Further aspects of IL-1 beta secretion revealed by transfected monkey kidney cells.

Because the cytokine interleukin-1 beta (IL-1 beta) lacks a classical hydrophobic signal sequence, it has been unclear how it is released from cells, and whether release proceeds via a novel mechanism or through non-specific leakage. To address this issue, we have examined the secretion of the recombinant forms of human IL-1 beta from COS monkey kidney cells, which express low levels of endogenous IL-1 beta. Four proteins were expressed: precursor and mature IL-1 beta and precursor and mature IL-1 beta fused to an amino terminal hydrophobic signal sequence from human tissue plasminogen activator. By monitoring the appearance of a known cytosolic protein (ATP citrate lyase) in the medium, we find that the unmodified IL-1 beta s are non-specifically released in very small quantities from the cytosol. On the other hand, the signal sequence-modified IL-1 beta s are glycosylated and efficiently secreted by the ER/Golgi pathway. The secreted, modified-mature protein is also biologically active, suggesting that this pathway has been bypassed for reasons other than maintaining the structural integrity of IL-1 beta. More likely the alternative pathway is a critical aspect of IL-1 biology. The differences in kinetics and quantity of IL-1 beta release from monocytic and COS cells suggest that COS cells lack critical components for the rapid release seen in monocytes.     

Identification of respiratory vagal feedback in awake normal subjects using pseudorandom unloading.

Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus.     

Physiology of the ECL cells.

The enterochromaffin-like (ECL) cells of the oxyntic mucosa (fundus) of the stomach produce, store and secrete histamine, chromogranin A-derived peptides such as pancreastatin, and an unanticipated but as yet unidentified peptide hormone. The cells are stimulated by gastrin and pituitary adenylate cyclase activating peptide and suppressed by somatostatin and galanin. Choline esters and histamine seem to be without effect on ECL cell secretion. The existence of a gastrin-ECL cell axis not only explains how gastrin stimulates acid secretion but also may help to explore the functional significance of the ECL cells with respect to the nature and bioactivity of its peptide hormone. From the results of studies of gastrectomized/fundectomized and gastrin-treated rats, it has been speculated that the anticipated ECL-cell peptide hormone acts on bone metabolism.     

Behaviour, natural history, and annual cycle of the Henderson Island rail Porzana atra (Aves: Rallidae)

The little known endemic Henderson Island rail (or Henderson rail) Porzflna atra , inhabits forest on the coastal plain and upraised plateau of Henderson Island. Rails were studied for 15 months from January 1991 to March 1992. The population was estimated at c. 6200 individuals living in pairs or cooperative groups of 3–4 adults on territories averaging about 1 ha. Two or three eggs were laid in covered or open nests near the ground from mid-July to mid-February. Up to five consecutive nesting attempts were made in cases where eggs or young chicks were lost. Adults laid a second clutch when chicks were fully feathered at about one month of age. Both sexes incubated and helped rear the young. Older chicks sometimes helped feed younger siblings. Dispersal of juveniles from the natal territory took place in April. Adult birds underwent a rapid, simultaneous post-nuptial moult of the remiges in February-April; the post-juvenile moult involved body feathers only. Data on morphometries, breeding ecology, courtship behaviour and voice are compared with available information for the spotless crake P. tabuensis , the Henderson rail's closest relative and probable ancestor. These comparisons provide some information on how these two taxa have differentiated since rails arrived on Henderson Island some time in the last 380000 years.     

Experimental evidence of environmental effects on age-specific reproductive success: the importance of resource quality.

Age-specific access to high-quality resources (e.g. territory or nest site) might be an important determinant for improved reproductive performance with increasing age. I experimentally investigated the effects of territory quality versus other age-related improvements in breeding competence (e.g. foraging skills, breeding experience and local knowledge) on age-specific reproductive success. Territory quality (i.e. territory field layer height) was manipulated in year 2 of northern wheatears (Oenanthe oenanthe) that were breeding in the same territory in two consecutive years. Changing territory quality by changing field layer height had a strong effect on within-individual change in the reproductive success of wheatears. This effect was mainly due to a corresponding change in nest predation risk. When territory quality was kept constant (i.e. no between-year change in territory field layer height), within-individual reproductive success did not change between subsequent years. Thus, age-related improvements in foraging skills, breeding experience and local familiarity had no significant effect on within-individual changes in reproductive success. Increased reproductive success with increased age in northern wheatears is therefore mainly explained by an improved access to high-quality territories with increasing age. I conclude that age-dependent access to high-quality breeding resources might be a widespread phenomenon in nature.