Biology subjects

Braun, R. D.

Publications and source records attributed to Braun, R. D..

3 recordsLinked to original sources

bioRxiv2024

Stimulation of otolith irregular fibers produces a rostro-caudal gradient in activity in the vestibular nuclear complex (VNC), but not the vestibulocerebellum (VeCb)

The vestibular system is important for posture, balance, motor control, and spatial orientation. Each of the vestibular end organs have specialized neuroepithelia with both regular and irregular afferents. In otolith organs, the utricle and saccule, afferents most responsive to linear jerk (jerk - derivative of acceleration) are located in the striola and project centrally to the vestibular nuclear complex (VNC) as well as the uvula and nodulus of the vestibulocerebellum (VeCb). The pattern of central neuronal activation attributed to otolith irregular afferents is relatively unknown. To address this gap, c-Fos was used as a marker of neuronal activity to map the distribution of active neurons throughout the rostro-caudal extent of the VNC and VeCb. Immunohistochemistry for c-Fos was performed to assess activation of VNC and VeCb neurons in response to a linear jerk stimulus delivered in the naso-occipital plane. Activated neurons were distributed throughout the VNC, including the lateral vestibular nucleus (LVe), magnocellular medial vestibular nucleus (MVeMC), parvocellular medial vestibular nucleus (MVePC), spinal vestibular nucleus (SpVe), and superior vestibular nucleus (SuVe). Notably, after stimulation, the MVePC exhibited the greatest number of c-Fos labeled nuclei. Significant increases in c-Fos labeling were found in mid-rostrocaudal and caudal regions of the VNC in the LVe, MVe, and SpVe. Additionally, c-Fos labeling was observed across all regions of the VeCb after jerk stimulation. Significant increases in the number of labeled nuclei were found throughout the rostro-caudal extent of the nodulus and uvula. However, jerk stimulated increases in activity for the paraflocculus were restricted to the caudal VeCb. The distribution of neuronal activity suggests that regions receiving the greatest direct otolith input exhibit the most substantial changes in response to otolith derived, irregular fiber stimulation. HighlightsO_LINuclei with descending projections (LVe, MVePC, and SpVe) demonstrated the greatest change in activity after naso-occipital jerk stimulation. C_LIO_LINaso-occipital jerk stimulation preferentially activates caudal VNC neurons C_LIO_LINaso-occipital jerk stimulation activates neurons throughout the VeCb C_LIO_LIJerk stimulation in the naso-occipital plane has the greatest effects on activity in VNC and VeCb regions with the greatest inputs from afferents originating in gravity receptors C_LI

neuroscience↗

bioRxiv2024

L-type calcium channel blockade with verapamil prevents noise induced neuronal dyssynchrony

Previous studies have established the protective effects of calcium channel blockade on the peripheral auditory system in response to noise exposure. While these studies implicate L-type calcium channels (LTCCs) in noise generated dysfunction in the auditory periphery, contributions of LTCCs to noise-induced central dysfunction remains unclear. To begin to elucidate the roles of LTCCs in hearing, peripheral and central auditory function were assessed longitudinally after LTCC blockade. Neuronal synchrony and activity were assessed by analyzing wave I (peripheral) and wave V (central) auditory brainstem responses (ABRs). Just prior to a noise exposure resulting in a temporary shift in hearing thresholds, rats were administered verapamil (LTCC blocker) or saline. Verapamil administration prevented the noise-induced decrease in ABR wave I and V amplitudes. Interestingly, when non-noise exposed animals were administered verapamil, wave V amplitude decreased, suggesting that LTCCs are critical for neuronal synchrony in the inferior colliculus. The inferior colliculus mediates inhibition of the acoustic startle reflex (giASR). Following noise exposure giASR was enhanced, but the enhancement was not prevented by LTCC blockade. These results suggest that while LTCCs are necessary for auditory-related synchronous activity, these channels do not contribute to noise-induced hyperactivity in the inferior colliculus.

neuroscience↗

bioRxiv2023

Using Manganese Enhanced Magnetic Resonance Imaging (MEMRI) to Assess Calcium Dependent Activity in Vestibular Pathways Following Linear Acceleration

Reliable methods for repetitive and longitudinal assessment of central vestibular pathway function in vivo are rather limited. Manganese-enhanced magnetic resonance imaging (MEMRI) has been used in various sensory systems to evaluate neuronal activity in central pathways, but MEMRI assessment of central vestibular pathways has been minimal. The present study addressed this gap in knowledge by assessing whether Mn2+ can be taken up in an activity-dependent manner through voltage-gated calcium channels in the vestibular nuclear complex (VNC) and the vestibulocerebellum (VeCb) of rats with and without mild linear acceleration stimulation. R1 maps were collected prior to, one day after, and two weeks after Mn2+ administration in stimulated and non-stimulated rats. Analysis of MRI R1 values showed that one day after Mn2+ administration the VNC and VeCb had significantly greater R1 values that returned to baseline levels after two weeks. Non-stimulated rats had greater R1 values than stimulated rats. Mid rostro-caudal sections of the VNC had greater R1 values than rostral and caudal VNC sections. R1 values also indicated that Mn2+ was differentially taken up across subdivisions of the VNC and VeCb. These results correlate well with expected patterns of neuronal activity after linear acceleration. MEMRI is a sensitive tool that may be used to evaluate activity patterns in central vestibular nuclei, proving useful for studying underlying mechanisms of central vestibular dysfunction.

neuroscience↗