Jean K. Lauber

Enzymatic Synthesis of Melatonin in Avian Pineal Body: Extraretinal Response to Light

In the chick pineal body, activity of the melatonin-forming enzyme hydroxyindole-O-methyl transferase is greater in the light than in darkness. Neither bilateral enucleation of the eyes nor sympathetic denervation prevented this light-induced elevation of enzyme activity. This fact indicates that in the bird, in contrast to mammals, neither the retinas nor sympathetic innervation of the pineal body are essential for environmental control of melatonin formation.

Intraocular pressure and aqueous outflow facility in light-induced avian buphthalmos

Chicks reared under continuous light from hatching develop buphthalmos by 16 weeks of age. This eye enlargement was found to be associated with increased intraocular pressure and impaired aqueous outflow facility. The time course of development of these abnormalities has been explored. Enhanced aqueous outflow facility was discernible as early as 2 weeks of age, when refractive errors and eye enlargement could already be detected, but no elevation of intraocular pressure was measurable. It is suggested that increased inflow may be the primary lesion in light-induced avian glaucoma.

Chicks blinded with formoguanamine do not develop lid suture myopia

The involvement of the retina in avian lid suture myopia was investigated by use of formoguanamine (FG), which induces blindness in chicks, characterized by damage to the retinal pigment epithelium and photoreceptor layers. In control chicks reared under a diurnal lighting schedule of 12L/12D, unilateral eyelid suture at 3 days of age induced a typical lid suture myopia response on the operated side (eye enlargement and bulging cornea) by 4 wks. of age. On the other hand, in FG-treated blind chicks also reared under 12L/12D, there was no difference in eye parameters, between sutured and non-sutured eyes. All globe parameters measured were very similar in FG-treated and control non-sutured chicks. Corneal diameter and anterior chamber depth in the eyes of FG-treated chicks were significantly smaller than in non-sutured control eyes.

Plasma corticosterone in chicks reared under several lighting schedules

Plasma corticosterone was determined by radioimmunoassay in 6-7-week-old male broiler type chicks, reared under several carefully controlled lighting regimes. When subjects were grouped by photoperiod of rearing, chicks reared in darkness had significantly lower hormone levels than diurnal controls, or than subjects reared in continuous light. Around-the-clock sampling revealed a diurnal corticosterone rhythm, with high daytime levels and lower night-time levels. This rhythm appeared to be retained in constant light, although phase shifted or free running. Neither analysis by light intensity level nor by lights on/lights off status at the time of blood sampling revealed differences in plasma corticosterone between the experimental groups which could be attributed to these factors.

Photoacceleration of avian embryogenesis.

1. 1. Chick embryos exposed to light via optic fiber during incubation developed faster than those in darkness. 2. 2. At 412 days, embryos under white light weighed 17 per cent more, and oxygen consumption was 10 per cent lower, than for controls. 3. 3. Green light (λmax 545 nm) advanced developmental age by almost one full H-H (Hamburger-Hamilton) stage by 4 days. 4. 4. In a further exploration of the action spectrum, photoacceleration of growth showed peaks at 566 and 400 nm (P<0·001). Oxygen consumption was lowest at the same wavelengths (P<0·01). 5. 5. The photostimulatory effect on body growth thus does not appear to depend directly on oxidative metabolism.

Aqueous Humor Inflow in Normal and Glaucomatous Avian Eyes

Abstract A new fluorometric method has been employed to measure inflow of aqueous humor (F) in normal and glaucomatous avian eyes. Most inflow determinations in previous studies have involved severe disturbance to the eye, or else F has been derived indirectly, as a function of outflow facility (C) or intraocular pressure (IOP). The procedure used in this study is readily accomplished, even with a large series of subjects, and F measurement involves no insult to the eye or extrapolations from parameters whose relationship to F is not fully understood. After inflow measurements had been completed, the same experimental animals were subjected to independent determinations of volume of the aqueous space, IOP, C, and several dimensional parameters, thus permitting a comprehensive assessment of aqueous fluid dynamics during eye development. Aqueous flow in normal adult domestic chickens was found to be 12·9±1·93 μl/min; IOP in the same eyes was 11·1±0·4 mmHg, C was 2·03±0·24 μl/min/mm, and volume of the aqueous space was 104·1±4.5 mm 3 . The same parameters were measured on abnormal eyes at several stages during the pathogenesis of avian glaucoma. The aqueous space was greatly reduced, to about one-third normal volume, in these glaucomatous eyes. Aqueous flow was less than half the normal adult value. In confirmation of previous findings, C was reduced, IOP was elevated, and the glaucomatous eyes were greatly enlarged. The pattern of development of the several lesions associated with avian glaucoma suggests a puzzling question: how can one explain eye enlargement which takes place in the absence of elevated IOP, and at a time when F is low and C is impaired? A search for the primary lesion in avian glaucoma continues.

