Deficits In Innervation Research Articles

Corneal Nerve Assessment by Aesthesiometry: History, Advancements, and Future Directions.

The measurement of corneal sensation allows clinicians to assess the status of corneal innervation and serves as a crucial indicator of corneal disease and eye health. Many devices are available to assess corneal sensation, including the Cochet-Bonnet aesthesiometer, the Belmonte Aesthesiometer, the Swiss Liquid Jet Aesthesiometer, and the newly introduced Corneal Esthesiometer Brill. Increasing the clinical use of in vivo confocal microscopy and optical coherence tomography will allow for greater insight into the diagnosis, classification, and monitoring of ocular surface diseases such as neurotrophic keratopathy; however, formal esthesiometric measurement remains necessary to assess the functional status of corneal nerves. These aesthesiometers vary widely in their mode of corneal stimulus generation and their relative accessibility, precision, and ease of clinical use. The development of future devices to optimize these characteristics, as well as further comparative studies between device types should enable more accurate and precise diagnosis and treatment of corneal innervation deficits. The purpose of this narrative review is to describe the advancements in the use of aesthesiometers since their introduction to clinical practice, compare currently available devices for assessing corneal innervation and their relative limitations, and discuss how the assessment of corneal innervation is crucial to understanding and treating pathologies of the ocular surface.

Early adversity causes sex-specific deficits in perforant pathway connectivity and contextual memory in adolescent mice

BackgroundEarly life adversity impairs hippocampal development and function across diverse species. While initial evidence indicated potential variations between males and females, further research is required to validate these observations and better understand the underlying mechanisms contributing to these sex differences. Furthermore, most of the preclinical work in rodents was performed in adult males, with only few studies examining sex differences during adolescence when such differences appear more pronounced. To address these concerns, we investigated the impact of limited bedding (LB), a mouse model of early adversity, on hippocampal development in prepubescent and adolescent male and female mice.MethodsRNA sequencing, confocal microscopy, and electron microscopy were used to evaluate the impact of LB and sex on hippocampal development in prepubescent postnatal day 17 (P17) mice. Additional studies were conducted on adolescent mice aged P29-36, which included contextual fear conditioning, retrograde tracing, and ex vivo diffusion magnetic resonance imaging (dMRI).ResultsMore severe deficits in axonal innervation and myelination were found in the perforant pathway of prepubescent and adolescent LB males compared to LB female littermates. These sex differences were due to a failure of reelin-positive neurons located in the lateral entorhinal cortex (LEC) to innervate the dorsal hippocampus via the perforant pathway in males, but not LB females, and were strongly correlated with deficits in contextual fear conditioning.ConclusionsLB impairs the capacity of reelin-positive cells located in the LEC to project and innervate the dorsal hippocampus in LB males but not female LB littermates. Given the critical role that these projections play in supporting normal hippocampal function, a failure to establish proper connectivity between the LEC and the dorsal hippocampus provides a compelling and novel mechanism to explain the more severe deficits in myelination and contextual freezing found in adolescent LB males.

Corneal Neurotization: Essentials for The Facial Paralysis Surgeon.

Deficits in corneal innervation lead to neurotrophic keratopathy (NK). NK is frequently associated with facial palsy, and corneal damage can be accelerated by facial palsy deficits. Corneal nerves are important regulators of limbal stem cells, which play a critical role in epithelial maintenance and healing. Nonsurgical treatments of NK have undergone recent innovation, and growth factors implicated in corneal epithelial renewal are a promising therapeutic avenue. However, surgical intervention with corneal neurotization (CN) remains the only definitive treatment of NK. CN involves the transfer of unaffected sensory donor nerve branches to the affected cornea, and a variety of donor nerves and approaches have been described. CN can be performed in a direct or indirect manner; employ the supraorbital, supratrochlear, infraorbital, or great auricular nerves; and utilize autograft, allograft, or nerve transfer alone. Unfortunately, comparative studies of these factors are limited due to the procedure's novelty and varied recovery timelines after CN. Regardless of the chosen approach, CN has been shown to be a safe and effective procedure to restore corneal sensation and improve visual acuity in patients with NK.

Long-term Musculoskeletal Consequences of Chemotherapy in Pediatric Mice.

