Photoperiod Reversal Research Articles

High-rate operant behavior in two mouse strains: A response-bout analysis

Operant behavior sometimes occurs in bouts characterized by an initiation rate, within-bout response rate, and bout length. The generality of this structure was tested using high-rate nose-poking in mice. Reinforcement of short interresponse times produced high response rates while a random-interval schedule held reinforcement rates constant. BALB/c mice produced bouts that were more frequent, longer, and contained a higher within-bout rate of responding (nine nose-pokes/s) than did the C57BL/6 mice (five nose-pokes/s). Adding a running wheel decreased total nose-pokes and bout length, and increased bout-initiation rate. Free-feeding reduced nose-poking by decreasing bout-initiation rate. Photoperiod reversal decreased bout-initiation rate but not total nose-poke rate. Despite strain differences in bout structure, both strains responded similarly to the interventions. The three bout measures were correlated with overall rate but not with each other. Log-survival analyses provided independent descriptors of the structure of high-rate responding in these two strains.

Entrainment of circadian rhythm to a photoperiod reversal shows retinal dystrophy in RPE65 −/− mice

Light entrainment of circadian rhythms is mediated by classical “visual” photoreceptors (rods and cones) as well as “nonvisual” photoreceptive elements (light-detecting cells that do not contribute to classical “vision”). This paper aimed to assess whether light entrainment of locomotor circadian rhythms in mice with impaired rods and cones differs from normal controls and whether this technique, alongside existing techniques, could be used to assess visual function. The study was primarily interested in differences between the entrainment of circadian rhythms of normal-sighted C57Bl/6J mouse and the C57Bl/RPE65 knockout mouse (RPE65 −/−), although C3H/HeJ ( rd/ rd) mice were included as a preexisting model of retinal degeneration. Circadian rhythms of motor activity before and after a 12-h light reversal were assessed in custom-built cages that continuously monitored movement. The controls showed a significantly higher mesor and amplitude when compared to the RPE65 −/− and rd/ rd mice. Despite the loss of rods and cones, the RPE65 −/− and rd/ rd maintained a 24-h circadian rhythm entrained to light similar to controls and were capable of circadian reentrainment to a 12-h light reversal. Importantly, this light reentrainment of the circadian phase occurred at a significantly slower rate in the retinal degenerate models than in the controls. The RPE65 −/− model demonstrates a retinal degenerate reentrainment phenotype when compared to the rd/ rd model. It is suggested that these retinal degenerate mice retain the ability to detect light for the purposes of circadian rhythm entrainment. However, alterations of specific parameters of the circadian rhythm with loss of rods and cones may provide measures of loss of visual function (sight).

Alteration of growth, advancement of puberty, and season-appropriate circannual breeding during 28 months of photoperiod reversal in woodchucks (Marmota monax).

In woodchucks (Marmota monax), as in other marmotine rodents, endogenous circannual metabolic and reproductive cycles persist and free-run at intervals of 10-12 mo for up to 4 yr in a neutral photoperiod of 12L:12D. The annual metabolic cycle is not altered by exposure to constant long days or short days for several months. In the wild, changes in food intake cause body weight to peak in late summer and reach nadirs in early spring, and there is a single annual breeding season in late winter. To determine whether normal changes in photoperiod entrain the endogenous circannual cycle, aspects of reproduction, food intake, and body weight were studied for 28 mo in eight groups of woodchucks housed in light-controlled rooms. These included four groups of 7-10 males and four groups of 7-10 females exposed to automated and continuous daily changes in photoperiod. The imposed changes in photoperiod resembled native Northern Hemisphere (boreal) changes or Southern Hemisphere (austral) changes in photoperiod. The treatments started at the summer solstice shortly after capture as 2.5-mo-old juveniles or 14.5-mo-old yearling adults. In austral vs. boreal woodchucks, started as juveniles, annual increases in testosterone and testis descent at 5, 14, and 23 mo of study were advanced by 2, 5, and 6 mo, respectively. Annual increases in progesterone at 7, 16, and 25 mo of study were advanced by 4, 5, and 6 mo, respectively. The older woodchucks were significantly but less dramatically affected by austral photoperiod for the first 6 mo of study, and by 8-12 mo were advanced the same as the younger animals. At 16-17 and 26-27 mo of photoperiod reversal, 16 austral females had normal pregnancy rates (78%) and produced normal-sized litters (4.3 +/- 0.2) that were advanced by 5 and 6 mo, respectively, relative to those of boreal controls. Body weights in austral vs. boreal juveniles were reduced at 3-5 mo of study but not in older woodchucks. At 1 and then 2 yr of austral lighting, peaks in body weight were advanced by 4 and then 5 mo relative to boreal controls in young animals, and by 2 and then 5 mo in older animals. Between 1 and 2 yr of austral lighting in both age groups the nadirs in food intake (45 g per day) were about 16-25% of peak food intake 6-8 mo earlier, as in boreals, but advanced by 5-6 mo relative to boreals.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes

Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.

The effect of environmental photoperiodicity on indole rhythms and locomotor activity in sighted and eye covered chickens

Direct (via the skull) and indirect (via the eyes) light on the rate of adaptation of circadian rhythms of pineal, retina and serum indoleamines and of locomotor activity was examined by observing photoperiod reversal in eye covered and normally sighted chickens. Eye covering did not affect indoleamine levels nor locomotor activity on the regular light:dark (L:D) cycle. However, following photoperiod reversal, the eye covered chickens showed slower rates of adaptation of retinal melatonin and locomotor activity to the new L:D cycle than did the normal sighted chickens. Pineal and serum indole levels were unaffected by eye covering. Our results in birds indicate that 1) light to the eye has a role in governing retinal melatonin and locomotor activity, 2) the pineal is directly photosensitive, and 3) the endogenous rhythm of pineal melatonin may play a role in the entrainment of the locomotor rhythm in the chicken.

The effects of reversal of seasonal changes in photoperiod on the growth and food consumption of cod, Gadus morhua L.

The effect of reversing the natural seasonal change in photoperiod on the feeding and growth of juvenile cod, Gadus morhua. was investigated in two experiments. In an experiment conducted in spring no photoperiod effects on overall growth and food consumption were observed; however, tissue analysis at the end of the experiment showed that treatment groups differed significantly in their muscle water content. A repeat experiment conducted in early winter similarly failed to reveal an effect of photoperiod reversal on overall growth and feeding, although a very marked decline in growth rate was observed for all fish. The decline in growth rate observed in the second experiment cannot be accounted for by any changes in experimental procedure and is interpreted as possible evidence for an endogenous circa‐annual rhythm in growth rate.

Effects of seasonal reversal of photoperiod on the reproductive rhythm of a small marsupial

Effects of seasonal reversal of photoperiod on the reproductive rhythm of a small marsupial

Pineal, retinal, serum melatonin, and N-acetylserotonin rhythms in chicks on reversing light regimen and eye covering.

After reversing a 12:12-h light-dark regimen of environmental lighting, pineal and retinal melatonin levels of white leghorn chicks recorded at the first mid-darkness were greatly enhanced and reached maximum levels after three more days; those recorded during the light periods indicate gradual decline but were far from the nadir of the original light period, even at the end of the experiment. The first mid-darkness serum melatonin levels recorded after photoperiod reversal were not much different from their original mid-light values. However, on continuing with the reversed regimen, the next mid-darkness levels were sharply increased, and maximum levels were reached after a further 2 days. Under the same experimental conditions light had much more drastic effects, and 6 h on the reversed regimen were sufficient to bring down completely the high value of the original mid-darkness period to the level of the starting mid-light nadir. Retinal N-acetylserotonin (NAS) measured simultaneously had a pattern similar to that of melatonin, but the pineal NAS rhythm did invert completely, albeit gradually. Eye covering did not prevent inversion of pineal and serum melatonin rhythms, which were identical in eye-covered and sighted control chicks on the reversed regimen of light. However, retinal melatonin values of the light periods were significantly less depressed in eye-covered than in sighted control chicks. Moreover, eye covering completely prevented the retinal NAS depression under light but did not affect pineal NAS. During darkness retinal and pineal NAS elevation was sluggish in the eye-covered chicks.

