Calcitonin gene-related peptide and chromogranin A: presence and intra-axonal transport in lumbar motor neurons in the rat, a comparison with synaptic vesicle antigens in immunohistochemical studies

Protein sorting in the synaptic vesicle life cycle

At early stages of differentiation neurons already contain many of the components necessary for synaptic transmission. However, in order to establish fully functional synapses, both the pre- and postsynaptic partners must undergo a process of maturation. At the presynaptic level, synaptic vesicles (SVs) must acquire the highly specialized complement of proteins, which make them competent for efficient neurotransmitter release. Although several of these proteins have been characterized and linked to precise functions in the regulation of the SV life cycle, a systematic and unifying view of the mechanisms underlying selective protein sorting during SV biogenesis remains elusive. Since SV components do not share common sorting motifs, their targeting to SVs likely relies on a complex network of protein-protein and protein-lipid interactions, as well as on post-translational modifications. Pleiomorphic carriers containing SV proteins travel and recycle along the axon in developing neurons. Nevertheless, SV components appear to eventually undertake separate trafficking routes including recycling through the neuronal endomembrane system and the plasmalemma. Importantly, SV biogenesis does not appear to be limited to a precise stage during neuronal differentiation, but it rather continues throughout the entire neuronal lifespan and within synapses. At nerve terminals, remodeling of the SV membrane results from the use of alternative exocytotic pathways and possible passage through as yet poorly characterized vacuolar/endosomal compartments. As a result of both processes, SVs with heterogeneous molecular make-up, and hence displaying variable competence for exocytosis, may be generated and coexist within the same nerve terminal.

Complete dissociation of motor neuron death from motor dysfunction by Bax deletion in a mouse model of ALS

The death of cranial and spinal motoneurons (MNs) is believed to be an essential component of the pathogenesis of amyotrophic lateral sclerosis (ALS). We tested this hypothesis by crossing Bax-deficient mice with mice expressing mutant superoxide dismutase 1 (SOD1), a transgenic model of familial ALS. Although Bax deletion failed to prevent neuromuscular denervation and mitochondrial vacuolization, MNs were completely rescued from mutant SOD1-mediated death. However, Bax deficiency extended lifespan and delayed the onset of motor dysfunction of SOD1 mutants, suggesting that Bax acts via a mechanism distinct from cell death activation. Consistent with this idea, Bax elimination delayed the onset of neuromuscular denervation, which began long before the activation of cell death proteins in SOD1 mutants. Additionally, we show that denervation preceded accumulation of mutant SOD1 within MNs and astrogliosis in the spinal cord, which are also both delayed in Bax-deficient SOD1 mutants. Interestingly, MNs exhibited mitochondrial abnormalities at the innervated neuromuscular junction at the onset of neuromuscular denervation. Additionally, both MN presynaptic terminals and terminal Schwann cells expressed high levels of mutant SOD1 before MNs withdrew their axons. Together, these data support the idea that clinical symptoms in the SOD1 G93A model of ALS result specifically from damage to the distal motor axon and not from activation of the death pathway, and cast doubt on the utility of anti-apoptotic therapies to combat ALS. Furthermore, they suggest a novel, cell death-independent role for Bax in facilitating mutant SOD1-mediated motor denervation.

Characterization of [(3)H]ucb 30889 binding to synaptic vesicle protein 2A in the rat spinal cord

The novel antiepileptic drug levetiracetam ((2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA possesses a specific binding site in brain, which has very recently been identified as the synaptic vesicle protein SV 2 A. The aim of this study was to evaluate the presence of a levetiracetam binding site in the spinal cord and compare its properties to that in rat brain. We used [(3)H]ucb 30889 ((2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide), a levetiracetam analogue, to perform binding assays, photoaffinity labelling and autoradiography experiments, and revealed the presence of SV 2 A by Western-blot analysis. [(3)H]ucb 30889 binding kinetics at 4 degrees C were biphasic and saturation binding curves were compatible with the labelling of a homogenous population of binding sites with a K(d) similar to that in brain. Competition curves with ligands known to interact with levetiracetam binding sites and photolabelling experiments indicated that [(3)H]ucb 30889 labels the same 90 kDa protein in both spinal cord and brain. Levetiracetam binding site was localised in the grey matter of the spinal cord and its expression was not modified in a model of neuropathic pain. This study demonstrates the presence of a specific levetiracetam binding site in the rat spinal cord, which is similar to that found in rat brain.

Chromogranin-mediated secretion of mutant superoxide dismutase proteins linked to amyotrophic lateral sclerosis

Here we report that chromogranins, components of neurosecretory vesicles, interact with mutant forms of superoxide dismutase (SOD1) that are linked to amyotrophic lateral sclerosis (ALS), but not with wild-type SOD1. This interaction was confirmed by yeast two-hybrid screen and by co-immunoprecipitation assays using either lysates from Neuro2a cells coexpressing chromogranins and SOD1 mutants or lysates from spinal cord of ALS mice. Confocal and immunoelectron microscopy revealed a partial colocalization of mutant SOD1 with chromogranins in spinal cord of ALS mice. Mutant SOD1 was also found in immuno-isolated trans-Golgi network and in microsome preparations, suggesting that it can be secreted. Indeed we report evidence that chromogranins may act as chaperone-like proteins to promote secretion of SOD1 mutants. From these results, and our finding that extracellular mutant SOD1 can trigger microgliosis and neuronal death, we propose a new ALS pathogenic model based on the toxicity of secreted SOD1 mutants.

Distribution of mRNAs for Chromogranins A and B and Secretogranin II in Rat Brain

The mRNA distribution of chromogranins A and B and secretogranin II was determined in rat brain. In Northern blots the oligonucleotide probes used hybridized with single mRNA species of the expected sizes. With tissue hybridization the mRNA signals for these three proteins were found throughout the brain. However, each of the three messages had a distinct distribution, which was exemplified by the fact that in the various regions either all three proteins, a combination of two or only one of them were apparently synthesized. Significant levels of all three mRNAs were found in several regions of the hippocampus and of the amygdala, in some thalamic nuclei and in the pyriform cortex. On the other hand the subiculum contained only the message for chromogranin A, the granule cell layer of the cerebellum only that for chromogranin B, and in posterior intralaminar thalamic and medial geniculate nuclei and in the nucleus of the solitary tract only secretogranin II mRNA was found. The distinct distributions of mRNAs for the chromogranins in various brain regions support the concept that these proteins are propeptides giving rise to functionally active components.

