Responses to noxious stimuli in mice lacking ??1d-adrenergic receptors:

Nociceptive behaviors were examined in the mice lacking alpha(ld)-adrenergic receptor ( alpha(ld)-AR) and wild type littermates using tail-flick, hot-plate (hindpaw-licking and jumping), tail-pinch and formalin tests. The distribution Of alpha(ld)-AR was studied using in situ hybridization in the wild type mice, Mutant mice showed longer tail-flick and hindpaw-licking latencies while their jumping latency was shorter. Mechanical and chemical nociception was not altered in alpha(ld)-knockout mice. In situ hybridization study revealed dense alpha(ld)-AR mRNA expression in the reticular thalamic nucleus, the hippocampus, the cingulate cortex and the spinal cord. These results suggest that alpha(ld)-AR in the spinal cord contributes to thermal pronociception; and that the jump behavior seen when escaping from heat is inhibited via the supraspinal alpha(ld)-AR.