RT Journal Article
SR Electronic
T1 Nucleus-Specific Chloride Homeostasis in Rat Thalamus
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 2348
OP 2354
DO 10.1523/JNEUROSCI.17-07-02348.1997
VO 17
IS 7
A1 Daniel Ulrich
A1 John R. Huguenard
YR 1997
UL http://www.jneurosci.org/content/17/7/2348.abstract
AB Synchronous thalamic network activity occurring during slow wave sleep and paroxysmal discharges critically depends on the ability of thalamocortical relay cells and inhibitory neurons of the nucleus reticularis thalami (nRt) to fire bursts of action potentials. Inhibitory synaptic potentials (IPSPs) originating from nRt cells are crucial in deinactivating T-channels and thus promoting burst firing in relay cells, but the functional role of intra-nRt IPSPs is less well understood. A major factor that regulates the net effects of IPSP generation is the chloride equilibrium potential (ECl). Here we applied the perforated patch-clamp technique, using the cation-selective ionophore gramicidin to assess the reversal potential of chloride in nRt and relay cells in brain slices. We found that the reversal potential of GABA-induced membrane currents (EGABA) was significantly more hyperpolarized in relay (−81 ± 2.6 mV), as compared with nRt cells (−71 ± 2.5 mV).EGABA was not significantly different from the reversal potential of evoked IPSCs (EIPSC; −82 ± 4.4 mV) in relay cells. In both relay and reticular neurons the chloride gradient was collapsed partially by the chloride cation cotransport blocker furosemide, suggesting an active chloride extrusion mechanism in thalamic neurons. Given the relatively hyperpolarized resting potentials (approximately −70 mV) reported for nRt and relay cells during in vitro thalamic oscillations, we conclude that under these conditions GABAA IPSPs lead to significant hyperpolarization in relay cells. By contrast, intra-nRt inhibition essentially would be shunting, i.e., would produce minimal membrane polarization but still could reduce the amplitude of excitatory events.