N-methyl-d-aspartate Receptor-mediated Preconditioning Mitigates Excitotoxicity in Human Induced Pluripotent Stem Cell-derived Brain Organoids.

Studies in rodent models of acute and chronic neurodegenerative disorders have uncovered that glutamate-induced excitotoxic cell death is mediated primarily by extrasynaptic N-methyl-d-aspartate receptors (NMDARs). Rodent neurons can also build up in an activity-dependent manner a protective shield against excitotoxicity. This form of acquired neuroprotection is induced by preconditioning with low doses of NMDA or by activation of synaptic NMDARs triggered by bursts of action potentials. Whether NMDARs in human neurons have similar dichotomous actions in cell death and survival is unknown. To investigate this, we established an induced pluripotent stem cell (iPSC)-derived forebrain organoid model for excitotoxic cell death and explored conditions of NMDAR activation that promote neuronal survival when applied prior to a toxic insult. We found that glutamate-induced excitotoxicity in human iPSC-derived neurons is mediated by NMDARs. Treatment of organoids with high concentrations of glutamate or NMDA caused the typical excitotoxicity pathology, comprising structural disintegration, neurite blebbing, shut-off of the transcription factor CRE binding protein (CREB), and cell death. In contrast, bath-applied low doses of NMDA elicited synaptic activity, a robust and sustained increase in CREB phosphorylation as well as function, and upregulation of immediate-early genes, including neuroprotective genes. Moreover, we found that conditions of enhanced synaptic activity increased survival of human iPSC-derived neurons if applied as pre-treatment before toxic NMDA application. These results revealed that both toxic and protective actions of NMDARs are preserved in human neurons. The experimental platform described in this study may prove useful for the validation of neuroprotective gene products and drugs in human neurons.

Npas4 regulates medium spiny neuron physiology and gates cocaine-induced hyperlocomotion.

We show here that the transcription factor Npas4 is an important regulator of medium spiny neuron spine density and electrophysiological parameters and that it determines the magnitude of cocaine-induced hyperlocomotion in mice. Npas4 is induced by synaptic stimuli that cause calcium influx, but not dopaminergic or PKA-stimulating input, in mouse medium spiny neurons and human iPSC-derived forebrain organoids. This induction is independent of ubiquitous kinase pathways such as PKA and MAPK cascades, and instead depends on calcineurin and nuclear calcium signalling. Npas4 controls a large regulon containing transcripts for synaptic molecules, such as NMDA receptors and VDCC subunits, and determines in vivo MSN spine density, firing rate, I/O gain function and paired-pulse facilitation. These functions at the molecular and cellular levels control the locomotor response to drugs of abuse, as Npas4 knockdown in the nucleus accumbens decreases hyperlocomotion in response to cocaine in male mice while leaving basal locomotor behaviour unchanged.

Possible role of calcitonin gene-related peptide in trigeminal modulation of glomerular microcircuits of the rodent olfactory bulb.

Chemosensation in the mammalian nose comprises detection of odorants, irritants and pheromones. While the traditional view assigned one distinct sub-system to each stimulus type, recent research has produced a more complex picture. Odorants are not only detected by olfactory sensory neurons but also by the trigeminal system. Irritants, in turn, may have a distinct odor, and some pheromones are detected by the olfactory epithelium. Moreover, it is well established that irritants change odor perception and vice versa. A wealth of psychophysical evidence on olfactory-trigeminal interactions in humans contrasts with a paucity of structural insight. In particular, it is unclear whether the two systems communicate just by sharing stimuli, or whether neuronal connections mediate cross-modal signaling. One connection could exist in the olfactory bulb that performs the primary processing of olfactory signals and receives trigeminal innervation. In the present study, neuroanatomical tracing of the mouse ethmoid system illustrates how peptidergic fibers enter the glomerular layer of the olfactory bulb, where local microcircuits process and filter the afferent signal. Biochemical assays reveal release of calcitonin gene-related peptide from olfactory bulb slices and attenuation of cAMP signaling by the neuropeptide. In the non-stimulated tissue, the neuropeptide specifically inhibited the basal activity of calbindin-expressing periglomerular interneurons, but did not affect the basal activity of neurons expressing calretinin, parvalbumin, or tyrosine hydroxylase, nor the activity of astrocytes. This study represents a first step towards understanding trigeminal neuromodulation of olfactory-bulb microcircuits and provides a working hypothesis for trigeminal inhibition of olfactory signal processing. This article is protected by copyright. All rights reserved.