Biology subjects

Bornschein, G.

Publications and source records attributed to Bornschein, G..

5 recordsLinked to original sources

bioRxiv2026

Pyramidal neuron synapses in M2 exhibit properties intermediate between prefrontal cortex and M1 synapses

Motor planning and control is executed by different motor areas within the neocortex. Despite their distinct functions these areas are built by the same archetypes of neurons as the rest of the cortex, with the pyramidal neurons (PNs) as their principal building blocks. Recent results suggest that the synapses of the PNs are modeled and adapted to their required functions in an area specific manner. PN synapses in a cortical area engaged in higher order functions, the prefrontal cortex (PFC), were found to operate with loose microdomain calcium-influx-to-release coupling and showed short-term facilitation, whereas synapses processing sensory information in a lower order cortical area, the primary somatosensory cortex (S1), featured tight nanodomain coupling and showed short-term depression. In the present study, we asked for the functional coupling configuration of an intermediate processing area. We focused on PN synapses in the premotor cortex M2 and compared their properties to those of PN synapses in the primary motor cortex M1. In both areas we found tight nanodomain coupling and high release probability, but a significant difference in short-term plasticity. Synapses in M1 showed paired-pulse depression similar to S1. In contrast, synapses in M2 exhibited paired-pulse facilitation. Our data suggest that this facilitation results from an accelerated recruitment of synaptic vesicles to the readily releasable pool from an enlarged replenishment pool. Thus, PN synapses in M2 appear to have properties intermediate between those in PFC and M1. Significance StatementNeocortical areas perform diverse computations despite being composed of the same principal neuronal cell types. How synaptic properties are adapted to these functional demands remains poorly understood. We show that L2/3-L5 pyramidal neuron synapses in the secondary motor cortex (M2) combine features of the primary motor cortex (M1), including tight nanodomain Ca{superscript 2}-influx-to-release coupling and high release probability, with paired-pulse facilitation, previously associated with higher-order cortical areas such as the prefrontal cortex (PFC). Our data suggest that this facilitation is mediated by an enlarged replenishment pool and accelerated vesicle recruitment rather than differences in coupling architecture, highlighting vesicle pool organization as an additional mechanism of area-specific synaptic specialization. Thus, L2/3-L5 pyramidal neuron synapses in M2 exhibit intermediate properties between M1 and PFC.

neuroscience↗

bioRxiv2025

Loose coupling between Ca2+ channels and release sensors as a synaptic correlate of higher order brain function

In the mature neocortex, functionally distinct areas are built by the same archetypes of neurons, but depending on the area, these neurons and their synapses are engaged in very different functions, ranging from lower order processing of sensory information to higher order associations and cognitive functions. We found significant differences in the functional presynaptic nanoarchitectures of the same types of pyramidal neuron synapses, depending on whether they are located in the prefrontal cortex (PFC) or in the primary somatosensory cortex (S1). Synapses in PFC operated with loose microdomain coupling as opposed to tight nanodomain coupling in S1. These differences were associated with significant differences in synaptic timing, efficacy and plasticity between areas. Our data suggest that the mature neocortex uses tuning of synaptic topographies to specialize seemingly identical types of neurons for their required function. They suggest that microdomain coupling in pyramidal neuron synapses could be a presynaptic structure-function correlate of higher order neocortical functions.

neuroscience↗

bioRxiv2024

Estimates of quantal synaptic parameters in light of more complex vesicle pool models

The subdivision of synaptic vesicles (SVs) into discrete pools is a leading concept of synaptic physiology. To better explain specific properties of transmission and plasticity, it has been suggested initially that the readily releasable pool (RRP) of SVs is subdivided into two parallel pools differing in their release probability. More recently, evidence was provided that sequential pools with a single RRP and a series-connected finite-size replacement pool (RP) inserted between the reserve pool (RSP) and RRP equally well or even better account for most aspects of transmission and plasticity. It was further suggest that a fraction of the presynaptic release sites (N) are initially unoccupied by SVs, with vesicle recruitment occurring rapidly during activity, and furthermore that the number of release sites itself changes with rapid dynamics during activity. Here we propose a framework that identifies specific signs of the presence of the series-connected RP, using a combination of two experimental electrophysiological standard methods, cumulative analysis (CumAna) and multiple probability fluctuation analysis (MPFA). In particular we show that if the y-intercept (y(0)) of CumAna is larger than N reported by MPFA (y(0) > NMPFA) this is a strong indication for a series-connected RP. This is due to the fact that y(0) reports the sum of RRP and RP. Our analysis further suggests that this result is not affected by unoccupied release sites, as such empty sites contribute to both estimates, y(0) and NMPFA. We discuss experimental findings and models in the recent literature in the light of our theoretical considerations.

neuroscience↗

bioRxiv2024

The intracellular Ca2+ sensitivity of transmitter release from neocortical boutons

Synaptotagmin 1 (Syt1) and Syt2 are the main Ca2+ sensors triggering synchronous release in the brain. The Ca2+-sensitivity of Syt2-triggered release has been studied in detail. However, for Syt1, the dominating isoform in the neocortex, quantitative detail is lacking. We measured the Ca2+-dependency of Syt1-triggered release at layer 5 pyramidal neuron synapses by laser photolysis of caged Ca2+. Syt1-triggered release had high Ca2+ affinity and positive cooperativity (EC50, 20 M; Hill coefficient, 3.57). It was steep in a dynamic range between [~]10 and [~]30 M that was covered by action potential-evoked release. A kinetic model reveals significant differences to models of Syt2-triggered release. Our results suggest that Syt1 optimizes neocortical synapses for high reliability at moderate local Ca2+ elevations and for high plastic controllability.

neuroscience↗

bioRxiv2023

Fully-primed slowly-recovering vesicles mediate presynaptic LTP at neocortical neurons

Pre- and postsynaptic forms of long-term potentiation (LTP) are candidate synaptic mechanisms underlying learning and memory. At layer 5 pyramidal neurons LTP increases the initial synaptic strength but also short-term depression during high-frequency transmission. This classical form of presynaptic LTP has been referred to as redistribution of synaptic efficacy. However, the underlying mechanisms remain unclear. We therefore performed whole-cell recordings from layer 5 pyramidal neurons in acute cortical slices of rats and analyzed presynaptic function before and after LTP induction by paired pre- and postsynaptic neuronal activity. LTP was successfully induced in about half of the synaptic connections tested and resulted in increased synaptic depression during high-frequency transmission and a decelerated recovery from depression due to an increased occurrence of a slow recovery component. Analysis with a recently established sequential two-step vesicle priming model indicates an increase in the abundance of fully-primed and slowly-recovering vesicles. A systematic analysis of short-term plasticity and synapse-to-synapse variability of synaptic strength at various types of synapses revealed that stronger synapses generally recover more slowly from synaptic depression. Finally, pharmacological stimulation of the cyclic adenosine monophosphate (cAMP) and diacylglycerol (DAG) signaling pathways, which are both known to promote synaptic vesicle priming mimicked electrically-induced LTP and slowed the recovery from depression. Our data thus demonstrate that LTP at layer 5 pyramidal neurons increases synaptic strength primarily by enlarging a subpool of fully-primed slowly-recovering vesicles.

neuroscience↗