Temperature-bounded development of Dirofilaria immitis larvae restricts the geographical distribution and seasonality of its transmission: case study and decision support system for canine heartworm management in Australia

Dirofilaria immitis is the causative agent of canine heartworm disease. We used the established heartworm development unit (HDU) principle to map the extrinsic incubation period (EIP) of D. immitis in Australia using historical weather data from 2013-2022. We found weather conditions suitable for EIP completion showed substantial seasonality and geographical variability. Whilst a considerable percentage of the Australian territory showed suitable weather conditions to always support EIP completion (17%), only 2.7% of the 2021 Australian human population lived in this region. Therefore, 97% of the population lived in an area that changed its EIP suitability within the study period. EIP completion is required prior to D. immitis transmission, meaning that infection risk of D. immitis is seasonal and location-dependent, being disrupted each year for most of the human population's dogs. We developed an online, open access tool allowing us to visualise EIP completion across Australia historically and in near real-time. We aim to support veterinarians to make risk-based recommendations for dirofilariosis prevention by using the tool, available at https://heartworm-mapping.adelaide.edu.au/shiny/.

Advancing novel therapies for neurodegeneration through an innovative model for industry-academia collaborations: A decade of the Eisai-UCL experience

External innovation initiatives in the pharmaceutical industry have become an integral part of research and development. Collaborations have been built to enhance innovation, mitigate risk, and share cost, especially for neurodegenerative diseases, a therapeutic area that has suffered from high attrition rates. This article outlines the Eisai-University College London (UCL) Drug Discovery and Development Collaboration as a case study of how to implement a productive industry-academic partnership. In the first 10 years, seven projects have been established and the first project, a novel anti-tau antibody for Alzheimer's disease, has entered clinical trials, providing early validation of this collaboration model.

Relative diagnostic accuracy of point-of-care tests to rule-in Dirofilaria immitis infection in clinically suspect dogs: A systematic review and meta-analysis

Canine heartworm, Dirofilaria immitis, can cause severe disease and sometimes death of the host. Associated clinical signs, lack of preventative usage and regional endemicity are unlikely sufficient by themselves to reach a definitive diagnosis. Several point-of-care (POC) diagnostic tests are commercially available to aid in-clinic diagnosis, however, there is variable diagnostic accuracy reported and no synthesis of published evidence. This systematic review aims at meta-analysing the likelihood ratio of a positive result (LR⁺) to inform the selection and interpretation of POC tests in practice to rule-in heartworm infection when there is clinical suspicion. Three literature index interfaces (Web of Science, PubMed, Scopus) were searched on November 11th, 2022, for diagnostic test evaluation (DTE) articles assessing at least one currently commercialised POC test. Risk of bias was assessed adapting the QUADAS-2 protocol and articles with no evidence of high risk of bias were meta-analysed if deemed applicable to our review objective. Substantial between DTE heterogeneity was investigated including potential threshold or covariate effects. A total of 324 primary articles were sourced and 18 were retained for full text review of which only three had low risk of bias in all four QUADAS-2 domains. Of the nine heartworm POC tests evaluated, only three, IDEXX SNAP (n DTEs = 6), Zoetis WITNESS (n DTEs = 3) and Zoetis VETSCAN (n DTEs = 5) could be analysed. Both WITNESS and VETSCAN DTEs showed substantial heterogeneity due to a putative threshold effect and no summary point estimates could be reported. SNAP DTEs showed acceptable heterogeneity, and a summary LR⁺ was estimated at 559.0 (95%CI: 24.3-12,847.4). The quality and heterogeneity of heartworm POC test DTEs was highly variable which restricted our summary of the diagnostic accuracy to only the SNAP test. A positive result from the SNAP test provides strong evidence of the presence of an infection with adult heartworm(s) in a dog patient and this test is warranted to rule-in clinical suspicion(s) in clinics. However, our review did not appraise the literature to assess the fitness of SNAP test, or any other POC tests, to rule-out heartworm infection in dogs without clinical suspicion or following heartworm therapy.

Selection and structural characterization of anti-TREM2 scFvs that reduce levels of shed ectodomain

Mutations in TREM2, a receptor expressed by microglia in the brain, are associated with an increased risk of neurodegeneration, including Alzheimer's disease. Numerous studies support a role for TREM2 in sensing damaging stimuli and triggering signaling cascades necessary for neuroprotection. Despite its significant role, ligands and regulators of TREM2 activation, and the mechanisms governing TREM2-dependent responses and its cleavage from the membrane, remain poorly characterized. Here, we present phage display generated antibody single-chain variable fragments (scFvs) to human TREM2 immunoglobulin-like domain. Co-crystal structures revealed the binding of two scFvs to an epitope on the TREM2 domain distal to the putative ligand-binding site. Enhanced functional activity was observed for oligomeric scFv species, which inhibited the production of soluble TREM2 in a HEK293 cell model. We hope that detailed characterization of their epitopes and properties will facilitate the use of these renewable binders as structural and functional biology tools for TREM2 research.

Inhibition of IL-34 Unveils Tissue-Selectivity and Is Sufficient to Reduce Microglial Proliferation in a Model of Chronic Neurodegeneration

The proliferation and activation of microglia, the resident macrophages in the brain, is a hallmark of many neurodegenerative diseases such as Alzheimer's disease (AD) and prion disease. Colony stimulating factor 1 receptor (CSF1R) is critically involved in regulating microglial proliferation, and CSF1R blocking strategies have been recently used to modulate microglia in neurodegenerative diseases. However, CSF1R is broadly expressed by many cell types and the impact of its inhibition on the innate immune system is still unclear. CSF1R can be activated by two independent ligands, CSF-1 and interleukin 34 (IL-34). Recently, it has been reported that microglia development and maintenance depend on IL-34 signaling. In this study, we evaluate the inhibition of IL-34 as a novel strategy to reduce microglial proliferation in the ME7 model of prion disease. Selective inhibition of IL-34 showed no effects on peripheral macrophage populations in healthy mice, avoiding the side effects observed after CSF1R inhibition on the systemic compartment. However, we observed a reduction in microglial proliferation after IL-34 inhibition in prion-diseased mice, indicating that microglia could be more specifically targeted by reducing IL-34. Overall, our results highlight the challenges of targeting the CSF1R/IL34 axis in the systemic and central compartments, important for framing any therapeutic effort to tackle microglia/macrophage numbers during brain disease.

