There are powerful pathways descending from the auditory cortex (AC) to the inferior colliculus (IC), yet their function is not fully understood. The aim of this study is to examine the effects of a reversible cortical inactivation, achieved by cooling of the AC, on the responses of neurons in the rat IC. Extracellular single-unit or multi-unit activity was recorded in the IC of anaesthetized rats with a 16-channel multielectrode probe introduced along the IC dorso-ventral axis through the dorsal cortex (DCIC) to the central nucleus of the IC (CIC). Cooling of the AC produced an increase in spontaneous activity and magnitude of the sound-evoked response in 47% of the IC neurons. Maximal changes in the neuronal activity were observed in the DCIC and the central part of the CIC. The final segments of the sustained responses to 60 ms stimuli and the off responses were more affected than the onset segments. Inactivation of the AC resulted in a suppression of the post-excitatory inhibition and neuronal adaptation, which was reflected in a pronounced enhancement of synchronized responses to a series of fast repeated clicks. The response parameters recovered, at least partly, to the pre-cooling levels 1 h after the cooling cessation. The frequency tuning properties of the IC neurons did not show any significant changes during the cooling period. The results demonstrate that AC cooling inactivates excitatory corticofugal pathways and results in a less activated intrinsic inhibitory network in the IC.

• MeSH
• akustická stimulace MeSH
• časové faktory MeSH
• colliculus inferior metabolismus   patologie   patofyziologie   MeSH
• fyziologická adaptace MeSH
• GABAergní neurony metabolismus   MeSH
• nervový útlum MeSH
• potkani Long-Evans MeSH
• sluchová dráha patofyziologie   MeSH
• sluchové evokované potenciály MeSH
• sluchové korové centrum metabolismus   patologie   patofyziologie   MeSH
• terapeutická hypotermie * MeSH
• termoregulace * MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH

Even brief acoustic trauma during the critical period of development that results in no permanent hearing threshold shift may lead to altered auditory processing in adulthood. By monitoring the acoustic startle response (ASR), we examined the development of auditory function in control rats and in rats exposed to intense noise at the 14th postnatal day (P14). First ASRs appeared on P10-P11 to intense low-frequency tones. By P14, the range of sound intensities and frequencies eliciting ASRs extended considerably, the ASR reactivity being similar at all frequencies (4-32 kHz). During the subsequent two weeks, ASR amplitudes to low-frequency stimuli (4-8 kHz) increased, whereas the ASRs to high-frequency tones were maintained (16 kHz) or even decreased (32 kHz). Compared to controls, noise exposure on P14 (125 dB SPL for 8, 12, or 25 min) produced transient hyper-reactivity to startle stimuli, manifested by a decrease of ASR thresholds and an increase of ASR amplitudes. ASR enhancement occurred regardless of permanent hearing loss and was more pronounced at high frequencies. The hyper-reactivity of ASRs declined by P30; the ASR amplitudes in adult exposed rats were lower than in controls. The histological control did not reveal loss of hair cells in adult exposed rats, however, the number of inner hair cell ribbon synapses was significantly decreased, especially in the high-frequency part of the cochlea. The results indicate that early acoustic trauma may result in complex changes of ASRs during development.

• MeSH
• akustická stimulace škodlivé účinky   MeSH
• kochlea cytologie   růst a vývoj   MeSH
• potkani Long-Evans MeSH
• senzorické prahy fyziologie   MeSH
• sluchová percepce fyziologie   MeSH
• sluchové kmenové evokované potenciály fyziologie   MeSH
• sluchové testy MeSH
• synapse fyziologie   MeSH
• úleková reakce fyziologie   MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The structure and function of the auditory system may be influenced by acoustic stimulation, especially during the early postnatal period. This study explores the effects of an acoustically enriched environment applied during the third and fourth week of life on the responsiveness of inferior colliculus neurons in rats. The enrichment comprised a spectrally and temporally modulated complex sound reinforced with several target acoustic stimuli, one of which triggered a reward release. The exposure permanently influenced neuronal representation of the sound frequency and intensity, resulting in lower excitatory thresholds at neuronal characteristic frequency, an increased frequency selectivity, larger response magnitudes, steeper rate-intensity functions and an increased spontaneous activity. The effect was general and non-specific, spanning the entire hearing range - no changes specific to the frequency band of the target stimuli were found. The alterations depended on the activity of animals during the enrichment - a higher activity of rats in the stimulus-reward paradigm led to more profound changes compared with the treatment when the stimulus-reward paradigm was not used. Furthermore, the exposure in early life led to permanent changes in response parameters, whereas the application of the same environment in adulthood influenced only a subset of the examined parameters and had only a temporary effect. These findings indicate that a rich and stimulating acoustic environment during early development, particularly when reinforced by positive feedback, may permanently affect signal processing in the subcortical auditory nuclei, including the excitatory thresholds of neurons and their frequency and intensity resolution.

• MeSH
• akční potenciály MeSH
• akustická stimulace metody   MeSH
• colliculus inferior růst a vývoj   fyziologie   MeSH
• mikroelektrody MeSH
• neurony fyziologie   MeSH
• odměna * MeSH
• potkani Long-Evans MeSH
• sluchová percepce fyziologie   MeSH
• životní prostředí MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH