For all sensory organs, the establishment of spatial and temporal cortical resolution is assumed to be initiated by the first sensory experience and a BDNF-dependent increase in intracortical inhibition. To address the potential of cortical BDNF for sound processing, we used mice with a conditional deletion of BDNF in which Cre expression was under the control of the Pax2 or TrkC promoter. BDNF deletion profiles between these mice differ in the organ of Corti (BDNF (Pax2) -KO) versus the auditory cortex and hippocampus (BDNF (TrkC) -KO). We demonstrate that BDNF (Pax2) -KO but not BDNF (TrkC) -KO mice exhibit reduced sound-evoked suprathreshold ABR waves at the level of the auditory nerve (wave I) and inferior colliculus (IC) (wave IV), indicating that BDNF in lower brain regions but not in the auditory cortex improves sound sensitivity during hearing onset. Extracellular recording of IC neurons of BDNF (Pax2) mutant mice revealed that the reduced sensitivity of auditory fibers in these mice went hand in hand with elevated thresholds, reduced dynamic range, prolonged latency, and increased inhibitory strength in IC neurons. Reduced parvalbumin-positive contacts were found in the ascending auditory circuit, including the auditory cortex and hippocampus of BDNF (Pax2) -KO, but not of BDNF (TrkC) -KO mice. Also, BDNF (Pax2) -WT but not BDNF (Pax2) -KO mice did lose basal inhibitory strength in IC neurons after acoustic trauma. These findings suggest that BDNF in the lower parts of the auditory system drives auditory fidelity along the entire ascending pathway up to the cortex by increasing inhibitory strength in behaviorally relevant frequency regions. Fidelity and inhibitory strength can be lost following auditory nerve injury leading to diminished sensory outcome and increased central noise.

• Keywords
• BDNF, Central hyperactivity, High-spontaneous rate, low-threshold fibers, Homeostatic plasticity, Inferior colliculus, Sound detection threshold,
• MeSH
• Inferior Colliculi pathology   physiopathology   MeSH
• Gene Deletion MeSH
• Noise * MeSH
• Integrases metabolism   MeSH
• Cochlea metabolism   MeSH
• Brain-Derived Neurotrophic Factor metabolism   MeSH
• Mice, Knockout MeSH
• Promoter Regions, Genetic genetics   MeSH
• Receptor, trkC metabolism   MeSH
• Risk Factors MeSH
• Hearing MeSH
• Evoked Potentials, Auditory, Brain Stem MeSH
• Auditory Cortex metabolism   pathology   physiopathology   MeSH
• Auditory Threshold MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cre recombinase MeSH Browser
• Integrases MeSH
• Brain-Derived Neurotrophic Factor MeSH
• Receptor, trkC MeSH

We investigated the representation of four typical guinea pig vocalizations in the auditory cortex (AI) in anesthetized guinea pigs with the aim to compare cortical data to the data already published for identical calls in subcortical structures - the inferior colliculus (IC) and medial geniculate body (MGB). Like the subcortical neurons also cortical neurons typically responded to many calls with a time-locked response to one or more temporal elements of the calls. The neuronal response patterns in the AI correlated well with the sound temporal envelope of chirp (an isolated short phrase), but correlated less well in the case of chutter and whistle (longer calls) or purr (a call with a fast repetition rate of phrases). Neuronal rate vs. characteristic frequency profiles provided only a coarse representation of the calls' frequency spectra. A comparison between the activity in the AI and those of subcortical structures showed a different transformation of the neuronal response patterns from the IC to the AI for individual calls: i) while the temporal representation of chirp remained unchanged, the representations of whistle and chutter were transformed at the thalamic level and the response to purr at the cortical level; ii) for the wideband calls (whistle, chirp) the rate representation of the call spectra was preserved in the AI and MGB at the level present in the IC, while in the case of low-frequency calls (chutter, purr), the representation was less precise in the AI and MGB than in the IC; iii) the difference in the response strength to natural and time-reversed whistle was found to be smaller in the AI than in the IC or MGB.

• MeSH
• Acoustic Stimulation MeSH
• Species Specificity MeSH
• Guinea Pigs MeSH
• Neurons physiology   MeSH
• Evoked Potentials, Auditory MeSH
• Auditory Cortex physiology   MeSH
• Vocalization, Animal physiology   MeSH
• Animals MeSH
• Check Tag
• Guinea Pigs MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH