Activity-dependent plasticity of hippocampal place maps

Hippocampal neurons encode a cognitive map of space. These maps are thought to be updated during learning and in response to changes in the environment through activity-dependent synaptic plasticity. Here we examine how changes in activity influence spatial coding in rats using halorhodopsin-mediated, spatially selective optogenetic silencing. Halorhoposin stimulation leads to light-induced suppression in many place cells and interneurons; some place cells increase their firing through disinhibition, whereas some show no effect. We find that place fields of the unaffected subpopulation remain stable. On the other hand, place fields of suppressed place cells were unstable, showing remapping across sessions before and after optogenetic inhibition. Disinhibited place cells had stable maps but sustained an elevated firing rate. These findings suggest that place representation in the hippocampus is constantly governed by activity-dependent processes, and that disinhibition may provide a mechanism for rate remappin

Optogenetic inhibition-mediated activity-dependent modification of CA1 pyramidal-interneuron connections during behavior

In vitro work revealed that excitatory synaptic inputs to hippocampal inhibitory interneurons could undergo Hebbian, associative, or non-associative plasticity. Both behavioral and learning-dependent reorganization of these connections has also been demonstrated by measuring spike transmission probabilities in pyramidal cell-interneuron spike cross-correlations that indicate monosynaptic connections. Here we investigated the activity-dependent modification of these connections during exploratory behavior in rats by optogenetically inhibiting pyramidal cell and interneuron subpopulations. Light application and associated firing alteration of pyramidal and interneuron populations led to lasting changes in pyramidal-interneuron connection weights as indicated by spike transmission changes. Spike transmission alterations were predicted by the light-mediated changes in the number of pre- and postsynaptic spike pairing events and by firing rate changes of interneurons but not pyramidal cells. This work demonstrates the presence of activity-dependent associative and non-associative reorganization of pyramidal-interneuron connections triggered by the optogenetic modification of the firing rate and spike synchrony of cells

Energy and protein intake in medical and geriatric inpatients with MEDPass versus conventional administration of oral nutritional supplements: study protocol for the randomized controlled MEDPass Trial

Abstract Background Disease-related malnutrition is highly prevalent in hospitalized medical and geriatric inpatients. It is associated with negative outcomes such as muscle wasting, decline of functional status, and increased morbidity and mortality. Oral nutritional supplements (ONS) are frequently used in nutritional therapy to increase intake. However, compliance to ONS is often limited and maybe improved by prescribing ONS in small portions timed with the medication (MEDPass). However, it is unknown whether the MEDPass administration enhances patients’ total energy and protein intake. Methods The MEDPass Trial is a randomized, controlled, open-label superiority trial. Patients in the MEDPass group receive 50 ml of ONS four times per day, distributed with the medication rounds. Patients in the control group receive ONS between meals. The primary outcome is average daily energy intake (% of calculated daily requirement). For our power analysis, we assumed that administration of ONS in the MEDPass administration mode increases energy intake by at least 10% (i.e., by 200 kcal for an average energy requirement of 2200 kcal/day). Thus, with the inclusion of 200 patients, this trial has 80% power to demonstrate that intervention group patients have an average intake of 2200 kcal/day (SD 500 kcal) versus 2000 kcal/day (SD 500 kcal) in control group patients. Energy and protein intakes from ONS and all food consumed are monitored continuously throughout the hospital stay and are statistically compared to the patient’s requirements. Secondary outcomes include average daily protein intake (% of calculated daily requirement), average intake of ONS/day, the course of body weight, handgrip strength, appetite, and nausea. Furthermore, hospital length of stay and 30-day mortality are assessed. The primary statistical analysis will be performed as an intention-to-treat analysis adjusted for the stratification factors used in randomization. Discussion To our knowledge, this is the first randomized controlled trial assessing total energy and protein intake for the entire hospitalization period in patients receiving MEDPass versus conventional ONS administration. Thus, the MEDPass Trial will fill a gap and answer this relevant clinical question

MEDPass versus conventional administration of oral nutritional supplements - A randomized controlled trial comparing coverage of energy and protein requirements.

