Progressive parkinsonism due to mitochondrial impairment: Lessons from the MitoPark mouse model

The cardinal pathophysiological finding of Parkinson's disease (PD) is a chronic, progressive degeneration of dopamine (DA) neurons in the substantia nigra, which is responsible for the motor and some of the non-motor symptomatology. While the primary causes of nigrostriatal degeneration are hotly debated, considerable evidence supports a central role for impaired mitochondrial function. Postmortem analysis of PD patients reveals impaired respiratory chains and increased mutations of mitochondrial DNA (mtDNA), in addition to increased markers of oxidative stress indicative of mitochondrial impairment. Most animal models of PD, both genetic and toxin-based, target some component of mitochondrial function to reproduce aspects of the human disease. One model that continues to gain attention is the MitoPark mouse, created through a cell type-specific knockout of mitochondrial transcription factor A specifically in midbrain DA neurons. This model effectively recapitulates the slowly developing, adult onset motor decline seen in PD due to mass loss of DA neurons. MitoPark mice therefore represent an effective tool for studying the sequence of events that occurs in the early stages of DA neuron degeneration following mitochondrial impairment, as well as for testing the efficacy of potential disease-modifying therapies in a progressive model of neurodegeneration. A targeted review of key findings from MitoPark mice has not been published since the early years following the initial report of the model in 2007. The current review synthesizes findings from several groups that are exploring MitoPark mice and discusses implications for the future identification of disease-modifying treatments for PD.

Female mice are resilient to age-related decline of substantia nigra dopamine neuron firing parameters

Degeneration of substantia nigra pars compacta dopamine neurons is a central feature in the pathology of Parkinson's disease, which is characterized by progressive loss of motor and cognitive functions. The largest risk factors for Parkinson's disease are age and sex; most cases occur after age 60 and males have nearly twice the incidence as females. Preclinical work has scarcely considered the influence of these 2 factors to disease risk and presentation. Here, we observed a progressive decline in dopamine neuron firing activity in male C57BL/6 mice by 18 months of age, while dopamine neurons from females remained largely unaffected. This was accompanied by increased mRNA expression of PINK1 in both males and females, and PARK2 primarily in males, both of which have been linked to Parkinson's. Since the declining cell properties were accompanied by only slight decreases in locomotion in both sexes, it is likely that these age-related impairments in males represent a vulnerability to further insults that could predispose the neurons to neurodegenerative processes such as in Parkinson's.

Biphasic modulation of parallel fibre synaptic transmission by co-activation of presynaptic GABAA and GABAB receptors in mice

KEY POINTS

Many excitatory synapses co-express presynaptic GABAA and GABAB receptors, despite their opposing actions on synaptic transmission. It is still unclear how co-activation of these receptors modulates synapse function. We measured presynaptic GABA receptor function at parallel fibre synapses onto stellate cells in the cerebellum using whole-cell patch-clamp recording and photolytic uncaging of RuBi-GABA. Activation of presynaptic GABA receptors results in a transient (∼100 ms) enhancement of synaptic transmission (mediated by GABAA receptors) followed by a long lasting (>500 ms) inhibition of transmission (mediated by GABAB receptors). When activated just prior to high-frequency trains of stimulation, presynaptic GABAA and GABAB receptors work together to reduce short-term facilitation/enhance depression, altering the filtering properties of synaptic transmission. Inhibition of synaptic transmission by GABAB receptors is more sensitive to GABA than enhancement by GABAA receptors, suggesting GABAB receptors may be activated by ambient GABA or release from greater distances.

ABSTRACT

GABAA and GABAB receptors are co-expressed at many presynaptic terminals in the central nervous system. Previous studies have shown that GABAA receptors typically enhance vesicle release while GABAB receptors inhibit release. However, it is not clear how the competing actions of these receptors modulate synaptic transmission when co-activated, as is likely in vivo. We investigated this question at parallel fibre synapses in the cerebellum, which co-express presynaptic GABAA and GABAB receptors. In acute slices from C57BL/6 mice, we find that co-activation of presynaptic GABA receptors by photolytic uncaging of RuBi-GABA has a biphasic effect on EPSC amplitudes recorded from stellate cells. Synchronous and asynchronous EPSCs evoked within ∼100 ms of GABA uncaging were increased, while EPSCs evoked ∼300-600 ms after GABA uncaging were reduced compared to interleaved control sweeps. We confirmed these effects are presynaptic by measuring the paired-pulse ratio, variance of EPSC amplitudes, and response probability. During trains of high-frequency stimulation GABAA and GABAB receptors work together (rather than oppose one another) to reduce short-term facilitation when GABA is uncaged just prior to the onset of stimulation. We also find that GABAB receptor-mediated inhibition can be elicited by lower GABA concentrations than GABAA receptor-mediated enhancement of EPSCs, suggesting GABAB receptors may be selectively activated by ambient GABA or release from more distance synapses. These data suggest that GABA, acting through both presynaptic GABAA and GABAB receptors, modulate the amplitude and short-term plasticity of excitatory synapses, a result not possible from activation of either receptor type alone.

