NMDA receptor-BK channel coupling regulates synaptic plasticity in the barrel cortex.

Postsynaptic N-methyl-D-aspartate receptors (NMDARs) are crucial mediators of synaptic plasticity due to their ability to act as coincidence detectors of presynaptic and postsynaptic neuronal activity. However, NMDARs exist within the molecular context of a variety of postsynaptic signaling proteins, which can fine-tune their function. Here, we describe a form of NMDAR suppression by large-conductance Ca2+- and voltage-gated K+ (BK) channels in the basal dendrites of a subset of barrel cortex layer 5 pyramidal neurons. We show that NMDAR activation increases intracellular Ca2+ in the vicinity of BK channels, thus activating K+ efflux and strong negative feedback inhibition. We further show that neurons exhibiting such NMDAR-BK coupling serve as high-pass filters for incoming synaptic inputs, precluding the induction of spike timing-dependent plasticity. Together, these data suggest that NMDAR-localized BK channels regulate synaptic integration and provide input-specific synaptic diversity to a thalamocortical circuit.

Pathogen reduction with methylene blue does not have an impact on the clinical effectiveness of COVID-19 convalescent plasma.

BACKGROUND AND OBJECTIVES: There is a concern about a possible deleterious effect of pathogen reduction (PR) with methylene blue (MB) on the function of immunoglobulins of COVID-19 convalescent plasma (CCP). We have evaluated whether MB-treated CCP is associated with a poorer clinical response compared to other inactivation systems at the ConPlas-19 clinical trial. MATERIALS AND METHODS: This was an ad hoc sub-study of the ConPlas-19 clinical trial comparing the proportion of patients transfused with MB-treated CCP who had a worsening of respiration versus those treated with amotosalen (AM) or riboflavin (RB). RESULTS: One-hundred and seventy-five inpatients with SARS-CoV-2 pneumonia were transfused with a single CCP unit. The inactivation system of the CCP units transfused was MB in 90 patients (51.4%), RB in 60 (34.3%) and AM in 25 (14.3%). Five out of 90 patients (5.6%) transfused with MB-treated CCP had worsening respiration compared to 9 out of 85 patients (10.6%) treated with alternative PR methods (p = 0.220). Of note, MB showed a trend towards a lower rate of respiratory progressions at 28 days (risk ratio, 0.52; 95% confidence interval, 0.18-1.50). CONCLUSION: Our data suggest that MB-treated CCP does not provide a worse clinical outcome compared to the other PR methods for the treatment of COVID-19.

Astrocytic IGF-IRs Induce Adenosine-Mediated Inhibitory Downregulation and Improve Sensory Discrimination.

Insulin-like growth factor-I (IGF-I) signaling plays a key role in learning and memory processes. While the effects of IGF-I on neurons have been studied extensively, the involvement of astrocytes in IGF-I signaling and the consequences on synaptic plasticity and animal behavior remain unknown. We have found that IGF-I induces long-term potentiation (LTPIGFI) of the postsynaptic potentials that is caused by a long-term depression of inhibitory synaptic transmission in mice. We have demonstrated that this long-lasting decrease in the inhibitory synaptic transmission is evoked by astrocytic activation through its IGF-I receptors (IGF-IRs). We show that LTPIGFI not only increases the output of pyramidal neurons, but also favors the NMDAR-dependent LTP, resulting in the crucial information processing at the barrel cortex since specific deletion of IGF-IR in cortical astrocytes impairs the whisker discrimination task. Our work reveals a novel mechanism and functional consequences of IGF-I signaling on cortical inhibitory synaptic plasticity and animal behavior, revealing that astrocytes are key elements in these processes.SIGNIFICANCE STATEMENT Insulin-like growth factor-I (IGF-I) signaling plays key regulatory roles in multiple processes of brain physiology, such as learning and memory. Yet, the underlying mechanisms remain largely undefined. Here we demonstrate that astrocytes respond to IGF-I signaling, elevating their intracellular Ca2+ and stimulating the release of ATP/adenosine, which triggers the LTD of cortical inhibitory synapses, thus regulating the behavioral task performance related to cortical sensory information processing. Therefore, the present work represents a major conceptual advance in our knowledge of the cellular basis of IGF-I signaling in brain function, by including for the first time astrocytes as key mediators of IGF-I actions on synaptic plasticity, cortical sensory information discrimination and animal behavior.

