Mitochondrial damage and impaired mitophagy contribute to disease progression in SCA6

Spinocerebellar ataxia type 6 (SCA6) is a neurodegenerative disease that manifests in midlife and progressively worsens with age. SCA6 is rare, and many patients are not diagnosed until long after disease onset. Whether disease-causing cellular alterations differ at different disease stages is currently unknown, but it is important to answer this question in order to identify appropriate therapeutic targets across disease duration. We used transcriptomics to identify changes in gene expression at disease onset in a well-established mouse model of SCA6 that recapitulates key disease features. We observed both up- and down-regulated genes with the major down-regulated gene ontology terms suggesting mitochondrial dysfunction. We explored mitochondrial function and structure and observed that changes in mitochondrial structure preceded changes in function, and that mitochondrial function was not significantly altered at disease onset but was impaired later during disease progression. We also detected elevated oxidative stress in cells at the same disease stage. In addition, we observed impairment in mitophagy that exacerbates mitochondrial dysfunction at late disease stages. In post-mortem SCA6 patient cerebellar tissue, we observed metabolic changes that are consistent with mitochondrial impairments, supporting our results from animal models being translatable to human disease. Our study reveals that mitochondrial dysfunction and impaired mitochondrial degradation likely contribute to disease progression in SCA6 and suggests that these could be promising targets for therapeutic interventions in particular for patients diagnosed after disease onset.

Endosomal dysfunction contributes to cerebellar deficits in spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) is a rare disease that is characterized by cerebellar dysfunction. Patients have progressive motor coordination impairment, and postmortem brain tissue reveals degeneration of cerebellar Purkinje cells and a reduced level of cerebellar brain-derived neurotrophic factor (BDNF). However, the pathophysiological changes underlying SCA6 are not fully understood. We carried out RNA-sequencing of cerebellar vermis tissue in a mouse model of SCA6, which revealed widespread dysregulation of genes associated with the endo-lysosomal system. Since disruption to endosomes or lysosomes could contribute to cellular deficits, we examined the endo-lysosomal system in SCA6. We identified alterations in multiple endosomal compartments in the Purkinje cells of SCA6 mice. Early endosomes were enlarged, while the size of the late endosome compartment was reduced. We also found evidence for impaired trafficking of cargo to the lysosomes. As the proper functioning of the endo-lysosomal system is crucial for the sorting and trafficking of signaling molecules, we wondered whether these changes could contribute to previously identified deficits in signaling by BDNF and its receptor tropomyosin kinase B (TrkB) in SCA6. Indeed, we found that the enlarged early endosomes in SCA6 mice accumulated both BDNF and TrkB. Furthermore, TrkB recycling to the cell membrane in recycling endosomes was reduced, and the late endosome transport of BDNF for degradation was impaired. Therefore, mis-trafficking due to aberrant endo-lysosomal transport and function could contribute to SCA6 pathophysiology through alterations to BDNF-TrkB signaling, as well as mishandling of other signaling molecules. Deficits in early endosomes and BDNF localization were rescued by chronic administration of a TrkB agonist, 7,8-dihydroxyflavone, that we have previously shown restores motor coordination and cerebellar TrkB expression. The endo-lysosomal system is thus both a novel locus of pathophysiology in SCA6 and a promising therapeutic target.

Activation of TrkB-Akt signaling rescues deficits in a mouse model of SCA6

Spinocerebellar ataxia type 6 (SCA6) is a neurodegenerative disease resulting in motor coordination deficits and cerebellar pathology. Expression of brain-derived neurotrophic factor (BDNF) is reduced in postmortem tissue from SCA6 patients. Here, we show that levels of cerebellar BDNF and its receptor, tropomyosin receptor kinase B (TrkB), are reduced at an early disease stage in a mouse model of SCA6 (SCA6^84Q/84Q). One month of exercise elevated cerebellar BDNF expression and improved ataxia and cerebellar Purkinje cell firing rate deficits. A TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF), likewise improved motor coordination and Purkinje cell firing rate and elevated downstream Akt signaling. Prolonged 7,8-DHF administration persistently improved ataxia when treatment commenced near disease onset but was ineffective when treatment was started late. These data suggest that 7,8-DHF, which is orally bioavailable and crosses the blood-brain barrier, is a promising therapeutic for SCA6 and argue for the importance of early intervention for SCA6.

