Activation of M1 cholinergic receptors in mouse somatosensory cortex enhances information processing and detection behaviour.

To optimise sensory representations based on environmental demands, the activity of cortical neurons is regulated by neuromodulators such as Acetylcholine (ACh). ACh is implicated in cognitive functions including attention, arousal and sleep cycles. However, it is not clear how specific ACh receptors shape the activity of cortical neurons in response to sensory stimuli. Here, we investigate the role of a densely expressed muscarinic ACh receptor M1 in information processing in the mouse primary somatosensory cortex and its influence on the animal's sensitivity to detect vibrotactile stimuli. We show that M1 activation results in faster and more reliable neuronal responses, manifested by a significant reduction in response latencies and the trial-to-trial variability. At the population level, M1 activation reduces the network synchrony, and thus enhances the capacity of cortical neurons in conveying sensory information. Consistent with the neuronal findings, we show that M1 activation significantly improves performances in a vibriotactile detection task.

Expectation violations enhance neuronal encoding of sensory information in mouse primary visual cortex.

The response of cortical neurons to sensory stimuli is shaped both by past events (adaptation) and the expectation of future events (prediction). Here we employed a visual stimulus paradigm with different levels of predictability to characterise how expectation influences orientation selectivity in the primary visual cortex (V1) of male mice. We recorded neuronal activity using two-photon calcium imaging (GCaMP6f) while animals viewed sequences of grating stimuli which either varied randomly in their orientations or rotated predictably with occasional transitions to an unexpected orientation. For single neurons and the population, there was significant enhancement in the gain of orientation-selective responses to unexpected gratings. This gain-enhancement for unexpected stimuli was prominent in both awake and anaesthetised mice. We implemented a computational model to demonstrate how trial-to-trial variability in neuronal responses were best characterised when adaptation and expectation effects were combined.

A protocol for simultaneous in vivo juxtacellular electrophysiology and local pharmacological manipulation in mouse cortex.

Here, we describe a protocol to simultaneously record and label single cortical neurons in vivo under local application of a chemical such as a receptor agonist. This protocol provides a useful tool to investigate how the chemical of interest affects the processing of sensory information by cortical neurons. The juxtacellular labeling allows identification of the cell type and morphology of the recorded neurons. We draw examples to show pharmacological modulations in encoding of vibrotactile stimuli in the mouse primary somatosensory cortex. For complete details on the use and execution of this protocol, please refer to Kheradpezhouh et al. (2020).

State-Dependent Changes in Perception and Coding in the Mouse Somatosensory Cortex.

An animal's behavioral state is reflected in the dynamics of cortical population activity and its capacity to process sensory information. To better understand the relationship between behavioral states and information processing, mice are trained to detect varying amplitudes of whisker-deflection under two-photon calcium imaging. Layer 2/3 neurons in the vibrissal primary somatosensory cortex are imaged across different behavioral states, defined based on detection performance (low to high-state) and pupil diameter. The neurometric curve in each behavioral state mirrors the corresponding psychometric performance, with calcium signals predictive of the animal's choice. High behavioral states are associated with lower network synchrony, extending over shorter cortical distances. The decrease in correlation across neurons in high state results in enhanced information transmission capacity at the population level. The observed state-dependent changes suggest that the coding regime within the first stage of cortical processing may underlie adaptive routing of relevant information through the sensorimotor system.

Enhanced Sensory Coding in Mouse Vibrissal and Visual Cortex through TRPA1.