Influence of photoperiod and photoperiod reversal on growth, mortality, and indicators of age of Dicrostonyx groenlandicus

After weaning, collared lemmings (Dicrostonyx groenlandicus) were exposed to 3 months of summer (S) photoperiod (18.5L:5.5D) or winter (W) photoperiod (6.5L: 17.5D) or to one of four 6-month photoperiod treatments (SS, SW, WW, or WS). Lemmings were weighed every 3 weeks, and at the end of treatment, eye lenses were weighed and 10 body and 22 skull measurements were taken. At the end of treatment, W, SW, and WW lemmings did not differ in weight, but were significantly heavier than S, SS, and WS lemmings. Animals in WS were significantly heavier than those in SS and both were significantly heavier than S lemmings. The marked contrast of the photoperiodically induced growth pattern of Dicrostonyx groenlandicus with that of other microtines may be due to a relatively larger investment in winter reproduction by collared lemmings. Lemmings that died during the experiment were significantly larger both in body weight and skull size than those that survived. Eye lens weights of S and W lemmings did not differ, but were significantly smaller than those of SS, SW, WW, and WS lemmings. Inequality of mean lens weights was evident among the 6-month treatments, but nevertheless, eye lens weight was the best univariate age criterion and performed approximately as well as linear combinations of body or skull measurements selected by stepwise discriminant analysis.

Entrainment of the female hamster to reversed photoperiod: Role of the pineal

The effects of pinealectomy and photoperiod reversal on locomotor activity and behavioral receptivity rhythms were investigated in the hamster. Activity rhythms of the control animals required 7.3 days to reentrain to the reversed photoperiod, while pinealectomized animals showed a precocious reentrainment of running activity. Behavioral receptivity reentrained to the new photoperiod within the first estrous cycle after photoperiod reversal in all animals. Thus there was a dissociation between the rhythms of activity and behavioral receptivity following photoperiod reversal, suggesting that two circadian thythms that are thought to be regulated by a common circadian system can become uncoupled from each other. The estrous cycle rhythms of estradiol, progesterone, FSH and uterine wet weight all appeared to be reentrained by at least the third estrous cycle after photoperiod reversal. This suggests that sex hormone rhythms are more rapidly reentrained than had been previously thought possible from studies on reentrainment of ovulation.

Dissimilar functional effects of pineal stalk and cerebral meningeal interruptions on phase shifts of circadian activity rhythms

Effects of surgical interruptions of the pineal stalk, superior sagittal sinus and cerebral meninges were studied using female rats in individual activity cages and with continuous recording of running activity in a controlled (LD 12:12) and periodically reversed photoperiod. Interruption of the pineal stalk was shown to lead to a reduction in pineal size and a transitory increase in initial rate of phase shift resembling that produced as a continuous effect after complete pinealectomy. Unhealed lesions of the dural membrane bilaterally over the cerebral hemispheres and oriented so as to probably reduce anterior-posterior tension led to an abnormal entrainment endpoint or final attrainment after reversal of photoperiod. The hypothesis is presented that dural transmission to the pineal body of periodic changes in intracranial pressure may contribute to the physiological mechanism for timing of endpoint in the circadian rhythm in running activity during resetting. Evidence relating to this hypothesis is discussed.