Thanks to recent progress in cancer research, most children treated for cancer survive into adulthood. Nevertheless, the long-term consequences of anticancer agents are understudied, especially in the pediatric population. We and others have shown that routinely administered chemotherapeutics drive musculoskeletal alterations, which contribute to increased treatment-related toxicity and long-term morbidity. Yet, the nature and scope of these enduring musculoskeletal defects following anticancer treatments and whether they can potentially impact growth and quality of life in young individuals remain to be elucidated. Here, we aimed at investigating the persistent musculoskeletal consequences of chemotherapy in young (pediatric) mice. Four-week-old male mice were administered a combination of 5-FU, leucovorin, irinotecan (a.k.a., Folfiri) or the vehicle for up to 5 wk. At time of sacrifice, skeletal muscle, bones, and other tissues were collected, processed, and stored for further analyses. In another set of experiments, chemotherapy-treated mice were monitored for up to 4 wk after cessation of treatment. Overall, the growth rate was significantly slower in the chemotherapy-treated animals, resulting in diminished lean and fat mass, as well as significantly smaller skeletal muscles. Interestingly, 4 wk after cessation of the treatment, the animals exposed to chemotherapy showed persistent musculoskeletal defects, including muscle innervation deficits and abnormal mitochondrial homeostasis. Altogether, our data support that anticancer treatments may lead to long-lasting musculoskeletal complications in actively growing pediatric mice and support the need for further studies to determine the mechanisms responsible for these complications, so that new therapies to prevent or diminish chemotherapy-related toxicities can be identified.

Chronic Desipramine Reverses Deficits in Cell Activity, Norepinephrine Innervation, and Anxiety-Depression Phenotypes in Fluoxetine-Resistant cF1ko Mice.

Selective serotonin (5-HT) reuptake inhibitors are only 30% effective for remission in subjects with major depression, and the best treatments for SSRI-resistant patients remain unclear. To model SSRI resistance, we used cF1ko mice with conditional deletion of the repressor Freud-1/CC2D1A in adult 5-HT neurons. Within weeks, this deletion leads to overexpression of 5-HT1A autoreceptors, reduced serotonergic activity, and fluoxetine-resistant anxiety-depression phenotype. We hypothesized that desipramine (DES), which targets norepinephrine (NE), may be effective in cF1ko mice. The actions of chronic DES treatment on behavior, chronic cellular activation, and NE projections were examined in both sexes of cF1ko and WT mice. In contrast to fluoxetine, chronic DES reversed the behavioral phenotypes in cF1ko mice, while in WT littermates DES slightly increased anxiety and depression-like behaviors. Deficits in FosB+ cell counts were seen in the entorhinal cortex, hippocampal CA2/3 layer, and BLA of cF1ko mice and were reversed by chronic DES treatment, especially in GABAergic neurons. In cF1ko mice, widespread reductions were seen in NE axons, varicosities, and especially 30-60% reductions in NE synaptic and triadic contacts, particularly to inhibitory gephyrin-positive sites. DES treatment also reversed these reductions in NE innervation. These results indicate the dynamic plasticity of the adult noradrenergic system within weeks of altering serotonergic function that can be normalized by DES treatment. Accompanying these changes, DES but not fluoxetine reversed the behavioral alterations in cF1ko mice, suggesting a key role for noradrenergic plasticity in antidepressant response in this model of reduced serotonin activity.

SorCS2 binds progranulin to regulate motor neuron development

Motor neuron (MN) development and nerve regeneration requires orchestrated action of a vast number of molecules. Here, we identify SorCS2 as a progranulin (PGRN) receptor that is required for MN diversification and axon outgrowth in zebrafish and mice. In zebrafish, SorCS2 knockdown also affects neuromuscular junction morphology and fish motility. In mice, SorCS2 and PGRN are co-expressed by newborn MNs from embryonic day 9.5 until adulthood. Using cell-fate tracing and nerve segmentation, we find that SorCS2 deficiency perturbs cell-fate decisions of brachial MNs accompanied by innervation deficits of posterior nerves. Additionally, adult SorCS2 knockout mice display slower motor nerve regeneration. Interestingly, primitive macrophages express high levels of PGRN, and their interaction with SorCS2-positive motor axon is required during axon pathfinding. We further show that SorCS2 binds PGRN to control its secretion, signaling, and conversion into granulins. We propose that PGRN-SorCS2 signaling controls MN development and regeneration in vertebrates.

