Biology subjects

Rais, C.

Publications and source records attributed to Rais, C..

3 recordsLinked to original sources

bioRxiv2025

Functional Connectivity Shapes Spine Stability in the Hippocampus

Synaptic connections between neurons determine the flow of information in the brain. Changes in synaptic weight, along with synapse formation and pruning, reshape the functional connectivity of neural circuits--key mechanisms underlying learning and memory. However, the relationship between functional strength and the structural dynamics of individual glutamatergic synapses in the living mammalian brain remains poorly understood. Specifically, how spine morphology and stability relate to functional adaptations is unclear. Here, we repeatedly recorded excitatory postsynaptic calcium transients in single postsynaptic spines of CA1 neurons in response to optogenetic stimulation of presynaptic CA3 cells in awake, head-fixed mice for over 2 weeks. We found that functional connectivity predicted both the structural stability and spatial proximity of synaptic inputs. Spines with large responses exhibited larger volume and higher stability compared to non-responding spines. Over time, responses were highly variable at individual synapses, but stable at the dendritic level, suggesting that dendritic branches receive stable input despite large fluctuations at individual synapses.

neuroscience↗

bioRxiv2025

Schaffer commissural inputs regulate the stability of CA1 spatial representation

Neuronal representations of the world are dynamic. A striking example is the rapid remapping of the hippocampal spatial code, which occurs even when the environment and behavior remain unchanged. CA3 input to CA1 has been shown to exert a key role in triggering synaptic plasticity in place-encoding CA1 cells -- a phenomenon which could provide the cellular foundations for the remapping of the hippocampal code for space. However, how CA3 input directly contributes to place field formation and remapping of the place code in CA1 remains incompletely understood. By combining longitudinal two-photon calcium imaging of CA1 place cells with optogenetic stimulation of presynaptic CA3 neurons in mice running on a linear treadmill, we demonstrate that CA3 transiently modulates the code for allocentric space in CA1. Activation of CA3 cells both induced a small pool of new CA1 place cells and altered the pre-existing CA1 place code. The latter occurred through an unbiased shift of existing place fields specifically, and not through modifications of place field precision or a loss of place tuning in pre-existing place cells. All CA3-driven changes in the CA1 place code were transient and almost completely disappeared by the next day. Taken together, stimulation of CA3 input to CA1 cells alters CA1-encoded spatial representations, leading to a transient decrease in place field precision rather than an overrepresentation of the stimulation zone. HIGHLIGHTSO_LIOptogenetic CA3 stimulation with two-photon CA1 imaging in behaving mice C_LIO_LIStimulation of CA3 input induces a small pool of new CA1 place cells C_LIO_LIPre-existing CA1 place fields shift without loss of tuning or precision C_LIO_LICA3-driven remapping is unbiased in space and largely disappears by next day C_LI

neuroscience↗

bioRxiv2020

Anesthetics uniquely decorrelate hippocampal network activity, alter spine dynamics and affect memory consolidation

General anesthesia is characterized by reversible loss of consciousness accompanied by transient amnesia. Yet, long-term memory impairment is an undesirable side-effect. How different types of general anesthetics (GAs) affect the hippocampus, a brain region central to memory formation and consolidation, is poorly understood. Using extracellular recordings, chronic 2-photon imaging and behavioral analysis, we monitor the effects of isoflurane (Iso), medetomidine/midazolam/fentanyl (MMF), and ketamine/xylazine (Keta/Xyl) on network activity and structural spine dynamics in the hippocampal CA1 area of adult mice. GAs robustly reduced spiking activity, decorrelated cellular ensembles, albeit with distinct activity signatures, and altered spine dynamics. CA1 network activity under all three anesthetics was different to natural sleep. Iso anesthesia most closely resembled unperturbed activity during wakefulness and sleep, and network alterations recovered more readily than with Keta/Xyl and MMF. Correspondingly, memory consolidation was impaired after exposure to Keta/Xyl and MMF, but not Iso. Thus, different anesthetics distinctly alter hippocampal network dynamics, synaptic connectivity, and memory consolidation, with implications for GA strategy appraisal in animal research and clinical settings.

neuroscience↗