LIST OF COLOR PLATES Color plates follow p 378 Color Plate 1 An electron micrograph of a CNS synapse. This example of a synaptic bouton-type synapse is located in the"molecular layer"of rat cerebellum. a single en passant bouton of the parallel fibers synapses onto a single Purkinje cell spine. Note the multiple synaptic vesicles in the presynaptic bouton terminal. Several vesicles seem to be linked by thin filaments in the cytoplasm. On average, the vesicles have a diameter of about 40 nm. One synaptic vesicle is clearly docked to the presynaptic membrane. Note also the narrow synaptic cleft, which contains a "fuzzyset of electron-dense material (this probably includes cell adhesion proteins that span the cleft). The opposing postsynaptic membrane in the postsynaptic spine has an electron-dense postsynaptic density(PSD), where glutamate receptors and modulatory proteins are located. A thin glial process wraps itself around the synaptic cleft and postsynaptic spine and also partially around the presynaptic bouton-type terminal(Electron micrograph courtesy of Constantino Sotelo, Instituto de Neurociencias de Alicante, Spain) Color Plate 2 A schematic diagram showing the sequence of events that leads to Wallerian(anterograde) degeneration. The normal cytology of a peripheral nerve is shown as a point of reference (expanded inset A). After axonal injury, the proximal stumps retract from the site of injury forming distinctive"retraction bulbs"(expanded inset B). Meanwhile, the distal portion of injured axons degenerate, but all other elements of the peripheral nerve remain intact (expanded inset C). Thereafter, Schwann cells begin to proliferate, and blood-borne macro- phages infiltrate the degenerating nerve stump and assist Schwann cells with phagocytosis of axonal and myelin debris(expanded inset B). Schwann cells then become arranged in columns known as the"bands of Bunger"within common basal laminae(expanded inset C). Such Schwann cell units provide a cellular pathway along which regenerating axons extend distal to the site of injury(see also Fig. 10) Color Plate 3(A)A three-dimensional rendition of early axonal regeneration after peripheral-nerve damage Growth cones(e.g, boxed profile) are seen extending into the lesion gap(blue profiles repre- senting connective tissue elements), and some make contact with Schwann cells(red profiles)in the distal stump ( Drawing kindly provided by Dr Susan E. Mackinnon, Washington Uni- versity School of Medicine and Barnes-Jewish Hospital. )(B) An axonal growth cone of an embryonic chick sensory neuron is shown. The growth cone is doubly stained with an antibody against tubulin (green), which labels microtubules, and rhodamine-phalloidin to label actin filaments red. The bundle of axonal microtubules(green)splays apart in the growth cone, and individual microtubules extend forward to interact with actin filament bundles and network These interactions between actin filaments and microtubules are important in determinin directions of axonal growth and branching(see text). A small axonal sprout has formed at the lower left margin of the growth cone( Figure generously provided by Paul C. Letourneau Ph. D, University of Minnesota.LIST OF COLOR PLATES Color plates follow p. 378. Color Plate 1 An electron micrograph of a CNS synapse. This example of a synaptic bouton-type synapse is located in the ‘‘molecular layer’’ of rat cerebellum. A single en passant bouton of the parallel fibers synapses onto a single Purkinje cell spine. Note the multiple synaptic vesicles in the presynaptic bouton terminal. Several vesicles seem to be linked by thin filaments in the cytoplasm. On average, the vesicles have a diameter of about 40 nm. One synaptic vesicle is clearly docked to the presynaptic membrane. Note also the narrow synaptic cleft, which contains a ‘‘fuzzy’’ set of electron-dense material (this probably includes cell adhesion proteins that span the cleft). The opposing postsynaptic membrane in the postsynaptic spine has an electron-dense postsynaptic density (PSD), where glutamate receptors and modulatory proteins are located. A thin glial process wraps itself around the synaptic cleft and postsynaptic spine and also partially around the presynaptic bouton-type terminal. (Electron micrograph courtesy of Constantino Sotelo, Instituto de Neurociencias de Alicante, Spain). Color Plate 2 A schematic diagram showing the sequence of events that leads to Wallerian (anterograde) degeneration. The normal cytology of a peripheral nerve is shown as a point of reference (expanded inset A). After axonal injury, the proximal stumps retract from the site of injury forming distinctive ‘‘retraction bulbs’’ (expanded inset B). Meanwhile, the distal portion of injured axons degenerate, but all other elements of the peripheral nerve remain intact (expanded inset C). Thereafter, Schwann cells begin to proliferate, and blood-borne macro￾phages infiltrate the degenerating nerve stump and assist Schwann cells with phagocytosis of axonal and myelin debris (expanded inset B). Schwann cells then become arranged in columns known as the ‘‘bands of Bunger’’ within common basal laminae (expanded inset C). Such Schwann cell units provide a cellular pathway along which regenerating axons extend distal to the site of injury (see also Fig. 10). Color Plate 3 (A) A three-dimensional rendition of early axonal regeneration after peripheral-nerve damage. Growth cones (e.g., boxed profile) are seen extending into the lesion gap (blue profiles repre￾senting connective tissue elements), and some make contact with Schwann cells (red profiles) in the distal stump. (Drawing kindly provided by Dr. Susan E. Mackinnon, Washington Uni￾versity School of Medicine and Barnes-Jewish Hospital.) (B) An axonal growth cone of an embryonic chick sensory neuron is shown. The growth cone is doubly stained with an antibody against tubulin (green), which labels microtubules, and rhodamine-phalloidin to label actin filaments red. The bundle of axonal microtubules (green) splays apart in the growth cone, and individual microtubules extend forward to interact with actin filament bundles and networks. These interactions between actin filaments and microtubules are important in determining directions of axonal growth and branching (see text). A small axonal sprout has formed at the lower left margin of the growth cone. (Figure generously provided by Paul C. Letourneau, Ph.D., University of Minnesota.) xiii