Circannual Changes Research Articles

Circannual Oscillations of Function Compared with Morphometric Changes in the Thyroid Gland of the Wistar-Rat

To investigate biological rhythms of the thyroid gland circannual oscillations of thyroxine (T4), triiodothyronine (T3), and thyrotropin (TSH) were compared in serum samples of untreated young male Wistar-rats with the circannual changes of thyroid weights and with the relative proportion of colloid, epithelium, and interstitium of the thyroids. Animals were kept under standard environmental conditions, however, lighting conditions simulated the natural day-night changes. Thyroid weights, T4, T3, and TSH showed a statistically significant circannual rhythm with maxima in winter and spring and minima in summer and autumn. The same circannual patterns were observed in the proportion of epithelium and interstitium of the thyroids, while the colloid exhibited an inverse circannual pattern. These data were verified by biomathematical methods, like locally adjusted functional approximation, analysis of variance, and Spearman rank correlation. Our results represent an example for the concordance between functional and morphometrical changes in the course of circannual oscillations. Furthermore, these data confirm our earlier results describing higher T4-levels in the winter time (short-day) and lower serum titers in the summer time (long-day).

Melatonin – a pleiotropic molecule involved in pathophysiological processes following organ transplantation

Mammals adjust their physiology in response to seasonal changes to environment (i.e. photoperiod, temperature, food availability). These changes are thought to predominantly occur for the conservation of energy during winter, by pervasive changes such as the inhibition of reproduction. Previous reports have suggested that circannual changes also occur to the immune system. In mammals, this chronological effect may be dependent on photoperiod, and evidence exists to suggest that there is a great deal of immune variation in response to light, or circadian rhythm. This is a clinically relevant, yet under-reported area of human transplantation. The aim of this review is to discuss immune variation, with specific emphasis on melatonin secretion, in the context of organ rejection, infection, neoplasia formation, and immunosuppression.

Circannual changes in the expression of vascular endothelial growth factor in the testis of roe deer ( Capreolus capreolus)

Adult roe deer males show seasonal cycles of testicular growth and involution. The exact timing of these cycles requires endocrine regulation and local testicular control by autocrine/paracrine factors. Recent findings suggest that the vascular endothelial growth factor (VEGF) might have effects on both vascular and germinative cells in testis. Thus, we studied the expression pattern of vascular endothelial growth factor (VEGF) in roe deer testis using quantitative RT-PCR. The strength of VEGF mRNA expression depended on season. It reached its highest level at the peak of spermatogenesis during the pre-rutting period and had its nadir at the end of the rut when involution already began. The results suggested that VEGF may directly affect the regulation of spermatogenesis but may not be involved predominantly in testicular microvasculature as initially expected.

Reproductive patterns of stray male dogs in the tropics

Two studies were performed to determine annual reproductive patterns in stray male dogs in the tropics. In Study 1, four dogs housed individually outdoors were monitored once monthly for 12 months, including collection and assessment of semen, measurements of scrotal width, and determination of serum testosterone and prolactin concentrations. In Study 2 (conducted concurrently), a single blood sample (for serum testosterone concentration) was collected from 220 clinically healthy dogs, and after euthanasia, scrotal width and morphology of epididymal sperm were determined. The year was divided into three seasons: warm–dry (March to June); warm–humid (July to October) and fresh–humid (November to February). In Study 1, scrotal width, ejaculate volume, sperm count and motility were significantly lower during the fresh–humid season and sperm midpiece abnormalities were significantly more common during the warm–humid and fresh–humid seasons. Serum testosterone concentrations remained constant during the year. Prolactin concentrations did not differ significantly among seasons, but had a well-defined increase from the beginning of March to the end of August. In Study 2, sperm morphology was similar to in Study 1 and serum testosterone concentrations varied nonsignificantly during the year. Environmental factors, e.g. daylength may have influenced circannual changes in prolactin secretion. Seasonal variations in some reproductive tract and seminal traits were significant but of small magnitude and the percentage of morphologically normal sperm did not vary significantly among seasons. In conclusion, healthy male dogs constantly produced sperm and were apparently fertile throughout the year.

