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PubMed2001

Threshold retinopathy of prematurity: ocular changes and sequelae following cryotherapy.

PURPOSE: To determine ocular changes and sequelae following cryotherapy for threshold retinopathy of prematurity (ROP). METHODS: This is a retrospective study of 49 eyes of 26 premature babies with threshold ROP treated with cryotherapy between 1995 and 1998. All eyes included in the study had favourable structural outcome after cryotherapy. Follow-up examination of all babies was done 12 - 62 months (average 28 months) after cryotherapy. Visual axis, fixation pattern, anterior segment examination, cycloplegic refraction and dilated fundus examination with indirect ophthalmoscopy were undertaken in all eyes during follow-up. RESULTS: Posterior pole retinal residuae observed following cryotherapy were tortousity of blood vessels in 32 (65.3%), narrow temporal arcade in 22 (44.89%), temporal crescent in 17 (34.69%), disc drag in 13 (26.53%) and macular heterotopia in 7 (14.28%) eyes. Myopia was observed in 20 (40.82%) eyes and strabismus in 5 (19.23%) babies. The significant risk factor for ocular changes was ROP with more clock hours of involvement (p < 0.05). Higher period of gestation was associated with posterior pole changes (p< 0.05). CONCLUSIONS: All premature babies with threshold ROP treated with cryotherapy require frequent and long-term follow up to look for retinal residuae, refractive status, and ocular motility disorders.

Cryotherapy↗

PubMed1999

Systematic biology of gymnotiform and mormyriform electric fishes: phylogenetic relationships, molecular clocks and rates of evolution in the mitochondrial rRNA genes

The phylogenetic relationships of both African and South American electric fish orders are reviewed at their intra-ordinal level taking into consideration recent studies in which cladistic principles have been employed. Several concordant topologies emerge from the different data sets, but some unsettled issues still remain. From the studies available, a consensus topology has been suggested for the Mormyriformes and for the Gymnotiformes. Subsequently, the evolutionary relationships of these two electric fish clades are considered within each respective superorder, i.e. in relation to the other osteoglossomorph and ostariophysan orders. The inter-ordinal phylogenies are used as a framework to test the molecular clock hypothesis with two gene fragments of the mitochondrial genome. Gymnotiformes, Siluriformes and Characiformes are accumulating mutations at the same pace in relation to their respective outgroups, but for all the other combinations of sister clades tested the molecular clock can be statistically rejected. Fossil records are then surveyed and used to calibrate absolute rates of genetic differentiation for each main lineage (orders) of both osteoglossomorphs and ostariophysans. The most conserved regions (stems) of the 12S and 16S gene fragments used are evolving at an average rate of 0.123 % 10(6 )years-1 for the osteoglossomorphs and 0.137 % 10(6 )years-1 for the ostariophysans, with no significant difference between these two values. The rate of mutation in the loops, the faster-evolving segments, estimated for closely related electric fish taxa is 0.82 % 10(6 )years-1 for four Brienomyrus species and 1.01 % 10(6 )years-1 for the four eigenmanniid genera. When the entire molecule (loops + stems) is considered, the rate of mutation in both mormyriforms and gymnotiforms converges to a rounded value of 0.23 % 10(6 )years-1.

Journal Article↗

PubMed1995

Direct cyclopexy for traumatic cyclodialysis with persisting hypotony. Report in 29 consecutive patients.