Transient receptor potential ankyrin 1 (TRPA1) is a non-selective cation channel, broadly expressed throughout the body. Despite its expression in the mammalian brain, little is known about the contribution of TRPA1 to cortical function. Here, we characterize how TRPA1 affects sensory information processing in two cortical areas in mice: the primary vibrissal (whisker) somatosensory cortex (vS1) and the primary visual cortex (V1). In vS1, local activation of TRPA1 by allyl isothiocyanate (AITC) increases the ongoing activity of neurons and their evoked response to vibrissal stimulation, producing a positive gain modulation. The gain modulation is reversed by TRPA1 inhibitor HC-030031 and is absent in TRPA1 knockout mice. Similarly, in V1, TRPA1 activation increases the gain of direction and orientation selectivity. Linear decoding of V1 population activity confirms faster and more reliable encoding of visual signals under TRPA1 activation. Overall, our findings reveal a physiological role for TRPA1 in enhancing sensory signals in the mammalian cortex.

Publisher Correction: Response dynamics of rat barrel cortex neurons to repeated sensory stimulation.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Oxidative stress promotes redistribution of TRPM2 channels to the plasma membrane in hepatocytes.

Transient Receptor Potential Melastatin (TRPM) 2 is a non-selective Ca2+ permeable cation channel and a member of the Transient Receptor Potential (TRP) channel family. TRPM2 has unique gating properties; it is activated by intracellular ADP-ribose (ADPR), whereas Ca2+ plays a role of an important co-factor in channel activation, increasing TRPM2 sensitivity to ADPR. TRPM2 is highly expressed in rat and mouse hepatocytes, where it has been shown to contribute to oxidative stress-induced cell death and liver damage due to paracetamol-overdose. The mechanisms regulating the activity of TRPM2 channels in hepatocytes, however, are not well understood. In this paper, we investigate the localisation of TRPM2 protein in hepatocytes. The presented results demonstrate that in rat hepatocytes under normal conditions, most of the TRPM2 protein is localised intracellularly. This was determined by confocal microscopy using TRPM2-and plasma membrane (PM)-specific antibodies and immunofluorescence, and biotinylation studies followed by western blotting. Interestingly, in hepatocytes treated with either H2O2 or paracetamol, the amount of TRPM2 co-localised with PM is significantly increased, compared to the untreated cells. It is concluded that trafficking of TRPM2 to the PM could potentially contribute to a positive feedback mechanism mediating Ca2+ overload in hepatocytes under conditions of oxidative stress.

Response dynamics of rat barrel cortex neurons to repeated sensory stimulation.

Neuronal adaptation is a common feature observed at various stages of sensory processing. Here, we quantified the time course of adaptation in rat somatosensory cortex. Under urethane anesthesia, we juxta-cellularly recorded single neurons (n = 147) while applying a series of whisker deflections at various frequencies (2-32 Hz). For ~90% of neurons, the response per unit of time decreased with frequency. The degree of adaptation increased along the train of deflections and was strongest at the highest frequency. However, a subset of neurons showed facilitation producing higher responses to subsequent deflections. The response latency to consecutive deflections increased both for neurons that exhibited adaptation and for those that exhibited response facilitation. Histological reconstruction of neurons (n = 45) did not reveal a systematic relationship between adaptation profiles and cell types. In addition to the periodic stimuli, we applied a temporally irregular train of deflections with a mean frequency of 8 Hz. For 70% of neurons, the response to the irregular stimulus was greater than that of the 8 Hz regular. This increased response to irregular stimulation was positively correlated with the degree of adaptation. Altogether, our findings demonstrate high levels of diversity among cortical neurons, with a proportion of neurons showing facilitation at specific temporal intervals.

TRPA1 expression and its functional activation in rodent cortex.