BACKGROUND & AIMS The use of oral nutritional supplements (ONS) in the hospital setting is important to reach individual protein and energy goals in patients at risk for malnutrition. Compliance with ONS can be challenging but may be improved by prescribing ONS in smaller portions with medication rounds (MEDPass). We compared the likelihood of meeting energy and protein requirements in patients receiving ONS with MEDPass versus conventional ONS administration. METHODS The MEDPass Trial is a randomized, controlled, open-label superiority trial conducted on medical and geriatric wards in a University Hospital in Switzerland. The MEDPass group was allocated to receive 50 ml of ONS four times per day with the medication rounds. The control group received ONS per conventional care between the meals. The primary outcome was the percentage of energy in relation to the individual requirement. Secondary outcomes included the coverage of protein intake in relation to the individual requirement, the amount of daily consumed ONS, the course of handgrip strength (HGS), body weight appetite and nausea. Furthermore, we compared 30-day mortality and hospital length of stay (LOS) was studied in medical patients. RESULTS From November 22nd, 2018 until November 30th, 2021, 204 patients were included in the trial (MEDPass group n = 100, control group n = 104). A total of 203 patients at nutritional risk were analyzed in the intention-to-treat analysis (ITT). Regarding the primary endpoint, there was no difference in the coverage of energy requirement between the MEDPass and control group (82 vs. 85% (Δ -3%, 95%CI -11 to 4%), p = 0.38). Similarly, no differences were found for the secondary outcomes including coverage of protein requirement (101 vs. 104% (Δ -3%, 95% CI -12 -7%), p = 0.57, average daily intake of ONS (170 vs 173 ml (Δ - 3 ml, 95% CI -14 to 8 ml), p = 0.58) and 30-day mortality (3 vs. 8 patients, OR 0.4 (95% CI 0.1-1.4), p = 0.15). The course of HGS, body weight, appetite and nausea did not differ between the groups (p = 0.29, p = 0.14, p = 0.65 and p = 0.94, respectively). The per protocol analysis including 178 patients showed similar results. CONCLUSION Within this controlled trial setting, we found a high compliance for ONS intake and high coverage of protein requirements but no further improvement when ONS was administered using MEDPass compared to conventional care. MEDPass administration may provide an alternative that is easy to integrate into nursing routines, which may lead to lower workload with cost benefits and reduction of food waste. TRIAL REGISTRATION ClinicalTrials.gov: NCT03761680

Temporal Control of Immediate Early Gene Induction by Light

BACKGROUND: The light-gated cation channel channelrhodopsin-2 (ChR2) is a powerful tool for the optical induction of action potentials in neurons. Mutations of the cysteine 128 (C128) residue have been shown to greatly extend the lifetime of the conducting state of ChR2. However, until now, only subthreshold depolarizations have been reported from C128 mutants. METHODS AND FINDINGS: Here we report the induction of long high-frequency spike trains by brief light pulses in ChR2(C128A)-transfected pyramidal cells in hippocampal slice culture. ChR2(C128A)-mediated spike bursts triggered expression of the immediate early gene c-fos in pyramidal neurons. Robust and cell-specific expression of c-Fos protein was detected after a single blue light pulse and depended on action potential firing, but not on synaptic activity. However, photocurrents diminished upon repeated stimulation and limited the number of action potential bursts that could be elicited. CONCLUSIONS: We conclude that the C128A mutant is not suitable for chronic stimulation of neurons, but very useful for light-controlled induction of immediate early genes. This property of ChR2(C128A) could be harnessed to control the expression of proteins under control of the c-fos promoter with precise timing and single cell specificity

Channelrhodopsin as a tool to study synaptic transmission and plasticity

The light-gated cation channel channelrhodopsin-2 (ChR2) has been used in a variety of model systems to investigate the function of complex neuronal networks by stimulation of genetically targeted neurons. In slice physiology, ChR2 opens the door to novel types of experiments and greatly extends the technical possibilities offered by traditional electrophysiology.In this short review, we first consider several technical aspects concerning the use of ChR2 in slice physiology, providing examples from our own work. More specifically, we discuss differences between light-evoked action potentials (APs) and spontaneous or electrically induced APs. Our work implies that light-evoked APs are associated with increased calcium influx and a very high probability of neurotransmitter release. Furthermore, we point out the factors limiting the spatial resolution of ChR2 activation.In the second part, we discuss how synaptic transmission and plasticity can be studied using ChR2. Postsynaptic depolarization induced by ChR2 can be combined with two-photon glutamate uncaging to potentiate visually identified dendritic spines. ChR2-mediated stimulation of presynaptic axons induces neurotransmitter release and reliably activates postsynaptic spines. In conclusion, ChR2 is a powerful tool to investigate activity-dependent changes in structure and function of synapses

Experimental Physiology Channelrhodopsin as a tool to investigate synaptic transmission and plasticity

