Effect of aging on ultrasonic vocalizations and laryngeal sensorimotor neurons in rats

Abstract

While decline in vocal quality is prevalent in an aging population, the underlying neurobiological mechanisms contributing to age-related dysphonia are unknown and difficult to study in humans. Development of an animal model appears critical for investigating this issue. Using an established aging rat model, we evaluated if 50-kHz ultrasonic vocalizations in 10, 32-month-old (old) Fischer 344/Brown Norway rats differed from those in 10, 9-month-old (young adult) rats. The retrograde tracer, Cholera Toxin β, was injected to the thyroarytenoid muscle to determine if motoneuron loss in the nucleus ambiguus was associated with age. Results indicated that older rats had vocalizations with diminished acoustic complexity as demonstrated by reduced bandwidth, intensity, and peak frequency, and these changes were dependent on the type of 50-kHz vocalization. Simple calls of old rats had reduced bandwidth, peak frequency, and intensity while frequency-modulated calls of old rats had reduced bandwidth and intensity. Surprisingly, one call type, step calls, had increased duration in the aged rats. These findings reflect phonatory changes observed in older humans. We also found significant motoneuron loss in the nucleus ambiguus of aged rats, which suggests that motoneuron loss may be a contributing factor to decreased complexity and quality of ultrasonic vocalizations. These findings suggest that a rat ultrasonic phonation model may be useful for studying age-related changes in vocalization observed in humans.

Cross-activation and detraining effects of tongue exercise in aged rats

“…Our findings were similar to age-related changes reported in previous studies examining aging rat vocalizations (Basken, et al, 2012,Johnson, et al, 2013), including reduced number of calls, increased duration, and decreased intensity in old versus young adult groups. In the Basken study, these age-related behavioral changes were correlated with significant motor neuron loss in the NA (Basken, et al, 2012). While motor neuron count in the NA was not examined in our study, it is possible that loss of NA motor neurons contributed to age-related behavioral decrements in the USVs observed to a greater extent than neurotrophin concentration.…”

“…Research in our laboratory has demonstrated that aging results in degenerative changes to the nucleus ambiguus (NA), hypoglossal nucleus (HN), and muscles involved in voice and swallowing (Basken, et al, 2012,Hodges, et al, 2004,Ota, et al, 2005,Schaser, et al, 2011,Schwarz, et al, 2009,Suzuki, et al, 2002) and that 8 weeks of tongue exercise leads to increased tongue forces across the lifespan in a rat model (Behan, et al, 2012,Connor, et al, 2009,Schaser, et al, 2012). In addition, our research suggests that brain derived neurotrophic factor (BDNF) and its receptor TrkB are a putative mechanism underlying age and exercise related change in tongue function, because the HN showed decreased TrkB with age and increased BDNF with exercise in adult rats (Schaser, et al, 2012).…”

Intrastriatal injection of pre-formed mouse α-synuclein fibrils into rats triggers α-synuclein pathology and bilateral nigrostriatal degeneration

“…To determine the effect of α-syn accumulation on a rat’s vocal ability, USVs from male rats were evoked using a sexual motivation paradigm [34, 35]. In this paradigm, each male was paired with a receptive female rat (in estrous) for several days until reliable sexual interest (sniffing, chasing, and mounting) was achieved.…”

“…Avisoft-SASlab Pro software (Avisoft Bioacoustics, Germany) was utilized to analyze acoustic parameters as previously described [34]. Briefly, spectrograms were generated under a 512 FFT (fast fourier transform) length and 75% overlap frame setup.…”

“…Calls (50-kHz) were separated based on their complexity and divided into two general types of categories: simple and complex. The simple category included both simple and simple compound calls while complex included frequency modulated calls [34]. Due to the fact that there were so few complex calls made within this cohort, only simple calls were analyzed for the aforementioned acoustic parameters.…”