Acoustic Trauma Changes the Parvalbumin-Positive Neurons in Rat Auditory Cortex

Abstract

Acoustic trauma is being reported to damage the auditory periphery and central system, and the compromised cortical inhibition is involved in auditory disorders, such as hyperacusis and tinnitus. Parvalbumin-containing neurons (PV neurons), a subset of GABAergic neurons, greatly shape and synchronize neural network activities. However, the change of PV neurons following acoustic trauma remains to be elucidated. The present study investigated how auditory cortical PV neurons change following unilateral 1 hour noise exposure (left ear, one octave band noise centered at 16 kHz, 116 dB SPL). Noise exposure elevated the auditory brainstem response threshold of the exposed ear when examined 7 days later. More detectable PV neurons were observed in both sides of the auditory cortex of noise-exposed rats when compared to control. The detectable PV neurons of the left auditory cortex (ipsilateral to the exposed ear) to noise exposure outnumbered those of the right auditory cortex (contralateral to the exposed ear). Quantification of Western blotted bands revealed higher expression level of PV protein in the left cortex. These findings of more active PV neurons in noise-exposed rats suggested that a compensatory mechanism might be initiated to maintain a stable state of the brain.

Chemogenetic Activation of Cortical Parvalbumin-Positive Interneurons Reverses Noise-Induced Impairments in Gap Detection

“…There are three main findings in the present study. First, contrary to previous reports of increased and unaltered PV neuron density, we found significantly reduced PV neuron density and PV expression in AI 5 and 10 d after loud noise exposure (Nguyen et al, 2017;Liu et al, 2018). In the case of Nguyen et al (2017), the researchers used a bilateral noise exposure paradigm with a free field speaker at a lower volume of 102-104 dB SPL which could account for our different results.…”

“…In the case of Nguyen et al (2017), the researchers used a bilateral noise exposure paradigm with a free field speaker at a lower volume of 102-104 dB SPL which could account for our different results. In the case of Liu et al (2018), although more similar to our paradigm, the hearing lesion was conducted at a higher frequency of 16 kHz (in rats, which have a lower hearing range), and only for 1 h rather than two. Our result is consistent with findings that NIHL reduced cortical inhibitory synaptic transmission and PV neuron function after noise exposure (Qiu et al, 2000;Seki and Eggermont, 2003;Kotak et al, 2005;Eggermont, 2006;Sun et al, 2008;Yang et al, 2011;Wang et al, 2019).…”

“…Depriving sound input in adulthood suppresses PV neuron function (Resnik and Polley, 2017). Previous studies also examined PV neurons following noise exposure but reported different effects; PV expression in primary auditory cortex (AI ) was found to be enhanced (Liu et al, 2018) and unaltered (Nguyen et al, 2017). These discrepancies, likely because of differences in noise exposure paradigms and other procedures, make it difficult to assess the involvement of PV neurons in noise-induced impairment in gap detection.…”

Increasing endogenous activity of NMDARs on GABAergic neurons increases inhibition, alters sensory processing and prevents noise-induced tinnitus

“…For tinnitus and likely other trauma-related brain diseases, an initial reduction in GABAergic transmission occurs prior to symptom onset 38 . In noise exposure-induced tinnitus, reduced IPSCs in AI excitatory neurons, GABAergic and glycinergic neurotransmission in inhibitory neurons, as well as PV-neuron density, have been reported [39][40][41][42][43][44] . Whether this reduced density is caused by loss of PV-neurons or reduced PV expression is still an open question that needs further experimentation.…”

Noise exposure alters MMP9 and brevican expression in the rat primary auditory cortex

“…Previous studies reported changes in PNNs in the primary auditory cortex following auditory deprivation [6,7]. Noise-induced hearing loss in postnatal 4-weekold mice reduced PNNs, and this change was initiated as early as 1 day after noise exposure [6].…”