Motivational Systems in Muroid Rodents

The releasing and directing stimuli of the upright posture have been studied in greater detail than those of other motor patterns of offense. However, the studies were conducted on defensive upright posture elicited by footshock rather than on offensive upright posture; thus, it is more appropriate to postpone their discussion until the later section under the defense motivational system.

Approach and the bite-and-kick attack may depend upon visual and vibrissal releasing and directing stimuli. Vision is indicated by the fact that the running away by one rat may elicit pursuit of it by another [Calhoun, 1962, p 182] although in the hamster, Me auratus, blinding does not reduce offensive attack [Murphy, 1976]. Offense is greatly reduced in R norvegicus following cautery of the vibrissae and exclusion of the visual system by testing in darkness [Thor, 1976] an effect which could be due to a decrease in approach, bite-and-kick, or both. Removal or anesthesia of the vibrissae without visual impairment has been reported to decrease attack in M musculus [Katz, 1976] but not in R norvegicus [Blanchard et al, 1977b]. Although M musculus will attack an unmoving or anesthetized opponent under certain circumstances [Krsiak and Steinberg, 1969; Cairns and Scholz, 1973], the probability is greatly reduced in comparison to attack on a normal opponent. And, although R norvegicus will also attack an anesthetized opponent [Alberts and Galef, 1973; Blanchard et al, 1975b], they prefer to attack a normal opponent if given the choice [Alberts and Galef, 1973]. The probability of attack can be increased by administration of drugs that increase the activity of the opponent [Sheard, 1973].

The bite-and-kick attack may also require a critical releasing stimulus related to the ventral tactile contact of the attacker to the dorsal surface of the opponent. In cases of weak offense motivation, these stimuli might not be strong enough to activate the bite-and-kick, which would explain why offense behavior sometimes terminates in full aggressive posture rather than the full bite-and-kick attack. Also, this can explain the effectiveness of the subordinate's behaviors of defensive upright posture and full submissive posture which deny access by the attacker to the dorsal surface of the subordinate and thereby prevent the occurrence of a bite-and-kick attack [Adams, 1976; Blanchard et al, 1977a].

Other motor patterning mechanisms of offense may not require any releasing or directing stimuli for their activation, but may be activated when the offense motivational mechanism is facilitated by motivating stimuli. Thus, teeth-chattering has been reported in Neotoma sp following presentation of strange male odor [Howe, 1977]. Both tail-rattling [Krsiak, 1974] and piloerection [Scott, 1958, p 14] have been reported in M musculus when exposed to a chamber where they have previously been offensive.