Ketolysis is required for the proper development and function of the somatosensory nervous system

Ketogenic diets are emerging as protective interventions in preclinical and clinical models of somatosensory nervous system disorders. Additionally, dysregulation of succinyl-CoA 3-oxoacid CoA-transferase 1 (SCOT, encoded by Oxct1), the fate-committing enzyme in mitochondrial ketolysis, has recently been described in Friedreich's ataxia and amyotrophic lateral sclerosis. However, the contribution of ketone metabolism in the normal development and function of the somatosensory nervous system remains poorly characterized. We generated sensory neuron-specific, Advillin-Cre knockout of SCOT (Adv-KO-SCOT) mice and characterized the structure and function of their somatosensory system. We used histological techniques to assess sensory neuronal populations, myelination, and skin and spinal dorsal horn innervation. We also examined cutaneous and proprioceptive sensory behaviors with the von Frey test, radiant heat assay, rotarod, and grid-walk tests. Adv-KO-SCOT mice exhibited myelination deficits, altered morphology of putative Aδ soma from the dorsal root ganglion, reduced cutaneous innervation, and abnormal innervation of the spinal dorsal horn compared to wildtype mice. Synapsin 1-Cre-driven knockout of Oxct1 confirmed deficits in epidermal innervation following a loss of ketone oxidation. Loss of peripheral axonal ketolysis was further associated with proprioceptive deficits, yet Adv-KO-SCOT mice did not exhibit drastically altered cutaneous mechanical and thermal thresholds. Knockout of Oxct1 in peripheral sensory neurons resulted in histological abnormalities and severe proprioceptive deficits in mice. We conclude that ketone metabolism is essential for the development of the somatosensory nervous system. These findings also suggest that decreased ketone oxidation in the somatosensory nervous system may explain the neurological symptoms of Friedreich's ataxia.

Elp1‐Mediated Mechanisms Underlying Trigeminal Ganglion Development

The trigeminal nerve is the largest of the cranial nerves and relays sensations of pain, touch, and temperature from the face and head back to the brain. Cell bodies for this nerve are positioned in the trigeminal ganglion, which arises from the coalescence of neurons and supporting glia derived from two important embryonic cell populations, neural crest cells and placode cells. While the dual cellular origin of the trigeminal ganglion has been known for over 60 years, the molecular mechanisms controlling trigeminal ganglion development remain obscure. Our prior work has shown that the chick embryonic trigeminal ganglion initially forms from cadherin‐based interactions between neural crest cells and placode cells. In an effort to elucidate pathways regulating cadherin‐mediated trigeminal ganglion assembly, we identified Elongator complex protein 1 (Elp1) as a new regulator of trigeminal ganglion neuron development. Mutations in ELP1cause Familial Dysautonomia, an ultimately fatal disease characterized, in part, by the presence of small trigeminal nerves and a reduced capacity to sense facial pain and temperature. In a mouse model of Familial Dysautonomia, embryos possess trigeminal ganglion innervation deficits and decreased expression of cadherins in trunk neural crest‐derived dorsal root ganglia. While Elp1 is vital for neurogenesis and has been implicated in protein trafficking, cell adhesion, and migration, the role of Elp1 in the trigeminal ganglion is unexplored. We hypothesize that Elp1 regulates trigeminal ganglion development by controlling cadherin levels important for continued interactions between neural crest cell and placode cell derivatives. To address this, we have first generated a spatio‐temporal expression profile of Elp1 in the chick trigeminal ganglion using section immunohistochemistry. Our preliminary data indicate that Elp1 is expressed in migratory neural crest cells, trigeminal placode cells, and trigeminal placode cell‐derived neurons. Additionally, immunocytochemistry of chick trigeminal ganglion explant cultures revealed colocalization of Elp1 and Rab proteins associated with vesicle trafficking. Future experiments will include loss of function assays to investigate the relationship between Elp1 and cadherin trafficking in the trigeminal ganglion. Our results have potential high significance for providing new insights into the function of Elp1 in trigeminal ganglion development and the etiology of diseases like Familial Dysautonomia and others arising from defects in neural crest cells and/or placode cells.

