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H Underwood

Publications and source records attributed to H Underwood.

At least 37 records · Page 2Linked to original sources
PubMed1988

Does a biological clock reside in the eye of quail?

The site (intra- vs. extraocular) of the circadian clock driving an ocular melatonin rhythm in Japanese quail was investigated by alternately covering the left and right eyes of individual quail, otherwise held in constant light (LL), for 12-hr periods. This procedure exposed each eye to a light-dark (LD) 12:12 light cycle 180 degrees (12 hr) out of phase with the LD 12:12 light cycle experienced by the other eye. This protocol entrained the melatonin rhythm in the left eye of quail 180 degrees out of phase with the rhythm expressed in the right eye. These results are compatible with the hypothesis that an independent light-entrainable circadian pacemaker resides in each eye; they are incompatible with the hypothesis that a single (or functionally single) extraocular pacemaker drives the ocular melatonin rhythm in both eyes. However, the results are also compatible with a model in which two independent extraocular circadian pacemakers, each with an exclusive photic input from one eye, drive the ocular melatonin rhythm.

Animals↗
PubMed1987

Pineal melatonin rhythms in the lizard Anolis carolinensis: I. Response to light and temperature cycles.

Both light and temperature can influence the pineal's synthesis of the indoleamine melatonin. An investigation of the effects of light and temperature cycles on the pineal melatonin rhythm (PMR) showed the following: (1) Both daily light cycles and daily temperature cycles could entrain the PMR; melatonin levels peaked during the dark phase of a light-dark cycle or the cool phase of a temperature cycle. (2) The PMR could be entrained by a temperature cycle as low as 2 degrees C in amplitude in lizards held in constant light or constant darkness. (3) The length of the photoperiod or thermoperiod affected the phase, amplitude, or duration of the PMR. (4) When presented together, the effects of light and temperature cycles on the PMR depended on the phase relationship between the light and temperature cycles, as well as on the strength of the entraining stimuli, such as the amplitude of the temperature cycle. (5) Exposure to a constant cold temperature (10 degrees C) eliminated the PMR, yet a rhythm could still be expressed under a 24-hr temperature cycle (32 degrees C/10 degrees C), and the rhythm peaked during the 10 degrees C phase of the cycle. (6) A 6-hr dark pulse presented during the day did not elicit a premature rise in melatonin levels. These studies show how environmental stimuli can control the pineal rhythm of melatonin synthesis and secretion. Previous studies have supported a model in which the lizard's pineal acts as a circadian pacemaker within a multioscillator circadian system, and have implicated melatonin as a hormone by which the pineal may communicate with the rest of the system. The lizard pineal, therefore, may act as a photo- and thermoendocrine transducer translating light and temperature information into an internal cue in the form of the PMR. The PMR, in turn, may control the phase and period of circadian clocks located elsewhere, insuring that the right internal events occur at the right time of day.

Animals↗
PubMed1987

Pineal melatonin rhythms in the lizard Anolis carolinensis: II. Photoreceptive inputs.

The pineal organ of the lizard Anolis carolinensis acts as a transducer of photoperiodic information, since light can affect the pineal melatonin rhythm (PMR). The synthesis and secretion of melatonin may be a major mechanism whereby a circadian pacemaker within the pineal can control circadian clocks located elsewhere. An investigation into potential routes by which light could affect the PMR showed that (1) removal of the photosensory parietal eye did not affect the PMR as compared to controls under either a light-dark (LD) 12:12 cycle and a constant temperature (32 degrees C) or an LD 12:12 cycle and a daily temperature cycle (32 degrees C/20 degrees C); (2) removal of both the parietal eye and the lateral eyes did not affect the PRM of anoles held in LD 12:12 (constant 32 degrees C); (3) the PMR of blinded anoles re-entrained to a 10-hr shift in the phase of the LD cycle as rapidly as that of sighted anoles; (4) blocking light penetration to the brains of anoles, but leaving the lateral eyes exposed, blocked the ability of anoles to re-entrain to a 10-hr shift in the phase of an LD cycle. The data support the hypothesis that light directly affects the PMR in Anolis and that other potential photic inputs (parietal eye, lateral eyes) play little or no role. This conclusion is supported by previous neurophysiological and ultrastructural studies showing that the lizard pineal possesses functional photoreceptors.