Increasing Tau 4R Tau Levels Exacerbates Hippocampal Tau Hyperphosphorylation in the hTau Model of Tauopathy but Also Tau Dephosphorylation Following Acute Systemic Inflammation

Inflammation is considered a mechanistic driver of Alzheimer's disease, thought to increase tau phosphorylation, the first step to the formation of neurofibrillary tangles (NFTs). To further understand how inflammation impacts the development of tau pathology, we used (hTau) mice, which express all six, non-mutated, human tau isoforms, but with an altered ratio of tau isoforms favoring 3R tau due to the concomitant loss of murine tau (mTau) that is predominantly 4R. Such an imbalance pattern has been related to susceptibility to NFTs formation, but whether or not this also affects susceptibility to systemic inflammation and related changes in tau phosphorylation is not known. To reduce the predominance of 3R tau by increasing 4R tau availability, we bred hTau mice on a heterozygous mTau background and compared the impact of systemic inflammation induced by lipopolysaccharide (LPS) in hTau mice hetero- or homozygous mTau knockout. Three-month-old male wild-type (Wt), mTau^+/-, mTau^-/-, hTau/mTau^+/-, and hTau/mTau^-/- mice were administered 100, 250, or 330 μg/kg of LPS or its vehicle phosphate buffer saline (PBS) [intravenously (i.v.), n = 8-9/group]. Sickness behavior, reflected by behavioral suppression in the spontaneous alternation task, hippocampal tau phosphorylation, measured by western immunoblotting, and circulating cytokine levels were quantified 4 h after LPS administration. The persistence of the LPS effects (250 μg/kg) on these measures, and food burrowing behavior, was assessed at 24 h post-inoculation in Wt, mTau^+/-, and hTau/mTau^+/- mice (n = 9-10/group). In the absence of immune stimulation, increasing 4R tau levels in hTau/mTau^+/- exacerbated pS202 and pS396/404 tau phosphorylation, without altering total tau levels or worsening early behavioral perturbations characteristic of hTau/mTau^-/- mice. We also show for the first time that modulating 4R tau levels in hTau mice affects the response to systemic inflammation. Behavior was suppressed in all genotypes 4 h following LPS administration, but hTau/mTau^+/- exhibited more severe sickness behavior at the 100 μg/kg dose and a milder behavioral and cytokine response than hTau/mTau^-/- mice at the 330 μg/kg dose. All LPS doses decreased tau phosphorylation at both epitopes in hTau/mTau^+/- mice, but pS202 levels were selectively reduced at the 100 μg/kg dose in hTau/mTau^-/- mice. Behavioral suppression and decreased tau phosphorylation persisted at 24 h following LPS administration in hTau/mTau^+/- mice.

A state of delirium: Deciphering the effect of inflammation on tau pathology in Alzheimer's disease

Alzheimer's disease (AD), the predominant form of dementia, is highly correlated with the abnormal hyperphosphorylation and aggregation of tau. Immune responses are key drivers of AD and how they contribute to tau pathology in human disease remains largely unknown. This review summarises current knowledge on the association between inflammatory processes and tau pathology. While, preclinical evidence suggests that inflammation can indeed induce tau hyperphosphorylation at both pre- and post-tangles epitopes, a better understanding of whether this develops into advanced pathological features such as neurofibrillary tangles is needed. Microglial cells, the immune phagocytes in the central nervous system, appear to play a key role in regulating tau pathology, but the underlying mechanisms are not fully understood. Their activation can be detrimental via the secretion of pro-inflammatory mediators, particularly interleukin-1β, but also potentially beneficial through phagocytosis of extracellular toxic tau oligomers. Nevertheless, anti-inflammatory treatments in animal models were found protective, but whether or not they affect microglial phagocytosis of tau species is unknown. However, one major challenge to our understanding of the role of inflammation in the progression of tau pathology is the preclinical models used to address this question. They mostly rely on the use of septic doses of lipopolysaccharide that do not reflect the inflammatory conditions experienced AD patients, questioning whether the impact of inflammation on tau pathology in these models is dose-dependent and relevant to the human disease. The use of more translational models of inflammation corroborated with verification in clinical investigations are necessary to progress our understanding of the interplay between inflammation and tau pathology.

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Inflammation modulates tau function in Alzheimer's disease.

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LPS induces tau phosphorylation in vivo.

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Modulation of late stage tau pathology is less clear.

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Microglial shows potential to slow spread of extracellular tau.

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A holistic approach will determine the role of inflammation in Alzheimer's disease.

Identification and optimisation of a series of tetrahydrobenzotriazoles as metabotropic glutamate receptor 5-selective positive allosteric modulators that improve performance in a preclinical model of cognition

Herein we describe a series of tetrahydrobenzotriazoles as novel, potent metabotropic glutamate receptor subtype 5 (mGlu5) positive allosteric modulators (PAMs). Exploration of the SAR surrounding the tetrahydrobenzotriazole core ultimately led to the identification of 29 as a potent mGlu5 PAM with a low maximal glutamate potency fold shift, acceptable in vitro DMPK parameters and in vivo PK profile and efficacy in the rat novel object recognition (NOR) assay. As a result 29 was identified as a suitable compound for progression to in vivo safety evaluation.

Influence of restraints on body-casted child ATDs in front and side sled tests

OBJECTIVE

The current study was designed to study hip spica casted and uncasted child dummies in front- and side-impact tests using a variety of restraints.

METHODS

Casted one- and three-year-old ATDs were restrained by a traditional child seat, a special hip spica child seat, and the vehicle seat belts. All tests positioned the child upright in either the rear-facing (one-year-old) or forward-facing (three-year-old) direction. One exception was vehicle seat belt tests for the one-year-old, which required the child to be positioned supine due to the position of the child's body imposed by the cast. The ATDs were tested in frontal impacts per FMVSS 213 (delta V of 30 mph) and in side impact using the pulse proposed for 213 (delta V of 20 mph). Corresponding control tests were performed with the uncasted ATDs. The FMVSS 213 mandated injury metrics (HIC36, 3 ms chest gs) and nonmandated due care metrics (HIC15, Nij) were evaluated.

RESULTS

For the one-year-old casted tests, 50 percent of the responses increased when compared to the uncasted control. A similar comparison for the three-year-old revealed an 80 percent increase when the dummy was fit with a body cast. HIC36 and chest gs were below the limits established in FMVSS 213 for all casted and uncasted tests. Frontal peak Nij values were in the tension-extension in nine out of ten cases and ranged from 0.8 to 0.83 (uncasted) and 1.02 to 1.92 (casted). Side-impact Nij was approximately 50 percent of the corresponding frontal tests.

CONCLUSIONS

The addition of a body cast increases head, neck, and chest responses in front- and side-impact tests. The increases are greatest for the three-year-old who was forward facing.

Alteration of the amount and morphology of wear particles by the addition of loading profile transitions during artificial hip wear testing

Current validation tests of total hip arthroplasty endo-prostheses capture only a single activity performed by patients: continuous walking. A more representative test that includes transitions from a static loaded position to dynamic motion would simulate common motions by patients in which they change from standing to walking. The introduction of such transitions into a traditional test protocol could provide insight into actual wear behaviours and more realistic wear particle properties such as size and shape. First, the introduction of transitions will increase the measured wear rate. Second, the amount of wear will be positively correlated to the number of transitions per day. Finally, the size and shape of polyethylene particle produced via testing with transitions will differ from those of a conventional continuous walking test. Three identical sets of four cobalt chromium femoral heads and sterilized acetabular cups sterilized in ethylene oxide were tested in 30 per cent bovine serum under three conditions: continuous walking (0 transitions/day), 10 transitions/day, and 100 transitions/day. A day was defined as 2500 steps. The static and peak dynamic loads were 260 N and 1.9 kN respectively. A testing duration of 106 cycles was completed for each of the three tests. The wear rate was found to be inversely related to the number of transitions. Particle analysis showed that the particle size decreased as the number of transitions increased. Particles from the 100 transitions/day test were more fibular and produced more particles of the size known to promote an immune reactive response. Contrary to our hypothesis, as the number of transitions performed by patients increased, the wear rate and accumulated wear decreased. In addition, as the number of transitions increased, a larger percentage of wear particles were in the submicron size range. Consequently, despite a decrease in wear due to the presence of loading profile transitions, there is a potentially greater risk of osteolysis owing to the increased production of immunoreactive particles.

ADX47273 [S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]-oxadiazol-5-yl]-piperidin-1-yl}-methanone]: a novel metabotropic glutamate receptor 5-selective positive allosteric modulator with preclinical antipsychotic-like and procognitive activities

Positive allosteric modulators (PAMs) of metabotropic glutamate receptor subtype 5 (mGlu5) enhance N-methyl-d-aspartate receptor function and may represent a novel approach for the treatment of schizophrenia. ADX47273 [S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone], a recently identified potent and selective mGlu5 PAM, increased (9-fold) the response to threshold concentration of glutamate (50 nM) in fluorometric Ca(2+) assays (EC(50) = 170 nM) in human embryonic kidney 293 cells expressing rat mGlu5. In the same system, ADX47273 dose-dependently shifted mGlu5 receptor glutamate response curve to the left (9-fold at 1 microM) and competed for binding of [(3)H]2-methyl-6-(phenylethynyl)pyridine (K(i) = 4.3 microM), but not [(3)H]quisqualate. In vivo, ADX47273 increased extracellular signal-regulated kinase and cAMP-responsive element-binding protein phosphorylation in hippocampus and prefrontal cortex, both of which are critical for glutamate-mediated signal transduction mechanisms. In models sensitive to antipsychotic drug treatment, ADX47273 reduced rat-conditioned avoidance responding [minimal effective dose (MED) = 30 mg/kg i.p.] and decreased mouse apomorphine-induced climbing (MED = 100 mg/kg i.p.), with little effect on stereotypy or catalepsy. Furthermore, ADX47273 blocked phencyclidine, apomorphine, and amphetamine-induced locomotor activities (MED = 100 mg/kg i.p.) in mice and decreased extracellular levels of dopamine in the nucleus accumbens, but not in the striatum, in rats. In cognition models, ADX47273 increased novel object recognition (MED = 1 mg/kg i.p.) and reduced impulsivity in the five-choice serial reaction time test (MED = 10 mg/kg i.p.) in rats. Taken together, these effects are consistent with the hypothesis that allosteric potentiation of mGlu5 may provide a novel approach for development of antipsychotic and procognitive agents.

Association of knee bone bruise frequency with time postinjury and type of soft tissue injury

This study correlated the frequency of bone bruises with soft tissue injuries in the knee and examined bruise frequency as a function of time postinjury. Magnetic resonance imaging of 1546 patients revealed bone bruises in 19% of patients without an associated meniscal or ligamentous injury. For those patients presenting with at least one meniscoligamentous injury, the frequency of bruising was 60% at 0 to 4 weeks, 42% at 4 to 10 weeks, and 31% at 10 to 26 weeks postinjury. The frequency of bruising varied with the presence of concomitant injuries, with the greatest frequency of bruises (78%) observed in patients with anterior cruciate ligament injuries.

SB-649915-B, a novel 5-HT1A/B autoreceptor antagonist and serotonin reuptake inhibitor, is anxiolytic and displays fast onset activity in the rat high light social interaction test

Preclinically, the combination of an SSRI and 5-HT autoreceptor antagonist has been shown to reduce the time to onset of anxiolytic activity compared to an SSRI alone. In accordance with this, clinical data suggest the coadministration of an SSRI and (+/-) pindolol can decrease the time to onset of anxiolytic/antidepressant activity. Thus, the dual-acting novel SSRI and 5-HT(1A/B) receptor antagonist, SB-649915-B, has been assessed in acute and chronic preclinical models of anxiolysis. SB-649915-B (0.1-1.0 mg/kg, i.p.) significantly reduced ultrasonic vocalization in male rat pups separated from their mothers (ED(50) of 0.17 mg/kg). In the marmoset human threat test SB-649915-B (3.0 and 10 mg/kg, s.c.) significantly reduced the number of postures with no effect on locomotion. In the rat high light social interaction (SI), SB-649915-B (1.0-7.5 mg/kg, t.i.d.) and paroxetine (3.0 mg/kg, once daily) were orally administered for 4, 7, and 21 days. Ex vivo inhibition of [(3)H]5-HT uptake was also measured following SI. SB-649915-B and paroxetine had no effect on SI after 4 days. In contrast to paroxetine, SB-649915-B (1.0 and 3.0 mg/kg, p.o., t.i.d.) significantly (p<0.05) increased SI time with no effect on locomotion, indicative of an anxiolytic-like profile on day 7. Anxiolysis was maintained after chronic (21 days) administration by which time paroxetine also increased SI significantly. 5-HT uptake was inhibited by SB-649915-B at all time points to a similar magnitude as that seen with paroxetine. In conclusion, SB-649915-B is acutely anxiolytic and reduces the latency to onset of anxiolytic behavior compared to paroxetine in the SI model.

