The influence of clinic care on perceptions and knowledge of non-communicable diseases and physical activity from a low-resourced community: a mixed-method study.

BACKGROUND: Health promotion for the management of risk factors for non-communicable diseases (NCDs) is an integral part of standard care in South Africa. Most persons presenting with NCDs utilise public primary health care centres for disease management. This mixed-methods study aimed at expanding current understanding of the the influence of standard clinic care (usual care) on perceptions and knowledge of risk factors for NCDs and physical activity (PA) among persons from a low-resourced community. Qualitatively the perceptions of women from a low-resourced community about risk factors for NCDs and PA were explored throughout 24-weeks of standard clinic care. Parallel quantitative data was collected to describe changes in risk factors for NCDs and trends in self-reported knowledge about risk factors of NCDs and PA. METHOD: A convergent-parallel mixed-methods research design was used. The study was carried out in a public primary health care setting, in the North West Province, South Africa. From a convenience sample of 100 participants, 77 African women aged between 34 and 79 years were recruited for the study. Data were collected at three time-points including baseline, 12 weeks, and 24 weeks of a standard clinic care health-promotion programme. The qualitative data was collected during focus group discussions, and the quantitative data included questionnaires on knowledge of physical activity and risk factors for NCDs as well as anthropometric and biological measurements. Qualitative and quantitative data were analysed independently for each phase and then consolidated for interpretation. All data was collected in the same setting. RESULTS: Participants' initial understanding and perceptions of NCD risk factors were poor. Qualitative findings showed that participants knew little about the specific physical activity they could engage in and the role of PA in NCD management. Participants preferred low-intensity activities. Heart-disease knowledge improved significantly at 12 weeks intervention compared to baseline MD = -3.655, p < 0.001. There were improvements in PA knowledge at 12 weeks from baseline MD = -0.625 p = 0.02. There were significant weight (MD = 1.420, p = 0.002) and waist circumference reductions (MD = 0.621, p = 0.02) from baseline to 24 weeks. CONCLUSION: Standard clinic care improved knowledge of physical activity and risk factors for NCDs, but perceptions of risk factors for NCDs and PA were unchanged. This study offers insight into the perceptions held by women from a low-resource setting and how future interventions to manage and prevent NCDs should be structured. TRIAL REGISTRATION: PACTR201609001771813 .

Quality of life, physical activity and cardiorespiratory fitness in black African women: B-Healthy project.

PURPOSE: To study the associations between physical activity (PA), cardiorespiratory fitness (CRF), and health-related quality of life (HRQoL) in black African women from a low socioeconomic community in South Africa. METHODS: Black African women (n = 146) aged 35-75 years from a low socioeconomic community in South Africa participated in this study. We measured PA levels via ActiHeart® accelerometers, and CRF by measuring peak oxygen consumption (V̇O2 peak). HRQoL was assessed once with the SF-8 Health Survey (SF-8). Participants were classified into groups based on age, moderate to vigorous PA (MVPA), and V̇O2 peak. Logistic regressions were used to compare the odds of having total HRQoL component scores above reported norms across PA and fitness groups. Two multiple linear regression models were developed using physical component summary (PCS) and mental component summary (MCS) as response variables respectively. RESULTS: V̇O2 peak and MVPA varied considerably across the sample and declined with increasing age. Participants in higher quartiles of MVPA and CRF showed trends to higher PCS scores. For CRF these trends were statistically significant, and persisted after adjustment for age and other possible confounders (p = 0.036). PCS was significantly associated with age, relative V̇O2 peak, and income (all p < 0.05), while MCS was associated with income (p = 0.028). CONCLUSIONS: CRF is the most significant predictor, together with age and income, on the PCS of the HRQoL among black African women. We recommend that when seeking improvements in HRQoL, interventions should focus on improving CRF, particularly V̇O2 peak.

