Different cellular types in mesopontine cholinergic nuclei related to ponto-geniculo-occipital waves

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Abstract
The only mesopontine neurons previously described as involved in the transfer of ponto-geniculo-occipital (PGO) waves from the brain stem to the thalamus were termed PGO-on bursting cells. We have studied, in chronically implanted cats, neuronal activities in brain-stem peribrachial (PB) and laterodorsal tegmental (LDT) cholinergic nuclei in relation to PGO waves recorded from the lateral geniculate (LG) thalamic nucleus during rapid-eye-movement (REM) sleep. We constructed peri-PGO histograms of PB/LDT cells9 discharges and analyzed the interspike interval distribution during the period of increased neuronal activity related to PGO waves. Six categories of PGO-related PB/LDT neurons with identified thalamic projections were found: 4 classes of PGO-on cells: PGO-off but REM-on cells: and post-PGO cells. The physiological characteristics of a given cell class were stable even during prolonged recordings. One of these cell classes (1) represents the previously described PGO-on bursting neurons, while the other five (2–6) are newly discovered neuronal types. (1) Some neurons (16% of PGO-related cells) discharged stereotyped low-frequency (120– 180 Hz) spike bursts preceding the negative peak of the LG-PGO waves by 20–40 msec. These neurons had low firing rates (0.5–3.5 Hz) during all states. (2) A distinct cell class (22% of PGO-related neurons) fired high-frequency spike bursts (greater than 500 Hz) about 20–40 msec prior to the thalamic PGO wave. These bursts were preceded by a period (150–200 msec) of discharge acceleration on a background of tonically increased activity during REM sleep. (3) PGO-on tonic neurons (20% of PGO-related neurons) discharged trains of repetitive single spikes preceding the thalamic PGO waves by 100–150 msec, but never fired high- frequency spike bursts. (4) Other PGO-on neurons (10% of PGO-related neurons) discharged single spikes preceding thalamic PGO waves by 15–30 msec. On the basis of parallel intracellular recordings in acutely prepared, reserpine-treated animals, we concluded that the PGO-on single spikes arise from conventional excitatory postsynaptic potentials and do not reflect tiny postinhibitory rebounds. (5) A peculiar cellular class, termed PGO-off elements (8% of PGO-related neurons), consisted of neurons with tonic, high discharge rates (greater than 30 Hz) during REM sleep. These neurons stopped firing 100– 200 msec before and during the thalamic PGO waves. (6) Finally, other neurons discharged spike bursts or tonic spike trains 100–300 msec after the initially negative peak of the thalamic PGO field potential (post-PGO elements, 23% of PGO-related neurons).(ABSTRACT TRUNCATED AT 400 WORDS)