Opiates and medial hypothalamic knife cuts cause hyperphagia through different mechanisms

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Endocrinology

Background:

• Medial hypothalamic knife cuts and opiate agonists can induce hyperphagia.
• The underlying mechanisms for these forms of hyperphagia are not fully understood.

Purpose of the Study:

• To investigate whether the hyperphagia induced by medial hypothalamic knife cuts and opiate agonists share a common mediating mechanism.
• To determine the relationship between opioid receptor systems and hypothalamic feeding pathways.

Main Methods:

• Rats underwent medial hypothalamic knife cuts or sham procedures.
• Food intake was measured after administration of naloxone and kappa opiate receptor agonists (ketocyclazocine, butorphanol tartrate).
• Diet composition and drug effects were analyzed in relation to surgical manipulation.

Main Results:

• Naloxone equally suppressed food intake in knife-cut and sham-operated rats.
• Ketocyclazocine increased food intake in sham-operated rats but had variable effects in knife-cut rats.
• Hypothalamic knife cuts did not significantly alter feeding responses to naloxone or butorphanol.

Conclusions:

• The opioid feeding system appears to be independent of the longitudinal feeding inhibitory pathway affected by medial hypothalamic knife cuts.
• Differential effects of ketocyclazocine were attributed to sedative effects and elevated baseline feeding in knife-cut subjects.