Enhanced synaptic inhibition in the cerebellar cortex of the ataxic PMCA2(-/-) knockout mouse.

Mice with genetic deletion of a calcium extrusion pump, the plasma membrane calcium ATPase isoform 2, PMCA2, exhibit overt cerebellar ataxia, but the cellular mechanisms are only partially understood. Here, we report an enhanced synaptic GABAergic inhibition within the molecular layer of cerebellar cortex slices from PMCA2 knockout (PMCA2(-/-)) mice, a finding that could contribute to the observed ataxia. Purkinje neurons from PMCA2(-/-) mice exhibited an increased frequency and amplitude of spontaneous inhibitory post-synaptic currents that was accompanied by an enhanced spontaneous firing frequency of molecular layer interneurons (both basket cells and stellate cells). The elevated inhibition was sufficient to reduce the frequency and regularity of spike firing by PMCA2(-/-) Purkinje neurons. Acute pharmacological inhibition of PMCA recapitulated some of these features in wild-type mice indicating that the changes were in part a direct result of PMCA2 removal. However, additional compensatory mechanisms within the PMCA2(-/-) mouse were also a major factor. Indeed, morphological studies revealed an abnormally large number of molecular layer interneurons (basket cells and stellate cells) and GABAergic synapses within the PMCA2(-/-) cerebellar cortex. We conclude that loss of PMCA2 adversely influences the function and organisation of Purkinje neuron synaptic inhibition as a major contributory mechanism to the ataxic phenotype of the PMCA2(-/-) mouse.

The contribution of the sodium-calcium exchanger (NCX) and plasma membrane Ca(2+) ATPase (PMCA) to cerebellar synapse function.

The cerebellum, a part of the brain critically involved in motor learning and sensory adaptation, expresses high levels of the sodium-calcium exchanger (NCX) and the plasma membrane calcium ATPase (PMCA). Both these transporters control calcium dynamics at a variety of synapses, and here, we draw upon the available literature to discuss how NCX and PMCA work together to shape pre-synaptic calcium dynamics at cerebellar synapses.

Functional contributions of the plasma membrane calcium ATPase and the sodium-calcium exchanger at mouse parallel fibre to Purkinje neuron synapses.

We investigated how two calcium clearance mechanisms, the sodium-calcium exchanger-NCX, and the plasma membrane calcium ATPase-PMCA2, function at the facilitating cerebellar parallel fibre to Purkinje neuron (PF-PN) synapse. Forward mode NCX helped recover PF presynaptic calcium elevations when the PFs received a double stimulation and the calcium load was sufficiently high. A smaller presynaptic calcium load evoked by a single PF stimulation failed to recruit NCX in wild-type mice but did so when PMCA2 was absent in PFs from PMCA2 knockout mice. Simulated calcium dynamics using a simple single-compartment model reported qualitatively similar effects. Functionally, reduced NCX activity in the absence of PMCA also prolonged the recovery of facilitation at the PF-PN synapse, beyond that seen by reduced NCX activity alone. We conclude that PMCA and NCX work in parallel to accurately shape residual presynaptic calcium recovery dynamics and fine-tune facilitation at this important cerebellar synapse.

Transient reversal of the sodium/calcium exchanger boosts presynaptic calcium and synaptic transmission at a cerebellar synapse.

The sodium/calcium exchanger (NCX) is a widespread transporter that exchanges sodium and calcium ions across excitable membranes. Normally, NCX mainly operates in its "forward" mode, harnessing the electrochemical gradient of sodium ions to expel calcium. During membrane depolarization or elevated internal sodium levels, NCX can instead switch the direction of net flux to expel sodium and allow calcium entry. Such "reverse"-mode NCX operation is frequently implicated during pathological or artificially extended periods of depolarization, not during normal activity. We have used fast calcium imaging, mathematical simulation, and whole cell electrophysiology to study the role of NCX at the parallel fiber-to-Purkinje neuron synapse in the mouse cerebellum. We show that nontraditional, reverse-mode NCX activity boosts the amplitude and duration of parallel fiber calcium transients during short bursts of high-frequency action potentials typical of their behavior in vivo. Simulations, supported by experimental manipulations, showed that accumulation of intracellular sodium drove NCX into reverse mode. This mechanism fueled additional calcium influx into the parallel fibers that promoted synaptic transmission to Purkinje neurons for up to 400 ms after the burst. Thus we provide the first functional demonstration of transient and fast NCX-mediated calcium entry at a major central synapse. This unexpected contribution from reverse-mode NCX appears critical for shaping presynaptic calcium dynamics and transiently boosting synaptic transmission, and is likely to optimize the accuracy of cerebellar information transfer.

Cost effectiveness of oromucosal cannabis-based medicine (Sativex®) for spasticity in multiple sclerosis.