Adaptive reactions of the endocrine system of children living under conditions of contrasting photoperiods

Age-related changes in the levels of pituitary, thyroid, and sex hormones and their dependence on the day length were studied in 242 healthy 10-to 16-year-old boys born and permanently living in the southern part of Arkhangel’sk oblast. It was found that the serum levels of thyroid hormones, gonadotropins, and sex steroids underwent circannual changes. The minimum concentrations of thyroxine, testosterone, and estradiol and the maximum concentrations of triiodothyronine, lutcinizing and follicle-stimulating hormones, and progesterone were associated with the shortest days. In contrast, the longest days were associated with the maximum concentrations of thyroxine, testosterone, and estradiol and the minimum concentrations of triiodothyronine, luteinizing and follicle-stimulating hormones, and progesterone. A factor dependence of the thyroxine, triiodothyronine, testosterone, estradiol, and prolactin concentrations on the day length was found in the group examined. This dependence was more pronounced during the second half of adolescence.

Seasonal Changes of Neutral α‐Glucosidase Activity in Human Semen

Although there are contradictory reports, the biochemical evaluation of the seminal activity of neutral alpha-glucosidase (NAG) has repeatedly been described as an important parameter to test epididymal patency and is recommended by the WHO. Because, for a number of diagnostic parameters, seasonal variations have been described even in the human, it was the aim of this study to investigate possible circannual changes of NAG. This is an important aspect of andrological diagnosis, as seasonal changes of specific diagnostic parameters might have an impact on the accuracy and predictive power of these parameters, which in turn might have an effect on the therapeutic concept for the patients. In a total of 473 patients, sperm concentration, volume of the ejaculate, total motility, progressive motility, pH value, number of peroxidase-positive cells, concentration of fructose, and NAG as functional markers of the seminal vesicles and the epididymis, respectively, were analyzed according to standard procedures. Seminal activity of NAG was significantly correlated with the sperm concentration (P < .0001), ejaculate volume (P < .0001), and the pH (P = .0025). Moreover, significant (P = .0008) seasonal changes in the activity of seminal NAG with the maximum in spring (76.87 mU/ejaculate) and the minimum in autumn (58.55 mU/ejaculate) were found. The incidence of low-ranged activity of the enzyme was 9.2% in spring, while it was 20.3% in autumn. Thus, our data clearly demonstrate circannual changes of the seminal activity of neutral alpha-glucosidase. This in turn has clinical impact as the predictive power of the test system changes throughout the year.

Autonomic nerves terminating on microvessels in the pineal organs of various submammalian vertebrates

In earlier works we have found that in the mammalian pineal organ, a part of autonomic nerves--generally thought to mediate light information from the retina--form vasomotor endings on smooth muscle cells of vessels. We supposed that they serve the vascular support for circadian and circannual periodic changes in the metabolic activity of the pineal tissue. In the present work, we investigated whether peripheral nerves present in the photoreceptive pineal organs of submammalians form similar terminals on microvessels. In the cyclostome, fish, amphibian, reptile and bird species investigated, autonomic nerves accompany vessels entering the arachnoidal capsule and interfollicular meningeal septa of the pineal organ. The autonomic nerves do not enter the pineal tissue proper but remain in the perivasal meningeal septa isolated by basal lamina. They are composed of unmyelinated and myelinated fibers and form terminals around arterioles, veins and capillaries. The terminals contain synaptic and granular vesicles. Comparing various vertebrates, more perivasal terminals were found in reptiles and birds than in the cyclostome, fish and amphibian pineal organs. Earlier, autonomic nerves of the pineal organs were predominantly investigated in connection with the innervation of pineal tissue. The perivasal terminals found in various submammalians show that a part of the pineal autonomic fibers are vasomotoric in nature, but the vasosensor function of some fibers cannot be excluded. We suppose that the vasomotor regulation of the pineal microvessels in the photosensory submamalian pineal--like in mammals--may serve the vascular support for circadian and circannual periodic changes in the metabolic activity of the pineal tissue. The higher number of perivasal terminals in reptiles and birds may correspond to the higher metabolic activity of the tissues in more differentiated species.

Autonomic nerves terminating on smooth muscle cells of vessels in the pineal organ of various mammals.