Distribution and intraneuronal trafficking of a novel member of the chromogranin family, NESP55, in the rat peripheral nervous system

NESP55 (neuroendocrine secretory protein of M(r) 55000) is a novel member of the chromogranin family. In the present study, we have investigated the distribution, axonal transport and proteolytic processing of NESP55 in the peripheral nervous system. The amount of NESP55 immunoreactivity in adrenal gland was more than 240 times higher than that in the vas deferens. Double or triple immunostaining demonstrated that NESP55 immunoreactivity was highly co-localized with tyrosine hydroxylase immunoreactivity in bundles of thin axons and postganglionic sympathetic neurons; that NESP55 immunoreactivity also co-existed with vesicular acetylcholine transporter immunoreactivity in large-sized axons in sciatic nerves, and that NESP55 immunoreactivity overlapped with calcitonin gene-related peptide immunoreactivity in some large-sized axons, but NESP55 immunoreactivity was not detected in sensory neurons. Strong NESP55 immunoreactivity was found in cell bodies and axons, but it was not detectable in any terminal region by immunohistochemistry. In crush-operated sciatic nerves, NESP55 immunoreactivity could be found as early as 1 h after operation, and accumulated amounts increased substantially with time. However, NESP55 immunoreactivity was only observed in axons proximal to the crush, but none or very little distal to the crush, which was consistent with the data from radioimmunoassay. Finally, extracts of the normal and crushed sciatic nerve and vas deferens were subjected to high-performance liquid chromatography followed by radioimmunoassay. The results indicate that NESP55 is processed slowly to small peptides (GAIPIRRH) during axonal transport. NESP55 immunoreactivity was only detected in axons proximal to the crush. The data in the present study indicate that NESP55 immunoreactivity is widely distributed in adrenergic, cholinergic, and peptidergic neurons, but not in sensory neurons, and that this peptide is anterogradely, but not retrogradely, transported with fast axonal transport and slowly processed to smaller peptides during axonal transport in the peripheral nervous system.

Localization of zinc-enriched neurons in the mouse peripheral sympathetic system

Growing evidence supports the notion that zinc ions located in the synaptic vesicles of zinc-enriched neurons (ZEN) play important physiological roles and are involved in certain pathological changes in the central nervous system. Here we present data revealing the distribution of zinc ions and the co-localization of zinc transporter 3 (ZnT3) and tyrosine hydroxylase (TH) in crush-operated sciatic nerves and lumbar sympathetic ganglia of mice, using zinc selenide autometallography (ZnSe(AMG)) and ZnT3 immunofluorescence combined with confocal scanning microscopy, respectively. Six hours after the crush operation, ZnSe(AMG) grains and ZnT3 immunoreactivity were predominantly present in a subpopulation of thin unmyelinated sciatic nerve axons. In order to identify the type(s) of ZEN axons involved, double labeling with ZnT3 and (1) TH, (2) vesicular acetylcholine transporter (VAChT), (3) calcitonin gene-related peptide (CGRP), and (4) neuropeptide Y (NPY) was performed. Confocal microscopic observations showed that ZnT3 was located in a subpopulation of sciatic axons in distended parts proximal and distal to the crush site. Most, if not all, ZnT3-positive axons contained TH immunofluorescence, a few showed co-localization of ZnT3 and VAChT with very weak immunostaining, while no congruence was observed between ZnT3 and CGRP or NPY. Studies of the lumbar sympathetic ganglia showed that not more than 5% of the neurons were ZnT3-positive and that almost all of these were TH-positive. Furthermore, approximately 5% of total lumbar sympathetic ganglionic cells were ZnSe(AMG) positive, 48 h after a local injection of sodium selenide into the sciatic nerve. The present data support the notion that a subgroup of mouse sympathetic postganglionic neurons are ZEN neurons.

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.

Cytoplasmic dynein conversion at a crush injury in rat peripheral axons

Cytoplasmic dynein is a motor for retrograde axonal transport for movement of membranous organelles toward the neuronal cell body. However, cytoplasmic dynein is synthesized in the cell body and conveyed along the axon to nerve terminals. To characterize the axonal transport of cytoplasmic dynein in relation to synaptic vesicles and other membrane compartments, immunocytochemical and cytofluorimetric scanning analyses of crush-operated rat sciatic nerves were performed. Distal to the crush, the kinetics of dynein accumulation were consistent with its role in the retrograde transport of membranous organelles. During the initial 3 hr after crush, only small amounts of dynein-immunoreactive material accumulated proximal to the crush. This is consistent with metabolic labeling studies showing that most of the dynein moving in the anterograde direction is in the slow component of axonal transport. Thereafter, the rate of proximal accumulation of dynein increased, and by 8 hr postcrush a large amount of dynein immunoreactivity was observed. This accelerated accumulation may be due to recruitment of dynein from slow component b onto organelles proximal to the crush. Double labeling demonstrated that dynein immunoreactivity colocalized with synaptophysin, a transmembrane protein found in small, clear synaptic vesicles. In contrast, dynein immunoreactivity did not colocalize well with calcitonin gene-related peptide (CGRP), a peptide matrix marker for some large dense-cored vesicles. Finally, dynein immunoreactivity colocalized with the anterograde transport motor kinesin both proximal and distal to a crush, suggesting that kinesin may carry some dynein-containing membrane compartments during fast anterograde axonal transport.

Proteolytic processing, axonal transport and differential distribution of chromogranins A and B, and secretogranin II (secretoneurin) in rat sciatic nerve and spinal cord

The chromogranin family comprises chromogranin A and B, and secretogranin II. The present study has focused on the axonal transport of chromogranins/secretogranin II and their detailed distribution in peripheral nerves and the spinal cord. With radioimmunoassay (RIA) and column chromatography, we first studied the processing of chromogranin B and secretogranin II during axonal transport. No larger precursors of these peptides were detected in the sciatic nerves, indicating that they are already processed to a high degree early during axonal transport. We also analysed nerve segments above and below a crush, using RIA, in order to compare these accumulation data with those obtained by the cytofluorimetric-scanning (CFS) technique. For the latter technique, the amounts of accumulation distal to the crush (presumably representing recycling and retrogradely transported peptides) were 30-40% of the amounts in the proximal accumulation for chromogranin A and secretoneurin, in contrast to chromogranin B, which showed 15% recycling. With the RIA, the corresponding values for secretoneurin and PE-11 (antibody against chromogranin B) were 42% and 14%, respectively. Therefore, the data obtained by CFS were in excellent agreement with those obtained by RIA. In crushed sciatic nerves, chromogranin A was present in large axons as well as in small- and medium-sized axons. Chromogranin B was mainly restricted to large axons, while secretoneurin was localized to bundles of small axons. This differential distribution was also found in the spinal roots and in the peripheral terminals. Chromogranin A was present in both ventral and dorsal roots, and chromogranin B was detected in ventral roots and in large sensory axons in the dorsal roots. Secretoneurin was dominant in the dorsal root. Double-labelling studies with antibodies against choline acetyltransferase/vesicular acetylcholine transporter, or against tyrosine hydroxylase, confirmed that chromogranin A was distributed in cholinergic, sensory, as well as adrenergic neurons. Chromogranin B was mainly present in cholinergic motor neurons and large sensory neurons, and secretoneurin was restricted to adrenergic and sensory neurons. The present study demonstrates that chromogranins A and B, and secretoneurin are transported with fast axonal transport in the peripheral nerves, with different amounts of recycling, and that they are differentially distributed in different types of neurons in the peripheral nervous system and the spinal cord, suggesting that each of them may play a special role in subsets of neurons.