TRPA1 is a non-selective cation channel involved in pain sensation and neurogenic inflammation. Although TRPA1 is well established in a number of organs including the nervous system, its presence and function in the mammalian cortex remains unclear. Here, we demonstrate the expression of TRPA1 in rodent somatosensory cortex through immunostaining and investigate its functional activation by whole-cell electrophysiology, Ca2+ imaging and two-photon photoswitching. Application of TRPA1 agonist (AITC) and antagonist (HC-030031) produced significant modulation of activity in layer 5 (L5) pyramidal neurons in both rats and mice; AITC increased intracellular Ca2+ concentrations and depolarized neurons, and both effects were blocked by HC-030031. These modulations were absent in the TRPA1 knockout mice. Next, we used optovin, a reversible photoactive molecule, to activate TRPA1 in individual L5 neurons of rat cortex. Optical control of activity was established by applying a tightly focused femtosecond-pulsed laser to optovin-loaded neurons. Light application depolarized neurons (n = 17) with the maximal effect observed at λ = 720 nm. Involvement of TRPA1 was further confirmed by repeating the experiment in the presence of HC-030031, which diminished the light modulation. These results demonstrate the presence of TRPA1 in L5 pyramidal neurons and introduce a highly specific approach to further understand its functional significance.

TRPM2 channels mediate acetaminophen-induced liver damage.

Acetaminophen (paracetamol) is the most frequently used analgesic and antipyretic drug available over the counter. At the same time, acetaminophen overdose is the most common cause of acute liver failure and the leading cause of chronic liver damage requiring liver transplantation in developed countries. Acetaminophen overdose causes a multitude of interrelated biochemical reactions in hepatocytes including the formation of reactive oxygen species, deregulation of Ca(2+) homeostasis, covalent modification and oxidation of proteins, lipid peroxidation, and DNA fragmentation. Although an increase in intracellular Ca(2+) concentration in hepatocytes is a known consequence of acetaminophen overdose, its importance in acetaminophen-induced liver toxicity is not well understood, primarily due to lack of knowledge about the source of the Ca(2+) rise. Here we report that the channel responsible for Ca(2+) entry in hepatocytes in acetaminophen overdose is the Transient Receptor Potential Melanostatine 2 (TRPM2) cation channel. We show by whole-cell patch clamping that treatment of hepatocytes with acetaminophen results in activation of a cation current similar to that activated by H2O2 or the intracellular application of ADP ribose. siRNA-mediated knockdown of TRPM2 in hepatocytes inhibits activation of the current by either acetaminophen or H2O2. In TRPM2 knockout mice, acetaminophen-induced liver damage, assessed by the blood concentration of liver enzymes and liver histology, is significantly diminished compared with wild-type mice. The presented data strongly suggest that TRPM2 channels are essential in the mechanism of acetaminophen-induced hepatocellular death.

Curcumin protects rats against acetaminophen-induced hepatorenal damages and shows synergistic activity with N-acetyl cysteine.

Acetaminophen is one of the most popular analgesic and antipyretic drugs and its overdose, which can cause severe damage to liver and kidneys, is one of the most common reasons of emergency admissions. In this study we investigated the effects of curcumin, derived from plant Curcuma longa, on acetaminophen toxicity, and the possibility of combining therapy of curcumin and N-acetyl cysteine (NAC) to treat this toxicity. The experiments were conducted on 72 male Sprague-Dawley rats randomly divided into 12 groups. Control group was left without treatment, and the other groups were treated with different combinations of acetaminophen, curcumin and NAC. 15min after intraperitoneal injection, the blood level of curcumin was measured using HPLC. Blood levels of AST (aspartate aminotransferase), ALT (alanine aminotransferase), blood urea nitrogen and creatinine were determined 18 and 42h after acetaminophen injection. One week later, the left kidney and the caudate lobe of the liver were harvested to assay glutathione peroxidase, catalase and malondialdehyde. The right kidney and the remaining lobes of the liver were used for histopathology. Analysis of organ function and oxidation parameters showed that curcumin significantly reduced toxic effects of acetaminophen on the liver and kidneys in a dose-dependent manner and significantly potentiated the protective effects of NAC. These findings were confirmed by histopathology. It is concluded that curcumin can protect the liver and kidney from the damage caused by acetaminophen overdose. Moreover, curcumin has the potential to be used in a combination therapy with NAC, significantly decreasing the therapeutic dose of NAC and therefore its side-effects.