The significance of autonomic nerves reaching the pincal organ was already investigated in connection to the innervation of pinealocytes and mediating light information from the retina for periodic melatonin secretion. In earlier works we found that some autonomic nerve fibers are not secretomotor but terminate on arteriolar smooth muscle cells in the pineal organ of the mink (Mustela vison). Studying in serial sections the pineal organ of the mink and 15 other mammalian species in the present work, we investigated whether similar axons of vasomotor-type are generally present in the wall of pineal vessels, further, whether they reach the organ via the conarian nerves or via periarterial plexuses. In all species investigated, axons of perivasal nerve bundles were found to form terminal enlargements on the smooth muscle layer of pineal arterioles. The neuromuscular endings contain several synaptic and some granular vesicles. Axon terminals are also present around pineal veins. In serial sections, we found that the so-called conarian autonomic nerves reach the pineal organ alongside pineal veins draining into the great internal cerebral vein. Similar nerves present near arteries of the arachnoid enter the pineal meningeal capsule and septa by arterioles, both perivenous and periarterial nerves form terminals of vasomotor-type. The arteriomotor and venomotor regulation of the tone of the vessels of the pineal organ may serve the vascular support for circadian and circannual periodic changes in metabolic activity of the pineal tissue.

Seasonal timing of sperm production in roe deer: interrelationship among changes in ejaculate parameters, morphology and function of testis and accessory glands

Roe deer are seasonal breeders with a short rutting season from mid-July to mid-August. The seasonality of reproductive activity in males is associated with cyclic changes between growth and involution of both testes and the accessory sex glands. This study characterizes morphological and functional parameters of these organs prior to, during and after breeding season in live adult roe deer bucks. Size and morphology of the reproductive tract was monitored monthly by transcutaneous (testes, epididymis) and transrectal (accessory glands) ultrasonography. Semen was collected by electroejaculation. Concentration, motility and morphological integrity of spermatozoa as well as the content of proteins and testosterone in semen plasma were evaluated. Proportions of haploid, diploid and tetraploid cells were estimated by flow cytometry in testicular tissue biopsies. Serum testosterone was measured by enzyme immunoassay. Most parts of the male reproductive tract showed distinct circannual changes in size and texture. These changes were most pronounced in the testes, seminal vesicles, and prostate. All reproductive organs were highly developed during the rut only. The volume of ejaculates, total sperm number and percentages of motile and intact spermatozoa also showed a maximum during this period and corresponded with high proportions of haploid cells in the testis. The highest percentages of tetraploid cells were found in the prerutting period. The production of motile and intact spermatozoa correlated with both the protein content of semen plasma and the concentration of testosterone in semen plasma and blood serum. These results suggest the importance of combined actions of the testes and accessory sex glands and the crucial role of testosterone in facilitating the optimal timing of intensified semen production to ensure sufficient numbers of normal spermatozoa in seasonal breeders.

Seasonal Variation in Bone Turnover: A Multifactorial Dependent Event

We would like to thank Dr. Zittermann for his interesting comments on our study on circannual rhythms of calcitropic hormones and biochemical markers of bone turnover.1 In his letter, Dr. Zittermann states that in premenopausal women, most of the observed seasonal fluctuations in bone turnover may in fact be caused by a dietary calcium deficit. Although we are unable to provide quantitative data on dietary calcium intake, we do have sufficient information on the participants' nutritional habits to state that during the entire study, the individual calcium intake was within the expected range of a mid-European population (i.e., approximately 800 mg calcium/day). This level is well below the recommended daily intake of 1000 mg calcium2 and may be considered insufficient to maintain a positive calcium balance. Because of the lower vitamin D levels during winter time, this calcium deficit may become even more aggravated, which may cause the observed season-dependent increase in bone resorption. Dr. Zittermann's own study3 seems to support the notion that under calcium replete conditions, variations in calcitropic hormones do not affect bone turnover. One should note, however, that this study was performed in students of nutritional science who actively achieved an optimal calcium intake. In contrast, the purpose of our study was to show seasonal changes of bone turnover in a representative population under “real-life” conditions without interference from any potential physiologic regulator. In such a population, the observed circannual rhythm of bone turnover is very likely to depend on a number of variables that have not been completely identified. However, whereas calcium deficiency may be one of the more important factors, it is very unlikely that seasonal changes in bone turnover are monocausally linked to calcium supplies. Many other factors shown to be associated with unfavorable outdoor conditions, such as reduced physical activity, increased alcohol intake,4 or even increased time spent in front of the television5 may, at least in part, explain the observed phenomenon independent of the actual calcium resource. Data from our study indicate that these factors interrelate and interact with each other but presenting or discussing all of these would be far beyond the scope of our paper. However, the net effect of all these factors seems obvious and was clearly demonstrated: in a western European population with all of its inherent anthropometric, nutritional, and lifestyle characteristics, bone turnover is subject to seasonal changes which, over the years, may contribute to bone loss. In summary, we certainly agree with Dr. Zittermann that in western European populations, nutritional calcium deficiency may be one of the mechanisms underlying the observed circannual changes in bone turnover. We believe, however, that our findings are complex and multifactorial in nature and have therefore initiated prospective investigations that will allow us to dissect some of these variables in more detail.