SB-649915, a novel, potent 5-HT1A and 5-HT1B autoreceptor antagonist and 5-HT re-uptake inhibitor in native tissue

An increase in brain 5-HT levels is thought to be the key mechanism of action which results in an antidepressant response. It has been proven that selective serotonin re-uptake inhibitors are effective antidepressants but the delay to therapeutic onset of these agents is thought to be due to the time required for 5-HT1A, and possibly 5-HT1B, autoreceptor desensitisation. Therefore an agent incorporating 5-HT re-uptake inhibition coupled with 5-HT1A and/or 5-HT1B autoreceptor antagonism may provide a fast acting clinical agent. The current studies describe the in vitro profile of SB-649915 (6-[(1-{2-[(2-methylquinolin-5-yl)oxy]ethyl}piperidin-4-yl)methyl]-2H-1,4-benzoxazin-3(4H)-one), a novel compound which has high affinity for human recombinant 5-HT1A, 5-HT1B and 5-HT1D receptors (pKi values of 8.6, 8.0, 8.8, respectively) and the human recombinant 5-HT transporter (pKi value of 9.3). SB-649915 also displays high affinity for rat, guinea pig, mouse and marmoset native tissue 5-HT1A, 5-HT1B and 5-HT1D receptors and rat native tissue 5-HT transporters (pKi values>or=7.5). In functional [35S]GTPgammaS binding studies, SB-649915 (up to 1 microM) does not display intrinsic activity in HEK293 cells expressing human recombinant 5-HT1A receptors but acts as a partial agonist at human recombinant 5-HT1B and 5-HT1D receptors with intrinsic activity values of 0.3 and 0.7, respectively, as compared to the full agonist 5-HT. From Schild analysis, SB-649915 caused a concentration-dependent, rightward shift of 5-HT-induced stimulation of basal [35S]GTPgammaS binding in cells expressing human recombinant 5-HT1A or 5-HT1B receptors to yield pA2 values of 9.0 and 7.9, respectively. In electrophysiological studies in rat dorsal raphe nucleus, SB-649915 did not affect the cell firing rate up to 1 microM but attenuated (+)8-hydroxy-2-(di-n-propylamino) tetralin-induced inhibition of cell firing with an apparent pKb value of 9.5. SB-649915 (1 microM) significantly attenuated exogenous 5-HT-induced inhibition of electrically-stimulated [3H]5-HT release from guinea pig cortex. In studies designed to enhance endogenous 5-HT levels, and therefore increase tone at 5-HT1B autoreceptors, SB-649915 significantly potentiated [3H]5-HT release at 100 and 1000 nM. In LLCPK cells expressing human recombinant 5-HT transporters and in rat cortical synaptosomes, SB-649915 inhibited [3H]5-HT re-uptake with pIC50 values of 7.9 and 9.7, respectively. In summary, SB-649915 is a novel, potent 5-HT1A/1B autoreceptor antagonist and 5-HT re-uptake inhibitor in native tissue systems and represents a novel mechanism that could offer fast acting antidepressant action.

Altered expression of G(q/11alpha) protein shapes mGlu1 and mGlu5 receptor-mediated single cell inositol 1,4,5-trisphosphate and Ca(2+) signaling

The metabotropic glutamate (mGlu) receptors mGlu1 and mGlu5 mediate distinct inositol 1,4,5-trisphosphate (IP(3)) and Ca(2+) signaling patterns, governed in part by differential mechanisms of feedback regulation after activation. Single cell imaging has shown that mGlu1 receptors initiate sustained elevations in IP(3) and Ca(2+), which are sensitive to agonist concentration. In contrast, mGlu5 receptors are subject to cyclical PKC-dependent uncoupling and consequently mediate coincident IP(3) and Ca(2+) oscillations that are largely independent of agonist concentration. In this study, we investigated the contribution of G(q/11)alpha protein expression levels in shaping mGlu1/5 receptor-mediated IP(3) and Ca(2+) signals, using RNA interference (RNAi). RNAi-mediated knockdown of G(q/11)alpha almost abolished the single-cell increase in IP(3) caused by mGlu1 and mGlu5 receptor activation. For the mGlu1 receptor, this unmasked baseline Ca(2+) oscillations that persisted even at maximal agonist concentrations. mGlu5 receptor-activated Ca(2+) oscillations were still observed but were only initiated at high agonist concentrations. Recombinant overexpression of G(q)alpha enhanced IP(3) signals after mGlu1 and mGlu5 receptor activation. It is noteworthy that although mGlu5 receptor-mediated IP(3) and Ca(2+) oscillations in control cells were largely insensitive to agonist concentration, increasing G(q)alpha expression converted these oscillatory signatures to sustained plateau responses in a high proportion of cells. In addition to modulating temporal Ca(2+) signals, up- or down-regulation of G(q/11)alpha expression alters the threshold for the concentration of glutamate at which a measurable Ca(2+) signal could be detected. These experiments indicate that altering G(q/11)alpha expression levels differentially affects spatiotemporal aspects of IP(3) and Ca(2+) signaling mediated by the mGlu1 and mGlu5 receptors.

3,4-Dihydro-2H-benzoxazinones are 5-HT1A receptor antagonists with potent 5-HT reuptake inhibitory activity

Starting from a high throughput screening hit, a series of 3,4-dihydro-2H-benzoxazinones has been identified with both high affinity for the 5-HT(1A) receptor and potent 5-HT reuptake inhibitory activity. The 5-(2-methyl)quinolinyloxy derivative combined high 5-HT(1A/1B/1D) receptor affinities with low intrinsic activity and potent inhibition of the 5-HT reuptake site (pK(i)8.2). This compound also had good oral bioavailability and brain penetration in the rat.

Determinants of metabotropic glutamate receptor-5-mediated Ca2+ and inositol 1,4,5-trisphosphate oscillation frequency. Receptor density versus agonist concentration

Diverse patterns of Ca(2+)(i) release differentially regulate Ca(2+)-sensitive enzymes and gene transcription, and generally the extent of agonist activation of phospholipase C-linked G protein-coupled receptors determines the type of Ca(2+) signal. We have studied global Ca(2+) oscillations arising through activation of the metabotropic glutamate receptor mGluR5a expressed in Chinese hamster ovary cells and find that these oscillations are largely insensitive to agonist concentration. Using an inducible receptor expression system and a non-competitive antagonist, in conjunction with the translocation of eGFP-PH(PLCdelta) to monitor inositol 1,4,5-trisphosphate (InsP(3)) oscillations in single cells, we show that mGluR5a density determines the frequency of these oscillations. The predominant underlying mechanism resulted from a negative feedback loop whereby protein kinase C (PKC) inhibited InsP(3) generation. Down-regulation of PKC by prolonged exposure to phorbol ester revealed a second form of Ca(2+)(i) oscillation at low agonist concentrations. These Ca(2+)(i) signals showed features typical of classic repetitive Ca(2+)-induced Ca(2+) release and were sensitive to agonist concentration. Therefore, a single receptor can stimulate two types of InsP(3)-mediated Ca(2+) signal dependent upon feedback inhibition, producing two distinct means of controlling the final pattern of Ca(2+)(i) release. Our results have physiological implications for Ca(2+) signaling in general and emphasize the importance of mGluR5 surface expression for modulating synaptic plasticity.

