We have developed a new technique for altering neural construction by implanting self-swelling, the hydrogel of water-absorbent polymer (WAPGEL) into restricted areas of the brain. Using this technique, we found that the VMH is responsible for expression of running activity. Implantation of 1.5 μl of WAPGEL into the dorsomedial portion of the ventromedial nucleus of the hypothalamus (VMH) of the rat specifically induced bursts of running, whereas implantation into other sites of hypothalamus, e.g., the anterior, lateral and posterior areas, and the dorsomedial nucleus, caused no significant running activity. The WAPGEL-injected rat showed less aversive reactions than the sham-operated rat. Since deafferentation of the VMH after WAPGEL injection prevented the induction of running activity, the output from the VMH appeared to be responsible for the running activity.
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