SGK1.1 limits brain damage after status epilepticus through M current-dependent and independent mechanisms.

Epilepsy is a neurological condition associated to significant brain damage produced by status epilepticus (SE) including neurodegeneration, gliosis and ectopic neurogenesis. Reduction of these processes constitutes a useful strategy to improve recovery and ameliorate negative outcomes after an initial insult. SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), has been shown to increase M-current density in neurons, leading to reduced excitability and protection against seizures. For this study, we used 4-5 months old male transgenic C57BL/6 J and FVB/NJ mice expressing near physiological levels of a constitutively active form of the kinase controlled by its endogenous promoter. Here we show that SGK1.1 activation potently reduces levels of neuronal death (assessed using Fluoro-Jade C staining) and reactive glial activation (reported by GFAP and Iba-1 markers) in limbic regions and cortex, 72 h after SE induced by kainate, even in the context of high seizure activity. This neuroprotective effect is not exclusively through M-current activation but is also directly linked to decreased apoptosis levels assessed by TUNEL assays and quantification of Bim and Bcl-xL by western blot of hippocampal protein extracts. Our results demonstrate that this newly described antiapoptotic role of SGK1.1 activation acts synergistically with the regulation of cellular excitability, resulting in a significant reduction of SE-induced brain damage in areas relevant to epileptogenesis.

SGK1.1 Reduces Kainic Acid-Induced Seizure Severity and Leads to Rapid Termination of Seizures.

Approaches to control epilepsy, one of the most important idiopathic brain disorders, are of great importance for public health. We have previously shown that in sympathetic neurons the neuronal isoform of the serum and glucocorticoid-regulated kinase (SGK1.1) increases the M-current, a well-known target for seizure control. The effect of SGK1.1 activation on kainate-induced seizures and neuronal excitability was studied in transgenic mice that express a permanently active form of the kinase, using electroencephalogram recordings and electrophysiological measurements in hippocampal brain slices. Our results demonstrate that SGK1.1 activation leads to reduced seizure severity and lower mortality rates following status epilepticus, in an M-current-dependent manner. EEG is characterized by reduced number, shorter duration, and early termination of kainate-induced seizures in the hippocampus and cortex. Hippocampal neurons show decreased excitability associated to increased M-current, without altering basal synaptic transmission or other neuronal properties. Altogether, our results reveal a novel and selective anticonvulsant pathway that promptly terminates seizures, suggesting that SGK1.1 activation can be a potent factor to secure the brain against permanent neuronal damage associated to epilepsy.

Endocannabinoid-Dependent Long-Term Potentiation of Synaptic Transmission at Rat Barrel Cortex.

Brain-derived neurotrophic factor (BDNF) plays a critical role in modulating plasticity in sensory cortices. Indeed, a BDNF-dependent long-term potentiation (LTP) at distal basal excitatory synapses of Layer 5 pyramidal neurons (L5PNs) has been demonstrated in disinhibited rat barrel cortex slices. Although it is well established that this LTP requires the pairing of excitatory postsynaptic potentials (PSPs) with Ca2+ spikes, its induction when synaptic inhibition is working remains unexplored. Here we show that low-frequency stimulation at basal dendrites of L5PNs is able to trigger a PSP followed by an action potential (AP) and a slow depolarization (termed PSP-Ca2+ response) in thalamocortical slices without blocking synaptic inhibition. We demonstrate that AP barrage-mediated release of endocannabinoids (eCBs) from the recorded L5PNs induces PSP-Ca2+ response facilitation and BDNF-dependent LTP. Indeed, this LTP requires the type 1 cannabinoid receptors activation, is prevented by postsynaptic intracellular 1,2-bis(2-aminophenoxy) ethane-N,N,N,N'-tetraacetic acid (BAPTA) or the anandamide membrane transporter inhibitor AM404, and only occurs in L5PNs neurons showing depolarization-induced suppression of inhibition. Additionally, electrical stimulation at the posteromedial thalamic nucleus induced similar response and LTP. These results reveal a novel form of eCB-dependent LTP at L5PNs that could be relevant in the processing of sensory information in the barrel cortex.

Astrocyte calcium signal and gliotransmission in human brain tissue.

