Adult Peripheral Nervous System Research Articles

A missense mutation in human INSC causes peripheral neuropathy

PAR3/INSC/LGN form an evolutionarily conserved complex required for asymmetric cell division in the developing brain, but its post-developmental function and disease relevance in the peripheral nervous system (PNS) remains unknown. We mapped a new locus for axonal Charcot–Marie-Tooth disease (CMT2) and identified a missense mutation c.209 T > G (p.Met70Arg) in the INSC gene. Modeling the INSCM70R variant in Drosophila, we showed that it caused proprioceptive defects in adult flies, leading to gait defects resembling those in CMT2 patients. Cellularly, PAR3/INSC/LGN dysfunction caused tubulin aggregation and necrotic neurodegeneration, with microtubule-stabilizing agents rescuing both morphological and functional defects of the INSCM70R mutation in the PNS. Our findings underscore the critical role of the PAR3/INSC/LGN machinery in the adult PNS and highlight a potential therapeutic target for INSC-associated CMT2.

Roles of Macrophages and Their Interactions with Schwann Cells After Peripheral Nerve Injury.

The adult peripheral nervous system has a significant ability for regeneration compared to the central nervous system. This is related to the unique neuroimmunomodulation after peripheral nerve injury (PNI). Unlike the repair of other tissues after injury, Schwann cells (SCs) respond immediately to the trauma and send out signals to precisely recruit macrophages to the injured site. Then, macrophages promote the degradation of the damaged myelin sheath by phagocytosis of local debris. At the same time, macrophages and SCs jointly secrete various cytokines to reconstruct a microenvironment suitable for nerve regeneration. This unique pathophysiological process associated with macrophages provides important targets for the repair and treatment of PNI, as well as an important reference for guiding the repair of other nerve injuries. To understand these processes more systematically, this paper describes the characteristics of macrophage activation and metabolism in PNI, discusses the underlying molecular mechanism of interaction between macrophages and SCs, and reviews the latest research progress of crosstalk regulation between macrophages and SCs. These concepts and therapeutic strategies are summarized to provide a reference for the more effective use of macrophages in the repair of PNI.

Differential Expression of microRNAs in Serum of Patients with Chronic Painful Polyneuropathy and Healthy Age-Matched Controls

Polyneuropathies (PNP) are the most common type of disorder of the peripheral nervous system in adults. However, information on microRNA expression in PNP is lacking. Following microRNA sequencing, we compared the expression of microRNAs in the serum of patients experiencing chronic painful PNP with healthy age-matched controls. We have been able to identify four microRNAs (hsa-miR-3135b, hsa-miR-584-5p, hsa-miR-12136, and hsa-miR-550a-3p) that provide possible molecular links between degenerative processes, blood flow regulation, and signal transduction, that eventually lead to PNP. In addition, these microRNAs are discussed regarding the targeting of proteins that are involved in high blood flow/pressure and neural activity dysregulations/disbalances, presumably resulting in PNP-typical symptoms such as chronical numbness/pain. Within our study, we have identified four microRNAs that may serve as potential novel biomarkers of chronic painful PNP, and that may potentially bear therapeutic implications.

Endoplasmic reticulum associated degradation is essential for maintaining the viability or function of mature myelinating cells in adults.

