. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RETINAL CIRCUITRY 341 drug can diminish the light falling on the retina only about fifteen-fold, provided that no complicating factor is present, such as opacification of the lens by a cataract. Clearly, the doctor's simple standard explanation must be in doubt in many cases. One can reasonably suspect a pharmacological action of the cholinergic drugs on the retina in addition to the change in pupil size. However, currently our standard methods for clinical investigations are too crude to tell easily what is actually happeni
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RETINAL CIRCUITRY 341 drug can diminish the light falling on the retina only about fifteen-fold, provided that no complicating factor is present, such as opacification of the lens by a cataract. Clearly, the doctor's simple standard explanation must be in doubt in many cases. One can reasonably suspect a pharmacological action of the cholinergic drugs on the retina in addition to the change in pupil size. However, currently our standard methods for clinical investigations are too crude to tell easily what is actually happening. Clinicians will be able to design effective clinical testing methods only when they can be guided by results from experimental neurobiology, showing what functions the cholinergic neurons may have. GABA NEURONS There is a similar story for another neurotransmitter, gamma-amino butyric acid, usually abbreviated GABA. There are good reasons to believe that GABA is a neurotransmitter in certain amacrine cells in the mammalian retina. It is present in high concentration in the same region of the retina as the amacrine cells, where the synthesizing enzyme can also be found (Kuriyama el ai, 1968; Graham, 1972; Voaden, 1978; Brandon el ai, 1979; Lam el ai, 1979; Brandon et ai, 1980; Famiglietti and Vaughn, 1981; Vaughn et ai, 1981; Wu et ai, 1981; Zucker et ai, 1984). There is also a highly selective and very active uptake mechanism for GABA in certain amacrine cells which can be illustrated by autoradiography (Fig. 7). Moreover, tritiated GABA can be released from the retina by light flashes. Finally, different types of experiments in several laboratories have shown GABA receptors to be present in the retina (reviews: Ehinger, 1982, 1983b). Ph. :OPL INL IPL ••:. FIGURE 7. Autoradiogram of a rabbit retina 4 hours after the intravitreal injection of (3H)-GABA. Amacrine cells, some ganglion cells (G), and the entire inner plexiform layer (IPL) have become labeled. Ph, photor
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
