Laminar-selective noradrenergic and serotoninergic modulation includes spinoparabrachial cells after inflammation

WE evaluated the effects of chemical lesions on hindpaw inflammation-induce d Fos protein expression in spinoparabrachial neurons that were retrogradel y labeled by Fluoro-Gold. The descending serotoninergic and noradrenergic p athways were destroyed by the selective neurotoxins, 5,7-DHT and DSP-4, res pectively. After 5,7-DHT treatment there was a significant increase in doub le-labeled neurons only in the lateral reticulated neck of the dorsal horn 24 h after inflammation compared with vehicle-injected controls. In contras t, the DSP-1 treatment resulted in a more robust increase in double-labeled neurons in the ipsilateral superficial dorsal horn than in the neck of the dorsal horn. These results indicate that after inflammation the enhanced m odulation from descending serotoninergic and noradrenergic pathways targets supraspinally projecting neurons to dampen increased ascending nociceptive input. Further, these pathways differentially suppress the responses of sp inoparabrachial neurons in the deep and superficial dorsal horn. NeuroRepor t 10:1757-1761 (C) 1999 Lippincott Williams & Wilkins.