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Relationship between vestibular hair cell loss and deficits in two anti-gravity reflexes in the rat
Alberto F Maroto1, Alejandro Barrallo-Gimeno2, Jordi Llorens2
1Departament de Ciències Fisiològiques, Institut de Neurociènces, Universitat de Barcelona, Feixa Llarga s/n, 08907 L'Hospitalet de Llobregat, Catalunya, Spain.
Abstract:
The tail-lift reflex and the air-righting reflex in rats are anti-gravity reflexes that depend on vestibular function. To begin identifying their cellular basis, this study examined the relationship between reflex loss and the graded lesions caused in the vestibular sensory epithelia by varying doses of an ototoxic compound. After ototoxic exposure, we recorded these reflexes using high speed video. The movies were used to obtain objective measures of the reflexes: the minimum angle formed by the nose, the back of the neck and the base of the tail during the tail-lift maneuver and the time to right in the air-righting test. The vestibular sensory epithelia were then collected from the rats and used to estimate the loss of type I (HCI), type II (HCII) and all hair cells (HC) in both central and peripheral parts of the crista, utricle, and saccule. As expected, tail-lift angles decreased, and air-righting times increased, while the numbers of HCs remaining in the epithelia decreased in a dose-dependent manner. The results demonstrated greater sensitivity of HCI compared to HCII to the IDPN ototoxicity, as well as a relative resiliency of the saccule compared to the crista and utricle. Comparing the functional measures with the cell counts, we observed that loss of the tail-lift reflex associates better with HCI than with HCII loss. In contrast, most HCI in the crista and utricle were lost before air-righting times increased. These data suggest that these reflexes depend on the function of non-identical populations of vestibular HCs.
Insights
Anti-gravity reflexes in rats, the tail-lift and air-righting reflexes, were studied by inducing graded lesions in vestibular sensory epithelia. Reflex loss correlated with hair cell loss, suggesting distinct cellular bases for these vestibular functions.
Area of Science:
- Neuroscience
- Vestibular System Research
- Auditory and Vestibular Toxicology
Background:
- Anti-gravity reflexes, including the tail-lift and air-righting reflexes in rats, are crucial for balance and orientation.
- These reflexes are known to depend on the proper functioning of the vestibular system.
- Understanding the cellular basis of these reflexes is essential for diagnosing and treating vestibular disorders.
Purpose of the Study:
- To investigate the relationship between graded lesions in vestibular sensory epithelia and the loss of tail-lift and air-righting reflexes in rats.
- To identify the specific types of vestibular hair cells (HCI and HCII) involved in these anti-gravity reflexes.
- To determine the dose-dependent effects of an ototoxic compound on vestibular hair cell populations and associated reflex function.
Main Methods:
- Rats were exposed to varying doses of an ototoxic compound to induce graded lesions in vestibular sensory epithelia.
- High-speed video recording was used to objectively measure tail-lift and air-righting reflexes.
- Vestibular sensory epithelia were collected to quantify the loss of type I (HCI) and type II (HCII) hair cells in the crista, utricle, and saccule.
Main Results:
- A dose-dependent decrease in tail-lift reflex performance and an increase in air-righting time were observed with increasing ototoxic exposure.
- Significant hair cell loss (HCI and HCII) occurred in the vestibular epithelia, with type I hair cells showing greater sensitivity to the ototoxin.
- The saccule demonstrated relative resilience compared to the crista and utricle.
- Loss of the tail-lift reflex was more strongly associated with type I hair cell loss, while air-righting reflex impairment occurred after substantial type I hair cell loss in the crista and utricle.
Conclusions:
- The tail-lift and air-righting reflexes are mediated by distinct populations of vestibular hair cells.
- Type I hair cells play a more critical role in the tail-lift reflex, while both hair cell types contribute to the air-righting reflex, with type I cells in the central vestibular system being particularly important.
- These findings provide insights into the cellular mechanisms underlying vestibular reflexes and have implications for understanding vestibular dysfunction.
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