Intrinsic membrane properties and plasticity in medial vestibular nucleus neurones

• Main Author: Him, Aydin
• Published: University of Edinburgh 2002
• Subjects: 612.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.652452

This thesis describes in vitro electrophysiological experiments on horizontal brainstem slices containing medial vestibular nucleus (MVN) from young adult and aged rats. The whole-cell patch clamp recording technique was used in MVN slices of young adult rats to study intrinsic membrane properties and spike firing characteristics of rostral MVN neurones and their role in vestibular compensation, the behavioral recovery that follows damage to the vestibular receptors or nerve of one inner ear. Extracellular recordings were made in MVN slices of young and aged rats to study age-related changes in the intrinsic activity and GABA receptor sensitivity of MVN neurones. MVN neurones were classified into Type A and Type B cells based on their action potential shapes. Type B cells were further grouped into Type B_DP cells, which showed depolarising plateau potentials, and Type B_LTS cells, which showed low threshold spikes, according to their firing behaviours in response to depolarising and hyperpolarising current pulses. The results showed that significant adaptive changes take place in intrinsic membrane properties and firing characteristics of specific subpopulations of vestibular neurones in the rostral region of the ipsilateral MVN during vestibular compensation following unilateral labyrinthectomy (UL). Type B cells had significantly higher resting discharges and more depolarised resting membrane potentials in post-UL slices, while Type A cells did not show any change in their in vitro firing rates and resting membrane potential. However, after UL, a greater number of Type A cells expressed spike frequency accommodation, and there was a significant increase in the gain of Type A cells. Significantly more Type B cells showed low threshold spikes in MVN slices of labyrinthectomised rats suggesting that T-type calcium currents were up-regulated in some MVN cells during vestibular compensation. Up-regulation of intrinsic excitability in Type B cells and changes in dynamic membrane properties of Type A cells could be important in vivo in recovery of neuronal activity of MVN cells which are silenced soon after UL.