Anterior cruciate ligament innervation in primary knee osteoarthritis.

To relate the Anterior Cruciate Ligament (ACL) innervation and histologic degeneration status to the knee osteoarthritis radiologic and functional status. Prospective observational study including 30 consecutive patients affected by primary knee osteoarthritis undergoing Total Knee Arthroplasty (TKA). All patients suffering secondary knee osteoarthritis, an antecedent of an infectious process, malignant process, autoimmune disorder, or previous knee surgery were excluded. We recorded biodemographic, clinical, and radiologic variables of all participants previous to the TKA procedure. ACL tissue was harvested during TKA standard procedure and the obtained sample was fixed in 4% formalin and paraffin-embedded. ACL cross-sections were stained by haematoxylin-eosin and Gallego staining for elastic and collagen fibers, and Sevier-Munger silver staining for nervous tissue. ACL samples histologic degeneration classification reported 15.4% normal, 23.1% slight, 26.9% mild, 11.5% moderate and 23.1% marked. We noted 46.2% large nervous fascicles, 15.4% medium fascicles, 3.8% small fascicles, and no nerve fibers were found in 34.6% ACL samples. No significant correlation was found between the histologic degeneration and the nervous fiber quantification (p>0.05, in all cases). We noted a significant histologic degeneration inverse correlation with the VAS scale (p=0.016), and nervous fiber quantification correlation with Lequesne maximum distance walked punctuation (p=0.043). We also noted greater nervous fiber quantification with minor radiological knee osteoarthritis (Kellgren-Lawrence grade II). ACL degeneration and innervation deficit may play a role in primary knee osteoarthritis onset, but the lack of a defining relationship among the different parameters assessed justifies further research in greater populations.

Cardiac Sympathetic Activity and Rhythm Control Following Pulmonary Vein Isolation in Patients with Paroxysmal Atrial Fibrillation-A Prospective 123I-mIBG-SPECT/CT Imaging Study.

Background: Pulmonary vein isolation (PVI) and antiarrhythmic drug therapy are established treatment strategies to preserve sinus rhythm in atrial fibrillation (AF). However, the efficacy of both interventional and pharmaceutical therapy is still limited. Solid evidence suggests an important role of the cardiac sympathetic nervous system in AF. In this blinded, prospective observational study, we studied left ventricular cardiac sympathetic activity in patients treated with PVI and with antiarrhythmic drugs. Prospectively, Iodine-123-benzyl-guanidine single photon emission computer tomography (123I-mIBG-SPECT) was performed in a total of 23 patients with paroxysmal AF, who underwent PVI (n = 20) or received antiarrhythmic drug therapy only (n = 3), respectively. 123I-mIBG planar and SPECT/CT scans were performed before and 4 to 8 weeks after PVI (or initiation of drug therapy, respectively). For semiquantitative SPECT image analysis, attenuation-corrected early/late images were analyzed. Quantitative SPECT analysis was performed using the AHA 17-segment model of the left ventricle. Results: PVI with point-by-point radiofrequency ablation led to a significantly (p < 0.05) higher visual sympathetic innervation defect score when comparing pre-and post PVI. Newly emerging innervation deficits post PVI were localized predominantly in the inferior lateral wall. These findings were corroborated by semiquantitative SPECT analysis identifying inferolateral segments with a reduced tracer uptake in comparison to SPECT before PVI. Following PVI, patients with an AF relapse showed a different sympathetic innervation pattern compared to patients with sufficient rhythm control. Conclusions: PVI results in novel defects of cardiac sympathetic innervation. Differences in cardiac sympathetic innervation remodelling following PVI suggest an important role of the cardiac autonomous nervous system in the maintenance of sinus rhythm following PVI.

