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PubMed1987

Seasonal variations in plasma phosphorus levels of transhumant sheep in Kordofan, Sudan.

Plasma phosphorus levels were evaluated for one hundred adult breeding ewes from transhumant producer flocks during the late rainy season (September 1984/1985), the mid-dry season (February 1985) and the late-dry season (May 1985). The percentage of non-pregnant/non-lactating ewes critically deficient in phosphorus increased from 9% in the rainy season to 56% in the late-dry season. In September 35% of pregnant ewes were critically deficient in phosphorus. During peak lactation (February) 87% of lactating ewes were critically deficient in phosphorus and 84% remained critically deficient until the start of the rainy season approximately 20 weeks postlambing. The low phosphorus content of grazing rations, which varied from 0.18% in the rainy season to 0.09% in the dry season, and low forage availability, which was especially acute during the late-dry season, appeared to be the most important factors limiting phosphorus intake.

Animals↗
PubMed2004

Eotaxin-1 (CCL11) up-regulation in tears during seasonal allergic conjunctivitis.

PURPOSE: To compare in-season eotaxin-1 levels in tears of patients suffering from seasonal allergic conjunctivitis (SAC) with (1) tears of normal subjects and (2) tears of SAC patients out of season. METHODS: Tears of 11 SAC patients and six control volunteers were collected during the pollen season. Tears of five SAC patients showing a strong sensitivity to grass pollen (skin-prick tests and specific serum IgE) were collected both in season and out of season. ELISA measured eotaxin-1 level. RESULTS: Eotaxin-1 concentration in tears of SAC patients [2,100+/-503 (SEM) pg/ml] and normal subjects (1,193+/-176 pg/ml) were significantly different (P=0.0049). Regarding allergic patients, the clinical score (sum of five allergic criteria) was significantly different in season and out of season (P=0.0043) as was also the case with eotaxin-1 concentration (P=0.024). CONCLUSIONS: The eotaxin-1 concentration in tears of patients showing hay fever could confirm a diagnosis of seasonal ocular allergy.

Adult↗
PubMed2006

Apoptosis is not the cause of seasonal testicular involution in roe deer.

Apoptosis is involved in the regulation of spermatogenesis. The involution of testes in seasonal breeders might be expected to involve enhanced apoptotic cell elimination. We have compared seasonally changing testicular apoptosis in roe deer with that in non-seasonally breeding cattle. Apoptotic cells were detected as TUNEL-positive cells by both flow-cytometric analysis and in situ localisation of fragmented DNA in tissue sections. Apoptosis-induced DNA fragments were also assessed by enzyme-linked immunosorbent assay (ELISA) in homogenised testicular parenchyma. As expected, the testis mass and the percentage of haploid cells in roe deer showed a seasonal pattern with a significant maximum during the rut (August), whereas no annual variation of these parameters was found in bulls. All three methods for determining apoptosis showed similar findings. Roe deer exhibited significant seasonal fluctuation of total apoptotic activity (ELISA, apoptotic cells per tubule cross section) with a maximum during the breeding season. However, the seasonal differences in the number of apoptotic cells corresponded to the variable total numbers of spermatogonia and spermatocytes per tubule cross section. Thus, the percentages of TUNEL-positive cells related to the combined number of both germ cell types showed no seasonal variance, as confirmed by percentages of apoptotic cells analysed flow-cytometrically. The maximum level of apoptosis during the rut in roe deer was similar to the values obtained during the invariably high spermatogenic activity in cattle. These results suggest that, in roe deer, apoptosis is not the cause of the seasonal involution of testes.

Animals↗
PubMed2003

Seasonal changes in pollen-packaging schedules in the protandrous plant Chamerion angustifolium.

