The function of lateral hypothalamic catecholamine and endorphin systems in the control of motor performance

Morphine (1 or 10 micrograms in 1 microliter) or beta-endorphin (1 microgram in 1 microliter) were injected bilaterally into the posterior lateral hypothalamus of Sprague-Dawley rats to determine what effect they may have on motor performance. Severe reductions in open field performance and motor reflex control were observed after the injection of 1 microgram of beta-endorphin or morphine into this area. The injection of 10 micrograms of morphine into the same area was less effective in causing motor impairment. The central (32.7 micrograms in 1 microliter) and peripheral (2 mg/kg) injection of naloxone did not prevent the motor impairment observed after the injection of beta-endorphin or morphine. Pretreatment with 6-hydroxydopamine into the lateral hypothalamus in a multistage regime did not prevent the motor impairment observed after beta-endorphin or morphine injection. These results indicate that lateral hypothalamic participation in the control of motor function may not involve the ascending nigrostriatal and mesocortical dopamine systems and that endogenous opiate systems may function independently to influence motor performance.