Mannose-binding lectin gene polymorphic variants predispose to the development of bronchopulmonary complications but have no influence on other clinical and laboratory symptoms or signs of common variable immunodeficiency.

Mannose-binding lectin (MBL), activating protein of the lectin pathway of the complement system, is an important component of the non-specific immune response. MBL2 gene polymorphisms, both in the coding and promoter regions, lead to low or deficient serum MBL levels. Low serum MBL levels were shown to be associated with serious infectious complications, mainly in patients in whom other non-specific immune system barriers were disturbed (granulocytopenia, cystic fibrosis). We have analysed two promoter (-550 and -221) and three exon (codons 52, 54 and 57) MBL2 polymorphisms in a total of 94 patients with common variable immunodeficiency (CVID) from two immunodeficiency centres. Low-producing genotypes were associated with the presence of bronchiectasis (P = 0.009), lung fibrosis (P = 0.037) and also with respiratory insufficiency (P = 0.029). We could not demonstrate any association of MBL deficiency with age at onset of clinical symptoms, age at diagnosis, the number of pneumonias before diagnosis or serum immunoglobulin (Ig)G, IgA and IgM levels before initiation of Ig treatment. No association with emphysema development was observed, such as with lung function test abnormalities. No effect of MBL2 genotypes on the presence of diarrhoea, granuloma formation, lymphadenopathy, splenomegaly, frequency of respiratory tract infection or the number of antibiotic courses of the patients was observed. Our study suggests that low MBL-producing genotypes predispose to bronchiectasis formation, and also fibrosis and respiratory insufficiency development, but have no effect on other complications in CVID patients.

A clockwork organ.

The vertebrate circadian clock was thought to be highly localized to specific anatomical structures: the mammalian suprachiasmatic nucleus (SCN), and the retina and pineal gland in lower vertebrates. However, recent findings in the zebrafish, rat and in cultured cells have suggested that the vertebrate circadian timing system may in fact be highly distributed, with most if not all cells containing a clock. Our understanding of the clock mechanism has progressed extensively through the use of mutant screening and forward genetic approaches. The first vertebrate clock gene was identified only a few years ago in the mouse by such an approach. More recently, using a syntenic comparative genetic approach, the molecular basis of the the tau mutation in the hamster was determined. The tau gene in the hamster appears to encode casein kinase 1 epsilon, a protein previously shown to be important for PER protein turnover in the Drosophila circadian system. A number of additional clock genes have now been described. These proteins appear to play central roles in the transcription-translation negative feedback loop responsible for clock function. Post-translational modification, protein dimerization and nuclear transport all appear to be essential features of how clocks are thought to tick.

Spontaneous c-Fos rhythm in the rat suprachiasmatic nucleus: location and effect of photoperiod.

A recently reported circadian rhythm in the spontaneous c-Fos immunoreactivity in the rat suprachiasmatic nucleus (SCN) is expressed mostly in the dorsomedial (dm) SCN, where vasopressinergic cells are located. The aim of the present study is to find out whether day length, i.e., photoperiod, affects the dm-SCN rhythm and, if so, how the rhythm adjusts to a change from a long to a short photoperiod. In addition, a question of whether the spontaneous c-Fos production is localized in vasopressin- producing cells or in other cells is also studied to characterize further the dm-SCN rhythmicity. Combined immunostaining for c-Fos and arginine vasopressin (AVP) revealed that most of c-Fos immunopositive cells were devoid of AVP; the results suggest that c-Fos-producing cells in the dm-SCN are mostly not identical with those producing AVP. In rats maintained under a long photoperiod with 16:8-h light-dark cycle (LD 16:8) daily and then released into darkness, the time of the afternoon and evening decline of the spontaneous c-Fos immunoreactivity in the dm-SCN differed just slightly from the time in rats maintained originally under a short LD 8:16 photoperiod; however, the morning c-Fos rise occurred about 4 h earlier under the long than under the short photoperiod. After a change from a long to a short photoperiod, a rough but not yet a fine adjustment of the morning c-Fos rise to the change was accomplished within 3-6 days. The results show that similar to the recently reported ventrolateral SCN rhythmicity, the intrinsic dm-SCN rhythmicity is also affected by the photoperiod and suggest that the whole SCN state is photoperiod dependent.

