Imagined gait modulates neuronal network dynamics in the human pedunculopontine nucleus

The pedunculopontine nucleus (PPN) is a part of the mesencephalic locomotor region and is thought to be important for the initiation and maintenance of gait. Lesions of the PPN induce gait deficits, and the PPN has therefore emerged as a target for deep brain stimulation for the control of gait and postural disability. However, the role of the PPN in gait control is not understood. Using extracellular single-unit recordings in awake patients, we found that neurons in the PPN discharged as synchronous functional networks whose activity was phase locked to alpha oscillations. Neurons in the PPN responded to limb movement and imagined gait by dynamically changing network activity and decreasing alpha phase locking. Our results indicate that different synchronous networks are activated during initial motor planning and actual motion, and suggest that changes in gait initiation in Parkinson's disease may result from disrupted network activity in the PPN

In vitro techniques for assessing neurotoxicity using human IPSC-derived neuronal models

The central nervous system consists of a multitude of different neurons and supporting cells that form networks for transmitting neuronal signals. Proper function of the nervous system depends critically on a wide range of highly regulated processes including intracellular calcium homeostasis, neurotransmitter release, and electrical activity. Due to the diversity of cell types and complexity of signaling processes, the (central) nervous system is very vulnerable to toxic insults. Nowadays, a broad range of approaches and cell models is available to study neurotoxicity. In this chapter we show the applicability of human induced pluripotent stem cell (hiPSC)-derived neuronal co-cultures for in vitro neurotoxicity testing. We demonstrate that immunocytochemistry can be used to visualize networks of cultured cells and to differentiate between different cell types. Live cell imaging and electrophysiology techniques demonstrate that the neuronal networks develop spontaneous activity, including synchronized calcium oscillations that coincide with spontaneous changes in membrane potential as well as spontaneous electrical activity with defined (network) bursting. Importantly, as shown in this chapter, spontaneously active human iPSC-derived neuronal co-cultures are suitable for in vitro neurotoxicity assessment. Future application of live imaging and electrophysiological techniques on hiPSC from different donors and/or patients differentiated in different cell types holds great promise for personalized neurotoxicity assessment and safety screening