BACKGROUND: Traumatic or postoperative cyclodialysis frequently is associated with persisting ocular hypotony, causing morphologic changes and visual loss. METHODS: The authors retrospectively analyzed the data of 29 eyes of 29 patients who underwent consecutive direct surgical cyclopexy for hypotonus cyclodialysis between 1980 and 1993 at the authors' institution. Cyclopexy was performed by directly suturing the ciliary body to the scleral spur under a scleral flap. RESULTS: The cyclodialysis clefts were posttraumatic (26 eyes) or postsurgical (3 eyes), extended for 3.6 +/- 1.7 clock hours (range, 1.5-9.5 clock hours), and were most frequently located superiorly. In eight eyes, argon laser photocoagulation of the cyclodialysis cleft (1-11 sessions) was performed before surgical cyclopexy but failed to permanently close the clefts. Preoperatively, all eyes showed persisting ocular hypotony with intraocular pressure of 3.1 +/- 2.3 mmHg (range, 0-8 mm Hg), macular edema, and disc swelling. Postoperatively, intraocular pressure was 14.0 +/- 3.7 mmHg (range, 6-20 mmHg), and visual acuity improved in 25 eyes (86%) and remained unchanged in 4 (14%) because of posttraumatic posterior segment problems. In 14 eyes, painful reversible pressure spikes of up to 58 mmHg developed during the first postoperative days, but no persisting secondary glaucoma was observed during further follow-up of 37.7 +/- 35.9 months (range, 2-134 months). All ten phakic eyes that were refracted preoperatively and postoperatively showed hyperopic shifts of more than 1 diopter after cyclopexy. CONCLUSIONS: Direct surgical cyclopexy is a successful treatment for large hypotonus cyclodialysis clefts that are unresponsive to or too large for laser photocoagulation. Painful early postoperative pressure spikes are frequent, but the development of glaucoma seems to be very uncommon. Postoperative visual acuity may be compromised due to posterior segment sequelae of preceding ocular trauma.

Adult↗

PubMed2002

Phylogenetic relationships, evolution of broodcare behavior, and geographic speciation in the wrasse tribe Labrini.

The family Labridae is a large assemblage of marine fish composed of about 580 species in 82 genera distributed in tropical and temperate marine waters around the world. Several subgroups, currently classified as tribes, have been identified in this large family, yet only a few phylogenetic analyses have been performed on labrid clades. We confirm monophyly of the labrid tribe Labrini and propose a phylogeny of the 23 species of the genera Acantholabrus, Centrolabras, Ctenolabrus, Labrus, Lappanella, Symphodus, Tautoga, and Tautogolabrus occurring in the eastern and western Atlantic and the Mediterranean. We analyzed a 577-bp segment of the mitochondrial 16S rDNA and a 506-bp segment of the mitochondrial control region in 22 species, for a total of up to 1069 bp per species. We used both parsimony and likelihood approaches under a variety of assumptions and models to generate phylogenetic hypotheses. The main features of the molecular phylogeny for the Labrini turned out to be the same for the two algorithms applied. The tree structure is similar to a previous, unpublished morphological phylogeny for a subset of labrine species. Estimated divergence times of the Labrini based on fossils and a molecular clock range from about 15 mya for the deepest splits to less than 1 mya for younger clades. Biogeographic patterns of the Symphodus species group and the genus Labrus are dominated by speciation events driven by the closing and opening of the Mediterranean Sea and periodic glaciation events during the past 1 million years. The Labrini are the only clade in the entire Labridae that exhibit nest-building and broodcare behavior. We use the phylogeny to show that similar broodcare behavior has evolved twice in the labrine fish and discuss scenarios for the evolution of broodcare from the diandric protogynous hermaphroditism found in ancestral labrines and many other wrasses.

Animals↗

PubMed1997

Modulation of the spinal network for locomotion by substance P in the neonatal rat.

The tachykinin substance P (SP) is present in the ventral and medial area of the lumbar spinal cord. Its localisation suggests that it could modulate the spinal network for locomotion. We have investigated its effects on motor outputs by applying SP, in vitro, to the lumbosacral segments of an isolated spinal cord of new-born rats. SP was applied to the lumbosacral spinal cord either on a quiescent preparation or during episodes of fictive locomotion induced by N-methyl-D,L-aspartate. When applied on quiescent preparations, SP induced a slow rhythmic activity (period >30 s). During fictive locomotion, SP increased both the locomotor frequency and the duration of the bursts of cyclic activity. Furthermore, SP stabilised the locomotor rhythm. These results demonstrate that SP is able to modulate both the "clock" and the pattern generator for locomotion.

Animals↗

PubMed2005

DNA taxonomy, phylogeny and Pleistocene diversification of the Cicindela hybrida species group (Coleoptera: Cicindelidae).

