MATERNAL AGGRESSION OF RATS IS IMPAIRED BY CUTANEOUS ANESTHESIA OF THE VENTRAL TRUNK, BUT NOT BY NIPPLE REMOVAL

Aggression toward conspecific and allospecific individuals by female m ammals is much more likely during lactation than during other reproduc tive states, a behavior that serves to protect the young. Previous res earch revealed that removal of nipples (thelectomy) prepartum greatly reduces the likelihood of postpartum aggression in house mice, but not in Sprague-Dawley Norway rats. The present work shows that prepartum thelectomy has no effect on the likelihood or intensity of postpartum aggression toward a strange male intruder in Long-Evans rats. In contr ast, anesthesia of each nipple and surrounding skin prevents or severe ly impairs the elicitation of biting and attacking by the intruder, bu t does not impair normal retrieval of pups. Following removal of the l itter, maternal aggression occurs readily at 1 h and somewhat less so at 5 h, but is absent at 24 h. These data suggest that while maternal aggression in postpartum rats does not require suckling, it is depende nt on somatosensory stimulation of the ventral trunk by pups: this sti mulation apparently produces a motivational change that lasts several hours.