[3H]-SB-269970 radiolabels 5-HT7 receptors in rodent, pig and primate brain tissues

The selective 5-HT7 receptor antagonist radioligand, [3H]-SB-269970, has been reported to radiolabel the human cloned 5-HT7(a) receptor and 5-HT7 receptors in guinea pig cortex (thomas et al, 2000). Saturation analysis of [3H]-SB-269970 binding to mouse forebrain, rat cortex, pig cortex, marmoset cortex and human thalamus membranes was consistent with labelling a homogenous population of binding sites in each tissue. K(D) values for [3H]-SB-269970 binding in these tissues ranged from 0.9 to 2.3 nM, being similar to those reported for the human cloned and guinea pig cortex 5-HT7 receptors (1.3 and 1.7 nM, respectively). Bmax values for [3H]-SB-269970 binding to the mouse, rat, pig, marmoset and human brain membranes were 20, 30, 31, 14 and 68 fmoles x mg x protein(-1), respectively. For each species the profile of inhibition of [3H]-SB-269970 binding, using a number of 5-HT7 receptor agonists and antagonists, correlated well with that reported for the human cloned 5-HT7(a) receptor (correlation coefficients were 0.95, 0.94, 0.92, 0.95, 0.97 versus the mouse, rat, pig, marmoset and human tissues, respectively). In conclusion, [3H]-SB-269970 has been shown to radiolabel 5-HT7 receptors in rodent, pig and primate brain and represents a valuable tool with which to further characterise the distribution and function of 5-HT7 receptors in native tissues and elucidate their potential role in disease states.

Injuries produced by blunt trauma to the human patellofemoral joint vary with flexion angle of the knee

Patellofemoral joint impact trauma during car accidents, sporting activities, and falls can produce acute gross fracture of bone, microfracture of bone, and soft tissue injury. Field studies of car accidents, however, show that most patellofemoral traumas are classified as 'subfracture' level injuries. While experimental studies have shown that the influence of flexion angle at impact is not well understood, flexion angle may influence injury location and severity. In the current study, 18 pairs of isolated human cadaver knees were subjected to blunt impact at flexion angles of 60 degrees, 90 degrees, or 120 degrees. One knee from each cadaver was sequentially impacted until gross fracture of bone was produced. The contralateral knee was subjected to a single, subfracture impact at 45% of the impact energy producing fracture in the first knee. The fracture experiments produced gross fracture of the patella and femoral condyles with the fracture plane positioned largely within the region of patellofemoral contact. The fracture location and character changed with flexion angle: at higher flexion angles the proximal pole of the patella and the femoral condyles were more susceptible to injury. For the 90 degrees flexion angle, the patella was fractured centrally, while at 60 degrees the distal pole fractured transversely at the insertion of the patellar tendon. In addition, the load magnitude required to produce fracture increased with flexion angle. In the 'subfracture' knees, injuries were documented for all flexion angles; occult microfractures of the subchondral and trabecular bone and fissures of the articular surface. Similar to the fracture-level experiments, the injuries coincided with the patellofemoral contact region. These data show that knee flexion angle plays an important role in impact related knee trauma. Such data may be useful in the clinical setting, as well as in the design of injury prevention strategies.

Impact responses of the flexed human knee using a deformable impact interface

Blunt impact trauma to the patellofemoral joint during car accidents, sporting activities, and falls can produce a range of injuries to the knee joint, including gross bone fracture, soft tissue injury, and/or microinjuries to bone and soft tissue. Currently, the only well-established knee injury criterion applies to knee impacts suffered during car accidents. This criterion is based solely on the peak impact load delivered to seated cadavers having a single knee flexion angle. More recent studies, however, suggest that the injury potential, its location, and the characteristics of the damage are also a function of knee flexion angle and the stiffness of the impacting structure. For example, at low flexion angles, fractures of the distal patella are common with a rigid impact interface, while at high flexion angles splitting of the femoral condyles is more evident. Low stiffness impact surfaces have been previously shown to distribute impact loads over the anterior surface of the patella to help mitigate gross and microscopic injuries in the 90 deg flexed knee. The objective of the current study was to determine if a deformable impact interface would just as effectively mitigate gross and microscopic injuries to the knee at various flexion angles. Paired experiments were conducted on contralateral knees of 18 human cadavers at three flexion angles (60, 90, 120 deg). One knee was subjected to a fracture level impact experiment with a rigid impactor, and the opposite knee was impacted with a deformable interface (3.3 MPa crush strength honeycomb material) to the same load. This (deformable) impact interface was effective at mitigating gross bone fractures at approximately 5 kN at all flexion angles, but the frequency of split fracture of the femoral condyles may not have been significantly reduced at 120 deg flexion. On the other hand, this deformable interface was not effective in mitigating microscopic injuries observed for all knee flexion angles. These new data, in concert with the existing literature, suggest the chosen impact interface was not optimal for knee injury protection in that fracture and other minor injuries were still produced. For example, in 18 cadavers a total of 20 gross fractures and 20 subfracture injuries were produced with a rigid interface and 5 gross fractures and 21 subfracture injuries with the deformable interface selected for the current study. Additional studies will be needed to optimize the knee impact interface for protection against gross and microscopic injuries to the knee.

Blunt injuries to the patellofemoral joint resulting from transarticular loading are influenced by impactor energy and mass

Various impact models have been used to study the injury mechanics of blunt trauma to diarthrodial joints. The current study was designed to study the relationship between impactor energy and mass on impact biomechanics and injury modalities for a specific test condition and protocol. A total of 48 isolated canine knees were impacted once with one of three free flight inertial masses (0.7, 1.5, or 4.8 kg) at one of three energy levels (2, 11, 22 J). Joint impact biomechanics (peak load, loading rate, contact area) generally increased with increasing energy. Injuries were typically more frequent and more severe with the larger mass at each energy level. Histological analyses of the patellae revealed cartilage injuries at low energy with deep injuries in underlying bone at higher energies.

Effect of contact stress in bones of the distal interphalangeal joint on microscopic changes in articular cartilage and ligaments

OBJECTIVE

To examine articular cartilage of the distal interphalangeal (DIP) joint and distal sesamoidean impar ligament (DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive responses to contact stress.

SAMPLE POPULATION

Specimens from 21 horses.

