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Patrol/Marking Motivational Mechanism
The hypothetical structure of a patrol/marking motivational system is based on data from a survey of muroid rodent behavior (Adams, 1980) as well as laboratory studies of the rat (Lee et al., 1984). More recent research supports an earlier proposal (Adams, 1983) that the medial preoptic area of the hypothalamus is the location of the proposed patrol/marking motivational mechanism. Edwards and Einhorn (1986) found decreased preference for a sexually receptive female by male rats following lesions here. Wheel running is produced in female rats by estrogen injections here (Fahrbach et al., 1985), and locomotion is produced by electrical and chemical stimulation (Sinnamon, 1993). Matochik et al. (1994) found increased gender-preference and urine-marking in response to female odors following testosterone implants here. Mink et al. (1983) recorded from single neurons here in male rats with activity specifically correlated to approach toward a female which could have reflected patrol/marking as well as sexual behavior. In recent years, several studies have investigated the behavioral patterns of patrol/marking (Brown, 1991; Peden and Timberlake, 1990), although Brown (1986) found lower correlations among the various motor patterns leading him to question the existence of a single motivational mechanism.
Interactions among Motivational Mechanisms
Studies in our laboratory have provided behavioral evidence that activation of defense inhibits both offense (Mink and Adams, 1981) and patrol/marking (Lee et al., 1984). Lacking specific data from brain research, it is most parsimonious to assume a direct interaction among the motivational mechanisms.
Hormone Effects on Motivational Mechanisms; Maternal Aggression
Behavioral methods indicate that the competitive fighting component of offense is facilitated by both androgens and estrogens (Adams et al., 1994), but the brain substrate of this effect has not been investigated. There are data indicating that other hormones may influence the territorial fighting component of offense by acting on the anterior hypothalamus, including cortisol (Hayden-Hixson and Ferris, 1991), oxytocin (Harmon et al., 2002), and an interaction of androgens and vasopressin (Ferris and Potegal, 1988; Potegal and Ferris, 1989; Harrison et al., 2000). Androgen/vasopression effects on offense have also been reported in the amygdala (Koolhaas et al., 1990; cf. Elkabir et al., 1990), lateral septum (DeLeon et al., 2002; Everts et al., 1997; Scordalakes and Rissman, 2004), bed nucleus of the stria terminalis (DeLeon et al., 2002; Bester-Meredith and Marler, 2001) as well as other regions of the hypothalamus (DeLeon et al., 2002; Delville et al., 1996). Whether these hormones affect offense under natural conditions, and, if so, what functions they perform, has not been conclusively demonstrated. There is speculation that cortisol could be involved in the intensification of offense during a single encounter (Hayden-Hixson and Ferris, 1991; Kruk et al., 2001), while oxytocin could be involved in the decreased intensity that occurs in offense over repeated encounters (Harmon et al., 2002). Others have speculated that vasopressin might be involved in postcopulatory offense in voles (Stribley and Carter, 1999) and the different levels of offense observed in related species of Peromyscus mice (Bester-Meredith and Marler, 2001). Vasopressin might also be involved in motivating stimulus functions of the septum and amygdala to be discussed below.
As mentioned above, androgens and estrogens may directly facilitate the neurons of the patrol/marking motivational mechanism in the medial preoptic area, which is one of several brain regions where neurons have both androgen and estrogen receptors (Wood and Newman, 1995).
Hormonal changes associated with pregnancy may directly or indirectly facilitate offense and defense, thus facilitating maternal aggression which is apparently a combination of offense and anti-predator defense behaviors (Ferrari et al., 2000; Lonstein and Gammie, 2002; Lucion and de Almeida, 1996; Sgoifo et al., 1992). Since neural studies of maternal aggression may affect both the offensive and defensive components, they are therefore difficult to evaluate (e.g. Gammie and Nelson, 2001; Hansen, 1989; Lonstein and Stern, 1997).