Regenerated synaptic terminals on a crayfish slow muscle identify with transplanted phasic or tonic axons

Abstract

Phasic or tonic nerves transplanted onto a denervated slow superficial flexor muscle in adult crayfish regenerated synaptic connections that displayed large or small excitatory postsynaptic potentials (EPSPs), respectively, suggesting that the neuron specifies the type of synapse that forms (Krause et al., J Neurophysiol 80:994–997, 1998). To test the hypothesis that such neuronal specification would extend to the synaptic structure as well, we examined the regenerated synaptic terminals with thin serial section electron microscopy. There are distinct differences in structure between regenerated phasic and tonic innervation. The phasic nerve provides more profuse innervation because innervation sites occurred more frequently and contained larger numbers of synaptic terminals than the tonic nerve. Preterminal axons of the phasic nerve also had many more sprouts than those of the tonic nerve. Phasic terminals were thinner and had a lower mitochondrial volume than their tonic counterparts. Phasic synapses were half the size of tonic ones, although their active zone‐dense bars were similar in length. The density of active zones was higher in the phasic compared with the tonic innervation, based on estimates of the number of dense bars per synapse, per synaptic area, and per nerve terminal volume. Because these differences mirror those seen between phasic and tonic axons in crayfish muscle in situ, we conclude that the structure of the regenerated synaptic terminals identify with their transplanted axons rather than with their target muscle. Therefore, during neuromuscular regeneration in adult crayfish, the motoneuron appears to specify the identity of synaptic connections. © 2000 John Wiley & Sons, Inc. J Neurobiol 45: 185–193, 2000

Electrospray ionization mass spectrometry coupled to liquid chromatography for detection of cisplatin and its hydrated complexes

“…In addition, the phasic axons in the deep extensor muscles had one‐fifth the number of mitochondria as the tonic axons in the superficial flexor muscles (Nguyen et al, 1997). Even in regenerate terminals, mitochondria occurred at a lower density in phasic axons than in their tonic counterparts in the crayfish abdominal superficial flexor muscle (Hirji et al, 2000). Clearly, differences in mitochondrial density are a hallmark of the phasic‐tonic dichotomy, reflecting the functional profiles of these two axon types.…”

Electrospray ionization mass spectrometry coupled to liquid chromatography for detection of cisplatin and its hydrated complexes

“…In addition, the phasic axons in the deep extensor muscles had one‐fifth the number of mitochondria as the tonic axons in the superficial flexor muscles (Nguyen et al, 1997). Even in regenerate terminals, mitochondria occurred at a lower density in phasic axons than in their tonic counterparts in the crayfish abdominal superficial flexor muscle (Hirji et al, 2000). Clearly, differences in mitochondrial density are a hallmark of the phasic‐tonic dichotomy, reflecting the functional profiles of these two axon types.…”

Remodeling of the proximal segment of crayfish motor nerves following transection

“…Previous studies of crustacean motor axons, although clearly acknowledging sprouting from the proximal segment, have not estimated the extent of this sprouting in terms of numbers of axon profiles (Nordlander and Singer, 1972; Kennedy and Bittner, 1974; Parnas et al, 1998). The best estimate of this comes from studies of allotransplanted deep flexor nerves to the crayfish superficial flexor muscle (Krause et al, 1998; Hirji et al, 2000) in which the regenerated nerve over the muscle displayed between 10 and 50 profiles for individual phasic axons. This would add up to between 100 and 500 axon profiles for the 10 single phasic axons of the deep flexor nerve, a range that comfortably encompasses the 100–300 profiles we counted in the proximal nerve of the 8‐week transected preparation.…”

Ultrastructural correlates of synapse withdrawal at axotomized neuromuscular junctions in mutant and transgenic mice expressing the Wld gene

“…Prints from TEM negatives of nerve terminal profiles taken at 13 000× magnification were scanned at 600 dpi using a Linoscan 1200 (Heidelberg) equipped with transparency adaptor and imported into Adobe Photoshop. A dot grid acetate sheet was superimposed on individual electron micrographs (adapted from the method described by Hirji et al. 2000).…”

