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1. Proportional loss of parvalbumin‐immunoreactive synaptic boutons and granule cells from the hippocampus of sea lions with temporal lobe epilepsy

   https://doi.org/10.1002/cne.24680  

   Cameron, Starr ; Lopez, Ariana ; Glabman, Raisa ; Abrams, Emily ; Johnson, Shawn ; Field, Cara ; Gulland, Frances M. D. ; Buckmaster, Paul S. ( March 2019 , Journal of Comparative Neurology)

   One in 26 people develop epilepsy and in these temporal lobe epilepsy (TLE) is common. Many patients display a pattern of neuron loss called hippocampal sclerosis. Seizures usually start in the hippocampus but underlying mechanisms remain unclear. One possibility is insufficient inhibition of dentate granule cells. Normally parvalbumin‐immunoreactive (PV) interneurons strongly inhibit granule cells. Humans with TLE display loss of PV interneurons in the dentate gyrus but questions persist. To address this, we evaluated PV interneuron and bouton numbers in California sea lions (Zalophus californianus) that naturally develop TLE after exposure to domoic acid, a neurotoxin that enters the marine food chain during harmful algal blooms. Sclerotic hippocampi were identified by the loss of Nissl‐stained hilar neurons. Stereological methods were used to estimate the number of granule cells and PV interneurons per dentate gyrus. Sclerotic hippocampi contained fewer granule cells, fewer PV interneurons, and fewer PV synaptic boutons, and the ratio of granule cells to PV interneurons was higher than in controls. To test whether fewer boutons was attributable to loss versus reduced immunoreactivity, expression of synaptotagmin‐2 (syt2) was evaluated. Syt2 is also expressed in boutons of PV interneurons. Sclerotic hippocampi displayed proportional losses of syt2‐immunoreactive boutons, PV boutons, and granule cells. There was no significant difference in the average numbers of PV‐ or syt2‐positive boutons per granule cell between control and sclerotic hippocampi. These findings do not address functionality of surviving synapses but suggest reduced granule cell inhibition in TLE is not attributable to anatomical loss of PV boutons.

    

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2. Synapsins regulate brain‐derived neurotrophic factor‐mediated synaptic potentiation and axon elongation by acting on membrane rafts

   https://doi.org/10.1111/ejn.13552  

   Kao, Hung‐Teh ; Ryoo, Kanghyun ; Lin, Albert ; Janoschka, Stephen R. ; Augustine, George J. ; Porton, Barbara ; Kano, ed., Masanobu ( March 2017 , European Journal of Neuroscience)

   In neurons, intracellular membrane rafts are essential for specific actions of brain‐derived neurotrophic factor (BDNF), which include the regulation of axon outgrowth, growth cone turning and synaptic transmission. Virtually, all the actions ofBDNFare mediated by binding to its receptor, TrkB. The association of TrkB with the tyrosine kinase, Fyn, is critical for its localization to intracellular membrane rafts. Here, we show that synapsins, a family of highly amphipathic neuronal phosphoproteins, regulate membrane raft lipid composition and consequently, the ability ofBDNFto regulate axon/neurite development and potentiate synaptic transmission. In the brains of mice lacking all synapsins, the expression of bothBDNFand TrkB were increased, suggesting thatBDNF/TrkB‐mediated signaling is impaired. Consistent with this finding, synapsin‐depleted neurons exhibit altered raft lipid composition, deficient targeting of Fyn to rafts, attenuated TrkB activation, and abrogation ofBDNF‐stimulated axon outgrowth and synaptic potentiation. Conversely, overexpression of synapsins in neuroblastoma cells results in corresponding reciprocal changes in raft lipid composition, increased localization of Fyn to rafts and promotion ofBDNF‐stimulated neurite formation. In the presence of synapsins, the ratio of cholesterol to estimated total phospholipids converged to 1, suggesting that synapsins act by regulating the ratio of lipids in intracellular membranes, thereby promoting lipid raft formation. These studies reveal a mechanistic link betweenBDNFand synapsins, impacting early development and synaptic transmission.

    

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3. Genetic inactivation of synaptosomal‐associated protein 25 (SNAP‐25) in adult hippocampal neural progenitors impairs pattern discrimination learning but not survival or structural maturation of newborn dentate granule cells

   https://doi.org/10.1002/hipo.23008  

   Gustus, Kymberly C. ; Li, Lu ; Chander, Praveen ; Weick, Jason P. ; Wilson, Michael C. ; Cunningham, Lee Anna ( November 2018 , Hippocampus)

