Dual orexin-A action on ionic currents in intergeniculate leaflet neurons of the thalamus

The intergeniculate leaflet (IGL) is an important component of mammalian biological clock, passing information to the suprachismatic nuclei (SCN) – master generator of biological rhythms. Its main function is to integrate photic with non-photic information, coming from retina and nonspecyfic brain systems, respectively. Arousal mediated by orexinergic system modulates various cellular mechanisms in different nuclei throughout whole brain. The aim of our experiments was to investigate the ionic mechanism underlying orexin-A (OXA) modulation of single IGL neurons. In vitro whole-cell patch clamp recording were performed on acute brain slices from 2–3 weeks old male Wistar rats. OXA (200 nM), tetrodotoxin (0.5 µM) and artificial cerebro-spinal fluid with changed ionic composition were applied by bath perfusion. Patch pipette were filled with intrapipete solution with 0.1% biocytin. Brain slices were stained with the use of anti-NPY antibodies and ExtrAvidinCy3, before the examination by confocal laser microscope. Our previous study showed depolarizing effect of OXA on IGL neurons. This patch clamp experiments revealed the major role of Na+ currents in this activation, possibly via nonselective cation channels. Moreover, our investigation proved the effect of OXA on K+ currents of single IGL neurons. Further research with the use of selective channel blockers is needed to evaluate the exact mechanism of OXA in IGL.