Telka M. Changes of the excitability of trigeminal ganglion neurons under noradrenergic modulation of calcium currents

The aim of this study was to reveal the properties of noradrenergic modulation of electrical activity and calcium currents in cultured trigeminal ganglion (TG) neurons. Noradrenaline (NA)-induced changes of electrophysiological characteristics were investigated using the patch-clamp whole-cell technique in current/voltage-clamp modes. NA application on the TG neuron soma simulates sympatho-sensory interaction in the trigeminal pathways. It was shown that changes in evoked electrical activity occur due to adrenoceptors interactions with hyperpolarization-activated cationic and calcium channels. In the first time, NA influence on calcium currents in TG neurons was analyzed. It was found that the adrenergic effect is present in the majority of the neurons (92%) and two electrophysiologically different types of the modulatory effect are present: a decrease in the current amplitude with no kinetic changes (62%, I type) and kinetic-slowing decreasing of the amplitude (29%, II type). It was established that the second type of modulation is carried out by the coupling of Gβγ-subunit with a calcium channel. It was shown that noradrenergic modulation of calcium currents partially (60%) mediates by α2-adrenoceptors activation. It was found that the NA effect on calcium currents realizes mainly via N-type channels (52% of the total effect), R- and P/Q-type channels contribute respectively 35 and 13%. The results are of fundamental value since they expand our knowledge of modulatory interactions between different parts of the peripheral nervous system. Practical significance of the results is due to the role of sympathetic-sensory interactions in neuropathies.