Biology subjects

Ashida, G.

Publications and source records attributed to Ashida, G..

3 recordsLinked to original sources

bioRxiv2025

Variation in Synaptic Inputs Drives Functional Versatility for Sound Encoding in Globular Bushy Cells

Synaptic convergence is fundamental to neuronal circuit function, underpinning computations such as coincidence detection and signal integration. Across sensory systems, convergence architecture and synaptic input strengths are key for extracting stimulus features and processing of sensory information. In the cochlear nucleus, globular bushy cells (GBCs) receive convergent inputs from multiple auditory nerve fibers via large endbulb of Held terminals. While these inputs vary considerably in size, even among those targeting the same cell, the functional consequences of this variation for sound encoding remain unclear. Here, we investigated how synaptic input variation shapes sound encoding in GBCs of Mongolian gerbils using in vitro conductance-clamp recordings and computational modeling. By simulating synaptic inputs with variable strength distributions, we found that increasing input variation enhances rate coding at the expense of temporal precision. These findings suggest that endbulb strength heterogeneity allows the GBC population to operate along a functional continuum, generating diverse information streams to downstream targets.

neuroscience↗

bioRxiv2025

Hyperpolarization-activated cation channels confer tonotopic specialization for temporal encoding of sound frequency in the cochlear nucleus

Sensory neurons are equipped with physiological properties vital for accurate signal processing. The functional importance of such properties is exemplified in auditory circuits where intrinsic excitability is optimized to detect frequency-specific features. In birds, the neurons of nucleus magnocellularis (NM) receive primary auditory input (Rubel and Parks, 1975a; Parks and Rubel, 1978; Jackson et al., 1982) and are arranged tonotopically. NM comprises a superficially homogenous neural population, but several physiological properties vary systematically along its tonotopic frequency axis. In particular, expression of voltage-gated conductances plays a pivotal role in creating selectivity that enables temporal precision. Here, we identify a previously undescribed gradient of hyperpolarization-activated cation channels (IH). Whole cell patch clamp techniques and immunostaining for HCN1, an IH channel subunit, demonstrated an expression gradient corresponding to NMs tonotopic axis. To investigate the function of tonotopic IH expression in NM, we applied a depolarizing ramp injection protocol to measure the impact of pharmacologically blocking IH on neural active properties (Ferragamo and Oertel, 2002; McGinley and Oertel, 2006; Oline et al. 2016). Next, we investigated whether this tonotopic patterning of HCN facilitates encoding of temporally patterned inputs. We injected depolarizing current pulse trains before and during HCN channel block. During pharmacological block, there was a reduction of NM spike entrainment to input pulses suggesting a key contribution of HCN channels to NMs ability to encode its synaptic drive. Results show that there is tonotopic distribution of HCN channels in NM which provides a novel mechanism that enables NM neurons to encode temporally patterned excitatory input. Significance StatementThis study is the first to describe a tonotopic gradient of IH channels in a vertebrate cochlear nucleus. Physiological and computational model assays suggest that the tonotopic expression pattern of HCN channels enables improved neural encoding of high frequency, temporally patterned input. Temporal response fidelity enables precise sound localization computations.

neuroscience↗

bioRxiv2023

Experience-Dependent Plasticity in Nucleus Laminaris of the Barn Owl

Barn owls experience increasing interaural time differences (ITDs) during development, because their head width more than doubles in the month after hatching. We therefore hypothesized that their ITD detection circuit might be modified by experience. To test this, we raised owls with unilateral ear inserts that delayed and attenuated the acoustic signal, then measured the ITD representation in the brainstem nucleus laminaris (NL) when they were adult. The ITD circuit is composed of delay line inputs to coincidence detectors, and we predicted that plastic changes would lead to shorter delays in the axons from the manipulated ear, and complementary shifts in ITD representation on the two sides. In owls that received ear inserts starting around P14, the maps of ITD shifted in the predicted direction, but only on the ipsilateral side, and only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. The contralateral map did not change. Experience-dependent plasticity of the ITD circuit occurs in NL, and our data suggest that ipsilateral and contralateral delays are independently regulated. Thus, altered auditory input during development leads to long-lasting changes in the representation of ITD. Significance StatementThe early life of barn owls is marked by increasing sensitivity to sound, and by increasing ITDs. Their prolonged post-hatch development allowed us to examine the role of altered auditory experience on the development of ITD detection circuits. We raised owls with a unilateral ear insert and found that their maps of ITD were altered by experience, but only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. Thus experience-induced plasticity allows the sound localization circuits to be customized to individual characteristics, such as the size of the head, and potentially to compensate for natural conductive hearing losses.

neuroscience↗