Comprehensive transcriptome profiling identifies distinct gene expression pattern of post‐stroke muscle compared to denervation and disuse muscles in mice

Ischemic stroke is a complex cerebral vascular incident resulting in widescale global systemic changes, including a significant loss of skeletal muscle mass and function. Post-stroke muscle atrophy is precipitous, in part a consequence of the simultaneous contribution of motor neuron inactivity, and long-term immobilization (IMM). Middle cerebral artery occlusion (MCAO) is a well-established model serving as an indispensable tool in human ischemic stroke research to study the clinical consequences and develop therapeutic strategies. Due to the intrinsic involvement of innervation deficits and disuse in stroke, MCAO is often compared to experimental models of denervation (DEN; e.g., nerve transection), and IMM (hind-limb immobilization). However, ischemic stroke catalyzes a systemic milieu, whereby DEN and IMM exist only as a standalone piece of the global puzzle affecting muscle. Recently, we uncovered myriad transcriptional alterations in skeletal muscle after 60min MCAO in mice. Although similar transcriptomic analyses have been conducted in skeletal muscle from mice that underwent DEN and IMM, it is unclear whether the molecular origin of post-stroke muscle atrophy is similar to or different from DEN and IMM models. To determine this, we performed a cross-study analysis in skeletal muscle using RNAseq data from MCAO, DEN and IMM models. FASTQ files were ascertained via NCBI (SRP220337) and compared to our published MCAO sequencing data (doi:10.3390/genes11070726) to determine differentially expressed genes (DEG) and gene ontology (GO) enrichment. MCAO exhibited 476 and 603 unique up- and down-regulated DEG, respectively compared to DEN and IMM. Our analysis revealed 19 GO terms exclusive to MCAO. Several unique terms were related to the nervous system (e.g., GO:0050769). 10 GO terms were shared between models, with several related to proteolysis (e.g., GO:0006511). Analysis of shared terms revealed differentially annotated genes within terms. Ubiquitin-dependent catabolic process was enriched in all models, however 13 of the annotated genes were unique to MCAO. Analysis also revealed shared GO terms between MCAO and DEN only, such as heterocycle metabolic process (GO: 0046483) and mitochondrial membrane (GO: 0031966). Although these terms were enriched in both models, the relative genes annotated to these terms varied. For example, heterocycle metabolic process (GO: 0031966) had only 1 annotated gene in common, with 79 genes unique to MCAO annotated to this term. Notably, all genes annotated to this term were up-regulated in MCAO, while conversely down-regulated in DEN. These results are the first to show unique transcriptomic profiles in mouse muscle between MCAO, DEN, and IMM models. These data suggest that stroke-induced muscle atrophy may involve additional contributory factors, potentially due to the systemic nature of stroke. Further research is necessary to better elucidate the potential upstream mechanisms unique to stroke, contributing to post-stroke skeletal muscle atrophy.

(H)Elping nerve growth factor: Elp1 inhibits TrkA's phosphatase to maintain retrograde signaling.

Nerve growth factor (NGF) regulates many aspects of neuronal biology by retrogradely propagating signals along axons to the targets of those axons. How this occurs when axons contain a plethora of proteins that can silence those signals has long perplexed the neurotrophin field. In this issue of the JCI, Li et al. suggest an answer to this vexing problem, while exploring why the Elp1 gene that is mutated in familial dysautonomia (FD) causes peripheral neuropathy. They describe a distinctive function of Elp1 as a protein that is required to sustain NGF signaling by blocking the activity of its phosphatase that shuts off those signals. This finding helps explain the innervation deficits prominent in FD and reveals a unique role for Elp1 in the regulation of NGF-dependent TrkA activity.

The Contribution of Environment to Impair Re‐Innervation in Age‐Related Failure of Muscle Regeneration Following Injury

