Inhibition of nociceptive withdrawal reflex by microinjection of interleukin 2 into rat locus coeruleus

This study was to examine the effects of microinjection of human recombinan t interleukin 2 (IL-2) into locus coeruleus (tc) on spinal nociception. Fol lowing application of IL-2 (0.1 mul, 10 pM) into LC, the percentage of inhi bition of nociceptive C responses of reflex at 3, 9, 15, 21 and 27 min afte r injection were 88.2 +/- 9.4%, 84.0 +/- 11.8%, 89.7 +/- 10.5%, 57.1 +/- 8. 7% and 26.3 +/- 12.2%, respectively. Also, the expression of Fos protein in superficial dorsal horn was reduced by 73.01 +/- 13.58% of control (P<0.00 01). Naloxone (10 <mu>g, i.p.) completely blocked the IL-2-induced inhibiti on of C responses. The results clearly show that IL-2 receptors present in LC mediate descending inhibition of the spinal nociception, which may coupl e with the activation of opioid receptors on LC neurons. (C) 2000 Harcourt Publishers Ltd.