Biology subjects

Beeson, K. A.

Publications and source records attributed to Beeson, K. A..

2 recordsLinked to original sources

bioRxiv2023

Altered hippocampal activation in seizure-prone CACNA2D2 knockout mice

The voltage-gated calcium channel subunit 2{delta}-2 controls calcium-dependent signaling in neurons, and loss of this subunit causes epilepsy in both mice and humans. To determine whether mice without 2{delta}-2 demonstrate hippocampal activation or histopathological changes associated with seizure activity, we measured expression of the activity-dependent gene c-fos and various histopathological correlates of temporal lobe epilepsy in hippocampal tissue from wildtype (WT) and 2{delta}-2 knockout (CACNA2D2 KO) mice using immunohistochemical staining and confocal microscopy. Both genotypes demonstrated similarly sparse c-fos expression within the hippocampal dentate granule cell layer (GCL) at baseline, consistent with no difference in basal activity of granule cells between genotypes. Surprisingly, when mice were assayed 1 hour after handling-associated convulsions, KO mice had fewer c-fos-positive cells in the dentate gyrus, indicating that activity in the dentate gyrus actually decreased. However, the dentate was significantly more active in KO mice compared to WT after administration of a subthreshold pentylenetetrazole dose, consistent with increased susceptibility to proconvulsant stimuli. Other histopathological markers of temporal lobe epilepsy in these mice, including markers of neurogenesis, glial activation, and mossy fiber sprouting, were similar in WT and KO mice, apart from a small but significant increase in hilar mossy cell density, opposite to what is typically found in mice with temporal lobe epilepsy. This suggests that the differences in seizure-associated hippocampal function in the absence of 2{delta}-2 protein are likely due to altered functional properties of the network without associated structural changes in the hippocampus at the typical age of seizure onset. Significance StatementCalcium channel 2{delta} subunits play important roles in controlling neuronal circuit structure and function, and mutation of the 2{delta}-2 isoform of this protein is associated with spontaneous seizures. In this study, we find that seizures in 2{delta}-2 mutant mice involve altered hippocampal activation without substantial histopathological changes in hippocampal structure. This suggests that the differences in seizure-associated hippocampal function are likely due to altered functional properties of the network as well as to the contribution of additional brain regions to seizures in mice lacking this protein.

neuroscience↗

bioRxiv2019

α2δ-2 protein controls structure and function at the cerebellar climbing fiber synapse

2{delta} proteins (Cacna2d1-4) are auxiliary subunits of voltage-dependent calcium channels that also drive synapse formation and maturation. Because cerebellar Purkinje cells (PCs) only express one isoform of this family, 2{delta}-2 (Cacna2d2), we used PCs as a model system to examine roles of 2{delta} in excitatory synaptic function in a Cacna2d2 knockout mouse. Whole-cell recordings of PCs from acute cerebellar slices revealed altered climbing fiber (CF)-evoked complex spike generation, as well as increased amplitude and faster decay of CF-evoked excitatory postsynaptic currents (EPSCs). CF terminals in the KO were localized more proximally on PC dendrites, as indicated by VGLUT2+ immunoreactive puncta, and computational modeling demonstrated that the increased EPSC amplitude can be partly attributed to the more proximal location of CF terminals. In addition, CFs in KO mice exhibited increased multivesicular transmission, corresponding to greater sustained responses during repetitive stimulation, despite a reduction in the measured probability of release. Electron microscopy demonstrated that mutant CF terminals had twice as many vesicle release sites, providing a morphologic explanation for the enhanced glutamate release. Though KO CFs evoked larger amplitude EPSCs, the charge transfer was the same as wildtype as a result of increased glutamate re-uptake, producing faster decay kinetics. Together, the larger, faster EPSCs in the KO explain the altered complex spike responses, which degrade information transfer from PCs and likely contribute to ataxia in Cacna2d2 KO mice. Our results also illustrate the multidimensional synaptic roles of 2{delta} proteins. Significance Statement2{delta} proteins (Cacna2d1-4) regulate synaptic transmission and synaptogenesis, but co-expression of multiple 2{delta} isoforms has obscured a clear understanding of how various 2{delta} proteins control synaptic function. We focused on roles of the 2{delta}-2 protein (Cacna2d2), whose deletion causes cerebellar ataxia and epilepsy in mice and humans. Because cerebellar Purkinje cells only expresses this single isoform, we studied excitatory climbing fiber synaptic function onto Purkinje cells in Cacna2d2 knockout mice. Using optical and electrophysiological analysis, we provide a detailed description of the changes in Purkinje cells lacking 2{delta}-2, and provide a comprehensive mechanistic explanation for how functional synaptic phenotypes contribute to the altered cerebellar output.

neuroscience↗