On-bipolar cells and depolarising third-order neurons as the origin of theERG-b-wave in the RCS rat

In the retinas of Royal College of Surgeons (RCS) rats light induces an inc rease in distal extracellular potassium irrespective of the age, between da ys 19-24 and days 29-35 postpartum, but by days 29-35 the ERG b-wave has be come reduced. The synaptic blocker 2-amino-4-phosphonobutyric acid (APB) ca uses the abolition of both the b-wave and the potassium increase at any age . MgCl2 greatly reduces the b-wave at all ages and abolishes the potassium increase in older rats, but in younger rats the potassium increase is enlar ged. Since this increase occurs in the absence of the b-wave it is unlikely that the on-bipolar cells are the only sources of the b-wave. Because the NMDA receptor blocker ketamine reduces the b-wave, third order neurons, whi ch possess NMDA receptors, could contribute to the b-wave. (C) 2001 Elsevie r Science Ltd. All rights reserved.