Brain function is recognized to rely on neuronal activity and signaling processes between neurons, whereas astrocytes are generally considered to play supportive roles for proper neuronal function. However, accumulating evidence indicates that astrocytes sense and control neuronal and synaptic activity, indicating that neuron and astrocytes reciprocally communicate. While this evidence has been obtained in experimental animal models, whether this bidirectional signaling between astrocytes and neurons occurs in human brain remains unknown. We have investigated the existence of astrocyte-neuron communication in human brain tissue, using electrophysiological and Ca(2+) imaging techniques in slices of the cortex and hippocampus obtained from biopsies from epileptic patients. Cortical and hippocampal human astrocytes displayed spontaneous Ca(2+) elevations that were independent of neuronal activity. Local application of transmitter receptor agonists or nerve electrical stimulation transiently elevated Ca(2+) in astrocytes, indicating that human astrocytes detect synaptic activity and respond to synaptically released neurotransmitters, suggesting the existence of neuron-to-astrocyte communication in human brain tissue. Electrophysiological recordings in neurons revealed the presence of slow inward currents (SICs) mediated by NMDA receptor activation. The frequency of SICs increased after local application of ATP that elevated astrocyte Ca(2+). Therefore, human astrocytes are able to release the gliotransmitter glutamate, which affect neuronal excitability through activation of NMDA receptors in neurons. These results reveal the existence of reciprocal signaling between neurons and astrocytes in human brain tissue, indicating that astrocytes are relevant in human neurophysiology and are involved in human brain function.

Bidirectional modulation of synaptic transmission by insulin-like growth factor-I.

Insulin-like growth factor-I (IGF-I) plays a key role in the modulation of synaptic plasticity and is an essential factor in learning and memory processes. However, during aging, IGF-I levels are decreased, and the effect of this decrease in the induction of synaptic plasticity remains unknown. Here we show that the induction of N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) at layer 2/3 pyramidal neurons (PNs) of the mouse barrel cortex is favored or prevented by IGF-I (10 nM) or IGF-I (7 nM), respectively, when IGF-I is applied 1 h before the induction of Hebbian LTP. Analyzing the cellular basis of this bidirectional control of synaptic plasticity, we observed that while 10 nM IGF-I generates LTP (LTPIGF-I) of the post-synaptic potentials (PSPs) by inducing long-term depression (LTD) of the inhibitory post-synaptic currents (IPSCs), 7 nM IGF-I generates LTD of the PSPs (LTDIGF-I) by inducing LTD of the excitatory post-synaptic currents (EPSCs). This bidirectional effect of IGF-I is supported by the observation of IGF-IR immunoreactivity at both excitatory and inhibitory synapses. Therefore, IGF-I controls the induction of Hebbian NMDAR-dependent plasticity depending on its concentration, revealing novel cellular mechanisms of IGF-I on synaptic plasticity and in the learning and memory machinery of the brain.

Endocannabinoid and Nitric Oxide-Dependent IGF-I-Mediated Synaptic Plasticity at Mice Barrel Cortex.

Insulin-like growth factor-I (IGF-I) signaling plays a key role in learning and memory. IGF-I increases the spiking and induces synaptic plasticity in the mice barrel cortex (Noriega-Prieto et al., 2021), favoring the induction of the long-term potentiation (LTP) by Spike Timing-Dependent Protocols (STDP) (Noriega-Prieto et al., 2021). Here, we studied whether these IGF-I effects depend on endocannabinoids (eCBs) and nitric oxide (NO). We recorded both excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) evoked by stimulation of the basal dendrites of layer II/III pyramidal neurons of the Barrel Cortex and analyzed the effect of IGF-I in the presence of a CB1R antagonist, AM251, and inhibitor of the NO synthesis, L-NAME, to prevent the eCBs and the NO-mediated signaling. Interestingly, L-NAME abolished any modulatory effect of the IGF-I-induced excitatory and inhibitory transmission changes, suggesting the essential role of NO. Surprisingly, the inhibition of CB1Rs did not only block the potentiation of EPSCs but reversed to a depression, highlighting the remarkable functions of the eCB system. In conclusion, eCBs and NO play a vital role in deciding the sign of the effects induced by IGF-I in the neocortex, suggesting a neuromodulatory interplay among IGF-I, NO, and eCBs.

IGF-1 facilitates extinction of conditioned fear.

