Figure 2.

Calcium channel PPN cell types, electrical coupling, and ensembles. (A) Pie chart showing the distribution of N + P/Q, N-only, and P/Q-only PPN cells according to electrophysiological type. Since type I PPN cells are non-cholinergic, type II are 2/3 cholinergic, and type III cells 1/3 cholinergic, it suggests that PPN neurons with one or both calcium channel types are represented in all transmitter types, cholinergic, glutamatergic, and GABAergic. That is, there are groups of PPN neurons that are N + P/Q that manifest all three transmitter types, as do groups of N-only and P/Q-only cells; (B) View of background activity in a PPN slice after loading with Fura2. Note that the majority of cells showing high levels of calcium in the absence of stimulation were found in pairs spaced about 100 μm apart. This suggests the presence of cell ensembles anchored by pairs of electrically coupled cells that are usually GABAergic. Calibration bar 25 μm; (C) Glutamatergic neurons are shown as green circles, cholinergic neurons as orange hexagons, and GABAergic cells as blue ovals, some being electrically coupled (red bars). Groups of cells with a 5:3:2 ratio would all need to express the same channel subtype. Ensembles expressing only N-type channels would fire during REM sleep (REM-on), those expressing only P/Q-type channels would fire during waking (Wake-on), and those expressing both would fire during both states (Wake/REM-on) [4].