Feasibility and resolution limits of opto-magnetic imaging of neural network activity in brain slices using color centers in diamond

We suggest a novel approach for wide-field imaging of the neural network dynamics of brain slices that uses highly sensitivity magnetometry based on nitrogen-vacancy (NV) centers in diamond. Invitro recordings in brain slices is a proven method for the characterization of electrical neural activity and has strongly contributed to our understanding of the mechanisms that govern neural information processing. However, this traditional approach only acquires signals from a few positions, which severely limits its ability to characterize the dynamics of the underlying neural networks. We suggest to extend its scope using NV magnetometry-based imaging of the neural magnetic fields across the slice. Employing comprehensive computational simulations and theoretical analyses, we determine the spatiotemporal characteristics of the neural fields and the required key performance parameters of an NV magnetometry-based imaging setup. We investigate how the technical parameters determine the achievable spatial resolution for an optimal 2D reconstruction of neural currents from the measured field distributions. Finally, we compare the imaging of neural slice activity with that of a single planar pyramidal cell. Our results suggest that imaging of slice activity will be possible with the upcoming generation of NV magnetic field sensors, while single-shot imaging of planar cell activity remains challenging

Silencing of spontaneous activity at α4β1/3δ GABAA receptors in hippocampal granule cells reveals different ligand pharmacology

BACKGROUND AND PURPOSE: The δ‐subunit‐containing GABA(A) receptors, α(4)β(1)δ and α(4)β(3)δ, in dentate gyrus granule cells (DGGCs) are known to exhibit both spontaneous channel openings (i.e. constitutive activity) and agonist‐induced current. The functional implications of spontaneous gating are unclear. In this study, we tested the hypothesis that constitutively active α(4)β(1/3)δ receptors limit agonist efficacy. EXPERIMENTAL APPROACH: Whole‐cell electrophysiological recordings of adult male rat and mouse hippocampal DGGCs were used to characterize known agonists and antagonists at δ‐subunit‐containing GABA(A) receptors. To separate constitutive and agonist‐induced currents, different recording conditions were employed. KEY RESULTS: Recordings at either 24°C or 34°C, including the PKC autoinhibitory peptide (19–36) intracellularly, removed spontaneous gating by GABA(A) receptors. In the absence of spontaneous gating, DGGCs responded to the α(4)β(1/3)δ orthosteric agonist Thio‐THIP with a four‐fold increased efficacy relative to recording conditions favouring constitutive activity. Surprisingly, the neutral antagonist gabazine was unable to antagonize the current by Thio‐THIP. Furthermore, a current was elicited by gabazine alone only when the constitutive current was silenced (EC(50) 2.1 μM). The gabazine‐induced current was inhibited by picrotoxin, potentiated by DS2, completely absent in δ(−/−) mice and reduced in β(1) (−/−) mice, but could not be replicated in human α(4)β(1/3)δ receptors expressed heterologously in HEK cells. CONCLUSION AND IMPLICATIONS: Kinase activity infers spontaneous gating in α(4)β(1/3)δ receptors in DGGCs. This significantly limits the efficacy of GABA(A) agonists and has implications in pathologies involving aberrant excitability caused by phosphorylation (e.g. addiction and epilepsy). In such cases, the efficacy of δ‐preferring GABA(A) ligands may be reduced