Spontaneous electrical activity regulates vasoactive intestinal peptide expression in dissociated spinal cord cell cultures.
Activity-dependent expression of vasoactive intestinal peptide (VIP) was investigated in spinal cord/dorsal root ganglia cultures derived from embryonic mice. Since all spinal cord neurons appear to exhibit spontaneous action potentials after one week in vitro, activity-dependent regulation of VIP-transcripts (mRNAVIP) could be studied with or without electrical blockade induced by tetrodotoxin (TTX). In 10-day-old cultures, a 50% decrease in mRNAVIP was observed after 3 days of treatment with TTX. The decrease in mRNAVIP was reversed upon removal of the TTX and was dependent on the age of the cultures: no decreases from control were observed in 5-day-old cultures and much smaller decrements were produced in one month old cultures treated with TTX. A variety of neuroactive substances were tested for effects on mRNAVIP in electrically active and electrically blocked cultures. Application of 8-bromo-cAMP (cAMP), N-methyl-D-aspartate (NMDA), substance P, muscimol, A23187 and VIP to electrically active cultures resulted in a 2- to 3-fold increase in mRNAVIP, while phorbol myristate 13-acetate (PMA) and 8-bromo-cGMP (cGMP) had no effect. In contrast, electrically inactive cultures exhibited a 3 to 4-fold increase in mRNAVIP after treatment with PMA, cAMP and VIP, while NMDA, substance P, muscimol, A23187 and cGMP produced no increases. In summary, the regulation of VIP gene expression in embryonic spinal cord neurons shows a temporal sensitivity to TTX-induced electrical blockade and may be mediated by multiple neurotransmitter inputs which converge on cAMP- and calcium-related processes in an activity-dependent manner.