Early postnatal GABAA receptor modulation reverses deficits in neuronal maturation in a conditional neurodevelopmental mouse model of DISC1.

Exploring drug targets based on disease-associated molecular mechanisms during development is crucial for the generation of novel prevention and treatment strategies for neurodevelopmental psychiatric conditions. We report that prefrontal cortex (PFC)-specific postnatal knockdown of DISC1 via in utero electroporation combined with an inducible knockdown expression system drives deficits in synaptic GABAA function and dendritic development in pyramidal neurons, as well as abnormalities in sensorimotor gating, albeit without profound memory deficits. We show for the first time that DISC1 is specifically involved in regulating cell surface expression of α2 subunit-containing GABAA receptors in immature developing neurons, but not after full maturation. Notably, pharmacological intervention with α2/3 subtype-selective GABAA receptor positive allosteric modulators during the early postnatal period ameliorates dendritic deficits and behavioral abnormalities induced by knockdown of DISC1. These findings highlight a critical role of DISC1-mediated disruption of postnatal GABA signaling in aberrant PFC maturation and function.

Effect of continuous aerobic vs. interval training on selected anthropometrical, physiological and functional parameters of adults with Down syndrome.

BACKGROUND: A large percentage of adults with Down syndrome (DS) are overweight and have extremely low aerobic capacities compared with the general population and persons with intellectual disability without DS. Previous aerobic training intervention studies showed limited potential to significantly ameliorate anthropometrical and cardiovascular variables. The primary purpose of this study was to determine the effect of continuous aerobic training (CAT) vs. interval training (IT) on selected anthropometrical, health, physical and functional parameters of adults with DS. METHODS: Forty-two adults with DS (25 men and 17 women) and a mean age of 33.8 (±8.6) years were randomly allocated to one of three groups (IT, CAT and control). Training was performed for 12 weeks. The IT group performed 10-30 s all out sprints with 90 s (1:3 work-rest ratio) of low cadence, low intensity cycling or walking. The CAT group performed continuous cycling and walking at an intensity of 70-80% of VO2 peak. Heart rate monitors were used for monitoring training intensities. After 6 weeks of training, the intensity of the CAT was increased to 85% of VO2 peak, whilst the intensity of the IT group remained 'all out'. An increase of 5 min in duration was implemented after 6 weeks for both training groups. To evaluate pre-post differences between groups, a repeated analysis of covariance with post hoc Bonferroni test was performed RESULTS: After 12 weeks of training, body weight and body mass index decreased significantly more in the IT group compared with control and CAT (P < 0.05). Participants in the IT group decreased their body weight from 71.4 ± 8 to 69.4 ± 8 kg and their body mass index from 29.3 ± 4 to 28.5 ± 4 kg/m2 . Significant ameliorations for functional parameters and leg strength were shown for CAT compared with control (P < 0.05). Participants in the CAT group improved their performance in the 6 minute walk distance (499 ± 78 to 563 ± 75 m), 8-ft up-and-go (5.9 ± 1.2 to 4.8 ± 0.9) and leg strength (13.1 ± 2 to 15.2 ± 2). VO2 peak and time to exhaustion significantly improved in both the IT and CAT group compared with control (P < 0.01). Moreover, a significant improvement for relative VO2 peak was also determined for IT compared with CAT (P < 0.05). Participants in the IT group increased their VO2 peak from 32 ± 8 to 37 ± 8 mL/min/kg. Submaximal heart rate and VO2 values improved significantly within both exercise groups (P < 0.05). CONCLUSION: Interval training and CAT can both be pursued by adults with DS to positively impact on various parameters of anthropometry, fitness and functional ability, with IT more appropriate for improving body weight and aerobic capacity.

The psychiatric disease risk factors DISC1 and TNIK interact to regulate synapse composition and function.

