Neuroscience

The compound eyes of Drosophila are widely used to gain valuable insights into genetics, developmental biology, cell biology, disease biology, and gene regulation. Various parameters, such as eye size, pigmentation loss, formation of necrotic patches, and disorientation, fusion, or disruption of ommatidial arrays, are commonly assessed to evaluate eye development and degeneration. We developed an improved imaging method named low-angle ring illumination stereomicroscopy (LARIS) to capture high-contrast images of the Drosophila compound eye. Different optical alignments were tested to capture the fly compound eye image under the stereomicroscope; the highest contrast with minimal reflection was achieved through the LARIS method. The images captured using LARIS clearly showed ommatidial fusion, disorientation, and pigmentation loss, which were hardly visible with a conventional imaging method in the degenerating compound eyes of Drosophila. In addition to its research applications, this protocol is cost-effective due to the low expenses associated with supplies and equipment. We anticipate that LARIS will facilitate high-contrast imaging of the compound eyes in Drosophila and other insects.

Vestibulo-ocular reflexes (VORs) are compensatory ocular reflexes that maintain stable vision during head movements. In research, VORs encompass angular VOR (aVOR) and off-vertical axis rotation (OVAR) tests, which various groups have employed to assess vestibular function in mice. This protocol outlines the process for measuring VORs in mice, including eye rotation calibration, immobilizing the mouse with a noninvasive setup, configuring the aVOR and OVAR stimulus modes, and interpreting the obtained waveforms to derive VOR values. As technology advances, VORs are expected to yield more qualitative and quantitative insights into the function of the horizontal semicircular canal cristae (HSCC) and the otolith organs. This methodology can serve as a standard for evaluating common vestibular deficits in mice.

Cerebrospinal fluid-contacting neurons (CSF-cNs) are a specialized group of multifunctional neurons located around the central canal of the spinal cord. They play critical roles in motor regulation, postural maintenance, and spinal cord injury repair. However, the molecular mechanisms underlying the multifunctionality of CSF-cNs remain poorly understood, partly due to the lack of established in vitro methods for their efficient selection and purification, which significantly hinders mechanistic investigations. In this study, we describe a standardized method using a PKD2L1 promoter-driven lentiviral system, which enables effective enrichment and identification of CSF-cNs in vitro through GFP labeling and puromycin selection. This protocol includes key steps such as construction of the PKD2L1 promoter-driven lentiviral vector, spinal cord tissue collection and digestion from neonatal mice, lentiviral infection, antibiotic selection, and immunofluorescence-based identification of CSF-cNs. Our method provides a reliable platform for obtaining high-purity CSF-cNs (>99%), which facilitates their functional and mechanistic studies for regenerative approaches in vitro.

Nociception is critically shaped by descending modulation of spinal circuits, yet its cellular and synaptic mechanisms remain poorly defined. Elucidating these mechanisms is technically challenging, as it requires simultaneous activation of primary afferents and descending fibers while monitoring the functioning of individual spinal neurons. Here, we present a method to investigate the influence of the rostral ventromedial medulla (RVM), a principal supraspinal structure mediating descending modulation, on the activity of spinal lamina I neurons. Our approach combines electrophysiological recordings in ex vivo intact spinal cord preparation with optogenetics, granting several advantages. First, ex vivo preparation spares rostrocaudal and mediolateral spinal architecture, preserving lamina I as well as primary afferent and descending inputs. Second, virally mediated channelrhodopsin-2 (ChR2) expression enables selective photostimulation of RVM-originating fibers. When coupled with patch-clamp recordings, this photostimulation allows identifying postsynaptic inputs from RVM to spinal neurons and revealing RVM-dependent presynaptic inhibition of primary afferent inputs. Overall, our approach is well-suited for investigating both pre- and postsynaptic mechanisms of descending modulation in physiological and pathological pain conditions.

The phototransduction cascade allows photoreceptors to detect light across a wide range of intensities without saturation, with cGMP serving as the second messenger and calcium feedback as the key regulatory mechanism. While experimental evidence suggests that cAMP may also play a role in modulating this cascade, such regulation would necessitate rapid changes in cAMP levels on a timescale of seconds. However, data on the dynamics of intracellular cAMP changes in photoreceptors remain scarce, primarily due to the limitations of conventional fluorescence-based methods in this specialized sensory system. To address this gap, we developed a methodology combining rapid cryofixation of retinal samples following light stimulation with the isolation of outer segment preparations. The rapid cryofixation setup comprises six computer-controlled sections, each with a high-speed stepper motor-driven lever that rapidly moves the specimen in a 180° arc within ~80 ms to press it against a liquid nitrogen-cooled copper cylinder for fixation. Using highly sensitive metabolomics techniques, we measured cAMP levels in these samples. This approach enables the investigation of rapid cAMP dynamics and its potential regulatory role in phototransduction, providing a foundation for understanding the interplay between cAMP and PKA signaling in photoreceptor function.

