Chemical sympathectomy and postganglionic nerve transection produce similar increases in galanin and VIP mRNA but differ in their effects on peptide content.

Large changes in neuronal gene expression occur in adult peripheral neurons after axonal transection. In the rat superior cervical ganglion, for example, neurons that do not normally express vasoactive intestinal peptide (VIP) or galanin do so after postganglionic nerve transection. These effects of axotomy could result from a number of aspects of the surgical procedure. To test the idea that the important variable might be the disconnection of axotomized neuronal cell bodies from their target tissues, we examined the effects of producing such a disconnection by means of the compound 6-hydroxydopamine (6-OHDA), a neurotoxin that causes degeneration of sympathetic varicosities and avoids many of the complications of surgery. Two days after 6-OHDA treatment, VIP and galanin immunoreactivities had increased two- and 40-fold, respectively. Nevertheless, these increases were substantially smaller than the 30- and 300-fold changes seen after surgical axotomy. When expression of VIP and galanin was examined at the mRNA level, however, comparable increases were found after either procedure. The results indicate that chemical destruction of sympathetic varicosities produces an equivalent signal for increasing VIP and galanin mRNA as does axonal transection. The differences in the neuropeptide levels achieved suggests that peptide expression after nerve transection is regulated both at the mRNA and protein levels.