Hormones, subjective night and season of the year.

Production and release of many mammalian hormones exhibit circadian rhythms controlled by a pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Under conditions when the circadian pacemaker free-runs with a period close to, but not equal to 24 h, subjective day and night may not be identical with the environmental day and night. The present study was aimed to define the phase and state of the circadian pacemaker when the circadian system is experiencing subjective night and to ascertain whether and how such a defined subjective night depends on the photoperiod. The results indicate that the subjective night may be defined as the time interval when i) light stimuli can reset the circadian system, ii) pineal melatonin production and photic induction of the c-Fos gene in the ventrolateral SCN are high, and iii) the spontaneous c-Fos protein production in the dorsomedial SCN is low. Such a defined subjective night and, logically, the whole circadian pacemaking system depend on the photoperiod and hence on the season of the year which the animals are experiencing.

Subchronic preexposure to carbon monoxide modifies heart response to a combined CO + isoproterenol challenge in rats.

The effect of repeated exposure to carbon monoxide (CO) on the response of middle-age rats to an acute CO exposure combined with a low dose of a sympathomimetic agent was studied. A group of 12 rats (male albino, Wistar, age 9 months) without ECG abnormalities was divided into two subgroups matched for weight, heart rate and ECG: one subgroup was exposed to 500 ppm CO for 6 h/d, 5 d/w, for 6 weeks (peak COHb 31.5%, SD 3.5); the other one (controls) was exposed to fresh air. Two or three days after the last exposure both groups underwent combined challenge with 0.025 mg/kg isoproterenol s.c. and 90 minute exposure to CO in a concentration increasing from 500 to 1500 ppm; ECG was recorded continuously. The hearts were examined morphometrically and histologically. The CO-preexposed subgroup had, as compared to controls: 1) significantly higher blood hemoglobin (by 25%), erythrocyte count (by 28%) and volume (by 6%), and hematocrit (by 33%); 2) the same peak COHb; 3) lower basic heart rate and an earlier decrease after isoproterenol, 4) significantly smaller increase in ECG abnormalities and arrhythmias after isoproterenol and during CO exposure; 5) nonsignificantly higher heart weight indexes; 6) a nonsignificantly lower score of histological abnormalities. The global score of ECG pathology during CO exposure (abnormal pattern or arrhythmia) correlated best (multiple corr. coef. >0.9) with end-exposure free (non CO bound) hemoglobin (negatively) and with mean heart rate during exposure (positively): the lower score in the preexposed subgroup was attributable primarily to the increased hemoglobin. Six-week intermittent CO exposure induced marked compensatory processes (hematological) but only a tendency to adaptational changes in the heart (by gross morphometry), and decreased the ECG response to CO+ isoproterenol challenge at the same COHb.

Spontaneous rhythm in c-Fos immunoreactivity in the dorsomedial part of the rat suprachiasmatic nucleus.

In rats maintained for 2 days in constant darkness, the suprachiasmatic nucleus exhibited a circadian rhythm in c-Fos immunoreactivity, with the maximum in the morning and trough during the subjective night. In contrast to the night-time photic c-Fos induction occurring in the ventrolateral part of the nucleus, the spontaneous rhythmic c-Fos induction in darkness occurred in the dorsomedial part and might indicate an elevated dorsomedial neuronal activity in the early subjective day.

Melatonin entrainment of the circadian N-acetyltransferase rhythm in the newborn rat pineal gland.

