Image_2_Parvalbumin and GABA Microcircuits in the Mouse Superior Colliculus.JPEG

<p>The mammalian superior colliculus (SC) is a sensorimotor midbrain structure responsible for orienting behaviors. Although many SC features are known, details of its intrinsic microcircuits are lacking. We used transgenic mice expressing reporter genes in parvalbumin-positive (PV<sup>+</sup>) and gamma aminobutyric acid-positive (GABA<sup>+</sup>) neurons to test the hypothesis that PV<sup>+</sup> neurons co-localize GABA and form inhibitory circuits within the SC. We found more PV<sup>+</sup> neurons in the superficial compared to the intermediate SC, although a larger percentage of PV<sup>+</sup> neurons co-expressed GABA in the latter. Unlike PV<sup>+</sup> neurons, PV<sup>+</sup>/GABA<sup>+</sup> neurons showed predominantly rapidly inactivating spiking patterns. Optogenetic activation of PV<sup>+</sup> neurons revealed direct and feedforward GABAergic inhibitory synaptic responses, as well as excitatory glutamatergic synapses. We propose that PV<sup>+</sup> neurons in the SC may be specialized for a variety of circuit functions within the SC rather than forming a homogeneous, GABAergic neuronal subtype as they appear to in other regions of the brain.</p>