In Vitro Gamma Mutagenesis Techniques in Rice (Oryza sativa L. var. Lazarroz FL).

Gamma radiation (60Co)-induced mutagenesis offers an alternative to develop rice lines by accelerating the spontaneous mutation process and increasing the pool of allelic variants available for breeding. Ionizing radiation works by direct or indirect damage to DNA and subsequent mutations. The technique can take advantage of in vitro protocols to optimize resources and accelerate the development of traits. This is achieved by exposing mutants to a selection agent of interest in controlled conditions and evaluating large numbers of plants in reduced areas. This chapter describes the protocol for establishing gamma radiation dosimetry and in vitro protocols for optimization at the laboratory level using seeds as the starting material, followed by embryogenic cell cultures, somatic embryogenesis, and regeneration. The final product of the protocol is a genetically homogeneous population of Oryza sativa that can be evaluated for breeding against abiotic and biotic stresses.

Novel strains of Actinobacteria associated with neotropical social wasps (Vespidae; Polistinae, Epiponini) with antimicrobial potential for natural product discovery.

Antimicrobial resistance has been considered a public health threat. The World Health Organization has warned about the urgency of detecting new antibiotics from novel sources. Social insects could be crucial in the search for new antibiotic metabolites, as some of them survive in places that favor parasite development. Recent studies have shown the potential of social insects to produce antimicrobial metabolites (e.g. ants, bees, and termites). However, most groups of social wasps remain unstudied. Here, we explored whether Actinobacteria are associated with workers in the Neotropical Social Wasps (Epiponini) of Costa Rica and evaluated their putative inhibitory activity against other bacteria. Most isolated strains (67%) have antagonistic effects, mainly against Bacillus thuringensis and Escherichia coli ATCC 25992. Based on genome analysis, some inhibitory Actinobacteria showed biosynthetic gene clusters (BGCs) related to the production of antimicrobial molecules such as Selvamycin, Piericidin A1, and Nystatin. The Actinobacteria could be associated with social wasps to produce antimicrobial compounds. For these reasons, we speculate that Actinobacteria associated with social wasps could be a novel source of antimicrobial compounds, mainly against Gram-negative bacteria.

The Retinal Ganglion Cell Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration Consortium.

Purpose: The Retinal Ganglion Cell (RGC) Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) consortium was founded in 2021 to help address the numerous scientific and clinical obstacles that impede development of vision-restorative treatments for patients with optic neuropathies. The goals of the RReSTORe consortium are: (1) to define and prioritize the most critical challenges and questions related to RGC regeneration; (2) to brainstorm innovative tools and experimental approaches to meet these challenges; and (3) to foster opportunities for collaborative scientific research among diverse investigators. Design and Participants: The RReSTORe consortium currently includes > 220 members spanning all career stages worldwide and is directed by an organizing committee comprised of 15 leading scientists and physician-scientists of diverse backgrounds. Methods: Herein, we describe the structure and organization of the RReSTORe consortium, its activities to date, and the perceived impact that the consortium has had on the field based on a survey of participants. Results: In addition to helping propel the field of regenerative medicine as applied to optic neuropathies, the RReSTORe consortium serves as a framework for developing large collaborative groups aimed at tackling audacious goals that may be expanded beyond ophthalmology and vision science. Conclusions: The development of innovative interventions capable of restoring vision for patients suffering from optic neuropathy would be transformative for the ophthalmology field, and may set the stage for functional restoration in other central nervous system disorders. By coordinating large-scale, international collaborations among scientists with diverse and complementary expertise, we are confident that the RReSTORe consortium will help to accelerate the field toward clinical translation. Financial Disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium.

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Synaptic and circuit mechanisms prevent detrimentally precise correlation in the developing mammalian visual system.

The developing visual thalamus and cortex extract positional information encoded in the correlated activity of retinal ganglion cells by synaptic plasticity, allowing for the refinement of connectivity. Here, we use a biophysical model of the visual thalamus during the initial visual circuit refinement period to explore the role of synaptic and circuit properties in the regulation of such neural correlations. We find that the NMDA receptor dominance, combined with weak recurrent excitation and inhibition characteristic of this age, prevents the emergence of spike-correlations between thalamocortical neurons on the millisecond timescale. Such precise correlations, which would emerge due to the broad, unrefined connections from the retina to the thalamus, reduce the spatial information contained by thalamic spikes, and therefore we term them 'parasitic' correlations. Our results suggest that developing synapses and circuits evolved mechanisms to compensate for such detrimental parasitic correlations arising from the unrefined and immature circuit.

