. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 524 DANIEL L. ALKON Impulse Zone - ~=&' 1 Synaptic Interactions. FIGURE 16. 25 fj-m thick section stained with toluidine blue showing the optic ganglion (40 ( across) and "optic tract," containing 19 axons: of 5 photoreceptors and 14 optic ganglion cells. The largest cell is unresponsive to light. "Impulse zone" indicates excitable focus which generates both optic ganglion and photoreceptor impulses. "Synaptic interactions" indicates area of terminal branches of photoreceptors (Alkon, 197
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 524 DANIEL L. ALKON Impulse Zone - ~=&' 1 Synaptic Interactions. FIGURE 16. 25 fj-m thick section stained with toluidine blue showing the optic ganglion (40 ( across) and "optic tract," containing 19 axons: of 5 photoreceptors and 14 optic ganglion cells. The largest cell is unresponsive to light. "Impulse zone" indicates excitable focus which generates both optic ganglion and photoreceptor impulses. "Synaptic interactions" indicates area of terminal branches of photoreceptors (Alkon, 1973). are spontaneously active in darkness and hyperpolarize with a transient cessation of activity in response to a light flash (Fig. 17). Type B (demonstrated with > 100 pairs) but not Type A photoreceptors (demonstrated with 30 pairs) inhibit ipsilateral optic ganglion cells. This synaptic inhibition produced the hyperpolarizing response of optic ganglion cells in response to light (Fig. 17). Present evidence suggests that the Type B photoreceptor in- hibits the optic ganglion cell monosynaptically (Alkon, 1973). A subsequent analysis of photoreceptor-optic ganglion cell interactions has revealed many addi- tional details of Type B photoreceptor interactions with optic ganglion cells (Tabata and Alkon, 1979; Tabata and Alkon, in preparation). Of particular interest is a synaptic excitation of the Type B cells by at least one ipsilateral optic ganglion cell. The site of these EPSPs probably occurs within or near the optic ganglion itself (, nearer than the site of IPSPs between photoreceptors) since they can often be transiently observed after the optic nerve has been severed near its point of entry into the pleural ganglion (Tabata and Alkon, in preparation).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original
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