PROCEDURE

Pressure-sensitive film was inserted between articular surfaces of the DIP joint. The digit was subjected to a load. Finite element models (FEM) were developed from the data. The navicular bone, distal phalanx, and distal attachments of the DSIL and DDFT were examined histologically.

RESULTS

Analysis of pressure-sensitive film revealed significant increases in contact area and contact load at dorsiflexion in the joints between the distal phalanx and navicular bone and between the middle phalanx and navicular bone. The FEM results revealed compressive and shear stresses. Histologic evaluation revealed loss of proteoglycans in articular cartilage from older horses (7 to 27 years old). Tidemark advancement (up to 14 tidemarks) was observed in articular cartilage between the distal phalanx and navicular bone in older clinically normal horses. In 2 horses with navicular syndrome, more tidemarks were evident. Clinically normal horses had a progressive increase in proteoglycans in the DSIL and DDFT.

CONCLUSIONS AND CLINICAL RELEVANCE

Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.

[(3)H]-SB-269970--A selective antagonist radioligand for 5-HT(7) receptors

Binding of the 5-HT(7) receptor antagonist radioligand [(3)H]-SB-269970 to human 5-HT(7(a)) receptors expressed in HEK293 cell membranes (h5-HT(7(a))/293) and to guinea-pig cerebral cortex membranes, was characterized and compared with [(3)H]-5-CT binding. [(3)H]-SB-269970 (1 nM) showed full association with h5-HT(7(a))/293 membranes after 40 min. Specific binding at equilibrium represented >90% of total binding and was fully reversible by methiothepin (10 microM), full dissociation occurring by 100 min. The association (k(+1)) and dissociation (k(-1)) rate constants were 0.05 nM(-1)min(-1) and 0.05 min(-1) respectively, giving a K(D) (k(-1)/k(+1)) of 1.0 nM. [(3)H]-SB-269970 bound saturably and apparently monophasically to both h5-HT(7(a))/293 and guinea-pig cortex membranes, with K(D) values of 1.25+/-0.05 and 1.7+/-0.3 nM respectively. The B(max) for [(3)H]-SB-269970 to both h5-HT(7(a))/293 and guinea-pig cortex membranes (5780+/-380 and 125+/-8.2 fmoles mg protein(-1) respectively) was similar to that for [(3)H]-5-CT (6190+/-940 and 143+/-19 fmoles mg protein(-1) respectively). These data suggest that, in each tissue, both radioligands labelled the same population of receptors, which appear to be present in an agonist high affinity state. The profile of compound inhibition of [(3)H]-SB-269970 binding to h5-HT(7(a))/293 and guineapig cortex membranes correlated well (corr. coeff. 0.98) with those for [(3)H]-5-CT binding and were consistent with the profiles reported previously for the human 5-HT(7(a)) and guinea-pig cortex 5-HT(7) receptors using [(3)H]-5-CT. Hill slopes for inhibition of [(3)H]-SB-269970 and [(3)H]-5-CT binding were close to 1, consistent with binding to a single receptor population in both tissues. [(3)H]-SB-269970 represents the first selective 5-HT(7) antagonist radioligand, which should aid further characterization of 5-HT(7) receptors in recombinant and native tissues and help establish their role in brain function.

Patellar tendon augmentation after removal of its central third limits joints tissue changes

The central third of the patellar tendon is commonly used to reconstruct the injured anterior cruciate ligament. Some studies have noted changes in joint tissues following this procedure. It has been postulated that these changes may be associated with increased stress on the remaining tendon following harvest of the graft. In our study, the central third of the patellar tendon was excised in three groups of rabbits. The central tendon defects in two of the three groups were fitted with different augmentation devices to augment the host tendon during the healing process. All rabbits followed a daily treadmill exercise regimen for 12 weeks following the operation. Biomechanical testing of the tendon revealed that in nonaugmented tendons the cross-sectional area and the length of the patellar tendon significantly increased 112 and 16%, respectively. There was histological evidence of host-tendon remodeling throughout the cross section and extensive fibrosis in the infrapatellar fat pad. Augmentation of the tendon significantly reduced these changes, with the least change noted in the group with the greatest augmentation. The rabbits with augmentation devices retained tendon dimensions similar to those of the contralateral intact tendon, and tendon remodeling occurred only in the defect area. The rabbits with augmentation devices exhibited little to no fibrosis of the fat pad. Structural properties of augmented and nonaugmented tendons were similar despite the size differences, indicating higher tissue quality in the augmented tendons. This study suggested that complications of the knee joint (i.e., tendon proliferation and fat pad fibrosis) noted after anterior cruciate-ligament reconstruction with the autogenous patellar tendon may be limited by the implantation of an augmentation device.

Detection of experimentally produced occult microfractures at the bone-cartilage interface in decalcified sections

We compared three histological preparation methods to detect experimentally produced occult microfractures in decalcified human patellae: a paraffin tape-transfer technique, a paraffin slab-cut method, and a paraffin method with methyl salicylate as the clearing agent. Microfractures were observed at the bone-cartilage interface and were oriented either parallel or perpendicular to the tidemark. Both types of microfractures were documented with each preparation method. The slab-cut method was time-consuming, but the section thickness allowed detailed analysis of the architecture of microcracks as they passed into the depth of the section. The methyl salicylate method was efficient and produced thin, serial sections with good morphological detail and minimal cutting artifact. Reliable histological data were also derived from the tape-transfer technique, but this method was inconsistent. The methods summarized here for processing decalcified human joint tissues provide a basis for future orthopaedic studies investigating occult microfractures at the bone-cartilage interface.

Patellar tendon and infrapatellar fat pad healing after harvest of an ACL graft

Clinical studies have documented proliferation of the host patellar tendon and fibrosis extending into adjacent tissues after reconstruction of the injured anterior cruciate ligament (ACL) using the central one-third of the patellar tendon (PT) as the graft. Such generalized arthrofibrosis has been implicated in knee locking and as possible source of anterior knee pain. However, it is not clinically feasible to measure changes in tendon morphology and mechanical properties and degeneration of peripheral tissues over time following graft harvest. In a rabbit experimental model proliferative changes in the tendon and the infrapatellar fat pad have been documented following harvest of a central third tendon graft without ACL reconstruction. Studies in larger animals have shown significant reductions in the strength and stiffness of the healing patellar tendon, but without assessment of the peripheral tissue response. In the current study an ACL reconstruction was performed in a goat model using an autogenous patellar tendon graft. Extensive tendon and fat pad proliferation were observed along with significant reductions in the biomechanical properties of the host tendon. Significant fat pad fibrosis was documented using biochemical methods. The current data confirm that harvest of an autogenous PT graft for reconstruction of the ACL results in significant changes in the PT and adjacent tissues. These data may help explain some of the clinical complications documented in the reconstructed joint.