Validation of the Lower Gastrointestinal Electronic Referral Protocol

Background

Recognition of people presenting to the general practitioner with symptoms suggestive of colorectal cancer varies considerably, as do the subsequent patterns of referral and treatment. The Lower Gastrointestinal Electronic Referral Protocol (e-RP) was developed to be used alongside the national Choose and Book programme. This paper addresses the validation of the e-RP.

Methods

The e-RP was validated using three datasets: 100 consecutive patients with colorectal cancer, 100 2-week wait (TWW) suspected cancer referrals and 100 routine referrals. The actual destination of referred patients, their clinical diagnosis and referral urgency were compared with destination and referral urgency assigned by the e-RP.

Results

Some 43·0 per cent of patients with colorectal cancer were actually referred through the TWW system and the e-RP successfully upgraded 85·0 per cent of these patients as TWW referrals (Pearson χ2 = 9·76, 1 d.f., P = 0·002). The e-RP also redirected three of four patients with colorectal cancer in routine referrals to TWW clinics. Right-sided cancers were appropriately directed to colonoscopy as the first contact in secondary care or to outpatients for investigation of a palpable mass. Most patients with left-sided cancers were directed to flexible sigmoidoscopy clinics.

Conclusion

A dedicated referral protocol addressing all colorectal symptoms would significantly improve the overall yield of colorectal cancers through the TWW route and reduce delays in patient pathways with ‘straight to test’ in secondary care.

Inter general practice variability in use of referral guidelines for colorectal cancer

OBJECTIVE

The Two-Week Wait (TWW) referral system for suspected colorectal cancers has a low yield. To examine this, we assessed the referral pattern of general practices within four primary care trusts and looked at the variability of yield of colorectal cancer amongst all TWW referrals and assessed the reasons for variability.

METHOD

A prospectively collected database of all colorectal cancers was examined for new cases diagnosed in the 12 months from April 1st 2004. Patients were cross-referenced via general practitioner (GP) codes to identify the referral origin. Reasons for the variability in referral patterns from each general practice were assessed in relation to TWW referrals, population demographics and through postal questionnaire of GPs.

RESULTS

A total of 175 patients diagnosed with colorectal cancer were referred from 49 general practices. Whilst there was a positive correlation between the number of TWW referrals and colorectal cancer per 1000-practice population (P = 0.001; Spearman correlation coefficient r(s=0.447,) two-tailed), there was a big discrepancy between referrals and cancer diagnosed in many general practices. Twenty-six general practices (53%) had no colorectal cancer diagnosed via the TWW route and these practices had significantly lower utilization of the TWW referral pathway. In the postal survey, 22% of GPs were unaware of TWW clinics or colorectal cancer referral guidelines and only 8% of GPs knew the number of referral criteria.

CONCLUSION

This study demonstrates wide variability within primary care, in the appropriate use of colorectal cancer referral guidelines. General practices should be targeted for education.

Should we pursue patients who fail to attend colorectal clinics? A 9-year study

INTRODUCTION

No uniform protocol exists on how to deal with patients who fail to attend colorectal clinics. Our aim was to identify whether the tendency to 'failure to attend' (FTA) in the colorectal clinic was associated with FTA in other clinics and also whether FTA patients have serious pathology.

PATIENTS AND METHODS

This was a retrospective study of a prospectively recorded list of FTA patients, in colorectal urgent or two-week wait clinics from 1996-2004.

RESULTS

A total of 151 patients, who failed to attend their first appointment, were included in the study. Of these, 61 (40.4%) were colorectal referrals, 76 (50.3%) were general surgical referrals, and for 14 (9.3%) case notes were not available. There were 59 FTA episodes in 61 colorectal patients associated with 59 FTA episodes in other clinics (Pearson correlation: r = 0.411; P = 0.01, two-tailed, SPSS v.12). Of 58 colorectal outcomes, five (8.6%) colorectal cancers (CRC) were diagnosed, 23 (39.6%) were persistent non-attendees, 16 (27.5%) had benign colorectal pathology, two (3.4%) benign non-colorectal outcomes and 12 (20.6%) normal outcomes.

