GAP-43 and its relation to autonomic and sensory neurons in sciatic nerve and gastrocnemius muscle in the rat

The differences in the anatomy of the thoracolumbar and sacral autonomic outflow are quantitative

PURPOSE

We have re-evaluated the anatomical arguments that underlie the division of the spinal visceral outflow into sympathetic and parasympathetic divisions.

METHODOLOGY

Using a systematic literature search, we mapped the location of catecholaminergic neurons throughout the mammalian peripheral nervous system. Subsequently, a narrative method was employed to characterize segment-dependent differences in the location of preganglionic cell bodies and the composition of white and gray rami communicantes.

RESULTS AND CONCLUSION

One hundred seventy studies were included in the systematic review, providing information on 389 anatomical structures. Catecholaminergic nerve fibers are present in most spinal and all cranial nerves and ganglia, including those that are known for their parasympathetic function. Along the entire spinal autonomic outflow pathways, proximal and distal catecholaminergic cell bodies are common in the head, thoracic, and abdominal and pelvic region, which invalidates the "short-versus-long preganglionic neuron" argument. Contrary to the classically confined outflow levels T1-L2 and S2-S4, preganglionic neurons have been found in the resulting lumbar gap. Preganglionic cell bodies that are located in the intermediolateral zone of the thoracolumbar spinal cord gradually nest more ventrally within the ventral motor nuclei at the lumbar and sacral levels, and their fibers bypass the white ramus communicans and sympathetic trunk to emerge directly from the spinal roots. Bypassing the sympathetic trunk, therefore, is not exclusive for the sacral outflow. We conclude that the autonomic outflow displays a conserved architecture along the entire spinal axis, and that the perceived differences in the anatomy of the autonomic thoracolumbar and sacral outflow are quantitative.

Genomic approaches to identify and investigate genes associated with atrial fibrillation and heart failure susceptibility

Atrial fibrillation (AF) and heart failure (HF) contribute to about 45% of all cardiovascular disease (CVD) deaths in the USA and around the globe. Due to the complex nature, progression, inherent genetic makeup, and heterogeneity of CVDs, personalized treatments are believed to be critical. To improve the deciphering of CVD mechanisms, we need to deeply investigate well-known and identify novel genes that are responsible for CVD development. With the advancements in sequencing technologies, genomic data have been generated at an unprecedented pace to foster translational research. Correct application of bioinformatics using genomic data holds the potential to reveal the genetic underpinnings of various health conditions. It can help in the identification of causal variants for AF, HF, and other CVDs by moving beyond the one-gene one-disease model through the integration of common and rare variant association, the expressed genome, and characterization of comorbidities and phenotypic traits derived from the clinical information. In this study, we examined and discussed variable genomic approaches investigating genes associated with AF, HF, and other CVDs. We collected, reviewed, and compared high-quality scientific literature published between 2009 and 2022 and accessible through PubMed/NCBI. While selecting relevant literature, we mainly focused on identifying genomic approaches involving the integration of genomic data; analysis of common and rare genetic variants; metadata and phenotypic details; and multi-ethnic studies including individuals from ethnic minorities, and European, Asian, and American ancestries. We found 190 genes associated with AF and 26 genes linked to HF. Seven genes had implications in both AF and HF, which are SYNPO2L, TTN, MTSS1, SCN5A, PITX2, KLHL3, and AGAP5. We listed our conclusion, which include detailed information about genes and SNPs associated with AF and HF.

Integrating genetic, transcriptional, and functional analyses to identify 5 novel genes for atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) affects >30 million individuals worldwide and is associated with an increased risk of stroke, heart failure, and death. AF is highly heritable, yet the genetic basis for the arrhythmia remains incompletely understood.