Disrupted in schizophrenia 1 (DISC1), a genetic risk factor for multiple serious psychiatric diseases including schizophrenia, bipolar disorder and autism, is a key regulator of multiple neuronal functions linked to both normal development and disease processes. As these diseases are thought to share a common deficit in synaptic function and architecture, we have analyzed the role of DISC1 using an approach that focuses on understanding the protein-protein interactions of DISC1 specifically at synapses. We identify the Traf2 and Nck-interacting kinase (TNIK), an emerging risk factor itself for disease, as a key synaptic partner for DISC1, and provide evidence that the DISC1-TNIK interaction regulates synaptic composition and activity by stabilizing the levels of key postsynaptic density proteins. Understanding the novel DISC1-TNIK interaction is likely to provide insights into the etiology and underlying synaptic deficits found in major psychiatric diseases.

Functional modulation of GABAA receptors by cAMP-dependent protein phosphorylation.

gamma-Aminobutyric acidA (GABAA) receptors are ligand-gated ion channels that mediate inhibitory synaptic transmission in the central nervous system. The role of protein phosphorylation in the modulation of GABAA receptor function was examined with cells transiently transfected with GABAA receptor subunits. GABAA receptors consisting of the alpha 1 and beta 1 or the alpha 1, beta 1, and gamma 2 subunits were directly phosphorylated on the beta 1 subunit by adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (PKA). The phosphorylation decreased the amplitude of the GABA response of both receptor types and the extent of rapid desensitization of the GABAA receptor that consisted of the alpha 1 and beta 1 subunits. Site-specific mutagenesis of the serine residue phosphorylated by PKA completely eliminated the PKA phosphorylation and modulation of the GABAA receptor. In primary embryonic rat neuronal cell cultures, a similar regulation of GABAA receptors by PKA was observed. These results demonstrate that the GABAA receptor is directly modulated by protein phosphorylation and suggest that neurotransmitters or neuropeptides that regulate intracellular cAMP levels may modulate the responses of neurons to GABA and consequently have profound effects on synaptic excitability.

Changes in coronary heart disease risk profile of adults with intellectual disabilities following a physical activity intervention.

BACKGROUND: Regular physical activity is one of the modifiable risk factors for coronary heart disease (CHD). With an increasing age profile and similar patterns of morbidity to the general population, persons with intellectual disabilities (ID) and their caregivers would benefit from data that indicate CHD risk factors. Knowledge of the CHD risk factors and the changes a physical activity intervention may have on theses risk factors will facilitate future intervention programmes. METHODS: A cohort of 100 men and women between the ages of 21 and 73 years with ID living in a community group home in the North-West Province of South Africa was recruited. A CHD risk profile was compiled by means of a questionnaire and physical assessment that included resting blood pressure, body mass index, non-fasting glucose and cholesterol and cardiorespiratory fitness. A 12-week physical activity intervention was then conducted 3 days/week after which the baseline measurements were repeated. RESULTS: The results indicated that 85% of the participants were inactive, while 67% were overweight and obese. Hypertension (6.1%) and smoking (6.1%) were relatively low in this population with ID. Glucose concentrations above the recommended cut-off values were observed in 28% of the participants. Total cholesterol concentrations above normal were measured in 23% of the participants. The physical activity intervention reduced inactivity to 50% and resulted in a significant increase in cardiorespiratory fitness and a decrease in percentage body fat in both men and women. CONCLUSION: Inactivity is a major risk factor in this population with ID living in a community group setting. The implementation of the physical activity intervention significantly reduced the risk factors for CHD.

Regulation of GABAA receptor function by protein kinase C phosphorylation.

