Photo-Chemical Stimulation of Neurons with Organic Semiconductors.

Recent advances in light-responsive materials enabled the development of devices that can wirelessly activate tissue with light. Here it is shown that solution-processed organic heterojunctions can stimulate the activity of primary neurons at low intensities of light via photochemical reactions. The p-type semiconducting polymer PDCBT and the n-type semiconducting small molecule ITIC (a non-fullerene acceptor) are coated on glass supports, forming a p-n junction with high photosensitivity. Patch clamp measurements show that low-intensity white light is converted into a cue that triggers action potentials in primary cortical neurons. The study shows that neat organic semiconducting p-n bilayers can exchange photogenerated charges with oxygen and other chemical compounds in cell culture conditions. Through several controlled experimental conditions, photo-capacitive, photo-thermal, and direct hydrogen peroxide effects on neural function are excluded, with photochemical delivery being the possible mechanism. The profound advantages of low-intensity photo-chemical intervention with neuron electrophysiology pave the way for developing wireless light-based therapy based on emerging organic semiconductors.

Functional expression of TrkB receptors on interneurones and pyramidal cells of area CA3 of the rat hippocampus.

The dentate gyrus and hippocampal area CA3 region of the mammalian brain contains the highest levels of brain-derived neurotrophic factor (BDNF) and its canonical membrane receptor, tropomyosin-related kinase B (TrkB). Therefore, the present study examines the expression and physiological responses triggered by activation of TrkB on hippocampal area CA3 interneurones and pyramidal cells of the rat hippocampus. Triple immunolabelling for TrkB, glutamate decarboxylase 67, and the calcium-binding proteins parvalbumin, calbindin or calretinin confirms the somatic expression of TrkB in all CA3 sublayers. TrkB-positive interneurones with fast-spiking discharge are restricted to strata oriens and lucidum, whereas regular-spiking interneurones are found in the strata lucidum, radiatum and lacunosum-moleculare. Activation of TrkB receptors with 7,8-dihydroxyflavone (DHF) modulates amplitude and frequency of spontaneous synaptic currents recorded from CA3 interneurones. Furthermore, the isolated excitatory postsynaptic currents (EPSC) of CA3 interneurones evoked by the mossy fibres (MF) or commissural/associational (C/A) axons, show input-specific synaptic potentiation in response to TrkB stimulation. On CA3 pyramidal cells, stimulation with DHF potentiates the MF synaptic transmission and increases the MF-EPSP - spike coupling. The latter exhibits a dramatic increase when picrotoxin is bath perfused after DHF, indicating that local interneurones restrain the excitability mediated by activation of TrkB. Therefore, we propose that release of BDNF on area CA3 reshapes the output of this hippocampal region by simultaneous activation of TrkB on GABAergic interneurones and pyramidal cells.

Long-Term Functional and Cytoarchitectonic Effects of the Systemic Administration of the Histamine H1 Receptor Antagonist/Inverse Agonist Chlorpheniramine During Gestation in the Rat Offspring Primary Motor Cortex.

The transient histaminergic system is among the first neurotransmitter systems to appear during brain development in the rat mesencephalon/rhombencephalon. Histamine increases FOXP2-positive deep-layer neuron differentiation of cortical neural stem cells through H1 receptor activation in vitro. The in utero or systemic administration of chlorpheniramine (H1 receptor antagonist/inverse agonist) during deep-layer cortical neurogenesis decreases FOXP2 neurons in the developing cortex, and H1R- or histidine decarboxylase-knockout mice show impairment in learning and memory, wakefulness and nociception, functions modulated by the cerebral cortex. Due to the role of H1R in cortical neural stem cell neurogenesis, the purpose of this study was to evaluate the postnatal impact of the systemic administration of chlorpheniramine during deep-layer cortical neuron differentiation (E12-14) in the primary motor cortex (M1) of neonates (P0) and 21-day-old pups (P21). Chlorpheniramine or vehicle were systemically administered (5 mg/kg, i.p.) to pregnant Wistar rats at gestational days 12-14, and the expression and distribution of deep- (FOXP2 and TBR1) and superficial-layer (SATB2) neuronal cortical markers were analyzed in neonates from both groups. The qRT-PCR analysis revealed a reduction in the expression of Satb2 and FoxP2. However, Western blot and immunofluorescence showed increased protein levels in the chlorpheniramine-treated group. In P21 pups, the three markers showed impaired distribution and increased immunofluorescence in the experimental group. The Sholl analysis evidenced altered dendritic arborization of deep-layer neurons, with lower excitability in response to histamine, as evaluated by whole-cell patch-clamp recording, as well as diminished depolarization-evoked [3H]-glutamate release from striatal slices. Overall, these results suggest long-lasting effects of blocking H1Rs during early neurogenesis that may impact the pathways involved in voluntary motor activity and cognition.

