Pineal opsin: a nonvisual opsin expressed in chick pineal.

Pineal opsin (P-opsin), an opsin from chick that is highly expressed in pineal but is not detectable in retina, was cloned by the polymerase chain reaction. It is likely that the P-opsin lineage diverged from the retinal opsins early in opsin evolution. The amino acid sequence of P-opsin is 42 to 46 percent identical to that of the retinal opsins. P-opsin is a seven-membrane spanning, G protein-linked receptor with a Schiff-base lysine in the seventh membrane span and a Schiff-base counterion in the third membrane span. The primary sequence of P-opsin suggests that it will be maximally sensitive to approximately 500-nanometer light and produce a slow and prolonged phototransduction response consistent with the nonvisual function of pineal photoreception.

Lability of circadian pacemaker amplitude in chick pineal cells: a temperature-dependent process.

Temperature is a major regulator of circadian rhythms. The authors report here three lines of evidence that temperature modulates the amplitude of the circadian pacemaker that drives rhythmic melatonin production in chick pineal cells. (1) The melatonin rhythm persists longer in constant conditions at 40 degrees C than at 37 degrees C. (2) the phase response curve to low-intensity (0.15 microW/cm2) light pulses of 6-h duration has a higher amplitude at 37 degrees C than at 40 degrees C; a nonphotic stimulus, anisomycin, also causes larger shifts at 37 degrees C than at 40 degrees C. These results suggest a general increase in sensitivity to phase-shifting stimuli as temperature decreases. (3) The light intensity necessary for a critical pulse that causes arrhythmicity is lower at 37 degrees C than at 40 degrees C. All three of these effects of temperature can be explained in a unified manner by a limit cycle model in which temperature increases circadian pacemaker amplitude. The use of critical pulse experiments provides a novel method for estimating relative circadian pacemaker amplitude under different conditions.

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.

The quail's eye: a biological clock.

The site (intraocular vs. extraocular) of the biological clock driving a rhythm in melatonin content in the eyes of Japanese quail was investigated by alternately patching the left and right eyes of individual birds, otherwise held in constant light, for 12-hr periods. This patching protocol, therefore, exposed each eye to a light-dark cycle (LD 12:12) 180 degrees (12 hr) out of phase with the LD cycle experienced by the other eye. The optic nerves to both eyes were transected prior to initiating the patching protocol. The ocular melatonin rhythm (OMR) of the left eyes of quail could be entrained by this procedure 180 degrees out of phase with the rhythm expressed by the right eyes. Since optic nerve section would have deprived any putative extraocular clocks of photic entrainment information, the results show conclusively that the clock driving the OMR is located within the eye itself. In addition, the OMR of Japanese quail is remarkably unaffected by removing two potential neural inputs to the eye (sympathetic innervation from the superior cervical ganglia, and input from the isthmo-optic nucleus of the midbrain); this suggests that these inputs are not required to maintain the OMR. Finally, the clock driving the OMR of one eye does not appear to be coupled to the clock driving the OMR in the other eye, since permanently patching one eye abolished the ability of the patched eye to re-entrain to an 8-hr shift in the phase of an LD 12:12 cycle, whereas the exposed eye rapidly re-entrained to the phase-shifted cycle.

Melatonin does not link the eyes to the rest of the circadian system in quail: a neural pathway is involved.

Blinding by enucleation has a dramatic effect on the circadian activity rhythm of Japanese quail. The activity patterns of enucleated birds held under 24-hr light-dark cycles are disrupted, although entrainment can persist in many birds. In constant darkness (DD), blinded birds are rendered arrhythmic. These results demonstrate that the eyes are a major component of the circadian system, and that insofar as enucleation produces arrhythmicity in DD, the eyes' role is not merely a photosensory one. The eyes of quail can synthesize and secrete the hormone melatonin, which has been implicated as a blood-borne messenger relaying timing information between elements of the circadian system in some avian species. However, the way in which the eyes communicate with the rest of the circadian system in quail appears to be neural, since (1) optic nerve section produces the same effects as blinding by enucleation on the circadian activity rhythm, and (2) eyes subjected to optic nerve section retain their ability to synthesize and secrete melatonin.

Molecular cloning of chick pineal tryptophan hydroxylase and circadian oscillation of its mRNA levels.

