The cellular and synaptic location of activated TrkB in mouse hippocampus during limbic epileptogenesis

Abstract

Understanding the mechanisms of limbic epileptogenesis in cellular and molecular terms may provide novel therapeutic targets for its prevention. The neurotrophin receptor, tropomyosinrelated kinase B (TrkB), is thought to be critical for limbic epileptogenesis. Enhanced activation of TrkB, revealed by immunodetection of enhanced phosphorylated TrkB (pTrkB), a surrogate measure of its activation, has been identified within hippocampus in multiple animal models. Knowledge of the cellular locale of activated TrkB is necessary to elucidate its functional consequences. Using an antibody selective to pTrkB in conjunction with confocal microscopy and cellular markers, we determined the cellular and subcellular locale of enhanced pTrkB induced by status epilepticus (SE) evoked by infusion of kainic acid into the amygdala of adult mice. SE induced enhanced pTrkB immunoreactivity in two distinct populations of principal neurons within hippocampus, the dentate granule cells and CA1 pyramidal cells. Enhanced immunoreactivity within granule cells was found within mossy fiber axons and giant synaptic boutons. By contrast, enhanced immunoreactivity was found within apical dendritic shafts and spines of CA1 pyramidal cells. A common feature of this enhanced pTrkB at these cellular locales is its localization to excitatory synapses between excitatory neurons, presynaptically in the granule cells and postsynaptically in CA1 pyramidal cells. Long term potentiation (LTP) is one cellular consequence of TrkB activation at these excitatory synapses that may promote epileptogenesis.

Complex Network Analysis of CA3 Transcriptome Reveals Pathogenic and Compensatory Pathways in Refractory Temporal Lobe Epilepsy

“…The selected genes of the complex network for the FS group (FS-CO) encompass only high-hubs and VIPs ( Table 2 ). Three high-hubs – SDAD1 , NTKR2 and N-PAC (aliase GLYR1 ) – are respectively involved in brain-derived neurotrophic factor (BDNF)-induced hippocampal neurite outgrowth [80] , [81] , BDNF modulation of seizure severity and susceptibility [82] , [83] and epigenetic regulation of BDNF upon seizures [84] , [85] . The other three high-hubs are: CIAPIM1 , which is linked to apoptosis inhibition [86] , [87] ; JAK3 that is involved in the differentiation of neural precursor cells [88] and survival of CA3 pyramidal neurons [89] ; and DST , acting on neuronal cytoskeleton organization maintenance [90] .…”

Developmental pattern of the neuronal intermediate filament inaa in the zebrafish retina

“…Mouse anti‐GFP antibody (Millipore, Cat# MAB3580, RRID:AB_94936) was tested by incubating with GFP‐expressing mouse brain sections, followed by an Alexa Fluor 555‐conjugated secondary antibody, and was proven that endogenous GFP was seen to overlap with augmented fluorescence (Helgager et al, ). The antibody has been used to detect EGFP in the transfected COS7 cells (Liu and Chien, ).…”

Brain‐derived neurotrophic factor but not vesicular zinc promotes TrkB activation within mossy fibers of mouse hippocampus in vivo

“…MAB3420, RRID:AB_94855) were employed for colocalization experiments. Tau antibody is a specific marker of axons (Huber and Matus, ), and this particular antibody was previously found to colocalize with mossy fiber axons of dentate granule cells in a transgenic line of mice expressing GFP in a subset of these neurons (Feng et al, ; Helgager et al, ). The synapsin‐1 antibody used in this study has previously been employed for immunohistochemistry as a synaptic marker (Armstrong et al, ).…”

“…To this end, two strains of genetically modified mice were used: 1) a conditional knockout of BDNF which eliminates it from hippocampal dentate granule and CA3 pyramidal cells (He et al, ), and 2) a knockout of ZnT3 (Cole et al, ), which eliminates vesicular zinc from CNS neurons. We conducted immunohistochemical studies of TrkB activation in hippocampal mossy fiber axons and boutons using an antibody detecting phosphorylated tyrosine residue 816 (pY816) (Helgager et al, ) in wildtype and mutant mice.…”