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1. Differential effect of NMDA receptor GluN2C and GluN2D subunit ablation on behavior and channel blocker-induced schizophrenia phenotypes

   https://doi.org/10.1038/s41598-019-43957-2  

   Shelkar, Gajanan P. ; Pavuluri, Ratnamala ; Gandhi, Pauravi J. ; Ravikrishnan, Aparna ; Gawande, Dinesh Y. ; Liu, Jinxu ; Stairs, Dustin J. ; Ugale, Rajesh R. ; Dravid, Shashank M. ( May 2019 , Scientific Reports)

   The GluN2C- and GluN2D-containing NMDA receptors are distinct from GluN2A- and GluN2B-containing receptors in many aspects including lower sensitivity to Mg²⁺block and lack of desensitization. Recent studies have highlighted the unique contribution of GluN2C and GluN2D subunits in various aspects of neuronal and circuit function and behavior, however a direct comparison of the effect of ablation of these subunits in mice on pure background strain has not been conducted. Using knockout-first strains for theGRIN2CandGRIN2Dproduced on pure C57BL/6N strain, we compared the effect of partial or complete ablation of GluN2C and GluN2D subunit on various behaviors relevant to mental disorders. A large number of behaviors described previously in GluN2C and GluN2D knockout mice were reproduced in these mice, however, some specific differences were also observed possibly representing strain effects. We also examined the response to NMDA receptor channel blockers in these mouse strains and surprisingly found that unlike previous reports GluN2D knockout mice were not resistant to phencyclidine-induced hyperlocomotion. Interestingly, the GluN2C knockout mice showed reduced sensitivity to phencyclidine-induced hyperlocomotion. We also found that NMDA receptor channel blocker produced a deficit in prepulse inhibition which was prevented by a GluN2C/2D potentiator in wildtype and GluN2C heterozygous mice but not in GluN2C knockout mice. Together these results demonstrate a unique role of GluN2C subunit in schizophrenia-like behaviors.

    

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2. NMDA receptors promote hippocampal sharp‐wave ripples and the associated coactivity of CA1 pyramidal cells

   https://doi.org/10.1002/hipo.23276  

   Howe, Timothy ; Blockeel, Anthony J. ; Taylor, Hannah ; Jones, Matthew W. ; Bazhenov, Maxim ; Malerba, Paola ( October 2020 , Hippocampus)

   Hippocampal sharp‐wave ripples (SWRs) support the reactivation of memory representations, relaying information to neocortex during “offline” and sleep‐dependent memory consolidation. While blockade of NMDA receptors (NMDAR) is known to affect both learning and subsequent consolidation, the specific contributions of NMDAR activation to SWR‐associated activity remain unclear. Here, we combine biophysical modeling with in vivo local field potential (LFP) and unit recording to quantify changes in SWR dynamics following inactivation of NMDAR. In a biophysical model of CA3‐CA1 SWR activity, we find that NMDAR removal leads to reduced SWR density, but spares SWR properties such as duration, cell recruitment and ripple frequency. These predictions are confirmed by experiments in which NMDAR‐mediated transmission in rats was inhibited using three different NMDAR antagonists, while recording dorsal CA1 LFP. In the model, loss of NMDAR‐mediated conductances also induced a reduction in the proportion of cell pairs that co‐activate significantly above chance across multiple events. Again, this prediction is corroborated by dorsal CA1 single‐unit recordings, where the NMDAR blocker ketamine disrupted correlated spiking during SWR. Our results are consistent with a framework in which NMDA receptors both promote activation of SWR events and organize SWR‐associated spiking content. This suggests that, while SWR are short‐lived events emerging in fast excitatory‐inhibitory networks, slower network components including NMDAR‐mediated currents contribute to ripple density and promote consistency in the spiking content across ripples, underpinning mechanisms for fine‐tuning of memory consolidation processes.

    

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3. Endogenous AT1 receptor–protein kinase C activity in the hypothalamus augments glutamatergic input and sympathetic outflow in hypertension

   https://doi.org/10.1113/JP278427  

   Ma, Huijie ; Chen, Shao‐Rui ; Chen, Hong ; Pan, Hui‐Lin ( July 2019 , The Journal of Physiology)

   The angiotensin AT1 receptor expression and protein kinase C (PKC)‐mediated NMDA receptor phosphorylation levels in the hypothalamus are increased in a rat genetic model of hypertension.

   Blocking AT1 receptors or PKC activity normalizes the increased pre‐ and postsynaptic NMDA receptor activity of hypothalamic presympathetic neurons in hypertensive animals.

   Inhibition of AT1 receptor–PKC activity in the hypothalamus reduces arterial blood pressure and sympathetic nerve discharges in hypertensive animals.

   AT1 receptors in the hypothalamus are endogenously activated to sustain NMDA receptor hyperactivity and elevated sympathetic outflow via PKC in hypertension.