We have previously shown that the level of [35S]methionine incorporation into tryptophan hydroxylase (TPH) shows a circadian rhythm in cultured chick pineal cells. The TPH protein oscillation persists in constant darkness, peaks in the early night and can be phase-shifted by light, in parallel to the effect of these treatments on melatonin synthesis. We have cloned and sequenced a full-length cDNA for chick pineal TPH. Levels of TPH mRNA show a robust diurnal oscillation both in vivo and in vitro. The rhythm in TPH mRNA also persists in constant darkness, suggesting that TPH mRNA synthesis and/or turnover is regulated by an endogenous circadian clock in cultured chick pineal cells. The circadian oscillation of TPH constitutes the first described circadian rhythm of a chick pineal gene at the mRNA level.

Retinally perceived light can entrain the pineal melatonin rhythm in Japanese quail.

The avian pineal organ contains a circadian oscillator that can drive a daily rhythm of melatonin synthesis. In some avian species the pineal organ may act, via the cyclic release of melatonin, as a pacemaker within a multioscillator circadian system. The routes by which light entrains the pineal melatonin rhythm were investigated in the Japanese quail. A 'patching' protocol was used to expose directly either the eyes or the pineal to a light-dark cycle while the rest of the bird was exposed to constant light. The results show that the pineal melatonin rhythm can be entrained (1) by light perceived directly or (2) by light perceived by the eyes. Furthermore, the pathway by which light entrains the pineal melatonin rhythm includes the optic nerves because transection of the optic nerve eliminates the ability of ocularly perceived light to entrain the pineal melatonin rhythm.

The superior cervical ganglia are not necessary for entrainment or persistence of the pineal melatonin rhythm in Japanese quail.

The avian pineal exhibits a daily rhythm in the synthesis and secretion of the hormone, melatonin, which is involved in maintaining temporal order within the circadian system of some species. The pineal is richly innervated by sympathetic nerves which originate in the superior cervical ganglia (SCG) and, in the chicken, these nerves play a role in generating the melatonin rhythm. In the Japanese quail, the pineal melatonin rhythm can be entrained by light perceived directly by the pineal or by light perceived by the eyes. The role of the sympathetic innervation of the pineal was investigated in the Japanese quail by subjecting birds to bilateral superior cervical ganglionectomy (SCGX) and determining if SCGX either abolished the ability of retinally perceived light to entrain the pineal melatonin rhythm or if it disrupted the rhythm under constant darkness (DD). The results show that SCGX neither prevented entrainment of the pineal melatonin rhythm by retinally perceived light nor affected the rhythm expressed in DD. An entrainment pathway between the eyes and pineal exists in quail which does not involve the SCG.

Streamer initiation in atmospheric pressure gas discharges by direct particle simulation.

A two-dimensional particle code that simulates electrical breakdown of gases by modeling avalanche evolution from the initial ion-electron pair up to the development of a streamer is presented. Trajectories of individual particles are followed, the self-field is included consistently and collision processes are accurately modeled using experimentally determined cross sections. It is emphasized that the tadpolelike structure of well-formed streamer heads is present throughout the avalanche phase, and that the transition to the self-similar evolution characteristic of the streamer phase merely reflects the continued development of this structure. The importance of this for conventional fluid simulations of streamers, where the initial conditions for the streamer are taken to be a structureless Gaussian concentration of neutral plasma with significant density, is discussed. In the (realistic) situation where several avalanches are present simultaneously the large self-fields that rapidly develop lead to a strong interaction between them, in accord with the standard "cartoon" of streamer evolution.

Elephant people: the phenomena of social withdrawal and self-imposed isolation of people dying with AIDS.

The phenomena of self-initiated isolation and social withdrawal of people dying from AIDS is described and explained in the context of its irony and detriment to the patients' well being, minimizing access to social support resources. The psychological and the therapeutic relevance of social support during the critical transition phase is explored. Recommendations for curbing the phenomena of self-imposed social death in PWAs, as well as suggestions for future research on the value of psychosocial support to the PWA's well being during the transition phase, are also discussed.

Temperature compensation and temperature entrainment of the chick pineal cell circadian clock.

