Biology subjects

Lippmann, K.

Publications and source records attributed to Lippmann, K..

4 recordsLinked to original sources

bioRxiv2024

Ultrastructural membrane dynamics of mouse and human cortical synapses

Live human brain tissues provide unique opportunities for understanding synaptic transmission. Investigations have been limited to anatomy, electrophysiology, and protein localization--while crucial parameters such as synaptic vesicle dynamics were not visualized. Here we utilize zap-and-freeze time-resolved electron microscopy to overcome this hurdle. First, we validate the approach with acute mouse brain slices to demonstrate that slices can be stimulated to produce calcium signaling. Next, we show that synaptic vesicle endocytosis is induced in both mouse and human brain slices. Crucially, clathrin-free endocytic pits appear immediately next to the active zone, where ultrafast endocytosis normally occurs, and can be trapped at this location by a dynamin inhibitor. In both species a protein essential for ultrafast endocytosis, Dynamin 1xA, localizes to the region peripheral to the active zone, the putative endocytic zone, indicating a possible conserved mechanism between mouse and human. This approach has the potential to reveal dynamic, high-resolution information about synaptic membrane trafficking in intact human brain slices.

neuroscience↗

bioRxiv2023

KATP channel mutation disrupts hippocampal network activity and nocturnal γ shifts

ATP-sensitive potassium (KATP) channels enable ATP to control the membrane potential and insulin secretion. Humans affected by severe activating mutations in KATP channels suffer from developmental delay, epilepsy and neonatal diabetes (DEND syndrome). While the diabetes in DEND syndrome is well understood, the pathophysiology of the neurological symptoms remains unclear. We hypothesized that parvalbumin-positive interneurons (PV-INs) are key for the pathophysiology and found, by using electrophysiology, that expressing the DEND mutation Kir6.2-V59M selectively in PV-INs reduced intrinsic gamma frequency preference and short-term depression as well as disturbed cognition-associated gamma oscillations and hippocampal sharp waves. Furthermore, risk of seizures is increased and day-night shift in gamma activity disrupted. Thus, PV-INs play a key role in DEND syndrome and this provides a framework for establishing treatment options. One Sentence SummaryOveractive KATP channels in PV-interneurons disturb cellular behaviour and cognition-associated network oscillations.

neuroscience↗

bioRxiv2022

Status epilepticus induces chronic silencing of burster and dominance of regular firing neurons during sharp wave-ripples in the mouse subiculum

Sharp wave-ripples (SWRs) are hippocampal oscillations associated with memory consolidation. The subiculum, as the hippocampal output structure, ensures that hippocampal memory representations are transferred correctly to the consolidating neocortical regions. Because patients with temporal lobe epilepsy often develop memory deficits, we hypothesized that epileptic networks may disrupt subicular SWRs. We therefore investigated the impact of experimentally induced status epilepticus (SE) on subicular SWRs and contributing pyramidal neurons using electrophysiological recordings in mouse hippocampal slices. Subicular SWRs expressed hyperexcitable features post-SE, including increased ripple and unit activity. While regular firing neurons normally remain silent during SWRs, selective disinhibition recruited more regular firing neurons for action potential generation during SWRs post-SE. By contrast, burster neurons generated fewer action potential bursts during SWRs post-SE. Furthermore, altered timing of postsynaptic and action potentials suggested distorted neuronal recruitment during SWRs. Distorted subicular SWRs may therefore impair information processing and memory consolidation in epilepsy.

neuroscience↗

bioRxiv2018

Synaptic vesicles undock and then transiently dock after an action potential

Synaptic vesicles fuse with the plasma membrane to release neurotransmitter following an action potential, after which new vesicles must dock to refill vacated release sites. To capture synaptic vesicle exocytosis at cultured mouse hippocampal synapses, we induced single action potentials by electrical field stimulation then subjected neurons to high-pressure freezing to examine their morphology by electron microscopy. During synchronous release, multiple vesicles can fuse at a single active zone; this multivesicular release is augmented by increasing extracellular calcium. Fusions during synchronous release are distributed throughout the active zone, whereas fusions during asynchronous release are biased toward the center of the active zone. Immediately after stimulation, the total number of docked vesicles across all synapses decreases by [~]40%. Between 8 and 14 ms, new vesicles are recruited to the plasma membrane and fully replenish the docked pool in a calcium-dependent manner, but docking of these vesicles is transient and they either undock or fuse within 100 ms. These results demonstrate that recruitment of synaptic vesicles to release sites is rapid and reversible.

neuroscience↗