Distinct Distribution Patterns of Potassium Channel Sub-Units in Somato-Dendritic Compartments of Neurons of the Medial Superior Olive

Abstract

Coincidence detector neurons of the medial superior olive (MSO) are sensitive to interaural time differences in the range of a few tens of microseconds. The biophysical basis for this remarkable acuity is a short integration time constant of the membrane, which is achieved by large low voltage-activated potassium and hyperpolarization-activated inward cation conductances. Additional temporal precision is thought to be achieved through a sub-cellular distribution of low voltage-activated potassium channel expression biased to the soma. To evaluate the contribution of potassium channels, we investigated the presence and sub-cellular distribution profile of seven potassium channel sub-units in adult MSO neurons of gerbils. We find that low- and high voltage-activated potassium channels are present with distinct sub-cellular distributions. Overall, low voltage-activated potassium channels appear to be biased to the soma while high voltage-activated potassium channels are more evenly distributed and show a clear expression at distal dendrites. Additionally, low voltage-activated potassium channel sub-units co-localize with glycinergic inputs while HCN1 channels co-localize more with high voltage-activated potassium channels. Functionally, high voltage-activated potassium currents are already active at low voltages near the resting potential. We describe a possible role of high voltage-activated potassium channels in modulating EPSPs in a computational model and contributing to setting the integration time window of coincidental inputs. Our data shows that MSO neurons express a large set of different potassium channels with distinct functional relevance.

Distribution of Kv3 Subunits in Cochlear Afferent and Efferent Nerve Fibers Implies Distinct Role in Auditory Processing

“…Auditory neurons are well known for their capability of firing brief APs with high frequency and thus, able to faithfully follow the temporal pattern of high frequency inputs [3][4][5]. Not surprisingly, many auditory neurons express high level of K v 3 channels [6,7]. Genetic or pharmacological manipulation of K v 3 channels in these neurons have significant impact on the firing pattern and ultimately the auditory function.…”

“…Another group of efferent nerve fiber contacting the OHCs are originated from the medial olivary complex (MOC efferent) and regulate the sensitivity of sound detection system [23]. Until now, most studies provided only limited amount of information on K v 3 subtypes in cochlear afferents [19,20,25,26] and efferent neuronal somas in the brainstem [6,7,27]. The subtype and subcellular localization of K v 3 channels in each neuronal component and their precise role at the hair cell synaptic transmission are yet to be discovered.…”

Structural refinement of the auditory brainstem neurons in baboons during perinatal development

“…The morphologic and physiologic properties of MSO neurons have well been described in rodents such as gerbils and mice 17,27,29 . However, most studies using rodents have focused on After hearing onset, spatial refinement of excitatory and inhibitory synaptic inputs on the dendritic and somatic surface is critical for MSO neurons to allow synaptic integration for finetuning of the coincidence mechanisms 15,16 .…”

“…MSO neurons play a role in detecting coincidences within interaural time differences in the range of a few tens of microseconds for computing sound location. To achieve this task with remarkable acuity, voltage-activated K + (K v ) channels critically contribute to setting a short integration time constant of the membrane and a typical spiking pattern 17,27,29,30 . In baboon 1 6 neonates, a single spike of MSO neurons in response to a long-depolarizing current injection displayed a relatively high threshold and a lower amplitude, similar to findings in rodents.…”

“…To determine whether developmental changes in synaptic and dendritic structures are accompanied with ion channel expression of MSO neurons, we examined K + channel expression in MSO neurons. MSO neurons in gerbils, rats, and mice exhibit low-and high-K v channels, which critically contribute to action potential firing in MSO neurons 17,27,29,30 . We examined…”