ABSTRACT
Stimulation of cell proliferation and neurogenesis in the adult dentate gyrus has been observed after focal and global brain ischemia but only little is known about the underlying mechanisms. We here analyzed neurogenesis in the dentate gyrus after small cortical infarcts leaving the hippocampal formation and subcortical regions intact. Using the photothrombosis model in adult rats, focal ischemic infarcts were induced in different cortical areas (sensorimotor forelimb and hindlimb cortex) and proliferating cells were labeled at days 3-14 after infarct induction with bromodeoxyuridine. At 2, 4, and 10 weeks after ischemia, immunocytochemistry was performed with immature neuronal (doublecortin), mature neuronal (neuronal nuclei antigen) and glial (calcium-binding protein beta S100beta) markers. When compared with sham-operated controls, animals with infarcts in the forelimb as well as hindlimb cortex revealed an increase in survival of newborn progenitor cells at four and 10 weeks after the insult with predominance at the ipsilateral side. Triple immunofluorescence and confocal laser scanning microscopy revealed an increase in neurogenesis in all groups that was more pronounced 10 weeks after the infarct. Application of the N-methyl-D-aspartate (NMDA)-receptor antagonist MK-801 during lesion induction significantly enhanced neurogenesis in the dentate gyrus. An even stronger increase in newborn neurons was observed after anti-inflammatory treatment with indomethacine during the first 16 days of the experiment. The present study demonstrates that small cortical infarcts leaving subcortical structures intact increase neurogenesis in the dentate gyrus and that these processes can be stimulated by N-methyl-D-aspartate receptor blockade and anti-inflammatory treatment.
Subject(s)
Anti-Inflammatory Agents/pharmacology , Cerebral Infarction/pathology , Dentate Gyrus/drug effects , Dentate Gyrus/pathology , Excitatory Amino Acid Antagonists/pharmacology , Nerve Regeneration/drug effects , Neurons/pathology , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Animals , Antimetabolites , Bromodeoxyuridine , Cell Survival/drug effects , Dizocilpine Maleate/pharmacology , Doublecortin Protein , Hindlimb/innervation , Immunohistochemistry , Indomethacin/pharmacology , Male , Motor Cortex/drug effects , Motor Cortex/pathology , Neural Pathways/pathology , Neurons/drug effects , Rats , Rats, Wistar , S100 Proteins/metabolism , Somatosensory Cortex/drug effects , Somatosensory Cortex/pathology , Thrombosis/pathologyABSTRACT
Electrophysiological studies in humans and animal models have revealed an intrinsic epileptogenicity of cortical dysplasias which are a frequent cause of drug-resistant epilepsy. An imbalance of inhibition and excitation has been causative related. Receptor-binding studies in rodents demonstrated reduced binding to GABA and increased binding to glutamate receptors within cortical dysplasias and increments of AMPA- and kainate-receptor binding in its surround. Immunohistochemically a differential downregulation of GABA(A) receptor subunits could be demonstrated in widespread areas within and around dysplasias. As receptor binding critically depends on receptor subunit composition the observed changes in binding properties might be related to this. Here, we immunohistochemically analyzed the regional expression of four NMDA receptor subunits and two major AMPA- and kainate-receptor complexes in adult rats after neonatal freeze lesions. These lesions are characterized by a three- to four-layered cortex and a microsulcus which mimic human polymicrogyria. Using antibodies against NR1, NR2A, NR2B, NR2D, GluR2,3, and GluR5,6,7 receptor subunits we demonstrated a pronounced disturbance of cortical immunostaining pattern in the cortical malformation. These changes reflected the structural disorganization of the microgyrus with some distortion of the apical dendrites of paramicrogyral pyramidal cells, a decrease and disorganization of cells at the bottom of the microsulcus, and an inflection of apical dendrites toward the microsulcus. The neuronal staining pattern of large pyramidal cells in the neighborhood of the dysplasia did not differ for any subunit investigated. No remote or widespread changes of glutamate-receptor subunit distribution could be detected. The lack of gross and/or widespread alterations of glutamate-receptor subunit distribution in the surround of focal cortical dysplasia suggests the presence of other or additional mechanisms underlying the increased excitatory neurotransmitter binding and excitability in cortical malformations.
