Mechanism of isoprenaline-stimulated diacylglycerol formation in rat parotid acinar cells

Alterations in hippocampal GAP-43, BDNF, and L1 following sustained cerebral ischemia

Alterations in factors involved in the regeneration of the neuronal network in the hippocampus of rats with microsphere embolism (ME) were examined. Nine hundred microspheres (48 microm in diameter) were injected into the right hemisphere, and immunochemical and immunohistochemical studies on the hippocampus were performed on the seventh day thereafter. Hematoxylin-eosin staining showed progressive and severe degeneration of the hippocampus after ME. The protein levels of brain-derived neurotrophic factor (BDNF), 43-kDa growth-associated protein (GAP-43), and adhesion protein L1 (L1) in the ipsilateral hippocampus of the ME animal, determined by Western blot analysis or enzyme immunoassay, were increased, unaltered, and decreased, respectively. In contrast, the immunohistochemical study showed increases in a marker of axonal sprouting GAP-43, and a neurotrophic factor BDNF, and a decrease in an adhesion molecule L1 in some areas of the hippocampal ischemic penumbra of such animals. These results suggest that some factors for regeneration of the neuronal network in the ischemic penumbra responded to sustained cerebral ischemia for a certain period, although functional network of the nerve cells in the microsphere-injected hemisphere would be unlikely established after ME.

Altered extracellular signal-regulated kinase signal transduction by the muscarinic acetylcholine and metabotropic glutamate receptors after cerebral ischemia

To determine whether muscarinic acetylcholine receptors (mAChR) in the post-ischemic hippocampus may be involved in altered extracellular signal-regulated kinases (ERK) signal transduction, we have investigated changes in the activity of ERK1/2 induced by a muscarinic agonist, carbachol. Cerebral ischemia was produced in the rat by injecting 900 microspheres (48 microm in diameter) into the right internal carotid artery. Applying carbachol to the contralateral hippocampal slices from ischemic rats increased the phosphorylation of ERK1/2 but did not increase phosphorylation in the ipsilateral hippocampus. Analysis of M(1) mAChR binding showed that there was no significant difference in the number and K(d) values between the hippocampi from naïve and ischemic rats. Immunoblotting analysis showed no significant difference in the amount of M(1) mAChR in both hemispheres. In contrast to carbachol stimulation, the protein kinase C activator induced an activation of ERK1/2 in the ipsilateral hippocampus. This increase was shown to occur in neurons by immunofluorescence colocalization study. Carbachol-stimulated tyrosine phosphorylation of the G alpha(q/11), inositol 1,4,5-trisphosphate formation, and association of G alpha(q/11) with phospholipase C beta 1 were attenuated in the ipsilateral hippocampus. We also found that stimulation of group I metabotropic glutamate receptors, which are linked to G alpha(q/11), failed to increase in phosphorylation of ERK1/2 in the ipsilateral hippocampus. These results suggest that failure in receptor-mediated tyrosine phosphorylation of the G alpha(q/11) subunit and a defect in receptor-G alpha(q/11-)effector coupling in the ischemic hippocampus may be involved in alterations of ERK signal transduction.