Impaired Pre-Motor Circuit Activity and Movement in a Drosophila Model of KCNMA1-Linked Dyskinesia

Background

Paroxysmal dyskinesias (PxDs) are characterized by involuntary movements and altered pre‐motor circuit activity. Causative mutations provide a means to understand the molecular basis of PxDs. Yet in many cases, animal models harboring corresponding mutations are lacking. Here we utilize the fruit fly, Drosophila, to study a PxD linked to a gain‐of‐function (GOF) mutation in the KCNMA1/hSlo1 BK potassium channel.

Objectives

We aimed to recreate the equivalent BK (big potassium) channel mutation in Drosophila. We sought to determine how this mutation altered action potentials (APs) and synaptic release in vivo; to test whether this mutation disrupted pre‐motor circuit function and locomotion; and to define neural circuits involved in locomotor disruption.

Methods

We generated a knock‐in Drosophila model using homologous recombination. We used electrophysiological recordings and calcium‐imaging to assess AP shape, neurotransmission, and the activity of the larval pre‐motor central pattern generator (CPG). We used video‐tracking and automated systems to measure movement, and developed a genetic method to limit BK channel expression to defined circuits.

Results

Neuronal APs exhibited reduced width and an enhanced afterhyperpolarization in the PxD model. We identified calcium‐dependent reductions in neurotransmitter release, dysfunction of the CPG, and corresponding alterations in movement, in model larvae. Finally, we observed aberrant locomotion and dyskinesia‐like movements in adult model flies, and partially mapped the impact of GOF BK channels on movement to cholinergic neurons.

Conclusion

Our model supports a link between BK channel GOF and hyperkinetic movements, and provides a platform to dissect the mechanistic basis of PxDs. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

A third copy of the Down syndrome cell adhesion molecule (Dscam) causes synaptic and locomotor dysfunction in Drosophila

Down syndrome (DS) is caused by triplication of chromosome 21 (HSA21). It is characterised by intellectual disability and impaired motor coordination that arise from changes in brain volume, structure and function. However, the contribution of each HSA21 gene to these various phenotypes and to the causal alterations in neuronal and synaptic structure and function are largely unknown. Here we have investigated the effect of overexpression of the HSA21 gene DSCAM (Down syndrome cell adhesion molecule), on glutamatergic synaptic transmission and motor coordination, using Drosophila expressing three copies of Dscam1. Electrophysiological recordings of miniature and evoked excitatory junction potentials at the glutamatergic neuromuscular junction of Drosophila larvae showed that the extra copy of Dscam1 changed the properties of spontaneous and electrically-evoked transmitter release and strengthened short-term synaptic depression during high-frequency firing of the motor nerve. Behavioural analyses uncovered impaired locomotor coordination despite preserved gross motor function. This work identifies DSCAM as a candidate causative gene in DS that is sufficient to modify synaptic transmission and synaptic plasticity and cause a DS behavioural phenotype.

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Drosophila expressing a third copy of Dscam have altered neuromuscular transmission.

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Drosophila expressing a third copy of Dscam have deficits in locomotor coordination.

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Drosophila are a powerful system for studying single-gene effects in Down syndrome.

Mutations in Membrin/GOSR2 Reveal Stringent Secretory Pathway Demands of Dendritic Growth and Synaptic Integrity

Mutations in the Golgi SNARE (SNAP [soluble NSF attachment protein] receptor) protein Membrin (encoded by the GOSR2 gene) cause progressive myoclonus epilepsy (PME). Membrin is a ubiquitous and essential protein mediating ER-to-Golgi membrane fusion. Thus, it is unclear how mutations in Membrin result in a disorder restricted to the nervous system. Here, we use a multi-layered strategy to elucidate the consequences of Membrin mutations from protein to neuron. We show that the pathogenic mutations cause partial reductions in SNARE-mediated membrane fusion. Importantly, these alterations were sufficient to profoundly impair dendritic growth in Drosophila models of GOSR2-PME. Furthermore, we show that Membrin mutations cause fragmentation of the presynaptic cytoskeleton coupled with transsynaptic instability and hyperactive neurotransmission. Our study highlights how dendritic growth is vulnerable even to subtle secretory pathway deficits, uncovers a role for Membrin in synaptic function, and provides a comprehensive explanatory basis for genotype-phenotype relationships in GOSR2-PME.

Twin pregnancies complicated by gestational diabetes mellitus: a single centre cohort study

AIMS

In women with a twin pregnancy, to determine the incidence of, risk factors for and outcomes of women with gestational diabetes mellitus, and assess how these have changed with a change in gestational diabetes screening.