The light-gated cation channel channelrhodopsin-2 (ChR2) has been used in a variety of model systems to investigate the function of complex neuronal networks by stimulation of genetically targeted neurons. In slice physiology, ChR2 opens the door to novel types of experiments and greatly extends the technical possibilities offered by traditional electrophysiology. In this short review, we first consider several technical aspects concerning the use of ChR2 in slice physiology, providing examples from our own work. More specifically, we discuss differences between lightevoked action potentials and spontaneous or electrically induced action potentials. Our work implies that light-evoked action potentials are associated with increased calcium influx and a very high probability of neurotransmitter release. Furthermore, we point out the factors limiting the spatial resolution of ChR2 activation. Secondly, we discuss how synaptic transmission and plasticity can be studied using ChR2. Postsynaptic depolarization induced by ChR2 can be combined with two-photon glutamate uncaging to potentiate visually identified dendritic spines. ChR2-mediated stimulation of presynaptic axons induces neurotransmitter release and reliably activates postsynaptic spines. In conclusion, ChR2 is a powerful tool to investigate activity-dependent changes in structure and function of synapses

Cell-specific c-Fos induction by light-triggered spike trains.

<p>(A) Immunostaining for endogenous c-Fos in CA1 area of rat hippocampal slice cultures under basal conditions (top) and 2 h after stimulation by extracellular application of 50 mM K⁺ (bottom). (B) c-Fos induction in a pyramidal neuron expressing ChR2(C128A) and cytosolic RFP after 10 stimulation pulses. Cultures were fixed 2 h after stimulation and stained for c-Fos. (C) c-Fos signal in non-stimulated cells (n = 27) and at different time points after light stimulation (n = 18, 24, 18, 25, 21). Green shaded bar indicates mean±SD of non-stimulated control cells. c-Fos induction was significant at all time points (p<0.01). (D) Significant c-Fos induction was observed after a single blue light pulse (n = 17, 15, 14, 21, 19, 11). Dashed line indicates average c-Fos signal after 50 mM K⁺ stimulation. (E) Light-triggered c-Fos induction was blocked by TTX, but not by NBQX or CPP. *: p<0.01 compared to control. (F) Green fluorescence in live organotypic slice cultures (CA3) from fosGFP transgenic mice under basal conditions (top) and 4 h after brief stimulation with 50 mM K⁺ (bottom). (G) Light-induced GFP expression in fosGFP reporter mouse neurons expressing ChR2(C128A) and RFP. (H) Light-induced GFP expression was quantified 4 h after light stimulation (10 pulses). Scale bars in (A,B,F,G): 10 µm.</p

Cell-attached recordings of light-induced spike trains.

<p>(A) Sample trace. Cell-autonomous activity was isolated by bath-application of NBQX. (B) In the majority of cells the number of spikes decreased with repeated stimulation (8/11 cells). Asterisks indicate cells presumably entering depolarization block after initial stimulation pulses. (C) Top: Spike raster for cell with long delay to first spike (10.75 ms). Bottom: Spike raster for cell with short delay to first spike (4.25 ms) presumably entering depolarization block. (D) Top: Long spike train containing 394 APs. Bottom: Spike train in current-clamped cell (355 APs) for comparison.</p

Photocurrent reduction can be alleviated by green switch-back pulses.

<p>(A) Neurons were stimulated with two blue pulses spaced 2.5 min apart. After a 2.5 min (gray, n = 10) or 15 min (black, n = 4) recovery period photocurrent reduction was comparable (p>0.5). (B) Following excitation by a blue light pulse, ChR2(C128A) photocurrents could be inactivated by a green switch-back pulse. Inactivation efficiency was 90.6±1.2% (n = 24). (C) Left: Photocurrent reduction was markedly diminished when activated channel was inactivated by a green switch-back pulse after a 3 s interval (black line). Application of a green light pulse after 20 s or 60 s was less effective in preventing current reduction (n = 3, 3). Gray line: Current reduction with single blue pulses for comparison. Right: Quantification of photocurrent reduction relative to the previous stimulation pulse without green switch-back (gray line) or with a green light pulse applied 3 s after blue light stimulation (black line). The green box indicates stimulation trials following a trial terminated with a green pulse. (D) Minimal model for the ChR2(C128A) photocycle, modified after Berndt et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008185#pone.0008185-Berndt1" target="_blank">[6]</a>. (E) Photocurrent reduction with repeated stimulation was also observed in ChR2(C128T) and ChR2(C128S) mutants.</p