Type 1 and 2 synaptic junctions: differences in distribution of concanavalin A binding sites and stability of the junctional adhesion.

Two classes of synaptosomes have been distinguished in subcellular fractions from rat forebrain. They differ in morphology and distribution of concanavalin A binding sites. Morphological examination suggests that the two classes correspond to the type 1 (excitatory) and type 2 (inhibitory) synapses of intact brain tissue. Under the conditions of incubation employed in this study, type 1 synaptosomes show splitting of the synaptic junctions, but the type 2 junctions are apparently stable. The chemical differences illustrated by the differences in concanavalin A binding sites suggest that type 1 and type 2 synaptic junctions differ fundamentally in supramolecular structure rather than being superficial variants of basically similar structures.

Emergency carotid endarterectomy.

A retrospective review of carotid endarterectomies performed by the Neurosurgical Service at Massachusetts General Hospital from July, 1976, through December, 1985, disclosed 64 procedures that were performed on an emergency basis. The patients included 40 men and 24 women, with a mean age of 64 years (range 32 to 87 years). Correlation of angiographic findings with outcome revealed that of the 27 patients with severe stenosis, usually with delay in blood flow, 25 (93%) were the same or improved postoperatively; of the 11 patients with stenosis and an intraluminal filling defect (six of whom had an intraluminal clot), eight (73%) were the same or improved after surgery; of the 16 patients with complete occlusion, 14 (88%) were the same or improved (backflow was established in all cases); and of the 10 patients with moderate to severe stenosis and/or severe ulceration (including three with transient ischemic attacks who were receiving heparin), eight (80%) were the same or improved. Pre- and postoperative clinical status were graded into five categories: intact; mild deficit; moderate deficit (significant impairment but able to perform activities of daily living); severe deficit (requiring assistance for daily activities); and death. Of the 36 patients who preoperatively were intact or had mild deficits, 33 (92%) were the same or improved postoperatively, three were worse, and there were no deaths. Among 15 patients presenting with moderate deficits, 12 (80%) were the same or improved, two were worse, and one died. Of the 13 patients with severe deficits, 10 (77%) were the same or improved and three died. Two patients with sudden severe deficits associated with loss of contralateral bruit were operated on without angiography and were intact postoperatively. Of the four deaths in the total series, two were attributed to cardiac causes and two to unrelated disease processes. The indications for emergency carotid endarterectomy are discussed.

Ultrastructure of the synaptic junctional lattice isolated from mammalian brain.

Synaptic membranes can be treated with detergents to yield postsynaptic densities from which the lipid unit membrane has been removed. The ultrastructure of these densities is identical to THAT of the synaptic lattice observed in undigested synaptic membranes; a1000-3000 A diameter planar array of 200 A diameter dense-staining subunits. The persistence of this synaptic lattice in the absence of lipid membrane may reflect a functional role in the maintenance of defined synaptic junctional structures in intact tissue.

Cerebrovascular projections from the sphenopalatine and otic ganglia to the middle cerebral artery of the cat.

The location of the postganglionic parasympathetic cell bodies projecting to cerebral arteries is unknown. Using axonal tracing techniques, we examined whether the sphenopalatine ganglia (associated with the seventh cranial nerve) and otic ganglia (associated with ninth cranial nerve) contain perikarya which send axons to the feline middle cerebral artery (MCA). The tracers horseradish peroxidase (HRP: 3 cats) or wheat germ agglutinin (WGA: 6 cats) were applied to the MCA in a slow release polymeric system. Three days later the SPG, otic ganglia, and rete mirabile were harvested bilaterally and processed for tracer by the TMB method (HRP) or immunohistochemistry (WGA). In a given animal, approximately equal numbers of cells containing axonal tracer were found in both SPG. Labeled fibers occasionally could be seen extending into the vidian nerve. Positive cells were also found in the otic ganglia and in the walls of the internal rete mirabile. These results provide the first identification of parasympathetic cell bodies projecting to cerebral blood vessels.

Junctional ultrastructure in isolated synaptic membranes.

The ultrastructure of synaptic junctions in whole brain tissue and isolated synaptic membranes has been compared. Type 1 junctions are present in the isolated membranes,readily identified by the presence of dense-staining material associated with the postsynaptic membrane, but the dense projections present at the presynaptic membrane in intact tissue are absent. Type 2 junctions are not easily recognized because of the absence of prominent junctional densities, but apposed membranes with the appearance of type 2 junctions are seen in isolated membrane preparations. Junctions without dense-staining material are also seen among SYNAPtosomes and survive the hypotonic conditions used during isolation of the membranes. It thus seems probable that both type 1 and 2 junctions are present in isolated synaptic membrane preparations. In type 1 junctions after isolation,the postsynaptic thickening and cleft substance are together seen to be composed of an array of 200 A dense-staining subunits spanning the postsynaptic unit membrane. The relationship of this structure to the ultrastructure of the cleft substance and postsynapticthickening in intact tissue is discussed.

Immunohistochemical demonstration of tubulin associated with microtubules and synaptic junctions in mammalian brain.

The distribution of tubulin in brain tissue has been investigated by light and electron microscopic immunohistochemistry using an antiserum raised against electrophoretically purified microtubule derived tubulin. The specificity of the staining is indicated by the lack of staining when non-immune serum is substituted for anti-tubulin serum and the quite different staining obtained with antisera against antigens other than tubulin. The anti-tubulin immunohistochemistry reveals tubulin antigen in microtubules and in the postsynaptic junctional lattice of most synapses. No antigen has been detected in either the synaptic cleft or in the axon terminal. This distribution confirms previous biochemical identification of tubulin as a major postsynaptic junctional component, but suggests that it is not common to all synaptic junctions.