METHODS

Retrospective cohort study of women with a twin pregnancy attending an Australian tertiary hospital, 2002-2013. Information on gestational diabetes status, gestational diabetes risk factors and pregnancy outcomes was ascertained. Pregnancy outcomes included hypertensive disorders, twin birthweight centile and a composite adverse pregnancy outcome. Analysis was stratified pre/post screening protocol change (epoch 1: 2002-2009, epoch 2: 2010-2013) and by gestational diabetes status.

RESULTS

Gestational diabetes was diagnosed in 86/982 (8.8%) women, increasing from 4.4% to 14.7% between epochs (P = 0.0001). The proportion of women with hypertensive disorders increased (11.7% vs. 13.4%, P = 0.009), but the proportion of infant's birthweight > 90th centile decreased (11.0% vs. 7.6%, P = 0.02) between epochs. Overall, 33.6% of women had ≥ 1 risk factors for gestational diabetes. Three-quarters (73.7%) of women overall had an adverse pregnancy outcome, with a slightly higher proportion in women with gestational diabetes compared with those with no gestational diabetes (79.7% vs. 73.1%, P = 0.06). The rate of the adverse pregnancy outcome did not change by epoch, after adjusting for maternal and pregnancy risk factors (adjusted odds ratio = 0.96, 95% confidence interval 0.73-1.26).

CONCLUSIONS

Almost 1 in 10 women with a twin pregnancy were diagnosed with gestational diabetes, with the incidence of gestational diabetes increasing threefold with a new screening protocol. The pregnancy outcomes of women with a twin pregnancy did not change with increased detection and treatment for gestational diabetes.

Cutaneous pseudovasculitis, antiphospholipid syndrome and obstetric misadventure

We present two women with severe obstetric complications from antiphospholipid (aPL) syndrome associated with a rare dermatological manifestation, cutaneous pseudovasculitis. Both of these women developed a rash on the palmar aspect of the hands during the post partum period, with histology consistent with microthrombotic disease, despite anticoagulation. Cutaneous pseudovasculitis appears to be a maternal manifestation of aPL coagulopathy, possibly reflecting the severity of the underlying pregnancy pathology.

Improving the performance of power plant cooling ponds

A study was conducted on the effectiveness of using vertical baffles to improve the thermal performance of power plant cooling ponds. A small scale physical model of a rectangular cooling pond was used. A base case was established using traditional horizontal baffles to create a serpentine flow pattern through the pond. The horizontal baffles were then replaced by a series of underflow weirs that spanned the pond. An improvement in cooling of over 30% was realized.

Drugs in pregnancy. Anticonvulsants and drugs for neurological disease

The use of anticonvulsant drugs in pregnancy presents unique challenges to clinicians and their patients. The need for control of maternal epilepsy must be balanced with the fetal and neonatal risks associated with anticonvulsant drugs. Anticonvulsant drugs may have potential effects on embryogenesis, neurological development, growth and subsequent paediatric progress. Drug selection and dose adjustment must be appropriate and based on a combination of known maternal and fetal risks as well as the clinical status of the patient. Overall, no one drug can be specifically recommended but monotherapy with most of the recognized first-line drugs will result in a satisfactory outcome. Polytherapy is associated with an increase in congenital malformations and should be avoided if possible. It is possible that newer second-line agents, for example, gabapentin, may be safer as add-on therapy. Neurological disorders such as migraine, and the less common conditions of myasthenia gravis and multiple sclerosis, may require the use of drugs which have not been well studied in pregnancy. Information is provided about the use of drugs to control symptoms and prevent disease progression in these disorders during pregnancy.

Anticoagulation in pregnancy and the puerperium

For the management of acute thrombotic events in pregnancy therapeutic doses of low molecular weight heparins (LMWH) may be used, unless the shorter half-life of intravenous unfractionated heparin (UH) and predictable reversibility by protamine are important. Treatment should be continued up until delivery and into the puerperium. Pregnant women who have had an acute thrombotic event should be delivered by a specialist team. In the case of recent thrombosis, delivery should be planned and the time during which anticoagulation therapy is ceased around the time of delivery should be minimised. Therapeutic doses of LMWH contraindicate the use of regional anaesthesia, and a switch to intravenous UH before delivery may allow greater flexibility in this regard. Prophylactic doses of LMWH can be used to reduce the risk of recurrent thromboembolic events in pregnancy. The regimen used will depend on the previous history, the family history and the presence of risk factors, including the genetic and acquired causes of thrombophilia. Women with mechanical heart valves are at high risk during pregnancy and require therapeutic anticoagulation throughout pregnancy under the direction of experienced specialists. Low-dose aspirin can reduce the risk of recurrent pre-eclampsia by about 15%, but the role of UH and LMWH in the prevention of recurrent miscarriage or obstetric complications associated with uteroplacental insufficiency is still uncertain.

