Production of platelet-activating factor by chick retina.

In the present study it is demonstrated that platelet-activating factor (PAF) was produced by chick retinas, upon stimulation with neurotransmitters such as acetylcholine (ACh), dopamine, or with calcium ionophore A23187, but not upon stimulation with gamma-amino-n-butyric acid, L-glycine, L-glutamate, epinephrine, or histamine. PAF produced in response to ACh, dopamine, or A23187 was not released into supernatants but was extractable from retinas. The amounts of extractable PAF increased after sonication of stimulated retinas. While no PAF activity could be recovered from unstimulated retinas, small amounts of this lipid can be detected following sonication of the tissue. The amount of extractable PAF from ACh-, dopamine-, or A23187-stimulated retinas was dependent upon the incubation time and concentration of the agonists. PAF was identified on the basis of chemical and lipase treatments, biological activity with washed rabbit platelets, behavior on thin layer chromatography, and high pressure liquid chromatography. Control cell preparations (leukocytes, erythrocytes, and embryogenic fibroblasts) did not produce PAF upon neurotransmitter stimulation. ACh and dopamine promoted PAF production by increasing dithiothreitol-insensitive cholinephosphotransferase activity, without affecting the acetyltransferase activity. In contrast, the A23187 ionophore stimulated the acetyltransferase activity but did not affect the dithiothreitol-insensitive cholinephosphotransferase

Critical Role of PI3K/Akt/GSK3β in Motoneuron Specification from Human Neural Stem Cells in Response to FGF2 and EGF

Fibroblast growth factor (FGF) and epidermal growth factor (EGF) are critical for the development of the nervous system. We previously discovered that FGF2 and EGF had opposite effects on motor neuron differentiation from human fetal neural stem cells (hNSCs), but the underlying mechanisms remain unclear. Here, we show that FGF2 and EGF differentially affect the temporal patterns of Akt and glycogen synthase kinase 3 beta (GSK3β) activation. High levels of phosphatidylinositol 3-kinase (PI3K)/Akt activation accompanied with GSK3β inactivation result in reduction of the motor neuron transcription factor HB9. Inhibition of PI3K/Akt by chemical inhibitors or RNA interference or overexpression of a constitutively active form of GSK3β enhances HB9 expression. Consequently, PI3K inhibition increases hNSCs differentiation into HB9+/microtubule-associated protein 2 (MAP2)+ motor neurons in vitro. More importantly, blocking PI3K not only enhances motor neuron differentiation from hNSCs grafted into the ventral horn of adult rat spinal cords, but also permits ectopic generation of motor neurons in the dorsal horn by overriding environmental influences. Our data suggest that FGF2 and EGF affect the motor neuron fate decision in hNSCs differently through a fine tuning of the PI3K/AKT/GSK3β pathway, and that manipulation of this pathway can enhance motor neuron generation