Species delimitation is complicated where morphological variation is continuous or poorly subdivided, but for taxonomic convenience it is common practice to separate and name geographical groups to capture this variation. DNA-based approaches may be used to test if these groups in fact represent historically divided, discrete species entities. The Cicindela hybrida complex (Coleoptera: Cicindelidae) is an assemblage of up to seven morphologically recognized species and 15 subspecies with wide distribution in the Palaearctic region. We sequenced a discontinuous segment of 1899 bp of mtDNA including three regions (coxI, rrnL+trnL2+nad1, cob) for a total of 99 specimens from 36 sampling localities across Europe, revealing 48 haplotypes. Four major clades could be identified corresponding to geographical groups from central Iberia, Ukraine, central Europe, and a band from the Atlantic Iberian coast to northern Europe. Taking into account further subdivisions within these clades, four of the six named species included in the analysis were recognizable by applying various procedures for species delimitation. Age estimates from calibrated molecular clocks date the diversification of the hybrida group within the past 2 million years (Myr), and the separation of the northern clade within 0.4 Myr. Nested clade analysis revealed the rapid range expansion of the northern group consistent with postglacial dispersal, but we did not find support for specific source population(s) in the postulated southern refugia. The evolutionary framework based on mtDNA sequences is shown to identify species entities as discrete clusters of closely related sequences and provides an objective system for delineating and recognizing hierarchically structured groups. In the case of the C. hybrida complex, these groups largely coincided with those established from morphology. The study adds further support to the utility of mtDNA-based sequence profiles (the 'DNA taxonomy') as a rapid and objective synthesis of evolutionary diversity and as reference system for communication.

Animals↗

PubMed2005

The porA pseudogene of Neisseria gonorrhoeae--low level of genetic polymorphism and a few, mainly identical, inactivating mutations.

N. meningitidis is the only Neisseria species known to express two outer membrane porins, PorA and PorB. However, a porA pseudogene has been identified in N. gonorrhoeae. The present study investigated the prevalence and genetic polymorphism of this porA pseudogene in 87 different N. gonorrhoeae strains. The porA pseudogene was identified in all isolates. The pseudogene comprised 12 (5.5%), of which 10 were located in the promoter spacer, and 11 (1.0%) polymorphic nucleotide sites in the upstream segment containing the promoter region, i.e. the putative -10 and -35 sequences and the promoter spacer in-between, and the hypothetical PorA coding sequence, respectively. A phylogenetic analysis of the upstream segment and the hypothetical coding sequence identified 36 sequence variants, of which 30 were not previously described. All strains comprised at least two identical confirmed inactivating deletions, of which one was located in the promoter region and one in the hypothetical PorA coding sequence. In conclusion, the porA pseudogene and its few inactivating mutations are widespread in the N. gonorrhoeae population and the homology with the N. meningitidis porA gene reflects their common evolutionary origin. The highly conserved N. gonorrhoeae porA pseudogene may reflect an evolutionary neutral molecular clock and may be a suitable genetic target for diagnosis of N. gonorrhoeae.

Base Sequence↗

PubMed2000

Somite development in zebrafish.

A full understanding of somite development requires knowledge of the molecular genetic pathways for cell determination as well as the cellular behaviors that underlie segmentation, somite epithelialization, and somite patterning. The zebrafish has long been recognized as an ideal organism for cellular and histological studies of somite patterning. In recent years, genetics has proven to be a very powerful complementary approach to these embryological studies, as genetic screens for zebrafish mutants defective in somitogenesis have identified over 50 genes that are necessary for normal somite development. Zebrafish is thus an ideal system in which to analyze the role of specific gene products in regulating the cell behaviors that underlie somite development. We review what is currently known about zebrafish somite development and compare it where appropriate to somite development in chick and mouse. We discuss the processes of segmentation and somite epithelialization, and then review the patterning of cell types within the somite. We show directly, for the first time, that muscle cell and sclerotome migrations occur at the same time. We end with a look at the many questions about somitogenesis that are still unanswered.

Animals↗

PubMed2001

Nucleotide sequence of coliphage HK620 and the evolution of lambdoid phages.

