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The role of microglia expressing the 5D4 epitope, a marker of keratan sulfate, was examined using mouse model of pilocarpine‐induced status epilepticus (SE). No microglia expressing the 5D4 epitope were found in the hippocampus at 1 day after SE onset (PILO‐1d), but they were scattered at 14 days post‐SE (PILO‐14d). The phagocytosis activity and the ratio of microglia‐synapse contact were higher in 5D4‐positive cells than in 5D4‐negative cells. Microglia expressing the 5D4 epitope may thus be engaged in synaptic pruning during the latent period after SE.


Abstract

Induction of keratan sulfate in microglia has been found in several animal models of neurological disorders. However, the significance of keratan sulfate‐expressing microglia is not fully understood. To address this issue, we analyzed the characteristics of microglia labeled by the 5D4 epitope, a marker of high‐sulfated keratan sulfate, in the mouse hippocampus during the latent period after pilocarpine‐induced status epilepticus (SE). Only 5D4‐negative (5D4−) microglia were found in the CA1 region of vehicle‐treated controls and pilocarpine‐treated mice at 1 day after SE onset. A few 5D4+ microglia appeared in the strata oriens and radiatum at 5 days post‐SE, and they were distributed into the stratum pyramidale at 14 days post‐SE. The expressions of genes related to both anti‐ and pro‐inflammatory cytokines were higher in 5D4+ cells than in 5D4– cells at 5 but not 14 days post‐SE. The expressions of genes related to phagocytosis were higher in 5D4+ cells than in 5D4− cells throughout the latent period. The phagocytic activity of microglia, as measured by engulfment of the zymosan bioparticles, was higher in 5D4+ cells than in 5D4− cells. The contact ratios between excitatory synaptic boutons and microglia were also higher in 5D4+ cells than in 5D4− cells at 5 and 14 days post‐SE. The excitatory/inhibitory ratios of synaptic boutons within the microglial domain were lower in 5D4+ cells than in 5D4− cells at 14 days post‐SE. Our findings indicate that 5D4+ microglia may play some role in epileptogenesis via pruning of excitatory synapses during the latent period after SE.

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We found at least 3 different opsins, Gq‐coupled rhodopsin, Opn5A, and xenopsin are all localized to the rhabdomere of the eye photoreceptor cells of the terrestrial slug Limax valentianus. Co‐expression of multiple kinds of opsin species may explain the shift of the spectral tuning curves of ERG between the dark‐ and light‐adapted states.


ABSTRACT

Visual opsins coupled with Gq‐type G protein have been considered to be responsible for the vision in mollusks. Recent transcriptomic studies, however, revealed the presence of opsin mRNA belonging to different groups of opsin subfamilies in the eyes of mollusks. In the present study, we found that at least 3 different opsins, Gq‐coupled rhodopsin, opsin5A, and xenopsin, are co‐expressed in the rhabdomeric photoreceptor cell in the eyes of the terrestrial slug Limax valentianus. These opsins were all localized to the microvilli of the rhabdomere. Co‐expression of rhodopsin and opsin5A mRNA was also demonstrated by dual fluorescence in situ hybridization. Co‐expression of multiple opsins in the rhabdomeric photoreceptors cells may explain the previously reported shift in the action spectra of the electroretinogram of eyes of Limax flavus between the light‐ and dark‐adapted states, which was also reproduced in the present study in Limax valentianus.

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CB1 signaling especially in cortical glutamatergic neurons is essential for the development of topographic maps in the cerebral cortex.


Abstract

Endocannabinoids and their receptors are highly abundant in the developing cerebral cortex and play major roles in early developmental processes, e.g. neuronal proliferation, migration and axonal guidance as well as postnatal plasticity. To investigate the role of the cannabinoid type 1 receptor (CB1) in the formation of sensory maps in the cerebral cortex, the topographic representation of the whiskers in the primary somatosensory cortex (barrel field) of adult mice with different cell type specific genetic deletion of CB1 was studied. A constitutive absence of CB1 (CB1‐KO) significantly decreased the total area of the somatosensory cortical map, affecting barrel and septal areas. Cell specificCB1 deletion in dorsal telencephalic glutamatergic neurons only (Glu‐CB1‐KO) or in both glutamatergic and forebrain GABAergic neurons (Glu/GABA‐CB1‐KO) resulted in an increased septa area in the barrel field map. No significant modifications in area parameters could be observed in GABA‐CB1‐KO mice. These data demonstrate that CB1 signaling especially in cortical glutamatergic neurons is essential for the development of topographic maps in the cerebral cortex.

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As revealed by tract tracing methods, the habenula is linked with the laterodorsal tegmental nucleus (LDTg) either by direct reciprocal projections from/to LHbM or indirectly via the MHb‐IP axis, Moreover, LDTg and IP are closely associated to a distributed network of structures that modulate hippocampal theta activity (blue letters).


