Resumo

Objectives: In mammals, environmental enrichment increased hippocampal neurogenesis and attenuated defensive responses to stressful stimuli. Nevertheless, data on these relationships in non-mammal vertebrates are lacking. Doublecortin immunoreactive cells (DCXirc), usually migrating-newly- born neurons in developing or adult brain, were examined in the hippocampus of pigeons housed at standard (SE) or enrichment environment (EE) and correlated to tonic immobility (TI), a defensive behavior in the domestic pigeon. Methods: 29 pigeons (Columba livia, male, 8-10 month old, 380-480g bw) homed for 40 days in SE visually isolated (SEi, n=6); or in SE with visual contact (SEc, n=5); or in SE outdoor (SEo, n=6); or in EE with visual contact (EEc, n=6) or in Communally housed outdoor (Co, n=6) had their time in TI recorded. Immediately after, SEi and EEc animals were euthanized and their brains were immunohystochemically processed to reveal DCXirc. Results: Compared to the number DCXirc in hippocampus of SEi, EEc group had significant 2-fold increase (T-test, p<0.05; mean+SEM: 55.3+6.7 cells/section, 106.7+34.4 cells/section). No correlation was found between the hippocampal DCXirc and TI response. The number of attempts to obtain immobility or in TI duration was similar among the groups. Conclusions: Alike mammals, EE increased the number of immature cells in the hippocampus of C. livia, however, it did not affect the defensive behavior TI. The data suggest that, even though the influence of environmental conditions on the newly born neurons of adult hippocampus seem to be common attribute to birds and mammals, their behavioral consequences may be taxa-specific in these amniotes.