Heterogeneity in Low Voltage-activated Ca2+ Channel-evoked Ca2+ Responses Within Neurons of the Thalamic Paraventricular Nucleus

Low voltage-activated Ca2+ channels (LVA or T-type Ca2+ channels) are crucial to burst firing and oscillations in thalamocortical relay cells and are exhibited by neurons in the paraventricular nucleus of thalamus (PVT), a dorsal midline nucleus deemed important in the neural representation of motivational behaviours. We used a functional approach (whole-cell patch-clamp electrophysiology combined with confocal laser scanning microscopy) to analyse the spatial distribution of LVA Ca2+ channel-evoked Ca2+ transients in PVT neurons. We observed that the magnitude of LVA Ca2+ channel-evoked Ca2+ transients was significantly greater in proximal dendrites (located up to 20 microm from the soma) than in the soma. In addition, the magnitudes of these Ca2+ transients varied significantly not only among different dendrites of the same cell but also within individual dendrites. These findings suggest that LVA Ca2+ channels are expressed (i) predominantly on the proximal dendrites and (ii) heterogeneously within individual dendrites of PVT neurons. The spatial characteristics of dendritic LVA Ca2+ channels in PVT neurons suggest that these channels may regulate burst firing by modulating dendritic afferent inputs.