Pattern of Driver-Like Input onto Neurons of the Mouse Ventral Lateral Geniculate Nucleus.

The ventral lateral geniculate nucleus (vLGN) is a retinorecipient region of thalamus that contributes to a number of complex visual behaviors. Retinal axons that target vLGN terminate exclusively in the external subdivision (vLGNe), which is also transcriptionally and cytoarchitectonically distinct from the internal subdivision (vLGNi). While recent studies shed light on the cell types and efferent projections of vLGNe and vLGNi, we have a crude understanding of the source and nature of the excitatory inputs driving postsynaptic activity in these regions. Here, we address this by conducting in vitro whole-cell recordings in acutely prepared thalamic slices and using electrical and optical stimulation techniques to examine the postsynaptic excitatory activity evoked by the activation of retinal or cortical layer V input onto neurons in vLGNe and vLGNi. Activation of retinal afferents by electrical stimulation of optic tract or optical stimulation of retinal terminals resulted in robust driver-like excitatory activity in vLGNe. Optical activation of corticothalamic terminals from layer V resulted in similar driver-like activity in both vLGNe and vLGNi. Using a dual-color optogenetic approach, we found that many vLGNe neurons received convergent input from these two sources. Both individual pathways displayed similar driver-like properties, with corticothalamic stimulation leading to a stronger form of synaptic depression than retinogeniculate stimulation. We found no evidence of convergence in vLGNi, with neurons only responding to corticothalamic stimulation. These data provide insight into the influence of excitatory inputs to vLGN and reveal that only neurons in vLGNe receive convergent input from both sources.

The parabigeminal nucleus is a source of "retinogeniculate replacement terminals" in mice that lack retinofugal input.

In the dorsal lateral geniculate nucleus (LGN) of mice that lack retinal input, a population of large terminals supplants the synaptic arrangements normally made by the missing retinogeniculate terminals. To identify potential sources of these "retinogeniculate replacement terminals," we used mutant mice (math5-/- ) which lack retinofugal projections due to the failure of retinal ganglion cells to develop. In this line, we labeled LGN terminals that originate from the primary visual cortex (V1) or the parabigeminal nucleus (PBG), and compared their ultrastructure to retinogeniculate, V1 or PBG terminals in the dLGN of C57Blk6 (WT) mice (schematically depicted above graph). Corticogeniculate terminals labeled in WT and math5-/- mice were similar in size and both groups were significantly smaller than WT retinogeniculate terminals. In contrast, the PBG projection in math5-/- mice was extensive and there was considerable overlap in the sizes of retinogeniculate terminals in WT mice and PBG terminals in math5-/- mice (summarized in histogram). The data indicate that V1 is not a source of "retinogeniculate replacement terminals" and suggests that large PBG terminals expand their innervation territory to replace retinogeniculate terminals in their absence.

The organization of cholinergic projections in the visual thalamus of the mouse.

Cholinergic projections from the brainstem serve as important modulators of activity in visual thalamic nuclei such as the dorsal lateral geniculate nucleus (dLGN). While these projections have been studied in several mammals, a comprehensive examination of their organization in the mouse is lacking. We used the retrograde transport of viruses or cholera toxin subunit B (CTB) injected in the dLGN, immunocytochemical labeling with antibodies against choline acetyltransferase (ChAT), brain nitric oxide synthase (BNOS), and vesicular acetylcholine transporter (VAChT), ChAT-Cre mice crossed with a reporter line (Ai9), as well as brainstem virus injections in ChAT-Cre mice to examine the pattern of thalamic innervation from cholinergic neurons in the pedunculopontine tegmental nucleus (PPTg), laterodorsal tegmental nucleus (LDTg), and the parabigeminal nucleus (PBG). Retrograde tracing demonstrated that the dLGN receives input from the PPTg, LDTg, and PBG. Viral tracing in ChAT-Cre mice and retrograde tracing combined with immunocytochemistry revealed that many of these inputs originate from cholinergic neurons in the PBG and PPTg. Most notable was an extensive cholinergic projection from the PBG which innervated most of the contralateral dLGN, with an especially dense concentration in the dorsolateral shell, as well as a small region in the dorsomedial pole of the ipsilateral dLGN. The PPTg was found to provide a sparse somewhat diffuse innervation of the ipsilateral dLGN. Neurons in the PPTg co-expressed ChAT, BNOS, and VAChT, whereas PBG neurons expressed ChAT, but not BNOS or VAChT. These results highlight the presence of distinct cholinergic populations that innervate the mouse dLGN.

