GABAergic neurons of the laterodorsal and pedunculopontine tegmental nuclei of the cat express c-fos during carbachol-induced active sleep

The laterodorsal and pedunculopontine tegmental nuclei (LDT-PPT) are involved in the generation of active sleep (AS; also called REM or rapid eye movement sleep). Although the LDT-PPT are composed principally of cholinergic neurons that participate in the: control of sleep and waking states, the function of the large number of GABAergic neurons that are also located in the LDT-PPT is unknown. Consequently, we sought to determine if these neurons are activated (as indicated by their L-fos expression) during active sleep induced by the microinjection of carbachol into the rostro-dorsal pens (AS-carbachol). Accordingly, immunocytochemical double-labeling techniques were used to identify GABA and Fos protein, as well as choline acetyltransferase (ChAT), in histological sections of the LDT-PPT. Compared to control awake cats, there was a larger number of GABAergic neurons that expressed c-fos during AS-carbachol (31.5+/-6.1 vs. 112+/-15.2. P<0.005). This increase in the number of GABA(+)Fos(+) neurons occurred on the ipsilateral side relative to the injection site: there was a small decrease in GABA(+)Fos(+) cells in the contralateral LDT-PPT. However. the LDT-PPT neurons that exhibited the largest increase in c-Sos expression during AS-carbachol were neither GABA(+) nor ChAT(+) (47+/-22.5 vs. 228.7+/-14.0, P<0.0005). The number of cholinergic neurons that expressed c-fors during AS-carbachol was not significantly different compared to wakefulness. These data demonstrate that, during AS-carbachol, GABAergic as well as an unidentified population of neurons are activated in the LDT-PPT. We propose that these non-cholinergic LDT-PPT neurons may participate in the regulation of active sleep. (C) 2001 Elsevier Science B.V. All rights reserved.