Understanding and Preventing Violence, Volume 2: Biobehavioral Influences (1994)
Chapter: 5-HT Correlates of Animal Aggression
literature during the last decade is the proposed role of brain serotonin in impulse control as manifested in an individual's tendency toward alcoholism, obsessive-compulsive disorders, suicide, irritability, hostile feelings, and violent outbursts (e.g., Asberg et al., 1987). Yet, the evidence on brain 5-HT systems and different kinds of aggressive and violent activities in animals and humans argues against a single direct link, and requires an evaluation that differentiates neural 5-HT pathways and their receptor subtypes in a range of aggressive and violent activities.
5-HT Correlates of Animal Aggression
Brain 5-HT or its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) have been assayed in animals that are subjected to conditions in which aggression is likely to occur or that have just engaged in aggressive behavior, but with varying outcomes (Table 3, section A). In whole brain, 5-HT has been found to increase after fighting or not to change in mice that were isolated for aggression (Modigh, 1973, 1974 versus Goldberg et al., 1973; Garattini et al., 1967). The metabolite 5-HIAA decreased, increased, or did not change in whole brains of mice isolated for aggression (Garattini et al., 1967; Goldberg et al., 1973; Lasley and Thurmond, 1985). Of course, isolated housing does not invariably lead to aggressive behavior; only a varying percentage of isolated mice will engage in aggressive behavior, whereas others remain nonaggressive or even develop heightened escape and defensive reactions ("isolation-induced timidity"; Krsiak, 1975b).
Large increases in indices of amygdaloid 5-HT turnover were found in mice that attacked for the first time (Haney et al., 1990), in rats that were muricidal (Broderick et al., 1985; but see Tani et al., 1987), and in group-housed mice after olfactory bulbectomy (Garris et al., 1984). In a carnivorous species such as mink, the elevated 5-HIAA level in hypothalamus and amygdala was associated with a sated state during which the animal was slow to initiate a predatory kill (Nikulina and Popova, 1988). No changes in 5-HT or 5-HIAA were detected in several hypothalamic, limbic, and mesencephalic regions of aggressive hamsters or in isolated mice after prolonged aggressive and defensive behavior (Payne et al., 1984, 1985; Hadfield and Milio, 1988). When rats react defensively to electric shock pulses, their 5-HT levels in raphe and striatum as well as their 5-HIAA in hippocampus decrease (Lee et al., 1987).
It appears possible that the activity of 5-HT in the amygdala