   Adult neurogenesis is necessary for proper cognition and behavior, however, the mechanisms that underlie the integration and maturation of newborn neurons into the pre‐existing hippocampal circuit are not entirely known. In this study, we sought to determine the role of action potential (AP)‐dependent synaptic transmission by adult‐generated dentate granule cells (DGCs) in their survival and function within the existing circuitry. We used a triple transgenic mouse (NestinCreER^T2:Snap25^fl/fl: tdTomato) to inducibly inactivate AP‐dependent synaptic transmission within adult hippocampal progenitors and their progeny. Behavioral testing in a hippocampal‐dependent A/B contextual fear‐discrimination task revealed impaired discrimination learning in mice harboring SNAP‐25‐deficient adult‐generated dentate granule cells (DGCs). Despite poor performance on this neurogenesis‐dependent task, the production and survival of newborn DGCs was quantitatively unaltered in tamoxifen‐treated NestinCreER^T2:Snap25^fl/fl: tdTomato SNAP compared to tamoxifen‐treated NestinCreER^T2:Snap25^wt/wt: tdTomato control mice. Although SNAP‐25‐deficient adult DGCs displayed a small but statistically significant enhancement in proximal dendritic branching, their overall dendritic length and distal branching complexity was unchanged. SNAP‐25‐deficient newborn DGCs also displayed robust efferent mossy fiber output to CA3, with normal linear density of large mossy fiber terminals (LMTs). These studies suggest that AP‐dependent neurotransmitter release by newborn DGCs is not essential for their survival or rudimentary structural maturation within the adult hippocampus.

    

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4. Genetic and physical interactions between the organellar mechanosensitive ion channel homologs MSL 1, MSL 2, and MSL 3 reveal a role for inter‐organellar communication in plant development

   https://doi.org/10.1002/pld3.124  

   Lee, Josephine S. ; Wilson, Margaret E. ; Richardson, Ryan A. ; Haswell, Elizabeth S. ( March 2019 , Plant Direct)

   Plant development requires communication on many levels, including between cells and between organelles within a cell. For example, mitochondria and plastids have been proposed to be sensors of environmental stress and to coordinate their responses. Here we present evidence for communication between mitochondria and chloroplasts during leaf and root development, based on genetic and physical interactions between threeMechanosensitive channel ofSmall conductance‐Like (MSL) proteins fromArabidopsis thaliana.MSLproteins areArabidopsishomologs of the bacterialMechanosensitivechannel ofSmall conductance (MscS), which relieves cellular osmotic pressure to protect against lysis during hypoosmotic shock.MSL1 localizes to the inner mitochondrial membrane, whileMSL2 andMSL3 localize to the inner plastid membrane and are required to maintain plastid osmotic homeostasis during normal growth and development. In this study, we characterized the phenotypic effect of a genetic lesion inMSL1, both in wild type and inmsl2 msl3mutant backgrounds.msl1single mutants appear wild type for all phenotypes examined. The characteristic leaf rumpling inmsl2 msl3double mutants was exacerbated in themsl1 msl2 msl3triple mutant. However, the introduction of themsl1lesion into themsl2 msl3mutant background suppressed othermsl2 msl3mutant phenotypes, including ectopic callus formation, accumulation of superoxide and hydrogen peroxide in the shoot apical meristem, decreased root length, and reduced number of lateral roots. All these phenotypes could be recovered by molecular complementation with a transgene containing a wild type version ofMSL1. In yeast‐based interaction studies,MSL1 interacted with itself, but not withMSL2 orMSL3. These results establish that the abnormalities observed inmsl2 msl3double mutants is partially dependent on the presence of functionalMSL1 and suggest a possible role for communication between plastid and mitochondria in seedling development.

    

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5. Induction of Temporal Lobe Epilepsy in Mice with Pilocarpine

   https://doi.org/10.21769/BioProtoc.3533  

   Arshad, M ; Naegele, J. ( January 2020 , Bioprotocol)

   null (Ed.)

   In the pilocarpine model of temporal lobe epilepsy (TLE) in rodents, systemic injections of pilocarpine induce continuous, prolonged limbic seizures, a condition termed “Status Epilepticus” (SE). With appropriate doses, many inbred strains of mice show behavioral seizures within an hour after pilocarpine is injected. With the behavioral scoring system based on a modification of the original Racine scale, one can monitor the seizures behaviorally, as they develop into more prolonged seizures and SE. SE is typically associated with damage to subsets of hippocampal neurons and other structural changes in the hippocampus and generally subsides on its own. However, more precise control of the duration of SE is commonly achieved by injecting a benzodiazepine into the mouse 1 to 3 h after the onset of SE to suppress the seizures. Several days following pilocarpine-induced SE, electrographic and behavioral seizures begin to occur spontaneously. The goal of this protocol is to reliably generate mice that develop spontaneous recurrent seizures (SRS) and show the typical neuropathological changes in the brain characteristic of severe human mesial temporal lobe epilepsy (mTLE), without high mortality. To reduce mortality, multiple subthreshold injections of pilocarpine are administered, which increases the percentage of mice developing SE without concomitant mortality. Precise control of the duration of SE (1 or 3 h) is achieved by suppressing SE with the benzodiazepine Midazolam (Versed). We have found that this protocol is an efficient means for generating mice that subsequently develop characteristics of human mTLE including high-frequency interictal spike and wave activity and SRS. In addition, we and others have shown that this protocol produces mice that show excitotoxic cell death of subsets of hippocampal GABAergic interneurons, particularly in the dentate gyrus and compensatory sprouting of excitatory projections from dentate granule cells (mossy fiber sprouting). Aspects of this protocol have been described in several of our previous publications. 

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