Alpha-motoneurons maintain biophysical heterogeneity in obesity and diabetes in Zucker rats.

Small diameter sensory dysfunction resulting from diabetes has received much attention in the literature, while the impact of diabetes on alpha-motoneurons (MN) has not. In addition to this, the chance of developing insulin resistance and diabetes is increased in obesity. No study has examined the impact of obesity or diabetes on the biophysical properties of MN. Lean Zucker rats and Zucker Diabetic Fatty (ZDF) rats were separated into Lean, Obese (ZDF fed standard chow) and Diabetic (ZDF fed high fat diet that led to diabetes) groups. Glass micropipettes recorded hind-limb motoneuron properties from identified flexor and extensor motoneurons. Motoneurons were separated within their groups based on input conductance, which created high and low input conductance subpopulations for each. A significant shorter (20%) afterhyperpolarization half-decay (AHP1/2) was found in low conductance motoneurons for the diabetic group only, while the AHP1/2 tended to be shorter in the Obese group (19%). Significant positive correlations were found among Rheobase and input conductance for both lean and obese animals. No differences were found between the groups for the afterhyperpolarization amplitude (AHPamp), input conductance (IC), rheobase or any of the rhythmic firing properties (Frequency-Current slope and spike frequency adaptation index). Motoneuron properties continue to be heterogeneous in obese and diabetic animals. Obesity does not seem to influence lumbar motoneurons. Despite the motoneurons resistance to the impact of diabetes, the reduced AHP 1/2 decay and the tendency for a reduction in AHPamp may be the first sign of change to motoneuron function.

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