The rate at which pollen is presented varies widely both among and within species of flowering plants. Although several studies have tried to explain between-species variation in this trait, few explanations exist for the variation that exists among individuals of the same species. I used protandrous fireweed, Chamerion angustifolium (Onagraceae), to examine seasonal changes in pollinator visitation, population sex ratio, and pollen presentation schedules. Most studies that make predictions about optimal pollen presentation assume conditions are constant throughout the flowering season. However, data presented here show that pollen presentation schedules vary seasonally: in early season flowers, anthers dehisce over a number of days, while late season flowers present all anthers simultaneously. I show that pollinator visitation rates to individual plants are higher but more variable early in the season than late in the season. Furthermore, per-male availability of female-phase flowers increases over the course of the flowering season in this population. I suggest that seasonal differences in the variability of pollinator visitation and the availability of female flowers has played an important role in selection for pollen presentation schedules.

Animals↗
PubMed2003

Water resource partitioning, stem xylem hydraulic properties, and plant water use strategies in a seasonally dry riparian tropical rainforest.

This study investigated seasonal variation in the origin of water used by plants in a riparian tropical rainforest community and explored linkages between plant water source, plant xylem hydraulic conductivity and response to the onset of dry conditions. The study focused on five co-dominant canopy species, comprising three tree species ( Doryphora aromatica, Argyrodendron trifoliolatum, Castanospora alphandii) and two climbing palms ( Calamus australis and Calamus caryotoides). Stable isotope ratios of oxygen in water (delta(18)O) from soil, groundwater, stream water and plant xylem measured in the wet season and the subsequent dry season revealed water resource partitioning between species in the dry season. Measurement of stem-area-specific hydraulic conductivity ( K(S)) in the wet season and subsequent dry season showed a significant dry-season loss of K(S) in three of the five species ( Castanospora alphandii, Calamus australis and C. caryotoides) and a decrease in mean K(S) for all species. This loss of hydraulic conductivity was positively correlated with the difference between wet-season and dry-season midday leaf water potentials and with leaf carbon isotope discrimination, indicating that plants that were less susceptible to loss of conductivity had greater control over transpiration rate and were more water-use efficient.

Adaptation, Physiological↗
PubMed2006

Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands.

The season in which a fire occurs may regulate plant seedling recruitment because of: (1) the interaction of season and intensity of fire and the temperature requirements for seed release, germination and growth; (2) post-fire rainfall and temperature patterns affecting germination; (3) the interaction of post-fire germination conditions and competition from surrounding vegetation; and (4) the interaction of post-fire germination conditions and seed predators and/or seedling herbivores. This study examined the effects of different fire intensities and fire seasons on the emergence and survival of shrubs representing a range of fire response syndromes from a summer rainfall cool climate region. Replicated experimental burns were conducted in two seasons (spring and autumn) in 2 consecutive years and fuel loads were increased to examine the effects of fire intensity (low intensity and moderate intensity). Post-fire watering treatments partitioned the effects of seasonal temperature from soil moisture. Higher intensity fires resulted in enhanced seedling emergence for hard-seeded species but rarely influenced survival. Spring fires enhanced seedling emergence across all functional groups. Reduced autumn recruitment was related to seasonal temperature inhibiting germination rather than a lack of soil moisture or competition. In Mediterranean-type climate regions, seedling emergence has been related to post-fire rainfall and exposure of seeds to seed predators. We think a similar model may operate in temperate summer rainfall regions where cold-induced dormancy over winter exposes seeds to predators for a longer time and subsequently results in recruitment failure. Our results support the theory that the effect of fire season is more predictable where there are strong seasonal patterns in climate. In this study seasonal temperature rather than rainfall appears to be more influential.

Climate↗
PubMed2005

Seasonal variations of organic-carbon and nutrient transport through a tropical estuary (Tsengwen) in southwestern Taiwan.