Loss of Flocculus Purkinje Cell Firing Precision Leads to Impaired Gaze Stabilization in a Mouse Model of Spinocerebellar Ataxia Type 6 (SCA6)

Spinocerebellar Ataxia Type 6 (SCA6) is a mid-life onset neurodegenerative disease characterized by progressive ataxia, dysarthria, and eye movement impairment. This autosomal dominant disease is caused by the expansion of a CAG repeat tract in the CACNA1A gene that encodes the α1A subunit of the P/Q type voltage-gated Ca²⁺ channel. Mouse models of SCA6 demonstrate impaired locomotive function and reduced firing precision of cerebellar Purkinje in the anterior vermis. Here, to further assess deficits in other cerebellar-dependent behaviors, we characterized the oculomotor phenotype of a knock-in mouse model with hyper-expanded polyQ repeats (SCA6^84Q). We found a reduction in the efficacy of the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) in SCA6 mutant mice, without a change in phase, compared to their litter-matched controls. Additionally, VOR motor learning was significantly impaired in SCA6^84Q mice. Given that the floccular lobe of the cerebellum plays a vital role in the generation of OKR and VOR calibration and motor learning, we investigated the firing behavior and morphology of floccular cerebellar Purkinje cells. Overall, we found a reduction in the firing precision of floccular lobe Purkinje cells but no morphological difference between SCA6^84Q and wild-type mice. Taken together, our findings establish that gaze stabilization and motor learning are impaired in SCA6^84Q mice and suggest that altered cerebellar output contributes to these deficits.

Molecular Identity and Location Influence Purkinje Cell Vulnerability in Autosomal-Recessive Spastic Ataxia of Charlevoix-Saguenay Mice

Patterned cell death is a common feature of many neurodegenerative diseases. In patients with autosomal-recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) and mouse models of ARSACS, it has been observed that Purkinje cells in anterior cerebellar vermis are vulnerable to degeneration while those in posterior vermis are resilient. Purkinje cells are known to express certain molecules in a highly stereotyped, patterned manner across the cerebellum. One patterned molecule is zebrin, which is expressed in distinctive stripes across the cerebellar cortex. The different zones delineated by the expression pattern of zebrin and other patterned molecules have been implicated in the patterning of Purkinje cell death, raising the question of whether they contribute to cell death in ARSACS. We found that zebrin patterning appears normal prior to disease onset in Sacs^–/– mice, suggesting that zebrin-positive and -negative Purkinje cell zones develop normally. We next observed that zebrin-negative Purkinje cells in anterior lobule III were preferentially susceptible to cell death, while anterior zebrin-positive cells and posterior zebrin-negative and -positive cells remained resilient even at late disease stages. The patterning of Purkinje cell innervation to the target neurons in the cerebellar nuclei (CN) showed a similar pattern of loss: neurons in the anterior CN, where inputs are predominantly zebrin-negative, displayed a loss of Purkinje cell innervation. In contrast, neurons in the posterior CN, which is innervated by both zebrin-negative and -positive puncta, had normal innervation. These results suggest that the location and the molecular identity of Purkinje cells determine their susceptibility to cell death in ARSACS.

Losing the Beat: Contribution of Purkinje Cell Firing Dysfunction to Disease, and Its Reversal

The cerebellum is a brain structure that is highly interconnected with other brain regions. There are many contributing factors to cerebellar-related brain disease, such as altered afferent input, local connectivity, and/or cerebellar output. Purkinje cells (PC) are the principle cells of the cerebellar cortex, and fire intrinsically; that is, they fire spontaneous action potentials at high frequencies. This review paper focuses on PC intrinsic firing activity, which is altered in multiple neurological diseases, including ataxia, Huntington Disease (HD) and autism spectrum disorder (ASD). Notably, there are several cases where interventions that restore or rescue PC intrinsic activity also improve impaired behavior in these mouse models of disease. These findings suggest that rescuing PC firing deficits themselves may be sufficient to improve impairment in cerebellar-related behavior in disease. We propose that restoring PC intrinsic firing represents a good target for drug development that might be of therapeutic use for several disorders.