Atrial natriuretic peptide in pregnancy: response to oral sodium supplementation

1. The control of extracellular fluid volume (ECFV) in normal pregnancy may be related to changes in atrial natriuretic peptide. Previous studies in non-pregnant subjects have suggested that plasma atrial natriuretic peptide (ANP) increases in response to dietary sodium supplementation because of an increase in plasma volume, although this has not been measured directly. 2. Nine women who were pregnant in the third trimester undertook oral sodium supplementation (136 mmol) for 5 days in addition to their usual diet. Twenty-four hour urinary sodium excretion increased by 125 +/- 54 mmol/day (mean +/- s.d.; P less than 0.01). Plasma volume was unchanged, although total ECFV tended to increase (P less than 0.09 and bodyweight increased (1.3 +/- 1.4 kg; P less than 0.01) at the end of these diets. 3. Plasma ANP increased by 30.7 [8.6, 34.5] pmol/L (median [25th, 75th percentile]; P less than 0.05), while plasma renin concentration decreased significantly from 7.3 [6.2, 11.2] to 2.6 [1.7, 3.9] pmol angiotensin I/mL (P less than 0.01), as did plasma aldosterone concentration (1435 [1162, 1722] to 753 [595, 1110] fmol/mL; P less than 0.01). Plasma vasoactive intestinal peptide was unchanged. 4. Pregnant women respond to increased dietary sodium with an increase in plasma ANP in the absence of a significant increase in plasma volume. The acute regulation of plasma ANP in response to increases in dietary sodium in pregnant women does not appear to be mediated by changes in intravascular fluid volume.

Acute and chronic regulation of atrial natriuretic peptide in human pregnancy: a longitudinal study

OBJECTIVE

To determine whether the increase in extracellular fluid volume (ECFV) that occurs during pregnancy alters: (1) the baseline regulation of atrial natriuretic peptide (ANP); or (2) the ANP response to intravascular volume expansion with either haemaccel or hypertonic saline.

DESIGN

A group of normal pregnant subjects was studied longitudinally on three occasions, commencing before 16 weeks of gestation. They were compared with a group of age-matched non-pregnant women. Dietary sodium intake and posture were carefully controlled.

METHODS

Plasma volume and total ECFV were determined by tracer dilution methods, using Evans Blue and 20% mannitol, respectively. Plasma ANP and aldosterone concentrations were measured by radioimmunoassay.

RESULTS

Plasma ANP did not increase during pregnancy despite increases in both plasma and total ECFV. The plasma ANP response to acute intravenous volume expansion in later pregnancy appears to be more sensitive than either in early pregnancy or in non-pregnant subjects. The initial ANP response to infusions of haemaccel during pregnancy was greater than the ANP response to saline.

CONCLUSIONS

During a normal pregnancy, plasma ANP is maintained in the normal non-pregnant range, despite an increase in plasma volume when the effects of dietary sodium intake and posture are carefully accounted for. The ANP response to intravenous volume expansion is enhanced in late pregnancy. The greater ANP response to haemaccel infusions during pregnancy suggests that an increase in atrial stretch mediates the secretion of ANP following intravenous volume expansion.

The pharmacological management of hypertension in pregnancy

PURPOSE

The management of pregnancy-induced hypertension (PIH) and preeclampsia using antihypertensive drug therapy remains contentious. Conflicts arise due to differences in diagnostic criteria and varying attitudes regarding the value of treating hypertension, which is only one aspect of this systemic disorder. The following review assesses the role of individual agents and their effects upon both maternal and foetal/neonatal wellbeing.

STUDY SELECTION

Human clinical trials of each of the main antihypertensive drugs used in the management of PIH/preeclampsia are reviewed. The value of randomized, placebo-controlled trials and long-term paediatric follow up is stressed.

RESULTS OF DATA ANALYSIS

A number of agents have a favourable benefit-risk profile for use in women with PIH/preeclampsia; these include alpha-methyldopa, beta-blockers, hydralazine, prazosin, calcium channel antagonists and ketanserin. Diazoxide and sodium nitroprusside may also be used for acute severe hypertension. Angiotensin converting enzyme inhibitors are contra-indicated. Low-dose aspirin is presently being investigated in multicentre trials and may play a major role in the prevention of preeclampsia.

CONCLUSION

Decisions regarding the need for antihypertensive treatment during pregnancy and the selection of a specific antihypertensive agent should be based upon an assessment of the relative benefits and risks for the individual patient. In future studies, the effects of antihypertensive agents upon the underlying pathophysiological processes involved in PIH/preeclampsia may guide therapeutic decision making.

