Physical exercise affects attentional orienting behavior through noradrenergic mechanisms

Area of Science:

• Neuroscience
• Behavioral Science
• Pharmacology

Background:

• Spontaneously hypertensive rats (SHRs), an animal model for attention-deficit/hyperactivity disorder (ADHD), show poor habituation to stimuli.
• Habituation is the decrease in response to a repeated, non-reinforced stimulus.
• Exercise is known to impact behavior and brain function.

Purpose of the Study:

• To investigate the hypothesis that exercise-induced improvements in orienting behavior in SHRs are linked to changes in noradrenergic function.
• To explore the role of the noradrenergic system in mediating the effects of exercise on habituation in SHRs.

Main Methods:

• SHRs were provided access to a running wheel for varying durations (2, 5, 10, or 21 days).
• Norepinephrine transporter levels in the medial prefrontal cortex were measured.
• Rats received propranolol (a beta-adrenergic receptor blocker) during exercise to assess the causal role of noradrenergic signaling.

Main Results:

• Prolonged exercise (5, 10, 21 days), but not short-term (2 days), led to robust habituation of the orienting response in SHRs.
• Exercise significantly reduced norepinephrine transporter levels in the medial prefrontal cortex after 5, 10, or 21 days.
• Blocking beta-adrenergic receptors with propranolol during exercise prevented the exercise-induced improvement in habituation.

Conclusions:

• Exercise duration is critical for improving orienting behavior and habituation in SHRs.
• Changes in noradrenergic function, specifically reduced norepinephrine transporter levels, are associated with exercise-induced behavioral improvements.
• Noradrenergic signaling is essential for exercise to exert its beneficial effects on orienting behavior in this ADHD model.