Circannual changes in the secondary sexual adornments of semifree-ranging male and female mandrills (Mandrillus sphinx).

Male mandrills (Mandrillus sphinx) have spectacular secondary sexual adornments. These include red and blue sexual skin on the face, rump, and genitalia; a sternal scent-marking gland; and a "fatted" rump. Mandrills are seasonal breeders, and in other seasonally-breeding primate species members of both sexes may show increased expression of secondary sexual characteristics during the mating season. We examined changes in male secondary sexual adornments and testosterone levels, in relation to seasonal changes in the female reproductive cycle and sexual skin morphology, in two semifree-ranging mandrill groups. Females showed circannual changes in sexual skin tumescence, and periods of tumescence peaked from May-July in a long-established group. However, formation of a second, smaller group, two years previous to commencement of the study, disrupted the seasonal pattern of sexual skin tumescence and births. As the groups occupied adjacent enclosures, it appears that social factors, as well as physical environment, affected the seasonal patterning of reproduction in females. Male mandrills, by contrast, did not exhibit marked circannual changes in secondary sexual traits. Although adult male testicular volume and circulating testosterone levels increased significantly during the mating season, sexual skin coloration and rump "fattedness" showed no consistent changes with season. There was some evidence to suggest that maturing males (ages 5-8 yr) showed increased development of red sexual skin during mating periods, but once males had fully developed secondary sexual adornments, they remained stable throughout the year. The possible reasons for this are discussed in relation to intermale competition and social organization in mandrills.

Environmental reprogramming of the expression of protein kinase CK2beta subunit in fish.

The dramatic segregation of the nucleolar components in winter-acclimatized carp is the most striking cellular-phenotypical feature observed during the seasonal adaptation of this fish toward the circannual changes in its habitat. Our studies also show that the carp habitat temperature and photoperiod winter conditions provoke a remarkable reduction of both rRNA transcription and the processing of their precursors. To gain knowledge on the mechanisms involved in the regulation of nucleolar activity during the seasonal adaptation process, we studied the behavior of some genes, specifically snoRNA U3 and protein kinase CK2. Consistent with the reduction in the synthesis and processing of pre-rRNA observed during the cold season, the level of CK2beta expression decreases in winter when compared to that attained in summer. Similarly, in winter, liver and kidney cells contain lower levels of CK2beta subunit protein compared to summer. CK2 is associated with or modifies different factors and enzymes involved in the nucleolar activity; therefore, its higher or lower content could be part of the molecular mechanisms underlying the nucleolar seasonal changes that occur during the compensatory acclimatization process.

