HYPOALGESIA IN MICE WITH A TARGETED DELETION OF THE TACHYKININ-1 GENE

The tachykinin neuropeptides, substance P and substance K, are produce d in nociceptive primary sensory neurons and in many brain regions inv olved in pain signaling, However, the precise role and importance of t hese neuropeptides in pain responses has been debated. We now show tha t mice that cannot produce these peptides display no significant pain responses following formalin injection and have an increased pain thre shold in the hotplate test. On the other hand, the mutant mice react n ormally in the tail flick assay and acetic acid-induced writhing tests . These results demonstrate that substance P and/or substance K have e ssential functions in specific responses to pain.