Biochemical and immunohistochemical demonstration of a tightly bound form of prostaglandin E 2 in the rat brain

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Basal levels of prostaglandin E 2 in the rat brain were determined by radioimmunoassay to be 0.68–0.79 pmol/g brain. About one-third of the prostaglandin E 2 (0.23–0.28 pmol/g) was resistant to extraction with ethanol, but could be recovered with a mixture of ethanol and 1 N HC1 (9:1, v/v), indicating that a tightly bound form of prostaglandin E 2 exists in the brain. The amount of the bound form of prostaglandin E 2 was almost unchanged by pentylenetetrazole-induced convulsion or by transcardial perfusion with a formaldehyde solution, although these treatments resulted in 40- to 80-fold increases in prostaglandin E 2 content extracted with ethanol at neutral pH. A polyclonal antibody against prostaglandin E 2-albumin conjugates recognized the bound form of prostaglandin E 2, giving a punctate appearance in many neuronal cell bodies in the brain. Although almost all of the neuronal perikarya were immunoreactive for prostaglandin E 2, intense immunoreactivity was observed in the mitral cell layer of the olfactory bulb, layer V of the cerebral neocortex, anterodorsal and reticular nuclei of the thalamus, supraoptic, paraventricular, accessory neurosecretory and lateral mammillary nuclei of the hypothalamus, mesencephalic trigeminal nucleus, nucleus of the trapezoid body and deep cerebellar nuclei. When the cerebral neocortical regions were observed electron microscopically, immunoreaction products were seen as fine granules which were clustered into small patches in the cytoplasm of neuronal cell bodies and proximal dendrites. No immunoreaction products were seen in glial cells or endothelial cells. These results suggest that prostaglandin E 2 is involved in fundamental processes of neurons.