The effects of calcium channel modulators, plant lectins and melanocortins on frog embryonic spinal neurons cultured in a small, applied electric field
An applied electric field affects the growth of dissociated Xenopus laevis neurites in a variety of ways. Growth rates are altered such that neurites grow faster to the cathode than to the anode, additionally neurites turn to grow towards the cathode. Effects of alterations in [Ca2+]i on these responses indicated entry of Ca2+ through voltage-dependent Ca2+ channels (VDCCs), as well Ca2+ released from internal stores, may be important in electric field alterations to growth rates and in the turning response of neurites. Lectin effects on growth of neurites were also studied. Lectins utilised were of varying simple sugar specificities, and subunit numbers and so may have a differential ability to crosslink their receptors. Neither of these factors could be used to predict the outcome of lectin addition. All the lectins studied affected rates of neurite outgrowth and reduced the turning response of neurites. The final group of experiments examined the combined addition of a melanocortin and an electric field on neurite growth. Both have effects on neurite outgrowth in vitro and also affect nerve regeneration in vivo. Experiments were carried out to determine if a combined regime of melanocortin and an electric field could prove beneficial in stimulating regeneration of damaged nerves. However, neither of these melanocortins, ACTH (1-4) and [Nle4, D-Phe7]-αMSH, could stimulate growth rates as well as maintain the orientation of neurite growth.