Pharmacological studies of grooming and scratching behavior elicited by spinal substance P and excitatory amino acids

Compounds that produce depolarization of nociceptive neurons in the dorsal horn of the spinal cord also elicit a rather specific kind of caudally directed biting, licking, and/or scratching behavior when they are injected intrathecally in mice. We sought to use this elicited grooming behavior as a test for compounds that might inhibit the neurons excited by the excitatory agents. All three neurokinins--substance P, neurokinin A (substance K), neurokinin B (neuromedin K)--and excitatory amino acids active at N-methyl-D-aspartate (NMDA) or quisqualate receptors produce similar behaviors, which last for 1 minute after i.t. injection. Our data indicate that mu opioid agonists or alpha adrenergic agonists block both neurokinin-elicited behavior and EAA-elicited behavior; delta opioid agonists block only neurokinin-elicited behavior; and PCP/sigma "opioid" agonists block only EAA-elicited behavior. Somatostatin and serotonin produce qualitatively different behaviors by themselves and, when administered with neurokinins, partially block neurokinin-elicited behavior.