Extinct in the wild: The precarious state of Earth's most threatened group of species

Extinct in the Wild (EW) species are placed at the highest risk of extinction under the International Union for Conservation of Nature Red List, but the extent and variation in this risk have never been evaluated. Harnessing global databases of ex situ animal and plant holdings, we report on the perilous state of EW species. Most EW animal species-already compromised by their small number of founders-are maintained at population sizes far below the thresholds necessary to ensure demographic security. Most EW plant species depend on live propagation by a small number of botanic gardens, with a minority secured at seed bank institutions. Both extinctions and recoveries are possible fates for EW species. We urgently call for international effort to enable the latter.

Testing a global standard for quantifying species recovery and assessing conservation impact

Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a "Green List of Species" (now the IUCN Green Status of Species). A draft Green Status framework for assessing species' progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species' viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species' recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard.

Prediction of antiferromagnetism in barium chromium phosphide confirmed after synthesis

We have carried out density-functional theory (DFT) calculations for the chromium pnictide BaCr₂P₂, which is structurally analogous to BaFe₂As₂, a parent compound for iron-pnictide superconductors. Evolutionary methods combined with DFT predict that the chromium analog has the same crystal structure as the latter. DFT also predicts Néel antiferromagnetic order on the chromium sites. Comparison with a simple electron-hopping model over a square lattice of chromium atoms suggests that it is due to residual nesting of the Fermi surfaces. We have confirmed the DFT predictions directly after the successful synthesis of polycrystalline samples of BaCr₂P₂. X-ray diffraction recovers the predicted crystal structure to high accuracy, while magnetic susceptibility and specific-heat measurements are consistent with a transition to an antiferromagnetically ordered state below [Formula: see text] K.

Quantifying species recovery and conservation success to develop an IUCN Green List of Species

Stopping declines in biodiversity is critically important, but it is only a first step toward achieving more ambitious conservation goals. The absence of an objective and practical definition of species recovery that is applicable across taxonomic groups leads to inconsistent targets in recovery plans and frustrates reporting and maximization of conservation impact. We devised a framework for comprehensively assessing species recovery and conservation success. We propose a definition of a fully recovered species that emphasizes viability, ecological functionality, and representation; and use counterfactual approaches to quantify degree of recovery. This allowed us to calculate a set of 4 conservation metrics that demonstrate impacts of conservation efforts to date (conservation legacy); identify dependence of a species on conservation actions (conservation dependence); quantify expected gains resulting from conservation action in the medium term (conservation gain); and specify requirements to achieve maximum plausible recovery over the long term (recovery potential). These metrics can incentivize the establishment and achievement of ambitious conservation targets. We illustrate their use by applying the framework to a vertebrate, an invertebrate, and a woody and an herbaceous plant. Our approach is a preliminary framework for an International Union for Conservation of Nature (IUCN) Green List of Species, which was mandated by a resolution of IUCN members in 2012. Although there are several challenges in applying our proposed framework to a wide range of species, we believe its further development, implementation, and integration with the IUCN Red List of Threatened Species will help catalyze a positive and ambitious vision for conservation that will drive sustained conservation action.

Collective mode at Lifshitz transition in iron-pnictide superconductors

We obtain the exact low-energy spectrum of two mobile holes in a t-J model for an isolated layer in an iron-pnictide superconductor. The minimum d xz and d yz orbitals per iron atom are included, with no hybridization between the two. After tuning the Hund coupling to a putative quantum critical point (QCP) that separates a commensurate spin-density wave from a hidden-order antiferromagnet at half filling, we find an s-wave hole-pair groundstate and a d-wave hole-pair excited state. Near the QCP, both alternate in sign between hole Fermi surface pockets at the Brillouin zone center and emergent electron Fermi surface pockets at momenta that correspond to commensurate spin-density waves (cSDW). The dependence of the energy splitting with increasing Hund coupling yields evidence for a true QCP in the thermodynamic limit near the putative one, at which the s-wave and d-wave Cooper pairs are degenerate. A collective s-to-d-wave oscillation of the macroscopic superconductor that couples to orthorhombic shear strain is also identified. Its resonant frequency is predicted to collapse to zero at the QCP in the limit of low hole concentration. This implies degeneracy of Cooper pairs with s, d and [Formula: see text] symmetry in the corresponding quantum critical state. We argue that the critical state describes Cooper pairs in hole-doped iron superconductors at the Lifshitz transition, where electron bands first rise above the Fermi level. We thereby predict that the s-to-d-wave collective mode observed by Raman spectroscopy in Ba1-x K x Fe2As2 at optimal doping should also be observed at higher doping near the Lifshitz transition.

