Central oxytocin modulates exercise-induced tachycardia.

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Exercise Physiology

Background:

• Vasopressinergic projections in the dorsal brainstem are known to activate during exercise and influence heart rate.
• Differential heart rate responses to exercise exist between trained and sedentary individuals.

Purpose of the Study:

• To investigate the role of oxytocinergic projections to the nucleus of the solitary tract-dorsal motor nucleus of the vagus (NTS/DMV) complex in the differential heart rate response to exercise.
• To determine if oxytocin (OT) release in the NTS/DMV influences exercise-induced tachycardia in trained (T) versus sedentary (S) rats.

Main Methods:

• Compared arterial pressure (AP) and heart rate (HR) responses to dynamic exercise in S and T rats.
• Administered vehicle, oxytocin (OT), or OT-receptor antagonist (OT(ant)) into the NTS/DMV.
• Measured OT content in brain regions and plasma at rest and post-exercise.
• Administered OT-receptor antagonist or OT into the fourth cerebral ventricle.

Main Results:

• Exercise increased OT content in the dorsal and ventral brainstem and spinal cord exclusively in T rats.
• Blockade of NTS/DMV OT receptors potentiated exercise-induced tachycardia by 26% in T rats but not S rats.
• Exogenous OT administration into the NTS/DMV blunted exercise tachycardia in both S and T rats.
• Neither OT receptor blockade nor OT administration into the fourth cerebral ventricle affected cardiovascular responses.

Conclusions:

• Oxytocinergic projections to the NTS/DMV are activated during exercise in trained rats.
• Oxytocin released in the NTS/DMV acts on OT receptors to restrain exercise-induced tachycardia.
• This suggests a novel central neural mechanism for regulating heart rate during exercise.