High-throughput sequencing has created a tremendous amount of information about the genes expressed in various cell types and tissues throughout the body. As such, there is a need for a quick and effective method to knock down genes of interest in order to investigate their roles. While there are many approaches for this in mammalian models, there are limited ways to knock down genes of interest in adult zebrafish. Unlike mammals, zebrafish have the natural ability to regenerate their neurons after injury or disease is detected, making them a staple in regenerative studies. Unfortunately, current approaches for gene knockdown in the retina of adult zebrafish are costly and provide a barrier for many scientists. We provide two cost-effective approaches for targeted gene knockdowns in adult zebrafish retinas. We describe this approach through the use of Vivo-morpholinos and lipid-encapsulated siRNAs that target the expression of the proliferating cell nuclear antigen (PCNA) gene in adult zebrafish. We also describe how to collect and process retina samples for downstream immunohistochemistry, imaging, and quantification. Overall, this protocol will provide researchers with a straightforward, cheap, and effective method to perform targeted gene knockdowns in adult zebrafish retinas.

The fatal motor neuron (MN) disease amyotrophic lateral sclerosis (ALS) is characterized by progressive degeneration of the phrenic MNs (phMNs) controlling the activity of the diaphragm, leading to death by respiratory failure. Human experimental models to study phMNs are lacking, hindering the understanding of the mechanisms of phMN degeneration in ALS. Here, we describe a protocol to derive phrenic-like MNs from human induced pluripotent stem cells (hiPSC-phMNs) within 30 days. During spinal cord development, phMNs emerge from specific MN progenitors located in the dorsalmost MN progenitor (pMN) domain at cervical levels, under the control of a ventral-to-dorsal gradient of Sonic hedgehog (SHH) signaling and a rostro-caudal gradient of retinoic acid (RA). The method presented here uses optimized concentrations of RA and the SHH agonist purmorphamine, followed by fluorescence-activated cell sorting (FACS) of the resulting MN progenitor cells (MNPCs) based on a cell-surface protein (IGDCC3) enriched in hiPSC-phMNs. The resulting cultures are highly enriched in MNs expressing typical phMN markers. This protocol enables the generation of hiPSC-phMNs and is highly reproducible using several hiPSC lines, offering a disease-relevant system to study mechanisms of respiratory MN dysfunction. While the protocol has been validated in the context of ALS research, it can be adopted to study human phrenic MNs in other research fields where these neurons are of interest.

Stroke is a worldwide leading cause of death and long-term disability, with ischemic strokes making up approximately 85% of all cases. There is a significant need for an ideal animal model that accurately replicates the disease’s pathology to study the molecular mechanisms of brain injury. Various experimental models have been created to induce middle cerebral artery occlusion (MCAO), including intraluminal MCAO, photothrombotic models, endothelin-1 injections, and electrocoagulation. However, these often result in large infarct or lesion volumes accompanied by considerable variability. In this study, we present a ministroke model that specifically targets the mouse barrel cortex, making it suitable for investigating the mechanisms of minor strokes and stroke recurrence. In our model, the distal branch of the right middle cerebral artery (MCA), which supplies the sensorimotor cortex, is permanently ligated using 10-0 sutures. This is followed by a 7-min occlusion of the bilateral common carotid arteries (CCAs) and subsequent reperfusion. This approach produces a mild stroke characterized by small and consistent lesion volumes and very low mortality rates. A well-trained experimenter can achieve nearly zero mortality with this technique. Furthermore, this model of localized ischemia induces lesions in the functionally defined barrel cortex, allowing the use of the vibrissae-evoked forelimb placing test to assess functional outcomes.

Drosophila larvae exhibit rolling motor behavior as an escape response to avoid predators and painful stimuli. We introduce an accessible method for applying optogenetics to study the motor circuits driving rolling behavior. For this, we simultaneously implement the Gal4-UAS and LexA-Aop binary systems to express two distinct optogenetic channels, GtACR and Chrimson, in motor neuron (MN) subsets and rolling command neurons (Goro), respectively. Upon exposure to white LED light, Chrimson permits the influx of positive ions into Goro neurons, leading to depolarization, whereas GtACR mediates chloride influx into MNs, resulting in hyperpolarization. This method allows researchers to selectively activate certain neurons while simultaneously inhibiting others within a circuit of interest, offering a unique advantage over current optogenetic approaches, which often utilize a single type of optogenetic actuator. Here, we provide a detailed protocol for the dual silencing-activation approach using GtACR and Chrimson optogenetic channels and present a robust methodological framework for investigating the neuromuscular basis of rolling in larvae. Our cost-effective and scalable approach utilizes readily accessible equipment and can be applied to study other locomotor behaviors in Drosophila larvae, thereby enhancing our understanding of the neural circuit mechanisms underlying sensorimotor transformation.

Adult mammals lack the ability to regenerate retinal neurons after injury. However, in previous studies from this lab, topical application of the selective alpha7 nicotinic acetylcholine receptor (nAChR) agonist, PNU-282987, has been associated with an increase in the number of retinal neurons in adult murine models both in the presence and absence of injury to the retina. Additionally, studies assaying mitotic markers have shown a substantial increase in the amount of mitotically active and proliferating cells with the topical application of the alpha7 nAChR agonist. However, these previous studies were performed using fluorescent immunolabeling and subsequent confocal microscopy, thus limiting the number of antibodies that can be multiplexed. As a result, we have developed a flow cytometry method that allows for the multiplexing and analysis of multiple external and internal markers in dissociated retinal cells. In this paper, a step-by-step protocol is described for the labeling of multiple retinal cell types such as retinal ganglion cells, rod photoreceptors, and Müller glia, concurrently with Müller glia–derived progenitor cells that arise after treatment with PNU-282987.