Detection of growth factors in the testis of roe deer (Capreolus capreolus)

Roe deer is a seasonal breeder characterised by a short rutting season in summer. Mature males show synchronised cycles of testicular involution and recrudescence. Therefore, this species is a valuable model to study seasonal regulation of spermatogenesis in ruminants. It is hypothesised that a time-dependent production of testicular growth factors is required to regulate seasonal changes in testis growth and spermatogenesis. To identify potential candidates, total RNA from roe deer testis tissue was extracted at three different seasonal periods (April, August, December), and using RT-PCR the presence of several growth factors (aFGF, bFGF, IGF-I, IGF-II, TGF-α, TGF-β1, TGF-β3 and two isoforms of VEGF) was detected. Sequencing of the growth factor PCR fragments revealed a high sequence homology between cattle and roe deer. To further explore the expression patterns of the identified growth factors in roe deer their expression levels were standardised using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression. The study demonstrates the expression of several growth factors in roe deer testis and supports the assumption of their seasonally diverse regulation. These results provide the basis to investigate the role of growth factors in the regulation of circannual changes of testicular activity.

Temperature-independence of circannual variations in circadian rhythms of golden-mantled ground squirrels.

In golden-mantled ground squirrels, phase angles of entrainment of circadian locomotor activity to a fixed light-dark cycle differ markedly between subjective summer and winter. A change in ambient temperature affects entrainment only during subjective winter when it also produces pronounced effects on body temperature (Tb). It was previously proposed that variations in Tb are causally related to the circannual rhythm in circadian entrainment. To test this hypothesis, wheel-running activity and Tb were monitored for 12 to 14 months in castrated male ground squirrels housed in a 14:10 LD photocycle at 21 degrees C. Animals were treated with testosterone implants that eliminated hibernation and prevented the marked winter decline in Tb; these squirrels manifested circannual changes in circadian entrainment indistinguishable from those of untreated animals. Both groups exhibited pronounced changes in phase angle and alpha of circadian wheel-running and Tb rhythms. Seasonal variation in Tb is not necessary for circannual changes in circadian organization of golden-mantled ground squirrels.

Endocrine-immune interaction: alteractions in immune function resulting from neonatal treatment with a GnRH antagonist and seasonality in male primates.

The effect of neonatal gonadotropin releasing hormone (GnRH) antagonist (Ant) treatment and seasonality on immune system development and function was investigated in male primates. Neonatal male rhesus monkeys and marmosets were treated with Ant, and its effect on immune system morphology, circulating lymphocyte subsets, and cell- and humorally-mediated immune responses was assessed during development. In adult rhesus monkeys, we correlated seasonal changes in immune function with circannual fluctuations in immunoactive hormones. In neonatal marmosets, Ant reduced the number of B cells and T cells in the thymic medulla and T cells in the periarterial lymphatic sheaths (PALS) of the spleen. Ant also altered the development of, but did not permanently impair, the proliferative index (PI) of blood lymphocytes to mitogens. In vitro treatment of control lymphocytes with GnRH analogues altered their response to these proliferative agents. In neonatal rhesus monkeys, Ant treatment increased the frequency of clinical problems, lowered circulating levels of lymphocytes, total T cells, CD8+ T cells and B cells, and altered the PI of lymphocytes to mitogens. As adults, the cell- and humorally-mediated immune responses remained impaired. We also documented seasonal fluctuations in the prevalence of diseases, circulating immune cells and immune function in rhesus monkeys. The number of cases of campylobacteriosis and shigellosis was lowest in the winter and highest in the spring. Circulating numbers of white blood cells (WBC) and neutrophils and the PI of lymphocytes to mitogens were higher in the winter than in the summer. Natural killer cell activity also varied with season. Cortisol and leptin secretion exhibited circannual rhythms, rising in concert with decreasing photoperiod and increasing testicular activity in the fall. Conversely, prolactin levels declined with decreasing photoperiod and then rose in the spring. Neonatal exposure of male primates to Ant appears to alter early postnatal programming of immune function. In the rhesus monkey, immune function shows seasonal fluctuations that may be driven by circannual changes in the secretion of immunoactive hormones.