Lactate induces synapse-specific potentiation on CA3 pyramidal cells of rat hippocampus.

Neuronal activity within the physiologic range stimulates lactate production that, via metabolic pathways or operating through an array of G-protein-coupled receptors, regulates intrinsic excitability and synaptic transmission. The recent discovery that lactate exerts a tight control of ion channels, neurotransmitter release, and synaptic plasticity-related intracellular signaling cascades opens up the possibility that lactate regulates synaptic potentiation at central synapses. Here, we demonstrate that extracellular lactate (1-2 mM) induces glutamatergic potentiation on the recurrent collateral synapses of hippocampal CA3 pyramidal cells. This potentiation is independent of lactate transport and further metabolism, but requires activation of NMDA receptors, postsynaptic calcium accumulation, and activation of a G-protein-coupled receptor sensitive to cholera toxin. Furthermore, perfusion of 3,5- dihydroxybenzoic acid, a lactate receptor agonist, mimics this form of synaptic potentiation. The transduction mechanism underlying this novel form of synaptic plasticity requires G-protein ßγ subunits, inositol-1,4,5-trisphosphate 3-kinase, PKC, and CaMKII. Activation of these signaling cascades is compartmentalized in a synapse-specific manner since lactate does not induce potentiation at the mossy fiber synapses of CA3 pyramidal cells. Consistent with this synapse-specific potentiation, lactate increases the output discharge of CA3 neurons when recurrent collaterals are repeatedly activated during lactate perfusion. This study provides new insights into the cellular mechanisms by which lactate, acting via a membrane receptor, contributes to the memory formation process.

Impaired Cortical Cytoarchitecture and Reduced Excitability of Deep-Layer Neurons in the Offspring of Diabetic Rats.

Maternal diabetes has been related to low verbal task scores, impaired fine and gross motor skills, and poor performance in graphic and visuospatial tasks during childhood. The primary motor cortex is important for controlling motor functions, and embryos exposed to high glucose show changes in cell proliferation, migration, and differentiation during corticogenesis. However, the existing studies do not discriminate between embryos with or without neural tube defects, making it difficult to conclude whether the reported changes are related to neural tube defects or other anomalies. Furthermore, postnatal effects on central nervous system cytoarchitecture and function have been scarcely addressed. Through molecular, biochemical, morphological, and electrophysiological approaches, we provide evidence of impaired primary motor cerebral cortex lamination and neuronal function in pups from diabetic rats, showing an altered distribution of SATB2, FOXP2, and TBR1, impaired cell migration and polarity, and decreased excitability of deep-layer cortical neurons, suggesting abnormalities in cortico-cortical and extra-cortical innervation. Furthermore, phase-plot analysis of action potentials suggests changes in the activity of potassium channels. These results indicate that high-glucose insult during development promotes complex changes in migration, neurogenesis, cell polarity establishment, and dendritic arborization, which in turn lead to reduced excitability of deep-layer cortical neurons.

Modulation of hippocampal excitability via the hydroxycarboxylic acid receptor 1.

