Giant Y79 retinoblastoma cells contain functionally active T-type calcium channels.

Retinoblastoma is the most common malignant intraocular tumor in children. Y79 human retinoblastoma cells are in vitro models of retinal tumors used for drug screening. Undifferentiated Y79 cells originate from a primitive multi-potential neuroectodermal cell and express neuronal and glial properties. However, the nature of cellular heterogeneity in Y79 cells is unclear because functional methods to characterize neurons or glial cells have not been employed to Y79 cells. Here, we perform patch-clamp recordings to characterize electrophysiological properties in retinoblastoma cells. We identified a population of large-sized Y79 cells (i.e., giant cells, ~ 40-µm diameter), hyperpolarized resting membrane potential (-54 mV), and low input resistance (~ 600 MΩ), indicating electrically mature cells. We also found that giant Y79 cells contain increased density of T-type calcium channels. Finally, we found that T-type calcium channels are active only in giant cells suggesting that cancer treatments aimed to prevent calcium influx in retinoblastomas should be tested in giant cells.

Parvalbumin+ interneurons obey unique connectivity rules and establish a powerful lateral-inhibition microcircuit in dentate gyrus.

Parvalbumin-positive (PV+) GABAergic interneurons in hippocampal microcircuits are thought to play a key role in several higher network functions, such as feedforward and feedback inhibition, network oscillations, and pattern separation. Fast lateral inhibition mediated by GABAergic interneurons may implement a winner-takes-all mechanism in the hippocampal input layer. However, it is not clear whether the functional connectivity rules of granule cells (GCs) and interneurons in the dentate gyrus are consistent with such a mechanism. Using simultaneous patch-clamp recordings from up to seven GCs and up to four PV+ interneurons in the dentate gyrus, we find that connectivity is structured in space, synapse-specific, and enriched in specific disynaptic motifs. In contrast to the neocortex, lateral inhibition in the dentate gyrus (in which a GC inhibits neighboring GCs via a PV+ interneuron) is ~ 10-times more abundant than recurrent inhibition (in which a GC inhibits itself). Thus, unique connectivity rules may enable the dentate gyrus to perform specific higher-order computations.

Synaptic mechanisms of pattern completion in the hippocampal CA3 network.

The hippocampal CA3 region plays a key role in learning and memory. Recurrent CA3-CA3 synapses are thought to be the subcellular substrate of pattern completion. However, the synaptic mechanisms of this network computation remain enigmatic. To investigate these mechanisms, we combined functional connectivity analysis with network modeling. Simultaneous recording from up to eight CA3 pyramidal neurons revealed that connectivity was sparse, spatially uniform, and highly enriched in disynaptic motifs (reciprocal, convergence, divergence, and chain motifs). Unitary connections were composed of one or two synaptic contacts, suggesting efficient use of postsynaptic space. Real-size modeling indicated that CA3 networks with sparse connectivity, disynaptic motifs, and single-contact connections robustly generated pattern completion. Thus, macro- and microconnectivity contribute to efficient memory storage and retrieval in hippocampal networks.