Relationship between dorsal brainstem sleep sites and intracranial self-stimulation

Based upon our previous findings that a reciprocal relationship exists between intracranial self-stimulation (ICSS) and rapid eye movement (REM) sleep, we hypothesized that the ICSS neural network is a part of the REM sleep system and fires during REM sleep. A series of experiments was designed to test a corollary to this hypothesis, that some sites involved in triggering REM sleep are also ICSS sites. We explored five locations: the locus coeruleus (LC), the medial longitudinal fasciculus (MLF) (both posterior midbrain and pontine level), the dorsal longitudinal fasciculus (DLF) (midbrain), and the ventral raphe (pontine level). We obtained rate-intensity functions from each animal that displayed ICSS. High to very high (15,000 per hour) rates of ICSS were obtained at several dorsal brain sites. These sites included the LC, pontine aspects of the MLF, and posterior midbrain aspects of the MLF and DLF. ICSS from the LC is interpreted as evidence that noradrenergic ICSS sites are part of the REM sleep neural network.