Fig. 1.

Long-lasting depression of inhibitory synapses in the LSO. A, Schematic of the inhibitory pathway from MNTB to LSO used in the present study is shown. LSO neurons receive a direct inhibitory projection from several MNTB neurons and excitatory inputs from several ipsilateral ventral cochlear nucleus (VCN) neurons. MNTB neurons also project to the MSO. B, IPSPs were recorded from the medial limb of the LSO, while electrical stimuli were delivered to the MNTB. In this P9 LSO neuron, IPSP amplitude remained fairly stable during the first 15 min recording period (the time at which each IPSP was obtained is shown beneatheachtrace). LFS (1 Hz for 15 min;graybar) was then provided to the MNTB at a stimulus intensity that evoked a maximum amplitude IPSP. IPSPs were depressed during the 1 hr period after LFS. Thebottomdashedlineindicates the initial resting membrane potential. During the pre-LFS period, the amplitude of an IPSP recorded at a −40 mV membrane potential (+0.02 nA) was augmented by ∼3 mV, and a similar depolarization 1 hr after LFS increased the depressed IPSP by ∼1 mV.