Effects of environmental stimuli on immunoreactivity: further studies on passive avoidance behavior

Rats were immunized against sheep red blood cells (SRBC) immediately after the passive avoidance test; 5 days later the antibody response was measured by determining the number of splenic antibody-secreting B cells. Subjection of rats to habituation trials in the passive avoidance apparatus (apparatus control group) resulted in an enhanced number of antibody secreting cells compared to rats that remained in their home cage. The same phenomenon was observed in rats that were immunized immediately after the learning trial (electric footshock). In animals that showed passive avoidance behavior when tested for retention 24 h after the learning trial, the initially enhanced immune response was down-regulated to the level of rats that remained in their home cage or even lower. The above-mentioned alteration in number of anti-SRBC antibody-secreting cells was only observed in rats that were immunized 15 min after the retention test. In rats that were immunized 1, 4, or 8 h after the retention test no alteration in primary antibody response was observed. In rats of the apparatus control group that were immunized immediately after the retention test an elevated primary antibody response was observed 4, 5, 6, and 7 days after immunization; thus, the changes in immune response were not the consequence of a delayed or accelerated induction of the anti-SRBC response. No change in the absolute number of leukocytes in peripheral blood was observed in the different experimental groups. Moreover, the observed differences in response were not caused by a shift in the percentage of total T, B, Th, or Ts/c cells. The alteration in primary antibody response was only observed in the spleen. The antibody titer in trunk blood did not differ among the different groups and no significant change in number of antibody-secreting cells in the parathymic lymph node was observed. These results show that rats can specifically register different environmental stimuli and as a consequence of that perception there is a change in antibody-secreting cells in the spleen.