Repetitive nociceptive stimuli in newborn rats do not alter the hippocampal neurogenesis

The aim of this study was to evaluate the effects of acute repetitive nociceptive stimuli to newborn rats over neurogenesis rate in the dentate gyrus of hippocampus. Newbom rats were randomly distributed in three groups, according to the type of stimulus received from d 1 to d 7 of life four times per day: acute nociceptive stimuli, tactile stimuli, and none (controls). At d 21 of life, rats received BrdU (5-bromo-2'-deoxyuridine, a marker of cell proliferation), and on d 28, they were killed. After brain sectioning, the tissue was processed for immunohistochemical identification of proliferating cells. BrdU-positive cell counts were performed in the granule cell layer of the dentate gyrus. Acute nociceptive stimulation during the first week of life was not associated to alterations in the weight gain among experimental groups. On examination 1 wk after BrdU injection, the number of BrdU-labeled cells in the dentate gyrus of the hippocampus was not significantly different between stimulated (painful and tactile stimuli) and nonstimulated animals. These results show that both types of stimuli used here, when applied very early in the development, do not affect the neurogenesis rate in the rat dentate gyrus.