Ventral posterolateral and ventral posteromedial thalamus neurons have distinct synaptic and cellular physiology

Abstract

Somatosensory information is propagated from the periphery to the cerebral cortex by two parallel pathways through the ventral posterolateral (VPL) and ventral posteromedial (VPM) thalamus. VPL and VPM neurons receive somatosensory signals from the body and head, respectively. VPL and VPM neurons also receive cell-type-specific GABAergic input from the reticular nucleus of the thalamus (nRT). Although VPL and VPM neurons have distinct connectivity and physiological roles, differences in the functional properties of VPL and VPM neurons remain unclear as they are often studied as one ventrobasal (VB) thalamus neuron population. Here, we directly compared synaptic and intrinsic properties of VPL and VPM neurons in C57Bl/6J mice of both sexes aged P25-P32. Recordings of spontaneous synaptic transmission suggested that VPL neurons receive excitatory synaptic input with higher frequency and strength than VPM neurons, while VPL neurons exhibited weaker inhibitory synapse strength than VPM neurons. Furthermore, VPL neurons showed enhanced depolarization-induced spike firing and greater spike frequency adaptation than VPM neurons. VPL and VPM neurons fired similar numbers of spikes during hyperpolarization rebound bursts, but VPM neurons exhibited shorter burst latency compared to VPL neurons, which correlated with increased sag potential during hyperpolarization. This work indicates that VPL and VPM thalamocortical neurons are functionally distinct populations. The observed functional differences could have important implications for their specific physiological and pathophysiological roles within the somatosensory thalamocortical network.