Monoamines and Fear-Related Behaviors

Abstract

The mesocortical dopamine (DA) neuronal system has been reported to show regional differences in sensitivity to various pharmacological and behavioral manipulations. For instance, cortical DA neuronal activity was facilitated following application of atypical antipsychotic drugs (Broderick and Piercey, 1998) or anxiogenic agent (Bradberry et al., 1991), but nigrostriatal and mesolimbic DA systems were not influenced by these drugs. Physiological stimuli such as tail-shock stress (Abercrombie et al., 1989) or prolonged handling (Feenstra et al., 1998) produced greater enhancement of DA release in the prefrontal cortex (PFC) than in the striatum and/or the nucleus accumbens. Recently, we have demonstrated that DA release in the PFC was enhanced by conditioned fear stress (CFS), an animal model of anxiety which is regarded as psychological stress without physical stimuli (Fanselow, 1980), whereas any changes of striatal DA levels were not found by exposure to CFS. These regional differences of characteristics of DA neurons may be pivotal for understanding the mechanism underlying the pathophysiology of DA neuronal function. The PFC receives not only dopaminergic inputs from the ventral tegmental area but also reciprocal projections of other neuronal systems. Among these neurotransmitters, serotonin (5-HT) has been focused on the regulation of DA neuronal activity in both cell bodies and terminal regions based on clinical and neurochemical studies (Broderick and Piercey, 1998; Saito et al, 1996).