preproenkephalin and Ischemic-Attack--Transient

Middle cerebral artery occlusion may result in increased activation of N-methyl-D-aspartate- or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type receptors by glutamate and lead to neuronal cell death. To characterize molecular events that precede cell death following transient focal ischemia, in situ hybridization histochemistry was used to measure levels of glutamate receptor subunit 1 (GluR1), GluR2, GluR3, N-methyl-D-aspartate receptor subunit 1 (NR1) and preproenkephalin messenger RNAs in adult rats at various recirculation times (1.5, 3 and 24 h) following a 90-min period of middle cerebral artery occlusion. At 1.5 and 3 h recirculation, autoradiography showed pronounced but differential decreases in AMPA, NR1 and preproenkephalin messenger RNA expression throughout the infarcted ipsilateral striatum. Non-uniform patterns of in situ hybridization grains emerged such that many striatal neurons were depleted of AMPA and preproenkephalin messenger RNAs, while others retained control levels. In cortical regions destined to undergo infarction, GluR2 and NR1 messenger RNAs were preferentially reduced relative to the contralateral side (to 75+/-8.5% and 66+/-4.5%, respectively); GluR1, GluR3 and preproenkephalin messenger RNAs were unaltered. At 24 h recirculation, depletion of striatal and cortical messenger RNAs became less selective. GluR3 and preproenkephalin messenger RNAs were up-regulated in ipsilateral spared regions of the striatum, and GluR1 and GluR2 messenger RNAs increased bilaterally in the cingulate cortex and in selective nuclei of the amygdala. Histological cell death or neurodegeneration was not detected in areas of reduced glutamate and preproenkephalin messenger RNA expression in either the ipsilateral striatum or cortex before 24 h. These findings suggest that complex and long-lasting decreases in messenger RNA expression occur prior to significant cell loss in regions destined to undergo infarction. Increased formation of Ca2+-permeable AMPA receptor assemblies may occur in "unspared" and "spared" regions via different mechanisms and contribute to alterations in post-ischemic synaptic activity. The possibility arises that there may be altered relationships between glutamatergic and enkephalin synapses, since the dorsolateral striatum, where preproenkephalin messenger RNA expression is acutely reduced, receives innervation by the affected ipsilateral cortical region.

Topics: Animals; Brain; Cerebral Infarction; Corpus Striatum; Down-Regulation; Enkephalins; Glutamic Acid; Ischemic Attack, Transient; Male; Neocortex; Nerve Degeneration; Neurons; Protein Precursors; Rats; Rats, Sprague-Dawley; RNA, Messenger; Tissue Distribution

The beneficial effects of exogenous kappa receptor agonists in preventing neuronal damage elicited by brain ischemia suggest a role for endogenous dynorphins. In agreement prodynorphin (PDYN) gene expression in granule cells of the dentate gyrus detected by in situ hybridization was drastically but transiently decreased 18-32 h after four-vessel cerebral ischemia for 20 min in rats. We propose that decreased dynorphin synthesis and release could contribute to the delayed neuronal death of hippocampal pyramidal cells in this model.

Topics: Animals; Dentate Gyrus; Enkephalins; Ischemic Attack, Transient; Male; Neurons; Protein Precursors; Rats; Rats, Wistar; Receptors, Opioid, kappa; RNA, Messenger

Astrocytic activation plays a major role in homeostatic maintenance of the central nervous system in response to neuronal damage. To assess the reactivity of astrocytes in transient cerebral ischemia of the gerbil, we studied the levels of glial fibrillary acidic protein (GFAP) and its mRNA. GFAP mRNA increased by 4 h after carotid artery occlusion, reached peak levels by 72 h with a 12-fold increase over control and then started declining as early as 96 h postischemia. An examination of the specific regions of the brain revealed an increase in GFAP mRNA associated with the forebrain, midbrain, hippocampus and striatum. GFAP mRNA in the non-ischemic cerebellum however, remained expressed at constitutively low levels. Immunoblot analysis with anti-GFAP antibodies demonstrated a 2- to 3-fold increase in the protein after 24 and 48 h of reperfusion. Pretreatment with pentobarbital and 1-(5'-oxohexyl)-3-methyl-7-propyl xanthine (HWA 285), the drugs that have been shown to protect against ischemic damage, prevented the increase in GFAP mRNA in the cortex following ischemic injury. Forebrain ischemia also induced vimentin mRNA and protein quantities by 12 h of reperfusion in the cortex. The levels of c-fos and preproenkephalin mRNA increased rapidly within 1 h after ischemic injury, demonstrating a temporal difference in mRNA changes following ischemia. These results indicate that an increase in GFAP and vimentin, the two glial intermediate filament proteins in the area of the ischemic lesion may be associated with a glial response to injury.

Topics: Animals; Astrocytes; Cerebral Cortex; Corpus Striatum; Enkephalins; Gene Expression; Gerbillinae; Glial Fibrillary Acidic Protein; Hippocampus; Ischemic Attack, Transient; Male; Protein Precursors; Proto-Oncogene Proteins c-fos; RNA, Messenger; Vimentin