Figure 3. Bicuculline microinjections into the posterior hypothalamus reversibly block the ability of pontine carbachol to elicit REM sleep-like episodes.

Records from an experiment with pontine carbachol injections made before, during and after a PF bicuculline injection (‘BIC’). REM sleep-like episodes could be elicited by pontine carbachol before bicuculline (‘Carb’ at 12.47 h), no component of the response to carbachol could be triggered when the drug was injected 15 min after the onset of the response to bicuculline (‘Carb’ at 13.48 h), but then carbachol was effective again when the effects of PF bicuculline had dissipated (‘Carb’ at 14.24 h). Note that all the effects of carbachol (the appearance of hippocampal theta-like activity, activation of the cortical EEG, depression of XII nerve activity and slowing of the central respiratory rate) were blocked during the response to bicuculline even though the effects of bicuculline itself on the hippocampal and cortical activities and respiratory rate were relatively small at the time of the carbachol injection made at 13.48 h. Dashed vertical lines mark the start times of successive microinjections of carbachol and bicuculline.