GABAA receptors possess consensus sequences for phosphorylation by PKC that are located on the presumed intracellular domains of beta and gamma 2 subunits. PKC phosphorylation sites were analyzed using purified receptor subunits and were located on up to 3 serine residues in beta 1 and gamma 2 subunits. The role of phosphorylation in receptor function was studied using recombinant receptors expressed in kidney cells and Xenopus oocytes and was compared with native neuronal GABAA receptors. For recombinant and native GABAA receptors, PKC phosphorylation caused a reduction in the amplitudes of GABA-activated currents without affecting the time constants for current decay. Selective site-directed mutagenesis of the serine residues reduced the effects of phorbol esters and revealed that serine 343 in the gamma 2 subunit exerted the largest effect on the GABA-activated response. These results indicate that PKC phosphorylation can differentially modulate GABAA receptor function.

Adjacent phosphorylation sites on GABAA receptor beta subunits determine regulation by cAMP-dependent protein kinase.

Activation of cAMP-dependent protein kinase (PKA) can enhance or reduce the function of neuronal GABAA receptors, the major sites of fast synaptic inhibition in the brain. This differential regulation depends on PKA-induced phosphorylation of adjacent conserved sites in the receptor beta subunits. Phosphorylation of beta 3 subunit-containing receptors at S408 and S409 enhanced the GABA-activated response, whereas selectively mutating S408 to alanine converted the potentiation into an inhibition, comparable to that of beta 1 subunits, which are phosphorylated solely on S409. These distinct modes of regulation were interconvertible between beta 1 and beta 3 subunits and depended upon the presence of S408 in either subunit. In contrast, beta 2 subunit-containing receptors were not phosphorylated or affected by PKA. Differential regulation by PKA of postsynaptic GABAA receptors containing different beta subunits may have profound effects on neuronal excitability.

Cyclic AMP-dependent protein kinase phosphorylation facilitates GABA(B) receptor-effector coupling.

GABA (gamma-aminobutyric acid)(B) receptors are heterodimeric G protein-coupled receptors that mediate slow synaptic inhibition in the central nervous system. Here we show that the functional coupling of GABA(B)R1/GABA(B)R2 receptors to inwardly rectifying K(+) channels rapidly desensitizes. This effect is alleviated after direct phosphorylation of a single serine residue (Ser892) in the cytoplasmic tail of GABA(B)R2 by cyclic AMP (cAMP)-dependent protein kinase (PKA). Basal phosphorylation of this residue is evident in rat brain membranes and in cultured neurons. Phosphorylation of Ser892 is modulated positively by pathways that elevate cAMP concentration, such as those involving forskolin and beta-adrenergic receptors. GABA(B) receptor agonists reduce receptor phosphorylation, which is consistent with PKA functioning in the control of GABA(B)-activated currents. Mechanistically, phosphorylation of Ser892 specifically enhances the membrane stability of GABA(B) receptors. We conclude that signaling pathways that activate PKA may have profound effects on GABA(B) receptor-mediated synaptic inhibition. These results also challenge the accepted view that phosphorylation is a universal negative modulator of G protein-coupled receptors.

GABA(A) receptor cell surface number and subunit stability are regulated by the ubiquitin-like protein Plic-1.

Controlling the number of functional gamma-aminobutyric acid A (GABA(A)) receptors in neuronal membranes is a crucial factor for the efficacy of inhibitory neurotransmission. Here we describe the direct interaction of GABA(A) receptors with the ubiquitin-like protein Plic-1. Furthermore, Plic-1 is enriched at inhibitory synapses and is associated with subsynaptic membranes. Functionally, Plic-1 facilitates GABA(A) receptor cell surface expression without affecting the rate of receptor internalization. Plic-1 also enhances the stability of intracellular GABA(A) receptor subunits, increasing the number of receptors available for insertion into the plasma membrane. Our study identifies a previously unknown role for Plic-1, a modulation of GABA(A) receptor cell surface number, which suggests that Plic-1 facilitates accumulation of these receptors in dendritic membranes.

Test-retest reliability and minimal detectable change scores of twelve functional fitness tests in adults with Down syndrome.

