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Age-related hearing loss frequently results in a loss in the ability to discriminate speech signals, especially in noise. This is attributable, in part, to a loss in temporal resolving power and ability to adjust dynamic range. Circuits in the adult dorsal cochlear nucleus (DCN) have been shown to preserve signal in background noise. Fusiform cells, major DCN output neurons, receive focused glycinergic inputs from tonotopically aligned vertical cells that also project to the ventral cochlear nucleus. Glycine-mediated inhibition onto fusiform cells results in decreased tone-evoked activity as intensity is increased at frequencies adjacent to characteristic frequency (CF). DCN output is thus shaped by glycinergic inhibition, which can be readily assessed in recordings from fusiform cells. Previous DCN studies suggest an age-related loss of markers for glycinergic neurotransmission. The present study postulated that response properties of aged fusiform cells would show a loss of inhibition, resembling conditions observed with glycine receptor blockade. The functional impact of aging was examined by comparing response properties from units meeting fusiform-cell criteria in young and aged rats. Fusiform cells in aged animals displayed significantly higher maximum discharge rates to CF tones than those recorded from young-adult animals. Fusiform cells of aged rats displayed significantly fewer nonmonotonic CF rate-level functions and an age-related change in temporal response properties. These findings are consistent with an age-related loss of glycinergic input, likely from vertical cells, and with findings from other sensory aging studies suggesting a selective age-related decrement in inhibitory amino acid neurotransmitter function. [ABSTRACT FROM AUTHOR]

Ornithologists often use simulated nests consisting of game bird or domestic poultry eggs to study nest survival. Researchers investigating cattle trampling of ground nests have sometimes used clay targets instead of actual eggs to avoid the confounding effects of nest depredation. To determine whether livestock respond similarly to clay targets and egg nests, we compared inadvertent trampling and intentional disturbance of clay targets versus clutches of 3 pheasant eggs by Angus x Holstein heifers. Overall trampling levels for clay target- and egg-nests were similar (35 and 36%, respectively). Cattle noticed andresponded to both types of nests. When noticed, simulated nests werekicked, sniffed, licked, or picked up in the mouth. Cattle disturbedan average of 25% of the clay targets and 8% of the egg nests during4 trials. Our results suggest that cattle are as likely to inadvertently trample egg nests as they are clay targets, but targets are morelikely to attract attention and are therefore disturbed more often than egg nests. The greater likelihood of intentional disturbance of clay targets by cattle reduces the confidence of extrapolating the fate of this type of simulated nest to that of actual nests. [ABSTRACT FROM AUTHOR]