Distribution of chromogranins A and B and secretogranin II (secretoneurin) in rat pelvic neurons and vas deferens

The family of chromogranins/secretogranin peptides comprises three major subtypes: chromogranin A, chromogranin B and secretogranin II. We have characterized these proteins in rat vas deferens and pelvic ganglia by using two approaches. Firstly, extracts of rat vas deferens were subjected to molecular sieve chromatography followed by radioimmunoassay. The results indicate that, in the peripheral nerves of this organ, chromogranin B and secretogranin II are processed to small peptides, i.e. PE-11 and secretoneuron, respectively. Secondly, we investigated the localization of each of these peptides in the rat pelvic ganglia and vas deferens. Comparisons with the distribution of tyrosine hydroxylase, choline acetyltransferase, vesicular acetylcholine transporter and SV2 were carried out in double labelling studies. All tyrosine hydroxylase-positive neurons contained neuropeptide Y, but many neuropeptide Y-containing neurons were negative for tyrosine hydroxylase. In the pelvic ganglia, chromogranin A was widely localized in the neuropeptide-positive neurons and 65% of chromogranin A-containing neurons were positive for tyrosine hydroxylase, suggesting their adrenergic nature. However, in nerve terminals of the vas deferens, chromogranin A was present at very low, or undetectable, levels. The chromogranin B-derived peptide PE-11, on the other hand, was absent from the large-sized, tyrosine hydroxylase-positive neurons, but present in some small-sized neurons that were choline acetyltransferase/vesicular acetylcholine transporter-positive and tyrosine hydroxylase-negative. In the vas deferens, PE-11 was present with intense immunoreactivity in nerve terminals of the lamina propria beneath the epithelium, but it was very sparse in the muscular layer and co-localized with vesicular acetylcholine transporter-like immunoreactivity, suggesting a cholinergic nature. The secretogranin II-derived peptide secretoneurin was distributed with strong immunoreactivity in the somata of pelvic ganglion neurons, 72% of which also contained tyrosine hydroxylase, as well as in nerve terminals in the muscular layer and the lamina propria of the vas deferens. Most, if not all, secretoneurin-positive terminals in the pelvic ganglia and the vas deferens were positive for choline acetyltransferase/vesicular acetylcholine transporter-like immunoreactivity. Retrograde tracing with FluoroGold demonstrated that the majority of FluoroGold-labelled neurons in the pelvic ganglia were positive for either chromogranin A or secretoneurin. The present study indicates that chromogranins A and B and secretogranin II are proteolytically processed to a high degree in the nerves of the rat vas deferens. Furthermore, they are heterogeneously localized in subsets of neurons of the pelvic ganglia and in different sets of nerve terminals in the vas deferens, suggesting that each of these peptides may play distinct roles in neurons of the autonomic nervous system to the vas deferens.

Intraneuronal trafficking and distribution of amphiphysin and synaptojanin in the rat peripheral nervous system and the spinal cord

Amphiphysin and synaptojanin are two nerve terminal proteins with a putative role in synaptic vesicle endocytosis and recycling. We have investigated the intraneuronal dynamics and distribution of these two proteins, using nerve crush techniques in combination with immunofluorescence, cytofluorimetric scanning (CFS), confocal laser scanning microscopy and immuno-electron microscopy (EM). Accumulations of amphiphysin and synaptojanin immunoreactivities at the crush site were detected as short as 1 h after the lesion, indicating that a pool of these two partially cytosolic proteins moves along the axon by fast axoplasmic transport. The amount of proximal accumulation increased linearly between 1 and 8 h. CFS analysis demonstrated that only 30% of fast anterogradely transported amphiphysin and synaptojanin was returned by fast retrograde transport, in contrast to the 70% value observed for synaptophysin, a transmembrane protein. This indicates that the majority of amphiphysin and synaptojanin is degraded/metabolized in the nerve terminals. Immuno-EM showed that both amphiphysin and synaptojanin are primarily associated with heterogeneous membrane profiles in the crushed sciatic nerve and the immunoperoxidase reaction product is concentrated in the nerve terminal cytomatrix of the spinal cord. Both proteins were differentially distributed in subsets of nerve terminals, indicating heterogeneous expression in neurons.

Axonal transport of synaptic vesicle proteins in the rat optic nerve

The optic nerve, as a part of the central nervous system (CNS), has been used to study axonal transport for decades. The present study has concentrated on the axonal transport of synaptic vesicle proteins in the optic nerve, using the "stop-flow/nerve crush" method. After blocking fast axonal transport, distinct accumulations of synaptic vesicle proteins developed during the first hour after crush-operation and marked increases were observed up to 8 h postoperative. Semiquantitative analysis, using cytofluorimetric scanning (CFS) of immunoincubated sections, revealed that the ratio between distal accumulations (organelles in retrograde transport) and proximal accumulations (organelles in anterograde transport) was much higher (up to 80-90%) for the transmembrane proteins than that for surface adsorbed proteins (only 10-20%). The pattern of axonal transport in the optic nerve was comparable to that in the sciatic nerve. However, clathrin and Rab3a immunoreactivities were accumulated in much lower amounts than that in the sciatic nerve. Most synaptic vesicle proteins were colocalized in the axons proximal to the crush. A differential distribution of synaptobrevin I and II, however, was observed in the optic nerve axons; synaptobrevin I was present in large-sized axons, while synaptobrevin II immunoreactivity was present in most axons, including the large ones. The two isoforms were, thus, partially colocalized. The results demonstrate that (1) cytofluorimetric scanning techniques could be successfully used to study axonal transport not only in peripheral nerves, but also in the CNS; (2) synaptic vesicles are transported with fast axonal transport in this nerve; and (3) some differences were noted compared with the sciatic nerve, especially for Rab3a and clathrin.

Distribution of Rab3a in rat nervous system: comparison with other synaptic vesicle proteins and neuropeptides

In the present study we have investigated the distribution of Rab3a in rat peripheral nervous system and compared it with the distribution of other synaptic vesicle proteins (synaptophysin, synapsin I), neuropeptides (CGRP, SP, NPY) and tyrosine hydroxylase (TH). Rab3a immunoreactivity (-IR) was always colocalized with synaptophysin-IR and synapsin I-IR in nerve terminals of the spinal cord and peripheral nerve endings. In many cases, Rab3a-IR was also present in the same axons and terminals as peptides. In crushed sciatic nerve axons, Rab3a was colocalized, proximal to the crush, with synaptophysin-IR, synapsin I-IR, CGRP-IR, and TH-IR, but only partially co-localized with NPY-IR and SP-IR. In the area distal to the crush, Rab3a-IR was very weakly positive in a few thin axons, while larger amount of synaptophysin, CGRP, NPY and SP immunoreactivities were detected. The subcellular distribution of peptides and Rab3a differed in that peptides were observed mainly in large granular structures, while Rab3a-IR was observed mainly as diffuse, finely granular immunoreactivity, in addition to a few exceptional large granules present in some axons. The results demonstrate that Rab3a is widely distributed in different types of neurons, i.e. motor, sensory, autonomic adrenergic and cholinergic neurons, and colocalized with other synaptic vesicle proteins, suggesting that Rab3a may play an essential role in neuronal function. Furthermore, Rab3a is present in many peptide containing axons and terminals, but with an apparently different subcellular distribution, being affiliated mostly with small synaptic vesicles and only occasionally with large vesicles, that may represent peptide contained vesicles.

