Contribution of somatic and dendritic SK channels in the firing rate of deep cerebellar nuclei: implication in cerebellar ataxia

Introduction: Loss of inhibitory output from Purkinje cells leads to hyperexcitability of the Deep Cerebellar Nuclei [DCN], which results in cerebellar ataxia. Also, inhibition of small-conductance calcium-activated potassium [SK] channel increases firing rate of DCN, which could cause cerebellar ataxia. Therefore, SK channel activators can be effective in reducing the symptoms of this disease, and used for the treatment of cerebellar ataxia. In this regard, we hypothesized that blockade of SK channels in different compartments of DCN would increase firing rate with different value. The location of these channels has different effects on increasing firing rate

Methods: In this study, multi-compartment computational model of DCN was used. This computational stimulation allowed us to study the changes in the firing activity of DCN neuron without concerns about interfering parameters in the experiment

Results: The simulation results demonstrated that blockade of somatic and dendritic SK channel increased the firing rate of DCN. In addition, after hyperpolarization [AHP] amplitude increased with blocking SK channel, and its regularity and resting potential changed. However, action potentials amplitude and duration had no significant changes. The simulation results illustrated a more significant contribution of SK channels on the dendritic tree to the DCN firing rate. SK channels in the proximal dendrites have more impact on firing rate compared to distal dendrites

Discussion: Therefore, inhibition of SK channel in DCN can cause cerebellar ataxia, and SK channel openers can have a therapeutic effect on cerebellar ataxia. In addition, the location of SK channels could be important in therapeutic goals. Dendritic SK channels can be a more effective target compared to somatic SK channels

Evaluation of mouse oocyte in vitro maturation developmental competency in dynamic culture systems by design and construction of a lab on a chip device and its comparison with conventional culture system

Objective: In conventional assisted reproductive technology [ART], oocytes are cultured in static microdrops within Petri dishes that contain vast amounts of media. However, the in vivo environment is dynamic. This study assesses in vitro oocyte maturation through the use of a new microfluidic device. We evaluate oocyte fertilization to the blastocyct stage and their glutathione [GSH] contents in each experimental group

Materials and Methods: In this experimental study, we established a dynamic culture condition. Immature oocytes were harvested from ovaries of Naval Medical Research Institute [NMRI] mice. Oocytes were randomly placed in static [passive] and dynamic [active] in vitro maturation [IVM] culture medium for 24 hours. In vitro matured oocytes underwent fertilization, after which we placed the pronucleus [PN] stage embryos in microdrops and followed their developmental stages to blastocyst formation after 3 days. GSH content of the in vitro matured oocytes was assessed by monochlorobimane [MCB] staining

Results: We observed significantly higher percentages of mature metaphase II oocytes [MII] in the passive and active dynamic culture systems [DCS] compared to the static group [P<0.01]. There were significantly less mean numbers of germinal vesicle [GV] and degenerated oocytes in the passive and active dynamic groups compared to the static group [P<0.01]. Fertilization and blastocyst formation rate in the dynamic systems were statistically significant compared to the static cultures [P<0.01]. There was significantly higher GSH content in dynamically matured oocytes compared to statically matured oocytes [P<0.01]

Conclusion: Dynamic culture for in vitro oocyte maturation improves their developmental competency in comparison with static culture conditions