Charles L. Ralph

THE PINEAL COMPLEX AND THERMOREGULATION

CONTENTS

Plasma melatonin in the trout: Day-night change demonstrated by radioimmunoassay

Abstract A melatonin radioimmunoassay technique, using a 125 I-labelled melatonin analog as the radiolabel, has been validated for rainbow trout ( Salmo gairdneri ). It was demonstrated that a dilution series of extracted trout plasma melatonin and a melatonin/PBS gel standard were parallel along a logit-transformed curve. Melatonin extracted from trout plasma was shown to comigrate with [ 3 H]melatonin. The RIA procedure did not differentiate between endogenous trout melatonin and [ 3 H]melatonin added to the same sample. Melatonin levels in plasma from trout anesthetized with MS-222 were not different from those found in plasma from trout killed by decapitation without anesthesia. Melatonin levels were high during the night (152.6 ± 15.8 pg of melatonin/ml of plasma) and low during the day (81.2 ± 19.3 pg of melatonin/ml of plasma).

Melatonin in the blood and cerebrospinal fluid of the green sea turtle (Chelonia mydas)

Abstract A melatonin radioimmunoassay was validated for the green sea turtle. A pronounced diurnal rhythm of melatonin content was evident in both serum and cerebrospinal fluid (CSF). In immature turtles, CSF melatonin levels paralleled those in serum but were always significantly lower. Despite the close anatomical juxtaposition of the sea turtles large pineal gland to the brain, our data suggest that the primary route of secretion into the CSF is through the peripheral vasculature via the choroid plexus. Light exposure reduced serum melatonin titers. Adult females that were either mating or nesting exhibited the lowest serum melatonin levels we measured for this species.

Nonrelationship between plasma melatonin and background adaptation in the rainbow trout (Salmo gairdneri)

Adult female rainbow trout (Salmo gairdneri) were maintained outdoors on black, white, and neutral colored backgrounds. Reflectometry readings were used to assess the color adaptation of the fish. Plasma samples were collected from the same individuals both before and after exposure to the backgrounds, as well as at both 1200 and 2400 hr. Using a sensitive radioimmunoassay, no significant differences in plasma melatonin levels could be detected for the fish kept on the three backgrounds. Since the fish did show significant color modification in response to 18–21.5 days on the backgrounds, it is concluded that melatonin may not participate in background adaptation in trout. A consistent nocturnal elevation in melatonin levels was noted on all backgrounds. The stress associated with taking multiple blood samples from the same fish may have caused a significant increase in post-treatment compared to pretreatment nocturnal melatonin titers.

Mode of secretion of pineal melatonin in the chicken

Abstract Pineal glands of White Leghorn chickens were autotransplanted to the anterior chamber of an eye when the birds were 2 days old. When 4 mo of age six chickens with intraocular transplants and five unoperated controls were decapitated at middark. Brains were extracted with chloroform and melatonin content was determined in a frog tadpole assay. Melatonin content of blood serum from the same animals also was determined. The amount of melatonin in both the brain and serum was lower in birds with pineal transplants than in controls, but the ratio of brain to serum melatonin in both groups was about 7:1.

Day - night rhythm in plasma melatonin in a mammal lacking a distinct pineal gland, the nine-banded armadillo.

Abstract A melatonin radioimmunoassay was validated for plasma in the nine-banded armadillo ( Dasypus novemcinctus ). A distinct diurnal rhythm of circulating melatonin was found. This rhythm was coupled to the photoperiod, with scotophase levels being approximately three times greater than photophase levels. The rhythm could be entrained to a photoperiod, and appeared to be coupled with the activity, body temperature, and metabolic rhythms. In addition, the melatonin rhythm was maintained under constant low-intensity illumination. Because this species naturally lacks a distinct pineal gland, it is suggested that the circulating melatonin is produced by one or more extrapineal sources.

Delayed effect of pinealectomy on hibernation of the golden-mantled ground squirrel

Pinealectomy or radical sham pinealectomy were performed on adult golden-mantled ground squirrels,Spermophilus (=Citellus) lateralis, approximately 1 month prior to the date of normal winter emergence. The first hibernatory period and subsequent active season were not different in either of the operated groups from intact animals. However, although the initiation of the second hibernatory period was not affected in the pinealectomized animals, this group failed to show the progressive increase in the length of heterothermic bouts that is characteristic of normal hibernation. Also, terminal arousal occurred approximately 6 weeks earlier in the second year after pinealectomy. Male squirrels showed a corresponding time compression in their annual gonadal cycle, as was assessed by testicular state.These results suggest that the pineal gland of the golden-mantled ground squirrel is involved in the expression of the annual hibernatory cycle. In the absence of the pineal gland the adult of this species is unable to sustain the normal depth and duration of hibernation in the second over-wintering period following pinealectomy.We have carried out additional experiments with young, laboratory-bornS. lateralis and with field-caught, adultS. richardsonii. The results of these studies also are described in this paper.

Encephalic photoreceptor involvement in the entrainment and control of circadian activity of young american alligators

Abstract Young American alligators, Alligator mississippensis , which have been previously shown to lack a pineal organ, possess functional encephalic extra-retinal photoreceptors. These receptors can effect the entrainment of circadian locomotor activity rhythms by light-dark cycles. They also mediate the effects of the intensity of constant illumination on circadian period length, as per the circadian rule for diurnally active animals. It is suggested that retinal and extra-retinal inputs may normally interact to determine overall entrainment and circadian organization.

The Role of the Pineal Complex in Behavioral Thermoregulation in the Collared Lizard Crotaphytus collaris under Seminatural Conditions

Collared lizards maintained in individual outdoor runways behaviorally selected a body temperature of 37-38 C. Removal of the parapineal component (parietalectomy) of the pineal complex elevated the temperature selected by lizards, although this increase was not statistically significant. On the other hand, pinealectomy or a combination of pinealectomy and parietalectomy significantly lowered lizard body temperatures. The available evidence indicates that the parietal eye and pineal organ mediate these responses through brain centers, such as the hypothalamus, by both neural and hormonal mechanisms. The role of the pineal complex as part of a homeostatic mechanism transducing thermal as well as photic environmental signals is discussed.

Thermal and photic preferences in intact and parietalectomized Anolis carolinensis

Adult female Anolis carolinensis were exposed to combinations of thermal and photic stimuli to test the relative importance of these stimuli to the parietal eye, a photoreceptive structure apparently controlling exposure to sunlight and, perhaps, directly influencing behavioral temperature selection. Exposure to a cool light source occurs significantly less often in sham-parietalectomized than in parietalectomized animals, and both groups are photophobic if the light source does not provide heat. Parietalectomized animals congregate around a heat source significantly more often than do intact controls, which gather in a cool dark area significantly more often than near a thermal source. Based upon these responses, it appears that parietal eyed animals are more thermophilic than photophilic, precisely choosing appropriate photothermal positions. Parietalectomy alters these behavioral responses and results in increased exposure to thermal and light sources, although attraction to a thermal source is much more pronounced than attraction to a light source. Because parietalectomized animals become even more thermophilic than sham-parietalectomized controls, but are comparably photo-phobic, it seems reasonable that increased exposure to sunlight after parietalectomy is not a response to a light stimulus, but is, instead, a response to the thermal characteristics of solar radiation. The parietal—pineal complex may have a more important role in behavioral temperature regulation than has previously been suggested.