Sonic hedgehog stimulates proliferation of human periodontal ligament stem cells

Regulation of cell renewal in the periodontium is a critical cell function that has not been clarified. Sonic hedgehog (Shh) is a secreted signaling molecule that plays a key role during development and adult tissue homeostasis. In the present study, we have analyzed the role played by Shh in human periodontal ligament stem cell (HPLSC) proliferation. HPLSC were isolated with anti-STRO-1 antibodies. Shh increased the expression of GLI1 and PTC-1 and selectively stimulated cell proliferation in STRO-1(+) derived from adult periodontal ligament. Shh components were localized to primary cilia in STRO-1(+) cells after Shh stimulation. STRO-1(+) also expressed Shh, suggesting an autocrine-regulated phenomenon. Thus, we propose that Shh plays a critical role in the regulation of cell proliferation in STRO-1(+)/HPLSC.

The impact of conservation on the status of the world's vertebrates

Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world's vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species.

Low ordered magnetic moment by off-diagonal frustration in undoped parent compounds to iron-based high-T(c) superconductors

A Heisenberg model over the square lattice recently introduced by Si and Abrahams to describe local-moment magnetism in the new class of Fe-As high-T(c) superconductors is analyzed in the classical limit and on a small cluster by exact diagonalization. In the case of spin-1 iron atoms, large enough Heisenberg exchange interactions between neighboring spin-1/2 moments on different iron 3d orbitals that frustrate true magnetic order lead to hidden magnetic order that violates Hund's rule. It accounts for the low ordered magnetic moment observed by elastic neutron diffraction in an undoped parent compound to Fe-As superconductors. We predict that low-energy spin-wave excitations exist at wave numbers corresponding to either hidden Néel or hidden ferromagnetic order.

Emergence of dissipative structures in current-carrying superconducting wires

We discuss the emergence of a spontaneous temperature and critical current spatial modulation in current-carrying high-temperature superconducting wire. The modulation of the critical current along the wire on a scale of 3-10 mm forces a fraction of the transport current to crisscross the resistive interface between the superconducting film and normal metal stabilizer attached to it. This generates additional heat that allows such a structure to be self-sustainable. Stability and the conditions for experimental observation of this phenomenon are also discussed.

One hundred questions of importance to the conservation of global biological diversity

We identified 100 scientific questions that, if answered, would have the greatest impact on conservation practice and policy. Representatives from 21 international organizations, regional sections and working groups of the Society for Conservation Biology, and 12 academics, from all continents except Antarctica, compiled 2291 questions of relevance to conservation of biological diversity worldwide. The questions were gathered from 761 individuals through workshops, email requests, and discussions. Voting by email to short-list questions, followed by a 2-day workshop, was used to derive the final list of 100 questions. Most of the final questions were derived through a process of modification and combination as the workshop progressed. The questions are divided into 12 sections: ecosystem functions and services, climate change, technological change, protected areas, ecosystem management and restoration, terrestrial ecosystems, marine ecosystems, freshwater ecosystems, species management, organizational systems and processes, societal context and change, and impacts of conservation interventions. We anticipate that these questions will help identify new directions for researchers and assist funders in directing funds.