Endoplasmic reticulum associated degradation (ERAD) is responsible for recognition and degradation of unfolded or misfolded proteins in the ER. Sel1L is essential for the ERAD activity of Sel1L-Hrd1 complex, the best-known ERAD machinery. Using a continuous Sel1L knockout mouse model (CNP/Cre; Sel1LloxP/loxP mice), our previous studies showed that Sel1L knockout in myelinating cells, oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS), leads to adult-onset myelin abnormalities in the CNS and PNS. Because Sel1L is deleted in myelinating cells of CNP/Cre; Sel1LloxP/loxP mice starting at very early stage of differentiation, it is impossible to rule out the possibility that the adult-onset myelin abnormalities in these mice results from developmental myelination defects caused by Sel1L knockout in myelinating cells during development. Thus, using an inducible Sel1L knockout mouse model (PLP/CreERT ; Sel1LloxP/loxP mice) that has normal, intact myelin and myelinating cells in the adult CNS and PNS prior to tamoxifen treatment, we sought to determine if Sel1L knockout in mature myelinating cells of adult mice leads to myelin abnormalities in the CNS and PNS. We showed that Sel1L knockout in mature myelinating cells caused ERAD impairment, ER stress and UPR activation. Interesting, Sel1L knockout in mature oligodendrocytes impaired their myelinating function by suppressing myelin protein translation, and resulted in progressive myelin thinning in the adult CNS. Conversely, Sel1L knockout in mature Schwann cells led to Schwann cell apoptosis and demyelination in the adult PNS. These findings demonstrate the essential roles of ERAD in mature myelinating cells in the adult CNS and PNS under physiological conditions.

The injured sciatic nerve atlas (iSNAT), insights into the cellular and molecular basis of neural tissue degeneration and regeneration.

Upon trauma, the adult murine peripheral nervous system (PNS) displays a remarkable degree of spontaneous anatomical and functional regeneration. To explore extrinsic mechanisms of neural repair, we carried out single-cell analysis of naïve mouse sciatic nerve, peripheral blood mononuclear cells, and crushed sciatic nerves at 1 day, 3 days, and 7 days following injury. During the first week, monocytes and macrophages (Mo/Mac) rapidly accumulate in the injured nerve and undergo extensive metabolic reprogramming. Proinflammatory Mo/Mac with a high glycolytic flux dominate the early injury response and rapidly give way to inflammation resolving Mac, programmed toward oxidative phosphorylation. Nerve crush injury causes partial leakiness of the blood-nerve barrier, proliferation of endoneurial and perineurial stromal cells, and entry of opsonizing serum proteins. Micro-dissection of the nerve injury site and distal nerve, followed by single-cell RNA-sequencing, identified distinct immune compartments, triggered by mechanical nerve wounding and Wallerian degeneration, respectively. This finding was independently confirmed with Sarm1-/- mice, in which Wallerian degeneration is greatly delayed. Experiments with chimeric mice showed that wildtype immune cells readily enter the injury site in Sarm1-/- mice, but are sparse in the distal nerve, except for Mo. We used CellChat to explore intercellular communications in the naïve and injured PNS and report on hundreds of ligand-receptor interactions. Our longitudinal analysis represents a new resource for neural tissue regeneration, reveals location- specific immune microenvironments, and reports on large intercellular communication networks. To facilitate mining of scRNAseq datasets, we generated the injured sciatic nerve atlas (iSNAT): https://cdb-rshiny.med.umich.edu/Giger_iSNAT/.

Satellite glia of the adult dorsal root ganglia harbor stem cells that yield glia under physiological conditions and neurons in response to injury.

The presence of putative stem/progenitor cells has been suggested in adult peripheral nervous system (PNS) tissue, including the dorsal root ganglion (DRG). To date, their identification and fate in pathophysiological conditions have not been addressed. Combining multiple invitro and invivo approaches, we identified the presence of stem cells in the adult DRG satellite glial population, and progenitors were present in the DRGs and sciatic nerve. Cell-specific transgenic mouse lines highlighted the proliferative potential of DRG stem cells and progenitors invitro. DRG stem cells had gliogenic and neurogenic potentials, whereas progenitors were essentially gliogenic. Lineage tracing showed that, under physiological conditions, adult DRG stem cells maintained DRG homeostasis by supplying satellite glia. Under pathological conditions, adult DRG stem cells replaced DRG neurons lost to injury in addition of renewing the satellite glial pool. These novel findings open new avenues for development of therapeutic strategies targeting DRG stem cells for PNS disorders.

Engineered Schwann Cell-Based Therapies for Injury Peripheral Nerve Reconstruction.