METHODS AND RESULTS

To identify new AF-related genes, we used a multifaceted approach, combining large-scale genotyping in 2 ethnically distinct populations, cis-eQTL (expression quantitative trait loci) mapping, and functional validation. Four novel loci were identified in individuals of European descent near the genes NEURL (rs12415501; relative risk [RR]=1.18; 95% confidence interval [CI], 1.13-1.23; P=6.5×10(-16)), GJA1 (rs13216675; RR=1.10; 95% CI, 1.06-1.14; P=2.2×10(-8)), TBX5 (rs10507248; RR=1.12; 95% CI, 1.08-1.16; P=5.7×10(-11)), and CAND2 (rs4642101; RR=1.10; 95% CI, 1.06-1.14; P=9.8×10(-9)). In Japanese, novel loci were identified near NEURL (rs6584555; RR=1.32; 95% CI, 1.26-1.39; P=2.0×10(-25)) and CUX2 (rs6490029; RR=1.12; 95% CI, 1.08-1.16; P=3.9×10(-9)). The top single-nucleotide polymorphisms or their proxies were identified as cis-eQTLs for the genes CAND2 (P=2.6×10(-19)), GJA1 (P=2.66×10(-6)), and TBX5 (P=1.36×10(-5)). Knockdown of the zebrafish orthologs of NEURL and CAND2 resulted in prolongation of the atrial action potential duration (17% and 45%, respectively).

CONCLUSIONS

We have identified 5 novel loci for AF. Our results expand the diversity of genetic pathways implicated in AF and provide novel molecular targets for future biological and pharmacological investigation.

Spinal subarachnoid adrenal medullary transplants reduce hind paw swelling and peripheral nerve transport following formalin injection in rats

Previous studies have demonstrated that adrenal medullary chromaffin cells transplanted into the spinal subarachnoid space significantly reduced pain-related behavior following hind paw plantar formalin injection in rats. The data suggests a centrally mediated antinociceptive mechanism. The spinal transplants may have effects on sciatic nerve function as well. To address this, the current study examined the effects of spinal adrenal transplants on hind paw edema and the anterograde transport of substance P (SP) that occur following formalin injection. Robust formalin-evoked edema, as well as hind paw flinching, was observed in striated muscle control-transplanted rats, which were not observed in adrenal-transplanted rats. To visualize transport of SP, the sciatic nerve was ligated ipsilateral to formalin injection and the nerve was processed 48 h later for immunocytochemistry. A significant formalin-induced accumulation of SP immunoreactivity (IR) was observed proximal to the ligation in control-transplanted rats. In contrast, there was significantly less SP IR observed from nerve of adrenal-transplanted rats, suggesting a diminution of anterograde axoplasmic transport by adrenal transplants. The change in SP IR may have been due to an alteration of transport due to formalin injection, thus, transport was visualized by the accumulation of growth-associated protein 43 (GAP43) at the ligation site. Formalin injection did not significantly increase proximal accumulation of GAP43 IR, indicating that formalin does not increase anterograde transport. Surprisingly, however, adrenal transplants significantly diminished GAP43 IR accumulation compared to control-transplanted rats. These data demonstrate that spinal adrenal transplants can attenuate the formalin-evoked response by modulating primary afferent responses.

The therapeutic potential of neuropeptide Y in central nervous system disorders with special reference to pain and sympathetically maintained pain

Neuropeptide Y (NPY), a widely distributed peptide, has been shown to have numerous effects in both the central and peripheral nervous systems. In particular, NPY has an important role in mediating analgesia and hyperalgesia by distinct central and peripheral mechanisms. At least six NPY receptor subtypes are known to exist and the development of subtype-specific ligands targeted at NPY receptors will offer novel therapeutic agents. This article will review the involvement of NPY in diverse pathologies of the nervous system, including pain, and will propose a role for NPY in the maintenance of sympathetically maintained pain.

Early nerve regeneration after achilles tendon rupture--a prerequisite for healing? A study in the rat

Nerve regeneration during healing of Achilles tendon rupture in the rat was studied by immunohistochemistry including semi-quantitative assessment. Neuronal markers for regenerating and mature fibers, ie., growth associated protein 43 (GAP-43) and protein gene product 9.5 (PGP 9.5), respectively, were analyzed at different time points (1-16 weeks) post-rupture. In the paratenon, both the ruptured and intact contralateral tendon (control) consistently exhibited immunoreactivity to the two neuronal markers. However, in the proper tendinous tissue only the ruptured tendon showed immunoreactivity to GAP-43 and PGP 9.5. This expression was seen already at week 1 post-rupture to reach a peak at week 6 followed by a successive drop till week 16. Also the occurrence of sensory and autonomic fibers according to immunoreactivity for calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY), respectively, was analyzed. CGRP-positivity was abundantly seen from weeks 2-6 in both perivascular and sprouting free nerve endings in the proper tendon tissue undergoing healing. NPY appeared later, at weeks 6-8 post-rupture around blood vessels mainly located in the surrounding loose connective tissue. Apart from a role in vasoaction (CGRP, vasodilatory; NPY, vasoconstrictory). both neuropeptides have been implicated in fibroblast and endothelial cell proliferation required for angiogenesis. The present study shows that early healing of ruptured tendons is characterized by an orchestrated, temporal appearance of nerve fibers expressing peptides with different actions. The observed pattern of neuronal regeneration and neuropeptide expression may prove to be important for normal connective tissue healing.