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

The presence of the growth-associated protein, GAP-43, in rat sciatic nerve and gastrocnemius muscle was studied, using indirect immunofluorescence, in lumbar sympathectomized and sham-sympathectomized rats. To study fast axonal transport and accumulation of immunogenic GAP-43, the sciatic nerves were crush operated, 6 h before perfusion fixation. In sections of normal, crushed sciatic nerve GAP-43-like immunoreactivity (LI) rapidly accumulated, on both sides of the crushes, in medium and thin sized axons. In double immunostaining experiments, GAP-43-LI was mainly colocalized with tyrosine hydroxylase (TH)-LI, or neuropeptide Y (NPY)-LI, markers of sympathetic nerves. In some axons, GAP-43-LI was colocalized with Substance P (SP)-LI. In perivascular nerve terminals in the gastrocnemic muscle, strong GAP-43-immunofluorescence was observed, in most cases colocalized with TH-LI, but in some terminals with SP-LI. Three days after lumbar sympathectomy (removal of the L1-L4 sympathetic ganglia bilaterally), TH-LI and NPY-LI positive axons in the sciatic nerve were reduced in number by more than 90%. GAP-43-LI positive axons were reduced by about 50%. In the gastrocnemic muscle, some GAP-43-LI positive terminals, but very few TH-LI positive nerve fibres, were found around blood vessels. No further changes were seen 8 days after sympathectomy. SP-LI in axons in the sciatic nerve and in perivascular nerve terminals of the gastrocnemic muscle, did not change after sympathectomy; most of these axons also contained GAP-43-LI. S-100-LI was present periaxonally in the sciatic nerves, but it did not colocalize with GAP-43, indicating that Schwann cells contained no GAP-43-LI in these experiments. The results show that, in normal adult rats, GAP-43-LI is mainly present in sympathetic and sensory nerve fibers in sciatic nerve and in perivascular nerve terminals. The peptide is axonally transported, mainly in sensory and adrenergic axons.

The polymeric immunoglobulin receptor accumulates in specialized endosomes but not synaptic vesicles within the neurites of transfected neuroendocrine PC12 cells

We have expressed in neuroendocrine PC12 cells the polymeric immunoglobulin receptor (pIgR), which is normally targeted from the basolateral to the apical surface of epithelial cells. In the presence of nerve growth factor, PC12 cells extend neurites which contain synaptic vesicle-like structures and regulated secretory granules. By immunofluorescence microscopy, pIgR, like the synaptic vesicle protein synaptophysin, accumulates in both the cell body and the neurites. On the other hand, the transferrin receptor, which normally recycles at the basolateral surface in epithelial cells, and the cation-independent mannose 6-phosphate receptor, a marker of late endosomes, are largely restricted to the cell body. pIgR internalizes ligand into endosomes within the cell body and the neurites, while uptake of ligand by the low density lipoprotein receptor occurs primarily into endosomes within the cell body. We conclude that transport of membrane proteins to PC12 neurites as well as to specialized endosomes within these processes is selective and appears to be governed by similar mechanisms that dictate sorting in epithelial cells. Additionally, two types of endosomes can be identified in polarized PC12 cells by the differential uptake of ligand, a housekeeping type in the cell bodies and a specialized endosome in the neurites. Recent findings suggest that specialized axonal endosomes in neurons are likely to give rise to synaptic vesicles (Mundigl, O., M. Matteoli, L. Daniell, A. Thomas-Reetz, A. Metcalf, R. Jahn, and P. De Camilli. 1993. J. Cell Biol. 122:1207-1221). Although pIgR reaches the specialized endosomes in the neurites of PC12 cells, we find by subcellular fractionation that under a variety of conditions it is efficiently excluded from synaptic vesicle-like structures as well as from secretory granules.

Synaptotagmin I is present mainly in autonomic and sensory neurons of the rat peripheral nervous system

The distribution of synaptotagmin I in the peripheral nervous system of the rat was investigated by immunofluorescence and confocal laser scanning microscopy. After crushing of the sciatic nerve, synaptotagmin I-like immunoreactivity accumulated proximally as well as distally to the crushes in thin and medium-sized axons. Double labelling studies revealed that synaptotagmin I co-localized with tyrosine hydroxylase, a marker of sympathetic adrenergic neurons, and with substance P, a marker for sensory neurons. No synaptotagmin I-like immunoreactivity was found in large axons, while accumulations of the synaptic vesicle proteins synaptophysin and synapsin I were found in all types of axons. Furthermore, no synaptotagmin I-like immunoreactivity was detected in motor endplates. In contrast, the protein was found in muscle spindles of young rats and in perivascular terminals, where it co-localized with synaptophysin and synapsin I. Lumbar sympathectomy resulted in a marked reduction of the amount and intensity of synaptotagmin I-like immunoreactivity in sciatic nerve. High magnification revealed that synaptotagmin I-like immunoreactivity was mainly distributed in a fine granular pattern, but large, brightly fluorescent granules which were not labelled by anti-synaptophysin or anti-synapsin I were occasionally observed. We conclude that synaptotagmin I is mainly expressed in adrenergic and sensory neurons and is absent from, or below detection levels, in motoneurons.

Fast and slow axonal transport-different methodological approaches give complementary information: contributions of the stop-flow/crush approach

This 'minireview' describes experiments in short term crush operated rat nerves, to study endogenous substances in anterograde and retrograde fast axonal transport. Immunofluorescence was used to recognize transported antigens, and cytofluorimetric scanning was employed to quantitate different antigens which had accumulated proximal and distal to the crushes. Vesicle membrane components p38 (synaptophysin) and SV2 accumulated on both sides of a crush. This was expected from a number of studies from different laboratories. Surface associated molecules, however, like synapsins and rab3a, have been studied by other groups with biochemical methods, and suggested to be transported with slow transport. The crush method, however, revealed that a considerable fraction of these two substances are transported with the fast transport system, and, thus, associated with fast transported organelles in the living neuron. Evidently, more than one technique is required to give a more complete picture of intraneuronal transport related events.

Calcitonin gene-related peptide-like immunoreactivity, in botulinum toxin-paralysed rat muscles

Changes in calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) at the motor endplates of botulinum toxin-paralysed rat muscles were investigated using immunohistochemistry. One day following toxin injection, a dramatic increase in CGRP-LI was detected at the motor endplates and within preterminal axons of the soleus and gastrocnemius muscles. The upregulation of CGRP-LI persisted throughout the period during which muscle fibres were paralysed and new neuromuscular junctions were being formed by the growing sprouts. Decline of CGRP-LI at the motor endplates coincided with clinical recovery. Both up- and down-regulation of CGRP-LI took place earlier in the soleus than in the gastrocnemius muscle. Up-regulation of CGRP-LI was also detected in a subpopulation of motor axons in the sciatic nerves and in the spinal motor neurons innervating the paralysed muscles. These results indicate that levels of CGRP are regulated, at least partly, by changes in the target innervation. They also suggest an important role for CGRP in the regenerative processes following muscle paralysis.

