The influence of social isolation and peripheral innervation on Ehrlich tumor growth in mice

The relationship between social isolation and Ehrlich tumor growth was investigated in seven male NIH mice about 2 months old living separately in small cages for 28 days. Fifteen control animals were kept grouped in conventional cages (10 animals in one and 5 in another) for the same period. After this period, 40 to 50 microliters of a cell tumor suspension at a concentration of 1 to 5 x 10(7) tumor cells/ml was inoculated into the footpad and footpad size was measured for 10 days. Isolated mice presented a 30% reduction in tumor growth. Sciatic and saphenous neurectomy in one leg of 5 isolated mice (experimental) and 5 grouped mice (control) performed 7 days before tumor inoculation abolished this difference, and more tumor growth was observed in the neurectomized paw compared to the non-neurectomized paw. The subordinate x dominant social relationship established between mice living in groups of two per cage (seven cages) did not modify the growth of tumor inoculated under the same conditions compared to the first experiment. We conclude that social isolation and an intact peripheral innervation are associated with reduced tumor growth, but dominance behavior has no effect.