A prospective study of handcuff neuropathies

Prior reports of handcuff-related neuropathies have been retrospective or small series of cases selected for their unusual electrophysiological or historical features. We conducted a prospective 27-month study at a large, urban, teaching hospital of all patients with a complaint of hand numbness, weakness, or paresthesias attributed to overtightened handcuffs. Forty-one patients were evaluated clinically, and electrodiagnostic testing was performed on 18. In the group with electrodiagnostic testing, neuropathies due to overtightened handcuffs were detected in 22 superficial radial, 12 median, and 9 ulnar nerves. The correlation between clinical and electrodiagnostic findings was best for superficial radial neuropathies, some of which were severe. Median and ulnar nerve injuries were generally mild. Similar clinical findings were obtained in the group without electrodiagnostic testing. Handcuff-related injury to the most commonly affected nerve, the superficial radial, can be severe and permanent.

Stroke-associated stuttering

OBJECTIVE

To present patients with stuttering speech in association with stroke.

DESIGN

Case series with follow-up for 5 years, or until the stuttering resolved.

SETTING

University and community hospital neurology wards, and ambulatory neurology clinics.

PATIENTS

Four patients who developed stuttering speech in association with an acute ischemic stroke. A 68-year-old man acutely developed stuttering with a large left middle cerebral artery distribution stroke. A 59-year-old man who had stuttered as a child began to stutter 2 months after a left temporal lobe infarction, as nonfluent aphasia was improving. Another childhood stutterer, a 59-year-old originally left-handed man developed severe but transient stuttering with a right parietal infarction. A 55-year-old man with a left occipital infarction had a right hemianopia and an acquired stutter, for which he was anosognosic.

CONCLUSION

The clinical presentation of stroke-associated stuttering is variable, as are the locations of the implicated infarctions.

Guillain-Barré syndrome in immunocompromised patients: a report of three patients and review of the literature

Both humoral and cell-mediated autoimmune mechanisms have been implicated in the pathogenesis of Guillain-Barré syndrome (GBS). Therefore, its occurrence in severely immunocompromised patients is not expected. We identified 3 severely immunocompromised patients who developed GBS. Two of the 3 patients had acquired immunodeficiency syndrome with CD4 counts of 5 and 4 cells/mm3, respectively. One post-cardiac transplant patient was taking azathioprine and cyclosporine at the time of onset of GBS. In all 3 patients, immunocompromise was induced by infectious or chemotherapeutic agents which preferentially suppress T-lymphocyte responses. All 3 had severe lymphocytopenia and incomplete recovery. We conclude that GBS can occur in patients with severe t-cell suppression. Although no conclusion regarding prognosis can be drawn from our small group of patients, their incomplete recovery is consistent with the idea that T-cells are important for recovery.

Vertebral fracture after aircraft ejection during Operation Desert Storm

During Operation Desert Storm, 21 United States and 2 Italian military personnel were held in Iraq as prisoners of war. Of these, 18 had ejected from fixed-wing, ejection seat-equipped, combat aircraft prior to their capture. Of the 18, 6 (33%) had sustained vertebral fractures; 4 of these were compression fractures. This fracture rate is comparable to that of previously studied groups. Fractures were noted to be at several different vertebral sites and after ejecting from a variety of aircraft. Apart from contusions and abrasions, vertebral fractures were the most common injuries discovered in this repatriated population. None of the vertebral fractures produced recognizable neurological disability. The development of vertebral fractures was neither associated with the use of any particular ejection system or aircraft nor did the development of vertebral fractures appear dependent on the age, height or length of service of the affected personnel. Ejected aircrew with low altitude mission profiles seemed more predisposed to vertebral fracture than those at high altitudes, but with a small sample population, this relationship was not statistically significant (p > 0.25). Reliable data were unavailable on aircrew positioning and preparation time for ejection.