Reciprocal age-related changes in GAP-43/B-50, substance P and calcitonin gene-related peptide (CGRP) expression in rat primary sensory neurones and their terminals in the dorsal horn of the spinal cord and subintima of the knee synovium

Age-related changes in the expression of the growth associated protein GAP-43/B-50, and the neuropeptides substance P and calcitonin gene-related peptide (CGRP) were investigated in the sensory neurones of rat dorsal root ganglia, dorsal horns of the spinal cord and subintimal knee synovium. The two time-points studied were 2 months (young adults) and 14-month (aged)-old Sprague Dawley rats. Dorsal root ganglia: In young adults, 40 and 35% of the L4-L5 dorsal root ganglion neurones were positive for GAP-43/B-50 with a 1.5 fold increase in frequency in aged rats at the L5 ganglion. GAP-43/B-50 was strongly expressed by the non-neuronal satellite cells of some medium and many large sized neurones in aged rats. There were marked reciprocal shifts between small and medium sized sensory neurones in respect to their substance P and CGRP expression profiles. Dorsal horn of the spinal cord: there was a 1.3 fold decrease of substance P at L5 level and a 1.3 and 1.5 fold decrease of CGRP at L4-L5 levels in aged rats, respectively. Synovial membrane: There was a 2.3 fold increase in GAP-43/B-50 and a 2.5 fold decrease of CGRP with no changes in substance P expression. These results indicate that (i) primary sensory neurones undergo age-related changes already in early stages of aging, (ii) aging may result in a reduction of substance P and CGRP axonal transport, and (iii) reduced numbers of CGRP containing synovial perivascular fibres may imply a deficient regulation of the synovial microvasculature and therefore metabolic homeostasis of the joint in aged subjects.

Evidence for nodose ganglion as the source of innervation to the anterior lobe of the pituitary gland

Recent studies have provided convincing evidence for the presence of peptidergic nerve fibers in the pituitary anterior lobe in several animal species. This study was aimed at elucidating the origin of this innervation by neuroanatomical tracing, denervation experiments, and immunohistochemistry. Immunohistochemistry against substance P and growth-associated protein 43 revealed a dense fiber plexus within the anterior lobe, and these markers were mostly colocalized. Retrograde tracing with Fluorogold from the pituitary gland stained neurons in the hypothalamus, superior cervical ganglia and the nodose ganglia. None of the Fluorogold-labelled neurons in the hypothalamus or superior cervical ganglion were substance P-immunoreactive, while many of the neuronal cell bodies in the nodose ganglion exhibited substance P immunoreactivity. There were no Fluorogold-labelled neurons in the trigeminal, otic or cervical dorsal root ganglia. Surgical transection of the pituitary stalk or bilateral removal of the superior cervical ganglion did not abolish the anterior lobe nerve fibers, and anterograde tracing with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate from the pituitary stalk failed to stain any nerve fibers within the anterior lobe. Our findings suggest that the nodose ganglion neurons likely innervate the pituitary anterior lobe, while neither hypothalamus nor sympathetic superior cervical ganglion may be a source of this innervation. By showing a distinct neuronal system in the pituitary anterior lobe our findings (i) support the previous functional studies demonstrating a distinct regulation of the morphology of the anterior lobe innervation by hormonal changes, and (ii) suggest that the innervation of the pituitary anterior lobe is a part of the visceral innervation by the vagus nerve rather than a part of the other intracranial innervation. These findings provide a neuroanatomic basis for the reported observations about the neural regulation of the pituitary anterior lobe.

Effects of nerve growth factor on expression of GAP-43 in right atria after sympathectomy in diabetic rats

AIM

The present study investigated the role of nerve growth factor (NGF) in the regeneration of noradrenergic nerves of right atria (following 6-hydroxydopamine; 6-OHDA, 100 mg/kg, i.p.) from non-diabetic and 8-week diabetic rats.