AIM: The purpose of the study was to explore the test-retest reliability and minimal detectable change of selected functional fitness test items in adults with Down syndrome. METHODS: Forty-three adults with Down syndrome (24 men and 19 women) aged 18-50 years completed a battery of tests twice in a two-week period. The battery of tests consisted of two balance items, two flexibility items, five muscular strength and endurance items, two aerobic items, and one functional task. All items were considered valid and reliable tests in a general elderly or intellectually disabled population. The test-retest relative reliability for all repeated tests was assessed with intraclass correlation coefficient performing one-way analysis of variance. The test-retest absolute variability was measured by using the standard error of measurement (SEM) to calculate the minimal detectable change at the 90% confidence interval (MDC90). Reliability data was visualised with a Bland-Altman plot. RESULTS: All tests showed excellent intraclass correlation coefficients (ICC's>0.9). All SEM values demonstrated acceptable measurement precision (SEM

Relationship of adiposity and cardiorespiratory fitness with resting blood pressure of South African adolescents: the PAHL Study.

Obesity and low level of cardiorespiratory fitness are associated with high blood pressure in both adolescents and adults. The objective of this study was to assess the relationship of adiposity and cardiorespiratory fitness with resting blood pressure in 14-year-old male and female adolescents. Cross-sectional data on 310 adolescents (31.8% boys) from six high schools, who were participating in the on-going Physical Activity and Health Longitudinal Study, were collected. Height, weight, body mass index (BMI), percentage of body fat, waist circumference, waist-to-height ratio, predicted and resting systolic (SBP) and diastolic blood pressure (DBP) were assessed according to standard procedures. The prevalence of elevated SBP and DBP were 4.9% and 6.5%, respectively. The highest prevalence of elevated blood pressure (SBP=10% and DBP=15%) were measured in overweight adolescents, who also performed poorly for predicted VO(2max)(M=26.66 ml kg(-1 )min(-1)±6.44) compared with underweight and normal-weight adolescents. Multiple regression showed that BMI was positively associated with SBP (ß=0.77, P=0.005) and VO(2max) was negatively associated with DBP (ß=-0.43, P=0.001). Overweight adolescents presented with a relatively high prevalence of elevated blood pressure and poor health-related fitness. Fatness and poor cardiorespiratory fitness were positively associated with elevated SBP and DBP, respectively. In view of the health implications of these findings, strategic interventions are needed to promote obesity-reduction programmes and physical activities in adolescents.

GABAC receptor sensitivity is modulated by interaction with MAP1B.

GABA(C) receptors contain rho subunits and mediate feedback inhibition from retinal amacrine cells to bipolar cells. We previously identified the cytoskeletal protein MAP1B as a rho1 subunit anchoring protein. Here, we analyze the structural basis and functional significance of the MAP1B-rho1 interaction. Twelve amino acids at the C terminus of the large intracellular loop of rho1 (and also rho2) are sufficient for interaction with MAP1B. Disruption of the MAP1B-rho interaction in bipolar cells in retinal slices decreased the EC(50) of their GABA(C) receptors, doubling the receptors' current at low GABA concentrations without affecting their maximum current at high concentrations. Thus, anchoring to the cytoskeleton lowers the sensitivity of GABA(C) receptors and provides a likely site for functional modulation of GABA(C) receptor-mediated inhibition.

Constitutive endocytosis of GABAA receptors by an association with the adaptin AP2 complex modulates inhibitory synaptic currents in hippocampal neurons.

