Gamma-aminobutyric acid and GABA(A) receptors are involved in directional selectivity of pretectal neurons in pigeons

The present study describes the effects of gamma-aminobutyric acid (GABA) a nd its antagonists, bicuculline and 2-hydroxysaclofen, on visual responses of neurons in the pigeon nucleus lentiformis mesencephali (nLM). The result s indicate that GABA significantly reduces both spontaneous activity and vi sual responsiveness, and GABA(A) antagonist bicuculline but not GABA(B) ant agonist 2-hydroxysaclofen enhances visual responses of nLM cells examined. Furthermore, inhibition produced by motion in the null-direction of pretect al neurons is diminished by bicuculline but not by 2-hydroxysaclofen. It is therefore concluded that the null-direction inhibition of directional cell s in the pigeon nLM is predominantly mediated by GABA and GABA(A) receptors . This inhibition may at least in part underlie directional asymmetry of op tokinetic responses.