Substance P induces brief, localized increase in [Ca2+](i) in dorsal horn neurons

WE determined the spatial and temporal dynamics of the increase in intracel lular Ca2+ levels [Ca2+](i) produced by substance P (SP) in dorsal horn neu rons. A microinjection technique was used to apply minute amounts of SP to small areas of cultured neurons loaded with the Ca2+ indicator fura-2. Five successive applications of SP to the soma produced short-lasting (< 50 s) increases in [Ca2+](i) that became gradually smaller, indicating receptor d esensitization. Focal application of SP to a distal locus in a neurite prod uced a brief (12 s) increase in [Ca2+](i) that travelled down the dendrite but did not spread into cell soma. Prolonged application of SP to these neu rons caused the appearance of varicosities in their dendrites. (C) 1998 Lip pincott Williams & Wilkins.