Alendronate in the prevention of osteoporosis: 7-year follow-up

In a 3-year study followed by a 2-year open-label extension, alendronate sodium (ALN) maintained or increased bone mineral density (BMD) in 445 recently postmenopausal women with a spine BMD T-score >-2. In a second 2-year extension, 84 women previously treated with either 5 or 10 mg ALN daily during the first 3 years and 5 mg ALN during the first extension (group A) were randomized to either 5 mg ALN or placebo (PBO). Another group of 59 women (group B) received 20 mg ALN during the first 2 years, PBO during year 3, and were then followed up without treatment during years 4-7. In group A, continuous ALN treatment for 7 years increased spine and trochanter BMD by 2.7-4.1 and 3.3-4.2%, respectively, while femoral neck BMD was maintained. Patients initially receiving 10 mg ALN maintained total body BMD, whereas those treated with 5 mg ALN experienced a small but significant loss after 7 years. Among women who received ALN 5 mg during years 4-7, those who had been treated with ALN 10 mg in the first 3 years had slightly greater increases in BMD at most sites at the end of the study, compared with women who received ALN 5 mg during the first 3 years. During years 6-7, patients who switched to PBO during the previous 2 years showed a significant loss in femoral neck BMD, whereas changes at the other sites were not significant. Women in group B showed significant loss in BMD at all skeletal sites during years 4-7, when they received no treatment. In conclusion, ALN 5 or 10 mg daily for up to 7 years prevents bone loss in recently postmenopausal women. Patients started on ALN 10 mg appear to gain more BMD than those initially treated with 5 mg ALN. Early postmenopausal women who discontinue ALN after 2 years of treatment experience significant bone loss at all skeletal sites despite the higher (20 mg) initial dosing. The ALN was generally well tolerated during 7 years of treatment.

Degradation of phase coherence by defects in a two-dimensional vortex lattice

The thermodynamic nature of two-dimensional vortex matter is studied through a duality analysis of the XY model over the square lattice with low uniform frustration. A phase-coherent vortex lattice state is found at low temperature if rigid translations are prohibited. It shows a nonzero phase rigidity that is degraded exclusively by the creation of dislocation pairs. The unbinding of such pairs causes the vortex lattice to simultaneously lose phase coherence and to melt at a continuous (Kosterlitz-Thouless) phase transition. General phase autocorrelation functions are also computed, and these results are used to argue for the existence of a continuous melting transition of vortex matter in layered superconductors.

Procedural learning in schizophrenia: further consideration on the deleterious effect of neuroleptics

Deficits in procedural learning remain a controversial issue in schizophrenia. This may be related to the nature of the neuroleptic treatment of schizophrenic patients as conventional neuroleptics may be more deleterious than new atypical neuroleptics. However, there is no comparative study on the effect of specific neuroleptics on procedural learning. In this study, three groups of patients treated with different neuroleptics were compared to normal controls on two procedural learning tasks. In a visuo-motor task, patients and controls showed similar learning rates, although schizophrenic patients showed generally lower performances than normal controls. However, patients treated with a conventional neuroleptic, but not those treated with the atypical neuroleptics, showed many fluctuations during the initial learning phase. In a problem-solving task, all groups were comparable in performance and learning fluctuations, but learning rates were lower in patients treated with the neuroleptic showing the higher incidence of extrapyramidal symptoms. This suggests that procedural learning abilities may be significantly affected by neuroleptics in schizophrenia, although the effect may differ between tasks and the specific neuroleptics. Fluctuations in the initial learning phase of the visuo-motor task probably results from a frontal dysfunction while reduced learning rates, such as those observed in the problem solving task, may be attributed to a striatal dysfunction. This is concordant with the differential pharmacological actions of the conventional and atypical neuroleptics in these two cerebral areas.