HK620 is a temperate lambdoid bacteriophage that adsorbs to the O-antigen of its host, Escherichia coli H. The genome of a temperature-sensitive clear-plaque mutant consists of 38,297 nucleotides in which we recognize 60 open reading frames (orfs). Eighteen of these lie in a region of the genome that we call the virion structure domain. The other 42 orfs lie in what we call the metabolic domain. Virions of HK620 resemble those of phage P22. The virion structural orfs encode three kinds of putative proteins relative to the virion proteins of P22: (1) those that are nearly (about 90 %) identical; (2) those that are weakly (about 30 %) identical; and (3) those composed of nearly and weakly identical segments. We hypothesize that these composite proteins form bridges between the virion proteins of the other two kinds. Three of the putative virion proteins that are only weakly identical to P22 proteins are 71, 60 and 79 % identical to proteins encoded by the phage APSE-1, whose virions also resemble those of P22. Because the hosts of APSE-1 and HK620 have been separated from each other by an estimated 200 My, we propose using the amino acid differences that have accumulated in these proteins to estimate a biological clock for temperate lambdoid phages. The putative transcriptional regulatory gene circuitry of HK620 seems to resemble that of phage lambda. Integration, on the other hand, resembles that of satellite phage P4 in that the attP sequence lies between the leftward promoter and int rather than downstream of int. Comparing the metabolic domains of several lambdoid phage genomes reveals seven short conserved sequences roughly defining boundaries of functional modules. We propose that these boundary sequences are foci of genetic recombination that serve to assort the modules and make the metabolic domain highly mosaic genetically.

Attachment Sites, Microbiological↗

PubMed2006

[Landmark of facial nerve in middle ear surgery].

OBJECTIVE: To re-evaluate landmarks for facial nerve in middle ear surgery through temporal bone dissection and facial nerve surgery. METHODS: Some relative landmarks were found through 44 facial nerves dissection in cadaver and 106 cases of facial nerve decompression surgery. RESULTS: (1) Landmarks for vertical segment of the facial nerve: the vertical line in combined point between posterior and middle 1/3 horizontal semicircular canal clews the posterior edge of facial nerve; the prolong line of superior radian of incus short process clues to the anterior edge of the facial nerve, the facial nerve and horizontal semicircular canal are almost in the same plane. (2) Landmarks for horizontal segment of the facial nerve: the facial nerve tracks forward inferior to short process of incus and anterior to horizontal semicircular canal carina in 30 angel. The facial nerve, locating posterior and superior to cochleariform process and parallel with it, forms the step of middle-superior tympanic cavity and tracks forward to geniculate ganglion. (3) location of geniculate ganglion: The same distance prolong line of stapes head to cochleariform process clues to geniculate ganglion. (4) Location of the chorda tympani nerve: chorda tympani nerve, leaving tympanic sulcus at 3 clock of bone canaline left ear and at 9 clock of bone canaline right ear, tracks forward along tympani sulcus and then cross between long process of incus and manubrium. It lies in the border of pars tensa and pars flaccid and is about 5 - 8 mm from the stylomastoid foramen to where the chorda tympani nerve leaves the facial nerve. There is no difference of facial nerve structure in temporal bone dissection and in surgery. CONCLUSIONS: The fixed landmarks of middle ear are the frame of reference of facial nerve, in which horizontal semicircular canal is most invariable; and the safety of surgery will be improved by the reference of the facial nerve.

Ear, Middle↗

PubMed2006

Silencing acid-sensing ion channel 1a alters cone-mediated retinal function.

The action of extracellular protons on retinal activity and phototransduction occurs through pH-sensitive elements, mainly membrane conductances present on the different cell types of the outer and inner nuclear layers and of the ganglion cell layer. Acid-sensing ion channels (ASICs) are depolarizing conductances that are directly activated by protons. We investigated the participation of ASIC1a, a particular isoform of ASICs, in retinal physiology in vivo using electroretinogram measurements. In situ hybridization and immunohistochemistry localized ASIC1a in the outer and inner nuclear layers (cone photoreceptors, horizontal cells, some amacrine and bipolar cells) and in the ganglion cell layer. Both the in vivo knockdown of ASIC1a by antisense oligonucleotides and the in vivo blocking of its activity by PcTx1, a specific venom peptide, were able to decrease significantly and reversibly the photopic a- and b-waves and oscillatory potentials. Our study indicates that ASIC1a is an important channel in normal retinal activity. Being present in the inner segments of cones and inner nuclear layer cells, and mainly at synaptic cleft levels, it could participate in gain adaptation to ambient light of the cone pathway, facilitating cone hyperpolarization in brightness and modulating synaptic transmission of the light-induced visual signal.

