Involvement of tachykinin NK1 receptor in the behavioral and immunological responses to swimming stress in mice.

This study investigated the influence of a selective tachykinin NK(1) receptor antagonist FK888 on the performance of mice in the elevated plus-maze test and on peripheral blood count after central treatment with substance P (SP) compared to animals submitted to a swim stress session. Percentage of time spent on open arms was significantly reduced by SP treatment as well as the percentage of entries into open arms and the number of head-dipping, indicating an anxiogenic-like profile of action to SP, as previously described. Nevertheless, SP did not affect the peripheral blood counting. The swim stress also promoted a marked reduction in the exploration of the open arms of the plus-maze as well as in the number of leukocytes, most notably lymphocytes. FK888 alone showed the reverse effect, i.e. an anxiolytic-like profile, increasing the frequency of entries and the time spent in the open arms, but did not affect the blood parameters used as an index of the immune system activity. Nevertheless, FK888 (100 pmol) inhibited the anxiogenic-like profile of SP and swimming stress and also prevented the effect promoted by the swimming stress on the immunological parameters, i.e., the reduction in the number of peripheral leukocytes. These findings are discussed in terms of the interaction between the CNS and the immune system and the involvement of the tachykininergic system.