Specific and nonspecific thalamocortical connectivity in the auditory and somatosensory thalamocortical slices

Abstract

Two classes of thalamic nuclei project to either middle layers or upper layers, including layer 1, of the neocortex, and are referred to as 'specific' and 'nonspecific' nuclei, respectively. The electrophysiological properties of the nonspecific nuclei have not been investigated, largely because of the paucity of in vitro slice preparations containing intact nonspecific pathways. In this study, we used flavoprotein autofluorescence imaging to show intact thalamocortical connectivity of nonspecific nuclei in slice preparations of the somatosensory and auditory systems. These preparations will enable the elucidation of electrophysiological properties of nonspecific pathways.

Figure 1

Connectivity in the modified somatosensory thalamocortical slice preparation. (A) Raw FA image for anatomical reference in electrical experiments (B–E). (B) Electrical stimulation of CL and resulting cortical activation. (C) Electrical stimulation in VM and resulting cortical activation. (D) Electrical stimulation in VP and cortical activation. (E) POm electrical stimulation and cortical activation. (F) Raw FA image for anatomical reference in photostimulation experiments (G–I). (G) Cortical response to photostimulation of CL. (H) Photostimulation of VM and resultant activity in S1. Arrow indicates stimulation site here and in all other imaging figures. (I) Cortical response to photostimulation in VP. Arrows in the lower right inset of (A and F) are for orientation: D = Dorsal, M = Medial. Color bar at bottom of (I) represents values of ΔF/F corresponding to colors in panels (B–E and G–I). Color bar also applies to all FA colormap images in Fig. 2.

Figure 2

Connectivity in the auditory thalamocortical slice preparation. (A) Electrical stimulation of MGBm and FA response in auditory cortex. (B) Electrical stimulation in MGBv and cortical response. (C) Raw FA image for anatomical reference. (D) Overlay of (A) and (B). Note the lack of overlap between stimulation sites and limitation of activation to the borders of the subnuclei. (E) Raw FA image for anatomical references for panels (F) and (G). (F) Cortical response to MGBm photostimulation. (C) Cortical response to photostimulation in MGBv. See Figure 1 for colormap. In (A) and (E): m = MGBm, v = MGBv, R = Rostral, M = Medial. See Figure 1 for FA colorbar and corresponding ΔF/F values. Single arrows in (B), (C), (F) and (G) correspond to stimulation sites.