Compared with the central nervous system, the adult peripheral nervous system possesses a remarkable regenerative capacity, which is due to the strong plasticity of Schwann cells (SCs) in peripheral nerves. After peripheral nervous injury, SCs de-differentiate and transform into repair phenotypes, and play a critical role in axonal regeneration, myelin formation, and clearance of axonal and myelin debris. In view of the limited self-repair capability of SCs for long segment defects of peripheral nerve defects, it is of great clinical value to supplement SCs in necrotic areas through gene modification or stem cell transplantation or to construct tissue-engineered nerve combined with bioactive scaffolds to repair such tissue defects. Based on the developmental lineage of SCs and the gene regulation network after peripheral nerve injury (PNI), this review summarizes the possibility of using SCs constructed by the latest gene modification technology to repair PNI. The therapeutic effects of tissue-engineered nerve constructed by materials combined with Schwann cells resembles autologous transplantation, which is the gold standard for PNI repair. Therefore, this review generalizes the research progress of biomaterials combined with Schwann cells for PNI repair. Based on the difficulty of donor sources, this review also discusses the potential of “unlimited” provision of pluripotent stem cells capable of directing differentiation or transforming existing somatic cells into induced SCs. The summary of these concepts and therapeutic strategies makes it possible for SCs to be used more effectively in the repair of PNI.

Signal Transduction Regulators in Axonal Regeneration.

Intracellular signal transduction in response to growth factor receptor activation is a fundamental process during the regeneration of the nervous system. In this context, intracellular inhibitors of neuronal growth factor signaling have become of great interest in the recent years. Among them are the prominent signal transduction regulators Sprouty (SPRY) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which interfere with major signaling pathways such as extracellular signal-regulated kinase (ERK) or phosphoinositide 3-kinase (PI3K)/Akt in neurons and glial cells. Furthermore, SPRY and PTEN are themselves tightly regulated by ubiquitin ligases such as c-casitas b-lineage lymphoma (c-CBL) or neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4) and by different microRNAs (miRs) including miR-21 and miR-222. SPRY, PTEN and their intracellular regulators play an important role in the developing and the lesioned adult central and peripheral nervous system. This review will focus on the effects of SPRY and PTEN as well as their regulators in various experimental models of axonal regeneration in vitro and in vivo. Targeting these signal transduction regulators in the nervous system holds great promise for the treatment of neurological injuries in the future.

Neuronal Redevelopment and the Regeneration of Neuromodulatory Axons in the Adult Mammalian Central Nervous System.

One reason that many central nervous system injuries, including those arising from traumatic brain injury, spinal cord injury, and stroke, have limited recovery of function is that neurons within the adult mammalian CNS lack the ability to regenerate their axons following trauma. This stands in contrast to neurons of the adult mammalian peripheral nervous system (PNS). New evidence, provided by single-cell expression profiling, suggests that, following injury, both mammalian central and peripheral neurons can revert to an embryonic-like growth state which is permissive for axon regeneration. This “redevelopment” strategy could both facilitate a damage response necessary to isolate and repair the acute damage from injury and provide the intracellular machinery necessary for axon regrowth. Interestingly, serotonin neurons of the rostral group of raphe nuclei, which project their axons into the forebrain, display a robust ability to regenerate their axons unaided, counter to the widely held view that CNS axons cannot regenerate without experimental intervention after injury. Furthermore, initial evidence suggests that norepinephrine neurons within the locus coeruleus possess similar regenerative abilities. Several morphological characteristics of serotonin axon regeneration in adult mammals, observable using longitudinal in vivo imaging, are distinct from the known characteristics of unaided peripheral nerve regeneration, or of the regeneration seen in the spinal cord and optic nerve that occurs with experimental intervention. These results suggest that there is an alternative CNS program for axon regeneration that likely differs from that displayed by the PNS.

Clinical Neurophysiology of Zika Virus-Related Disorders of the Peripheral Nervous System in Adults.

