The involvement of serotonin neurones in the inhibition of renal nerve activity during desynchronized sleep

Numerous 5-hydroxytryptamine (5-HT)-containing cell bodies were visualized by fluorescence microscopy in the caudal brainstem rostal to the decussation of the pyramids in a region from which a desynchronized sleep-like pattern of sympathetic activity was obtained in a previous study. In unanaesthetized mid-collicular decerebrated cats recordings were made of sympathetic activity in a renal nerve. The inhibition of renal nerve activity occurring during desynchronized sleep-like state induced by physostigmine was attenuated significantly by procedures which interfered with the pathways from the 5-HT-containing neurones. Small cuts in the dorsolateral funiculus of the cervical spinal cord reduced the inhibition from43 ± 6%to14.0 ± 3%. Microinjection of 5,7-dihydroxytryptamine into cervical spinal cord reduced the serotonin content of the thoracic cord by 22.4% and attenuated the desynchronized sleep-like state inhibition of renal nerve activity by a similar amount. Depletion of serotonin withp-chlorophenylalanine significantly reduced the inhibition of renal nerve activity during the desynchronized sleep-like state, from42.5 ± 5%to10.0 ± 2.0%. It was suggested that serotonin-containing neurones are likely to be involved in the inhibition of renal nerve activity occurring during desynchronized sleep.