A method to increase the sensitive range of pressure sensitive film

Pressure-sensitive film is frequently used in biomechanics to document intra- and extra-articular contact pressures. This often involves the contact of two surfaces of varying curvature producing non-uniform pressure distributions. The purpose of this study was to determine the feasibility of using multiple films in such experiments to yield accurate pressure and contact area data. A composite arrangement of film was dynamically loaded using cylindrical indenters of five radii. An analytical model of each indentation was constructed to provide a standard for error analysis. The study showed that several ranges of pressure sensitive film can be used simultaneously to accurately transduce contact pressures arising from loading scenarios that produce contact pressure gradients and contact pressures that involve suprathreshold loading of a given film range.

Evaluation of cannabinoid receptor agonists and antagonists using the guanosine-5'-O-(3-[35S]thio)-triphosphate binding assay in rat cerebellar membranes

Cannabinoid receptors are members of the superfamily of G protein-coupled receptors. Their activation has previously been shown to stimulate guanosine 5'-O-(3-[35S]thio)-triphosphate ([35S]GTP gamma S) binding in a range of brain regions using both membrane preparations and autoradiography. This study evaluates the activities of structurally diverse cannabinoid receptor ligands in the GTP gamma S binding assay, comparing the relationship between receptor binding and activation and also examining efficacy differences between compounds. Using rat cerebellar membrane preparations, the effects of GDP concentration on GTP gamma S binding and the activities of a range of cannabinoid receptor ligands, including the CB1 selective antagonist SR141716A, were investigated. GDP concentration was found to have differing effects on cannabinoid-stimulated [35S]GTP gamma S binding depending on the nature of the agonist used. The stimulation produced by high efficacy compounds, such as CP 55,940 and WIN 55212-2, was increased by raising the GDP concentration, but that of a low efficacy agonist, (-)-delta-tetrahydrocannabinol, was decreased. Of the cannabinoid compounds tested, a wide range of potencies (EC50) and levels of maximal stimulation (Emax) were observed. These ranged from CP 55,244 (Emax of 165, 148-183%, and an EC50 of 0.47, 0.22-0.96, nM) through (-)-delta-tetrahydrocannabinol, cannabinol and anandamide, which produced no concentration-dependent stimulation of [35S]GTP gamma S binding under the same conditions. SR141716A competitively antagonized all the agonists against which it was tested, providing equilibrium dissociation constants (Kd values) in the sub-nanomolar range (0.06-0.40 nM), implicating a CB1 receptor mediated response. These results provide a more detailed characterization of the cannabinoid-stimulated [35S]GTP gamma S binding assay than has previously been reported.

Predominant enteroviral serotypes causing meningitis

All enteroviral reports to the Public Health Laboratory Service from 1975 to 1994 which had been proved by culture were analysed. Of the 40,366 isolates, 5741 reports (14%) were from cultures of cerebrospinal fluid. The groups and serotypes accounting for the largest number of cerebrospinal fluid isolates were A9, E7, E9, E11, E19, and E30, accounting for 70% of all cultured isolates of cerebrospinal fluid. It may be possible to prevent most cases of viral meningitis in the UK with the development of an enteroviral vaccine.

Breaking strength retention and histologic effects around 1.3-mm. ORTHOSORB polydioxanone absorbable pins at various sites in the rabbit

Absorbable 1.3-mm polydioxanone (ORTHOSORB) pins were implanted in 75 New Zealand White rabbits in three sites: within the lateral subcutaneous tissue parallel to the femur, down the femoral intramedullary canal, and mediolaterally across the femoral condyles (transcondylar). Pins were harvested at periodic intervals up to 56 and 365 days for mechanical and histologic analyses, respectively. Mechanical analyses were performed by loading the pin in double shear. Histologic analyses were performed on the pin and surrounding tissue. Histologic observations revealed a typical nonspecific foreign-body reaction at all implant sites that resolved at 1 year after resorption of the pin. On histologic examination, there was complete resorption of the pin material in the subcutaneous site by day 182, and there was complete resolution of all response to the pin in six of nine rabbits by day 365. In the intramedullary site, pin material was completely resorbed, based on histologic examination, in five of six rabbits by day 182, and there was complete resolution of the response to the pin in eight of nine rabbits by day 365. The pin material was completely resorbed based on histologic examination of the transcondylar site by day 210, and there was complete resolution of the response to the pin in four of six rabbits by day 270 and in four of nine rabbits by day 365. No enlarged pin tracks or sinus formations were observed in or near the implants sites. The average initial shear strength as 171.4+/ 5.1 MPa, and the breaking strength retention decreased with increasing implantation time. Pins from the subcutaneous regions maintained above 97% of their initial strengths at 28 days, and those from the intramedullary canals maintained above 92%. At later times the strength of the pins implanted in the intramedullary canal decreased more rapidly than those from the subcutaneous region. Overall, the average breaking strength of the subcutaneous pins was significantly greater than that of the intramedullary pins at all time points beyond 14 days. These data indicate that the pins exhibited a strength retention profile sufficient to allow normal healing of bone without enlarged pin tracts, allergic reactions, or sinus formations.

Subfracture insult to the human cadaver patellofemoral joint produces occult injury

The current criterion used by the automotive industry for injury to the lower extremity is based on visible bone fracture. Studies suggest, however, that chronic joint degeneration may occur after subfracture impact loads on the knee. We hypothesized that subfracture loading of the patellofemoral joint could result in previously undocumented microtrauma in areas of high contact pressure. In the current study, seven patellofemoral joints from human cadavers were subjected to impact with successively greater energy until visible fracture was noted. Transverse and comminuted fractures of the patella were noted at 6.7 kN of load. Approximately 45% of the impact energy then was delivered to the contralateral joint. Subfracture loads of 5.2 kN resulted in no gross bone fracture in five of seven specimens. Histological examination of the patellae horizontal split fracture in the subchondral bone, at the tidemark, or at the interface of calcified cartilage and subchondral bone. The trauma appeared predominantly on the lateral facet, adjacent to or directly beneath preexisting fibrillation of the articular surface. Surface fibrillation was noted in histological sections of control patellae (not subjected to impact loading), but occult damages were not observed. Although the mechanism of this occult trauma is unknown, similar damage has been shown to occur from direct shear loading. As these microcracks can potentiate a disease process in the joint, this study may suggest that the current criterion for injury, based on bone fracture alone, is not sufficiently conservative.