Effects of irradiation on neuropeptide expression in rat salivary gland and spinal cord

It is well-known that a large number of factors can influence the expression of neuropeptides in the nervous system. In the present study, the effects of unilateral and bilateral irradiation to the rat head and neck on the expression of neuropeptides in the innervation of the submandibular gland and in the ganglionic cells of the submandibular ganglion was examined ten days and six months after treatment. Antisera directed against enkephalin and bombesin and immunohistochemical methods were used. The effects of bilateral irradiation on the staining pattern of various neuropeptides in the cervical spinal cord were also studied. In the submandibular gland and in the submandibular ganglionic cells, there was a markedly increased neuropeptide expression ten days after bilateral treatment, as seen after staining with both antisera used, while no changes occurred after unilateral treatment. Six months after treatment, the pattern of neuropeptide expression in the submandibular gland/ganglion corresponded to that seen in controls. Irradiation did not lead to any changes in the staining pattern of neuropeptides in the spinal cord. The observations show that there is a great complexity in the susceptibility of nervous tissues to radiotherapy with respect to influences on the expression of neuropeptides.

Bundles of amyloid precursor protein-immunoreactive axons in human cerebrovascular white matter lesions

Cerebral white matter lesions commonly observed in Binswanger's disease, multi-infarct encephalopathy and elderly people are neuropathologically characterized by diffuse incomplete demyelination and considered to be ischemic in nature. Arteriolosclerosis in the white matter is a common feature in these white matter lesions. To investigate a possible alteration of the distribution of amyloid precursor protein (APP), chromogranin A (CgA) and synaptophysin (Syn) in such white matter lesions, we examined 15 cases with white matter lesions and 5 without white matter lesions. Many bundles of axons with APP-like immunoreactivity (LI) were observed particularly in mild white matter lesions. Such bundles of axons showed similar but less intense CgA-LI and Syn-LI. They appeared to occur in areas with many ameboid or ramified microglia labeled with anti-leukocyte common antigen and few astrocytes labeled with anti-glial fibrillary acidic protein. In the center of moderate of severe white matter lesions bundles of axons with APP-LI were never observed. Since APP, CgA and Syn undergo fast axonal transport, and since following ischemic insults to central nervous system microglial reaction occurs earlier than astroglial changes, our results suggest that axonal damage, which induces disturbance of fast axonal transport, can occur even in the early stage of white matter lesions.

Pan-neuronal expression of chromogranin A in rat nervous system

Sensitive and specific in situ hybridization detection of CGA mRNA, and immunohistochemistry with an antibody recognizing the CGA(316-329) epitope within CGA and its proteolytic fragments were employed to determine whether or not CGA mRNA or protein expression are restricted to specific neuronal subpopulations within the central and peripheral nervous systems. Virtually all neurons in sympathetic, sensory, and parasympathetic ganglia examined, as well as enteric nervous system and spinal cord, expressed both CGA mRNA and the 316-329 (WE-14) CGA epitope. Chromogranin A expression was also ubiquitous within all telencephalic and diencephalic brain nuclei examined, including frontal cortex, striatum, and hippocampus. In addition, CGA mRNA was expressed in nonneuronal cells that appeared to be glia in dorsal root ganglion, spinal cord, and brain. In contrast to earlier reports, neuronal expression of CGA appears to be unrestricted within the central and peripheral nervous systems. Nonneuronal expression of CGA also occurs in the nervous system, albeit at levels much lower than in neuronal cells.

GAP 43-like immunoreactivity in normal adult rat sciatic nerve, spinal cord, and motoneurons: axonal transport and effect of spinal cord transection

Using immunofluorescence and cytofluorimetric scanning techniques in the rat, the fast anterograde and retrograde axonal transport of growth-associated protein-43-like immunoreactivity in normal sciatic nerves, and after spinal cord transection in the lower thoracic region, were investigated. Spinal roots and motor endplates in the peroneal muscles were also studied. For comparison, anti-synaptophysin (p38) was used. In intact adult animals, the amounts of immunoreactive growth-associated protein-43 increased linearly, both proximally and distally to the crush site, between 1 and 24 h after crushing the sciatic nerve. The accumulations were present in thick as well as in thin axons. Distal accumulations in the sciatic nerve were about 40-60% of the proximal amounts, indicating a recycling of organelles with growth-associated protein-43-like immunoreactivity. During the week after spinal cord transection, no clear changes were observed; the anterograde transport of growth-associated protein-43-like immunoreactivity showed a tendency to decrease at day 1 and then a tendency to increase, reaching 120% of control at seven days (not significant). Transported p38-like immunoreactivity showed similar but smaller changes. In the lumbar spinal cord gray matter many nerve terminals with growth-associated protein-43-like immunoreactivity were seen in intact animals. After spinal transection, these terminals gradually decreased, suggesting that they belonged to descending pathways. However, p38-positive terminals were not obviously decreased. After crushing ventral and dorsal roots, accumulations of pf growth-associated protein-43-like immunoreactivity were present in thick axons in the ventral roots and in thin to medium-sized axons in the dorsal roots. In peroneal muscles, growth-associated protein-43-like immunoreactivity was present in some (but not all) motor endplates in all groups. These results indicate that: (i) growth-associated protein-43 is normally present in nerve terminals of many descending projections of the spinal cord; (ii) growth-associated protein-43-like immunoreactivity is expressed and bidirectionally transported in neurons (motor as well as sensory) of normal sciatic nerves; (iii) growth-associated protein-43-like immunoreactivity is present in some adult motor endplates; and (iv) inhibited supraspinal input causes minor, if any, alterations--paralleled by p38--in axonal transport of growth-associated protein-43-like immunoreactivity.

Distribution of GAP-43 in relation to CGRP and synaptic vesicle markers in rat skeletal muscles during development

GAP 43 in nerve terminal structures of rat skeletal muscles, was investigated during postnatal development using immunofluorescence and confocal laser scanning microscopy. Comparison with synaptophysin, synapsin, SV2, CGRP, SP and NF was done in double immunoincubation studies. GAP 43-like immunoreactivity (LI) was demonstrated in preterminal axons and motor endplates in all age groups (from E18 to adult), although the intensity of immunofluorescence was considerably higher in the younger rats. The outgrowing nerve sprouts in E18 muscles were strongly GAP 43-positive. The intensity decreased with increasing age, but even in adult animals GAP 43-LI was present in some p38- or SV2-positive endplates. GAP 43-LI was also present in muscle spindles and preterminal nerve branches, and likewise decreased with age. Perivascular nerve terminals (around arteries mainly) were, however, strong in GAP 43-LI during both development and adulthood. GAP 43-LI was strong, and present in both small and large granules. SP-LI was observed in a few thin, presumably sensory, axons around vessels, which also contained a few GAP 43-positive large granules. Most of the strongly GAP 43-positive terminals around vessels were probably autonomic postganglionic terminals. The results suggest that GAP 43, in addition to development and regeneration, may play a significant role also in normal adult rats, especially in perivascular nerve terminals, possibly connected with a high potential for plasticity in this kind of nerve terminals.