BACKGROUND: Spasticity is common in patients with multiple sclerosis (MS) and is a major contributor to disability. Sativex®, an oromucosal spray containing cannabis-based medicinal products, has been found to be effective in reducing spasticity symptoms. OBJECTIVE: Our objective was to estimate the cost effectiveness of Sativex® plus oral anti-spasticity medicines compared with the current standard treatment for moderate or severe spasticity in MS in the UK. METHODS: A Markov model was used to assess the costs and benefits of Sativex® plus oral anti-spasticity medicines or current standard treatment based on their effects on the quality of life of patients. The main outcome was the incremental cost-effectiveness ratio (ICER) in terms of costs per additional QALY gained over 5 years of treatment. One-way, multi-way and probabilistic sensitivity analyses were conducted to explore the impact of uncertainties on the findings. RESULTS: In the base case, Sativex® plus oral anti-spasticity medicines resulted in incremental costs of £7600 and a QALY gain of 0.15 per person over 5 years (ICER = £49 300 per QALY).[year 2009 data for costs]. Findings were sensitive to the costs of Sativex® (price and dose) and differences in utilities between responders and non-responders. CONCLUSIONS: Using a willingness-to-pay threshold of £30 000 per QALY, Sativex® appears unlikely to be considered cost effective by UK funders of healthcare for spasticity in MS. This is unfortunate, since it appears that Sativex® use is likely to benefit some patients in the management of this common consequence of MS.

Cost-effectiveness of alemtuzumab for T-cell prolymphocytic leukemia.

OBJECTIVES: The aim of this study was to evaluate the cost-effectiveness of alemtuzumab (CAMPATH-1H) compared with conventional chemotherapy in people with T-cell prolymphocytic leukemia (T-PLL). METHODS: We developed a decision-analytic model to assess the costs and benefits of alemtuzumab or conventional therapy based on their effects on quality of life of patients. The main outcome was the incremental cost-effectiveness ratio incorporating costs per additional quality-adjusted life-year (QALY) gained over lifetime. Due to the limited data available, a large number of assumptions had to be made to construct the cost-utility model. One-way, multi-way, and probabilistic sensitivity analyses (PSA) were conducted to explore the impact of these uncertainties. Expected values of perfect information were also calculated for four specific scenarios. RESULTS: Depending on different key assumptions made, the PSA suggested distinct conclusions using a willingness-to-pay threshold of 30,000 GBP per QALY gained. Using this threshold, the probability that alemtuzumab would be cost-effective varies from 0 percent to 53 percent for the four modeled scenarios. Population expected value of perfect information analysis suggests that resolving the parameter uncertainty in the analysis for people with T-PLL in the United Kingdom would have considerable value--up to 5.3 million euro. CONCLUSIONS: Alemtuzumab appears more likely to be cost-effective if used earlier in the course of T-PLL and where it replaces the use of multiple alternative therapies. However, cost-effectiveness is highly uncertain and future research is clearly justified. Nevertheless, our analysis demonstrates the feasibility of considering the cost-effectiveness of an agent despite the presence of significant uncertainty to provide appropriate assessment information to policy makers.

Cost-effectiveness analysis of degarelix for advanced hormone-dependent prostate cancer.

OBJECTIVE: To evaluate the cost-effectiveness of degarelix vs luteinizing hormone-releasing hormone analogue (triptorelin) plus short-term antiandrogen treatment for advanced prostate cancer. METHODS: We developed a decision analytic model based on a clinical trial and literature review. The two interventions evaluated were: (i) monthly injection of degarelix and (ii) 3-monthly triptorelin therapy plus short-term flutamide, cyproterone or bicalutamide treatment. The model consisted of a decision tree monitoring a hypothetical cohort of patients aged 70 years from the start of hormonal treatment to the end of the first month, and a Markov model monitoring patients from the end of month 1 for a time horizon of 10 years (i.e. when 96% of patients are assumed to have died). The base-case analysis assumed patients present with asymptomatic metastatic prostate cancer. Costs and outcomes were collected over the model time horizon. Outcome measures were quality-adjusted life years (QALYs), lifetime costs and incremental cost-effectiveness ratios. Sensitivity analyses (one-way and multi-way) and probabilistic sensitivity analyses were conducted to explore the uncertainties around the assumptions. RESULTS: In the base-case analysis, the incremental cost-effectiveness ratio (ICER) for degarelix vs triptorelin plus antiandrogen was £59,000 per QALY gained. The model was most sensitive to the rate of significant adverse events in the triptorelin plus antiandrogen group. The model was also sensitive to the assumed survival of patients with metastatic prostate cancer and the price of degarelix. The results of the probabilistic sensitivity analyses suggested that there was a low probability (9.6%) of degarelix being the most cost-effective treatment option when a willingness-to-pay threshold of £30,000 per QALY gained is assumed. CONCLUSION: Degarelix is unlikely to be cost-effective compared to triptorelin plus short-term antiandrogen in the management of advanced prostate cancer with respect to the usual thresholds of cost-effectiveness used in the UK: £20,000-30,000 per QALY gained (used by the National Institute for Health and Clinical Excellence).

Assessment of the contribution of the plasma membrane calcium ATPase, PMCA, calcium transporter to synapse function using patch clamp electrophysiology and fast calcium imaging.

The plasma membrane calcium ATPase, or PMCA, functions to extrude calcium out of cells as a key component necessary for adequate calcium homeostasis in all cells. However, calcium is particularly important at synapses between neurons, where communication relies on the controlled rise and fall in presynaptic calcium that precedes the release of neurotransmitter. Here we show how to infer the real-time contribution of PMCA-mediated calcium extrusion to this presynaptic calcium dynamic and how this influences the properties of the synapse. To do this we have taken advantage of a well-studied synapse in the cerebellum. We use electrophysiology to assess the timing of short-term facilitation at this synapse in the presence and absence of PMCA2 using PMCA2 knockout mice and pharmacology and fast calcium imaging to measure the presynaptic calcium dynamics. These approaches are all highly applicable to other synapses and can help determine the contribution of PMCA, and other transporters or exchangers, to the calcium dynamics that underpin reliable synaptic transmission.