Origins of sympathetic innervation to the mesenteric vein vessel in cats

Physiological and histochemical studies have clearly demonstrated the control and innervation of the sympathetic nerve on the splanchnic veins. However, the origins of postganglionic fibers remain to be determined. In this study, we used the retrograde transport of horseradish peroxidase (HRP) technique to trace the origins of postganglionic neurons in pre- and paravertebral sympathetic ganglia that innervate the mesenteric vein. A segment (6-8 mm) of mesenteric vein close to the duodeno-jejunal junction was isolated. HRP was applied externally on the vein segment to allow uptake into the nerve endings. In 10 cats, there was a total of 9275 HRP-labeled neurons in the pre- and paravertebral ganglia. The neuron distribution (mean ± S.E.M.) was as follows: 452 ± 77 (49%) in the superior mesenteric ganglion (SMG), 248 ± 62 (27%) in the right celiac ganglion (RCG), 111 ± 23 (12%) in the left celiac ganglion (LCG) and 58 ± 16 (6%) in the splanchnic ganglia. Although the appearance of HRP neurons in the paravertebral ganglia (T₁₀-L₃) was relatively sparse, there were still significant numbers in L₁ (26 ± 13, 3%), T₁₃ (15 ± 5, 2%) and other ganglia. The results indicate that more than 90% of the presynaptic sympathetic neurons innervating the mesenteric vein make their synaptic connections in the prevertebral ganglia, mostly SMG and then RCG as well as LCG. Postsynaptic neurons arising directly from the paravertebral ganglia (mostly L₁ and T₁₃) constitute to about 6% of the total.