Acid Sensing Ion Channels↗

PubMed1983

Qualitative and quantitative assessment of the circadian rhythm of cortisol in pregnancy.

The effect of pregnancy on the circadian rhythm and diurnal excursion of plasma cortisol and urinary free corticoids was examined in a sequential study during the second and third trimester and 6 to 12 weeks post partum. Hourly blood samples from six subjects and 8-hour urine collections from eight subjects were obtained around the clock. While the circadian rhythm was maintained during gestation, plasma cortisol levels (24-hour mean, nadir, peak, and nadir-peak excursion) increased. The relative excursion of plasma cortisol (expressed as the percentage of deviation from the 24-hour mean) exhibited remarkable blunting compared with postpartum values. This pregnancy-associated blunting of plasma cortisol excursion was indicated by a significant reduction in the: (1) mean peak and nadir excursion, (2) integrated area between the percent deviation curve and the 24-hour mean, and (3) mean slope of the major incremental and decremental segments of the percent deviation curve. The circadian rhythm and diurnal excursion of plasma cortisol were reflected in urinary free corticoid values. Mean 24-hour urinary free corticoid concentrations increased 180% during gestation over nonpregnant levels. Nadir concentrations of urinary free corticoids in pregnancy exceeded peak nonpregnant levels. The gestational rise of metabolically active free cortisol and adrenocorticotropin (ACTH), and the pregnancy-associated blunting of the excursion of plasma cortisol may be explained by an autonomous source of ACTH during gestation.

Adolescent↗

PubMed1998

Nonsynonymous substitution in abalone sperm fertilization genes exceeds substitution in introns and mitochondrial DNA.

Strong positive Darwinian selection acts on two sperm fertilization proteins, lysin and 18-kDa protein, from abalone (Haliotis). To understand the phylogenetic context for this dramatic molecular evolution, we obtained sequences of mitochondrial cytochrome c oxidase subunit I (mtCOI), and genomic sequences of lysin, 18-kDa, and a G protein subunit. Based on mtDNA differentiation, four north Pacific abalone species diverged within the past 2 million years (Myr), and remaining north Pacific species diverged over a period of 4-20 Myr. Between-species nonsynonymous differences in lysin and 18-kDa exons exceed nucleotide differences in introns by 3.5- to 24-fold. Remarkably, in some comparisons nonsynonymous substitutions in lysin and 18-kDa genes exceed synonymous substitutions in mtCOI. Lysin and 18-kDa intron/exon segments were sequenced from multiple red abalone individuals collected over a 1,200-km range. Only two nucleotide changes and two sites of slippage variation were detected in a total of >29,000 nucleotides surveyed. However, polymorphism in mtCOI and a G protein intron was found in this species. This finding suggests that positive selection swept one lysin allele and one 18-kDa allele to fixation. Similarities between mtCOI and lysin gene trees indicate that rapid adaptive evolution of lysin has occurred consistently through the history of the group. Comparisons with mtCOI molecular clock calibrations suggest that nonsynonymous substitutions accumulate 2-50 times faster in lysin and 18-kDa genes than in rapidly evolving mammalian genes.

Animals↗

PubMed1989

Headache: classification, mechanism and principles of therapy, with particular reference to migraine.