Cre driver mouse lines for thalamocortical circuit mapping.

Subpopulations of neurons and associated neural circuits can be targeted in mice with genetic tools in a highly selective manner for visualization and manipulation. However, there are not well-defined Cre "driver" lines that target the expression of Cre recombinase to thalamocortical (TC) neurons. Here, we characterize three Cre driver lines for the nuclei of the dorsal thalamus: Oligodendrocyte transcription factor 3 (Olig3)-Cre, histidine decarboxylase (HDC)-Cre, and corticotropin-releasing hormone (CRH)-Cre. We examined the postnatal distribution of Cre expression for each of these lines with the Cre-dependent reporter CAG-tdTomato (Ai9). Cre-dependent expression of tdTomato reveals that Olig3-Cre expresses broadly within the thalamus, including TC neurons and interneurons, while HDC-Cre and CRH-Cre each have unique patterns of expression restricted to TC neurons within and across the sensory relay nuclei of the dorsal thalamus. Cre expression is present by the time of natural birth in all three lines, underscoring their utility for developmental studies. To demonstrate the utility of these Cre drivers for studying sensory TC circuitry, we targeted the expression of channelrhodopsin-2 to thalamus from the CAG-COP4*H134R/EYFP (Ai32) allele with either HDC-Cre or CRH-Cre. Optogenetic activation of TC afferents in primary visual cortex was sufficient to measure frequency-dependent depression. Thus, these Cre drivers provide selective Cre-dependent gene expression in thalamus suitable for both anatomical and functional studies.

Diverse GABAergic neurons organize into subtype-specific sublaminae in the ventral lateral geniculate nucleus.

In the visual system, retinal axons convey visual information from the outside world to dozens of distinct retinorecipient brain regions and organize that information at several levels, including either at the level of retinal afferents, cytoarchitecture of intrinsic retinorecipient neurons, or a combination of the two. Two major retinorecipient nuclei which are densely innervated by retinal axons are the dorsal lateral geniculate nucleus, which is important for classical image-forming vision, and ventral LGN (vLGN), which is associated with non-image-forming vision. The neurochemistry, cytoarchitecture, and retinothalamic connectivity in vLGN remain unresolved, raising fundamental questions of how it receives and processes visual information. To shed light on these important questions, used in situ hybridization, immunohistochemistry, and genetic reporter lines to identify and characterize novel neuronal cell types in mouse vLGN. Not only were a high percentage of these cells GABAergic, we discovered transcriptomically distinct GABAergic cell types reside in the two major laminae of vLGN, the retinorecipient, external vLGN (vLGNe) and the non-retinorecipient, internal vLGN (vLGNi). Furthermore, within vLGNe, we identified transcriptionally distinct subtypes of GABAergic cells that are distributed into four adjacent sublaminae. Using trans-synaptic viral tracing and in vitro electrophysiology, we found cells in each these vLGNe sublaminae receive monosynaptic inputs from retina. These results not only identify novel subtypes of GABAergic cells in vLGN, they suggest the subtype-specific laminar distribution of retinorecipient cells in vLGNe may be important for receiving, processing, and transmitting light-derived signals in parallel channels of the subcortical visual system.

