spatiotemporal-analysis-microglial-ca2-activity-at-single-cell

Spatiotemporal Analysis of Microglial Ca<sup>2+</sup> Activity at Single-Cell Resolution

Microglia are the sole resident immune cells in the central nervous system. Their morphology is highly plastic, changing depending on their activity. ...

National Institute for Physiological Sciences

Recent studies have shown that protons can function as neurotransmitters in cultured neurons. To further investigate regional and neural activity-dependent proton dynamics in the brain, the development of a device with both wide-area detectability and high spatial-ltemporal resolution is necessary. Therefore, we develop an image sensor with a high spatial-temporal resolution specifically designed for measuring protons in vivo. Here, we demonstrate that spatially deferent neural stimulation by visual stimulation induced distinct patterns of proton changes in the visual cortex. This result indicates that our biosensor can detect micrometer and millisecond scale changes of protons across a wide area. Our study demonstrates that a CMOS-based proton image sensor with high spatial and temporal precision can be used to detect pH changes associated with biological events. We believe that our sensor may have broad applicability in future biological studies.

CMOS-based bio-image sensor spatially resolves neural activity-dependent proton dynamics in the living brain.

The cardiac plexus, which contains parasympathetic ganglia, plays an important role in regulating cardiac function. Histamine is known to excite intracardiac ganglion neurons, but the underlying mechanism is obscure. In the present study, therefore, the effect of histamine on rat intracardiac ganglion neurons was investigated using perforated patch-clamp recordings. Histamine depolarized acutely isolated neurons with a half-maximal effective concentration of 4.5 μM. This depolarization was markedly inhibited by the H receptor antagonist triprolidine and mimicked by the H receptor agonist 2-pyridylethylamine, thus implicating histamine H receptors. Consistently, reverse transcription-PCR (RT-PCR) and Western blot analyses confirmed H receptor expression in the intracardiac ganglia. Under voltage-clamp conditions, histamine evoked an inward current that was potentiated by extracellular Ca removal and attenuated by extracellular Na replacement with N-methyl-D-glucamine. This implicated the involvement of non-selective cation channels, which given the link between H receptors and G-protein-phospholipase C signalling, were suspected to be transient receptor potential canonical (TRPC) channels. This was confirmed by the marked inhibition of the inward current through the pharmacological disruption of either G signalling or intracellular Ca release and by the application of the TRPC blockers Pyr3, Gd and ML204. Consistently, RT-PCR analysis revealed the expression of several TRPC subtypes in the intracardiac ganglia. Whilst histamine was also separately found to inhibit the M-current, the histamine-induced depolarization was only significantly inhibited by the TRPC blockers Gd and ML204, and not by the M-current blocker XE991. These results suggest that TRPC channels serve as the predominant mediator of neuronal excitation by histamine.

Histamine depolarizes rat intracardiac ganglion neurons through the activation of TRPC non-selective cation channels.

Extensive activation of glial cells during a latent period has been well documented in various animal models of epilepsy. However, it remains unclear whether activated glial cells contribute to epileptogenesis, i.e., the chronically persistent process leading to epilepsy. Particularly, it is not clear whether interglial communication between different types of glial cells contributes to epileptogenesis, because past literature has mainly focused on one type of glial cell. Here, we show that temporally distinct activation profiles of microglia and astrocytes collaboratively contributed to epileptogenesis in a drug-induced status epilepticus model. We found that reactive microglia appeared first, followed by reactive astrocytes and increased susceptibility to seizures. Reactive astrocytes exhibited larger Ca2+ signals mediated by IP3R2, whereas deletion of this type of Ca2+ signaling reduced seizure susceptibility after status epilepticus. Immediate, but not late, pharmacological inhibition of microglial activation prevented subsequent reactive astrocytes, aberrant astrocyte Ca2+ signaling, and the enhanced seizure susceptibility. These findings indicate that the sequential activation of glial cells constituted a cause of epileptogenesis after status epilepticus. Thus, our findings suggest that the therapeutic target to prevent epilepsy after status epilepticus should be shifted from microglia (early phase) to astrocytes (late phase).

Article	Year
CMOS-based bio-image sensor spatially resolves neural activity-dependent proton dynamics in the living brain. Nature communications\| PubMed ID: 32024837	2020
Histamine depolarizes rat intracardiac ganglion neurons through the activation of TRPC non-selective cation channels. European journal of pharmacology\| PubMed ID: 32896550	2020
Reactive astrocyte-driven epileptogenesis is induced by microglia initially activated following status epilepticus. JCI insight\| PubMed ID: 33830944	2021

Dennis Lawrence Cheung

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