Animals↗
PubMed1986

Circadian rhythms in lizards: phase response curve for melatonin.

Single biweekly injections of melatonin were administered to lizards (Sceloporus occidentalis) free-running (exhibiting their endogenous circadian activity rhythm) in constant dim illumination. The injections caused phase shifts in the activity rhythm whose magnitude and direction were a function of the time of the melatonin injections, relative to activity onsets. Plotting the direction and amount of phase shift versus the time (phase) at which the injection was given generates a phase-response curve (PRC). The PRC shows that injections administered between midsubjective day and early subjective night (6-15 hr after activity onset) elicit phase advances in the activity rhythm, whereas injections given at other phases of the activity cycle induce phase delays. The existence of a PRC for melatonin suggests that the daily endogenous rhythm of melatonin (i.e., of pineal origin) may be involved in phasing, or entraining, the circadian system of lizards. The shape of the PRC also allows predictions as to the effects of continuous exogenous melatonin administration on the period of free-running activity rhythms as well as on the mechanism of entrainment of activity rhythms to daily melatonin injections.

Animals↗
PubMed1985

Annual testicular cycle of the lizard Anolis carolinensis: effects of pinealectomy and melatonin.

The effects of pinealectomy and exogenous melatonin treatment on the reproductive system of male anoles were examined at several different times of year. In September pinealectomy of anoles exposed to either a stimulatory LD 14:10 light cycle or a nonstimulatory LD 10:14 light cycle induced significant testicular growth and development over that observed in sham-operated anoles. At a nonphotosensitive time of year (December) pinealectomy also had a significant progonadal effect but no effect of pinealectomy was seen in February-March. Daily melatonin injections given either in the morning or afternoon (or both) failed to block gonadal growth either (1) in sham-operated or pinealectomized anoles exposed to LD 14:10 in the fall or (2) in pinealectomized lizards exposed to LD 10:14 in the fall. Continuous melatonin administration via subcutaneous silastic implants blocked the progonadal effects of pinealectomy in the winter (December). The results show that pinealectomy can have significant progonadal effects; these effects are seasonal but can encompass phases of the annual testicular cycle which are either photoperiod-dependent or temperature-dependent; and melatonin may be a reproductively active factor involved.

Animals↗
PubMed1985

Pineal melatonin rhythms in the lizard Anolis carolinensis: effects of light and temperature cycles.

Pineal and ocular melatonin was assessed, over 24 h periods, in male lizards (Anolis carolinensis) entrained to 24 h light-dark (LD) cycles and a constant 32 degrees C, and in lizards entrained to both 24 h LD cycles and 24 h temperature cycles (32 degrees C/20 degrees C). At a constant temperature, the duration of the photoperiod has a profound effect on the duration, amplitude, and phase of the pineal melatonin rhythm (Fig. 1). The pineal melatonin rhythm under cyclic temperature peaks during the cool (20 degrees C) phase of the cycle regardless of whether or not the cool phase occurs during the light or dark phase of a LD 12:12 cycle (Fig. 3). Under a temperature cycle and constant dim illumination, a pineal melatonin rhythm is observed which peaks during the cool phase of the temperature cycle, but the amplitude of the rhythm is depressed relative to that observed under LD (Fig. 2). Illumination up to 2 h in duration does not suppress the nocturnal melatonin peak in the Anolis pineal (Fig. 4). No melatonin rhythm was observed in the eyes of Anolis under either 24 h LD cycles and a constant temperature (Fig. 1), or under simultaneous light and temperature cycles (Fig. 3). Ocular melatonin content was, in all cases, either very low or non-detectable.

Animals↗
PubMed1985

Entrainment of the circadian activity rhythm of a lizard to melatonin injections.

The circadian activity rhythms of lizards (Sceloporus occidentalis) can be entrained (synchronized) to a period of 24 hr by melatonin injections given every other day at the same time of day, but not by saline injections. The activity onsets of the entrained lizards exhibited two preferred phase-relationships (approximately 165 degrees and approximately 30 degrees) with the time of melatonin injections with the 30 degree phase only rarely observed. These results suggest that endogenous rhythms of melatonin secretion (i.e., from the pineal organ) may be involved in synchronizing circadian oscillations within the lizard's multioscillator circadian system.

Animals↗
PubMed1985

Parietalectomy does not affect testicular growth in photoregulating lizards.

