Paired recordings from distant inhibitory neuron pairs by a sequential scanning approach

Simultaneous recordings from connected neuron pairs have brought important insights into synaptic communication between neurons. However, patch clamp recordings from neuron pairs have been largely restricted to brain areas in which connections among nearby neurons exist at a relatively high probability. In the case of more distant connections or in areas in which neurons are connected with low probability, recordings from synaptically connected neuron pairs have remained scarce. Here, we present a method that allows dual recordings from remotely connected neuron pairs by scanning potential presynaptic neurons. The applicability of this new approach was tested in the inhibitory pathway from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO), a sound localization pathway in the auditory brainstem. Using a three-step approach that sequentially combines focal uncaging of glutamate, pressure application of glutamate, and loose patch recordings allowed us to reliably achieve recordings from distant, synaptically connected GABA/glycinergic MNTB-LSO neuron pairs. Our results demonstrate that single MNTB neurons evoke highly variable mono-synaptic responses in developing LSO neurons, and heterogeneous short term synaptic dynamics, suggesting local variations in the refinement of these inhibitory connections. Paired recordings, enabled by scanning of remotely connected pairs, will be highly useful to perform detailed investigations of the synaptic function and plasticity from these circuits during the period of developmental refinement. In general, this method should provide a valuable tool to find connected neurons in other brain areas in which recording from candidate pairs has a low success rate.