This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropical river (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highly variable temporally, due primarily to temporal variations in river discharge and suspended load. The sediment yield of the drainage basin during the study period (1995-1996, 616 tonne km(-2) year(-1)) was ca. 15 times lower than that of the long-term (1960-1998) average (9379 tonne km2 year(-1)), resulting mainly from the damming effect and historically low record of river water discharge (5.02 m3 s(-1)) in 1995. The flushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wet season and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary. Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOC fluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceeded DOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time was insignificant and may contribute little amount of CO2 to the estuary during the wet season and flood period. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (or additions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonally variable, and these processes must be considered for net flux estimates from the river to the sea. As a result, nonconservative fluxes of dissolved inorganic phosphorus (deltaDIP) from the estuary are -0.002, -0.09 and -0.59 mmol m(-2) day(-1), respectively, for dry season, wet season and flood period, indicating internal sinks of DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, deltaDIP in the flood period may be derived largely from geochemical processes rather than biological removal, and this deltaDIP should not be included in an annual estimate of carbon budget. The internal sink of phosphorus corresponds to a net organic carbon production (photosynthesis-respiration, p-r) during dry (0.21 mmol m(-2) day(-1)) and wet (9.5 mmol m(-2) day(-1)) seasons. The magnitude of net production (p-r) is 1.5 mol m(-2) year(-1), indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss (nitrogen fixation-denitrification < 0) in 1995, but the magnitude is small (-0.17 mol m(-2) year(-1)).

Animals↗
PubMed2005

Morphometric studies on the testis of Korean ring-necked pheasant (Phasianus colchicus karpowi) during the breeding and non-breeding seasons.

The purpose of this study was to obtain detailed quantitative information on all cell types in the testis interstitium of Korean ring-necked pheasants and to combine these data with changes in the steroidogenic function of the testis during the breeding and non-breeding seasons. For animals collected during the breeding season, their testis weights, sperm production, serum testosterone levels and leuteinizing hormone (LH)-stimulated testosterone secretion were significantly (p < 0.01) increased compared to the non-breeding season. Testes of the pheasants during the non-breeding season displayed a 98% reduction in testis volume that was associated with a decrease in the absolute volume of seminiferous tubules (98% reduction), tubular lumen (100%), interstitium (90%), blood vessels (84%), lymphatic spaces (97%), Leydig cells (79%), mesenchymal cells (51%) and myoid cells (61%) compared to the breeding season. The numbers of Leydig cells, mesenchymal cells and myoid cells per testis in the breeding season were much higher than in the non-breeding season. Although the mean volume of a Leydig cell was 74% lower in the non-breeding season, the mean volumes of myoid and mesenchymal cells remained unchanged. These results demonstrate that there are striking differences in the testicular structure of the Korean ring-necked pheasant during the breeding and non-breeding seasons. Every structural parameter of the Leydig cell was positively correlated with both testosterone serum levels and LH-stimulated testosterone secretion. The correlation of changes in hormonal status with the morphometric alterations of Leydig cells suggests that the Korean-ring necked pheasant may be used as a model to study structure-function relationships in the avian testis.

Animals↗
PubMed1988

Testosterone control of territorial behavior: tonic-release implants fully restore seasonal and short-term aggressive responses in free-living castrated lizards.

Two aspects of hormonal control of aggressive territorial behavior in male mountain spiny lizards Sceloporus jarrovi were studied. First, testosterone (T) implants were given to free-living castrated males during the breeding season. These implants fully restored breeding season levels of aggressive and sexual behavior. Earlier studies showed that identical implants given to free-living males during the nonbreeding season did not induce full breeding season levels of aggression. The full effectiveness of these implants during the breeding season indicates that the lack of effectiveness in the nonbreeding season was not due (1) to the need to replace additional gonadal factors or (2) to ineffectiveness of tonic delivery by the implants. It is more likely that males are less sensitive to T during the nonbreeding season or that other cues present in the breeding season environment synergize with T to induce full levels of aggression. Thus, seasonal changes in aggressive behavior in male S. jarrovi cannot be explained simply as a direct response to changes in circulating levels of T; other environmental factors play a necessary role as well. In the second phase of the study, changes in aggressive behavior of free-living T-implanted castrates were monitored following staged encounters with other males. Despite their inability to alter secretion rates of T, the T-implanted castrates still showed a rapid postencounter increase in aggressive displays that was identical to controls. Previous results showed that this dramatic postencounter increase in aggressive behavior is not accompanied by simultaneous changes in circulating T. Together, these results now allow the hypothesis that this rapid behavioral change in aggressive behavior is caused by simultaneous changes in circulating T levels to be confidently rejected.

