Regulation of brain-derived neurotrophic factor messenger RNA levels in avian hypothalamic slice cultures

Mechanisms regulating the expression of brain-derived neurotrophic factor, a member of the neurotrophin family, have been extensively studied in the rat cerebral cortex, hippocampus and cerebellum. In contrast, little is known regarding the regulation of this growth factor in the hypothalamus. Here we present an analysis of the regulation of brain-derived neurotrophic factor messenger RNA levels in chick embryo hypothalamic slice cultures following exposure to potassium chloride, glutamate agonists and sex steroids. Following a week in chemically-defined media the tissue was depolarized by exposure to 50 mM potassium chloride for 6h, resulting in a significant 4.2-fold increase in the level of brain-derived neurotrophic factor messenger RNA. This result is consistent with studies of other brain regions. Similar 6-h acute exposures of the hypothalamic cultures to 25 microM N-methyl-D-aspartic acid, 25 microM kainic acid and 25 microM alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid also significantly increased messenger RNA levels 2.5-, 2.1- and 1.4-fold, respectively. It was previously reported that brain-derived neurotrophic factor levels within the rat cerebral cortex, olfactory bulb and hippocampus are altered by exposure to 17beta-estradiol. Here we show that in hypothalamic slice cultures neither acute nor chronic treatments with 10 and 100 nM 17beta-estradiol and 10nM testosterone significantly altered the steady-state level of this growth factor. These findings show that neuronal activity, induced by glutamate agonists and potassium chloride, can regulate brain-derived neurotrophic factor messenger RNA levels within embryonic hypothalamic slice cultures. This regulation could play a critical role in the modulation of programmed cell death and synaptic maturation during development of the hypothalamus.