Characteristics of GABAergic neurons in the superficial superior colliculus in mice

We investigated characteristics of identified GABAergic neurons in slices of the superficial superior colliculus (sSC) using transgenic mice in which green fluorescent protein (GFP) is specifically expressed in GABAergic neurons. Whole-cell patch clamp recordings and intracellular staining with biocytin revealed electrophysiological and morphological properties of GFP-positive neurons. GFP-positive neurons had a tangentially elongated wide dendritic field. In response to depolarizing current pulses, most of the GFP-positive neurons showed either of two firing properties; 55% (n=36/65) generated successive spikes with a constant firing frequency and 22% (n=14/65) showed transient burst firing at a threshold level for spike generation. These results elucidate a functional heterogeneity of GABAergic neurons, and provide fundamental information to understand the function of the GABAergic system in the sSC.