CONCLUSIONS

Tendency to FTA is habitual. Care needs to be exercised in the management of FTAs to avoid delayed presentation of colorectal cancer.

Theoretic Fit and Empirical Fit: The Performance of Maximum Likelihood versus Generalized Least Squares Estimation in Structural Equation Models

In research the goal is often to construct models that reflect the structures and parameters of some unobservable causal mechanism. The degree of isomorphis between such a theoretic model and a "true" model can be labeled "theoretic fit." In the absence of direct evidence that the researcher's theoretic model accurately reflects the true model, indices of "empirical fit" (Chi-Square, etc.) are used as indirect evidence of versimilitude. The issue addressed here is: Is empirical fit necessarily a good indicator of theoretic fit? This study uses simulation to compare the ability of Maximum Likelihood (ML) and Generalized Least Squares (GLS) estimation to provide theoretic fit in models that are parsimonious representations of a true model. We find that empirical fit using GLS was actually superior to that obtained when parameters in the incomplete model were constrained to the true values of the generating model. However, this apparent goodness of fit of GLS is obtained through greater distortion of the parameter estimates. In short, better empirical fit obtained for GLS, compared with ML, was obtained at the cost of lower theoretic fit.

Antiplatelet activity of nipecotamides in experimental thrombosis in mice

A group of nipecotamides (3-carbamoylpiperidines) were designed, synthesized, and evaluated for their ability to protect platelets from induced aggregation. An in vivo mouse thrombosis model was used to determine the protection afforded by these compounds from sudden thrombotic death induced by intravenous collagen plus epinephrine. Enantioselectivity appears to play a pivotal role in determining the activity of these compounds. Lipophilicity, whereas previously found to correlate well with in vitro activity, did not directly influence in vivo activity. The presence of an amide function on the 3-position of the piperidine ring was essential for activity. Of the 10 compounds reported here, alpha,alpha'-bis[3-(N-benzyl-N-methylcarbamoyl)-piperidino]-p-xyle ne dihydrobromide (4) was the most potent in preventing induced intravascular platelet aggregation in mice, with a 50% effective dose of (ED50) of 27.5 mumol (20 mg)/kg.

Cadmium and lead residues in field-collected red swamp crayfish (Procambarus clarkii) and uptake by alligator weed, Alternanthera philoxiroides

The whole-body residues of Cd and Pb in the tissues of Louisiana swamp crayfish (Procambarus clarkii) were determined by flame AAS technique. Test animals were collected from roadside ditches (18 locations) alongside major highways. The water and soil samples were also collected from the same sites. The mean Cd and Pb concentrations (mg/l) in crayfish tissues were 0.46 and 0.07, respectively. The levels of Cd and Pb in the water were 0.09 and 0.04; and in soil were 2.85 and 0.87 mg/l, respectively. The concentration of cadmium was 32 and Pb 12 times more than in the water. The bioaccumulation factors (BF) for Cd and Pb in crayfish tissues were 5.1 and 1.7, Alligator weed (Alternanthera philoxiroides) plants were exposed to 0.5 mg/l Cd-chloride or Pb-nitrate solutions for 3 wk period, thrice. The mean Pb accumulation in roots was 1.31 mg/l, followed by stem (0.078 mg/l), but Cd only accumulated in root (0.83 mg/l). The BF for Pb and Cd in plant tissues were 14.8 and 16.6, respectively. The uptake of metals was time-dependent (P = < 0.01). These data suggest that although there is no biomagnification of Cd and Pb from alligator weed to crayfish, both metals readily accumulate in field-collected crayfish and laboratory-exposed alligator weed.

Effects of two types of head coverings in the rewarming of patients after coronary artery bypass graft surgery

In this experimental study we examined the effects of two types of head coverings in the rewarming of patients who have had coronary artery bypass graft surgery during the initial 8-hour postoperative period. A third group with no head coverings served as a control. Eighty-one patients were randomly assigned to one of the three treatment groups; rectal temperatures were recorded on admission and hourly for the next 8 hours. An analysis of variance between the three groups revealed no statistically significant differences (p less than 0.05) in the length of time for patients to reach normothermia and in the net temperature gain achieved. Irrespective of the groupings, however, patients who took 5 hours or less to reach normothermia exhibited statistically significant differences (p less than 0.05) compared with patients who took longer: the former patients tended to be younger, the lowest induced operating room temperature tended to be higher, their admission temperatures tended to be higher, and minutes of cardiopulmonary bypass tended to be fewer.