During the 2013 to 2016 outbreak in the Pacific and Americas, Zika virus infection resulted not only in febrile and cutaneous manifestations but also in (severe) neurologic complications. These included both central and peripheral nervous system disorders. The most frequent was Guillain-Barré syndrome that typically developed 1 to 2 weeks after the acute infection. Later, other peripheral nervous system syndromes were recognized in association with the viral infection, broadening the spectrum of Zika virus-related peripheral nervous system syndromes. In the current article, the authors review all available clinical neurophysiology data on Guillain-Barré syndrome and other peripheral nervous system syndromes in an attempt to characterize the major patterns of involvement related to Zika virus. The authors also highlight the clinical usefulness of nerve conduction studies and needle EMG in the investigation of suspected Zika virus-related Guillain-Barré syndrome.

Negative regulation by proBDNF signaling of peripheral neurogenesis in the sensory ganglia of adult rats

Neurogenesis in the adult brain is well recognized and plays a critical role in the maintenance of brain function and homeostasis. However, whether neurogenesis also occurs in the adult peripheral nervous system remains unknown. Here, using sensory ganglia (dorsal root ganglia, DRGs) as a model, we show that neurogenesis also occurs in the peripheral nervous system, but in a manner different from that in the central nervous system. Satellite glial cells (SGCs) express the neuronal precursor markers Nestin, POU domain, class 4, transcription factor 1, and p75 pan-neurotrophin receptor. Following sciatic nerve injury, the suppression of endogenous proBDNF by proBDNF antibodies resulted in the transformation of proliferating SGCs into doublecortin-positive cells in the DRGs. Using purified SGCs migrating out from the DRGs, the inhibition of endogenous proBDNF promoted the conversion of SGCs into neuronal phenotypes in vitro. Our findings suggest that SGCs are neuronal precursors, and that proBDNF maintains the SGC phenotype. Furthermore, the suppression of proBDNF signaling is necessary for neuronal phenotype acquisition by SGCs. Thus, we propose that peripheral neurogenesis may occur via the direct conversion of SGCs into neurons, and that this process is negatively regulated by proBDNF.

Novel Glial Cell Functions: Extensive Potency, Stem Cell-Like Properties, and Participation in Regeneration and Transdifferentiation

Glial cells are the most abundant cells in both the peripheral and central nervous systems. During the past decade, a subpopulation of immature peripheral glial cells, namely, embryonic Schwann cell-precursors, have been found to perform important functions related to development. These cells have properties resembling those of the neural crest and, depending on their location in the body, can transform into several different cell types in peripheral tissues, including autonomic neurons. This review describes the multipotent properties of Schwann cell-precursors and their importance, together with innervation, during early development. The heterogeneity of Schwann cells, as revealed using single-cell transcriptomics, raises a question on whether some glial cells in the adult peripheral nervous system retain their stem cell-like properties. We also discuss how a deeper insight into the biology of both embryonic and adult Schwann cells might lead to an effective treatment of the damage of both neural and non-neural tissues, including the damage caused by neurodegenerative diseases. Furthermore, understanding the potential involvement of Schwann cells in the regulation of tumor development may reveal novel targets for cancer treatment.

PI 3-kinase delta enhances axonal PIP3 to support axon regeneration in the adult CNS.

Peripheral nervous system (PNS) neurons support axon regeneration into adulthood, whereas central nervous system (CNS) neurons lose regenerative ability after development. To better understand this decline whilst aiming to improve regeneration, we focused on phosphoinositide 3‐kinase (PI3K) and its product phosphatidylinositol (3,4,5)‐trisphosphate (PIP 3). We demonstrate that adult PNS neurons utilise two catalytic subunits of PI3K for axon regeneration: p110α and p110δ. However, in the CNS, axonal PIP 3 decreases with development at the time when axon transport declines and regenerative competence is lost. Overexpressing p110α in CNS neurons had no effect; however, expression of p110δ restored axonal PIP 3 and increased regenerative axon transport. p110δ expression enhanced CNS regeneration in both rat and human neurons and in transgenic mice, functioning in the same way as the hyperactivating H1047R mutation of p110α. Furthermore, viral delivery of p110δ promoted robust regeneration after optic nerve injury. These findings establish a deficit of axonal PIP 3 as a key reason for intrinsic regeneration failure and demonstrate that native p110δ facilitates axon regeneration by functioning in a hyperactive fashion.