In addition to its prominent role as an energetic substrate in the brain, lactate is emerging as a signaling molecule capable of controlling neuronal excitability. The finding that the lactate-activated receptor (hydroxycarboxylic acid receptor 1; HCA1) is widely expressed in the brain opened up the possibility that lactate exerts modulation of neuronal activity via a transmembranal receptor-linked mechanism. Here, we show that lactate causes biphasic modulation of the intrinsic excitability of CA1 pyramidal cells. In the low millimolar range, lactate or the HCA1 agonist 3,5-DHBA reduced the input resistance and membrane time constant. In addition, activation of HCA1 significantly blocked the fast inactivating sodium current and increased the delay from inactivation to a conducting state of the sodium channel. As the observed actions occurred in the presence of 4-CIN, a blocker of the neuronal monocarboxylate transporter, the possibility that lactate acted via neuronal metabolism is unlikely. Consistently, modulation of the intrinsic excitability was abolished when CA1 pyramidal cells were dialyzed with pertussis toxin, indicating the dependency of a Gαi/o -protein-coupled receptor. The activation of HCA1 appears to serve as a restraining mechanism during enhanced network activity and may function as a negative feedback for the astrocytic production of lactate.

Probiotics and Prebiotics as a Therapeutic Strategy to Improve Memory in a Model of Middle-Aged Rats.

Aging is associated with morphological, physiological and metabolic changes, leading to multiorgan degenerative pathologies, such as cognitive function decline. It has been suggested that memory loss also involves a decrease in neurotrophic factors, including brain-derived neurotrophic factor (BDNF). In recent years, microbiota has been proposed as an essential player in brain development, as it is believed to activate BDNF secretion through butyrate production. Thus, microbiota modulation by supplementation with probiotics and prebiotics may impact cognitive decline. This study aimed to evaluate the effects of probiotics and prebiotics supplementation on the memory of middle-aged rats. Sprague-Dawley male rats were randomized in four groups (n = 13 per group): control (water), probiotic (E. faecium), prebiotic (agave inulin), symbiotic (E. faecium + inulin), which were administered for 5 weeks by oral gavage. Spatial and associative memory was analyzed using the Morris Water Maze (MWM) and Pavlovian autoshaping tests, respectively. Hippocampus was obtained to analyze cytokines [interleukin (IL-1ß) and tumor necrosis factor (TNF-α)], BDNF and γ-aminobutyric acid (GABA) by enzyme-linked immunosorbent assay (ELISA). Butyrate concentrations were also evaluated in feces. The symbiotic group showed a significantly better performance in MWM (p < 0.01), but not in Pavlovian autoshaping test. It also showed significantly lower concentrations of pro-inflammatory cytokines (p < 0.01) and the reduction in IL-1ß correlated with a better performance of the symbiotic group in MWM (p < 0.05). Symbiotic group also showed the highest BDNF and butyrate levels (p < 0.0001). Finally, we compared the electrophysiological responses of control (n = 8) and symbiotic (n = 8) groups. Passive properties of CA1 pyramidal cells (PCs) exhibited changes in response to the symbiotic treatment. Likewise, this group showed an increase in the N-methyl-D-aspartate receptor (NMDA)/AMPA ratio and exhibited robust long-term potentiation (LTP; p < 0.01). Integrated results suggest that symbiotics could improve age-related impaired memory.

Aging-related impairments of hippocampal mossy fibers synapses on CA3 pyramidal cells.

The network interaction between the dentate gyrus and area CA3 of the hippocampus is responsible for pattern separation, a process that underlies the formation of new memories, and which is naturally diminished in the aged brain. At the cellular level, aging is accompanied by a progression of biochemical modifications that ultimately affects its ability to generate and consolidate long-term potentiation. Although the synapse between dentate gyrus via the mossy fibers (MFs) onto CA3 neurons has been subject of extensive studies, the question of how aging affects the MF-CA3 synapse is still unsolved. Extracellular and whole-cell recordings from acute hippocampal slices of aged Wistar rats (34 ± 2 months old) show that aging is accompanied by a reduction in the interneuron-mediated inhibitory mechanisms of area CA3. Several MF-mediated forms of short-term plasticity, MF long-term potentiation and at least one of the critical signaling cascades necessary for potentiation are also compromised in the aged brain. An analysis of the spontaneous glutamatergic and gamma-aminobutyric acid-mediated currents on CA3 cells reveal a dramatic alteration in amplitude and frequency of the nonevoked events. CA3 cells also exhibited increased intrinsic excitability. Together, these results demonstrate that aging is accompanied by a decrease in the GABAergic inhibition, reduced expression of short- and long-term forms of synaptic plasticity, and increased intrinsic excitability.