Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy.

J M Chung, J R Huguenard, D A Prince

Index: J. Neurophysiol. 70(1) , 20-7, (1993)

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Abstract

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)