**2.3.2 Emotional locomotor behaviors**

The MLR was initially established as a functional region involved in the initiation of locomotion on the basis of its connections with limbic structures and the basal ganglia (Armstrong, 1986; Megensen et al., 1991). Regardless of the nature of emotional stimuli, they usually elicit alert responses that produce stereotyped movements such as increased postural muscle tone and/or locomotion that accompanies autonomic sympathetic responses. The limbic-hypothalamic systems play crucial roles in these processes. Sinnamon (1993) proposed the following three types of locomotor systems that function in different behavioral or motivational contexts; an appetitive system, a primary defensive system, and an exploratory system. In cats with chronically implanted electrodes, stimulation of the SLR elicited alerting responses followed by exploratory (searching) or defensive behaviors (Fig.3Cc; Mori et al., 1989). Signals from the SLR are mediated by dense fibers in the medial forebrain bundle projecting to the midbrain (Rossignol, 1996). On the other hand, stimulation of the MLR abruptly elicited machine-like explosive locomotion (Fig.3Cd). Neural circuits connecting the nucleus accumbens (the oldest part of the striatum), the hippocampus, and the amygdala, are involved in emotional memory, and projections from the nucleus accumbens to the MLR may contribute to the expression of exploratory behaviors (Mogenson, 1991). In addition, projections from the lateral and the medial hypothalamic areas to the MLR are thought to operate as defensive and appetitive systems, respectively (Grillner et al., 1997; Jordan, 1998). The orexin-containing neurons located in the prefornical lateral hypothalamic area are considered to control appetite, energy balance, and vigilance states via projections to various areas in the nervous system (Peyron et al., 1998; Sakurai, 2002; Siegel, 2004). The orexinergic projections to the MLR facilitated the activity of the locomotor system (Takakusaki et al., 2005), indicating that the hypothalamic orexinergic system contributes to appetitive behaviors.
