title: Behavioral characterization of escalated aggression induced by GABA(B) receptor activation in the dorsal raphe nucleus.
abstract: BACKGROUND
  Pharmacological activation of GABA(B) receptors in the dorsal raphe nucleus (DRN) can escalate territorial aggression in male mice.
  
  
  OBJECTIVE
  We characterized this escalated aggression in terms of its behavioral and environmental determinants.
  
  
  METHODS
  Aggressive behavior of resident male (CFW or ICR mouse) was assessed in confrontations with a group-housed intruder. Either baclofen (0.06 nmol/0.2 μl) or vehicle (saline) was microinjected into the DRN 10 min before the confrontation. We examined baclofen-heightened aggression in five situations: aggression in a neutral arena and after social instigation (experiment 1), aggression during the light phase of the cycle (experiment 2), aggression without prior fighting experience (experiment 3), aggression toward a female (experiment 4), and aggression after defeat experiences (experiment 5). In addition, we examined the body targets towards which bites are directed and the duration of aggressive bursts after baclofen treatment.
  
  
  RESULTS
  Regardless of the past social experience, baclofen escalated aggressive behaviors. Even in the neutral arena and after defeat experiences, where aggressive behaviors were inhibited, baclofen significantly increased aggression. Baclofen increased attack bites directed at vulnerable body areas of male intruders but not toward a female and only in the dark. Also, baclofen prolonged the duration of aggressive bursts.
  
  
  CONCLUSIONS
  For baclofen to escalate aggression, specific stimulation (male intruder) and tonic level of serotonin (dark cycle) are required. Once aggressive behavior is triggered, intra-DRN baclofen escalates the level of aggression to abnormal levels and renders it difficult to terminate. Also, baclofen counteracts the effects of novelty or past experiences of defeat.
authors.affiliation: Mouse Genomics Resource Laboratory, National Institute of Genetics (NIG), 1111 Yata, Mishima, Shizuoka 411-8540, Japan. aktakaha@lab.nig.ac.jp
authors.forename: Aki
authors.initials: A
authors.lastname: Takahashi
authors.forename: Arielle N
authors.initials: AN
authors.lastname: Schilit
authors.forename: Jisoo
authors.initials: J
authors.lastname: Kim
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Debold
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Koide
authors.forename: Klaus A
authors.initials: KA
authors.lastname: Miczek
mesh_terms: D000374:Aggression / Q000187:drug effects*; D000818:Animals; D001418:Baclofen / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects; D003624:Darkness; D005260:Female; D058786:GABA-B Receptor Agonists / Q000494:pharmacology*; D008027:Light; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism; D018080:Receptors, GABA-B / Q000187:drug effects* / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D013997:Time Factors
chemical_list: D058786:GABA-B Receptor Agonists; D018080:Receptors, GABA-B; D012701:Serotonin; D001418:Baclofen