Effects of cutting nervi conarii and tentorium cerebelli on pineal composition and activity shifting following reversal of photoperiod

Two series of S 1 strain, littermate, female rats (final number = 35) were studied in individual cages in which running activity was recorded continuously. When 12 1 2 –14 1 2 (series A) or 5 1 2 –6 1 2 weeks old (series B), the transverse sinus was cut bilaterally (= S 1 sham-operation) or the tentorium and the contained nervi conarii and transverse sinus were cut surgically bilaterally about 2 mm from the pineal gland (= NC, nerve-cut operation). Normal levels of time spent in running activity per day were restored in about 10 days in the younger animals (series B) and more gradually in the older ones (series A). Reversals in the timing of the daily artificial photoperiod (LD 12 : 12) 1–5 days after surgery and again 16 days later failed to reveal any significant difference in activity phase-shifting between NC and S animals and between these and normals after postoperative recovery. Autopsy examination was used to exclude from the analyses all animals with brain injury, to confirm by means of histochemistry the reduction in pineal content of sympathetic nerves, and to demonstrate normal pineal volume, histology and cytology in all animals. It is concluded that intact nervi conarii and tentoria are unnecessary for either pineal-based delay in activity phase-shifting or maintenance of normal pineal structure.

Precocious entrainment and associated characteristics of activity patterns following pinalectomy and reversal of photoperiod.

Spontaneous running activity was studied in individual female S1 rats under controlled conditions. Matched siblings, pinealectomized (p), sham-operated (s) and unoperated (u) at 2212–2412 weeks of age, were studied in their responses to four successive reversals (ΔΦ = 12) of the environmental photoperiod (LD 12:12; 200–800:3–15 lux) when they were 2712–3712 weeks old. Initial mean shift in activity starting time following ΔΦ was 6–7 hr ahead in the p animals as compared with the controls, and mean re-entrainment time, according to activity starting time, was 3.03 ± 1.00 days in the p animals as compared to the controls (s −8.60 ± 0.97; u −9.36 ± 1.16; p < 0.01). The post ΔΦ activity of the p animals also differed in showing a sharp differentiation of circadian (pre-lights-off) and photoperiod-dependent (post-lights-off) segments of activity phase (α), and in having an unusually close temporal relation and suggested dependency to the white-lights-off Zeitgeber during the first days following ΔΦ. Possible contributions of age, experience and central mechanisms underlying the pineal effects are discussed.

The role of photoperiod and temperature in the determination of parthenogenetic and sexual forms in the aphid Megoura viciae Buckton—III. Further properties of the maternal switching mechanism in apterous aphids

In the aphid Megoura the maternal photoperiodic process is initiated about 2 days before the birth of the apterous parent, whereas her first embryos are determined as virginoparae or oviparae several days after her birth. The prenatal light régime nevertheless influences the progeny sequence in several ways. First, a reversal from long to short day photostimulation at birth greatly accelerates the response to a second reversal of photoperiod (that is, from short to long days) during the adult life of the same individual. This suggests that the controlling (endocrine?) system is ‘switched on’ by long photoperiods and that full functional activity is hastened by a previous partial activation. Secondly, the effect of a brief long day treatment during the prenatal period is seen in the progeny sequence, provided the subsequent short photoperiod is intrinsically ‘weak’. The ease of reversal of a previous photoperiodic treatment can be used for evaluating the intensity of photoperiodic stimuli. Photoperiods 30 min longer or shorter than the critical length exert weak long and short day effects. Short photoperiods within the 4–14 hr range are ‘strong’, but permanent darkness again exerts a weak short day effect. At 15°C the critical daily photoperiod is approximately 14 hr 55 min. Near this point a difference of only 15 min produces a significant change in the response. Within the 10–20°C range the response is virtually temperature compensated, the only overt effect being that the critical photoperiod shortens by about 15 min/5°C rise of temperature. Above 23°C temperature compensation is progressively lost and virginoparae are produced even under strong short day conditions. It is suggested that the photoperiodic mechanism involves a light receptor and a humoral component, both possibly located in the neuroendocrine system. Under near-neutral photoperiodic conditions the endocrine moiety acts autonomously and ‘drifts’ irregularly between activity and inactivity.