Toward a self-wired active reconstruction of the hippocampal trisynaptic loop: DG-CA3

Abstract

The mammalian hippocampus functions to encode and retrieve memories by transiently changing synaptic strengths, yet encoding in individual subregions for transmission between regions remains poorly understood. Toward the goal of better understanding the coding in the trisynaptic pathway from the dentate gyrus (DG) to the CA3 and CA1, we report a novel microfabricated device that divides a micro-electrode array into two compartments of separate hippocampal network subregions connected by axons that grow through 3 × 10 × 400 μm tunnels. Gene expression by qPCR demonstrated selective enrichment of separate DG, CA3, and CA1 subregions. Reconnection of DG to CA3 altered burst dynamics associated with marked enrichment of GAD67 in DG and GFAP in CA3. Surprisingly, DG axon spike propagation was preferentially unidirectional to the CA3 region at 0.5 m/s with little reverse transmission. Therefore, select hippocampal subregions intrinsically self-wire in anatomically appropriate patterns and maintain their distinct subregion phenotype without external inputs.

Narrow microtunnel technology for the isolation and precise identification of axonal communication among distinct hippocampal subregion networks

“…Directional propagation from DG to CA3 was 64, 67 and 64% of paired spikes from 2.5, 5 and 10 μm tunnels, respectively. This directionality is in agreement with previous results in 10 μm wide tunnels [8]. From 2.5, 5 and 10 μm tunnels, we detected insignificantly different average speeds of 0.43 ± 0.04, 0.48 ± 0.05 and 0.38 ± 0.02 m/s respectively in the predominant direction (DG->CA3) (F(2,46) = 2.05, p = 0.14).…”

Morphological and functional characterization of human induced pluripotent stem cell‐derived neurons (iCell Neurons) in defined culture systems

“…All cultures examined were negative for the upper layer marker, SATB2, suggesting the remaining cells did not possess an upper layer cortical phenotype. The presence of a significant number of upper and lower level pyramidal markers which are stable in culture would be beneficial for investigators looking to model complex layered brain architecture such as that of the CA1 region of the hippocampus . However, given that the examined cultures were almost 99% positive for MAP2 but only 44% positive for CTIP2, there remains some ambiguity as to the specific neuronal identity of a significant proportion of these iCell neurons.…”

“…The presence of a significant number of upper and lower level pyramidal markers which are stable in culture would be beneficial for investigators looking to model complex layered brain architecture such as that of the CA1 region of the hippocampus. 22,23 However, given that the examined cultures were almost 99% positive for MAP2 but only 44% positive for CTIP2, there remains some ambiguity as to the specific neuronal identity of a significant proportion of these iCell neurons. Further in-depth characterization of these neurons would be useful for a complete understanding of the phenotypic origin of the cell sub-populations.…”

Recording Large Extracellular Spikes in Microchannels along Many Axonal Sites from Individual Neurons

“…Dworak and Wheeler created a five-compartment structure interconnected by channels placed on top of several long electrodes that monitored action potential propagation direction and velocity [ 38 ]. A number of groups have integrated commercial multi-electrode array (MEA) systems featuring 60 low-density electrodes with commercial or custom microfluidic devices in order to functionally connect cultures of either one cell type or to create co-cultures of different cell types [ 39 – 41 ]. Brewer et al demonstrated self orientation when co-culturing different areas of the hippocampus [ 41 ].…”