PGO activity after carbachol delivery in the oral and caudal pontine reticular nuclei: similarities and differences with spontaneous REM sleep in cats

Introduction Carbachol in the ventral part of the oral pontine reticular nucleus (vRPO) generates REM sleep with all its polygraphic characteristics. In contrast, cholinergic stimulation of the nearby rostral caudal pontine reticular nucleus (RPC) produces atonia and PGOs but with EEG sychronization. By quantifying PGO activity, this study further characterizes the effects of carbachol in these two pontine sites. Materials and methods Eight cats wearing electrodes for sleep polygraphic recordings were used; each had a guide-tube aimed at the vRPO or the RPC to administer carbachol (0.1 M, 20–30 nl) microinjections. Isolated PGO waves (Type I) and clusters with interspike intervals of ⩽ 330 ms of 2, 3 and ⩾ 4 PGOs (Type II, III and IV respectively) were quantified using one-minute epochs of 4 consecutive spontaneous REM sleep episodes (control) and then after carbachol in the vRPO and the RPC at the following times: when PGO activity was first detected (T0) and 10–15 (T10), 30–45 (T30) and 60–75 (T60) min later. Data from the different experimental conditions were compared with ANOVAs for repeated measures and the post hoc Fisher test. Results Atonia, desynchronized EEG and different types of PGOs occurred shortly after carbachol delivery in the vRPO, while a predominance of Type IV PGO clusters, numerous REMs, atonia and with a striking EEG theta synchronization occurred after carbachol in the RPC. The total number of PGOs and Type IV clusters were significantly higher in RPC experiments than in either spontaneous or vRPO Rem sleep in the T0 to T60 samples. These parameters were slightly lower than the spontaneous REM sleep values after vRPO carbachol delivery but, significant decreases only occurred immediately after the first appearance of PGO activity (T0). Also, the four PGO type proportions were fairly well preserved in carbachol vRPO experiments. In the RPC experiments, the proportions of the PGO patterns were different from spontaneous or carbachol vRPO Rem sleep (Types I and II significantly decreased and Type IV significantly increased). Conclusion These results indicate that the vRPO is not only the prime region for the simultaneous appearance of tonic REM sleep signs (atonia and EEG desynchonization) but it can also to promote the cascade of events that establish the physiological pattern of PGO phasic activities. Cholinergic stimulation of the rostral RPC does not generate true REM sleep, but it is involved in the generation of atonia and of long trains of clustered PGO activity. Acknowledgements Supported by Grant BFU2009-06991 from MCyT, Spain.