Localization of calcitonin gene-related peptide (CGRP) at a neuronal nicotinic synapse

Synaptic organization of amphibian sympathetic ganglia

The synaptic organization of the amphibian sympathetic ganglia was studied, especially in the last two abdominal paravertebral ganglia of the frog. These ganglia appear to form a monosynaptic relay, not containing interneurons. They consist of two systems working in parallel: the principal neurons, by far the most numerous, and a small number of chromaffin (i.e., SIF) cells, usually arranged in clusters. Each principal neuron is innervated by a preganglionic branch forming a set of cholinergic synapses which exhibit classical ultrastructure. The only peculiarity is the presence of a subsynaptic apparatus in a variable percentage of synaptic complexes. Electrophysiological studies have demonstrated that synaptic transmission is due to ACh release and involves several postsynaptic potentials. Moreover, the principal neurons are of two types, B and C, whose preganglionic axons and their own axons have different conduction velocities. C neurons tend to be small in diameter, and B neurons are larger, but the size distribution of the two populations overlaps. More recently, it was demonstrated that these two neuronal systems have different immunocytochemical features. The C preganglionic fibers contain an LHRH-like peptide, which is responsible for late synaptic events. The B preganglionic fibers contain CGRP, whose role has not yet been established. The principal neurons all contain adrenaline, but neuropeptide Y is also present in C neurons and could be a second transmitter at peripheral junctions. SP-containing fibers also pass through the ganglia, but give rise to intraganglionic synapses only rarely, except in the celiac plexus. Galanin can coexist with neuropeptide Y in certain C neurons. Numerous principal neurons are immunoreactive for VIP. Chromaffin cells contain noradrenaline and metenkephalin, and some contain SP or LHRH; they are endocrine cells controlled by preganglionic fibers and can have a modulatory effect on principal neurons endowed with appropriate receptors. The accessibility of frog abdominal ganglia and the anatomical separation of B and C preganglionic fiber pathways provide interesting systems in which to carry out experimentation on the stability and specificity of synaptic contacts. After postganglionic axotomy, the majority of synapses disappear by disruption of synaptic contacts. There is a certain discrepancy between the recovery of synaptic transmission and the reappearance of morphologically identifiable synapses, suggesting that a certain amount of transmission is possible at contacts devoid of synaptic complexes. The selective deafferentation of B or C neurons showed that the subsynaptic apparati are mainly found at B neuron synapses. The course of reinnervation following selective deafferentation reveals the existence of different specificities at B and C synapses: C neurons are easily reinnervated by B preganglionic fibers, whereas C fibers appear fairly ineffective at reinnervating B neurons, even after a long interval. Attempts were made to reinnervate ganglionic neurons with somatic motor nerve fibers. Reinnervation was achieved only rarely, and it is concluded that the ganglionic synapses in the frog have a higher specificity and lower plasticity than in mammals.

Maffucci's syndrome--the result of neural abnormalities? Evidence of mitogenic neurotransmitters present in enchondromas and soft tissue hemangiomas

BACKGROUND

Maffucci's syndrome (MS) is distinguished by the enigmatic association of benign cartilaginous bone tumors and soft tissue hemangiomas.

METHODS

This study was conducted to define the distribution of nerves and neuropeptides around these tumors. Results were measured by quantitative image analysis of immunohistochemical staining. Four types of tissues were compared: connective tissues around normal muscles, solitary hemangiomas, MS hemangiomas, and MS enchondromas (the last two from a single patient).

RESULTS

The number of nerves was found to be quadrupled in both types of hemangiomas as compared to normal connective tissue. A unique feature of MS tissues is the presence of an increased number of nerve fibers not only in the lesions but also in histologically normal margins of resection surrounding the lesions. Furthermore, hemangiomas of both types were found to contain a significantly higher number of calcitonin gene-related peptide-, substance P-, and methionine enkephalin-positive fibers than did normal muscle or its related fibroconnective tissue. These neuropeptides are mitogens, and their presence stimulates the growth of the abnormal blood vessels. Enchondroma fragments from an MS patient contained numerous methionine enkephalin-positive nerves. This neuropeptide is known to act as a growth factor in cartilage proliferation.

CONCLUSIONS

A neural abnormality of the neuropeptidergic nervous system seems to relate to the abnormal tumors seen in MS.