An age‐related decline in the structure and function of the neuromuscular junction (NMJ) has been hypothesised to play an important role in the loss of muscle mass and force generating capacity that occurs during ageing and to contribute to the incomplete regeneration of skeletal muscle following damage.The aim of this study was to determine the relative levels of innervation of muscle fibres from adult and old wild type (WT) mice and in mice lacking superoxide dismutase (SOD1) SodKO mice prior to and during regeneration following extensive muscle damage induced by barium chloride (BaCl2). Based on the known role of environment as a contributor to the success of muscle regeneration, an additional aim was to test whether the deficits in innervation, muscle mass, and force generation seen in muscles of old mice was evident in muscles transplanted from old donors into adult hosts and vice versa.Male B6.Cg‐Tg (Thy1‐YFP) mice aged 8–10 months (adult) or 24 months (old), male adult (8–10 months) mice lacking SOD1 (C57Bl/6 Sod1KO mice) and male adult SOD1KO mice crossed with Thy1‐CFP (SOD1KO‐CFP) were used for the BaCl2 study. Mice were anaesthestised and the extensor digitorum longus (EDL) muscle was injected with 50ul BaCl2, (1.2% wt/vol in sterile saline). Adult and old WT mice were allowed to recover for up to 60 days. SOD1KO mice were studied prior to‐ and at 28 days post damage, the time point where failure in recovery of contractile force was seen in old WT mice.Male WT adult (6–8 months) and old (22 – 24 months) mice were used for the muscle transplant studies. EDL muscles were transferred to the new host, where the tendons were hen repaired and the nerve from the host implanted into the transplanted muscle. At 28 and 60 days following transplantation, mice were culled and EDL muscles were removed, contractile function measured and NMJ structure examined.For analysis of NMJ structure the post‐synaptic regions of fixed EDL muscles were stained with alpha‐bungarotoxin and Dapi. Multiple images were collected from each muscle and the innervation status of each NMJ was assessed.Data demonstrated that although the 30% full denervation of NMJ structure in association with some reduction in fibre diameter may be responsible for the 35% muscle force deficit that occurred in mice that lack SOD1, the level of denervation could not solely explain the substantial force deficit in muscle from old WT mice following extensive damage and regeneration. In contrast, data support the conclusion that the deficit in force seen in muscles from old WT mice following regeneration from damage is caused by the environment in which the muscle regenerated since transplantation of EDL muscles from either adult or old mice into old mice leads to defective regeneration of those muscles; however, experiments aimed at determining whether the environment impacted the effectiveness of re‐innervation remained inconclusive with substantial disruption evident in all instances.Support or Funding InformationWith thanks to National Institute of Ageing (AG051442) and University of Liverpool for their support.

Prenatal Protein Malnutrition Produces Resistance to Distraction Similar to Noradrenergic Deafferentation of the Prelimbic Cortex in a Sustained Attention Task.

Exposure to malnutrition early in development increases likelihood of neuropsychiatric disorders, affective processing disorders, and attentional problems later in life. Many of these impairments are hypothesized to arise from impaired development of the prefrontal cortex. The current experiments examine the impact of prenatal malnutrition on the noradrenergic and cholinergic axons in the prefrontal cortex to determine if these changes contribute to the attentional deficits seen in prenatal protein malnourished rats (6% casein vs. 25% casein). Because prenatally malnourished animals had significant decreases in noradrenergic fibers in the prelimbic cortex with spared innervation in the anterior cingulate cortex and showed no changes in acetylcholine innervation of the prefrontal cortex, we compared deficits produced by malnutrition to those produced in adult rats by noradrenergic lesions of the prelimbic cortex. All animals were able to perform the baseline sustained attention task accurately. However, with the addition of visual distractors to the sustained attention task, animals that were prenatally malnourished and those that were noradrenergically lesioned showed cognitive rigidity, i.e., were less distractible than control animals. All groups showed similar changes in behavior when exposed to withholding reinforcement, suggesting specific attentional impairments rather than global difficulties in understanding response rules, bottom-up perceptual problems, or cognitive impairments secondary to dysfunction in sensitivity to reinforcement contingencies. These data suggest that prenatal protein malnutrition leads to deficits in noradrenergic innervation of the prelimbic cortex associated with cognitive rigidity.

Calcitonin-Receptor-Like Receptor Signaling Governs Intestinal Lymphatic Innervation and Lipid Uptake.