The testicular response of male anoles maintained at a constant 32 degrees C was similar in both parietalectomized and sham-parietalectomized lizards exposed to either constant light (40 lux intensity) or to photic gradients (40-300 lux). The results support the hypothesis that the acceleration of gonadal growth in parietalectomized lizards noted by others depends on the ability of lizards to self-regulate exposure to thermal, but not photic, stimuli.

Animals↗
PubMed1985

Photoperiodic time measurement in the male deer mouse, Peromyscus maniculatus.

Weanling male deer mice, Peromyscus maniculatus, were exposed for three weeks either to light-dark (LD) cycles with periods (T=L+D) ranging from T=23 (1L:22D) to T=25.16 (1L:24.16D) or to 24-h LD cycles with photoperiods ranging from 1 (1L:23D) to 19 (19L:5D) h. Both the circadian locomotor activity rhythms and the response of the reproductive system to these LD cycles were assessed. The results demonstrate that the photoperiodic effectiveness of light depends on the phase of the light relative to the animal's circadian system, as marked by the circadian activity rhythm. Light falling during the animal's subjective night, from activity onset to at least 11.8 h after activity onset, stimulates growth and maturation of the reproductive system, whereas light falling during the rest of the circadian cycle is nonstimulatory.

Activity Cycles↗
PubMed1985

Melatonin rhythms in quail: regulation by photoperiod and circadian pacemakers.

The profile of melatonin in the eyes, pineal, and blood of Japanese quail was assessed in birds held under LD 16:8 and LD 6:18 photoperiods. Melatonin levels in all three tissues showed a robust daily rhythm with higher levels occurring at night. The amplitude of the rhythm was depressed and its duration lengthened on LD 6:18 relative to LD 16:8. The blood melatonin rhythm precisely reflected the rhythms shown by the pineal and eyes, supporting the idea that the blood rhythm is a result of melatonin secretion by both the eyes and pineal. The ocular melatonin rhythm continued after sectioning of the optic nerve, was reentrainable to a shift in the phase of the LD cycle, and persisted for at least 2 days in constant darkness. It was concluded that either an intraocular circadian clock drives the ocular melatonin rhythm, or an extraocular clock drives the ocular melatonin rhythm via a route other than the efferent innervation (which enters the eye via the optic tract).

Animals↗
PubMed1985

Extraretinal photoreception in the lizard Sceloporus occidentalis: phase response curve.

All submammalian vertebrates have extraretinal photoreceptors (ERR) that can mediate entrainment of circadian rhythms to 24-h light-dark (LD) cycles. Phase response curves (PRC) for 6-h fluorescent light pulses were generated for lizards (Sceloporus occidentalis) previously subjected to sectioning of both optic nerves (ONX). The PRC for ONX lizards (only ERRs present) shows a threefold increase in the amplitude of both the advance and delay portions of the PRC compared with a PRC previously generated for sighted S. occidentalis. Also, in contrast to sighted lizards the area of the advance part of the PRC of ONX lizards is greater than the delay portion. Consistent with the shape of the respective PRCs in ONX vs. sighted lizards are the following facts. 1) The range of entrainment to LD cycles is greater in ONX lizards; some sighted lizards free-ran when exposed to LD 6:21.5 or LD 6:23.5 but entrained after ONX lizards reentrained to an 8-h shift in the phase of a LD 6:18 cycle significantly faster than sighted lizards. 3) Forty-two percent of ONX lizards showed a shorter free-running period (tau) in LL than DD, whereas 90% of sighted lizards showed a longer free-running period in LL than in DD. In those lizards in which tau LL greater than tau DD, the the average tau change in ONX lizards in was significantly less than that observed in sighted lizards. These results are consistent with the hypothesis that the eyes have an "inhibitory" role in the circadian system of S. occidentalis.

Animals↗
PubMed1984

Circadian organization in Japanese quail.