The Benefit of Acetyl-L-Carnitine in Chemotherapy Induced Peripheral Neuropathy: A Systematic Review

Peripheral neuropathy (PN) is the most common disorder of the peripheral nervous system in adults, and its prevalence increases with age. Estimating its prevalence in the general population is difficult because the documentation of this disease is often poor and insufficient.

The Benefit of Acetyl-L-Carnitine in Chemotherapy Induced Peripheral Neuropathy: A Systematic Review

Peripheral neuropathy (PN) is the most common disorder of the peripheral nervous system in adults, and its prevalence increases with age. Estimating its prevalence in the general population is difficult because the documentation of this disease is often poor and insufficient.

Dynamic expression of Slit1-3 and Robo1-2 in the mouse peripheral nervous system after injury.

The Slit family of axon guidance cues act as repulsive molecules for precise axon pathfinding and neuronal migration during nervous system development through interactions with specific Robo receptors. Although we previously reported that Slit1-3 and their receptors Robo1 and Robo2 are highly expressed in the adult mouse peripheral nervous system, how this expression changes after injury has not been well studied. Herein, we constructed a peripheral nerve injury mouse model by transecting the right sciatic nerve. At 14 days after injury, quantitative real-time polymerase chain reaction was used to detect mRNA expression of Slit1-3 and Robo1-2 in L4-5 spinal cord and dorsal root ganglia, as well as the sciatic nerve. Immunohistochemical analysis was performed to examine Slit1-3, Robo1-2, neurofilament heavy chain, F4/80, and vimentin in L4-5 spinal cord, L4 dorsal root ganglia, and the sciatic nerve. Co-expression of Slit1-3 and Robo1-2 in L4 dorsal root ganglia was detected by in situ hybridization. In addition, Slit1-3 and Robo1-2 protein expression in L4-5 spinal cord, L4 dorsal root ganglia, and sciatic nerve were detected by western blot assay. The results showed no significant changes of Slit1-3 or Robo1-2 mRNA expression in the spinal cord within 14 days after injury. In the dorsal root ganglion, Slit1-3 and Robo1-2 mRNA expression were initially downregulated within 4 days after injury; however, Robo1-2 mRNA expression returned to the control level, while Slit1-3 mRNA expression remained upregulated during regeneration from 4-14 days after injury. In the sciatic nerve, Slit1-3 and their receptors Robo1-2 were all expressed in the proximal nerve stump; however, Slit1, Slit2, and Robo2 were barely detectable in the nerve bridge and distal nerve stump within 14 days after injury. Slit3 was highly ex-pressed in macrophages surrounding the nerve bridge and slightly downregulated in the distal nerve stump within 14 days after injury. Robo1 was upregulated in vimentin-positive cells and migrating Schwann cells inside the nerve bridge. Robo1 was also upregulated in Schwann cells of the distal nerve stump within 14 days after injury. Our findings indicate that Slit3 is the major ligand expressed in the nerve bridge and distal nerve stump during peripheral nerve regeneration, and Slit3/Robo signaling could play a key role in peripheral nerve repair after injury. This study was approved by Plymouth University Animal Welfare Ethical Review Board (approval No. 30/3203) on April 12, 2014.