VATS Uniportal, masterclass Guatemala / VATS Uniportal, masterclass Guatemala

En las dos últimas décadas la evolución de la cirugía mínimamente invasiva del tórax ha transmutado de un abordaje de tres puertos, siguiendo dos puertos hasta llegar a puerto único, conocido también como VATS Uniportal, procurando un confort mucho mejor para el paciente y resultados quirúrgicos similares. Objetivos. Presentar la técnica quirúrgica de VATS Uniportal en un hospital nacional, efectuadas por un experto internacional en este campo. Pacientes y Métodos. Se presentan dos casos clínicos quirúrgicos: El de una paciente con Miastenia Gravis a quien se le realizó timectomía por abordaje sub-xifoideo y otra paciente, a quien se le completó una lobectomía inferior derecha por hallazgos de patología posterior a la resección de un nódulo pulmonar solitario, reportado como cáncer primario de pulmón. Conclusiones. La técnica de cirugía mínimamente invasiva, VATS Uniportal, ofrece grandes beneficios para el paciente, tanto estéticos como funcionales y su aprendizaje es posible con la transmisión de conocimientos y experiencias directa con la presencia del experto o indirectas a través de la información publicada. (AU)

In the last two decades, the evolution of minimally invasive chest surgery has transmuted from a three-port approach, following two ports until reaching a single port, also known as VATS Uniportal, seeking much better comfort for the patient and similar surgical results. Objective. Present the VATS Uniportal surgical technique in a national hospital, performed by an international expert in this field. Patients and Methods. Two surgical clinical cases are presented: that of a patient with Myasthenia Gravis who underwent thymectomy through the sub-xiphoid approach and another patient, who underwent a right lower lobectomy due to findings of pathology after the resection of a pulmonary nodule. solitary, reported as primary lung cancer. Conclusions. The minimally invasive surgery technique, VATS Uniportal, offers great benefits for the patient, both aesthetic and functional and its learning is possible with the transmission of knowledge and experiences directly with the presence of the expert or indirectly through published information. (AU)

Differential Distribution of Ca2+ Channel Subtypes at Retinofugal Synapses.

Retinofugal synapses serve as models for understanding how sensory signals from the periphery are relayed to the brain. Past studies have focused primarily on understanding the postsynaptic glutamatergic receptor subtypes involved in signal transmission, but the mechanisms underlying glutamate release at presynaptic retinal terminals remains largely unknown. Here we explored how different calcium (Ca2+) channel subtypes regulate glutamatergic excitatory synaptic transmission in two principal retinorecipient targets, the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) of the mouse. We used an in vitro slice preparation to record the synaptic responses of dLGN and SC neurons evoked by the electrical stimulation of optic tract (OT) fibers before and during the application of selective Ca2+ channel blockers. We found that synaptic responses to paired or repetitive OT stimulation were highly sensitive to extracellular levels of Ca2+ and to selective antagonists of voltage gated Ca2+ channels, indicating that these channels regulate the presynaptic release of glutamate at retinal synapses in both dLGN and SC. Bath application of selective Ca2+ channel blockers revealed that P/Q-type Ca2+ channels primarily operate to regulate glutamate release at retinal synapses in dLGN, while N-type Ca2+ channels dominate release in the SC.

Synaptic properties of the feedback connections from the thalamic reticular nucleus to the dorsal lateral geniculate nucleus.

The thalamic reticular nucleus (TRN) is a shell-like structure comprised of GABAergic neurons that surrounds the dorsal thalamus. While playing a key role in modulating thalamocortical interactions, TRN inhibition of thalamic activity is often thought of as having an all-or-none impact. Although TRN neurons have a dynamic firing range, it remains unclear how variable rates of TRN activity gate thalamocortical transmission. To address this, we examined the ultrastructural features and functional synaptic properties of the feedback connections in the mouse thalamus between TRN and the dorsal lateral geniculate nucleus (dLGN), the principal relay of retinal signals to visual cortex. Using electron microscopy to identify TRN input to dLGN, we found that TRN terminals formed synapses with non-GABAergic postsynaptic profiles. Compared with other nonretinal terminals in dLGN, those from TRN were relatively large and tended to contact proximal regions of relay cell dendrites. To evoke TRN activity in dLGN, we adopted an optogenetic approach by expressing ChR2, or a variant (ChIEF) in TRN terminals. Both in vitro and in vivo recordings revealed that repetitive stimulation of TRN terminals led to a frequency-dependent inhibition of dLGN activity, with higher rates of stimulation resulting in increasing levels of membrane hyperpolarization and corresponding decreases in spike firing. This relationship suggests that alterations in TRN activity lead to graded changes in relay cell spike firing.NEW & NOTEWORTHY The thalamic reticular nucleus (TRN) modulates thalamocortical transmission through inhibition. In mouse, TRN terminals in the dorsal lateral geniculate nucleus (dLGN) form synapses with relay neurons but not interneurons. Stimulation of TRN terminals in dLGN leads to a frequency-dependent form of inhibition, with higher rates of stimulation leading to a greater suppression of spike firing. Thus, TRN inhibition appears more dynamic than previously recognized, having a graded rather than an all-or-none impact on thalamocortical transmission.

