Our research focuses on ion channels'role in functional plasticity on brain disorders. In particular, we study here whether neurons from the visual thalamus can undergo plasticity of intrinsic neuronal excitability. We have established for the first time that neurons from the lateral geniculate nucleus do express the plasticity of intrinsic neural excitability following monocular deprivation or following stimulation of regional inputs.
We provide a simple way to induce long-lasting plasticity of neuronal excitability in visual thalamic neurons of the rat in vitro. For this purpose, we use patch-clamp electrophysical recordings and pharmacological tools on ex vivo brain tissue. Our results raise the possibility of exploring the intrinsic plasticity of other subcortical visual nuclei of the brain.
To begin, prepare the dissecting tools and two ice platforms. Put ice in the outer tank and fill the slicing chamber of the vibratome with an ice-cold cutting solution. Place the head of the euthanized rat on the first iced platform, and using small scissors, cut the scalp in a caudal direction, followed by the skull bilaterally.
With blunt forceps and spatula, open the skull, rapidly extract the brain from the skull, and place it on the second ice platform. Make an incision in the frontal plane to remove the anterior cortex and olfactory bulbs, followed by a second cut at the inferior colliculus level to remove the posterior cortex and cerebellum. Affix the brain block onto the vibratome's plate with the rostral side up.
Regularly water the brain during the procedure until it is fully submerged in the slicing chamber. Using the vibratome, cut 350 micrometer slices containing the dorsal lateral geniculate nucleus. Then, with a pencil, gently remove the cortex and hippocampus from the midbrain.
To begin, obtain the rat brain slice containing the dorsal lateral geniculate nucleus, or dLGN, and mount it to a submerged chamber on an upright microscope. Place the U-shaped platinum wire on the slice. Using differential interference contrast infrared video microscopy, identify a healthy neuron in the dLGN for patch-clamp recording.
Using the micro-manipulator, position the patch pipette on the selected neuron with constant positive pressure. Set the amplifier on VC mode and inject a 10 millivolts voltage step. Set the voltage to minus 65 millivolts.
Next, set the amplifier on CC mode, balance the bridge to compensate for access resistance, and hold the neuron at minus 65 millivolts. For data acquisition, set a control period of about 10 minutes with a positive pulse of current at a frequency of 0.1 hertz and monitor the neuronal excitability. Then, observe the input resistance of the neuron throughout with a brief negative pulse of current.
After the control period, elicit trains of 15 spikes evoked by 15 short steps of two to five milliseconds of depolarizing current, delivered at 40 hertz for 10 minutes. Choose the amplitude of the current pulse to elicit a single action potential each time. Finally, test neuronal excitability after the induction protocol.
The dLGN neurons were recorded in whole cell configuration, and LTP-IE was induced by action potential firing at 40 hertz for 10 minutes in the presence of ionotropic glutamate and GABA receptor antagonists. A threefold increase in the number of action potentials was observed 20 to 30 minutes after the induction of LTP-IE without any change in input resistance.