Electrospray ionization mass spectrometry coupled to liquid chromatography for detection of cisplatin and its hydrated complexes

“…In addition, the phasic axons in the deep extensor muscles had one‐fifth the number of mitochondria as the tonic axons in the superficial flexor muscles (Nguyen et al, 1997). Even in regenerate terminals, mitochondria occurred at a lower density in phasic axons than in their tonic counterparts in the crayfish abdominal superficial flexor muscle (Hirji et al, 2000). Clearly, differences in mitochondrial density are a hallmark of the phasic‐tonic dichotomy, reflecting the functional profiles of these two axon types.…”

Remodeling of the proximal segment of crayfish motor nerves following transection

“…Previous studies of crustacean motor axons, although clearly acknowledging sprouting from the proximal segment, have not estimated the extent of this sprouting in terms of numbers of axon profiles (Nordlander and Singer, 1972; Kennedy and Bittner, 1974; Parnas et al, 1998). The best estimate of this comes from studies of allotransplanted deep flexor nerves to the crayfish superficial flexor muscle (Krause et al, 1998; Hirji et al, 2000) in which the regenerated nerve over the muscle displayed between 10 and 50 profiles for individual phasic axons. This would add up to between 100 and 500 axon profiles for the 10 single phasic axons of the deep flexor nerve, a range that comfortably encompasses the 100–300 profiles we counted in the proximal nerve of the 8‐week transected preparation.…”

Ultrastructural correlates of synapse withdrawal at axotomized neuromuscular junctions in mutant and transgenic mice expressing the Wld gene

“…Prints from TEM negatives of nerve terminal profiles taken at 13 000× magnification were scanned at 600 dpi using a Linoscan 1200 (Heidelberg) equipped with transparency adaptor and imported into Adobe Photoshop. A dot grid acetate sheet was superimposed on individual electron micrographs (adapted from the method described by Hirji et al. 2000).…”

Electrospray ionization mass spectrometry coupled to liquid chromatography for detection of cisplatin and its hydrated complexes

“…In addition, the phasic axons in the deep extensor muscles had one‐fifth the number of mitochondria as the tonic axons in the superficial flexor muscles (Nguyen et al, 1997). Even in regenerate terminals, mitochondria occurred at a lower density in phasic axons than in their tonic counterparts in the crayfish abdominal superficial flexor muscle (Hirji et al, 2000). Clearly, differences in mitochondrial density are a hallmark of the phasic‐tonic dichotomy, reflecting the functional profiles of these two axon types.…”

Remodeling of the proximal segment of crayfish motor nerves following transection

“…Previous studies of crustacean motor axons, although clearly acknowledging sprouting from the proximal segment, have not estimated the extent of this sprouting in terms of numbers of axon profiles (Nordlander and Singer, 1972; Kennedy and Bittner, 1974; Parnas et al, 1998). The best estimate of this comes from studies of allotransplanted deep flexor nerves to the crayfish superficial flexor muscle (Krause et al, 1998; Hirji et al, 2000) in which the regenerated nerve over the muscle displayed between 10 and 50 profiles for individual phasic axons. This would add up to between 100 and 500 axon profiles for the 10 single phasic axons of the deep flexor nerve, a range that comfortably encompasses the 100–300 profiles we counted in the proximal nerve of the 8‐week transected preparation.…”

Ultrastructural correlates of synapse withdrawal at axotomized neuromuscular junctions in mutant and transgenic mice expressing the Wld gene

“…Prints from TEM negatives of nerve terminal profiles taken at 13 000× magnification were scanned at 600 dpi using a Linoscan 1200 (Heidelberg) equipped with transparency adaptor and imported into Adobe Photoshop. A dot grid acetate sheet was superimposed on individual electron micrographs (adapted from the method described by Hirji et al. 2000).…”