A Review on Prevalence and Causes of Peripheral Neuropathy and Treatment of Different Etiologic Subgroups with Neurotropic B Vitamins

Peripheral neuropathy (PN) is the most common disorder of the peripheral nervous system in adults, and its prevalence increases with age. Because PN is often poorly documented and strongly underdiagnosed, estimating its prevalence in the general population is difficult. Only few epidemiological studies on the prevalence of PN in the general population are available, mostly from industrialized countries. Especially in developing countries, figures from different sources vary considerably. Available data often focus on certain etiological subgroups-particularly diabetics-or on neuropathic pain (NeP), which contributes to this variation. More epidemiological prevalence studies from the general population are required to gain a better picture on sizes of patient groups and cause patterns. To provide an overview of current prevalence data, we performed a selective literature search in PubMed, Cochrane and Google Scholar and used relevant examples along with comprehensive reviews covering the past 15+ years identified through the use of the authors’ own files. These data indicate that PN is frequent and often undiagnosed for a long time. Although diabetes is the number one cause of PN worldwide, there are various causes beyond, making it hard for physicians to gain a clear patient picture and recognize symptoms. Most clinical studies also focus on diabetic PN treatment only; thus, data comparing the treatment of PN of several etiologies are rare, which contributes to the lack of awareness of PN causes. In order to demonstrate that different PN subgroups can benefit from treatment with B vitamins progressively over time-regardless of underlying PN causes, we also present some subgroup results of a recent non-interventional study (Neurobion non-interventional; NENOIN) herein. The NENOIN study showed that treating PN of different etiologies including idiopathic neuropathy is possible with a fixed dose of neurotropic B vitamins. Therefore, we conclude that this is an effective treatment option for different PN subgroups from which even patients with unknown PN causes can benefit.

Progenitor Cell Heterogeneity in the Adult Carotid Body Germinal Niche.

Somatic stem cells confer plasticity to adult tissues, permitting their maintenance, repair and adaptation to a changing environment. Adult germinal niches supporting somatic stem cells have been thoroughly characterized throughout the organism, including in central and peripheral nervous systems. Stem cells do not reside alone within their niches, but they are rather accompanied by multiple progenitor cells that not only contribute to the progression of stem cell lineage but also regulate their behavior. Understanding the mechanisms underlying these interactions within the niche is crucial to comprehend associated pathologies and to use stem cells in cell therapy. We have described a stunning germinal niche in the adult peripheral nervous system: the carotid body. This is a chemoreceptor organ with a crucial function during physiological adaptation to hypoxia. We have shown the presence of multipotent stem cells within this niche, escorted by multiple restricted progenitor cell types that contribute to niche physiology and hence organismal adaptation to the lack of oxygen. Herein, we discuss new and existing data about the nature of all these stem and progenitor cell types present in the carotid body germinal niche, discussing their role in physiology and their clinical relevance for the treatment of diverse pathologies.

The carotid body: a physiologically relevant germinal niche in the adult peripheral nervous system.

Oxygen constitutes a vital element for the survival of every single cell in multicellular aerobic organisms like mammals. A complex homeostatic oxygen-sensing system has evolved in these organisms, including detectors and effectors, to guarantee a proper supply of the element to every cell. The carotid body represents the most important peripheral arterial chemoreceptor organ in mammals and informs about hypoxemic situations to the effectors at the brainstem cardiorespiratory centers. To optimize organismal adaptation to maintained hypoxemic situations, the carotid body has evolved containing a niche of adult tissue-specific stem cells with the capacity to differentiate into both neuronal and vascular cell types in response to hypoxia. These neurogenic and angiogenic processes are finely regulated by the niche and by hypoxia itself. Our recent data on the cellular and molecular mechanisms underlying the functioning of this niche might help to comprehend a variety of different diseases coursing with carotid body failure, and might also improve our capacity to use these stem cells for the treatment of neurological disease. Herein, we review those data about the recent characterization of the carotid body niche, focusing on the study of the phenotype and behavior of multipotent stem cells within the organ, comparing them with other well-documented neural stem cells within the adult nervous system.

