CHOLINERGIC MODULATION OF A DECREMENT IN SOCIAL-INVESTIGATION FOLLOWING REPEATED CONTRACTS BETWEEN MICE

Social recognition has been inferred from a decline in olfactory inves tigation of conspecific intruders during repeated or protracted confro ntation with a resident rat. A stimulus-response relationship defined by lack of response remains somewhat ambiguous. Since it is likely tha t behavior continues to be emitted by the resident becomes familiar wi th an intruder represents an important issue in the characterization o f recognition. We examined the decline in olfactory investigation of o variectomized females by adult male mice. The duration and frequency o f olfactory investigation was measured during four 1 minute confrontat ions with 10-min intertrial interval (Training trials). If the same fe male was presented in each trial, investigation declined to less than 50% of initial levels. Aggressive behavior gradually increased with re peated trials. No decline in investigation of increased aggression was measured when females were changed in each trial. Administration of d oses of scopolamine (0.16-1.0 mg/kg, IP) blocked decrements in olfacto ry investigation in repeated confrontations and significantly reduced aggression. Co-administration of heptylphysostigmine (0.32-5.0 mg/kg, IP) reversed scopolamine's effects on olfactory investigation but not aggression. Acetylcholinesterase inhibitors heptylphysostigmine, galan thamine (0.63-2.5 mg/kg, IP) and tacrine (0.63-10.0 mg/kg, IP) all enh anced the rate of decrement of olfactory investigation when administer ed alone, but had differential effects on aggression. The decline in i nvestigation corresponds to criteria for habituation. Increased respon sivity expressed as aggression indicates recognition may also be chara cterized as a change in behavioral strategy dependent on the sexual an d social status of the stimulus animal. Pharmacological data support a role for acetylcholine release in the development of social recogniti on as an olfactory memory, or through modulation of olfactory percepti on.