Type A GABA receptors (GABA(A)) mediate the majority of fast synaptic inhibition in the brain and are believed to be predominantly composed of alpha, beta, and gamma subunits. Although changes in cell surface GABA(A) receptor number have been postulated to be of importance in modulating inhibitory synaptic transmission, little is currently known on the mechanism used by neurons to modify surface receptor levels at inhibitory synapses. To address this issue, we have studied the cell surface expression and maintenance of GABA(A) receptors. Here we show that constitutive internalization of GABA(A) receptors in hippocampal neurons and recombinant receptors expressed in A293 cells is mediated by clathrin-dependent endocytosis. Furthermore, we identify an interaction between the GABA(A) receptor beta and gamma subunits with the adaptin complex AP2, which is critical for the recruitment of integral membrane proteins into clathrin-coated pits. GABA(A) receptors also colocalize with AP2 in cultured hippocampal neurons. Finally, blocking clathrin-dependant endocytosis with a peptide that disrupts the association between amphiphysin and dynamin causes a large sustained increase in the amplitude of miniature IPSCs in cultured hippocampal neurons. These results suggest that GABA(A) receptors cycle between the synaptic membrane and intracellular sites, and their association with AP2 followed by recruitment into clathrin-coated pits represents an important mechanism in the postsynaptic modulation of inhibitory synaptic transmission.

Heteromeric assembly of GABA(B)R1 and GABA(B)R2 receptor subunits inhibits Ca(2+) current in sympathetic neurons.

Neuronal GABA(B) receptors regulate calcium and potassium currents via G-protein-coupled mechanisms and play a critical role in long-term inhibition of synaptic transmission in the CNS. Recent studies have demonstrated that assembly of GABA(B) receptor GABA(B)R1 and GABA(B)R2 subunits into functional heterodimers is required for coupling to potassium channels in heterologous systems. However whether heterodimerization is required for the coupling of GABA(B) receptors to effector systems in neurons remains to be established. To address this issue, we have studied the coupling of recombinant GABA(B) receptors to endogenous Ca(2+) channels in superior cervical ganglion (SCG) neurons using nuclear microinjection to introduce both sense and antisense expression constructs. Patch-clamp recording from neurons injected with both GABA(B)R1a/1b and GABA(B)R2 cDNAs or with GABA(B)R2 alone produced marked baclofen-mediated inhibition of Ca(2+) channel currents via a pertussis toxin-sensitive mechanism. The actions of baclofen were blocked by CGP62349, a specific GABA(B) antagonist, and were voltage dependent. Interestingly, SCGs were found to express abundantly GABA(B)R1 but not GABA(B)R2 at the protein level. To determine whether heterodimerization of GABA(B)R1 and GABA(B)R2 subunits was required for Ca(2+) inhibition, the GABA(B)R2 expression construct was microinjected with a GABA(B)R1 antisense construct. This resulted in a dramatic decrease in the levels of the endogenous GABA(B)R1 protein and a marked reduction in the inhibitory effects of baclofen on Ca(2+) currents. Therefore our results suggest that in neurons heteromeric assemblies of GABA(B)R1 and GABA(B)R2 are essential to mediate GABAergic inhibition of Ca(2+) channel currents.

Subunit-specific association of protein kinase C and the receptor for activated C kinase with GABA type A receptors.

GABA receptors (GABA(A)) are the major sites of fast synaptic inhibition in the brain and can be assembled from five subunit classes: alpha, beta, gamma, delta, and epsilon. Receptor function can be regulated by direct phosphorylation of beta and gamma2 subunits, but how kinases are targeted to GABA(A) receptors is unknown. Here we show that protein kinase C-betaII (PKC-betaII) is capable of directly binding to the intracellular domain of the receptor beta1 and beta3 subunits, but not to those of the alpha1 or gamma2 subunits. Moreover, associating PKC-betaII is capable of specifically phosphorylating serine 409 in beta1 subunit and serines 408/409 within the beta3 subunit, key residues for modulating GABA(A) receptor function. The receptor for activated C kinase (RACK-1) was found also to bind to the beta1 subunit intracellular domain, but PKC binding appeared to be independent of this protein. Using immunoprecipitation, the association of PKC isoforms and RACK-1 with neuronal GABA(A) receptors was seen. Furthermore, PKC isoforms associating with neuronal receptors were capable of phosphorylating the receptor beta3 subunit. Together, these observations suggest GABA(A) receptors are intimately associated with PKC isoforms via a direct interaction with receptor beta subunits. This interaction may serve to localize PKC activity to GABA(A) receptors in neurons allowing the rapid regulation of receptor activity by cell-signaling pathways that modify PKC activity.