Ocular responses of genetically blind chicks to the light environment and to lid suture

Blind rc chicks were examined as to growth characteristics of the developing eye. We also explored the relationship between hereditary blindness and two environmental interventions affecting eye development, light-induced avian glaucoma (LIAG) and the axial lengthening associated with lid-suture. Genetically blind rc chicks could be identified by their behavior even during the first hours after hatching. However, they retained the pupillary reflex, at least to 5 weeks of age. Blind chicks reared under a diurnal lighting schedule had eyes 18% larger (by eye weight) than sighted hatchmates, with corresponding increases in globe diameters. Of the anterior segment parameters, neither corneal diameter, anterior chamber depth nor corneal curvature was demonstrably different from sighted controls. When rc chicks were reared under continuous light, the environmental condition which brings on LIAG, their already enlarged eyes showed no superimposed increases in either eye weight or globe dimensions. The corneas showed some characteristic LIAG effects: small anterior chamber depth and increased corneal radius of curvature (flat cornea), as compared with diurnal rc birds. Some birds were subjected to unilateral eyelid-suture, a protocol which usually induces axial lengthening and corneal bulging. Blind rc birds did not respond to this surgical intervention: in comparison by paired t-test between sutured and contralateral eye, there was little or no difference in eye weight, globe diameters or anterior segment parameters. Thus vision, or at least an intact retina/RPE, seems to be necessary for development of the characteristic axial lengthening in response to eyelid suture. The globe enlargement of LIAG also appears to be vision-dependent, although the anterior segment manifestations of LIAG are systemic effects.

Environmental control of the rearing conditions and early preglaucomatous lesions in chicks

We previously reported that domestic chicks reared under continuous environmental light develop lesions reminiscent of human glaucoma, including elevated intraocular pressure. We have called the condition light-induced avian glaucoma. This paper reports similar lesions in subjects first exposed to continuous light at 4 weeks of age. The modified environmental design permits identification of several early preglaucomatous lesions: within the first 3 days, volume of the aqueous space is reduced, outflow facility is impaired, and eye enlargement has begun. By 3 weeks, the rate of accumulation of fluorescein in the aqueous, after intravenous injection, is less in preglaucomatous eyes, and intraocular pressure is, at this stage, low. A model is proposed to elucidate the early lesions leading to light-induced avian glaucoma. We suggest that, in its vegetative physiology, the eye represents a delicately balanced homeostatic system. The first lesion in avian glaucoma may be an aqueous flowthrough imbalance such that net outflow is less than inflow; this is caused, for reasons and by mechanisms unknown, by exposure to continuous environmental light. Present findings suggest that loss of homeostatic control may already be underway, and that a pathological course is already set for the eye, within the first 3 days after environmental change in the rearing conditions.

Sympathetic denervation effects of avian eye development and aqueous fluid dynamics.

Sympathetic denervation of the eye in experimental mammals, either by surgical means (1, 2) , or pharmacologically (3), has been reported to cause a decrease in intraocular pressure (IOP), an increase in outflow facility (C) (1, 2), no change (4) or a decrease (5) in aqueous secretion, no change in episckral venoaq pressure (4, mydriasis (6) or miosis (7) , suparsensitivity to alphaadrenergic drugs (7), decreased vascular tone and increased blood flow to the anterior segment of the eye (4, 8). Many of these effects are transient, the peak response occurring about 1 day after anterior cervical ganglionectomy. This “24-hr ganglionectomy effect” has been attributed to the release of stored catecholamines, primarily norepinephrine, from degenerating postganglionic nerve terminals (1, 9). This hypothesis was strengthened by Eakins and Eakins (10), and by Sears et al. (11), who showed that catecholamine stores in the weal tissues were depleted over a time period which coincided with postganglionectomy changes in IOP and C. There are conflicting reports regarding the long-term effects of ganglionectomy on the eye: a recturn to normal may occur within 3 days (2), especially after unilateral rather than bilateral ganglionectomy. However, Sears et al. (11) reported that, following a transient rise, outflow facility was greatly reduced for almost 4 weeks after unilateral ganglionectomy, and C did not return to normal until 12 weeks after bilateral sympathetic dmervation. Langham (7) found that supersensitivity to norepinephrine was still evident 8 days after unilateral ganglionectomy, and in the experiments of Holland and Mimhls (3), miosis during the first 48 hr was followed by mydriasis lasting as long as 5 weeks in chemically sympathectomized monkeys. From the reduced IOP and increased C, these authors postulated that postganglionectomy effects were accoqpanied by reduced intraocular pressure and miosis (3).

Melatonin reduction by lithium and albinism in quail and hamsters

Melatonin was measured by radioimmunoassay in several genetic strains of Japanese quail. Plasma melatonin (PM), measured at the nighttime peak, was highest in wild type quail reared on a diurnal lighting schedule; this PM peak was suppressed in continuous light. Albino quail had low melatonin levels, whether reared under diurnal conditions or in continuous light. Ocular melatonin was also suppressed in albinos and in dilute mutants. At midday sampling, melatonin was only half as high in albinos as in wild types. Intraocular pressure (IOP, daytime readings) was uniformly low in diurnal birds and was elevated in all quail reared under continuous light. Thus in pigmented birds, a high melatonin level was associated with high IOP, but in albinos displaying high IOP, ocular melatonin was not elevated. Lithium chloride, mixed in the feed, brought about a pronounced reduction in plasma, pineal, and ocular melatonin, in wild-type quail reared on a diurnal schedule. This confirms earlier findings in lithium-fed rats. Golden hamsters displayed a characteristic diurnal cycle of pineal melatonin, with a sharp middark peak; in albino hamsters, also kept on a diurnal schedule, this peak occurred at the same time, but albinos had melatonin levels only about one-third as high as those of pigmented animals.