Author/Editor		Stušek, Peter; Drašlar, Kazimir; Belušič, Gregor; Zupančič, Gregor
Title		Adaptation mechanisms in insect eyes
Translated title		Adaptacijski mehanizmi v žuželjčjem očesu
Type		članek
Source		Acta Biol Slov
Vol. and No.		Letnik 43, št. 3
Publication year		2000
Volume		str. 41-70
Language		eng
Abstract		Adaptation proccsscs in insect eyes occur on several levels, but two of the most prominent are the distal and proximal adaptation levels. In the distal, dioptrical part of the eye, adaptation is brought about by pupillary mechanisms; however, in the proximal, photoreceptive part of eye, adaptation is based predominantly on changes in the signaling cascade efficiency and on the successful delivery of oxygen to the mitochondria. For investigations of both types of adaptation, Ascalaphus (=Libelluloides) macaronius, a specialized neuropterian, provcd successful as a suitablc model lor studying both levels of adaptation. In this animal, the retinulac of the frontal part of eye exhibit just one type of photoreceptor sensitive only to ultraviolet light; the pupillary response, however, is also triggered by light of longer wavelengths. Thus, it suggests that the screening of light in the distal part of the eye is independent of the receptor rnechanisms in the proximal part of the eye. In addition, the pupillary response also exhibits double time-dependent dynamics and thereby a double regulation of the photon flux of both the regenerating and the adapting light. With the aid of microscope techniques (TEM, SEM, LM), it was deterrnined that there is no massive displacement of pigment granules in the secondary pigment cells of Ascalaphus during the screening process as is characteristic for a typical superposition eye. The electron micrographs indicate that the pupil appearing at the tip of crystalline cone is formed as a result of interaction between the primary and secondary pigment cells and the distal columns of the retinular cells. The imporant phase of adaptation in the proximal receptive part of the eye is the termination of receptor potential, the response of which is also an indicator of the phototransductional cascade dynamic. (Abstract truncated at 2000 characters).
Summary		V žuželčjem očesu poteka proces adaplacije na več nivojih. V distalnem, dioptričnem delu očesa, so to zenični mehanizmi, v proksimalnem, fotoreceptornem delu pa temelji adaptacija predvsem na spremembi prevodnosti membrane retinalnih celic in procesov na notranji mitohondrijski membrani. Za preučevanje obeh tipov adaptacij se je izkazal za primeren objekt mrežekrilec Ascalaphus macaronius. K rabdomu v frontalnem delu očesa te žuželke prispevajo samo fotoreceptorji, ki zaznavajo UV svetlobo, medtem ko na delovanje roženice v območju dioptričnega aparata vplivajo tudi svetlobe z drugo valovno dolžino. Oba adaptacijska nivoja se razlikujeta tako v mehanizmu delovanja kot tudi v spektralnih in časovnih značilnostih. Prilagoditve na spremenjene svetlobne razmere v distalnem delu se zgodijo v sekundah ali minutah, v proksimalnem pa v milisekundah. Meritve lastnosti zeničnega mehanizma so pokazale, da sproži spremembo optičnih lastnosti v območju dioptričnega aparata tudi svetloba, ki ne izzove več receptorskega odziva. To kaže, da je proces zastiranja svetlobe v distalnem delu neodvisen od receptorskih mehanizmov v proksimalnem delu očesa. Receptorski odziv pri ascalaphusu ima svoj maksimum pri 345 nm, medtem ko odgovor zenice sproži svetloba v pasu od UV do modrozelene. Poleg tega ima zenični mehanizem dvojno časovno dinamiko, s katero uravnava tako tok stimulacijske kot regeneracijske svetlobe. Z mikroskopskimi raziskavami (TEM, SEM, SM) smo ugotovili, da v stranskih pigmentnih celicah pri ascalaphusu med zastiranjem ni masivnega premika zaščitnega pigmenta, kot je to značilno za tipično superpozicijsko oko. Elektronske mikrografije nakazujejo prisotnost zenice, ki se formira ob konici kristalnega stožca kot interakcija med primarnimi in sekundarnimi pigmentnimi celicami ter distalnim odstavkom retinula celic.
Descriptors		EYE PHOTORECEPTORS, INVERTEBRATE OXYGEN CONSUMPTION ADAPTATION, OCULAR RETINA MICROSCOPY, ELECTRON INSECTS