PubMed · 4700713
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R P Erickson. 1973-03-30. Adaptation and the neural code for visual form.. https://doi.org/10.1016/0006-8993(73)90674-4
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The first optic neuropil of the compound eye, the lamina, of the skipper butterfly Parnara guttata, was examined by light microscopy after Golgi-impregnation and by electron microscopy (EM) to clarify the cellular and synaptic organization. In the lamina, five different types of lamina neurons (L neurons) were characterized by using Golgi-impregnation. By EM, each cartridge was found to contain all nine receptor axons from an ommatidium, five L neurons, and a few putative centrifugal elements. Axons from photoreceptors (retinula cells) R2, R3, R4, R6, R7, and R8 terminate as short visual fibers (svfs) in the lamina cartridge. Those from R1, R5, and R9 penetrate the lamina and terminate in the medulla as long visual fibers (lvfs). In the cartridges, the synaptic contacts were formed from svfs onto L neurons, from the lvfs of R1 and/or R5 to the lvf of R9 and L neurons, and from the lvf of R9 to L neurons. The putative centrifugal fibers also make synapses to svfs and L neurons. At the most distal level of the cartridge, one of the centrifugal fibers containing dense-core vesicles makes presynaptic contacts to the putative long collaterals of the L neuron. A novel characteristic feature of this lamina is that svfs of R3 and R7 and the lvfs of R1 or R5 have long collaterals extending into neighboring cartridges. Presynaptic contacts were confirmed in such long collaterals from the svf. These results imply that receptor axons provide direct intercartridge connections as well as providing indirect connections to neighboring cartridges by way of their input upon L neurons.
A circadian clock modulates the functional organization of the Japanese quail retina. Under conditions of constant darkness, rods dominate electroretinogram (ERG) b-wave responses at night, and cones dominate them during the day, yielding a circadian rhythm in retinal sensitivity and rod-cone dominance. The activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, also exhibits a circadian rhythm in the retina with approximately threefold higher levels during the day than at night. The rhythm of tyrosine hydroxylase activity is opposite in phase to the circadian activity of tryptophan hydroxylase, the first enzyme in the melatonin biosynthetic pathway. We tested whether dopamine may be related to the physiological rhythms of the retina by examining the actions of pharmacological agents that effect dopamine receptors. We found that blocking dopamine D2 receptors in the retina during the day mimics the nighttime state by increasing the amplitude of the b-wave and shifting the retina to rod dominance. Conversely, activating D2 receptors at night mimics the daytime state by decreasing the amplitude of the b-wave and shifting the retina to cone dominance. A selective antagonist for D1 dopamine receptors has no effect on retinal sensitivity or rod-cone dominance. Reducing retinal dopamine partially abolishes rhythms in sensitivity and yields a rod-dominated retina regardless of the time of day. These results suggest that dopamine, under the control of a circadian oscillator, has a key role in modulating sensitivity and rod-cone dominance in the Japanese quail retina.
BACKGROUND: There is a growing body of evidence that abnormalities of the cell membrane, particularly depletion of n-3 essential fatty acids (EFA), are found in patients suffering from schizophrenia. These fatty acids particularly Docosohexaenoic acid (DHA) are found in particularly high concentrations in the photoreceptor cells of the retina and abnormalities of light sensitivity have been reported in patients with schizophrenia. Animal studies have demonstrated that reduced EFA levels are associated with changes in the electrophysiological response of the retina to light as measured by the electroretinogram (ERG). METHODS: We measured the ERG of 9 patients with schizophrenia and 9 age and sex matched control subjects. All but one of the patients was medicated. RESULTS: Schizophrenic subjects had significantly reduced a-wave amplitudes on the ERG when compared with control subjects and the a-wave amplitude was independent of the dose of antipsychotic agents being taken. The a-wave of the ERG is thought to reflect activity of the photoreceptor cells. CONCLUSIONS: These findings support the hypothesis that patients with schizophrenia have abnormalities of photoreceptor function, which may be a result of reduced levels of n-3 EFA in the cell membrane.