   Increased synapticN‐methyl‐d‐aspartate receptor (NMDAR) activity in the hypothalamic paraventricular nucleus (PVN) plays a major role in elevated sympathetic output in hypertension. Although exogenous angiotensin II (AngII) can increase NMDAR activity in the PVN, whether endogenous AT1 receptor–protein kinase C (PKC) activity mediates the augmented NMDAR activity of PVN presympathetic neurons in hypertension is unclear. Here we show that blocking AT1 receptors with losartan or inhibiting PKC with chelerythrine significantly decreased the frequency of NMDAR‐mediated miniature excitatory postsynaptic currents (mEPSCs) and the amplitude of puff NMDA currents of retrogradely labelled spinally projecting PVN neurons in spontaneously hypertensive rats (SHRs). Also, treatment with chelerythrine abrogated the potentiating effect of AngII on mEPSCs and puff NMDA currents of labelled PVN neurons in SHRs. In contrast, neither losartan nor chelerythrine had any effect on mEPSCs or puff NMDA currents in labelled PVN neurons in Wistar–Kyoto (WKY) rats. Furthermore, levels of AT1 receptor mRNA and PKC‐mediated NMDAR phosphorylation in the PVN were significantly higher in SHRs than in WKY rats. In addition, microinjection of losartan or chelerythrine into the PVN substantially reduced blood pressure and renal sympathetic nerve discharges in SHRs but not in WKY rats. Chelerythrine blocked sympathoexcitatory responses to AngII microinjected into the PVN. Our findings suggest that endogenous AT1 receptor–PKC activity is essential for presynaptic and postsynaptic NMDAR hyperactivity of PVN presympathetic neurons and for the augmented sympathetic outflow in hypertension. This information advances our mechanistic understanding of the interplay between angiotensinergic and glutamatergic excitatory inputs in hypertension.

    

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4. Individual differences in the positive outcome from adolescent ketamine treatment in a female mouse model of anorexia nervosa involve drebrin A at excitatory synapses of the medial prefrontal cortex

   https://doi.org/10.1002/syn.22253  

   Temizer, Rose ; Chen, Yi‐Wen ; Aoki, Chiye ( October 2022 , Synapse)

   Anorexia nervosa (AN) is a mental illness with the highest rates of mortality and relapse, and no approved pharmacological treatment. Using an animal model of AN, called activity‐based anorexia (ABA), we showed earlier that a single intraperitoneal injection of ketamine at a dose of 30 mg/kg (30mgKET), but not 3 mg/kg (3mgKET), has a long‐lasting effect upon adolescent females of ameliorating anorexia‐like symptoms through the following changes: enhanced food consumption and body weight; reduced running and anxiety‐like behavior. However, there were also individual differences in the drug's efficacy. We hypothesized that individual differences in ketamine's ameliorative effects involve drebrin A, an F‐actin‐binding protein known to be required for the activity‐dependent trafficking of NMDA receptors (NMDARs). We tested this hypothesis by electron microscopic quantifications of drebrin A immunoreactivity at excitatory synapses of pyramidal neurons (PN) and GABAergic interneurons (GABA‐IN) in deep layer 1 of prefrontal cortex (PFC) of these mice. Results reveal that (1) the areal density of excitatory synapses on GABA‐IN is greater for the 30mgKET group than the 3mgKET group; (2) the proportion of drebrin A+ excitatory synapses is greater for both PN and GABA‐IN of 30mgKET than 3mgKET group. Correlation analyses with behavioral measurements revealed that (3) 30mgKET's protection is associated with reduced levels of drebrin A in the cytoplasm of GABA‐IN and higher levels at extrasynaptic membranous sites of PN and GABA‐IN; (5) altogether pointing to 30mgKET‐induced homeostatic plasticity that engages drebrin A at excitatory synapses of both PN and GABA‐IN.

    

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5. Piezo1 channels mediate trabecular meshwork mechanotransduction and promote aqueous fluid outflow

   https://doi.org/10.1113/JP281011  

   Yarishkin, Oleg ; Phuong, Tam T. T. ; Baumann, Jackson M. ; De Ieso, Michael L. ; Vazquez‐Chona, Felix ; Rudzitis, Christopher N. ; Sundberg, Chad ; Lakk, Monika ; Stamer, W. Daniel ; Križaj, David ( December 2020 , The Journal of Physiology)

   Trabecular meshwork (TM) is a highly mechanosensitive tissue in the eye that regulates intraocular pressure through the control of aqueous humour drainage.

   Its dysfunction underlies the progression of glaucoma but neither the mechanisms through which TM cells sense pressure nor their role in aqueous humour outflow are understood at the molecular level.

   We identified the Piezo1 channel as a key TM transducer of tensile stretch, shear flow and pressure.

   Its activation resulted in intracellular signals that altered organization of the cytoskeleton and cell‐extracellular matrix contacts and modulated the trabecular component of aqueous outflow whereas another channel, TRPV4, mediated a delayed mechanoresponse.

   This study helps elucidate basic mechanotransduction properties that may contribute to intraocular pressure regulation in the vertebrate eye.

   Chronic elevations in intraocular pressure (IOP) can cause blindness by compromising the function of trabecular meshwork (TM) cells in the anterior eye, but how these cells sense and transduce pressure stimuli is poorly understood. Here, we demonstrate functional expression of two mechanically activated channels in human TM cells. Pressure‐induced cell stretch evoked a rapid increase in transmembrane current that was inhibited by antagonists of the mechanogated channel Piezo1, Ruthenium Red and GsMTx4, and attenuated in Piezo1‐deficient cells. The majority of TM cells exhibited a delayed stretch‐activated current that was mediated independently of Piezo1 by TRPV4 (transient receptor potential cation channel, subfamily V, member 4) channels. Piezo1 functions as the principal TM transducer of physiological levels of shear stress, with both shear and the Piezo1 agonist Yoda1 increasing the number of focal cell‐matrix contacts. Analysis of TM‐dependent fluid drainage from the anterior eye showed significant inhibition by GsMTx4. Collectively, these results suggest that TM mechanosensitivity utilizes kinetically, regulatory and functionally distinct pressure transducers to inform the cells about force‐sensing contexts. Piezo1‐dependent control of shear flow sensing, calcium homeostasis, cytoskeletal dynamics and pressure‐dependent outflow suggests potential for a novel therapeutic target in treating glaucoma.

    

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