The sensation of pain derived from intracranial and extracranial blood vessels is conveyed to the central nervous system chiefly by the trigeminal nerve, with first order neurones terminating in the nucleus caudalis of the spinal trigeminal tract and an area lateral to the dorsal horn of the spinal cord at the second cervical segment. The evoked discharge of second order neurons can be suppressed by activation of the endogenous pain control system or, in about one third of cases, by the local application of ergot derivatives or the serotonin (5HT1) agonist sumatriptan (GR43175). Stimulation of brainstem structures such as locus ceruleus, raphe nuclei and the trigeminal system induce changes in the cerebral and extracranial circulations of the experimental animal that mimic those of migraine with aura (classical migraine). Clinical and laboratory observations have led to a neural hypothesis for migraine in which changes in hypothalamic function (an 'internal clock') and reactions to stress or excessive afferent stimuli are thought to initiate brainstem activity, causing secondary vascular changes and release of inhibition of the trigeminal pain pathways to cause headache. Painful distension of cranial blood vessels may contribute the throbbing component to migraine headache. Migraine is associated with a lowered level of platelet serotonin that is thought to reflect monoamine depletion in brainstem nuclei. Migraine headache can be precipitated by reserpine, which releases serotonin from body stores, and relieved by the intravenous infusion of serotonin. The new 5HT1 agonist sumatriptan promises to have the beneficial effects of serotonin without the side-effects that limited its clinical use.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed2006

Operator volume and outcomes of primary angioplasty for acute myocardial infarction in a single high-volume centre.

OBJECTIVE: The guidelines for the management of ST-elevation myocardial infarction (STEMI) state the minimum operator volume for percutaneous coronary interventions (PCIs), without strong evidence of a relationship between operator volume and outcomes of primary angioplasty, at variance with elective practice. We sought to investigate the effect of operator volume on primary PCI for STEMI. METHODS: Three hundred and thirty-one consecutive STEMI patients were treated over 19 months with primary PCI in a high-volume centre without on-site cardiac surgery. Three skilled operators, with very different volumes of interventional practice, performed the PCI procedures around-the-clock. RESULTS: Operators were divided into very high (A), intermediate high (B) and low high volume (C). Demographic, clinical, angiographic, and procedural characteristics of the patient population did not differ among operators, with the exception of three-vessel disease (P = 0.016), circumflex infarct-related artery (P = 0.002), mechanical support (P = 0.02), use of abciximab (P = 0.003) for operator C, use of tirofiban for operator B (P = 0.02), and type of stent for operator A (P = 0.0004). Similarly, no differences were observed among operators in in-hospital outcomes (death, a composite of major adverse cardiovascular events, ST-segment resolution, thrombolysis in myocardial infarction flow grade 3, length of hospitalization) and haemorrhagic complications. CONCLUSIONS: Our data show that there is not a significant relationship between operator volume over the threshold indicated by the guidelines, and both primary PCI early outcomes and complications in STEMI, and suggest that expertise and experience of the whole professional team rather than just of the individual operator play a major role.

Age Factors↗

PubMed1997

Pacemaker activity in a sensory ending with multiple encoding sites: the cat muscle spindle primary ending.

1. A combined physiological, histological and computer modelling study was carried out on muscle spindles of the cat tenuissimus muscle to examine whether there was any correlation between the functional interaction of putative encoding sites, operated separately by static and dynamic fusimotor neurones, and the topological structure of the preterminal branches of the primary sensory ending. 2. Spindles, whose I a responses to stretch and separate and combined static and dynamic fusimotor stimulation were recorded in physiological experiments, were located in situ. Subsequently the ramifications of the sensory ending were reconstructed histologically, and the topology of the branch tree was used in computer simulations of I a responses to examine the effect of the electronic separation of encoding sites on the static-dynamic interaction pattern. 3. Interactions between separate static and dynamic inputs, manifest in responses to combineed stimulation, were quantified by a coefficient of interaction (Ci) which, by definition, was 1 for strictly linear summation of separate inputs and zero for maximum occlusion between inputs. 4. For the majority of spindles static-dynamic interactions were characterized by pronounced occlusion (C1 < 0.35). In these spindles putative encoding sites (the peripheral heminodes of the branches supplying the intrafusal fibres activated by individual fusimotor efferents) were separated by a minimum conduction path of between three and ten myelinated segments (2-9 nodes of Ranvier). In contrast, significant summation (C1, approximately 0.7) was found in only one spindle. In this case putative encoding sites were separated by a single node. 5. Occlusion was not due to encoder saturation and it could not be accounted for by any other known physiological mechanisms (intrafusal fatigue or unloading). It is therefore attributed to competitive pacemaker interaction between encoding sites which are largely selectively operated by static and dynamic fusimotor efferents. 6. Model simulations of real preterminal-branch tree structures confirmed that short conduction paths between encoding sites were associated with manifest summation, whereas longer minimum conduction paths favoured pronounced occlusion. 7. In the extreme, occlusion could be so pronounced as to give rise to negative values of C1 during critical segments of response cycles. This was associated with lower discharge rates during combined static and dynamic stimulation than the higher of the individual stimulation effects. This phenomenon is referred to as hyperocclusion. Computer simulations demonstrated that hyperocclusion could be accounted for by a slow ionic adaptation process. e.g. by a very slowly activating K+ conductance.