Sabeluzole administration does not enhance fast axonal transport in normal adult rat sciatic nerve

Sabeluzole (R58735, Janssen Research Foundation) increased rates of axonal transport in short term tissue culture experiments and in rats with streptozotocin-induced diabetes. The drug was tested for its subacute (3 days) net effect on axonally transported substances in motor, sensory, and adrenergic axons of normal adult rats. Sabeluzol was given once daily for 3 days, 1 or 10 mg/kg/day intraperitoneally. Immunofluorescence was used to identify transported material. Three or 6 hr after crushing the sciatic nerves, to interrupt anterograde and retrograde intraaxonal transport, cytofluorimetric scanning was used to quantitate accumulated immunoreactive material. Compared with vehicle treated control rats, no clear differences in the net amounts of accumulated material, or in rates of accumulation, were detected in any axonal type. Since the short-term crush procedure interrupts ongoing axonal transport, the accumulation pattern reflects the transport characteristics in the crushed axons. The absence of clear increases in transport of several substances in this study indicates that sabeluzole did not enhance net axonal transport above control levels in peripheral axons of normal adult rats. Possible reasons for the discrepancy with earlier observations on the effect of sabeluzole on fast axonal transport is discussed.

Influence of spinal cord transection on the presence and axonal transport of CGRP-, chromogranin A-, VIP-, synapsin I-, and synaptophysin-like immunoreactivities in rat motor nerve

Using immunofluorescence and cytofluorimetric scanning (CFS), we investigated the short-term (1-7 days) influence of lower thoracic spinal cord transection on lumbar motor neurons. The content of calcitonin gene-related peptide- (CGRP) like immunoreactivity (LI), chromogranin A (Chr A)-LI, vasoactive intestinal polypeptide (VIP)-LI, Syn I-LI, and synaptophysin (p38)-LI in motor perikarya, and the anterograde and retrograde axonal transport of these substances in the sciatic nerve, were studied in nerve crush (6 h) experiments. During the week after transection, CGRP-LI in perikarya decreased, whereas Chr A-LI increased. VIP-LI, co-localized with Chr A-LI in motor perikarya, did not change after transection. The antero- and retrograde transport of CGRP-LI in the sciatic nerve, occurring in both motor and sensory axons, appeared unchanged in cytofluorimetric scanning (CFS) graphs, but the microscopical picture clearly showed that large motor axons had a decreased content of CGRP-LI at 3 and 7 days posttransection, whereas thinner axons were unchanged in fluorescence intensity. The anterograde transport of Chr A-LI, present in both motor and postganglionic adrenergic axons, was decreased 1 and 3 days after lesion, but returned to control by day 7. There was a marked decrease in anterograde transport of VIP-LI, present mainly in postganglionic sympathetic axons, at day 3, but at 7 days transport was normal. The amounts of transported p38, the synaptic vesicle marker, were in the normal range during the whole period. Syn I-LI accumulation anterogradely was somewhat decreased at 3 and 7 days posttransection, and at 1 day the retrograde accumulation was significantly increased. The results suggest that removal of supraspinal input to intact lower motor neurons causes alterations in metabolism and axonal transport of organelle-associated substances, partly probably related to the complex pattern of transmitter leakage from degenerating, descending nerve terminals. These alterations appear to take place also in postganglionic sympathetic neurons in the sciatic nerve, that originate in the lumbar sympathetic chain.

Development of calcitonin-gene-related peptide, chromogranin A, and synaptic vesicle markers in rat motor endplates, studied using immunofluorescence and confocal laser scanning

The presence of calcitonin-gene-related peptide (CGRP) and chromogranin A was investigated in the developing rat (E18-adult) motor system, using immunofluorescence and confocal laser scanning, and compared with synaptic vesicle markers, synaptophysin and synapsin I. In lumbar motor perikarya CGRP-LI and Chr A-LI were present in high intensities in E18 and P1 perikarya in the anterior horn. With increasing age immunoreactivity decreased. Chr A-LI was sparse in the adult. In peroneal endplates, p38-LI and SYN I-LI were present in all stages, including E18. Peptide-LI was very weak or absent in early stages (E18 and P1), but abundant in P8 and P18, especially CGRP-LI, and decreased again in P32 and adult animals. These observations indicate that the peptides have precise functions during certain developmental stages, possibly related to synapse maturation, receptor concentration, and reduction of supernumerary endplates. Both peptides are rapidly transported anterogradely in adult motor axons, and may serve physiological functions also in the adult.

Changes of chemoarchitectural organization of the rat spinal cord following ventral and dorsal root transection

Time-related changes in the distribution of chemical messengers in the rat spinal cord following the transection of dorsal and ventral roots were observed by using immunohistochemistry for the following antigens: microtubule-associated protein 2 (MAP2), calcitonin gene-related peptide (CGRP), substance P (SP), galanin (Gal), Met-enkephalin (Enk), neuropeptide Y (NPY), and serotonin (5-HT). To investigate dendrocytoarchitectonic organizational changes, morphometric analyses were performed on both the gray and the white matter of tissue samples stained with MAP2 antiserum. A significant reduction in the area of gray matter on the lesioned side was seen from 1 to 24 weeks postoperation, and progressive changes in the shape of the gray matter were also observed. CGRP-immunoreactive fibers were reduced in number in the posterior horn after root transection, except in the lateral part of lamina I. In contrast, CGRP immunoreactivity in the anterior horn cells of the ipsilateral side was increased early after transection, but later it progressively decreased. Root transection also caused significant reduction in the number of SP-immunoreactive fibers in the posterior horn, but no changes were seen in the anterior horn. Gal immunoreactivity was also affected by root transection, and it changed in a similar way to CGRP immunoreactivity. 5-HT-immunoreactive fibers were increased in the posterior horn after transection, and later decreased. In the anterior horn, there were no changes in the intensity or distribution pattern of 5-HT-immunoreactive nerve fibers following root transection. Enk and NPY immunoreactivity in the anterior and posterior horns was not affected by root transection up to 24 weeks postoperative. These results show that spinal root transection caused significant changes in the chemoarchitectural organization of nerve fibers containing certain types of chemical messengers, such as CGRP, SP, Gal, and 5-HT, in addition to altering dendritic geometry in the spinal cord.

Studies on the distribution of calcitonin gene-related peptide-like and substance P-like immunoreactivities in rat hind limb muscles

The tibialis anterior, extensor digitorum longus and soleus muscles in the rat were examined with respect to the presence of calcitonin gene-related peptide-like as well as substance P-like immunoreactivity. In some of the motor endplates in these muscles, identified by staining for acetylcholinesterase activity, calcitonin gene-related peptide-like immunoreactivity was detected, but in others it was not. Calcitonin gene-related peptide-like immunoreactivity was found to coexist with substance-P-like immunoreactivity in nerve fibres located outside and inside the capsule of the muscle spindles, as well as in nerve fibres located in nerve fascicles. These fibres presumably represent sensory nerve fibres. Calcitonin gene-related peptide-like immunoreactivity, but not substance P-like immunoreactivity, was also detected in cap-like structures located on the surface of the intrafusal muscle fibres in the polar regions of the spindles, structures which are likely to correspond to motor plate endings. The observations suggest that calcitonin gene-related peptide is heterogeneously present in the endplates of rat hind limb muscles, and gives for the first time immunohistochemical evidence for the presence of calcitonin gene-related peptide and substance P in the innervation of muscle spindles.

Organelles in fast axonal transport. What molecules do they carry in anterograde vs retrograde directions, as observed in mammalian systems?

