Sex differences in investigatory and grooming behaviors of laboratory rats (Rattus norvegicus) following exposure to novelty.

Prior research suggested that during exposure to novel stimuli, rodent investigation and self-grooming behaviors may be sexually dimorphic and interact with ambient illumination. To test this notion we compared the behavior of adult male and female groups of Long-Evans hooded rats in normal room lighting (860 lx) and in very dim, red light (0.2 lx) following exposure to a novel juvenile conspecific. Illuminance level had little or no effect, but investigatory and subsequent self-grooming behaviors of males were substantially greater than those of females, and females engaged in greater ambulatory activity than did males. In a second experiment adult males and females were exposed to a novel inanimate object. No reliable sex differences were observed. We conclude that social novelty, as provided by exposure to a juvenile conspecific, stimulates greater investigation and postinvestigatory self-grooming than exposure to a novel inanimate object and that exposure to novel conspecifics presents a useful method for the investigation of sex differences, gonadal hormone effects, and interactions of hormones with neurotransmitter systems governing motor control systems.