Paul K. Brown

Visual Pigments in Single Rods and Cones of the Human Retina

Difference spectra of the visual pigments have been measured in single rods and cones of a parafoveal region of the human retina. Rods display an absorption maximum (λmax) at about 505 m� associated with rhodopsin. Three kinds of cones were measured: a blue-sensitive cone with Amaxe about 450 mpf; two green-sensitive cones with Xmaa about 525 mu�; and a red-sensitive cone with λmax about 555 m� These are presumably samples of the three types of cone responsible for human color vision.

The Problem of Visual Excitation

This paper attempts to come to grips with the problem, how the action of light on a visual pigment results in a nervous excitation. The only action of light in vision is to isomerize retinene, the chromophore of the visual pigments, from the 11-cis to the all-trans configuration. This change triggers a progressive opening-up of the protein structure, exposing new reactive groups. Since the absorption of one photon by one molecule of visual pigment may stimulate a dark-adapted rod, some large amplification process is needed between the act of absorption and the response. This may be an enzymatic catalysis, or the consequence of puncturing a critical membrane. A microspectrophotometric study of retinas and single rods shows the outer segment to have a quasi-crystalline structure, in which the visual pigments are almost perfectly oriented, and even “free” molecules capable of diffusion maintain a degree of orientation. Examination of mud puppy retinas in the electron microscope has revealed several new aspects of structure: (1) A system of cytoplasmic filaments (“dendrites”) springing from the inner segments of the rods and cones and standing like palisades around the outer segments. These may facilitate exchanges of material between the inner and outer segments. (2) Systems of particles in the membranes of the dendrites and pigment epithelium processes, which may be involved in interchanges of material with the outer segments. (3) A system of particles in crystalline array in the rod lamellae, which may contain the visual pigment. If so, measurements of the visual pigment in situ show that each particle should contain about 50 molecules of pigment. Such typically solid-state processes as exciton migration and photoconduction probably have at most very limited scope in the outer segments of rods and cones. The seat of excitation is probably the plasma membrane which envelops rod outer segments and composes also the lamellae in cones.

[243] Methodology of vitamin A and visual pigments

Publisher Summary This chapter discusses methodology for the assay and preparation of vitamin A and visual pigments, such as rhodopsin, rod opsin, iodopsin, and cone opsin. The assay for rhodopsin depends upon the fact that rhodopsin bleaches in the light to all-trans retinal and opsin. Opsin has no absorption at wavelengths longer than about 300 nm, but retinal has some absorption in the visible, and this absorption varies with the pH and the purity of the rhodopsin preparation. The assay is therefore best performed in the presence of hydroxylamine that combines with retinal to form retinaldehyde oxime, a compound with essentially no absorption at wavelengths longer than 450 nm. The assay for rod opsin depends upon the fact that opsin combines with its molar equivalent of 11-cis-retinal to form rhodopsin that has characteristic absorption properties. Iodopsin, a cone visual pigment, has been prepared from chicken, pigeon, and sea turtle retinas. As with rhodopsin, a detergent such as digitonin is required to solubilize it. Because all these animals have both rods and cones in their retinas, the extracts contain mixtures of rhodopsin and iodopsin, and the assay must detect iodopsin in the presence of what is usually an excess of rhodopsin.

A System for Microspectrophotometry Employing a Commercial Recording Spectrophotometer

The present paper describes the design and performance of an attachment for the Cary model 14 recording spectrophotometer, which permits the accurate recording of absorption spectra in small areas. A special compartment built into the light path of the spectrophotometer holds a low-magnification microscope (“macroscope”) consisting of two opposed quartz condensers, with which measurements can be made between 300 and 700 mμ in fields 0.1 to 1 mm in diameter. This can be replaced by a conventional microscope with which spectra can be measured from about 350–650 mμ in fields as small as 4 μ in diameter. These arrangements have been used to measure the absorption spectra of visual pigments in situ. With the macroscope, such measurements have been made in small areas of surviving retinas; and with the microscope, they have been made in single isolated outer segments of rods. The present paper contains examples of each type of measurement.

Rhodopsins, retinula cell ultrastructure, and receptor potentials in the developing pupal eye of the mothManduca sexta