RESULTS

In cryostat sections of the right atria, GAP-43 immunoreactivity was concentrated in nerve terminals, preterminal axons of the endocardium, epicardium and myocardium, as well as in nerve fibres innervating the blood vessels and ganglionic cells. In serial sections, all positive staining for GAP-43 showed immunoreactivity for the neuronal marker PGP-9.5. In untreated non-diabetic rats, the total GAP-43 immunoreactivity was reduced to 60% relative to pretreatment levels, at day 14 after 6-OHDA, as quantified by Western blotting. In diabetic rats, 6-OHDA treatment produced a marked increase in the levels of total GAP-43 at days 28 and 49. NGF treatment (1 mg/kg, s.c., 3 times/week, for 2 weeks) had no effect on the level of total GAP-43 in right atria from non-diabetic and diabetic rats before treatment with 6-OHDA. However, it normalized the reduced GAP-43 immunoreactivity observed in 6-OHDA-treated non-diabetic rats. Interestingly, NGF treatment alone produced an increase in GAP-43 phosphorylation relative to total GAP-43 in right atria from both non-diabetic (44%) and diabetic groups (42%).

CONCLUSIONS

These findings suggest that nerve terminals of the right atria retain, in the mature adult, the capacity for structural and functional plasticity. The expression of GAP-43 in right atria of control and diabetic rats was differentially affected by 6-OHDA treatment. In injured noradrenergic neurones of the right atria, NGF modified the expression of GAP-43 only in non-diabetic rats and not in diabetic rats.

Synaptic vesicle proteins and neuronal plasticity in adrenergic neurons

The neurons in the superior cervical ganglion are active in plasticity and re-modelling in order to adapt to requirements. However, so far, only a few studies dealing with synaptic vesicle related proteins during adaptive processes have been published. In the present paper, changes in content and expression of the synaptic vesicle related proteins in the neurons after decentralization (cutting the cervical sympathetic trunk) or axotomy (cutting the internal and external carotid nerves) were studied. Immunofluorescence studies were carried out using antibodies and antisera against integral membrane proteins, vesicle associated proteins, NPY, and the enzymes TH and PNMT. For colocalization studies, the sections were simultaneously double labelled. Confocal laser scanning microscopy was used for colocalization studies as well as for semi-quantification analysis, using the computer software. Westen blot analysis, in situ 3'-end DNA labelling, and in situ hybridization were also employed. After decentralization of the ganglia several of the synaptic vesicle proteins (synaptotagmin I, synaptophysin, SNAP-25, CLC and GAP-43) were increased in the iris nerve terminal network, but with different time patterns, while TH-immunoreactivity had clearly decreased. In the ganglia, these proteins had decreased at 1 day after decentralization, probably due to degeneration of the pre-ganglionic nerve fibres and terminals. At later intervals, these proteins, except SNAP-25, had increased in the nerve fibre bundles and re-appeared in nerve fibres outlining the principal neurons.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.

Immunohistochemical and molecular studies of serotonin, substance P, galanin, pituitary adenylyl cyclase-activating polypeptide, and secretoneurin in fibromyalgic muscle tissue

OBJECTIVE

Because former investigations have reported abnormal changes in the expression of serotonin (5-hydroxytryptamine [5-HT]) and substance P (SP) in serum and cerebrospinal fluid, this study sought to determine whether 5-HT and pain-modulating neuropeptides (SP, galanin [GA], pituitary adenylyl cyclase-activating polypeptide, and secretoneurin) were expressed abnormally in the muscle tissue of patients with fibromyalgia (FM).

METHODS

Snap-frozen muscle tissue specimens (deltoid muscles) from 10 patients with FM (mean disease duration 15 years) and from 10 healthy control subjects were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) of RNA preparations from muscle cells, and by immunohistochemistry methods (alkaline phosphatase-anti-alkaline phosphatase and immunogold-silver) using specific primers as well as antibodies. When specific messenger RNA (mRNA) was detected by RT-PCR, in situ RT-PCR was performed for mRNA localization.

RESULTS

Specific mRNA for the examined substances was absent in 9 of 10 FM patients and in 10 of 10 controls. No differences between the FM patients and controls could be detected in the muscle tissue by immunohistochemistry. In 1 FM patient, mRNA for the GA receptor could be shown.

CONCLUSION

This study showed that 5-HT and neuropeptides are not produced in the muscle of patients with FM, and therefore do not appear to be involved in the peripheral induction of pain in this chronic, painful disorder.