The present minireview describes experiments carried out, in short-term crush-operated rat nerves, using immunofluorescence and cytofluorimetric scanning techniques to study endogenous substances in anterograde and retrograde fast axonal transport. Vesicle membrane components p38 (synaptophysin) and SV2 are accumulating on both sides of a crush, but a larger proportion of p38 (about 3/4) than of SV2 (about 1/2) is recycling toward the cell body, compared to the amount carried with anterograde transport. Matrix peptides, such as CGRP, ChRA, VIP, and DBH are recycling to a minor degree, although only 10-20% of surface-associated molecules, such as synapsins and kinesin, appear to recycle. The described methodological approach to study the composition of organelles in fast axonal transport, anterograde as compared to retrograde, is shown to be useful for investigating neurobiological processes. We make use of the "in vivo chromatography" process that the fast axonal transport system constitutes. Only substances that are in some way either stored in, or associated with, transported organelles can be clearly observed to accumulate relative to the crush region. Emphasis in this paper was given to the synapsins, because of diverging results published concerning the degree of affiliation with various neuronal organelles. Our previously published results have indicated that in the living axons the SYN I is affiliated with mainly anterogradely fast transported organelles. Therefore, some preliminary, previously unpublished results on the accumulations of the four different synapsins (SYN Ia, SYN Ib, SYN IIa, and SYN IIb), using antisera specific for each of the four members of the synapsin family, are described. It was found that SYN Ib clearly has a stronger affiliation to anterogradely transported organelles than SYN Ia, and that both SYN IIa and SYN IIb are bound to some degree to transported organelles.

Calcitonin gene-related peptide in rat spinal cord motoneurons: subcellular distribution and changes induced by axotomy

Using light and electron microscopy, a study has been made of the changes of calcitonin gene-related peptide-like immunoreactivity in rat lumbar spinal cord motoneurons during cell body response to sciatic nerve injury. At light microscopy level, calcitonin gene-related peptide-like immunoreactivity was evaluated using an indirect immunofluorescence technique combined with Fast Blue retrograde tracing and a peroxidase-antiperoxidase procedure. The calcitonin gene-related peptide changes to sciatic nerve transection and crushing were compared. Calcitonin gene-related peptide-like immunoreactivity was transiently increased after the peripheral nerve lesion, but the response was sustained for a longer period when the peripheral nerve was transected and nerve regeneration prevented. The first changes in calcitonin gene-related peptide-like immunoreactivity were detected four days after nerve crush or transection. In animal spinal cords to which nerve crush had been applied, the maximal enhancement of immunoreactivity was found 11 days after lesion. This was followed by a gradual decline, normal levels being attained 45 days after nerve crushing. When the nerve was transected, the response was similar, but the maximal calcitonin gene-related peptide-like immunoreactivity was maintained over a period of between 11 and 30 days. As with crushing, an important decrease was observed after 45 days. The ultrastructural compartmentation of calcitonin gene-related peptide-like immunoreactivity was studied using either peroxidase-antiperoxidase method or immunogold labelling. Calcitonin gene-related peptide-like immuno-reactivity was located in restricted sacs of the Golgi complex, multivesicular bodies, small vesicles and tubulo-vesicular structures. Large, strongly labelled vesicles resembling secretory granules were also observed in neuronal bodies. Our results reveal that the increase of calcitonin gene-related peptide in motoneurons is a relevant change the cell body undergoes in response to peripheral injury. The ultrastructural location of the peptide distribution suggests specific compartmentation on tubulo-vesicular structures connected with the Golgi complex which form a network in the neuronal cytoplasm. The distribution pattern observed may be related to the sorting and delivery of calcitonin gene-related peptide to secretory vesicles.

A synaptic vesicle specific GTP-binding protein from ray electric organ

A cDNA encoding a synaptic vesicle associated GTP-binding protein was identified by screening a lambda gt11 expression library derived from the electric lobe of Discopyge ommata with polyclonal antibodies recognizing vesicle-specific proteins of Mr 25,000. Nucleotide sequence analysis defines an open reading frame of 218 amino acids. The protein belongs to the ras superfamily and shares about 75% amino acid identity with smg-25A, B and C identified in bovine brain and rab3A characterized in rat brain. Northern blot analysis revealed a 4.5 kb transcript present only in neural tissues, the highest level of expression being observed in electric lobe. Western blot analysis of total tissue homogenates derived from D. ommata detected the protein in electric organ, forebrain and to a lesser extent in electric lobe and spinal cord. No immunoreactivity was detected in non-neuronal tissues. Blotting of subcellular fractions derived from electric ray electric organ revealed that the GTP-binding protein co-purifies with synaptic vesicles. The neural specific expression and the localization to synaptic vesicles suggest a role of this protein in synaptic vesicle trafficking and targeting.

Expression of synaptophysin during the prenatal development of the rat spinal cord: correlation with basic differentiation processes of neurons

The development of the spinal cord involves the proliferation of neurons, their migration to well-defined areas, fiber outgrowth and synapse formation. The present study was designed to correlate the spatiotemporal pattern of expression of synaptophysin, an integral membrane protein of small synaptic vesicles, with these basic processes occurring during the embryonic development of the rat spinal cord. Thoracic segments of spinal cords from embryonic days 12, 14, 16, 18, 20 and of adult spinal cords were studied. S1 nuclease protection assays and immunoblots revealed minute amounts of specific mRNA and synaptophysin at embryonic day 12. There was a steep increase of mRNA between embryonic days 14 and 16, after which levels reached a plateau. A rise in the amount of synaptophysin in the spinal cord occurred between embryonic days 12 and 14, and the levels changed only slightly until the end of embryonic development. Even higher levels of synaptophysin, found in the adult spinal cord, may indicate that its biosynthesis continued after birth. In situ hybridization histochemistry revealed the localization of specific synaptophysin mRNA in the neuroepithelium. However, immunocytochemistry failed to detect synaptophysin in the neuroepithelial cells. Following migration of the neuroblasts, synaptophysins was found in neurons concomitantly with the onset of fiber outgrowth. Thus, already at embryonic day 12, outgrowing fibers of the dorsal root sensory neurons and of motoneurons were synaptophysin positive. From embryonic day 14 throughout the prenatal period, strong synaptophysin immunoreactivity was seen in the ventrolateral and dorsal parts of the marginal layer. Most likely this staining pattern indicates transient functional synaptic contacts because, in the adult spinal cord, the corresponding region, the white matter, exhibited only faint synaptophysin immunoreactivity. In the intermediate layer of the embryonic spinal cord, which corresponds to the gray matter of the adult spinal cord, synaptophysin-positive fibers were observed prior to the formation of functional synapses. The latter are most likely permanent, since synaptophysin in the adult spinal cord is mainly confined to the gray matter. Our data (i) show transcription and translation of synaptophysin within the neurons of the spinal cord and correlate these processes with proliferation, migration, fiber outgrowth and the formation of transient or permanent synapses, and (ii) prove that synaptophysin is a marker for fiber outgrowth in addition to synapse formation.

