UVM Theses and Dissertations
Format:
Print
Author:
Yoon, Yone Jung
Dept./Program:
Biology
Year:
2011
Degree:
PhD
Abstract:
Network-driven spontaneous electrical activity in the chicken spinal cord regulates a variety of developmental processes including neuronal differentiation and formation of neuromuscular structures. In this study we have examined the effect of chronic inhibition of spinal cord activity on motoneuron survival and differentiation. Early spinal cord activity in chick embryos was blocked using an· avian replication-competent retroviral vector RCASBP (B) carrying the inward rectifier potassium channel Kir2.l. Chicken embryos were infected with one of the following constructs: RCASBP(B), RCASBP(B)-Kir2.l, or RCASBP(B)-GFP. Infection of chicken embryos at E2 resulted in widespread expression of the viral protein marker p27 gag throughout the spinal cord. Electrophysiological recordings revealed the presence of functional Kir2.1 channels in RCASBP(B)-Kir2.1 but not in RCASBP(B)-infected embryos. Kir2.1 expression significantly reduced the generation of spontaneous motor movements in chicken embryos developing in ovo.
Suppression of spontaneous electrical activity has no noticeable effect on the number of motoneurons in the ventral spinal cord or the number of synapses in hindlimb muscle tissue. However, disruption of the normal pattern of activity in chicken embryos resulted in a significant downregulation in the functional expression of large-conductance Ca²-dependent K⁺ channels. Reduction of spinal cord activity also generated a significant acceleration in the inactivation rate of A-type K⁺ currents without any significant change in current density. Kir2.1 expression did not affect the expression of voltage-gated Na⁺ channels or cell capacitance. These experiments demonstrated that chronic inhibition of chicken spinal cord activity caused a significant change in the electrical properties of developing motoneurons.
Excitatory GABAergic neurotransmission is involved in the generation of spontaneous electrical activity in the spinal cord. Although excitatory GABAergic neurotransmission is an early feature of the developing nervous system, we have a limited understanding regarding the developmental role of GABA receptor activation. Therefore, we also explored the role of excitatory GABA neurotransmission in regulating the dendritic morphology and network function in the developing chicken spinal cord. Both the GABA agonist muscimol and the GABA receptor antagonist bicuculline inhibited the generation of spontaneous network activity in the isolated spinal cord at E8 or ElO. Daily treatment of chicken embryos with muscimol or bicuculline between E5 and E8 (or between E8 and E 10), caused a significant decrease in the dendritic complexity of the motoneurons when compared to vehicletreated embryos.
The inhibitory effect of muscimol and bicuculline was likely due to inhibition of network activity because a similar effect was also observed following reduction of network activity by overexpression of Kir2.1 in the spinal cord. The inhibitory effect of muscimol and bicuculline was not caused by an adverse effect on cell survival. Surprisingly, chronic treatment of chicken embryos with muscimol or bicuculline had no effect on the shape and duration of the episodes of spontaneous activity. These results indicated that GABA-driven activity regulates the maturation of dendritic morphology of developing motoneurons, and that compensatory mechanisms could restore normal network function following disruption of GABAreceptor function and inhibition of dendritic outgrowth.
Suppression of spontaneous electrical activity has no noticeable effect on the number of motoneurons in the ventral spinal cord or the number of synapses in hindlimb muscle tissue. However, disruption of the normal pattern of activity in chicken embryos resulted in a significant downregulation in the functional expression of large-conductance Ca²-dependent K⁺ channels. Reduction of spinal cord activity also generated a significant acceleration in the inactivation rate of A-type K⁺ currents without any significant change in current density. Kir2.1 expression did not affect the expression of voltage-gated Na⁺ channels or cell capacitance. These experiments demonstrated that chronic inhibition of chicken spinal cord activity caused a significant change in the electrical properties of developing motoneurons.
Excitatory GABAergic neurotransmission is involved in the generation of spontaneous electrical activity in the spinal cord. Although excitatory GABAergic neurotransmission is an early feature of the developing nervous system, we have a limited understanding regarding the developmental role of GABA receptor activation. Therefore, we also explored the role of excitatory GABA neurotransmission in regulating the dendritic morphology and network function in the developing chicken spinal cord. Both the GABA agonist muscimol and the GABA receptor antagonist bicuculline inhibited the generation of spontaneous network activity in the isolated spinal cord at E8 or ElO. Daily treatment of chicken embryos with muscimol or bicuculline between E5 and E8 (or between E8 and E 10), caused a significant decrease in the dendritic complexity of the motoneurons when compared to vehicletreated embryos.
The inhibitory effect of muscimol and bicuculline was likely due to inhibition of network activity because a similar effect was also observed following reduction of network activity by overexpression of Kir2.1 in the spinal cord. The inhibitory effect of muscimol and bicuculline was not caused by an adverse effect on cell survival. Surprisingly, chronic treatment of chicken embryos with muscimol or bicuculline had no effect on the shape and duration of the episodes of spontaneous activity. These results indicated that GABA-driven activity regulates the maturation of dendritic morphology of developing motoneurons, and that compensatory mechanisms could restore normal network function following disruption of GABAreceptor function and inhibition of dendritic outgrowth.