Single Cell Activity Patterns of Pedunculopontine Tegmentum Neurons Across the Sleep-Wake Cycle in Freely Moving Rats

In paper citation: (Datta & Siwek, 2002)

The new findings in this paper:

• There are three types of cells in the PPT of the rat (from measurements of 70 individual cells):
• ~12.86% of the cells are REM-on cells. These cells are more active during REM sleep than wakefulness or SWS. They start firing 5-10 seconds before the onset of REM and stop firing 5-8 seconds before the end of REM. These cells fire tonically with ISI modes of 90-110ms.
• ~60% of the cells are Wake-REM-on cells. These cells are more active during wakefulness and REM than SWS. They become silent at the onset of SWS and stay silent until 5-8 seconds  before the onset of REM. These cells fire tonically, but their firing rate was lower during REM, dropping from 15Hz (wake) to 10Hz  (REM). 
• ~27.14% of the cells are state-independent.
• There was no evident spatial differentiation within the PPT.
• None of the PPT cells fired in a bursting manner at any time.
• The average duration of spikes was around 1ms for all three types of cells, indicating that they were probably not GABAergic cells (which have spike duration of .5ms) but rather cholinergic cells
• When awake, the 70 cells fired 854 spikes/second. When in SWS, the 70 cells fired 63 spikes/second. When in REM sleep, the 70 cells fired 559 spikes/second. The activity of the cholinergic cells is thus assumed to be about 65% of the wakefulness baseline during REM sleep.

Other important information:

• Glutamate microinjection in the PPT increases the duration of REM sleep in the rat (Datta et al., 2001a)
• Choline microinjection in the PRF induces REM sleep in the rat (Gnadt & Pegram, 1986)
• Thus it is hypothesized that the PPT is a major source of cholinergic input to the PRF that can induce choline agonist-induced sleep
• Aminergic cells in the pons remain silent during REM sleep (Chu & Bloom, 1973; Hobson et al. 1975; (for more see paper))
• The cat has 5 types of neurons. The 2 not seen in the rat are: REM-off and PGO-on (Saito et al, 1977; El Mansari et al., 1989,1990;(for more see paper))
• REM-off cells are aminergic.These were only found in the cat.
• PGO-on cells discharge in bursts just prior to and during PGO wave activity. These are seen in the cat (Koyama & Sakai, 2002)
• The latency from increased PPT activity to REM sleep is longer in the cat (20-60s*) than in the rat (5-10s). However the cat has longer REM sleep episodes (10-30min) than the rat (3-13 min) (Foote, 1973; Datta & Hobson, 2000)
• LDT cholinergic cells are just like the PPT in distribution and action.

Remaining Questions:

• What coordinates the wake-REM-on and REM-on cells so that they both start  firing 5-8 seconds before REM and stop 5-8 seconds before the end of REM?
• Are there no bursting cells inside the PPT or were they just not found?
• What in development determines a W-REM-on from a REM-on from a state independent cell?