Electrical activity increases growth cone calcium but fails to inhibit neurite outgrowth from rat sympathetic neurons

Previous studies have shown that the growth of axons from both mouse dorsal root ganglion neurons and Helisoma neurons is arrested when the cells are electrically stimulated (Cohan and Kater, 1986; Fields et al., 1990a). Furthermore, in the case of Helisoma neurons, this arrest has been attributed to a rise in the calcium concentration in the growth cones (Cohan et al., 1987). To test the generality of these results, we examined the response of cultured rat superior cervical ganglion (SCG) neurons to electrical stimulation and changes in cytoplasmic calcium. Suprathreshold electrical stimulation of SCG neurons at 10 Hz by extracellular patch electrodes for periods of up to 1 hr had no measurable effect on their rate of growth. In agreement with previous studies, electrical stimulation was accompanied by a rise in the internal calcium concentration: when measured by the fluorescence of fura-2, growth cone calcium levels rose from about 100 nM to greater than 500 nM and then settled to a plateau value of about 350 nM. Despite this increase, however, growth of SCG neurons' processes continued. Our results show that electrical activity is not a universal signal for neurons to stop growing and that a rise in internal calcium does not always arrest the migration of growth cones

The Effect of Electrical Stimulation on Neuronal Outgrowth and the Development of a New Method for Chronic Long-Term Stimulation and Recording from Groups of Neurons in Culture

In this dissertation, I shall examine the response of neurite outgrowth from cultured rat superior cervical ganglion (SCG) neurons to electrical stimulation and to changes in cytoplasmic calcium. Previous studies have shown that suprathreshold electrical stimulation arrests axonal growth from mouse dorsal root ganglion (DRG) and Helisoma neurons (Fields et al., 1990; Cohan and Kater, 1986). Cohan and collaborators (1987) have attributed the arrest of neurite outgrowth from Helisoma neurons to a rise in the growth-cone calcium concentration, [Ca]gc. In the experiments presented in this dissertation, neurite outgrowth from neonatal rat SCG neurons continued unabated during continuous suprathreshold electrical stimulation at 10 Hz for up to one hour. As in previous studies, the internal calcium concentration rose during stimulation. Fura-2 measurements showed that growth cone calcium levels rose from about 100 nM to greater than 500 nM, before settling at about 350 nM during stimulation. Despite this increase, neurite outgrowth continued. My results suggest that electrical activity is not a universal signal for neurons to stop growing and that a rise in internal calcium does not always arrest the migration of growth cones. I was also able to record from and stimulate rat SCG neurons using a new device that allows maintained two-way communication between neurons and electronic circuitry. The new device or "neuron well array" holds individual neurons in surface micromachined holes. A self-supporting overhanging grillwork restrains the neurons in the holes. Each hole has an electrical contact which allows recording from and stimulation of the cell trapped therein. Neurons that grow in the holes appeared to suffer no observable ill effects of entrapment. Future neuronal development studies are planned with the wells.</p

Impact of high-throughput screening in biomedical research

High Throughput Screening (HTS) has been postulated in several quarters to be a contributory factor to the widespread decline in Pharma industry productivity. Moreover, it has been promoted as anti-scientific and labeled as responsible for stifling the creativity that has long been the lifeblood of drug discovery. In this article we aim to dispel some of these myths and present the case for the use of HTS as part of a proven scientific toolkit, the wider use of which is essential for the discovery of new chemotypes. As we gain an even deeper understanding of the underlying mechanistic causes of disease, HTS has been further embraced in academic quarters for the discovery of tool compounds. Its wide adoption in industry and academia is a clear indicator that this technique is a valuable asset for the discovery of novel bioactive substances that can be used as molecular probes or optimized to pharmaceutical products