Aggression↗
PubMed1996

Seasonal changes in urinary odors and in responses to them by blind subterranean mole rats.

Breeding and nonbreeding season male and female mole rats from two chromosomal species of the Spalax ehrenbergi superspecies were tested in a tunnel T-maze to assess their responses to urine collected from breeding- and nonbreeding season male and female conspecific and heterospecific donors. The results indicate that S. ehrenbergi mole rat urine contains species-, sex-, and season-specific chemosensory cues and that male and female mole rats change their responses to these chemosensory cue depending upon the season. During the nonbreeding season, mole rats avoid conspecific and heterospecific urine of both sexes. In contrast, during the breeding season, mole rats do not avoid conspecific urine and males do not avoid heterospecific urine. These changes in responses to the chemosensory cues in urine are adaptive to their seasonal life underground because they could help the animals avoid aggressive encounters during the nonbreeding season and facilitate their approaching potential mates and competitors during the breeding season. The results suggest that chemical communication could play a role in social encounters, reproduction, and species isolation in the S. ehrenbergi superspecies.

Animals↗
PubMed2006

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders.

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders (n=8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group 2 ganders (n=8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August-March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Animals↗
PubMed2004

Seasonal variation of mortality in the Antiarrhythmics Versus Implantable Defibrillators (AVID) study registry.

OBJECTIVES: We postulated that the pattern of death would be nonrandom with respect to temporal variables. BACKGROUND: Previous studies have demonstrated increased sudden death is associated with periods of relative stress, and overall mortality is associated with temporal variables. METHODS: In the Antiarrhythmics Versus Implantable Defibrillators (AVID) registry, vital status was obtained for 4,450 patients (who had a recent episode of sustained ventricular arrhythmias or unexplained syncope and inducible ventricular tachycardia) through the National Death Index Service as of December 31, 1997 (follow-up 25.5 +/- 13.7 months). RESULTS: Mortality was not associated with the day of the week or with holidays but was associated with season (P = .033). Seasonal variation was present both in northern and southern sites. Mortality was higher during the winter months compared to the remaining months (111.2% in winter vs 96.5% in other months, P = .036). In addition, increased mortality was associated with a high-risk season variable defined (prior to evaluation of treatment arm associations) as spring in the north and winter in the south (P < .001). The hazard ratio for death associated with this "high-risk season" measured 1.25 (P = .001) compared to the other seasons in each region. A test of interaction between "high-risk" season and implantable cardioverter-defibrillator (ICD) status suggested that the group with ICDs experienced reduced mortality during the "high-risk season" compared to the group without ICDs (P = .047). CONCLUSIONS: Mortality was higher in the winter months and in the respective regional "high-risk" seasons. Furthermore, seasonal variation in mortality may have been due to variation in sudden arrhythmic death, and associated increases in mortality were reduced by ICD therapy.

Anti-Arrhythmia Agents↗
PubMed2006

Distribution of phytoplankton in the Three-Gorge Reservoir during rainy and dry seasons.

After damming of the Yangtze River, in order to explore the impacts of the Three-Gorge Dam (TGD) on the aquatic ecosystem, phytoplankton composition, abundance and biomass spatial distribution were studied in the Three-Gorge Reservoir (TGR), and the closest upstream anabranch Xiangxi River, which is 38 km away from the Three-Gorge Dam (TGD) during August (rainy season) 2004 and April (dry season) 2005. In surveys, 6 transects (2 downstream and 4 cross-stream) and 25 stations have been investigated and 314 samples were collected from the surface to the river bed with water samplers. In TGR, 63 taxa and 60 taxa were identified in the rainy and dry seasons, respectively. In the Xiangxi River, 39 taxa were observed in the rainy and dry seasons. Algal blooms occurred in the Xiangxi River and at the influx region of the Yangtze and Xiangxi in both seasons, but had not occurred prior to damming. In the rainy season, the dominant species was Chroomonas acuta with 1.84x10(7) cells l-1, and in the dry season the dominant species were Asterionella formosa and Cryptomonas ovata with 1.34x10(7) cells l-1 and 1.79x10(6) cells.l-1, respectively. In the main channel of TGR, there were no significant correlations between phytoplankton abundance and the concentrations of the main soluble nutrients. In the Xiangxi River, significant negative correlations were observed between phytoplankton abundance and nitrate (Spearman, p<0.01, n=21), phosphate (Spearman, p<0.05, n=21) and silicate (Spearman, p<0.01, n=21) in the rainy season, and similar correlations were also observed with nitrate (Spearman, p<0.05, n=28) and silicate (Spearman, p<0.01, n=28), but not with phosphate in the dry season. Since the damming of the Yangtze River, eutrophication in the anabranch within the backwater has occurred and become severe, and the frequency of algal bloom within TGR and anabranches is expected to increase.

