Rapid stimulatory effects of brain-derived neurotrophic factor and neurotrophin-3 on somatostatin release and intracellular calcium rise in primary hypothalamic cell cultures
F. Marmigere et al., Rapid stimulatory effects of brain-derived neurotrophic factor and neurotrophin-3 on somatostatin release and intracellular calcium rise in primary hypothalamic cell cultures, NEUROENDOCR, 74(1), 2001, pp. 43-54
Although the long-lasting effects of neurotrophins have been extensively st
udied, less data are available on their rapid effects, especially on peptid
e release. In the present report, we investigated rapid effects of neurotro
phins on somatostatin release and on intracellular calcium concentration (I
Ca2+](i)) in primary cultures of hypothalamic neurons. RT-PCR experiments r
evealed mRNA expression of the three high-affinity neurotrophin receptors t
yrosine kinase (Trk) TrkA, TrkB and TrkC, indicating potential responses to
their preferential ligands: nerve growth factor (NGF), brain-derived neuro
trophic factor (BDNF) and neurotrophin 3 (NT-3), respectively. We demonstra
ted that BDNF, and to a lesser extent NT-3, induced significant time- and c
oncentration-dependent somatostatin release, while NGF was devoid of any ef
fect. BDNF or NT-3 induction of somatostatin release was inhibited by the T
rk inhibitors K-252a and genistein, whereas K-252b, a less effective inhibi
tor, had no effect. BDNF- and NT-3-induced somatostatin release depended up
on extra- and intracellular Ca2+ since it was completely abolished in the p
resence of the Ca2+ chelators BAPTA (bis-(alpha -aminophenoxy)-ethane-N,N,N
' ,N ' -tetraacetic acid) or BAPTA-AM (bis-(alpha -aminophenoxy)ethane-N,N
,N ' ,N ' -tetraacetoxymethylester respectively. In addition, BDNF and NT-3
induced a sustained and rapid increase in [Ca2+](i) which depended on the
extracellular Ca2+ concentration. MK-801 (dizocilpine) and tetrodotoxin (TT
X) entirely blocked neurotrophin-evoked somatostatin release and [Ca2+](i)
rise in response to BDNF and NT-3 application in most neurons. Neurotrophin
-induced [Ca2+](i) rise was completely blocked by K-252a. The present resul
ts are consistent with: (1) an indirect effect of neurotrophins on somatost
atin release via endogenous glutamate release and subsequent NMDA receptor
activation, (2) a major indirect effect of neurotrophins on Ca2+ rise in hy
pothalamic neurons which very likely occurs through NMDA receptor activatio
n. Taken altogether, these results indicate that BDNF and NT-3 can rapidly
affect the activity of hypothalamic neurons. Copyright (C) 2001 S. Karger A
G, Basel.