The absorption of dietary fat requires complex neuroendocrine-mediated regulation of chylomicron trafficking through enterocytes and intestinal lymphatic vessels. Calcitonin-receptor-like receptor (Calcrl) is a G protein-coupled receptor that can bind either a lymphangiogenic ligand adrenomedullin, with coreceptor RAMP2, or the neuropeptide CGRP, with coreceptor RAMP1. The extent to which this common GPCR controls lipid absorption via lymphatics or enteric innervation remains unclear. We used conditional and inducible genetic deletion of Calcrl in lymphatics to elucidate the pathophysiological consequences of this receptor pathway under conditions of high-fat diet. Inefficient absorption of dietary fat coupled with altered lymphatic endothelial junctions in Calcrl fl/fl /Prox1-CreER T2 mice results in excessive, transcellular lipid accumulation and abnormal enterocyte chylomicron processing and failure to gain weight. Interestingly, Calcrl fl/fl /Prox1-CreER T2 animals show reduced and disorganized mucosal and submucosal innervation. Consistently, mice with genetic loss of the CGRP coreceptor RAMP1 also displayed mucosal and submucosal innervation deficits, substantiating the CGRP-biased function of Calcrl in the neurolymphocrine axis. Thus, the common Calcrl receptor is a critical regulator of lipid absorption through its cell-specific functions in neurolymphocrine crosstalk.

Role of Noradrenergic Brain Nuclei in the Regulation of Carotid Artery Blood Flow: Pharmacological Evidence from Anesthetized Pigs with Alpha-2 Adrenergic Receptor Modulator Drugs.

Cerebral hypoperfusion and degeneration of the noradrenergic locus coeruleus (LC) occur early in Alzheimer's disease (AD). Cerebral blood vessels are densely innervated by noradrenergic projections from the LC suggesting a functional role for the regulation of cerebral blood flow (CBF). Experimental LC stimulation, however, has provided no clarity as decreases or increases in CBF were reported from different experimental settings and investigators. To find out with pharmacological methods whether endogenously released norepinephrine (NE) increases or decreases carotid artery blood flow (CABF) in anesthetized pigs by investigating the effect of centrally acting alpha-2 adrenergic drugs, which increase (atipamezole) or decrease (xylazine) NE in the brain. CABF was measured by a Doppler-flow probe placed around the left carotid artery in pentobarbital anesthetized young pigs. Neither current antihypertensive drugs nor pharmacological stimulation of dopamine, histamine, serotonin or acetylcholine receptors changed CABF. The alpha-2 adrenergic-receptor agonist xylazine decreased, while the antagonist atipamezole raised CABF. This rise was abolished by a combined treatment with endothelial NO-synthase inhibitor Nω-Nitro-L-arginine methyl ester (L-NAME) and the non-selective β-receptor antagonist propranolol. Propranolol alone did not decrease CABF in contrast to L-NAME but decreased CABF after L-NAME, surprisingly. Pharmacological evidence suggests that NE released in the brain of anesthetized pigs raises CABF involving β-adrenergic mechanisms and nitric oxide. If in awake humans NE released from the LC had vasodilator effects early LC degeneration could be involved in early cerebral hypoperfusion of AD. Moreover, a cerebral adrenergic vascular innervation deficit, possibly resulting from LC degeneration, and systemic endothelial dysfunction together may act synergistically to reduce CBF.

The BDNF Val66Met Prodomain Disassembles Dendritic Spines Altering Fear Extinction Circuitry and Behavior

A human variant in the BDNF gene (Val66Met; rs6265) is associated with impaired fear extinction. Using super-resolution imaging, we demonstrate that the BDNF Met prodomain disassembles dendritic spines and eliminates synapses in hippocampal neurons. Invivo, ventral CA1 (vCA1) hippocampal neurons undergo similar morphological changes dependent on their transient co-expression of a SorCS2/p75NTR receptor complex during peri-adolescence. BDNF Met prodomain infusion into the vCA1 during this developmental time frame reduces dendritic spine densityand prelimbic (PL) projections, impairing cued fearextinction. Adolescent BdnfMet/Met mice display similar spine and PL innervation deficits. Using fiber photometry, we found that, in wild-type mice, vCA1 neurons projecting to the PL encode extinction by enhancing neural activity in threat anticipation and rapidly subsiding their response. This adaptation is absent in BDNFMet/Met mice. We conclude that the BDNF Met prodomain renders vCA1-PL projection neurons underdeveloped, preventing their capacity for subsequent circuit modulation necessary for fear extinction. VIDEO ABSTRACT.

