Yohimbine reduces inhibition of lamina X neurones by stimulation of the locus coeruleus.

The effects of yohimbine, on inhibition of C-fibre evoked responses of spinal lamina X neurones by electrical stimulation of the locus coeruleus (LC) were studied in rats. LC stimulation inhibited by 67.33 +/- 25.14%, the C-fibre evoked responses in 24 out of 30 WDR neurones and the C-component of the flexion reflex by 77.62 +/- 18.77%. The A-fibre evoked responses with wide dynamic range (WDR) and low threshold (LT) neurones were not significantly affected by LC stimulation. After administration of yohimbine, LC-induced inhibition of lamina X neurones was attenuated by 77.43 +/- 23.22% without significant changes in C-fibre evoked responses. The results suggest that alpha 2-adrenoceptors may be involved in mediation of LC-induced inhibition on lamina X neurones.