End structure and neuropeptide immunoreactivity of axons in sciatic neuromas following nerve section in neonatal rats

The formation of neuromas after neonatal nerve injury was studied in rats. In neonatal pups, the sciatic nerve was cut and tightly ligated, and a portion of the distal stump was removed. After 6-10 weeks, a nerve-end neuroma had formed in about 70% of the animals. In the remaining animals the nerve had grown on the side of the ligature. The end structure of the neuroma axons was studied using anterogradely transported WGA-HRP injected into the L5 dorsal root ganglion. HRP labeling occurred in the entire proximal sciatic nerve. In the neuroma, labeled fibers branched profusely and either terminated with minor end swellings or turned in the retrograde direction. Immunohistochemistry showed that the fibers which projected into the neuroma presented a moderate immunoreactivity to substance P and neuropeptide Y and a strong reactivity to calcitonin gene-related peptide. The results show that many sensory and sympathetic sciatic nerve fibers survive chronic axotomy in the newborn and contribute to the formation of nerve-end neuromas. There are, however, important structural differences between adult and neonatally induced neuromas.

Calcitonin gene-related peptide identifies spinal motoneurons in vitro

Cell dissociation of E6 chick spinal cord followed by isolation of larger low-density cells by using a discontinuous density metrizamide gradient resulted in the obtention of a motoneuron-enriched fraction of cells. These cells were cultured in the presence of horse serum and muscle extract for a period of 8 days and examined for the presence of calcitonin gene-related peptide. More than 90% of such cells were positive for calcitonin gene-related peptide. When E14 spinal cord was examined, calcitonin gene-related peptide was present only in the axons of primary sensory neurons and in the somas of motoneurons in the ventral horns. It is concluded that more than 90% of the neurons in our cultures are motoneurons.

Sympathetic axons and nerve terminals: the protein composition of small and large dense-core and of a third type of vesicles

Homogenates of bovine splenic nerve and of vas deferens were subjected to differential and density gradient centrifugation to investigate their noradrenaline-storing organelles. The subcellular fractions obtained were analysed by immunoblotting in order to define the presence of various antigens in small dense-core and large dense-core vesicles. In both large granule and microsomal fractions from splenic nerve only one type of noradrenaline-storing vesicle was found, which represents the large dense-core vesicles. These organelles contained chromogranin A, chromogranin B, cytochrome b-561, carboxypeptidase H, glycoprotein II, glycoprotein III, dopamine beta-hydroxylase and the monoamine carrier which are also present in adrenal chromaffin granules. The subcellular distribution of synaptin/synatophysin was more complex since this protein was apparently present in two organelles: in a light vesicle which did not contain significant amounts of antigens found in large dense-core vesicles (dopamine beta-hydroxylase, cytochrome b-561 and the monoamine carrier) and in the dense fractions of the gradient, possibly within large dense-core vesicles. In the microsomal gradient from vas deferens several markers (catecholamines, synaptin/synaptophysin and dopamine beta-hydroxylase) were found in a bimodal distribution, which is consistent with their presence in small and large dense-core vesicles. When the larger granules were removed with higher centrifugation speed a microsomal fraction containing only light vesicles was obtained. After gradient centrifugation of this fraction several components (catecholamines, dopamine beta-hydroxylase, cytochrome b-561, the monoamine carrier and synaptin/synaptophysin) were concentrated in a peak at low density; apparently only small dense-core vesicles were now present.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromogranin A in the olfactory system of the rat

The olfactory bulb of the rat contains chromogranin A at a similar level as the adrenal gland or the hypophysis as revealed by immunoblots. Olfactory chromogranin A also displays the same size as chromogranin A of endocrine cells. In the hippocampus and other brain regions, we could not detect chromogranin A by immunoblotting. In contrast, chromogranin A messenger ribonucleic acid (using S1 nuclease protection assays) was observed in all brain regions examined, including the olfactory bulb. By in situ hybridization histochemistry with a complementary ribonucleic acid probe (280 nucleotides), and by immunocytochemistry, chromogranin A synthesis could be localized to cell bodies of the mitral cell layer, of the external plexiform layer and of the periglomerular region of the olfactory bulb. Immunocytochemically, chromogranin A was also detected in the central projection areas of mitral and tufted cells in the primary olfactory cortex and the anterior amygdaloid area but not in the olfactory glomeruli, where the incoming olfactory nerve fibers of the primary olfactory neurons establish synaptic contacts. Taken together the data show that chromogranin A, following biosynthesis in the perikarya of the mitral and tufted cells, is specifically transported into their axonal terminals but not into their primary dendrites. We propose that the rat olfactory system could serve as a model for the study of chromogranin A regulation and function in neurons.

Evidence for differential storage of calcitonin gene-related peptide, substance P and serotonin in synaptosomal vesicles of rat spinal cord

Homogenates of rat ventral and dorsal spinal cords were subjected to differential and gradient centrifugation on linear sucrose gradients following lysis of a synaptosomal fraction. The distribution of calcitonin gene-related peptide (CGRP) and substance P (SP) in dorsal spinal cord as well as the distribution of serotonin (5-HT) and SP in ventral spinal cord was determined, using radioimmunoassay (RIA) for CGRP and SP and high-performance liquid chromatography for 5-HT. In dorsal spinal cord. CGRP and SP had an almost identical distribution, with one peak in an intermediate density fraction which according to electron microscopy contained i.a. large dense-cored vesicles, and a second peak in a heavy fraction enriched in synaptosome-like structures. In ventral spinal cord, 5-HT and SP had different distribution patterns; 5-HT peaked in a light fraction containing many small synaptic vesicles, whereas SP peaked in an intermediate density fraction similar to the one in dorsal spinal cord. Both 5-HT and SP had second peaks in high density fractions containing synaptosome-like structures. The study demonstrates that the peptides CGRP and SP, partly coexisting in dorsal spinal cord, both seem to be stored in large vesicles inside synaptosomes, whereas the amine 5-HT and the peptide SP, coexisting in ventral spinal cord, appear to have a differential storage with 5-HT mainly in small vesicles and SP in large vesicles, both inside synaptosomes.

Substance P-, CGRP- and NPY-immunoreactive nerve fibers in rat sciatic nerve-end neuromas

Substance P (SP)-, calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined in experimental sciatic nerve-end neuromas in the rat with immunohistochemical techniques. At 1-3 days after nerve ligation and section of the sciatic nerve there was an accumulation of SP-like immunoreactivity (SP-LI). Six days after the lesion there was, however, a marked reduction and the neuromas remained virtually depleted from SP-LI at survival times between 8 days and 3 months. CGRP-LI was strong at 1-5 days post-operatively. By 8 days, CGRP-LI was reduced, but a large number of axons were still immunoreactive, and remained immunolabelled up to 3 months. CGRP-LI nerve fibers formed endbulbs, and appeared to grow in both anterograde and retrograde directions. Fine fibers sprouts were first observed at 8 days, but preterminal branching in neuromas aged less than a month was uncommon. At early stages (1-3 days) after ligation, there was a marked accumulation of NPY-LI proximal to the nerve constriction. NPY-LI was reduced from 5 days and on, but many fibers remained NPY-positive and their growth pattern through proximal and distal neuroma segments could be determined. The present results thus may indicate a differential effect of nerve injury on neuropeptide expression: immunohistochemically detectable SP-LI rapidly disappears from sciatic nerve fibers trapped in nerve-end neuromas, but CGRP-LI and NPY-LI remain and are useful as neuroanatomical markers for two subclasses of sprouting axons. Furthermore, the findings suggest that both CGRP and NPY, but not SP, could be involved in ectopic electrical activity in experimental neuromas.