Seasonal Variations in Cytokine Expression and Cell-Mediated Immunity in Male Rhesus Monkeys

Our objectives in this study were to examine seasonal changes in immune responses including cytokine profiles of male rhesus monkeys housed under natural lighting conditions. We also monitored circannual changes in the secretion of several immunomodulatory hormones as potential mediators of the seasonal shifts in immune status. Retrospectively, the medical records of a large group of rhesus monkeys were examined to determine whether a common disease (campylobacteriosis) in this species shows a seasonal pattern of prevalence. Results of the study showed that there was a seasonal shift in the frequency of cells expressing TH1 cytokines (interleukin-2 and interferon-γ) versus the TH2 prototype cytokine (interleukin-4) by peripheral blood mononuclear cells (PBMC) collected during the winter and summer. The frequency of TH1-type cytokine synthesis in the summer was markedly greater than in the winter whereas TH2-type cytokine expression did not vary between the two seasons. The proliferative response of PBMC to mitogens and natural killer cell activity of PBMC also varied with the season. Several hormones (testosterone, leptin, and prolactin) that modulate immune function exhibited circannual patterns of secretion. The prevalence of Campylobacter infections was higher in the spring than during the summer, fall, or winter. The data suggest that seasonal fluctuations in immune system status may alter the ability of primates to successfully respond to pathogens, and this may be related to circannual patterns of secretion of immunomodulatory hormones.

Circannual changes in free thyroxine, prolactin, testes, and relative food intake in woodchucks, Marmota monax.

Woodchucks (n = 12-14/group) with circannual cycles entrained to northern versus southern hemisphere photoperiods were assessed monthly for 16 mo. Changes in serum total triiodothyronine (TT(3)), free thyroxine (T(4)), total thyroxine (TT(4)), and prolactin were determined in a subset of five animals per group. Metabolic hormone results were examined in relation to changes in body weight, food intake, and serum testosterone (n = 12-14/group). Seasonal changes in each parameter were similar in both groups as were nadir and peak TT(3) (162 +/- 6 and 392 +/- 12 ng/ml, respectively), free T(4) (19 +/- 2 and 86 +/- 7 ng/ml, repectively), TT(4) (3.2 +/- 0.2 and 8.0 +/- 0.5 ng/ml, respectively), and prolactin (0.6 +/- 0.1 and 14 +/- 2 ng/ml, respectively). In late winter and early spring, simultaneous increases in both free T(4) and prolactin were associated with 1) a large increase in food intake, 2) a decline in body weight to nadir values, 3) a corresponding negative energy balance, 4) a peak and decline in serum testosterone, and 5) a modest increase in TT(4) and large decline in serum TT(3). Low levels of free T(4) and prolactin were observed in summer when energy balance was very positive. The results demonstrate that, in woodchucks, serum T(4) and prolactin undergo seasonal changes during annual cycles entrained by photoperiod. The results suggest that changes in free T(4), acting as a calorigenic hormone, and changes in both T(4) and prolactin, potentially acting as lipolytic, antilipogenic, and/or orectic hormones, are likely involved in the mechanisms underlying the corresponding seasonal changes in food intake, fat metabolism, and energy balance in this species. Their potential roles in gonadal regression and recrudescence are less clear.

Influences of biological rhythms on the effects of psychotropic drugs.

The efficacy of psychotropic drugs varies depending on the time of administration. This phenomenon is observed with antipsychotics, antidepressants, mood stabilizers, benzodiazepines, barbiturates, and psychostimulants. The presence or absence of this phenomenon and the rhythm phase in the efficacy of each drug varies depending on the drug, dose, parameter measured, animal species, and strain. A recent study demonstrating circannual changes in the phases of circadian rhythm of drug efficacy suggests that discrepancies between studies may be considerably explained by the presence of a circannual rhythm. The rhythms in drug effects are suggested not to be due to rhythmic changes in the pharmacokinetics of the drugs but rather to an endogenous rhythm in drug susceptibility resulting from a circadian rhythm in the intracerebral neurotransmission system. The presence of this phenomenon and its law have been demonstrated to a considerable extent in animals, but corresponding clinical reports in humans remain insufficient despite its clinical importance. Further study in humans is certainly warranted.

