The present paper is devoted to second-and higher-tier test methods for the characterization of behavioral changes produced in rodents by exposure to noxious agents during development. The paper analyzes a series of end points that are informative about specific processes and underlying regulatory mechanisms but require greater technical sophistication and larger investments than first-tier end points. This applies to ultrasonic emissions in successive postnatal periods; to mother-pup interactions, including appropriate cross-fostering controls; to social (including sexual) interaction tests from the infantile to the young adult stage; and to a variety of conditioning and learning tests using both positive and negative reinforcement. Environ Health Perspect 104(Suppl 2): 307-315 (1996)
There is evidence that activity at the GABA/benzodiazepine receptor complex in specific brain areas might be enhanced during rodent motherhood. We tested the hypothesis that the manipulation of this neurochemical system by prenatal benzodiazepine exposure affects typical behavioral responses of lactating mouse dams. Outbred CD-1 mouse fetuses were administered either oxazepam (OX, 15 mg/kg) or vehicle twice a day on embryonic days 12-16 and fostered at birth to untreated dams. Female offspring were subsequently mated at the young adult stage. In a first experiment, the behavioural repertoire of the two groups of lactating females was scored (single 10-min session) from postpartum days 3 to 18. When compared with VEH dams, OX females showed a shorter duration of pup-sniffing at 7-10 days and enhanced crouching behaviour when pups had reached the age of 14-18 days. In addition, OX-treated dams used more cotton for nest construction than the controls. The two female groups were differentiated only in the presence of their offspring. In a second experiment aimed at investigating possible OX-induced changes in pup-stimulus perception, the same lactating females were challenged in sequence on postpartum day 8 with three different patterns of pup-related cues consisting of: three 8-day-old live male pups (LP), three same-age dead pups DP, or three dead pups accompanied by pre-recorded ultrasounds (DPU). In the absence of carry-over effects of prenatal dam treatment, LP stimuli elicited a higher frequency of sniffing and digging than the others, whereas the level of licking, and grooming was reduced. In conclusion, the present results indicate that the slight alteration in maternal care resulting from prenatal OX treatment can be dissociated from changes in pup-related stimulus perception.
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