Dermatan sulfate proteoglycans from the mineralized matrix of the avian eggshell

The eggshell of the chicken is a useful model to study matrix components which affect biomineralization. As an extension of our previous immunohistochemical work which suggested the presence of dermatan sulfate proteoglycans in the mineralized region of the eggshell, a study was undertaken to characterize these molecules biochemically. After demineralization with HCl and extraction with 4 M guanidinium chloride containing protease inhibitors, the extract was partitioned by anion exchange chromatography. Step elution with 0.25 M and 1.0 M sodium chloride resulted in the generation of two fractions, both of which contain chondroitinase-sensitive proteoglycans with molecular weights estimated at 200,000 by gel electrophoresis. The proteoglycans in each fraction have core proteins with molecular weights of approximately 120,000 and glycosaminoglycans with average molecular weights of 22,000. Based on differential sensitivity to chondroitinase ABC and AC II, these glycosaminoglycans contain a small proportion of dermatan sulfate. The disaccharide compositions of these glycosaminoglycans differ for the proteoglycans eluted with 0.25 M and 1.0 M sodium chloride. Those eluted with lower sodium chloride are enriched in unsulfated chondroitin and have much more 4-sulfated than 6-sulfated disaccharides; those eluted with 1.0 M sodium chloride contain primarily 4-sulfated disaccharides, a small amount of 6-sulfated disaccharides, and less unsulfated disaccharides than the proteoglycans eluted with 0.25 M sodium chloride. The large difference in the proportions of unsulfated chondroitin may be the reason for the elution at different sodium chloride concentrations. Both of the anion exchange column fractions contain other proteins in addition to the proteoglycans. These proteins are not separated from the proteoglycans by a second anion exchange column or by molecular sieve chromatography under dissociative conditions. Of particular interest is the observation that the eggshell proteoglycans and their core proteins are recognized by a monoclonal antibody which recognizes an epitope on the core protein of avian versican. This suggests that, in spite of the large differences in the sizes of the core proteins of versican and the eggshell proteoglycans, these core proteins share some homology. Because anionic molecules are thought to be important regulators of biomineralization, and because preparations like those analyzed in this study have been shown to influence in vitro calcium carbonate crystallization, the eggshell proteoglycans may play a role in eggshell mineralization.

Geographic Distribution of Endangered Species in the United States

Geographic distribution data for endangered species in the United States were used to locate "hot spots" of threatened biodiversity. The hot spots for different species groups rarely overlap, except where anthropogenic activities reduce natural habitat in centers of endemism. Conserving endangered plant species maximizes the incidental protection of all other species groups. The presence of endangered birds and herptiles, however, provides a more sensitive indication of overall endangered biodiversity within any region. The amount of land that needs to be managed to protect currently endangered and threatened species in the United States is a relatively small proportion of the land mass.

Incidence and significance of cardiac arrhythmia in geriatric oral surgery patients

We recorded heart rhythms of 40 older patients (20 medicated for cardiovascular disease and 20 not medicated for cardiovascular disease) during an outpatient oral surgery visit to determine overall arrhythmia incidence and severity, differences in incidence associated with cardiovascular medication status, and the impact of surgical intervention on arrhythmia incidence. We hypothesized that both groups would show similar arrhythmia numbers and types during surgical visits and that a history of medication for cardiovascular disease would not be an indicator of cardiac arrhythmia. Enrollment remained open until 20 patients older than 60 years of age from each group agreed to participate. Data were analyzed using the chi square statistic and Fisher's exact test (2-tailed). Included in the study were 24 women and 16 men; their mean age was 70.5 years (range, 60 to 86 years). Arrhythmias were detected in 17 patients and 33 of the 160 recorded rhythms. None of the detected arrhythmias were considered life-threatening. Significantly more arrhythmias occurred before administration of anesthesia than during administration of epinephrine-containing local anesthetics (p = 0.0001), and a greater number of rhythm disturbances were seen during the surgical procedure when compared with anesthesia administration (p = 0.0170). No differences in arrhythmia incidence were seen with increasing age, when male patients were compared with female patients, or when patients pharmacologically treated for cardiovascular disease were compared with patients not taking cardiovascular therapeutic medications. We conclude that although arrhythmias in this ambulatory population are common, they are typically benign in character and cardiovascular medication status is not indicative of their presence. In addition, minor oral surgery intervention with local anesthetics used in recommended dosages has no effect on cardiac arrhythmia status in the ambulatory geriatric population.

