Observations on the Fine Structure and Cytochemistry of Mouse and Human Intercostal Neuromuscular Junctions

Abstract

The fine structure of the mouse and human intercostal muscle neuromuscular junction was studied after brief fixation in a new formol-sucrose fixative. This primary formalin fixation was followed by brief postosmication in buffered 1 per cent osmium tetroxide. Muscle blocks were embedded in methacrylate or Epon 812 epoxy resin. Marked similarities between mouse and human motor end-plates were observed. Neuromuscular junctions from both mouse and human intercostal muscle showed synaptic vesicles, primary and secondary synaptic clefts, and layered differentiation of the amorphous surface material (ASM) present on the surface of the Schwann ccll plasma membrane and on the muscle surface membrane in the region of the neuromuscular junction. An attempt to stain the ASM with lead was unsuccessful. Observations on thick and thin plastic-embedded sections stained by PAS after diastase digestion showed that the ASM within the subneural apparatus is PAS positive. Alcian blue stained the cndoneurium and pcrineurium of peripheral nerve bundles and portions of the end-plates. The similarity of the PAS-positive ASM to other basement membranes described in other sites is discussed and its possible physiologic significance within the subsynaptic apparatus is considered.

On the Connection between the Sarcoplasmic Reticulum and the Junctional Folds in Mouse Neuromuscular Junction

“…These findings are consistent with those of Csillik (1965), but inconsistent with those of Zacks and Blumberg (1961), who were unable to detect the lead deposits in both the synaptic clefts and junctional folds. It seems that the absence of lead deposits in the synaptic cleft and junctional fold, as reported in the latter paper, may be due to the poor penetration of lead ions into the neuromuscular junction, as they used immersion method instead of injection.…”

“…There are only few reports (Zacks et al 1961, Csillik 1965) about the electron microscopic investigation on the lead-binding sites in the neuromuscular junction. Furthermore, there is a discrepancy between them concerning the location of the lead desposition.…”

Electron Microscopic Demonstration of Cholinesterase in the Human Intercostal Muscle by an Indoxyl Acetate Esterase Method

“…In the rest part of the human intercostal muscle, no enzyme activity was observed in the present study, though Davis and Koelle (7) reported the activity of cholinesterase in Schwann cells, Barrnett (l, 2) observed acetylcholinesterase activity in synaptic vesicles in the axon terminals, Zacks and Blumberg (15,16) observed the enzyme reaction in the mitochondria in both the axon terminals and sarcoplasma and Bergman et al (4), Barrnett and Hagstrom (3), Karnovsky (8) and Miladic (13) indicated the activity in the sarcoplasmic reticulum in the intermyofibrillar spaces.…”

Submicroscopic Organization of the Postsynaptic Membrane in the Myoneural Junction

“…Presence of this materiai in motor end plates has already been described by Noel (35) and, more recently, by Zacks and Blumberg (57). Noel claims that this material is an element of the "manchon perit61oneuritique," identical with Couteaux's subneural apparatus.…”

“…According to Zacks and Blumberg (56,57), in muscles treated with lead nitrate solution the lead precipitate is located "primarily in the sarcoplasmie columns of the subsynaptic apparatus." It should be pointed out, however, that in these electron micrographs the density of the sarcoplasmic columns is very poor; lead-treated specimens can hardly be distinguished from the sections treated with osmium tetroxide alone.…”