LA RISPECIFICAZIONE DEL TRASMETTITORE E DEL RECETTORE È UNA NUOVA FORMA DI PLASTICITÀ DEL SISTEMA NERVOSO NELL’ADULTO

After some words on the scientific role of Professor Paolo Mantegazza atthe University of Milan (4, 5, 6), I briefly illustrate some studies related to the occurrence of neurotransmitter and receptor re-specification in the adult animals. The greatdiscoveries of the early twentieth century on neuronal communication have established that the majority of communication between nerve cells occurs through a special structure, the synapse, allowing the one-way transfer of information between twocells through the release of a neurotransmitter from the presynaptic cell and its recognition by receptors localized in the postsynaptic cell. According to H. Dale axiom (9) each neuron could be identified on the basis of the neurotransmitter released and theinnervated cell by the type of receptors expressed; then neurons could be classified asexcitatory if they release acetylcholine, glutamate or other transmitters, or inhibitory ifthey release GABA or glycine. However, in recent years many studies have shown that, especially during development, a neuron could release and co-release several neuro-transmitters, sometimes even simultaneously, changing its classification from excitatory to inhibitory and vice versa(7). This researches opened a new field of study onsynaptic plasticity: the neurotransmitter and receptor re-specification. Our group, together with Prof. Mantegazza, tried to “force” it through experiments of denervation and heterologous re-innervation in the autonomic nervous system and at the neuromuscular junction. In a first series of experiments we studied the regenerative capabilities of the peripheral nervous system in three experimental models: a) re-innervation of the denervated superior cervical ganglion (SCG) (14, 15, 22) by cholinergicefferent vagal fibers, b) re-innervation of peripheral effectors smooth muscles (nicti-tating membrane) by the cholinergic preganglionic fibers; c) re-innervation in an in vivo transplant model of peripheral organs by the SCG. In these researches we haveestablished: 1) that a sympathetic ganglion could be re-innervated by vagal fibersforming normal ganglionic synapses, but with a strong reshaping, in vivo, of the cen-tral neural circuits so that sympathetic stimuli occurred through a vagal excitation; 2) preganglionic cholinergic fibers innervate the smooth muscle of the nictitating mem-brane releasing catecholamines instead of acetylcholine; 3) that in an in vivo model ofSCG transplant together with iris or adrenal medulla fragments, the SCG was able todistinguish between organs that required a postsynaptic innervation, iris, which wasinnervated, and organs that require a presynaptic innervation, the adrenal medulla,that was not innervated. We were then in the presence, even in the adult animal, of anew nervous plasticity with re-specification the neurotransmitter. These resultsdemonstrate that heterologous innervation could “force” plasticity in adult peripheralnervous system, alters the biological properties of neurons, upsets central neuronal circuits, but continues to maintain in experimental transplants basic rules of innervation between neurons and peripheral organs. Thirty years later, the group of prof. Brunelliin Brescia (23), along with pharmacologists and physiologists, had highlighted the pos-sibility of re-innervate striated muscles in a functional way with nerve fibers derivedfrom the red nucleus of the vestibular complex. The interest was, once again, in thefact that the re-innervating fibers were of glutamatergic type, and not cholinergic likethose of normal motor neurons, and that neuromuscular transmission was transformedfrom nicotinic cholinergic in glutamatergic. A new type of plasticity: the receptor re-specification had occurred also in this experimenal model. In close cooperationbetween our Milan and the Brescia group we could reconfirm with more appropriateexperiments that the re-innervation occurred; that neuromuscular junction had a glutamatergic transmission; that new re-innervating fibers made synapses at the same sitesof the previous neuromuscular junctions; that the new fibers release glutamate; andthat muscle cells expressed new glutamate receptors (24). Once again we were in thepresence of an extraordinary phenomenon of synaptic plasticity, in this case a receptorre-specification, and again with a strong impact on the central nervous system circuits.These experiences, along with many others now available in the literature, show thatthe adult peripheral nervous system, both autonomous and musculoskeletal, has aplasticity unthinkable before and open a field of great interest aiming at the understanding how neuronal specificity is regulated and at the investigation of non-canonical, but perhaps functional, re-innervation experiments in transplants and in post-traumatic surgery.