The cellular distribution of GAP-43 immunoreactivity in human neocortical areas using immunofluorescence and confocal microscopy: post-ischemic influence

The distribution of growth associated protein-43 (GAP-43) immunoreactive (IR) neurons were studied in human neocortical areas, using immunofluorescence and confocal microscopy. The GAP-43-IR cells were generally localised close to blood vessels, and contained fewer lipofuscin granules than GAP-43 negative cells. Quantification of the relative number of GAP-43-IR cells in control cases showed that the highest number of GAP-43-IR cells were present in layers III and V in the motor and visual cortices, fewer in the temporal cortex, and the lowest number in the frontal cortex. After general ischemia, GAP-43-IR cells were significantly reduced at various survival times, with the counts being lowest in the 1 week surviving case, and higher, but still subcontrol, in the 1 year post-ischemic case.

B-50, the growth associated protein-43: modulation of cell morphology and communication in the nervous system

The growth-associated protein B-50 (GAP-43) is a presynaptic protein. Its expression is largely restricted to the nervous system. B-50 is frequently used as a marker for sprouting, because it is located in growth cones, maximally expressed during nervous system development and re-induced in injured and regenerating neural tissues. The B-50 gene is highly conserved during evolution. The B-50 gene contains two promoters and three exons which specify functional domains of the protein. The first exon encoding the 1-10 sequence, harbors the palmitoylation site for attachment to the axolemma and the minimal domain for interaction with G0 protein. The second exon contains the "GAP module", including the calmodulin binding and the protein kinase C phosphorylation domain which is shared by the family of IQ proteins. Downstream sequences of the second and non-coding sequences in the third exon encode species variability. The third exon also contains a conserved domain for phosphorylation by casein kinase II. Functional interference experiments using antisense oligonucleotides or antibodies, have shown inhibition of neurite outgrowth and neurotransmitter release. Overexpression of B-50 in cells or transgenic mice results in excessive sprouting. The various interactions, specified by the structural domains, are thought to underlie the role of B-50 in synaptic plasticity, participating in membrane extension during neuritogenesis, in neurotransmitter release and long-term potentiation. Apparently, B-50 null-mutant mice do not display gross phenotypic changes of the nervous system, although the B-50 deletion affects neuronal pathfinding and reduces postnatal survival. The experimental evidence suggests that neuronal morphology and communication are critically modulated by, but not absolutely dependent on, (enhanced) B-50 presence.

Effects of decentralization on the levels of GAP-43 and p38 (synaptophysin) in sympathetic adrenergic neurons: a semi-quantitative study using immunofluorescence and confocal laser scanning microscopy

The distribution of GAP-43 in superior cervical ganglion (SCG) and iris were studied in normal animals and following decentralization using immunofluorescence and confocal laser scanning microscopy (CLSM). GAP-43-like immunoreactivity (LI) was compared with p38 (synaptophysin)-LI, and tyrosin hydroxylase (TH)-LI. In the control SCG, GAP-43-LI and p38-LI were mainly localized in nerve terminals around the principal neurons. The neuronal perikarya were negative for GAP-43, but positive for p38 in a perinuclear zone, as well as positive for TH. SIF cells (Small Intensely Fluorescent cells, ganglionic interneurons) were positive for GAP-43, TH and p38. One day after decentralization, GAP-43-LI and p38-LI in nerve terminals around principal neurons had disappeared. Some of the principal neurons showed a weak GAP-43-immunoreactivity. Three days post-decentralization, GAP-43- and p38-positive nerve terminals around the neurons had reappeared in considerable numbers and the intra-ganglionic nerve bundles were positive for both antibodies. In the control irides, GAP-43-LI and p38-LI were distributed in a varicose pattern in the nerve bundles, around blood vessels and in the network of terminals. Double labelling studies showed that GAP-43-LI was colocalized with TH-LI and p38-LI. The network of terminals in the dilator plate of the irides was quantified by measuring the fluorescence intensity of randomly selected areas, using CLSM. Three days after decentralization the intensity of GAP-43-LI and p38-LI had significantly increased. TH-LI had decreased 8 days after decentralization. The results indicate that GAP-43-LI and p38-LI are normally present in the nerve fibers and terminals of both pre- and post-ganglionic neurons in adult rats. The expression of GAP-43-LI and p38-LI in post-ganglionic neurons is preganglionically regulated, as indicated by the increased expression after decentralization. The expression of p38 in these neurons is probably regulated via mechanisms that are separate from those which regulate GAP-43, since it showed a different time course than that of GAP-43-LI.