Retinal inputs signal astrocytes to recruit interneurons into visual thalamus.

Inhibitory interneurons comprise a fraction of the total neurons in the visual thalamus but are essential for sharpening receptive field properties and improving contrast-gain of retinogeniculate transmission. During early development, these interneurons undergo long-range migration from germinal zones, a process regulated by the innervation of the visual thalamus by retinal ganglion cells. Here, using transcriptomic approaches, we identified a motogenic cue, fibroblast growth factor 15 (FGF15), whose expression in the visual thalamus is regulated by retinal input. Targeted deletion of functional FGF15 in mice led to a reduction in thalamic GABAergic interneurons similar to that observed in the absence of retinal input. This loss may be attributed, at least in part, to misrouting of interneurons into nonvisual thalamic nuclei. Unexpectedly, expression analysis revealed that FGF15 is generated by thalamic astrocytes and not retino-recipient neurons. Thus, these data show that retinal inputs signal through astrocytes to direct the long-range recruitment of interneurons into the visual thalamus.

Chronic optical pacing conditioning of h-iPSC engineered cardiac tissues.

The immaturity of human induced pluripotent stem cell derived engineered cardiac tissues limits their ability to regenerate damaged myocardium and to serve as robust in vitro models for human disease and drug toxicity studies. Several chronic biomimetic conditioning protocols, including mechanical stretch, perfusion, and/or electrical stimulation promote engineered cardiac tissue maturation but have significant technical limitations. Non-contacting chronic optical stimulation using heterologously expressed channelrhodopsin light-gated ion channels, termed optogenetics, may be an advantageous alternative to chronic invasive electrical stimulation for engineered cardiac tissue conditioning. We designed proof-of-principle experiments to successfully transfect human induced pluripotent stem cell derived engineered cardiac tissues with a desensitization resistant, chimeric channelrhodopsin protein, and then optically paced engineered cardiac tissues to accelerate maturation. We transfected human induced pluripotent stem cell engineered cardiac tissues using an adeno-associated virus packaged chimeric channelrhodopsin and then verified optically paced by whole cell patch clamp. Engineered cardiac tissues were then chronically optically paced above their intrinsic beat rates in vitro from day 7 to 14. Chronically optically paced resulted in improved engineered cardiac tissue electrophysiological properties and subtle changes in the expression of some cardiac relevant genes, though active force generation and histology were unchanged. These results validate the feasibility of a novel chronically optically paced paradigm to explore non-invasive and scalable optically paced-induced engineered cardiac tissue maturation strategies.

Developmental Remodeling of Thalamic Interneurons Requires Retinal Signaling.

The dorsal lateral geniculate nucleus (dLGN) of the mouse is a model system to study the development of thalamic circuitry. Most studies focus on relay neurons of dLGN, yet little is known about the development of the other principal cell type, intrinsic interneurons. Here we examined whether the structure and function of interneurons relies on retinal signaling. We took a loss-of-function approach and crossed GAD67-GFP mice, which express GFP in dLGN interneurons, with math5 nulls (math5-/-), mutants that lack retinal ganglion cells and retinofugal projections. In vitro recordings and 3-D reconstructions of biocytin-filled interneurons at different postnatal ages showed their development is a multistaged process involving migration, arbor remodeling, and synapse formation. Arbor remodeling begins during the second postnatal week, after migration to and dispersion within dLGN is complete. This phase includes a period of exuberant branching where arbors grow in number, complexity, and field size. Such growth is followed by branch pruning and stabilization, as interneurons adopt a bipolar architecture. The absence of retinal signaling disrupts this process. The math5-/- interneurons fail to branch and prune, and instead maintain a simple, sparse architecture. To test how such defects influence connectivity with dLGN relay neurons, we used DHPG [(RS)-3,5-dihydroxyphenylglycine], the mGluR1,5 agonist that targets F2 terminals. This led to substantial increases in IPSC activity among WT relay neurons but had little impact in math5-/- mice. Together, these data suggest that retinal signaling is needed to support the arbor elaboration and synaptic connectivity of dLGN interneurons.SIGNIFICANCE STATEMENT Presently, our understanding about the development of the dorsal lateral geniculate nucleus is limited to circuits involving excitatory thalamocortical relay neurons. Here we show that the other principal cell type, intrinsic interneurons, has a multistaged developmental plan that relies on retinal innervation. These findings indicate that signaling from the periphery guides the maturation of interneurons and the establishment of inhibitory thalamic circuits.

