Dynamic behavioural changes in the Spontaneously Hyperactive Rat: 1. Control by place, timing, and reinforcement rate

Area of Science:

• Neuroscience
• Behavioral Science
• Pharmacology

Background:

• Theoretical models link Attention Deficit Hyperactivity Disorder (ADHD) to altered learning rates, potentially modulated by dopamine.
• The Spontaneously Hypertensive Rat (SHR) model exhibits dopamine transporter (DAT) dysfunction, predicting a hyper-dopaminergic state and accelerated learning.

Purpose of the Study:

• To investigate if Spontaneously Hypertensive Rats (SHR) exhibit faster learning rates as predicted by theoretical models.
• To assess the role of learning rate alterations in the behavioral differences observed in SHR compared to control Wistar-Kyoto (WKY) rats.

Main Methods:

• Utilized a variable interval reinforcement schedule to assess response rates in SHR and WKY rats.
• Monitored responding patterns relative to predicted interval durations to identify learning rate differences.

Main Results:

• SHR showed a significant (10%) increase in responding at predicted interval times, unlike WKY rats which suppressed responding.
• The observed effect size of altered responding in SHR was insufficient to account for their overall higher operant responding rates.
• WKY rats displayed stress-induced suppression of responding, contrasting with SHR's increased responding, suggesting anxiety influences behavior.

Conclusions:

• Altered learning rates in SHR, while present, do not sufficiently explain the behavioral phenotype associated with ADHD.
• Variable interval schedules are valuable tools for dissecting behavioral causes, especially those with short timecourses.
• The study highlights the complexity of ADHD models, suggesting factors beyond learning rate are critical.