Hyperpolarisation rectification in cat lateral geniculate neurons modulated by intact corticothalamic projections.

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Thalamic neuron intrinsic properties are shaped by synaptic inputs and neuromodulators.
• Corticothalamic projections significantly influence thalamic neuronal activity.

Purpose of the Study:

• To investigate the impact of corticothalamic projections on the hyperpolarization-activated cation current (Ih) in dorsal lateral geniculate (dLG) nucleus neurons.
• To determine how cortical network states affect Ih expression in dLG neurons.

Main Methods:

• Intracellular recordings from dLG neurons in anesthetized cats, preserving intact corticothalamic loops.
• Photic stimulation via optic tract and light-emitting-diodes to identify dLG neurons.
• Application of concentrated K+ solution to the visual cortex to induce cortical depression.

Main Results:

• The expression of Ih, a depolarizing sag current, in dLG neurons was dependent on the cortical network state.
• Ih was detected during cortical disfacilitation (slow oscillations) but absent during active (depolarized) cortical periods.
• Inducing cortical depression with K+ enabled Ih expression in previously non-expressing dLG neurons.

Conclusions:

• Intact corticothalamic projections prevent the generation of thalamic clock-like delta oscillations in dLG neurons.
• The interplay between Ih and low-threshold calcium current (IT) for delta oscillations is modulated by cortical activity.
• Cortical states dynamically regulate the intrinsic excitability of thalamic neurons via Ih.