trimethyltin-hydroxide and Brain-Injuries

Insulin-like growth factor-1 (IGF-1) protects neurons from apoptosis and in vivo offers neuroprotective support to hippocampal CA1 pyramidal neurons following ischemia or seizure. IGF-1 signals through IGF-1 receptors activating phosphytidylinositol 3-kinase (PI3K)/Akt or pMAPK pathways. IGF-1 can be induced with injury and microglia and astrocytes may serve as a source of this neurotrophic factor to promote neuronal survival. An acute systemic injection of trimethyltin (TMT; 2 mg/kg, ip) to mice induces apoptosis of dentate granule neurons within 24 h and a differential response of microglia with ramified microglia present in the CA-1 region. Using this model, we studied the role of IGF-1 in the survival of CA-1 pyramidal neurons under conditions of altered synaptic input due to changes in the dentate gyrus. Within 24 h of injection, IGF-1 mRNA levels were elevated in the hippocampus and IGF-1 protein detected in both astrocytes and microglia. IGF-1 was redistributed within the CA-1 neurons corresponding with an increase in cytoplasmic pAkt, elevated PKBalpha/Akt protein levels, and a decrease in the antagonist, Rho. pMAPK was not detected in CA-1 neurons and ERK2 showed a transient decrease followed by a significant increase, suggesting a lack of recruitment of the pMAPK signaling pathway for neuronal survival. In mice deficient for IGF-1, a similar level of apoptosis was observed in dentate granule neurons as compared to wildtype; however, TMT induced a significant level CA-1 neuronal death, further supporting a role for IGF-1 in the survival of CA-1 neurons.

Topics: Animals; Animals, Newborn; Brain Injuries; CA1 Region, Hippocampal; Caspase 3; Dentate Gyrus; Disease Models, Animal; Fluoresceins; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Glycoproteins; Insulin-Like Growth Factor I; Mice; Mice, Knockout; Microglia; Mitogen-Activated Protein Kinase Kinases; Nerve Tissue Proteins; Neurons; Oncogene Protein v-akt; Organic Chemicals; Seizures; Signal Transduction; Time Factors; Trimethyltin Compounds

Using a chemical-induced model of dentate granule (DG) cell death, cDNA microarray analysis was used to identify gene profiles from the laser-captured microdissected (LCM) hippocampal DG cell region versus the CA pyramidal cell layer (CA) from 21-day-old male CD1 mice injected with trimethyltin hydroxide (TMT; 3.0 mg/kg, i.p.). At 6 h post-TMT, lectin + microglia displaying a reactive morphology were in contact with active caspase 3+ neurons. By 18 h, amoeboid microglia and signs of phagocytosis, and a mild astrocytic response were present in the DG. There was no evidence of IgG extravasation in the hippocampus, or cell death and glial reactivity in the CA. Atlas 1.2K Clontech array detected 115 genes changed in the hippocampus with TMT and included genes associated with immediate-early responses, calcium homeostasis, cellular signaling, cell cycle, immunomodulation and DNA repair. Early responses localized to LCM DG samples consisted of elevations in inflammatory factors such as tumor necrosis factor-alpha and receptors, as well as MIP1alpha, CD14, CD18, and a decrease in factors associated with calcium buffering. By 18 h, in the DG, changes occurred in transcripts associated with apoptosis, cell adhesion, DNA repair, cell proliferation and growth. In the CA, a differential level of elevation was seen in CD86 antigen, zinc finger protein 38 and DNA damage inducible transcript 3. A significant number of genes was decreased at these early time points in both hippocampal regions.

Topics: Animals; Astrocytes; Brain Injuries; Caspase 3; Caspases; Cell Count; Cell Death; Disease Models, Animal; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hippocampus; Immunohistochemistry; Lasers; Lectins; Male; Mice; Microarray Analysis; Microdissection; Neurons; Phosphopyruvate Hydratase; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors; Trimethyltin Compounds

The proinflammatory cytokines tumor necrosis factor (TNFalpha), interleukin-1 (IL-1alpha), and interleukin-6 (IL-6) have been associated with various models of hippocampal damage. To examine their role in initiation of an acute hippocampal injury response, 21-day-old male CD-1 mice received an acute intraperitoneal (i.p.) injection of trimethyltin hydroxide (TMT; 2.0 mg/kg) to produce necrosis of dentate granule neurons, astrocyte, and microglia reactivity. Tremors and intermittent seizures were evident at 24 hr. Intercellular adhesion molecule-1 (ICAM-1), glial fibrillary acidic protein (GFAP), anti-apoptotic TNFalpha-inducible early response gene (A-20), macrophage inflammatory protein (MIP)-1alpha, TNFalpha, IL-1alpha, IL-6, and caspase 3 mRNA levels were significantly elevated. Pretreatment with the antioxidant, ebselen, decreased ICAM-1, A-20, and TNFbeta elevations. Pentoxifylline blocked elevations in A-20 and decreased elevations in GFAP mRNA levels. Neither prevented histopathology or behavioral effects. Intracisternal injection of TNFalpha-neutralizing antibody significantly inhibited both behavioral effects and histopathology. RNase protection assays showed that TMT-induced elevations in mRNA levels for ICAM-1, A-20, GFAP, MIP-1alpha, IL-1alpha, TNFalpha, TNFbeta, and caspase 3 were blocked by anti-TNFalpha. These data demonstrate a significant role for TNFalpha in an acute neuro-injury in the absence of contribution from infiltrating cells. The cerebellum shows limited if any damage after TMT; however, in combination with the i.c.v. injection, elevations were seen in GFAP and in EB-22, a murine acute-phase response gene homologous to the alpha (1)-antichymotrypsin gene. Elevations were similar for artificial cerebral spinal fluid and anti-IL-1alpha, and significantly increased with anti-TNFalpha, anti-IL-6, or the combination of antibodies. Responses seen in the cerebellum suggest synergistic interactions between the baseline state of the cell and manipulations in the cytokine environment. Data suggests a role for TNFalpha in the pathogenesis of hippocampal injury induced by TMT.

Topics: Animals; Antibodies; Azoles; Brain Injuries; Cerebellum; Cytokines; Disease Models, Animal; Drug Combinations; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hippocampus; Interleukin-1; Interleukin-6; Isoindoles; Lectins; Male; Mice; Mice, Inbred Strains; Microglia; Neuroprotective Agents; Neurotoxins; Nuclease Protection Assays; Organoselenium Compounds; Pentoxifylline; RNA, Messenger; Trimethyltin Compounds; Tumor Necrosis Factor-alpha