Biology subjects

Udakis, M.

Publications and source records attributed to Udakis, M..

3 recordsLinked to original sources

bioRxiv2024

Hippocampal OLM interneurons regulate CA1 place cell plasticity and remapping

OLM interneurons selectively target inhibition to the distal dendrites of CA1 pyramidal cells in the hippocampus but the role of this unique morphology in controlling place cell physiology remains a mystery. Here we show that OLM activity prevents associative synaptic plasticity at Schaffer collateral synapses on CA1 pyramidal cells by inhibiting dendritic Ca2+ signalling initiated by entorhinal synaptic inputs. Furthermore, we find that OLM activity is reduced in novel environments suggesting that reducing OLM activity and thereby enhancing excitatory synaptic plasticity is important for the formation of new place cell representations. Supporting this, we show that selectively increasing OLM activity in novel environments enhances place cell stability and reduces remapping of newly formed place cells whilst increasing OLM activity in familiar environments led only to a transient silencing of place cells. Our results therefore demonstrate a critical role for distal dendrite targeting interneurons in regulating plasticity of neuronal representations.

neuroscience↗

bioRxiv2020

Acetylcholine prioritises direct synaptic inputs from entorhinal cortex to 1 CA1 by differential modulation of feedforward inhibitory circuits

Acetylcholine release in the hippocampus plays a central role in the formation of new memory representations by facilitating synaptic plasticity. It is also proposed that memory formation requires acetylcholine to enhance responses in CA1 to new sensory information from entorhinal cortex whilst depressing inputs from previously encoded representations in CA3, but this influential theory has not been directly tested. Here, we show that excitatory inputs from entorhinal cortex and CA3 are depressed equally by synaptic release of acetylcholine in CA1. However, greater depression of feedforward inhibition from entorhinal cortex results in an overall enhancement of excitatory-inhibitory balance and CA1 activation. Underpinning the prioritisation of entorhinal inputs, entorhinal and CA3 pathways engage distinct feedforward interneuron subpopulations and depression is mediated differentially by presynaptic muscarinic M3 and M4 receptors respectively. These mechanisms enable acetylcholine to prioritise novel information inputs to CA1 during memory formation and suggest selective muscarinic targets for therapeutic intervention.

neuroscience↗

bioRxiv2019

Interneuron-specific plasticity at parvalbumin and somatostatin inhibitory synapses onto CA1 pyramidal neurons shapes hippocampal output

The formation and maintenance of spatial representations within hippocampal cell assemblies is strongly dictated by patterns of inhibition from diverse interneuron populations. Although it is known that inhibitory synaptic strength is malleable, induction of long-term plasticity at distinct inhibitory synapses and its regulation of hippocampal network activity is not well understood. Here, we show that inhibitory synapses from parvalbumin and somatostatin expressing interneurons undergo long-term depression and potentiation respectively (PV-iLTD and SST-iLTP) during physiological activity patterns. Both forms of plasticity rely on T-type calcium channel activation to confer synapse specificity but otherwise employ distinct mechanisms. Since parvalbumin and somatostatin interneurons preferentially target perisomatic and distal dendritic regions respectively of CA1 pyramidal cells, PV-iLTD and SST-iLTP coordinate a reprioritisation of excitatory inputs from entorhinal cortex and CA3. Furthermore, circuit-level modelling reveals that PV-iLTD and SST-iLTP cooperate to stabilise place cells while facilitating representation of multiple unique environments within the hippocampal network.

neuroscience↗