Microglia target synaptic sites early during excitatory circuit disassembly in neurodegeneration.

During development, microglia prune excess synapses to refine neuronal circuits. In neurodegeneration, the role of microglia-mediated synaptic pruning in circuit remodeling and dysfunction is important for developing therapies aimed at modulating microglial function. Here we analyzed the role of microglia in the synapse disassembly of degenerating postsynaptic neurons in the inner retina. After inducing transient intraocular pressure elevation to injure retinal ganglion cells, microglia increase in number, shift to ameboid morphology, and exhibit greater process movement. Furthermore, due to the greater number of microglia, there is increased colocalization of microglia with synaptic components throughout the inner plexiform layer and with excitatory synaptic sites along individual ganglion cell dendrites. Microglia depletion partially restores ganglion cell function, suggesting that microglia activation may be neurotoxic in early neurodegeneration. Our results demonstrate the important role of microglia in synapse disassembly in degenerating circuits, highlighting their recruitment to synaptic sites early after neuronal injury.

Scalable method for micro-CT analysis enables large scale quantitative characterization of brain lesions and implants.

Anatomic evaluation is an important aspect of many studies in neuroscience; however, it often lacks information about the three-dimensional structure of the brain. Micro-CT imaging provides an excellent, nondestructive, method for the evaluation of brain structure, but current applications to neurophysiological or lesion studies require removal of the skull as well as hazardous chemicals, dehydration, or embedding, limiting their scalability and utility. Here we present a protocol using eosin in combination with bone decalcification to enhance contrast in the tissue and then employ monochromatic and propagation phase-contrast micro-CT imaging to enable the imaging of brain structure with the preservation of the surrounding skull. Instead of relying on descriptive, time-consuming, or subjective methods, we develop simple quantitative analyses to map the locations of recording electrodes and to characterize the presence and extent of hippocampal brain lesions.

Biolistic Labeling of Retinal Ganglion Cells.

Labeling of cellular structures is of fundamental importance in the investigation of diseases of the central nervous system. Biolistic labeling of retinal ganglion cells (RGCs) allows visualization of dendritic and synaptic structures of RGCs in retinal explants from animal models of experimental glaucoma. This technique sparsely labels RGCs, and, due to the stochastic nature of the particle delivery, all RGC types can be potentially observed in the labeled tissue. Quantification of dendritic and synaptic properties permits examination of the specific alterations to RGC morphology at different stages of degeneration, such as dendritic shrinkage and excitatory synapse loss.