The lumbar preganglionic sympathetic supply to rat tail and hindpaw

The segmental origins of the preganglionic sympathetic neurons which control the circulation of the rat tail were investigated and compared with those that supply the hindpaw. The left ventral roots of the first, second and sometimes the third lumbar segments were stimulated with 2-min pulse trains in 10 male Sprague-Dawley rats, which were anaesthetised with urethane (1-1.5 g/kg i.v.) and paralysed with pancuronium. Rats were warmed to increase cutaneous blood flow, and vasoconstrictor responses were detected by thermocouples as stimulus-locked falls in skin temperature. Stimulating the L2 ventral root always vasoconstricted the tail: in 50% of the rats, it also vasoconstricted the ipsilateral hindpaw, while in 50%, it did not. Stimulating the L1 ventral root always vasoconstricted both tail and hindpaw. Stimulating the L3 ventral root caused no measurable effect. Electrodermal potentials were recorded from the ipsilateral hindpaw pad in 7 rats: these accompanied hindpaw vasoconstrictor responses but were not seen otherwise. We conclude that at least in 50% of rats, the preganglionic neurons supplying hindpaw and tail skin are not clearly segregated by spinal segment. Sweat glands and blood vessels in the hindpaw are supplied by the same segments.