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Abstract: Auditory cortex (AI) shows age-related decreases in pre-synaptic markers for gamma-aminobutyric acid (GABA) and degraded AI neuronal response properties. Previous studies find age-related increases in spontaneous and driven activity, decreased spectral and directional sensitivity, and impaired novelty detection. The present study examined expression of GABAA receptor (GABAAR) subunit message, protein, and quantitative GABAAR binding in young, middle-aged, and aged rat AI, with comparisons with adjoining parietal cortex. Significant loss of GABAAR α1 subunit message across AI layers was observed in middle-aged and aged rats and α1 subunit protein levels declined in layers II and III. Age-related increases in GABAAR α3 subunit message and protein levels were observed in certain AI layers. GABAAR subunits, including β1, β2, γ1, γ2s, and γ2L, primarily, but not exclusively, showed age-related declines at the message and protein levels. The ability of GABA to modulate [3H]t-butylbicycloorthobenzoate binding in the chloride channel showed age-related decreases in peak binding and changes in desensitization kinetics. Collectively, age-related changes in GABAAR subunit composition would alter the magnitude and temporal properties of inhibitory synaptic transmission and could underpin observed age-related functional changes seen in the elderly. [Copyright &y& Elsevier]

Abstract: Presbycusis can be considered a slow age-related peripheral and central deterioration of auditory function which manifests itself as deficits in speech comprehension, especially in noisy environments. The present study examined neural correlates of a simple broadband noise stimulus in primary auditory cortex (A1) of young and aged Fischer–Brown Norway (FBN) rats. Age-related changes in unit responses to broadband noise bursts and spontaneous activity were simultaneously recorded across A1 layers using a single shank, 16-channel electrode. Noise bursts were presented contralateral to the left A1 at 80dB SPL. Aged A1 units displayed increased spontaneous (29%), peak (24%), and steady state response rates (38%) than did young A1 units. This was true across all A1 layers, although age-related differences were significantly greater for layers I–III (43% vs 18%) than lower layers. There was a significant age-related difference in the depth and duration of post-onset suppression between young and aged upper layer A1 units. The present functional differences across layers were consistent with studies showing greatest losses of gamma-aminobutyric acid (GABA) markers in superficial layers of A1 and with anatomic studies showing highest levels of inhibitory neurons located in superficial cortical layers. The present findings were also consistent with aging studies suggesting loss of functional inhibition in other cortical sensory systems. [Copyright &y& Elsevier]

Measuring tinnitus in laboratory animals is difficult, involving weeks or months of operant training. Preliminary data suggest that rapid screening for tinnitus in rats can be accomplished using an unconditioned acoustic startle reflex. In control animals, a gap in an otherwise constant acoustic background inhibits a subsequent startle response to a sound impulse. If, however, the background signal is qualitatively similar to the animal’s tinnitus, poorer detection of the gap and less inhibition of the startle might be expected. Fourteen animals with putative tinnitus at 10 kHz and 13 control animals were tested for gap detection using three different background signals: broadband noise, and filtered bandpass noise centered either at 16 kHz (15.5–16.5 kHz) or at their suspected tinnitus locus of 10 kHz (9.5–10.5 kHz). As predicted, animals with evidence of tinnitus exhibited significantly worse gap detection at 10 kHz, and were not significantly different than control animals at 16 kHz and broadband noise. These results suggest a new methodology for rapidly detecting tinnitus in individual animals. Equipment donated by Hamilton-Kinder Inc Behavioral Testing Systems in the memory of SIU graduate Dorothy Jean Kinder (Walker). [Work supported by NIH grants AG023910-01 (JT), DC4830 (TB & CB), and DC00151 (DC).] [ABSTRACT FROM AUTHOR]

The study describes a novel method for tinnitus screening in rats by use of gap detection reflex procedures. The authors hypothesized that if a background acoustic signal was qualitatively similar to the rat's tinnitus, poorer detection of a silent gap in the background would be expected, Rats with prior evidence of tinnitus at 10 kHz (n = 14) exhibited significantly worse gap detection than controls (n = 13) when the gap was embedded in a background similar to their tinnitus. No differences between tinnitus and control rats were found with 16 kHz or broadband noise backgrounds, which helped to rule out explanations related to hearing loss or general performance deficits. The results suggest that gap detection reflex procedures might be effective for rapid tinnitus screening in rats. [ABSTRACT FROM AUTHOR]