Atrial natriuretic peptide and plasma volume in pregnancy-induced hypertension

Pregnancy-induced hypertension (PIH) is characterized by a relative decrease in plasma volume and renin and aldosterone concentrations as well as increased capillary permeability compared with normal pregnancy. As many of these features could be explained by the actions of atrial natriuretic peptide (ANP), we examined the relationship between plasma volume and plasma ANP in women with PIH and in normal third trimester pregnant women, and whether ANP responses to alterations in posture were intact in women with PIH. Basal plasma ANP measured after 20 min lateral recumbency in women with PIH was 24.0 (13.9, 33.1) pmol/L (median [25th, 75th percentile]), which was significantly greater than in normal pregnant women (9.9 [6.3, 16.0]), (P less than .05). Plasma ANP did not differ between those with and without proteinuria in the PIH group. Plasma volume was decreased in women with PIH (20.1 [19.0, 23.2] mL/cm) v 23.5 [21.4, 25.3], P less than .05). Plasma renin concentration but not plasma aldosterone concentration was also decreased significantly in women with PIH compared with normal pregnant women (P less than .001) and both were correlated negatively with plasma ANP. Following prolonged lateral recumbency, plasma ANP rose to 26.9 [19.1, 44.1] pmol/L in women with PIH (P less than .05), which was still significantly greater than in normal pregnant women (15.5 [6.7, 21.9] pmol/L) (P less than .05). In a subgroup of these subjects, 30 min head-up tilt decreased plasma ANP by 5.2 [0.9, 22.3] pmol/L in women with PIH and by 6.1 [2.2, 10.3] pmol/L in normal pregnant women, a nonsignificant difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of atrial natriuretic peptide release in pregnancy: responses to posture

The response of plasma atrial natriuretic peptide to three changes in posture that alter atrial stretch was examined in the late phase of pregnancy: (1) after 20 minutes in lateral recumbency, remaining upright for 2 hours decreased median plasma atrial natriuretic peptide values from 37.8 (25th percentile, 22.9 and 75th percentile; 64.2) to 21.8 (10.1 and 28.4) pg/ml in pregnant women (p less than 0.05) and from 39.2 (27.8 and 51.2) to 24.0 (18.9 and 35.4) pg/ml (p less than 0.001) in age-matched nonpregnant women; (2) prolongation of lateral recumbency from 20 to 80 minutes increased median plasma atrial natriuretic peptide levels from 31.9 (25.6 and 37.3) to 47.8 (33.0 and 74.6) pg/ml in pregnant women (p less than 0.001) and from 36.5 (22 and 58.6) to 54.0 (36.3 and 111.7) pg/ml in nonpregnant women (p less than 0.01); (3) adoption of supine posture during the late phase of normal pregnancy did not alter median plasma atrial natriuretic peptide values significantly [30.4 (26.7 and 42.5) pg/ml during lateral recumbency compared with 34.2 (25.4 and 43.5) pg/ml while supine]. Plasma atrial natriuretic peptide values fell after supine posture in only half the women and supine hypotension occurred in one subject. These studies demonstrate that upright and prolonged lateral recumbent postures significantly influence plasma atrial natriuretic peptide values during pregnancy, as they do in the nonpregnant state, but that supine posture does not alter plasma atrial natriuretic peptide values significantly. Posture must be carefully accounted for in any study of plasma atrial natriuretic peptide in pregnancy.

Capillary permeability and extracellular fluid volumes in pregnancy-induced hypertension

1. Capillary permeability was determined by the disappearance rate of Evans Blue dye from plasma in healthy non-pregnant women, normal third-trimester primigravidae and primigravidae with pregnancy-induced hypertension. 2. Extracellular fluid volume was determined from the disappearance curves of injected mannitol in the same subjects and the plasma volume was measured by the Evans Blue dye dilution technique. 3. In normal pregnancy capillary permeability was not altered from that of non-pregnant subjects. Although extracellular fluid volume and plasma volume were increased in normal pregnant compared with non-pregnant women, the distribution of fluid between plasma volume and interstitial fluid volume was unaltered. 4. Women with established pregnancy-induced hypertension had a more rapid Evans Blue disappearance rate and a lower plasma volume than normal pregnant women, independent of the presence of proteinuria. Maternal plasma volume correlated positively and significantly with fetal birth weight in women with pregnancy-induced hypertension, emphasizing the important relationship between maternal plasma volume and fetal outcome. 5. The increased capillary permeability in women with pregnancy-induced hypertension was associated with a reduction in the plasma volume/interstitial fluid volume ratio but a normal extracellular fluid volume, suggesting that the reduced plasma volume did not result from sodium loss but rather from a redistribution of the total extracellular fluid volume. These changes did not differ significantly in subgroups with and without oedema.