Biomass↗
PubMed2006

Laparoscopic ovum pick-up and in vitro production of sika deer embryos: effect of season and culture conditions.

Amongst the 200 deer subspecies worldwide, more than 40 are considered as endangered. In vitro embryo production may represent an efficient way to produce and disseminate offspring from sparse remaining individuals in these species. With a view to establishing a method of in vitro embryo production, we assessed the ovarian response after hormonal stimulation (oFSH), oocyte yield following laporoscopic ovum pick-up (LOPU) and oocyte developmental competence according to seasonal reproductive status in sika deer (Cervus nippon nippon). Twelve adult sika deer hinds were allocated between two groups and submitted weekly to oFSH follicular growth stimulation followed by LOPU. Hinds in Group A (n=6) were treated first during the breeding season (5 weeks), and then during the non-breeding season (3 weeks). Hinds in Group B (n=6) were submitted to similar procedures but in the reverse order (treated first during the non-breeding season). Cumulus-oocytes complexes (COC) recovered from Group B were allowed to mature in vitro for 24 h in TCM-199 medium supplemented with oFSH, goat follicular fluid and 100 microM cysteamine. In vitro fertilization was performed with frozen/thawed semen in SOFaa medium supplemented with 20% estrous sheep serum and presumptive zygotes were cultured in the presence or absence of ovine oviductal epithelial cell monolayer (oOEC) in SOFaa-BSA medium. Mean number of follicles aspirated per hind per session decreased significantly between breeding and non-breeding season in Group A (9.8+/-0.7 versus 3.2+/-0.7, mean+/-S.E.M., respectively, P<0.001) but did not change between the non-breeding and the subsequent breeding season in Group B (5.3+/-0.7 and 5.7+/-0.7, respectively, P>0.05). Irrespective of the season, good quality COC with complete and compact cumulus investments were recovered allowing a high cleavage rate after in vitro maturation and fertilization. Whereas development to the blastocyst stage did not occur in SOF medium alone, high development rates to the blastocyst stage were observed in oOEC co-culture regardless of season (22% and 34% of total oocytes in co-culture during non-breeding and breeding season, respectively).

Animals↗
PubMedDate not supplied

Seasonal mood change and neuroticism: the same construct?

The personality trait of neuroticism has been found to be associated with a polymorphism in the regulatory region of the serotonin (5-HT) transporter gene (5-HTTLPR). This same genetic polymorphism has also been associated with seasonal changes in mood and behavior, or seasonality. The purpose of the current study was to determine whether seasonality and neuroticism are actually the same construct given that they are both associated with the same genetic polymorphism. We administered the Seasonal Pattern Assessment Questionnaire (SPAQ), which measures the severity of seasonality, and the Revised NEO Personality Inventory (NEO-PI-R), which measures the severity of neuroticism, to 45 subjects diagnosed with seasonal affective disorder (SAD). SAD is a clinical expression of seasonality in which patients develop a major depressive disorder in the winter that remits in the summer and can be treated with light therapy. No significant correlation was found between neuroticism and seasonality. We conclude that seasonality and neuroticism are not the same construct, even though the 5-HTTLPR polymorphism is a genetic risk factor for each.

Adult↗
PubMed1990

Immunotherapy abrogates the generation of eosinophil and neutrophil chemotactic activity during pollen season.