Insulin-like growth factor-1 (IGF-1) plays a key role in synaptic plasticity, spatial learning, and anxiety-like behavioral processes. While IGF-1 regulates neuronal firing and synaptic transmission in many areas of the central nervous system, its signaling and consequences on excitability, synaptic plasticity, and animal behavior dependent on the prefrontal cortex remain unexplored. Here, we show that IGF-1 induces a long-lasting depression of the medium and slow post-spike afterhyperpolarization (mAHP and sAHP), increasing the excitability of layer 5 pyramidal neurons of the rat infralimbic cortex. Besides, IGF-1 mediates a presynaptic long-term depression of both inhibitory and excitatory synaptic transmission in these neurons. The net effect of this IGF-1-mediated synaptic plasticity is a long-term potentiation of the postsynaptic potentials. Moreover, we demonstrate that IGF-1 favors the fear extinction memory. These results show novel functional consequences of IGF-1 signaling, revealing IGF-1 as a key element in the control of the fear extinction memory.

Relationship between the ABO blood group and COVID-19 susceptibility, severity and mortality in two cohorts of patients.

BACKGROUND: Several articles reported the existence of an association between ABO blood groups and COVID-19 susceptibility. Group A and group O individuals showed a higher and lower risk, respectively, of becoming infected. No association was observed between ABO groups and mortality. To verify this association, we performed a retrospective study of two cohorts of patients with different demographic and clinical characteristics. MATERIAL AND METHODS: A total of 854 regular blood donors were recruited for convalescent plasma donation after recovering from a mild COVID-19 infection, and a group of 965 patients more severely affected who were transfused during hospitalisation were also included. We also investigated the potential role of the different risk factors on patient outcome and death. To eliminate the confounding effect of risk factors on mortality, a propensity score analysis was performed. RESULTS: Blood group A and blood group O COVID-19 blood donors showed a higher and lower risk, respectively, for acquiring COVID-19. In contrast, this association was not found in the group of patients transfused during hospitalisation, probably due to the great differences in demographic and clinical characteristics between the two groups. Regarding severity, age was one of the most significant risk factors. ABO blood groups were also seen to represent important risk factors for COVID-19 severity and mortality. Mortality risk in group A individuals was significantly higher than in group O individuals (OR: 1.75, 95% CI: 1.22-2.51). DISCUSSION: The association between the ABO blood groups and the susceptibility to acquire COVID-19 infection was confirmed in the group of blood donors. ABO blood groups were also associated to COVID-19 severity and mortality in the group of patients transfused during hospitalisation. Therefore, blood groups A and O are two important factors to be considered when evaluating the prognosis of patients with COVID-19.

Nitric Oxide-Dependent LTD at Infralimbic Cortex.

Dendritic calcium (Ca2+) spikes play a key role in the genesis of long-term synaptic plasticity. Although synaptic plasticity in the infralimbic cortex is critical for the extinction of fear-conditioned memory, the role of Ca2+-spikes in the induction of synaptic plasticity at this cortex has not been explored in depth. Here we show that Ca2+-spikes in layer 5 pyramidal neurons (L5 PNs) of the rat infralimbic cortex are crucial in the induction of long-term depression of the excitatory postsynaptic currents (EPSCs). The lack of effect on the postsynaptic currents evoked by puffing glutamate and the changes in the variance of the EPSC amplitude that paralleled its inhibition suggest that this LTD of the EPSCs is mediated presynaptically. However, its induction requires cytosolic calcium elevations because it is prevented when the recorded L5 PN is loaded with BAPTA. Moreover, it depends on the synthesis of nitric oxide (NO) because it is absent on slices incubated with nitric oxidase synthase inhibitor L-NAME. Therefore, Ca2+-spikes can trigger LTD of the ESPCs through the NO dependent presynaptic form of synaptic plasticity, thus providing a novel form of inducing synaptic plasticity at L5 PNs of the rat infralimbic cortex.

Role of cellular prion protein on LTP expression in aged mice.

Cellular prion protein (PrP(c)) has been associated with some physiological functions in the last few years. In a previous paper, we have demonstrated an increased hippocampal synaptic transmission in adult mice lacking this protein. In the present study, we investigate the impact of aging on the generation and maintenance of hippocampal long-term Potentiation (LTP) in 9-month-old mice devoid of PrP(c) protein (Prnp(0/0)). We observed a lower threshold for inducing LTP in 9-month-old Prnp(0/0) mice compared to wild-type ones at the same age. The maintenance of dentate gyrus LTP was more persistent in hippocampal slices from Prnp(0/0) mice. Furthermore, the expression of mRNA for NR2A and NR2B subunits of the NMDA glutamatergic receptor in hippocampus of aged Prnp(0/0) animals showed an increase compared to the wild type. We propose that increased hippocampal glutamatergic transmission in Prnp(0/0) mice is related to the enhanced plasticity and persistence of the dentate LTP.