GABA(B2) is essential for g-protein coupling of the GABA(B) receptor heterodimer.

GABA(B) receptors are unique among G-protein-coupled receptors (GPCRs) in their requirement for heterodimerization between two homologous subunits, GABA(B1) and GABA(B2), for functional expression. Whereas GABA(B1) is capable of binding receptor agonists and antagonists, the role of each GABA(B) subunit in receptor signaling is unknown. Here we identified amino acid residues within the second intracellular domain of GABA(B2) that are critical for the coupling of GABA(B) receptor heterodimers to their downstream effector systems. Our results provide strong evidence for a functional role of the GABA(B2) subunit in G-protein coupling of the GABA(B) receptor heterodimer. In addition, they provide evidence for a novel "sequential" GPCR signaling mechanism in which ligand binding to one heterodimer subunit can induce signal transduction through the second partner of a heteromeric complex.

The C-terminal domains of the GABA(b) receptor subunits mediate intracellular trafficking but are not required for receptor signaling.

GABA(B) receptors are G-protein-coupled receptors that mediate slow synaptic inhibition in the brain and spinal cord. These receptors are heterodimers assembled from GABA(B1) and GABA(B2) subunits, neither of which is capable of producing functional GABA(B) receptors on homomeric expression. GABA(B1,) although able to bind GABA, is retained within the endoplasmic reticulum (ER) when expressed alone. In contrast, GABA(B2) is able to access the cell surface when expressed alone but does not couple efficiently to the appropriate effector systems or produce any detectable GABA-binding sites. In the present study, we have constructed chimeric and truncated GABA(B1) and GABA(B2) subunits to explore further GABA(B) receptor signaling and assembly. Removal of the entire C-terminal intracellular domain of GABA(B1) results in plasma membrane expression without the production of a functional GABA(B) receptor. However, coexpression of this truncated GABA(B1) subunit with either GABA(B2) or a truncated GABA(B2) subunit in which the C terminal has also been removed is capable of functional signaling via G-proteins. In contrast, transferring the entire C-terminal tail of GABA(B1) to GABA(B2) leads to the ER retention of the GABA(B2) subunit when expressed alone. These results indicate that the C terminal of GABA(B1) mediates the ER retention of this protein and that neither of the C-terminal tails of GABA(B1) or GABA(B2) is an absolute requirement for functional coupling of heteromeric receptors. Furthermore although GABA(B1) is capable of producing GABA-binding sites, GABA(B2) is of central importance in the functional coupling of heteromeric GABA(B) receptors to G-proteins and the subsequent activation of effector systems.

Ageing of the human corneal stroma: structural and biochemical changes.

High and low angle X-ray diffraction patterns from the corneal stroma give information about the mean intermolecular spacing of the collagen molecules and the mean interfibrillar spacing of the collagen fibrils, respectively. X-ray data were collected, using a high intensity synchrotron source, from human corneas and sclera at approximately physiological hydration. The spacings were measured as a function of tissue age. Between birth and 90 years there is an increase in the cross-sectional area associated with each molecule in corneal collagen from approx. 3.04 nm2 to 3.46 nm2, and an increase in scleral collagen from approx. 2.65 nm2 to 3.19 nm2. These changes may be due to an increase in the extent of non-enzymic cross-linking between collagen molecules over the age range. We have investigated this possibility by measuring collagen glycation using the thiobarbituric acid assay and the subsequent advanced glycation end-products (AGEs) using fluorescence emission. The results obtained have shown an age-related increase in glycation and AGEs in both tissues. We have also demonstrated a decrease in the interfibrillar spacing of corneal collagen with increasing age which may be related to changes in the proteoglycan composition of the interfibrillar matrix.