Acute cocaine effects on stereotypy and defense: an ethoexperimental approach

Cocaine administration to laboratory animals may produce locomotor hyperactivity and stereotypies that include sniffing and rearing, in addition to anxiety-like effects. A time-sampling study of the effects of 3, 10 or 30 mg/kg cocaine (i.p.) over time following injection indicated early enhancement of locomotion and crouching, with the latter most increased in low- and intermediate-dose cocaine groups, with increased rearing and standing during the second hour of the test period. Additional analyses at 30-60 min post-injection suggested qualitative changes in rearing, with high dose animals showing more, but shorter, rears, and a higher frequency of sniffing. The high dose cocaine enhancement of sniffing was strongly associated with rear and stand behaviors, but also occurred while the animal was crouching. This pattern of changes, with initial crouching/freezing and locomotion (flight?), followed by rearing, standing, and sniffing behaviors similar to those seen in risk assessment suggests that cocaine, particularly at high doses, may elicit defense. An additional study using only saline or the high (30 mg/kg) dose indicated that cocaine produced more sniffing regardless of the direction from which the air stream entered the test cage (i.e. top or bottom). However, cocaine animals oriented their sniffing behaviors toward the incoming air, with reliably more sniffs up in cages with the air stream entering from the top, and more sniffs down, when the air stream entered through a wire mesh cage bottom. Controls showed the same pattern, but their sniff orientation differences were not reliable. These results indicate that the sniffing that follows acute high dose cocaine administration is appropriately oriented toward relevant environmental stimuli, a factor disconsonant with the interpretation of sniffing as a stereotypical behavior, but one that is in agreement with the view that it may reflect a risk assessment component of the defense pattern. (C) 1998 Elsevier Science Ltd. All rights reserved.