Effect of the overcrowding stress on hemopoietic colony formation in mice.

Mice were stressed by overcrowding (20 mice/cage instead of 5-6) for up to 4 weeks. They served either as donors of bone marrow cells for the exogenous spleen colony assay, or as irradiated recipients for the exogenous or endogenous colony assay. The colony counts were in either case suppressed by overcrowding that lasted up to 2 weeks or so before the assay, and were slightly stimulated by prolonged exposure. Neuroendocrine mechanisms affecting the microenvironment, the proliferation rate, and/or the recirculation of hemopoietic cells, were discussed as an alternative to more conventional explanations (e.g., reduced nutrition, increased bacterial load).