Our recent studies have implicated both the eyes and pineal as major components of the circadian system of Japanese quail. We assessed the role of these organs by examining the effect of their removal on the circadian activity rhythm of quail exposed to either 24 hr light-dark (LD) cycles or to continuous darkness (DD). Removal of only the pineal had no effect on the activity rhythm of quail in either LD or DD. Blinding (by orbital enucleation) had a major effect under both LD and DD. One third of the blinded birds showed entrainment under LD although entrainment patterns were very variable, whereas two thirds of blinded birds were arrhythmic. All blinded plus pinealectomized birds were arrhythmic in LD as were all blinded and blinded plus pinealectomized birds in DD. Accordingly, effects of pinealectomy can be seen only when pinealectomy is combined with blinding. The fact that blinding disrupts circadian organization in both LD and DD indicates that the eyes must act as major components of the quail's circadian system. In view of the postulated role for melatonin, an indoleamine, in circadian systems, the eyes, pineal, and blood of quail were assayed for this compound. Robust daily rhythms in melatonin content were observed in all three tissues. The blood rhythm is due to secretion of melatonin into the vascular system by both the pineal and eyes. The ocular melatonin rhythm continued after sectioning of the optic nerve, was reentrainable to a shift in the phase of the LD cycle, and persisted for at least 2 days in DD. These data suggest that the eyes play a major role within the circadian system and support the hypothesis that circadian pacemakers may reside within the eyes of quail. The results are discussed in view of the findings of others in both quail and other avian species. A general model for circadian organization in birds is presented in which the eyes, the pineal, and the suprachiasmatic nuclei of the hypothalamus comprise major elements of a multioscillator circadian system.

Acetylserotonin O-Methyltransferase↗
PubMed1984

Melatonin rhythms in the eyes, pineal bodies, and blood of Japanese quail (Coturnix coturnix japonica).

Melatonin levels in the eyes, pineal bodies, and blood of Japanese quail exposed to 12L:12D show robust daily rhythms with high levels occurring in the night and low levels occurring during the day. Since melatonin is synthesized in both the eyes and pineal bodies of birds, the relative contribution of these structures to the blood melatonin levels was determined. A rhythm of blood melatonin persisted in 12L:12D in birds blinded by complete orbital enucleation and in pinealectomized birds but the nighttime levels were reduced by 33 and 54%, respectively, as compared to melatonin levels in control quail. Only a small melatonin rhythm (13% of control levels) was detected in the blood of pinealectomized, blinded quail. This "residual" rhythm could indicate either the contribution of extrapineal, extraocular sources of melatonin or melatonin secretion from remnants (if any) of pineal body tissue remaining after pinealectomy. Blinding did not obviously affect pineal melatonin levels nor did pinealectomy affect ocular melatonin levels. It was concluded that (1) daily rhythms in melatonin content occur in the pineal bodies, the eyes, and the blood of quail; (2) the blood rhythm is the result of melatonin secretion from both the pineal body and the eyes; (3) extraretinal photoreceptors can mediate entrainment of the pineal melatonin rhythm; and (4) obvious compensatory changes in melatonin levels do not occur in the eye following pinealectomy or in the pineal body following blinding.

Animals↗
PubMed1984

Influence of melatonin on pubertal development in male deer mice (Peromyscus maniculatus).

The role of melatonin in pubertal development was assessed in male deer mice (Peromyscus maniculatus bairdii) exposed to photoperiodic and social stimuli. Exogenous melatonin retarded puberty in males reared in a long photoperiod, but was without effect in males reared in short days. Melatonin did not retard pubertal development induced by exposure of short-day males to an adult female. These results suggest that pineal melatonin mediates photoperiodic, but not social, control of pubertal development.

Animals↗
PubMed1983

Photoperiodic stimulation of pubertal development in male deer mice: involvement of the circadian system.

Pubertal development in prairie deer mice (Peromyscus maniculatus bairdii) is accelerated by exposure of juveniles to a long-day photoperiod, and, conversely, retarded by exposure to short days. The purpose of the present study was to evaluate the possible involvement of the circadian system in the photoperiodic regulation of puberty. Weanling males, previously housed on a short-day light cycle of 6L:18D, were subjected to a "resonance" protocol in which they received one of the following light cycles: 6L:18D, 6L:30D, 6L:42D, 6L:54D, or 16L:8D. Post-weaning exposure to cycles of 16L:8D, 6L:30D, and 6L:54D stimulated reproductive organ growth as measured at 6 weeks of age. Exposure to cycles of 6L:18D and 6L:42D failed to stimulate reproductive development. These data support the hypothesis that young male deer mice use a circadian rhythm of responsiveness to light to measure photoperiodic time and, consequently, regulate pubertal development.

Animals↗