Postnatal development of cholinergic input to the thalamic reticular nucleus of the mouse.

The thalamic reticular nucleus (TRN), a shell-like structure comprised of GABAergic neurons, gates signal transmission between thalamus and cortex. While TRN is innervated by axon collaterals of thalamocortical and corticothalamic neurons, other ascending projections modulate activity during different behavioral states such as attention, arousal, and sleep-wake cycles. One of the largest arise from cholinergic neurons of the basal forebrain and brainstem. Despite its integral role, little is known about how or when cholinergic innervation and synapse formation occurs. We utilized genetically modified mice, which selectively express fluorescent protein and/or channelrhodopsin-2 in cholinergic neurons, to visualize and stimulate cholinergic afferents in the developing TRN. Cholinergic innervation of TRN follows a ventral-to-dorsal progression, with nonvisual sensory sectors receiving input during week 1, and the visual sector during week 2. By week 3, the density of cholinergic fibers increases throughout TRN and forms a reticular profile. Functional patterns of connectivity between cholinergic fibers and TRN neurons progress in a similar manner, with weak excitatory nicotinic responses appearing in nonvisual sectors near the end of week 1. By week 2, excitatory responses become more prevalent and arise in the visual sector. Between weeks 3-4, inhibitory muscarinic responses emerge, and responses become biphasic, exhibiting a fast excitatory, and a long-lasting inhibitory component. Overall, the development of cholinergic projections in TRN follows a similar plan as the rest of sensory thalamus, with innervation of nonvisual structures preceding visual ones, and well after the establishment of circuits conveying sensory information from the periphery to the cortex.

The absence of retinal input disrupts the development of cholinergic brainstem projections in the mouse dorsal lateral geniculate nucleus.

BACKGROUND: The dorsal lateral geniculate nucleus (dLGN) of the mouse has become a model system for understanding thalamic circuit assembly. While the development of retinal projections to dLGN has been a topic of extensive inquiry, how and when nonretinal projections innervate this nucleus remains largely unexplored. In this study, we examined the development of a major nonretinal projection to dLGN, the ascending input arising from cholinergic neurons of the brainstem. To visualize these projections, we used a transgenic mouse line that expresses red fluorescent protein exclusively in cholinergic neurons. To assess whether retinal input regulates the timing and pattern of cholinergic innervation of dLGN, we utilized the math5-null (math5-/-) mouse, which lacks retinofugal projections due to a failure of retinal ganglion cell differentiation. RESULTS: Cholinergic brainstem innervation of dLGN began at the end of the first postnatal week, increased steadily with age, and reached an adult-like pattern by the end of the first postnatal month. The absence of retinal input led to a disruption in the trajectory, rate, and pattern of cholinergic innervation of dLGN. Anatomical tracing experiments reveal these disruptions were linked to cholinergic projections from parabigeminal nucleus, which normally traverse and reach dLGN through the optic tract. CONCLUSIONS: The late postnatal arrival of cholinergic projections to dLGN and their regulation by retinal signaling provides additional support for the existence of a conserved developmental plan whereby retinal input regulates the timing and sequencing of nonretinal projections to dLGN.

Development, form, and function of the mouse visual thalamus.

The dorsal lateral geniculate nucleus (dLGN) of the thalamus is the exclusive relay of retinal information en route to the visual cortex. Although much of our understanding about dLGN comes from studies done in higher mammals, such as the cat and primate, the mouse as a model organism has moved to the forefront as a tractable experimental platform to examine cell type-specific relations. This review highlights our current knowledge about the development, structure, and function of the mouse dLGN.