Parvalbumin-expressing interneurons (PVs) in the dentate gyrus provide activity-dependent regulation of adult neurogenesis as well as maintain inhibitory control of mature neurons. In mature neurons, PVs evoke GABAA postsynaptic currents (GPSCs) with fast rise and decay phases that allow precise control of spike timing, yet synaptic currents with fast kinetics do not appear in adult-born neurons until several weeks after cell birth. Here we used mouse hippocampal slices to address how PVs signal to newborn neurons prior to the appearance of fast GPSCs. Whereas PV-evoked currents in mature neurons exhibit hallmark fast rise and decay phases, newborn neurons display slow GPSCs with characteristics of spillover signaling. We also unmasked slow spillover currents in mature neurons in the absence of fast GPSCs. Our results suggest that PVs mediate slow spillover signaling in addition to conventional fast synaptic signaling, and that spillover transmission mediates activity-dependent regulation of early events in adult neurogenesis.

Rod and cone photoreceptors degenerate in retinitis pigmentosa (RP). While downstream neurons survive, they undergo physiological changes, including accelerated spontaneous firing in retinal ganglion cells (RGCs). Retinoic acid (RA) is the molecular trigger of RGC hyperactivity, but whether this interferes with visual perception is unknown. Here, we show that inhibiting RA synthesis with disulfiram, a deterrent of human alcohol abuse, improves behavioral image detection in vision-impaired mice. In vivo Ca 2+ imaging shows that disulfiram sharpens orientation tuning of visual cortical neurons and strengthens fidelity of responses to natural scenes. An RA receptor inhibitor also reduces RGC hyperactivity, sharpens cortical representations, and improves image detection. These findings suggest that photoreceptor degeneration is not the only cause of vision loss in RP. RA-induced corruption of retinal information processing also degrades vision, pointing to RA synthesis and signaling inhibitors as potential therapeutic tools for improving sight in RP and other retinal degenerative disorders.

Lateral inhibition in the vertebrate retina depends on a negative feedback synapse between horizontal cells (HCs) and rod and cone photoreceptors. A change in pH is thought to be the signal for negative feedback, but its spatial profile in the synaptic cleft is unknown. Here we use three different membrane proteins, each fused to the same genetically-encoded pH-sensitive Green Fluorescent Protein (GFP) (pHluorin), to probe synaptic pH in retina from transgenic zebrafish (Danio rerio) of either sex. We used the cone transducin promoter to express SynaptopHluorin (pHluorin on vesicle-associated membrane protein (VAMP2)) or CalipHluorin (pHluorin on an L-type Ca 2ϩ channel) and the HC-specific connexin-55.5 promoter to express AMPApHluorin (pHluorin on an AMPA receptor). Stimulus light led to increased fluorescence of all three probes, consistent with alkalinization of the synaptic cleft. The receptive field size, sensitivity to surround illumination, and response to activation of an alien receptor expressed exclusively in HCs, are consistent with lateral inhibition as the trigger for alkalinization. However, SynaptopHluorin and AMPApHluorin, which are displaced farther from cone synaptic ribbons than CalipHluorin, reported a smaller pH change. Hence, unlike feedforward glutamatergic transmission, which spills over to allow cross talk between terminals in the cone network, the pH change underlying HC feedback is compartmentalized to individual synaptic invaginations within a cone terminal, consistent with private line communication.

FeRIC (Ferritin iron Redistribution to Ion Channels) is a magnetogenetic technique that uses radiofrequency (RF) waves to activate the transient receptor potential channels, such as TRPV1 and TRPV4, coupled to cellular ferritins. In cells expressing ferritin-tagged TRPV, RF stimulation increases the cytosolic Ca2+ levels via a biochemical pathway. The interaction between RF and ferritin increases the free cytosolic iron level that in turn, triggers chemical reactions producing reactive oxygen species and oxidized lipids that activate the ferritin-tagged TRPV. In this pathway, it is expected that experimental factors that disturb the ferritin expression, the ferritin iron load, the TRPV functional expression, or the cellular redox state will impact the RF efficacy to activate ferritin-tagged TRPV. Here, three in vitro protocols were compared for using FeRIC to remotely activate ferritin-tagged TRPV. Further, several experimental factors were examined that either enhance or abolish the RF control of ferritin-tagged TRPV. The findings may help establish reproducible magnetogenetic experimental protocols.

Azobenzene photoswitches are promising drug candidates for bestowing light sensitivity onto retinal neurons after photoreceptors degenerate in blinding disorders such as retinitis pigmentosa (RP). A potent photoswitch, BENAQ, targets a subset of retinal ganglion cells (RGCs), interacting with voltage‐gated ion channels to enable light‐triggered action potential firing. In mouse models of RP, injection of BENAQ into the vitreous of the eye photosensitizes RGCs to non‐damaging wavelengths and intensities of light. While the concentration required to elicit light responses is non‐toxic, effective drug delivery to the retina in vivo has remained a serious challenge. BENAQ aggregates near the injection site, causing non‐uniform photosensitization with a half‐life of 7 days, too transient for therapeutic vision restoration. Here, cyclodextrins are used to encapsulate BENAQ via host–guest chemistry to increase solubility and improve retinal delivery. SBE‐CD, a sulfobutylether β‐cyclodextrin, envelops the aromatic moieties of BENAQ to form a stable complex that dramatically enhances photosensitization, prolonging light responses to a half‐life of 31 days. SBE‐CD also ensures dispersal of BENAQ, resulting in uniform photosensitization across the retina. Hence the host–guest interaction between SBE‐CD and BENAQ overcomes limitations of intraocular delivery, guiding how photoswitches may be formulated as a possible treatment for human blindness.