PICs in motoneurons do not scale with the size of the animal: a possible mechanism for faster speed of muscle contraction in smaller species.

The majority of studies on the electrical properties of neurons are carried out in rodents, and in particular in mice. However, the minute size of this animal compared with humans potentially limits the relevance of the resulting insights. To be able to extrapolate results obtained in a small animal such as a rodent, one needs to have proper knowledge of the rules governing how electrical properties of neurons scale with the size of the animal. Generally speaking, electrical resistances of neurons increase as cell size decreases, and thus maintenance of equal depolarization across cells of different sizes requires the underlying currents to decrease in proportion to the size decrease. Thus it would generally be expected that voltage-sensitive currents are smaller in smaller animals. In this study, we used in vivo preparations to record electrical properties of spinal motoneurons in deeply anesthetized adult mice and cats. We found that PICs do not scale with size, but instead are constant in their amplitudes across these species. This constancy, coupled with the threefold differences in electrical resistances, means that PICs contribute a threefold larger depolarization in the mouse than in the cat. As a consequence, motoneuronal firing rate sharply increases as animal size decreases. These differences in firing rates are likely essential in allowing different species to control muscles with widely different contraction speeds (smaller animals have faster muscle fibers). Thus from our results we have identified a possible new mechanism for how electrical properties are tuned to match mechanical properties within the motor output system.NEW & NOTEWORTHY The small size of the mouse warrants concern over whether the properties of their neurons are a scaled version of those in larger animals or instead have unique features. Comparison of spinal motoneurons in mice to cats showed unique features. Firing rates in the mouse were much higher, in large part due to relatively larger persistent inward currents. These differences likely reflect adaptations for controlling much faster muscle fibers in mouse than cat.

Practical and Statistical Considerations for the Long Term Follow-Up of Gene Therapy Trial Participants.

Study sponsors and market authorization holders are required by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) to enroll patients administered a gene therapy product, whether in a trial setting or post-licensure, in a long term follow-up safety study to continue the safety assessments of their product. These follow-up studies range between 5 and 15 years after dosing. This unprecedented duration of engagement with patients and caregivers raises logistical challenges that will require innovation and collaboration across sponsors and regulators. In this paper we delineate some of the key considerations for designing long term follow-up protocols in the gene therapy setting, with an eye toward platform and master protocol approaches, and offer guidance for innovative operational and statistical methods that can help assess the safety profile and durability of response for these novel therapeutics.

Impact of genetically modified organism requirements on gene therapy development in the EU, Japan, and the US.

Advanced therapies are emerging as an important class of medicinal products; among these, gene therapies are advancing at an exceptional rate. However, one of the major challenges for gene therapies relates to the additional regulatory requirements for genetically modified organisms. In this paper, we provide an overview of the regulatory requirements for genetically modified organisms in the European Union, Japan, and the United States. We share our experience in managing these requirements and their impact on the adeno-associated virus gene therapies that are under development at Pfizer. Specifically, we discuss the relative complexity of the approval process and the impact of risk assessment expectations on the clinical development of genetically modified organisms. We also compare the regulatory processes and timelines of various regions based on our experience with adeno-associated viral vectors. Finally, we propose that genetically modified organisms, for which pathogenicity and replication competency are well controlled, should be regulated solely under medicinal product regulations and be exempt from additional requirements for genetically modified organisms. Even if an exemption is not implemented, it should still be possible to significantly reduce the sponsor and agency burden by simplifying and harmonizing documentation and data requirements as well as timelines for applications for genetically modified organisms.

Time Course of Alterations in Adult Spinal Motoneuron Properties in the SOD1(G93A) Mouse Model of ALS.

Although amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease, motoneuron electrical properties are already altered during embryonic development. Motoneurons must therefore exhibit a remarkable capacity for homeostatic regulation to maintain a normal motor output for most of the life of the patient. In the present article, we demonstrate how maintaining homeostasis could come at a very high cost. We studied the excitability of spinal motoneurons from young adult SOD1(G93A) mice to end-stage. Initially, homeostasis is highly successful in maintaining their overall excitability. This initial success, however, is achieved by pushing some cells far above the normal range of passive and active conductances. As the disease progresses, both passive and active conductances shrink below normal values in the surviving cells. This shrinkage may thus promote survival, implying the previously large values contribute to degeneration. These results support the hypothesis that motoneuronal homeostasis may be "hypervigilant" in ALS and a source of accumulating stress.