Hippocampal synaptic plasticity in mice devoid of cellular prion protein.

The cellular prion protein plays a role in the etiology of transmissible and inherited spongiform encephalopathies. However, the physiological role of the cellular prion protein is still under debate. Results regarding the synaptic transmission using the same strain of animals where the cellular prion protein gene was ablated are controversial, and need further investigation. In this work, we have studied the hippocampal synaptic transmission in mice devoid of normal cellular prion protein, and have shown that these animals present an increased excitability in this area by the lower threshold (20 Hz) to generate long-term potentiation (LTP) in hippocampal dentate gyrus when compared to wild-type animals. The mice devoid of normal cellular prion protein are also more sensitive to the blocking effects of dizocilpine and 2-amino-5-phosphonopentanoic acid on the hippocampal long-term potentiation generation. In situ hydridization experiments demonstrated overexpression of the mRNAs for the N-methyl-D-aspartate (NMDA) receptor NR2A and NR2B subunits in mice devoid of normal cellular prion protein. Therefore, our results indicate that these animals have an increased hippocampal synaptic plasticity which can be explained by a facilitated glutamatergic transmission. The higher expression of specific N-methyl-d-aspartate receptor subunits may account for these effects.

Environmental changes modify the expression of Diazepam withdrawal.

Early results from our laboratory have demonstrated a positive correlation between increased hippocampal synaptic plasticity and development of tolerance to hypolocomotive effect of Diazepam (DZ). We have found recently, that pre-exposure to DZ administration context impairs increase of hippocampal synaptic plasticity in conjunction with tolerance to DZ. These findings have suggested, that the tolerance to DZ is context specific. Furthermore, the hippocampus can be critically involved in the behavioral expression of conditioned tolerance to DZ. The results of the present investigation show that animals chronically treated with DZ for 18 days exhibit withdrawal signs, evaluated as an increased anxiety in an elevated plus maze. These animals also show, a facilitation in the threshold to induce long-term potentiation in the hippocampal formation. These phenomena have a strong dependency on the drug administration context, since both are reversed after the introduction of some changes in the drug administration environment. Furthermore, the alteration of some environmental cues increased the locomotive activity in animals that did not show anxiety as a withdrawal signs. We conclude that a common neural system could underlie the behavioral expression of the conditioned tolerance and dependence on DZ.

Involvement of nNOS/NO/sGC/cGMP signaling pathway in cocaine sensitization and in the associated hippocampal alterations: does phosphodiesterase 5 inhibition help to drug vulnerability?

RATIONALE: Repeated cocaine administration induces behavioral sensitization in about 50 % of treated animals. Nitric oxide could be involved in the acquisition and maintenance of behavioral cocaine effects, probably by activation of neuronal nitric oxide synthase (nNOS)/NO/soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP) signaling pathway, since inhibition of the nNOS enzyme attenuates development of sensitization in rats. On the other hand, increased cGMP availability by phosphodiesterase 5 inhibitors has been correlated to the misuse and recreational use of these agents and also to the concomitant use with illicit drugs in humans. Hippocampus is an important brain region for conditioning to general context previously associated to drug availability, influencing drug-seeking behavior and sensitization. Moreover, cocaine and other drugs of abuse can affect the strength of glutamate synapses in this structure, lastly modifying neuronal activity in main regions of the reward circuitry. OBJECTIVE: The objective of this study is to determine whether the pharmacological manipulation of nNOS/NO/sGC/cGMP signaling pathway altered changes induced by repeated cocaine exposure. RESULTS: The present investigation showed a relationship between behavioral cocaine sensitization, reduced threshold to generate long-term potentiation (LTP) in hippocampal dentate gyrus, and increased nNOS activity in this structure. However, when nNOS or sGC were inhibited, the number of sensitized animals was reduced, and the threshold to generate LTP was increased. The opposite occurred when cGMP availability was increased. CONCLUSION: We demonstrate a key role of the nNOS activity and NO/sGC/cGMP signaling pathway in the development of cocaine sensitization and in the associated enhancement of hippocampal synaptic transmission.