SummaryThe compound eye of the tobacco hornworm mothManduca sexta differentiates during the 3 to 4 week period of the pupal instar. We used a morphological system to divide pupal development into 17 stages, each stage representing from 1 to 2 days of chronological age. We followed the progressive maturation of retinular ultrastructure, measured rhodopsin in slices of retina by microspectrophotometry (MSP), and recorded electroretinograms (ERGs) from stages 8 to 17.1.Endomembrane that accumulates within the receptor cells between stages 5 and 7 (Fig. 3) appears to contribute to the formation of rhabdomere microvilli beginning at stage 9 or 10 (Fig. 4). Rhabdomere volume increases by at least 30-fold between pupal stage 11 and the adult moth.2.The first ERGs were recorded at stage 10 (Fig. 6, 7) when the rhabdomeres begin to differentiate. The earliest ERGs are pure receptor potentials; higher order components do not appear until stage 14–15. Photoreceptor response, determined by the light intensity required to elicit 1 mV criterion responses from dark-adapted eyes at peak ultradian or circadian sensitivity, increases by a factor of 105 between stages 11 and 15. A further 3 log unit increase between stages 15 and 16, brings it nearly to the adult level. This final jump in responsiveness results from the initial migration of distal screening pigment into its normal dark-adapted position during stage 15.3.The retina of the adult contains three visual pigments: a green sensitive rhodopsin (R520) and smaller amounts of blue sensitive (R440) and ultraviolet sensitive (R345) rhodopsins. No rhodopsin was measured prior to pupal stage 6. R520, the easiest of the rhodopsins to measure, is first present in developing retinas at stage 6–7 (Fig. 9). We have evidence that R440 is present from at least stage 12, and R345 from at least stage 15. At stage 10, when the rhabdom is just beginning to form, the retina already contains 10–20% of the adult concentration of R520 (Fig. 11). At stage 11 and later, R520 is transformed by orange light to stable metarhodopsin (M485), which can be photoregenerated to R520 with blue light (Fig. 10). At stages 7 and 8, the metarhodopsin of R520 differs from that of the later pupal stages and the adult moth (Fig. 12). Itsλmax is about 470 nm, and photoreversal does not occur.4.Since the retina contains rhodopsin prior to the formation of the rhabdomere microvilli, and a relatively large amount is present when the rhabdomeres are just forming, there must be an extrarhabdomeric pool of rhodopsin. During these early pupal stages, rhodopsin may be associated with the endomembranes of the differentiating photoreceptor cells.

Properties of the visual pigments of the moth Manduca sexta and the effects of two detergents, digitonin and CHAPS

The three known visual pigments (P520, P450, P357) of the moth, Manduca sexta (Lepidoptera, Sphingidae), were extracted in two different detergents (2% digitonin, 6 or 12 mM CHAPS). As is the case in unextracted membranes, the metarhodopsins are quite stable in CHAPS extracts, while in digitonin the metarhodopsins of P520 and P450 decay rapidly at 15 degrees C to opsin and free retinal. The relative absorbance ratios are: 1.0:1.6 (P520:M485), 1.0:1.1 (P450:M485), and 1.0:0.8 (P357:M470). The relative amounts of the visual pigments found in digitonin extracts is 100:25:8 (P520:P450:P357); about 60 picomoles of P520 can be extracted from one Manduca retina.

Hypnotherapy for Traumatic Grief: Janetian and Modern Approaches Integrated

Traumatic grief occurs when psychological trauma obstructs mourning. Nosologically, it is related to pathological grief and posttraumatic stress disorder (PTSD). Therapeutic advances from both fields make it clear that the trauma per se must be accessed before mourning can proceed. The gamut of psychotherapies has been employed, but hypnosis appears to be the most specific. Pierre Janet provided a remarkably modern conceptual basis for diagnosis and treatment based on a dissociation model. His approach is combined with contemporary innovations to present a systematic and integrated account of hypnotherapy for traumatic grief.

Trauma-Induced Dissociative Amnesia in World War I Combat Soldiers:

Objective: This study relates trauma-induced dissociative amnesia reported in World War I (WW I) studies of war trauma to contemporary findings of dissociative amnesia in victims of childhood sexual abuse. Method: Key diagnostic studies of post-traumatic amnesia in WW I combatants are surveyed. These cover phenomenology and the psychological dynamics of dissociation vis-à-vis repression. Results: Descriptive evidence is cited for war trauma-induced dissociative amnesia. Conclusion: Posttraumatic amnesia extends beyond the experience of sexual and combat trauma and is a protean symptom, which reflects responses to the gamut of traumatic events.

THE ROLE OF HYDRATION IN THE PHOTOTRANSFORMATION OF PHYTOCHROME

Abstract— Changes in the visible absorption spectrum and in phototransformation of phytochrome have been found to be associated with dehydration and rehydration. These spectral properties explain the previously reported rapid appearance of phytochrome in imbibing seeds. No evidence was found for the orientation of the phytochrome chromophore in gelatin films or in preparations subjected to a shearing force.

Janet and Freud: revealing the roots of dynamic psychiatry

Objectives: Interest in the work of Pierre Janet is presently undergoing a scholarly revival and, in the process, his contribution to dynamic psychiatry is increasingly being recognised. This article compares and contrasts Pierre Janets early studies on hysteria and the neuroses with those of Freud. Method: The study surveys original works by Janet and Freud and contemporary scholarly exegeses. It particularly focuses on ideation and memory, consciousness and dissociation, psychological trauma, the self, therapeutic influence, and treatment by integration versus abreaction. Results: Grounds are presented for either preferring Janets notions to Freuds, or for integrating them. Conclusion: It is concluded that a number of Janets contributions to psychopathology and psychotherapy, particularly in the field of dissociative disorders, deserve further exploration and application.