Developmental hearing loss-induced perceptual deficits are rescued by genetic restoration of cortical inhibition

Abstract

Even a transient period of hearing loss during the developmental critical period can induce long-lasting deficits in temporal and spectral perception. These perceptual deficits correlate with speech perception in humans. In gerbils, these hearing loss-induced perceptual deficits are correlated with a reduction of both ionotropic GABA_A and metabotropic GABA_B receptor-mediated synaptic inhibition in auditory cortex, but most research on critical period plasticity has focused on GABA_A receptors. Therefore, we developed viral vectors to express proteins that would upregulate gerbil postsynaptic inhibitory receptor subunits (GABA_A, Gabra1; GABA_B, Gabbr1b) in pyramidal neurons, and an enzyme that mediates GABA synthesis (GAD65) presynaptically in parvalbumin-expressing interneurons. A transient period of developmental hearing loss during the auditory critical period significantly impaired perceptual performance on two auditory tasks: amplitude modulation depth detection and spectral modulation depth detection. We then tested the capacity of each vector to restore perceptual performance on these auditory tasks. While both GABA receptor vectors increased the amplitude of cortical inhibitory postsynaptic potentials, only viral expression of postsynaptic GABA_B receptors improved perceptual thresholds to control levels. Similarly, presynaptic GAD65 expression improved perceptual performance on spectral modulation detection. These findings suggest that recovering performance on auditory perceptual tasks depends on GABA_B receptor-dependent transmission at the auditory cortex parvalbumin to pyramidal synapse and point to potential therapeutic targets for developmental sensory disorders.

Keywords: auditory cortex; critical period; hearing loss; inhibition; parvalbumin.

Fig. 1.

Viral vector design and validation. (A) For both Gabra1 and Gabbr1b AAVs, primary auditory cortex layer 2/3 was injected. After 3 wk, a thalamocortical slice preparation was made and whole-cell recordings (current clamp) from ACx L2/3 pyramidal cells were carried out. (B) Top, Diagram showing Gabra1 vector. Bottom, micrograph from ACx L2/3 showing Gabra1 infected cells (mCherry) and one patched pyramidal neuron. (C) Representative evoked IPSPs showing the larger GABA_A potential in the Gabra1-infected pyramidal neuron (fluorescing patched cell from B) vs. local uninfected (nonfluorescing) pyramidal neuron from the same slice. (D) Plot diagram showing the difference in GABA_A IPSP amplitudes for uninfected versus Gabra1 infected pyramidal neurons in adults. (E) Top, Diagram showing Gabbr1b vector. Bottom, micrograph from AC L2/3 showing Gabbr1b infected cells (turboRFP) and one patched pyramidal neuron. (F) Representative evoked IPSPs showing the larger GABA_B potential in the Gabbr1b infected pyramidal neuron (from E) vs. local uninfected (nonfluorescing) pyramidal neuron from the same slice, in the presence of bicuculline to block GABA_A receptors. (G) Plot diagram showing the difference in GABA_B IPSP amplitudes for uninfected versus Gabbr1b infected pyramidal neurons in adults. (H) Micrograph from AC L2/3 showing Gabbr1b–infected cells and one patched pyramidal neuron (I) Representative evoked IPSPs showing the larger GABA_B potential in the Gabbr1b infected pyramidal neuron (from H) vs. a local uninfected (nonfluorescing) pyramidal neuron from the same slice in a P45 animal. Bicuculline was added to block GABA_A receptors. (J) Plot diagram showing the difference in GABA_B IPSP amplitudes for uninfected versus Gabbr1b infected pyramidal neurons in P45 animals.

Fig. 2.

Experimental paradigm. (A) The experimental timeline, and each of the experimental groups is shown. (B) Stimulus waveform diagrams are shown for the AM depth detection task (Top) and the SM depth detection task (Bottom). (C) The Go-Nogo paradigm used for psychometric testing.

Fig. 3.

Gabbr1b expression restores AM detection. (A) Representative behavior for a HL-reared gerbil expressing Gabbr1b (HL+Gabbr1b) and a HL-reared gerbil expressing GFP (HL+GFP) in AC, both tested after transient hearing loss (HL). (B) AM depth thresholds achieved by each group over training days. Mean ± SEM. (C) Gabbr1b expression in AC rescued AM perception relative to GFP expression on day 1 of psychometric testing (bars with solid outlines). Gabbr1b expression in AC rescued AM perception relative to GFP expression on day 7 of psychometric testing (bars with dashed outlines). Gray lines show changes in threshold for each animal from day 1 to 7 of testing. Significant differences indicated by asterisks (see text for statistical values).

Fig. 4.

Gabbr1b and GAD65 expression restore SM detection. (A) Example psychometric curves of individuals showing d′ at each of the 5 modulation depths presented in a single session. The leftward shift of the HL+Gabbr1b function, relative to HL+GFP function indicates improved performance. Bars indicate significant differences (see text for statistical values). (B) Group performance on each day of psychometric testing. (C) SM thresholds on day 1 (solid bars) and 7 (dashed bars) of psychometric testing. There are no differences in SM modulation thresholds on the first day of psychometric testing, as calculated by psychometric fit crossing d′ = 1. HL+Gabbr1b, HL+GAD65, and NH+GFP groups performed significantly better than HL+GFP animals. Gray lines show changes in threshold for each animal from day 1 to 7 of testing. Significant differences indicated by asterisks (see text for statistical values).