In 15-day-old control and vehicle-treated rats, the evening rise of the pineal N-acetyltransferase occurred at the same time as in their mothers, whereas in 5-day-old pups, the rise occurred by 2-3 hr earlier. Four-day administration of melatonin in the late day phase advanced the N-acetyltransferase rise in 15-day-old rats as compared with the rise in the vehicle-treated animals; a slight melatonin induced phase advance in 5- and 27-day-old rats was not significant. The data indicate that the newborn rat's circadian pacemaker controlling the rhythmic N-acetyltransferase rise may be entrained by exogenous melatonin. It appears, however, that the maternal melatonin transferred via milk cannot entrain the pup's pacemaker by phase advancing it, since the N-acetyltransferase rise in the pups begins earlier or at the same time as maternal melatonin production driven by the N-acetyltransferase rhythm.

Photoperiod-dependent correlation between light-induced SCN c-fos expression and resetting of circadian phase.

In rodents, brief light pulses that shift the phase of the circadian locomotor rhythm also increase c-fos gene expression in the suprachiasmatic nucleus (SCN), site of an endogenous clock that regulates such rhythmicity. Because the magnitude of photic phase shifts varies when light pulses are applied at different time points over the course of the subjective night, we examined the degree of SCN c-fos gene expression after single 30-min light pulses were delivered at time points that spanned the early and late subjective night in rats maintained in either short (8:16-h light-dark cycle) or long (16:8-h light-dark cycle) photoperiods. The light-induced level of c-fos mRNA and the number of cells expressing immunoreactive c-Fos protein were measured in the SCN by in situ hybridization and immunohistochemistry, respectively, and compared with the magnitude of the corresponding phase shifts of the circadian rhythm of pineal N-acetyltransferase (NAT) activity. We found a robust correlation between c-fos photoinduction and NAT phase shifts, but this relationship was dependent on photoperiod. The degree of c-fos gene expression was strongly correlated with the magnitude of NAT phase advances and delays under the short photoperiod and with phase advances under the long photoperiod, but not with phase delays under the long photoperiod. The data suggest that c-fos gene expression in the SCN may be involved in the photic resetting of the pineal NAT rhythm. Under the long photoperiod, however, the magnitude of phase delays may be limited by the functional state of the circadian pacemaking system.

Memory on long but not on short days is stored in the rat suprachiasmatic nucleus.

In order to follow adjustment of the rat circadian pacemaking system to a change of the photoperiod, the rhythm in the light-induced c-fos expression was used as a marker of the intrinsic rhythmicity of the suprachiasmatic nucleus (SCN). After a change from a long photoperiod with 16 h of light per day to a short one with 8 h of light, the interval enabling high c-fos photoinduction decompressed gradually and the full extension by 5-6 h was achieved only within 2 weeks. After a change from a short to a long photoperiod, the interval was compressed by 5-6 h within 3 days. The data indicate a rapid adjustment of the photoperiod dependent-state of the SCN pacemaker to long days but only a slow one to short days.

The rat suprachiasmatic nucleus is a clock for all seasons.

Seasonal changes of daylength (photoperiod) affect the expression of hormonal and behavioral circadian rhythms in a variety of organisms. In mammals, such effects might reflect photoperiodic changes in the circadian pace-making system [located in the suprachiasmatic nucleus (SCN) of the hypothalamus] that governs these rhythms, but to date no functionally relevant, intrinsic property of the SCN has been shown to be photoperiod dependent. We have analyzed the temporal regulation of light-induced c-fos gene expression in the SCN of rats maintained in long or short photoperiods. Both in situ hybridization and immunohistochemical assays show that the endogenous circadian rhythm of light responsiveness in the SCN is altered by photoperiod, with the duration of the photosensitive subjective night under the short photoperiod 5-6 h longer than under the long photoperiod. Our results provide evidence that a functional property of the SCN is altered by photoperiod and suggest that the nucleus is involved in photoperiodic time measurement.