The avian eggshell extracellular matrix as a model for biomineralization

The avian eggshell is a complex, extracellularly assembled structure which contains both mineralized and non-mineralized regions. The composition of the hen eggshell organic matrix was examined by immunohistochemistry with antibodies to different extracellular matrix molecules. Type I collagen is found in the shell membranes, but only after treatment of the tissue sections with pepsin. When incomplete eggshells are removed from the oviduct and immunostained, type I collagen can be detected in the shell membranes without pepsin treatment. The shell membranes, which are non-mineralized, also contain type X collagen, and this immunostaining does not require pepsin treatment. The occurrence of type X collagen in the shell membranes is surprising, since this collagen has not been found in any tissue other than hypertrophic cartilage. Immunostaining for various glycosaminoglycans shows the presence of keratan sulfate and dermatan sulfate. Several different antibodies to keratan sulfate stain different regions of the eggshell; one keratan sulfate epitope is prominent in the calcium reserve assemblies. Dermatan sulfate staining is very intense in the palisade region. Demineralized matrix from the palisade region was extracted with guanidine and fractionated by ion exchange chromatography. A approximately 200-kDa dermatan sulfate proteoglycan is found in these extracts, along with a number of protein components. This preparation was tested for its ability to affect calcium carbonate crystal formation in vitro. Pieces of demineralized shell membranes were used as a substrate for crystal formation and various amounts of the palisade matrix dermatan sulfate proteoglycan preparation were added to the solution from which the crystals were formed. This material causes a concentration-dependent change in crystal morphology to one in which the crystals are smaller and more rounded, which more closely approximates the crystals normally observed in eggshells. These results suggest that the dermatan sulfate proteoglycans may be important in modulating crystal morphology in the hen eggshell and correlate with mineralization-modulating biomolecules from other calcified tissue, which are generally anionic.

Quantified EEG changes associated with a positive clinical response to clozapine in schizophrenia

1. The authors conducted a retrospective exploratory computerized EEG study on the effect of clozapine in treatment-refractory schizophrenics, 10 high-responders (HRs) and 10 low-responders (LRs), in an attempt to correlate amplitude but especially coherence changes with a positive clinical response to clozapine. 2. EEGs with eyes closed were obtained before and during a clozapine treatment. Both groups had a similar drug profile with regards to non-clozapine medication. Probability maps were computed to illustrate changes of amplitude and coherence (for all combinations of paired electrodes) for 4 frequency bands (theta, alpha, beta 1 and 2). 3. The effect on AMPLITUDE was a generalized increase in lower bands and a decrease in anterior regions in higher bands of both HRs and LRs. Considerable changes of COHERENCE were observed on a wide set of paired electrodes in most frequency bands with some electrodes involved in HRs but uninvolved or differently involved in LRs suggesting differences in selected brain regions. 4. Changes of coherence but not amplitude were correlated with changes on the BPRS, thus to clinical improvement, and concerned mostly the right anterior-medial temporal (T4) and central (C4) electrodes paired with prefrontal electrodes, left central (C3), temporal (T3) and parietal (P3) electrodes in the theta band. 5. Clozapine has both generalized and regional effects as can be suspected considering its effect on many subtypes of brain receptors. A brain dysfunction centralized on the right anterior-medial temporal region may characterize treatment-refractory schizophrenics.

