Aim: 

The leptin hormone modulates the hypothalamic pathways that maintain energy homeostasis. We investigated whether the lack of leptin signalling interferes with the physiological changes in cardiac vagal control among wake-sleep states.

Methods: 

Leptin-deficient B6.V-Lep^ob/OlaHsd obese mice (ob/ob, n = 6) and lean wild-type littermates (WT, n = 10) were implanted with microelectrodes for discriminating wake-sleep states and a telemetric blood pressure transducer (TA11PA-C10, DSI). Ten days later, recordings were performed with the mice undisturbed and freely moving in their own cages. Heart period (HP) was computed from the blood pressure signal in episodes of wakefulness (W), non-rapid-eye-movement (non-REM) sleep, and REM sleep of duration >60 s. The vagal modulation of HP was estimated with validated techniques in the time domain (pNN8, the percentage of HP values that differ from the following one by >8 msec) and in the frequency domain (RSA, the square root of the HP spectral power in the frequency band 2.5–5.0 Hz). Data were analyzed with a 2-way analysis of variance and t-test with significance at p < 0.05.

Results: 

The interaction effect between the wake-sleep state and the genetic group was significant both on pNN8 and RSA. Neither pNN8 nor RSA differed significantly among wake-sleep states in ob/ob mice. Conversely, in WT mice, both pNN8 and RSA were significantly higher in non-REM sleep than either in W or REM sleep. Both pNN8 and RSA were significantly lower in ob/ob than in WT mice during non-REM sleep and REM sleep.

Conclusion: 

These results demonstrate that congenital leptin deficiency in obese mice interferes with the physiological sleep-dependent changes in the vagal control of HP.