Biphasic functions for the GDNF-Ret signaling pathway in chemosensory neuron development and diversification

The development of the taste system relies on the coordinated regulation of cues that direct the simultaneous development of both peripheral taste organs and innervating sensory ganglia, but the underlying mechanisms remain poorly understood. In this study, we describe a novel, biphasic function for glial cell line-derived neurotrophic factor (GDNF) in the development and subsequent diversification of chemosensory neurons within the geniculate ganglion (GG). GDNF, acting through the receptor tyrosine kinase Ret, regulates the expression of the chemosensory fate determinant Phox2b early in GG development. Ret-/- mice, but not Retfx/fx ; Phox2b-Cre mice, display a profound loss of Phox2b expression with subsequent chemosensory innervation deficits, indicating that Ret is required for the initial amplification of Phox2b expression but not its maintenance. Ret expression is extinguished perinatally but reemerges postnatally in a subpopulation of large-diameter GG neurons expressing the mechanoreceptor marker NF200 and the GDNF coreceptor GFRα1. Intriguingly, we observed that ablation of these neurons in adult Ret-Cre/ERT2; Rosa26LSL-DTA mice caused a specific loss of tactile, but not chemical or thermal, electrophysiological responses. Overall, the GDNF-Ret pathway exerts two critical and distinct functions in the peripheral taste system: embryonic chemosensory cell fate determination and the specification of lingual mechanoreceptors.

Reciprocal Connections Between Cortex and Thalamus Contribute to Retinal Axon Targeting to Dorsal Lateral Geniculate Nucleus.

The dorsal Lateral Geniculate Nucleus (dLGN) is the primary image-forming target of the retina and shares a reciprocal connection with primary visual cortex (V1). Previous studies showed that corticothalamic input is essential for the development of thalamocortical projections, but less is known about the potential role of this reciprocal connection in the development of retinal projections. Here, we show a deficit of retinal innervation in the dLGN around E18.5 in Tra2β conditional knockout (cKO) "cortexless" mice, an age when apoptosis occurs along the thalamocortical tract and in some dLGN neurons. In vivo electrophysiology experiments in the dLGN further confirmed the loss of functional retinal input. Experiments with N-methyl-d-aspartic acid-induced V1 lesion as well as Fezf2 cKO mice confirmed that the disruption of connections between the dLGN and V1 lead to abnormal retinal projections to the dLGN. Interestingly, retinal projections to the ventral Lateral Geniculate Nucleus (vLGN) and Superior Colliculus (SC) were normal in all 3 mice models. Finally, we show that the cortexless mice had worse performance than control mice in a go-no go task with visual cues. Our results provide evidence that the wiring of visual circuit from the retina to the dLGN and V1 thereafter is coordinated at a surprisingly early stage of circuit development.

Region-specific role of growth differentiation factor-5 in the establishment of sympathetic innervation.

BackgroundNerve growth factor (NGF) is the prototypical target-derived neurotrophic factor required for sympathetic neuron survival and for the growth and ramification of sympathetic axons within most but not all sympathetic targets. This implies the operation of additional target-derived factors for regulating terminal sympathetic axon growth and branching.ResultsHere report that growth differentiation factor 5 (GDF5), a widely expressed member of the transforming growth factor beta (TGFβ) superfamily required for limb development, promoted axon growth from mouse superior cervical ganglion (SCG) neurons independently of NGF and enhanced axon growth in combination with NGF. GDF5 had no effect on neuronal survival and influenced axon growth during a narrow window of postnatal development when sympathetic axons are ramifying extensively in their targets in vivo. SCG neurons expressed all receptors capable of participating in GDF5 signaling at this stage of development. Using compartment cultures, we demonstrated that GDF5 exerted its growth promoting effect by acting directly on axons and by initiating retrograde canonical Smad signalling to the nucleus. GDF5 is synthesized in sympathetic targets, and examination of several anatomically circumscribed tissues in Gdf5 null mice revealed regional deficits in sympathetic innervation. There was a marked, highly significant reduction in the sympathetic innervation density of the iris, a smaller though significant reduction in the trachea, but no reduction in the submandibular salivary gland. There was no reduction in the number of neurons in the SCG.ConclusionsThese findings show that GDF5 is a novel target-derived factor that promotes sympathetic axon growth and branching and makes a distinctive regional contribution to the establishment of sympathetic innervation, but unlike NGF, plays no role in regulating sympathetic neuron survival.