Investigation of the effects of transport and lairage on hydration state and resting behaviour of calves for export

Plasma sodium concentrations, packed cell volume, total plasma protein concentration and dermal skinfold thickness were used to assess the state of hydration of 113 transported calves before and after lairage and in 30 control calves on the farm of origin. Skin thickness increased significantly (P less than 0.05) and total protein increased slightly during transport and decreased during lairage. These changes suggest that transport may cause dehydration and lairage may help in recovery. Plasma potassium concentration decreased during transport, but the effect was inversely related to the distance travelled, and the concentration increased during lairage. These changes are consistent with recovery from initially high cortisol levels at loading. The resting behaviour of 150 transported calves was recorded hourly for six hours. More time was spent resting and sleeping by the transported calves than has been reported for non-transported calves and more still by small transported calves, suggesting that transport is exhausting, that lairage helps recovery and that small calves are more adversely affected. During lairage the numbers of calves asleep decreased to values reported for normal calves, suggesting that 10 hours lairage was adequate. However, small calves did not return to their normal rest patterns within the observation period.

A controlled trial of nandrolone decanoate in the treatment of rheumatoid arthritis in postmenopausal women

To determine whether an anabolic steroid had any benefit in the treatment of rheumatoid arthritis 47 patients entered a parallel group study. Twenty four received nandrolone decanoate 50 mg intramuscularly every third week for two years and 23 patients received no anabolic steroids. Other therapy was unaltered. Patients attended for clinical and biochemical assessments as well as the objective assessments of elementary body composition by in vivo neutron activation analysis and measurement of the mineral content of the distal femur by single photon absorptiometry on five occasions. A modest clinical deterioration (except for grip strength) was seen in both groups. No significant changes in calcium or alkaline phosphatase were seen. There was no significant change in total body calcium, total body phosphorus, body weight, or bone index/bone width measurements in either group. Significant increases occurred in total body nitrogen, total body potassium, haemoglobin, and packed cell volume (by six months) in the group treated with nandrolone decanoate. Comparison of 10 patients in the group treated with nandrolone decanoate also receiving oral steroid therapy with 14 patients in this group not receiving oral steroid therapy showed no significant differences. The main side effect of nandrolone decanoate was hoarseness. No radiological changes were seen. Nandrolone decanoate, in a dose that produces a significant anabolic effect, has no demonstrable action on bone metabolism in rheumatoid arthritis but may improve the chronic anaemia by six months.

Skeletal and blood biochemical characteristics of sheep during growth and breeding: a comparison of flocks with and without broken mouth

Two-hundred female Scottish Blackface sheep ranging in age from 3 months to 5 1/2 years were used to investigate the relationships between blood biochemical characteristics, skeletal metabolism and dental health on 5 farms, 3 with broken mouth and 2 with no incidence of the disease. Skeletal growth to 6 months of age was faster in lambs from control flocks than in lambs from affected farms although growth thereafter was slower in the control group. A generally lower protein intake on control farms may account for this reduced growth rate. In general, adult dimensions of bones were attained between 14 and 30 months of age but age of maturation varied between bones; tibial endochondral growth ended after 14 to 21 months while the rib still showed evidence of endochondral growth at 70 months of age. This growth was episodic, being maximal during lactation and possible causes are discussed. There was no significant differences in calcium or phosphorus status between control and affected populations, an inadequate phosphorus intake during pregnancy was common to both groups. Lower serum magnesium concentration in affected than in control sheep was a consistent finding and is discussed.

The shear strength between bone and porous ceramic root implants in the guinea pig incisor socket

Porous alumina and apatite implants have been placed in 67 guinea pig incisor tooth sockets after tooth extraction under anaesthetic. Bone readily grew into the spaces of the implant, and reduced the fibrous connective tissue between implant and bone. 'Pushout' tests have monitored the shear strength of the interlock between bone and implant. Despite considerable variation in the interlock strength, apatite produced the strongest bone interlock. The interlock with alumina tended to be more fibrous. The relative merits of fibrous and bone interlocks in immediate root implants are considered for the augmentation of the alveolar ridge and prosthetic treatment.

Changes in the protein components of rat incisor enamel during tooth development

Enamel-matrix components from rat incisor enamel were extracted from tissue at different stages of development on single teeth. Separations of proteins using urea and SDS acrylamide gel electrophoresis were compared. The bulk of the matrix exhibited SDS mol. wt of 25-30,000 with smaller amounts at approximately 18,000 and about 10-12,000. Trace amounts of material at -50,000 and 70,000 were detected. These were presumably associated with the mineral phase as their yield increased after demineralization. The proportion of small molecular weight components increased with tissue age. Using urea, many more proteins were separated (up to 20) into fast, intermediate and slowly-migrating components. Disappearance of small bands of intermediate mobility at the end of matrix secretion suggested that they were early ameloblast products which were rapidly degraded after secretion. Both slowly- and rapidly-migrating components increased with tissue age indicating progressive degradation of parent molecules of intermediate mobility into highly charged and relatively uncharged molecules.

Histology of enamel organ and chemical composition of adjacent enamel in rat incisors

By avoiding chemical fixation and using a freeze-drying technique, it proved possible to examine the enamel organ of rat mandibular incisors histologically while retaining the adjacent enamel of the same tooth for chemical analysis. The dramatic alterations which occur in enamel organ histology, such as ameloblast shortening and the development of hte papillary layer, could then be compared directly with mineral uptake and mineral content of the adjacent enamel. Both enamel and adjacent enamel organ were sampled as a continuous series of pieces, 0.5 mm in width, from youngest (apical) to oldest (incisal) tissue. Short ameloblasts were associated directly with the beginning of a rapid uptake of phosphate ions during the maturation phase and also coincided with the beginning of a steep rise in mineral content. By implication, some loss of matrix may also occur at this point. Development of the highly vascular papillary layer preceded ameloblast shortening and may be associated with changes in the organic matrix prior to its disappearance from the tissue. Further development of this layer was associated with ameloblast shortening. This may also therefore be associated with mineral uptake during maturation.

Chemical changes during formation and maturation of human deciduous enamel

The appearance and chemical composition of a number of developing human deciduous incisors indicated that the enamel passes through the following four developmental stages: 1. Partially mineralized matrix is secreted and some extracellular breakdown occurs. 2. Selective replacement of matrix proteins by tissue fluid begins. 3. Almost all of the matrix protein is replaced by tissue fluid and an influx of calcium phosphate occurs. 4. The enamel becomes almost fully mineralized, mature and hard. These stages of development are similar to those described in rat and bovine tissue. the number of stages simultaneously present in a single tooth differed from rat and bovine enamel, however, as did the rate of change in amino acid composition from developing to mature tissue.