Crystallization studies on avian eggshell membranes: implications for the molecular factors controlling eggshell formation

The avian eggshell is a natural biopolymer and mineral composite. It is a very useful model for biomimetic mineralization, since it is among the fastest forming hard tissues known. Isolated eggshell membranes, which were demineralized in vitro, were used to investigate the in vitro modulation of CaCO3 crystal deposition by organic matrix materials. Crystallization on the demineralized eggshell membrane occurred almost exclusively at the peripheries of residual calcium reserve assemblies, which contain a high concentration of sulfur. Similar structures are observed for eggshell membranes after natural demineralization. The characteristic rhombohedral crystal morphologies of the calcite crystals grown in this in vitro system are much less regular when grown in the presence of organic matrix or partially purified dermatan sulfate proteoglycans obtained from the eggshell. The effect of these macromolecules on the morphology and size of CaCO3 crystals is concentration-dependent. These studies indicate the complexity of the molecular and ionic interactions involved in the initiation and formation of the eggshell, with the focus on the role of the organic matrix.

Membrane-associated proteoglycans produced by Sertoli cells are not randomly distributed on the cell surface

Sertoli cells in culture synthesize two membrane-associated proteoglycans (PGs) containing as glycosaminoglycan (GAG) moieties either chondroitin sulfate (CS) or CS and heparan sulfate (HS); the latter PG is, therefore, referred to as the mixed PG. To determine if these PGs are randomly distributed on the cell surface, Sertoli cell monolayers were treated with chondroitinase ABC, and then the remaining PGs were analyzed by DEAE-Sephacel chromatography. The results obtained with Sertoli cell monolayers show that the CS of the mixed PG is degraded by chondroitinase, while the CS-PG is not degraded. In contrast, chondroitinase treatment of Sertoli cells in suspension shows that both the mixed PG and the CS-PG are degraded. From this, it is inferred that the mixed PG is apically oriented and the CS-PG is basolaterally oriented. Studies of the adhesion of germ cells to Sertoli cell monolayers give further support to the apical location of the mixed PG and suggest that its HS moiety is involved in the attachment of germ cells to Sertoli cells.

Nocturnal prolactin and growth hormone levels in children with complex partial and generalized tonic-clonic seizures

This study measures whether there is a rise in the secretion of nocturnal prolactin and growth hormone (GH), during the delta phase of the first sleep cycle in children who are suffering from either complex partial or generalized tonic-clonic seizures. The findings are compared with those obtained in the control group of patients which is made up who suffer from pseudoseizures. There is a moderate but significant rise in the nocturnal prolactin plasma level in both types of infantile seizures. No significant difference was found in the GH.

Clot-trapper device for transjugular thrombectomy from the inferior vena cava

The clot-trapper device for transjugular thrombectomy was used in 10 dogs with acute thrombosis and two dogs with chronic thrombosis. In eight of these animals, the clots were trapped with the clot-trapper device, then a mechanical thrombectomy device was used to destroy the clots. In 10 animals, including eight with in vitro thrombi and two with in situ thrombi, thrombi were efficiently trapped with the clot-trapper device. In two animals, pulmonary embolism occurred because of a discrepancy between the diameter of the inferior vena cava and the diameter of the bag opening. After increasing the size of the loop to match the diameter of the inferior vena cava, trapping of all thrombi was possible in both experiments (acute and chronic thrombosis). The clot-trapper device, in conjunction with an embolectomy balloon catheter and/or a mechanical thrombectomy device, facilitates the removal of thrombi from the inferior vena cava and iliac veins.

Interstitial collagen synthesis by somatic testicular cells in culture

The synthesis, distribution and types of collagen produced by somatic testicular cells in culture was studied. To investigate whether changes in collagen synthesis correlate with the age of the animal, cultures derived from immature and pubertal rats were established. Immature rats synthesize 40 per cent more collagen than pubertal rats. Both groups of animals synthesize procollagen types I and III. Pro-collagen type I is present in the culture medium as well as in the cell fraction, while type III is only detected in the culture medium. In the transition from immature to pubertal rat, the ratio of procollagen type III to procollagen type I diminishes from 5.7 to 1.7. These results indicate that the synthesis, distribution and molecular characteristics of interstitial collagens changes with the age of the animal. Since, the content of other extracellular matrix components such as proteoglycans and collagen type IV also varies with age, we postulate that the composition of the extracellular matrix in the testes is not constant but changes with sexual development.