ABSTRACT

The laterodorsal tegmental nucleus (LDTg) is a hindbrain cholinergic cell group thought to be involved in mechanisms of arousal and the control of midbrain dopamine cells. Nowadays, there is increasing evidence that LDTg is also engaged in mechanisms of anxiety/fear and promotion of emotional arousal under adverse conditions. Interestingly, LDTg appears to be connected with other regulators of aversive motivational states, including the lateral habenula (LHb), medial habenula (MHb), interpeduncular nucleus (IP), and median raphe nucleus (MnR). However, the circuitry between these structures has hitherto not been systematically investigated. Here, we placed injections of retrograde or anterograde tracers into LDTg, LHb, IP, and MnR. We also examined the transmitter phenotype of LDTg afferents to IP by combining retrograde tracing with immunofluorescence and in situ hybridization techniques. We found LHb inputs to LDTg mainly emerging from the medial division of the LHb (LHbM), which also receives axonal input from LDTg. The bidirectional connections between IP and LDTg displayed a lateralized organization, with LDTg inputs to IP being predominantly GABAergic or cholinergic and mainly directed to the contralateral IP. Moreover, we disclosed reciprocal LDTg connections with structures involved in the modulation of hippocampal theta rhythm including MnR, nucleus incertus, and supramammillary nucleus. Our findings indicate that the habenula is linked with LDTg either by direct reciprocal projections from/to LHbM or indirectly via the MHb‐IP axis, supporting a functional role of LDTg in the regulation of aversive behaviors, and further characterizing LHb as a master controller of ascending brainstem state‐setting modulatory projection systems.

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Robo3 Cre mice provide genetic access to all commissural neurons in the spinal cord, revealing their diverse developmental origins and broad transcriptional, positional, and molecular heterogeneity.


Abstract

The two sides of the nervous system coordinate and integrate information via commissural neurons, which project axons across the midline. Commissural neurons in the spinal cord are a highly heterogeneous population of cells with respect to their birthplace, final cell body position, axonal trajectory, and neurotransmitter phenotype. Although commissural axon guidance during development has been studied in great detail, neither the developmental origins nor the mature phenotypes of commissural neurons have been characterized comprehensively, largely due to lack of selective genetic access to these neurons. Here, we generated mice expressing Cre recombinase from the Robo3 locus specifically in commissural neurons. We used Robo3 Cre mice to characterize the transcriptome and various origins of developing commissural neurons, revealing new details about their extensive heterogeneity in molecular makeup and developmental lineage. Further, we followed the fate of commissural neurons into adulthood, thereby elucidating their settling positions and molecular diversity and providing evidence for possible functions in various spinal cord circuits. Our studies establish an important genetic entry point for further analyses of commissural neuron development, connectivity, and function.

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Using positron emission tomography (PET) molecular imaging with a specific tracer for the α4β2 nicotinic acetylcholine receptors (nAChR), 18F‐F‐A‐85380, we have shown an association between nAChR availability in the salience network and the heart rate variability. A higher nAChR availability in the bilateral dorsal anterior cingulate cortex and in the right anterior insula (AI)/frontal operculum was associated with a lower HFnu, a parameter of the parasympathetic tone. This study shows a neurochemical correlate to the autonomic function of the anterior cingulate cortex and the AI.


Abstract

The dorsal anterior cingulate cortex (dACC) and the anterior insula (AI) constitute the salience network and form as well the major cortical components of the central autonomic nervous system. These two cortical regions have the highest density in α4β2 nicotinic acetylcholine receptors (nAChRs) within the whole cortex.The aim of the study was to test the association between nAChRs density/availability in the salience network and the heart rate variability in humans. We selected subjects from a previous positron emission tomography (PET) imaging study in epilepsy with 18F‐FA‐85380, a specific marker for α4β2 nAChRs, including 10 healthy controls, 10 patients with nonlesional focal epilepsy and 8 patients with idiopathic generalized epilepsy. Participants underwent a 10 min‐resting electrocardiogram as they were lying still in a semi‐supine position while watching an emotionally neutral video. We tested the association between parasympathetic tone and the regional brain nAChR availability, as measured by 18F‐F‐A‐85380 binding potential (BP), using linear regression. We observed an association between higher nAChRs availability in the bilateral dACC and the right dorsal AI/frontal operculum and a lower parasympathetic tone, without significant effect of the clinical group on this relation. Our study is the first one to show a neurochemical correlate to the parasympathetic role of the anterior cingulate cortex and the AI. The nicotinic system, which plays a major role in the peripheral autonomic nervous system intervening both in the parasympathetic and sympathetic chains, seems also to play a role in the central autonomic nervous system.

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Immunohistochemical staining for neurofilament H (SMI‐32) reveals the presence of exceptionally large motor neurons in the hypoglossal nucleus of the caudal medulla oblongata in the brain of the tree pangolin, presumably for control of the long protrusible tongue. In this image dorsal is to the top and medial toward the left. Scale bar = 200 μm.


