Figure 3. HVC_Av neurons receive selective input from premotor HVC_RA neurons.

a) Schematic of in vitro brain slice preparation in which whole cell voltage clamp recordings were made from retrogradely-labeled HVC_Av neurons while either HVC_RA or HVC_X axons were electrically stimulated to evoke antidromic propagation of activity into the HVC local circuit (HVC_RA: 40 – 80 μA; HVC_X axons: 40 – 300 μA). Left inset, excitatory synaptic currents evoked in an HVC_Av neuron in response to HVC_RA axon bundle stimulation (80 μA). Right inset, absence of synaptic currents recorded in the same HVC_Av neuron following HVC_X axon bundle stimulation (160 μA; V_h = − 70 mV in both examples). b) Schematic of whole cell voltage and current clamp recordings made from retrogradely labeled HVC_RA or HVC_X cells while electrically stimulating HVC_X axon bundles. Left inset, excitatory synaptic currents evoked in an HVC_RA cell following HVC_X axon bundle stimulation (80 μA; V_h = −70 mV). Right inset, antidromic action potential evoked in an HVC_X cell following HVC_X axon bundle stimulation (80 μA; V_rest = −80 mV). In all inset panels, individual currents or potentials are shown in gray and mean current or potential is shown in black.