Neuromodulation of ligand- and voltage-gated channels in the amphibian retina

To understand information processing in the retina, it is important to identify and characterize the types of synaptic receptors and intrinsic ion channels in retinal neurons. In order to achieve a high degree of adaptability, retinal synapses have evolved multiple neuromodulatory mechanisms. Light or modulatory agents can alter the efficacies of both electrical and chemical synaptic transmission in the retina. Recent studies indicate that interaction of voltage-gated channels with those activated by neurotransmitters plays a significant role in shaping the light-evoked postsynaptic responses of retinal neurons. The fact that both types of channels are subject to modulation by multiple second messenger-mediated intracellular processes is a clear indicator of the importance of neuromodulation in retinal function. The whole-cell patch clamp technique provides a means to study mechanisms of regulation of ion channels by controlling intracellular as well as the extracellular environment. This review describes the experimental evidence, mostly obtained in our laboratory, which indicates the important role of Ca-dependent neuromodulatory processes in the regulation of signal transmission in the vertical pathway of the amphibian retina.