Alteration of Mesopontine Cholinergic Function by the Lack of KCNQ4 Subunit

KCNQ4 potassium channel subunit deletion leads to exaggerated acoustic startle reflex in mice

The potassium voltage-gated channel subfamily Q member 4 (KCNQ4) subunit forms channels responsible for M-current, a muscarine-sensitive potassium current regulating neuronal excitability. In contrast to other KCNQ subunits, its expression is restricted to the cochlear outer hair cells, the auditory brainstem and other brainstem nuclei in a great overlap with structures involved in startle reflex. We aimed to show whether startle reflexis affected by the loss of KCNQ4 subunit and whether these alterations are similar to the ones caused by brainstem hyperexcitability. Young adult KCNQ4 knockout mice and wild-type littermates, as well as mice expressing hM3D chemogenetic actuator in the pontine caudal nucleus and neurons innervating it were used for testing acoustic startle. The acoustic startle reflex was significantly increased in knockout mice compared with wild-type littermates. When mice expressing human M3 muscarinic (hM3D) in nuclei related to startle reflex were tested, a similar increase of the first acoustic startle amplitude and a strong habituation of the further responses was demonstrated. We found that the acoustic startle reflex is exaggerated and minimal habituation occurs in KCNQ4 knockout animals. These changes are distinct from the effects of the hyperexcitability of nuclei involved in startle. One can conclude that the exaggerated startle reflex found with the KCNQ4 subunit deletion is the consequence of both the cochlear damage and the changes in neuronal excitability of startle networks.

Behavior of KCNQ Channels in Neural Plasticity and Motor Disorders

The broad distribution of voltage-gated potassium channels (VGKCs) in the human body makes them a critical component for the study of physiological and pathological function. Within the KCNQ family of VGKCs, these aqueous conduits serve an array of critical roles in homeostasis, especially in neural tissue. Moreover, the greater emphasis on genomic identification in the past century has led to a growth in literature on the role of the ion channels in pathological disease as well. Despite this, there is a need to consolidate the updated findings regarding both the pharmacotherapeutic and pathological roles of KCNQ channels, especially regarding neural plasticity and motor disorders which have the largest body of literature on this channel. Specifically, KCNQ channels serve a remarkable role in modulating the synaptic efficiency required to create appropriate plasticity in the brain. This role can serve as a foundation for clinical approaches to chronic pain. Additionally, KCNQ channels in motor disorders have been utilized as a direction for contemporary pharmacotherapeutic developments due to the muscarinic properties of this channel. The aim of this study is to provide a contemporary review of the behavior of these channels in neural plasticity and motor disorders. Upon review, the behavior of these channels is largely dependent on the physiological role that KCNQ modulatory factors (i.e., pharmacotherapeutic options) serve in pathological diseases.