Analgesia produced by injection of lidocaine into the lateral hypothalamus

The local anesthetic lidocaine was injected into the lateral hypothalamus (LH) of awake, freely moving rats immediately prior to pain testing with either the formalin or the foot-flick test. Regional anesthesia of the LH resulted in a significant bilateral reduction of pain scores in the formalin test but had no effect in the foot-flick test. The decreased pain in the formalin test was not due to the diffusion of lidocaine into areas surrounding the LH or other possible artifacts. The results provide further evidence of hypothalamic involvement in pain perception and indicate that different neural systems subserve different types of pain.