Focal paresthesias with cervical magnetic stimulation

Subjects undergoing cervical magnetic stimulation with an appropriate coil report focal hand paresthesias in a dermatomal distribution, but the physiologic accuracy of such subjective experiences has been uncertain. In six subjects, we used a butterfly-shaped magnetic coil to stimulate positions on the back of the neck at 1-cm intervals, constant output, and random order, while the subject-estimated location and intensity of paresthesias and sensory nerve action potentials (SNAPs) were recorded from the thumb or index finger. Three subjects each also had recording of finger accelerometry or compound motor action potentials (CMAPs) in the hand and forearm. We found a consistent correlation between subjective paresthesias and SNAPs but an appropriate anatomic divergence between paresthesias and accelerometry or CMAPs. Focal paresthesias from cervical magnetic stimulation are reliable and anatomically accurate, strengthening the hypothesis that other magnetic sensory phenomena are valid as well.

Illness and injury among U.S. prisoners of war from Operation Desert Storm

United States prisoners of war had to endure a variety of medical problems during Operations Desert Shield and Desert Storm. All but one of the prisoners suffered some form of injury or illness. Orthopedic injuries were most common. Hematologic, dermatologic, neurologic, and infectious disorders were also noted. Some injuries were combat-related and others were due to mistreatment during incarceration. The prisoners' condition upon repatriation reflected their limited access to appropriate medical care, sanitation, and nutritional support.

Handcuff neuropathy among U.S. prisoners of war from Operation Desert Storm

Handcuff neuropathy was the most common neurologic problem acquired by U.S. prisoners of war during Operation Desert Storm. Neurologic deficits were exclusively sensory in all those affected and began to resolve shortly after their release from captivity. Some individuals expressed concern that these injuries could be career-threatening. One of those repeatedly restrained felt that he had discovered measures that could be undertaken to lessen the likelihood of developing neuropathy.

A multidisciplinary process to determine, communicate, and manage an antibiotic formulary

This article describes a collaborate process developed by the Pharmacy & Therapeutics Committee to define, determine, communicate, and manage an effective antibiotic formulary. Multiple professional disciplines represented by the antibiotic subcommittee evaluated each classification of antibiotics and recommended a preferred drug(s) for each classification. Decisions were based on relative safety, efficacy, and cost with minimal duplication of therapeutic equivalent antibiotics. A therapeutic interchange policy was unnecessary because extensive communication measures developed by the committee proved effective. The strategy used strengthened pharmacist/physician working relationships. This process permitted rationality and understanding by the medical staff, which resulted in unanimous formulary acceptance.

An integrated nursing-pharmacy approach to a computerized medication dispensing/administration system

This paper describes the collaborative efforts of the nursing and pharmacy departments to develop a nurse-generated/pharmacist-verified computerized medication administration record (MAR). The objectives were to improve accuracy in dispensing and administering medications and a avoid duplicate labor efforts created by separate records to dispense and to administer the medications. These efforts provided the nurses with an accurate record to administer the medication and the physicians with an informative record with which to review their patient's drug therapy.

Operational characteristics of hospital pharmacies in Indiana--1976 vs. 1981

The operating characteristics and services provided by hospital pharmacies in Indiana were determined. Survey questionnaires were mailed to the pharmacy director for each of the 120 licensed hospitals in Indiana; 62 responded. Pharmacy departments were open an average of 106.3 hours weekly, 51 pharmacies maintained patient profiles, and 29 pharmacies used unit-dose for all beds. Involvement in preparing I.V. solutions was reported by 67.7% of the pharmacies. The mean number of total pharmacy staff (FTEs) reported was 17.1. The ratio of staff FTEs per patient day was larger for pharmacies using a unit-dose distribution system. The most commonly provided clinical services were drug consultation with nursing, drug utilization review, and inservice education. Ratios of average dollar drug inventory and operating expenses per patient day indicated that larger hospitals were more effective with inventory control, but had higher expenses per patient day.