Brief, high-frequency stimulation of the corticomedial amygdala induces a delayed and prolonged increase of aggressiveness in male Syrian golden hamsters

Brief 200-Hz stimulation of the corticomedial amygdala (CMA) increases the aggressiveness of male Syrian golden hamsters for about 30 min; the effect peaks 10-15 min after stimulation. This effect is sensitive to stimulation amplitude and frequency. Stimulation at the parameters that reduce attack latency increases flank marking but does not affect copulation latency or general activity. Immunocytochemical analysis suggests that stimulation effects may be coupled to c-fos expression and that unilateral stimulation has bilateral effects. CMA stimulation effects appear to mimic part of the time course of behaviorally induced attack priming. The temporal persistence of aggression may result from long-term potentiation-like changes within CMA-related neural circuitry. Once sufficiently aroused, aggressive behavior in various species of fish (e.g., Heiligenberg, 1974), birds (e.g., Curio, 1975), and mammals (e.g., Potegal, 1992) tends to persist in time. Under experimental circumstances in which the aggression-provoking stimulus remains constant, temporal fluctuations in aggressive behavior imply the existence of fluctuations in central control processes. When aggression persists even after the provoking stimulus is withdrawn (e.g., Curio, 1975; Heiligenberg, 1974), such central processes must certainly play a role. We believe that these important but poorly understood internal processes contribute to a variety of phenomena within the domain of aggressive behavior and that any theory of aggression that fails to take them into account must remain incomplete (Potegal, 1994). Accordingly, we have developed an experimental model for the analysis of these processes