In a group of 40 birch pollen-allergic patients with a history of rhinoconjunctivitis and wheezing during the pollen season, 20 were immunotherapy (IT) treated preseasonally with birch-pollen extract (Pharmacia, Uppsala, Sweden). Blood samples for determination of the levels of heat-labile eosinophil chemotactic activity (HL-ECA), heat-labile neutrophil chemotactic activity (HL-NCA), and heat-stable neutrophil chemotactic activity were collected before the season, at the beginning of the study, at the start of the season, at the peak, at the end, and after the birch-pollen season. The symptoms from rhinoconjunctivitis and airways, peak expiratory flow, and use of medication were recorded throughout the season. Significant increases of HL-ECA and HL-NCA were observed in untreated compared with IT-treated patients at the start of the season (p less than 0.0001 for both activities) and at the peak of the birch-pollen season (p less than 0.0005 and p less than 0.01, respectively). At the end of the season, HL-ECA levels were not significantly different between the patient groups, whereas HL-NCA levels were still higher in untreated patients (p less than 0.005). We conclude that IT completely abrogates the generation of HL-ECA and HL-NCA during a pollen season.

Adolescent↗
PubMed2002

Electrophysiological evidence suggesting a seasonal modulation of retinal sensitivity in subsyndromal winter depression.

BACKGROUND: An anomaly in the retinal adaptation processes to the decreased light exposure in winter has been suggested as a contributing factor in winter depression. The purpose of this study was to investigate seasonal variations in rod sensitivity in normal subjects and in subjects with seasonal mood variations. METHODS: Nine normal subjects (5 men, 4 women, aged 21-28 years) and 12 subjects with subsyndromal seasonal affective disorder (S-SAD)(3 men, 9 women, aged 21-44 years) were selected based on their global seasonality score (GSS) from the Seasonal Pattern Assessment Questionnaire. Scotopic electroretinograms (ERGs) were obtained once in winter and once in summer. Retinal sensitivity, which represents a relative threshold, was obtained from the rod ERG luminance-response functions. RESULTS: A difference in retinal sensitivity between the two groups appeared only in the winter with lower retinal sensitivity found in the S-SAD group. A positive correlation between the GSS and the magnitude of the winter decrease in rod sensitivity was also observed. LIMITATIONS: The S-SAD subjects studied in this research did not receive a formal psychiatric evaluation. This will be necessary in future studies to determine if the changes in retinal sensitivity are specific to seasonal affective disorders. In addition, in the present study, the differences in age and gender between the two groups limit the interpretation of the possible contribution of these two parameters to the results. CONCLUSION: The seasonal changes in retinal sensitivity that parallel seasonal mood variations suggest that the ERG may represent a useful tool to investigate seasonal affective disorders.

Adaptation, Ocular↗
PubMed2004

Do monthly or seasonal variations exist in suicides in a high-risk setting?

An unequal distribution of suicides over months and seasons has been a consistent finding in epidemiological surveys on suicide. Jails and prisons are a high-risk setting for suicide all over the world. The high prevalence of both outward and self-directed violence in prison populations indicates dysfunctional central serotonin (5-HT) neurotransmission and, therefore, could account for an unequal distribution of suicides over months and seasons due to underlying bioclimatic factors. Within a total survey of suicides in the Austrian penitentiary system, the weekly, monthly and seasonal distribution of custodial suicides between 1947 and 1999 was studied. After an explorative comparison of suicide distribution over weekdays, months and seasons of the year by chi2-tests, a harmonic Poisson regression model was performed to detect seasonality of suicides. No unequal distribution of suicides was evident over the 53-year period. A limitation of this study was its sample size of 412, a low number compared with population-based samples, where a spring suicide peak was consistently found. An explanation for lacking seasonality could be that bioclimatic factors are less relevant in urban, industrialized areas, where jails and prisons usually are located. One of the core characteristics of penal institutions is the limited possibility for communication and social interaction. This social isolation is independent of seasonal changes. If the individual's possibilities for social interactions are limited, the influence of seasonal changes in social activities may be less relevant. This could explain the absence of seasonal changes in custodial suicide incidence.

Austria↗