mediation of unconditioned fear has not yet been demonstrated.
  
  
  OBJECTIVE
  The purpose of the present study was to characterize the effects of sulpiride injections (4 and 8 μg/0.2 μl) in the dlSC and dPAG in rats that were subjected to unconditioned fear paradigms.
  
  
  METHODS
  Switch-off responses to light and exploratory behavior in the elevated plus maze were used to evaluate unconditioned fear in rats.
  
  
  RESULTS
  Intra-dlSC microinjections of sulpiride increased the number of SORs to light. Intra-dlSC and intra-dPAG injections of sulpiride reduced the number of entries into and time spent on the open arms and decreased end-arm exploration and head dipping in the elevated plus maze.
  
  
  CONCLUSIONS
  These findings suggest that dopamine, through D2 receptors in the dlSC and dPAG, is involved in defense reactions that are organized in the midbrain tectum.
authors.affiliation: Laboratory of Neuropsychopharmacology, FFCLRP, Universidade de São Paulo, Campus USP, Ribeirão Preto, SP 14049-901, Brazil; Instituto de Neurociencias e Comportamento, Avenida do Café, 2450, Ribeirão Preto, São Paulo, 14050-000, Brazil.
authors.forename: Sangu
authors.initials: S
authors.lastname: Muthuraju
authors.affiliation: Instituto de Neurociencias e Comportamento, Avenida do Café, 2450, Ribeirão Preto, São Paulo, 14050-000, Brazil; Department of Neurosciences and Behavior, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirao Preto, São Paulo, Brazil.
authors.forename: Teddy
authors.initials: T
authors.lastname: Talbot
authors.affiliation: Laboratory of Neuropsychopharmacology, FFCLRP, Universidade de São Paulo, Campus USP, Ribeirão Preto, SP 14049-901, Brazil; Instituto de Neurociencias e Comportamento, Avenida do Café, 2450, Ribeirão Preto, São Paulo, 14050-000, Brazil. Electronic address: mbrandao@usp.br.
authors.forename: Marcus Lira
authors.initials: ML
authors.lastname: Brandão
mesh_terms: D000818:Animals; D002408:Catheters, Indwelling; D004298:Dopamine / Q000378:metabolism; D065127:Dopamine D2 Receptor Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005106:Exploratory Behavior / Q000187:drug effects / Q000502:physiology; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010487:Periaqueductal Gray / Q000187:drug effects / Q000378:metabolism*; D010775:Photic Stimulation; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D013216:Reflex, Startle / Q000187:drug effects / Q000502:physiology; D013469:Sulpiride / Q000494:pharmacology; D013477:Superior Colliculi / Q000187:drug effects / Q000378:metabolism*
chemical_list: C000607792:DRD2 protein, rat; D065127:Dopamine D2 Receptor Antagonists; D017448:Receptors, Dopamine D2; D013469:Sulpiride; D004298:Dopamine
keywords: Anxiety; Dopamine receptor; Midbrain tectum; Sulpiride; Unconditioned fear