Circannual variations of lizard circadian activity rhythms in constant darkness

The daily pattern of locomotor activity of Podarcis sicula in the field changes from unimodal in spring to bimodal in summer, becoming unimodal again in autumn. Short-term experiments in which P. sicula collected in different months were tested under constant conditions immediately after capture showed that the activity pattern typical of each season is retained in the lizard circadian locomotor rhythm. In constant conditions, the bimodal pattern is associated with a short free-running period (τ) of the circadian locomotor rhythm and a long circadian activity (α), while the unimodal pattern is associated with a long τ and short α. To test whether seasonal changes in circadian locomotor rhythms are driven by a circannual clock, we recorded locomotor activity of lizards over 12–15 months in constant temperature and darkness. The present results demonstrate, for the first time in a vertebrate, the existence of circannual changes in constant darkness of both τ and α. In most lizards, the longest τ along its circannual cycle is associated with a short α, and the shortest τ in the same cycle with a long α, so that the pattern of mutual association between τ and α is the same as in short-term experiments. Most lizards, however, stayed unimodal all the time. This shows that changes in activity pattern from unimodal to bimodal (and vice versa) are induced by seasonal changes in environmental factors, instead of being incorporated into a circannual rhythm. Circannual changes in τ and α of locomotor rhythms may adaptively predispose the circadian system of P. sicula to a change in activity pattern as soon as seasonal changes in the environment demand it.

Comparative histology of pineal calcification.

The pineal organ (pineal gland, epiphysis cerebri) contains several calcified concretions called "brain sand" or acervuli (corpora arenacea). These concretions are conspicuous with imaging techniques and provide a useful landmark for orientation in the diagnosis of intracranial diseases. Predominantly composed of calcium and magnesium salts, corpora arenacea are numerous in old patients. In smaller number they can be present in children as well. The degree of calcification was associated to various diseases. However, the presence of calcified concretions seems not to reflect a specific pathological state. Corpora arenacea occur not only in the actual pineal tissue but also in the leptomeninges, in the habenular commissure and in the choroid plexus. Studies with the potassium pyroantimonate (PPA) method on the ultrastructural localization of free calcium ions in the human pineal, revealed the presence of calcium alongside the cell membranes, a finding that underlines the importance of membrane functions in the production of calcium deposits. Intrapineal corpora arenacea are characterized by a surface with globular structures. Meningeal acervuli that are present in the arachnoid cover of the organ, differ in structure from intrapineal ones and show a prominent concentric lamination of alternating dark and light lines. The electron-lucent lines contain more calcium than the dark ones. There is a correlation between the age of the subject and the number of layers in the largest acervuli. This suggests that the formation of these layers is connected to circannual changes in the calcium level of the organ. The histological organization of the human pineal is basically the same as that of mammalian experimental animals. Pineal concretions present in mammalian animal species are mainly of the meningeal type. Meningeal cells around acervuli contain active cytoplasmic organelles and exhibit alkaline phosphatase reaction in the rat and mink, an indication of a presumable osteoblast-like activity. Using Kossa's method for the staining of calcium deposits, a higher calcium concentration was detected in the rat pineal than in the surrounding brain tissue. Since in parathyroidectomised rats calcified deposits are larger and more numerous than in controls, the regulation of the production of acervuli by the parathyroid gland has also been postulated. In most of submammalian species, the pineal organs (pineal-, parapineal organ, frontal organ, parietal eye) are photoreceptive and organized similarly to the retina. Acervuli were found in the pineal of some birds. The pineal organs of lower vertebrates (fish, amphibians, reptiles) exhibit a high calcium content by ultrastructural calcium histochemistry (PPA-method). However, concrements are not formed. The accumulation of Ca2+ seems to depend on the receptor function of the organ. Comparing pineal and retinal photoreceptors in the frog, the photoreceptor outer segments of pinealocytes as well as retinal cones and rods show a large amount of Capyroantimonate deposits. In dark adapted animals calcium ions are present in both sides of the photoreceptor membranes of the outer segment, whereas calcium is shifted extra-cellularly following light adaptation. Overviewing the data available about the pineal calcification, we can conclude that a multifactorial mechanism may be responsible for the calcification. The pineal of higher vertebrates is not just a simple endocrine gland, rather, its histological organization resembles a folded retina having both hormonal and neural efferentation. Mammalian pinealocytes preserve several characteristics of submammalian receptor cells and accumulate free Ca2+ on their membranes (1). In the thin walled retina and in the similarly organized pineal of submammalian species, the diffusion of extracellular calcium is probably easy and there is a lesser tendency to form concrements. (ABSTRACT TRUNCATED)