Abstract

The brainstem (midbrain, pons, and medulla oblongata) and cerebellum (diencephalic prosomere 1 through to rhombomere 11) play central roles in the processing of sensorimotor information, autonomic activity, levels of awareness and the control of functions external to the conscious cognitive world of mammals. As such, comparative analyses of these structures, especially the understanding of specializations or reductions of structures with functions that have been elucidated in commonly studied mammalian species, can provide crucial information for our understanding of the behavior of less commonly studied species, like pangolins. In the broadest sense, the nuclear complexes and subdivisions of nuclear complexes, the topographical arrangement, the neuronal chemistry, and fiber pathways of the tree pangolin conform to that typically observed across more commonly studied mammalian species. Despite this, variations in regions associated with the locus coeruleus complex, auditory system, and motor, neuromodulatory and autonomic systems involved in feeding, were observed in the current study. While we have previously detailed the unusual locus coeruleus complex of the tree pangolin, the superior olivary nuclear complex of the auditory system, while not exhibiting additional nuclei or having an altered organization, this nuclear complex, particularly the lateral superior olivary nucleus and nucleus of the trapezoid body, shows architectonic refinement. The cephalic decussation of the pyramidal tract, an enlarged hypoglossal nucleus, an additional subdivision of the serotonergic raphe obscurus nucleus, and the expansion of the superior salivatory nucleus, all indicate neuronal specializations related to the myrmecophagous diet of the pangolins.

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In addition to typical artiodactyl retinal topographic features, we found that the Nubian ibex has an unusual dorsotemporal area of high ganglion cell density. Given its cliff‐dwelling lifestyle, this specialization indicates enhanced visual sampling in the lower visual field, which may facilitate the control of locomotion in their precarious habitats.


Abstract

The Nubian ibex (Capra nubiana) occurs in information‐rich visual habitats including the edges of cliffs and escarpments. In addition to needing enhanced spatial resolution to find food and detect predators, enhanced visual sampling of the lower visual field would be advantageous for the control of locomotion in such precarious terrains. Using retinal wholemounts and stereology, we sought to measure how the ganglion cell density varies across the retina of the Nubian ibex to reveal which portions of its surroundings are sampled with high resolution. We estimated a total of ~1 million ganglion cells in the Nubian ibex retinal ganglion cell layer. Topographic variations of ganglion cell density reveal a temporal area, a horizontal streak, and a dorsotemporal extension, which are topographic retinal features also found in other artiodactyls. In contrast to savannah‐dwelling artiodactyls, the horizontal streak of the Nubian ibex appears loosely organized possibly reflecting a reduced predation risk in mountainous habitats. Estimates of spatial resolving power (~17 cycles/degree) for the temporal area would be reasonable to facilitate foraging in the frontal visual field. Embedded in the dorsotemporal extension, we also found an unusual dorsotemporal area not yet reported in any other mammal. Given its location and spatial resolving power (~6 cycles/degree), this specialization enhances visual sampling toward the lower visual field, which would be advantageous for visually guided locomotion. This study expands our understanding of the retinal organization in artiodactyls and offers insights on the importance of vision for the Nubian ibex ecology.

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Prokr2 is expressed in postmitotic immature neuroblasts in the SVZ‐RMS‐OB, whereas Prok2 expression is observed in a few cells in the medial part of the RMS, in a subset of granule cells and tufted cells in the OB. Analysis of Prokr2 and Prok2 null mice showed that PROK2/PROKR2 signaling is crucial for the tangential and radial migration of OB interneurons.


Abstract

Neural stem cells in the subventricular zone (SVZ) of the lateral ventricle generate new interneurons, which migrate tangentially through the rostral migratory stream (RMS) to the olfactory bulb (OB). The PROK2 (prokineticin 2) and PROKR2 (prokineticin receptor 2) signaling pathway has been identified to cause human Kallmann syndrome, a developmental disease that associates hypogonadism with anosmia (OB developmental defects). However, the identities and properties of PROK2+ and PROKR2+ cells in the SVZ‐RMS‐OB remain largely unknown. Here we examine the expression patterns of Prok2 and Prokr2 in the SVZ‐RMS‐OB using Prok2 EGFP transgenic and Prokr2 LacZ/+ knockin mice. Our results show that Prokr2 is expressed in postmitotic immature interneurons in the SVZ‐RMS‐OB. Prok2 is not expressed in the SVZ, but a few PROK2 + cells are found in the medial part of the RMS; they are not neural progenitors or migrating neuroblasts. In the OB, Prok2 is expressed in a subset of granule cells and tufted cells, but no coexpression of Prok2 and Prokr2 in the OB cells is observed. In Prok2 and Prokr2 mutant mice, severe tangential and radial migration defects of neuroblasts in the SVZ‐RMS‐OB result in loss of ~75% of GABAergic interneurons in the OB. These analyses demonstrate that PROK2/PROKR2 signaling is crucial for the tangential and radial migration of OB interneurons.

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