Abstract
The inferior colliculus (IC) is a major center for integration of auditory information as it receives ascending projections from a variety of brainstem nuclei as well as descending projections from the thalamus and auditory cortex. The ascending projections are both excitatory and inhibitory and their convergence at the IC results in a microcircuitry that is important for shaping responses to simple, binaural, and modulated sounds in the IC. Here, we examined the role inhibition plays in shaping selectivity to vocalizations in the IC of awake, normal-hearing adult mice (CBA/CaJ strain). Neurons in the IC of mice show selectivity in their responses to vocalizations, and we hypothesized that this selectivity is created by inhibitory microcircuitry in the IC. We compared single unit responses in the IC to pure tones and a variety of ultrasonic mouse vocalizations before and after iontophoretic application of GABAA receptor (GABAAR) and glycine receptor (GlyR) antagonists. The most pronounced effects of blocking GABAAR and GlyR on IC neurons were to increase spike rates and broaden excitatory frequency tuning curves in response to pure tone stimuli, and to decrease selectivity to vocalizations. Thus, inhibition plays an important role in creating selectivity to vocalizations in the IC.
Highlights
Neural processing of sensory information relies on the microcircuitry and cellular properties of neurons in the sensory pathway
Characteristic frequencies (CFs) of the units ranged from 6 kHz to 65 kHz (Figure 1)
We found that inhibitory inputs modulate responses to simple stimuli by modulating firing rate, shaping frequency tuning curves in a variety of ways, and altering temporal firing patterns
Summary
Neural processing of sensory information relies on the microcircuitry and cellular properties of neurons in the sensory pathway. Ascending projections into the IC are glutamatergic, GABAergic, or glycineric (Willard and Ryugo, 1983; Saint Marie and Baker, 1990; Saint Marie, 1996; Cant, 2005; Schofield, 2005) and commissural projections are GABAergic (Reetz and Ehret, 1999). This convergence of excitatory and inhibitory inputs onto single neurons in the IC results in microcircuits that are important for regulating response properties. There has been much less focus, on how inhibitory inputs to IC neurons shape responses to more complex sounds such as social vocalizations
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