Neuropeptidergic innervation of intramuscular hemangiomas

Intramuscular hemangiomas are idiopathic lesions which are either tumoral or developmental in origin. A close association of abnormal blood vessels with nerve fibers is found and may suggest that nerves have a primary inciting role in the development of these lesions. In the current study, the number of nerve fibers in different zones around the tumors, as well as the type of neuropeptides present in these fibers, was quantitatively assessed by computer-assisted image analysis of immunohistochemical staining of histological slides. The number of nerve fibers as determined by positive staining by anti-protein S-100 antibodies was found to be elevated in the immediate vicinity of the abnormal blood vessels. The density of the nerve fibers rapidly declined with increasing distance from the hemangiomas, reaching normal values at distances of over 2 mm. Furthermore, hemangiomas contain a significantly higher number of calcitonin gene-related peptide (CGRP), substance P, and Met-enkephalin-positive fibers. The most significant rise in number is that of CGRP-positive fibers. This neuropeptide is a known mitogen, which could be responsible for the growth of the hemangiomatous blood vessels. Substance P is a nociceptive neurotransmitter and its presence can explain the pain which often accompanies even tiny intramuscular hemangiomas.

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.

Vasoconstrictor, vasodilator and pilomotor pathways in sympathetic ganglia of guinea-pigs

Triple-labelling immunofluorescence and retrograde axonal tracing with fluorescent dyes have been combined to identify and characterize the neuropeptide content of vasoconstrictor, vasodilator and pilomotor neurons in the lumbar sympathetic ganglia of guinea-pigs. Postganglionic noradrenergic pilomotor neurons lacked immunoreactivity to neuropeptide Y and comprised up to about 30% of postganglionic neurons. Most post-ganglionic noradrenergic neurons that contained neuropeptide Y immunoreactivity were likely to be vasoconstrictor neurons, although some noradrenergic neurons containing neuropeptide Y projected to pelvic viscera. Vasoconstrictor neurons comprised up to about 60% of postganglionic neurons. About 15% of postganglionic neurons were non-noradrenergic and contained immunoreactivity to vasoactive intestinal peptide, neuropeptide Y and dynorphin. They mostly innervated blood vessels supplying skeletal muscles and were likely to be vasodilator neurons. Endings of presumed preganglionic neurons containing immunoreactivity to substance P were exclusively associated with vasodilator neurons. Conversely, presumed preganglionic endings containing immunoreactivity to calcitonin gene-related peptide were exclusively associated with vasoconstrictor neurons, although not all vasoconstrictor neurons had such endings associated with them. Presumed preganglionic terminals containing immunoreactivity to enkephalin were associated with some postganglionic neurons in each functional class. These results show that preganglionic and postganglionic sympathetic neurons lying in different functional pathways can be distinguished by their neuropeptide content as well as their projections. The identification of neurochemically distinct functional pathways begins to explain how the sympathetic nervous system is organized to allow the precise control of discrete target tissues.

Effect of calcitonin gene-related peptide on synaptic transmission at the neuromuscular junction of the frog

The effects of calcitonin gene-related peptide (CGRP) on synaptic mechanisms were studied at the frog neuromuscular junction by using classical electrophysiological techniques. CGRP reduced the quantal content of evoked neurotransmitter release, as well as the sensitivity of postsynaptic nicotinic acetylcholine receptors (AChRs). No effect on the frequency of the miniature end-plate potentials or on the desensitization of the AChRs could be observed. Both the measured effects may depend on the stimulation of the cyclic AMP second messenger system.

Development of calcitonin gene-related peptide (CGRP) immunoreactivity in relationship to the formation of neuromuscular junctions in Xenopus myotomal muscle

Immunoreactivity (IR) to calcitonin gene-related peptide (CGRP) has recently been found in chick motoneurons. Bath application of this peptide causes an increase in surface acetylcholine receptor (AChR) density and cAMP level in cultured chick muscle cells. These results suggest a role for this peptide in the formation of synaptic specializations. In this study, we examined the development of CGRP IR in larval Xenopus myotomal muscle in relation to synaptogenesis. Using an antiserum against CGRP, a monoclonal antibody against the p65 synaptic vesicle antigen and a fluorescence conjugate of alpha-bungarotoxin, we followed the development of synaptic specializations with fluorescence microscopy in whole-mount specimens. We found that the postsynaptic specialization in the form of AChR clusters was first detected in stage 22 (24 hour) embryos. The presynaptic specializations, including the synaptic vesicle clusters as evidenced by p65 antibody staining and CGRP IR, were first detected at stage 32 (40 hours). The appearance of these two presynaptic specializations followed the same time course. Subsequently, all three structures, the AChR clusters, CGRP IR, and synaptic vesicle clusters, were colocalized at the neuromuscular junction (NMJ). This shows that CGRP is unlikely to be involved in signaling the development of the postsynaptic apparatus. This premise is further examined in cultures of Xenopus myotomal muscle cells. CGRP at concentrations up to 1 microM did not affect the number of AChR clusters, nor did it interfere with the formation of clusters induced by polycation-coated beads. In contrast, an extract from the basement membrane of Torpedo electric organ promoted the formation of AChR clusters and interfered with the clustering activity of the beads. These results suggest that CGRP, an integral component of the presynaptic specialization, is not involved in signaling synaptogenesis at the NMJ.