Animals↗

PubMed2001

Lake level fluctuations synchronize genetic divergences of cichlid fishes in African lakes.

Water level fluctuations are important modulators of speciation processes in tropical lakes, in that they temporarily form or break down barriers to gene flow among adjacent populations and/or incipient species. Time estimates of the most recent major lowstands of the three African Great Lakes are thus crucial to infer the relative timescales of explosive speciation events in cichlid species flocks. Our approach combines geological evidence with genetic divergence data of cichlid fishes from the three Great East African Lakes derived from the fastest-evolving mtDNA segment. Thereby, we show for each of the three lakes that individuals sampled from several populations which are currently isolated by long geographic distances and/or deep water form clusters of equally closely related haplotypes. The distribution of identical or equally closely related haplotypes in a lake basin allows delineation of the extent of lake level fluctuations. Our data suggest that the same climatic phenomenon synchronized the onset of genetic divergence of lineages in all three species flocks, such that their most recent evolutionary history seems to be linked to the same external modulators of adaptive radiation. A calibration of the molecular clock of the control region was elaborated by gauging the age of the Lake Malawi species flock through the divergence among the utaka-cichlid and the mbuna-cichlid lineages to minimally 570,000 years and maximally 1 Myr. This suggests that the low-lake-level period which established the observed patterns of genetic relatedness dates back less than 57,000 years, probably even to 17,000-12,400 years ago, when Lake Victoria dried up and Lakes Malawi and Tanganyika were also low. A rapid rise of all three lakes about 11,000 years ago established the large-scale population subdivisions observed today. Over that period of time, a multitude of species originated in Lakes Malawi and Victoria with an impressive degree of morphological and ecological differentiation, whereas the Tanganyikan taxa that were exposed to the same habitat changes hardly diverged ecologically and morphologically. Our findings also show that patterns of genetic divergences of stenotopic organisms provide valuable feedback on geological and sedimentological time estimates for lake level changes.

Africa↗

PubMed2003

Intraluminal pressure oscillation enhances subsequent airway contraction in isolated bronchial segments.

A period of deep inspiration in humans has been shown to attenuate subsequent bronchoconstriction, a phenomenon termed bronchoprotection. The bronchoprotective effect of deep inspiration may be caused though a depression in the force production of airway smooth muscle (ASM). We determined the response of whole airway segments and isolated ASM to a period of cyclic stretches. Isovolumetric contraction to electrical field stimulation (EFS) was assessed in porcine bronchial segments before and after intraluminal pressure oscillation from 5 to 25 cmH(2)O for 10 min at 0.5 Hz. Morphometry showed that this pressure oscillation stretched ASM length by 21%. After pressure oscillation, the response to EFS was not reduced but instead was modestly enhanced (P < 0.01). Airway responses to EFS returned to preoscillation levels 10 min after the end of oscillation. The increase in EFS response after pressure oscillation was not altered by the addition of indomethacin. In a separate experiment, we assessed isometric force in isolated ASM strips before and after length oscillation. The amplitude, frequency, and duration of length oscillation were similar to those induced in bronchial segments. In contrast to bronchial segments, length oscillation of ASM produced a significant depression in isometric force induced by EFS (P < 0.01). These results suggest that the response of ASM to length oscillation is modified by the airway wall. They also suggest that the phenomenon of bronchoprotection reported in some in vivo studies may not be an intrinsic property of the airway.

Animals↗