Intrapleural CTB‐saporin selectively kills phrenic motor neurons: a motor neuron disease model

Abstract

Amyotrophic lateral sclerosis (ALS) is a devastating disease leading to progressive motor neuron degeneration and ultimately, ventilatory failure. In a rodent model of ALS (SOD1G93Arats), ventilatory capacity is preserved despite >;50% loss of phrenic and intercostal motor neurons (i.e. compensatory respiratory plasticity preserves breathing capacity). Here, our intent was to develop an experimental model to study compensatory plasticity without many of the complications attendant to ALS. Thus, we tested the hypothesis that intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB‐SAP) selectively kill respiratory motor neurons to mimic motor neuron death in ALS. Phrenic motor output was assessed in anesthetized, paralyzed and ventilated Sprague Dawley rats 3–28 days following bilateral intrapleural injections of: 1) CTB‐SAP (25–50μg), or 2) un‐conjugated CTB and SAP (control). CTB‐SAP elicited dose‐dependent phrenic motor neuron death; 25μg CTB‐SAP (7 days) most closely resembled cell death in end‐stage (ES) ALS rats (36±7% survival; n=9; p<0.05 vs. controls); CTB‐SAP diminished phrenic motor output (CTB‐SAP: 0.3±0.07 volts vs. Control: 1.5±0.3; n=9; p<0.05) to a level resembling ES ALSrats (0.4 volts). Intrapleural CTB‐SAP injections represent a novel inducible and repeatable model to study the impact of respiratory motor neuron death on breathing.[Supported by NIH NS057778 and HL080209 and the Francis Families Foundation]