Experiments with social instigation or the omission of scheduled reinforcement show that serotonergic mechanisms may be involved in escalated aggression in animals. 5-HT 1B receptor agonists have anti-aggressive effects in individuals who show moderate as well as high levels of aggression. The present study compared the effects of the 5-HT 1B agonist anpirtoline (0.125-1.5 mg/kg) on (1) species-typical aggressive behavior in male mice, (2) aggression "instigated" or primed by prior exposure to the opponent, and (3) aggression heightened by "frustration" caused by omission of scheduled reinforcement. The effects of anpirtoline on species-typical behavior were also assessed after pretreatment with the 5-HT 1B/1D receptor antagonist GR127935 (10 mg/kg). Anpirtoline, like other 5-HT 1Bagonists 253, zolmitriptan) The development of valid experimental protocols that model clinically relevant, excessive levels of aggressive behavior is a continuing challenge for pre-clinical research on aggression (Miczek 2001). The leading neurobiological hypothesis attributes such intense aggressive behavior, often related to expressions of impulsivity, to a deficit in brain serotonin (Linnoila et al. 1983;Virkkunen et al. 1989;Coccaro 1989). An early example of this research strategy was the demonstration that mice would exhibit intense aggressive behavior after prolonged isolated housing, and this isolation-induced aggression is associated with lower serotonin turnover in the brainstem ). Long-standing concerns with the validity and reliability of isolation-induced aggression and its limited species generality prompt the search for alternate approaches (Brain 1975;Krsiak 1975). Similarly, correlation of aggressive behavior with a single tissue or CSF measurement of serotonin or its metabolite need to be reconciled with the anti-aggressive effects of agonist NO . 2 and antagonist treatment of specific serotonin receptor subtypes (Olivier et al. 1995;de Almeida et al. 2001).The exposure of an experimental subject to a potential rival for a short time prior to the actual confrontation engenders intense levels of aggression, as originally described in mice (Lagerspetz 1969;Tellegen and Horn 1972). For example, mice, rats, and hamsters initiate attacks with very short latency and at high frequency when tested with an intruder in their home cage or in an unfamiliar locale after having been provoked previously by an opponent (Potegal 1992;Fish et al. 1999). Instigation or priming is specific for increasing aggressive behavior and does not activate locomotion, feeding, or sexual behavior (Lagerspetz and Hautojarvi 1967;Potegal and Tenbrink 1984;Potegal 1992). Even after removal of the instigating or priming stimulus, high levels of aggression persist in fish and rodents, presumably from increased "aggressive arousal" or "attack readiness" (Heiligenberg 1974;Potegal and Tenbrink 1984;Potegal 1992). At the neurochemical level, animals that have been instigated to fight are characterized by a long-lasting decrease in serotonin in hypoth...

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The existence of the teneurin C-terminal associated peptides (TCAP) was reported in 2004 after screening a rainbow trout hypothalamic cDNA for corticotropin-releasing factor (CRF)-related homologs. In vertebrates, there are four TCAP paralogs, where each peptide is associated with a teneurin transmembrane protein. The TCAPs are 40 or 41 amino acids in length and possess less than 20% residue identity with the CRF family of paralogs. Orthologs of TCAP are found in all metazoans with the possible exception of poriferans and cnidarians. Recent evidence indicates that TCAP and the teneurins may have been introduced into the Metazoa via horizontal gene transfer from prokaryotes into a basal protistan. Thus, the origin of the TCAPs likely predated that of the CRF family. In the mammalian brain, TCAP-1 is transcribed independently from teneurin-1. Moreover, TCAP-1 acts on neurons by a CRF-receptor independent signal transduction pathway to regulate cellular cytoskeletal function to stimulate cell activity. Administration of synthetic TCAP-1 to rodents inhibits a number of CRF- and stress-associated behaviors via a hypothalamic–pituitary–adrenal (HPA) axis-independent mechanism.