Functional and Structural Development of Mouse Cone Photoreceptor Ribbon Synapses

PurposeCone photoreceptors of the retina use a sophisticated ribbon-containing synapse to convert light-dependent changes in membrane potential into release of synaptic vesicles (SVs). We aimed to study the functional and structural maturation of mouse cone photoreceptor ribbon synapses during postnatal development and to investigate the role of the synaptic ribbon in SV release.MethodsWe performed patch-clamp recordings from cone photoreceptors and their postsynaptic partners, the horizontal cells during postnatal retinal development to reveal the functional parameters of the synapses. To investigate the occurring structural changes, we applied immunocytochemistry and electron microscopy.ResultsWe found that immature cone photoreceptor terminals were smaller, they had fewer active zones (AZs) and AZ-anchored synaptic ribbons, and they produced a smaller Ca²⁺ current than mature photoreceptors. The number of postsynaptic horizontal cell contacts to synaptic terminals increased with age. However, tonic and spontaneous SV release at synaptic terminals stayed similar during postnatal development. Multiquantal SV release was present in all age groups, but mature synapses produced larger multiquantal events than immature ones. Remarkably, at single AZs, tonic SV release was attenuated during maturation and showed an inverse relationship with the appearance of anchored synaptic ribbons.ConclusionsOur developmental study suggests that the presence of synaptic ribbons at the AZs attenuates tonic SV release and amplifies multiquantal SV release. However, spontaneous SV release may not depend on the presence of synaptic ribbons or voltage-sensitive Ca²⁺ channels at the AZs.     

Early migration of cutaneous lymphocyte-associated antigen (CLA) positive T cells into evolving psoriatic plaques

The majority of T cells in lesional psoriatic skin express the skin homing receptor, cutaneous lymphocyte-associated antigen (CLA). We investigated whether this reflects the selective migration of CLA positive cells into evolving psoriatic plaques, consistent with an important role in disease onset, or whether this occurs in the context of an established cutaneous inflammatory response. We identified the advancing edge of plaques in 16 patients with chronic plaque psoriasis using scanning laser Doppler fluxmetry, and performed immunohistochemical analysis of i) lesional psoriatic skin, ii) clinically normal skin immediately in front of the advancing plaque edge, and iii) uninvolved skin distant from the plaque edge. The T-cell infiltrate was characterized using monoclonal antibodies to CD3, CLA and the integrin alphaEbeta7, which is associated with the retention of lymphocytes at mucosal sites. Epithelial proliferation was assessed using a monoclonal antibody to the nuclear proliferation marker Ki67. There was enrichment of CLA positive T cells in evolving psoriatic skin compared to distant, uninvolved skin (mean CLA positive 75.9% vs 47.8%; P<0.003). This accumulation of CLA positive cells occurred before epidermal hyperproliferation was evident, suggesting that this population of cells plays an important, early role in disease pathogenesis. Established lesional psoriatic skin contained a mixed infiltrate of CLA positive (mean 53.2%) and alphaEbeta7 positive (mean 18.2%) cells, suggesting less tissue-specific T-cell infiltration, although an additional, specific role for alphaEbeta7 in cutaneous inflammation cannot be excluded. Furthermore, this study has highlighted scanning laser Doppler fluxmetry as a useful investigative tool, permitting analysis of the earliest and therefore potentially most important changes in psoriatic plaque formation.     

Ca2+ and phospholipid-dependent protein kinase (protein kinase C) activity is not necessarily required for secretion by human neutrophils

Ca2+-dependent and phospholipid-dependent protein kinase (PKC) is a receptor for and is activated by phorbol esters. This enzyme is reportedly involved in the mechanism of superoxide anion (O2-) production and the release of intracellular granule contents from human neutrophils. As previously reported by others, we found that greater than 75% of the total cellular PKC activity existed in a soluble form in untreated neutrophils and that this activity was enhanced in a dose- dependent manner by phorbol 12-myristate 13-acetate (PMA) and by phorbol 12,13-dibutyrate (PDBu). Furthermore, mezerein, an analogue of PMA that is thought to be a competitive inhibitor, did not activate PKC, and on the contrary, inhibited PMA-stimulated activity in a dose- dependent manner. Pretreatment of intact neutrophils with PMA or PDBu caused the "translocation" of PKC activity to the insoluble cell fraction; PKC translocation was not detected after mezerein stimulation at any of the tested concentrations. Neither did mezerein cause an increase in intracellular Ca2+, as monitored by Quin 2 fluorescence. Both phorbol esters and mezerein stimulated intact neutrophils to generate O2- and release lysosomal enzymes into the extracellular medium. Finally sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis demonstrated key differences in the patterns of endogenous phosphoproteins of neutrophils stimulated with phorbol as compared with mezerein. We therefore suggest that PKC activation may not be the only pathway required to elicit neutrophil responses.     

Awareness of swimming pool suction injury among tour operators

A 6 year old girl suffered rectal prolapse after being sucked onto a swimming pool drain from which the cover had been removed. After six days in hospital she made a full recovery. The severe form of this injury may result in evisceration of small bowel, short bowel syndrome, and the need for long term parenteral nutrition. A survey of travel agents revealed a low awareness of this potentially devastating hazard, and a failure on the part of some companies to take adequate responsibility for customer safety. Preventive measures are reviewed.     

The effect of acute aerobic exercise on pulse wave velocity and oxidative stress following postprandial hypertriglyceridemia in healthy men

Oxidative stress is postulated to be responsible for the postprandial impairments in vascular function. The purpose of this study was to measure pulse wave velocity (PWV) and markers of postprandial oxidative stress before and after an acute bout of moderate exercise. Ten trained male subjects (age 21.5 ± 2.5 years, VO₂ max 58.5 ± 7.1 ml kg⁻¹ min⁻¹) participated in a randomised crossover design: (1) high-fat meal alone (2) high-fat meal followed 2 h later by a bout of 1 h moderate (60% max HR) exercise. PWV was examined at baseline, 1, 2, 3, and 4 h postprandially. Blood Lipid hydroperoxides (LOOHs), Superoxide dismutase (SOD) and other biochemical markers were measured. PWV increased at 1 h (6.49 ± 2.1 m s⁻¹), 2 h (6.94 ± 2.4 m s⁻¹), 3 h (7.25 ± 2.1 m s⁻¹) and 4 h (7.41 ± 2.5 m s⁻¹) respectively, in the control trial (P < 0.05). There was no change in PWV at 3 h (5.36 ± 1.1 m s⁻¹) or 4 h (5.95 ± 2.3 m s⁻¹) post ingestion in the exercise trial (P > 0.05). LOOH levels decreased at 3 h post ingestion in the exercise trial compared to levels at 3 h (P < 0.05) in the control trial. SOD levels were lower at 3 h post ingestion in the control trial compared to 3 h in the exercise trial (0.52 ± 0.05 vs. 0.41 ± 0.1 units μl⁻¹; P < 0.05). These findings suggest that a single session of aerobic exercise can ameliorate the postprandial impairments in arterial function by possibly reducing oxidative stress levels.