We have used an in vitro model system of the circadian clock, dispersed chick pineal cells, to examine the effects of temperature on the circadian clock of a homeotherm. This preparation enabled us to isolate a circadian clock from in vivo homeostatic temperature regulation and expose cells to both constant temperatures and abrupt temperature changes. By manipulating the temperature of the pineal cells, we have demonstrated that (1) the circadian clock compensates its period for temperature changes over the range of 34-40 degrees C; Q10 = 0.83, a value within the range of Q10 values measured for poikilothermic circadian clocks; (2) temperature pulses (42 degrees C, 6 hr duration) shift the phase (advance and delay) of the circadian rhythm in a phase-dependent manner; and (3) a temperature cycle (18 hr at 37 degrees C, 6 hr at 42 degrees C) will entrain the circadian clock in vitro. This is the first demonstration of temperature entrainment of the circadian clock of a homeotherm in vitro. In addition we have found that temperature directly influences the synthesis and release of melatonin, the primary hormonal product of the pineal gland. The biosynthesis of melatonin is strongly temperature dependent with a Q10 > 11 when melatonin release is measured at ambient temperatures between 31 degrees C and 40 degrees C. In contrast, 6 hr 42 degrees C temperatures pulses acutely inhibit melatonin release in a manner similar to that seen previously with light pulses. These results demonstrate that a circadian clock from a homeothermic vertebrate is temperature compensated, yet temperature cycles can entrain the circadian melatonin rhythm. Thus, the chick pineal circadian oscillator has retained all the fundamental properties of circadian rhythms.

Effects of light on circadian pacemaker development. I. The freerunning period.

1. The effects of raising cockroaches, Leucophaea maderae, in non-24 h light cycles on circadian rhythms in adults were examined. The average period (tau) of freerunning rhythms of locomotor activity of animals exposed to LD 11:11 (T22) during post-embryonic development was significantly shorter (tau = 22.8 +/- 0.47 SD, n = 85) than that of animals raised in LD 12:12 (T24) (tau = 23.7 +/- 0.20 h, n = 142), while animals raised in LD 13:13 (T26) had significantly longer periods (tau = 24.3 +/- 0.21 h, n = 65). Animals raised in constant darkness (DD) had a significantly shorter period (tau = 23.5 +/- 0.21 h, n = 13) than siblings raised in constant light (LL) (tau = 24.0 +/- 0.15 h, n = 10). 2. The differences in tau between animals raised in T22 and T24 were found to be stable in DD for at least 7 months and could not be reversed by exposing animals to LD 12:12 or LD 6:18. 3. Animals raised in either T24 or DD and then exposed as adults to T22 exhibited average freerunning periods that were not different from animals not exposed to T22. 4. Measurement of freerunning periods at different temperatures of animals raised in T22, T24, or T26 showed that the temperature compensation of tau was not affected by the developmental light cycle. These results indicate that the lighting conditions during post-embryonic development can permanently alter the freerunning period of the circadian system in the cockroach, but do not affect its temperature compensation.

Effects of light on circadian pacemaker development. II. Responses to light.

The effects of raising cockroaches, Leucophaea maderae, in non-24-h light cycles on the response of the circadian system to light was examined. 1. Phase response curves (PRC) were measured for 6-h light pulses for animals raised in LD 11:11 (T22), LD 12:12 (T24), and LD 13:13 (T26). The delay portion of the PRC was found to be significantly reduced in T22 animals (compared to T24 animals) while the advance portion of the PRC was reduced in T26 animals. Compared to T26 animals, phase shifts were more positive at every phase for animals raised in T22. 2. When transferred from constant darkness (DD) to constant light (LL) the freerunning period lengthened significantly less for T22 animals than T24 animals, and in some cases tau in LL was actually shorter than tau in DD in T22 animals. Animals raised in LL were inactive when exposed to LL as adults, and unlike T24 animals, were consistently reset to the beginning of the subjective night (near CT 12) when transferred to DD. 3. Roaches raised in T22 would entrain to LD 6:18, but a few animals exhibited periods of relative coordination indicating that the 24-h light cycle was near the limits of entrainment. These results indicate that the circadian system's responsiveness to light, as well as its freerunning period (Barrett and Page 1989), is dependent on the lighting conditions to which the animals are exposed during development.