Expression of brain-derived neurotrophic factor in the rat forebrain and upper brain stem during postnatal development: an immunohistochemical study

The present study was undertaken to characterize the regional and temporal patterns of brain-derived neurotrophic factor (BDNF) in the rat forebrain and upper brain stem during postnatal development using an immunohistochemical approach. Results indicated that BDNF-immunoreactive (IR) cells could be divided into three groups based on their postnatal developmental patterns: (group 1) BDNF-IR cells were first detected between postnatal days (PND) 1 and 7, and thereafter they increased in number and remained stable during later stages of ontogeny; (group 2) BDNF-IR cells progressively increased in number with age, and then decreased in adults; (group 3) numerous BDNF-IR cells detected between PND 1 and 7 showed a dramatic reductions in number with few IR cells in adults. In contrast, the developmental pattern of most BDNF-IR fibers differed from that of IR neurons, i.e. they appeared between PND 1-28 and thereafter continued to increase in number showing a maximum level in adults. Additionally, BDNF-IR cells in the superficial layer of the neocortex and IR fibers in the stratum oriens of CA2 first appeared as late as PND 28 and in adults, respectively. After colchicine treatment, reexpression or a marked increase in the number of BDNF-IR neurons was observed in many areas of the adult brain where a progressive decrease in BDNF-IR cell numbers during development and scant or some IR neurons in adults were shown. These results showed both transient and persistent expression of BDNF in various regions of the developing rat brain.