VASOACTIVE INTESTINAL POLYPEPTIDE MODULATES GABA-A RECEPTOR FUNCTION IN BIPOLAR CELLS AND GANGLION-CELLS OF THE RAT RETINA

1. The effect of vasoactive intestinal polypeptide (VIP) on bipolar cells and ganglion cells freshly dissociated from the rat retina was studied under voltage clamp with the use of patch-clamp recording in the whole-cell configuration. 2. Application of VIP (1-100-mu-M) by itself resulted in no detectable current response in either bipolar cells or ganglion cells. However, gamma-aminobutyric acid (GABA)-activated macroscopic current responses elicited in both neuronal populations were potentiated on superimposed exposure to the neuropeptide. 3. GABA-activated chloride currents and muscimol-induced current responses were similarly potentiated on exposure to VIP, suggesting a synergistic interaction between VIP and GABA(A) receptor mechanisms. 4. We postulate that VIP plays a neuromodulatory role by regulating the excitability of inner retinal neurons and in this way modulates the efficacy of synaptic transmission in the retina.