Pontine-wave generator activation-dependent memory processing of avoidance learning involves the dorsal hippocampus in the rat

The aim of this study was to test the hypothesis that the dorsal hippocampus plays a critical role in pontine-wave (P-wave) generator activation-dependent memory processing of two-way active avoidance (TWAA) learning. To achieve this objective, rats were given small bilateral lesions in the CA1, dentate gyrus (DG), or CA3 region of the dorsal hippocampus by microinjecting ibotenic acid. After recovery, lesioned and sham-lesioned rats were trained on a TWAA learning paradigm, allowed a 6-hr period of undisturbed sleep, and then were tested on the same TWAA paradigm. It was found that lesions in the CA3 region impaired retention of avoidance learning. Conversely, lesions in the CA1 and DG regions had no effect on TWAA learning retention. None of the groups showed any changes in the baseline sleep-wake cycle or in the acquisition of TWAA learning. All rats showed increased rapid eye movement (REM) sleep and increased REM sleep P-wave density during the subsequent 6-hr recording period. Impaired retention in the CA3 group occurred despite an increase in REM sleep and P-wave density, suggesting that during REM sleep, the P-wave generator interacts with the CA3 region of the dorsal hippocampus to aid in consolidation of TWAA learning. The results of the present study thus demonstrate that P-wave generator activation-dependent consolidation of memory requires an intact CA3 subfield of the dorsal hippocampus. The results also provide evidence that under mnemonic pressure, the dorsal hippocampus may not be involved directly in regulating the sleep-wake cycle.

Novel role of brain stem pedunculopontine tegmental adenylyl cyclase in the regulation of spontaneous REM sleep in the freely moving rat

Physiological activation of kainate receptors and GABA(B) receptors within the pedunculopontine tegmentum (PPT) is involved in regulation of rapid-eye-movement (REM) sleep. Because these two types of receptors may also directly and/or indirectly activate the intracellular cyclic adenosine monophosphate (cAMP) signaling pathway, we hypothesized that this signaling pathway may be involved in the PPT to regulate spontaneous REM sleep. To test this hypothesis, four different doses (0.25, 0.50, 0.75, and 1.0 nmol) of a specific adenylyl cyclase (AC) inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536), were microinjected bilaterally (100 nl/site) into the PPT, and the effects on REM sleep in freely moving chronically instrumented rats were quantified. By comparing alterations in the patterns of REM sleep after control injections of vehicle or one of the four different doses of SQ22536, the contributions made by each dose of SQ22536 to REM sleep were evaluated. The results demonstrated that the local microinjection of AC inhibitor SQ22536 into the PPT decreased the total amount of REM sleep for 3 h and increased slow-wave sleep (SWS) for 2 h in a dose-dependent manner. This reduction in REM sleep was due to increased latency and decreased frequency of REM sleep episodes. These results provide evidence that inhibition of AC within the PPT can successfully reduce REM sleep. These findings suggest that activation of the cAMP-signaling pathway within the cholinergic cell compartment of the PPT is an intracellular biochemical/molecular step for generating REM sleep in the freely moving rat.

Volume and dose effects of experimenter-administered ethanol preloads on ethanol seeking and self-administration

The present experiment used a behavioral model developed to separate the initial behavior required to obtain access to ethanol (appetitive responding or lever presses) from the actual self-administration (consummatory responding or intake) to test the hypothesis that these responses are under the control of different behavioral/physiological processes, and therefore differentially affected by an ethanol priming dose. In male, Long Evans rats, "preload" volume (0.5 and 2.0ml) and dose (approximately 10%, 25%, and 50% of the total normally consumed in nontreatment sessions translating to 0.1, 0.25, and 0.5g/kg) of ethanol were varied and administered by the experimenter via oral gavage prior to an operant session. Overall, there were no priming effects, or increases, in ethanol-reinforced responding resulting from the ethanol preloads. The findings showed that the low preload volume produced linear, dose-dependent decreases in both intake and seeking. However, while the high volume also produced a linear dose-dependent decrease in ethanol seeking, there was a decrease in intake at every dose. That is, ethanol seeking was insensitive to preload volume, while intake was affected in a dose-dependent manner except at the lowest dose when preload volume did play a role in intake regulation. These findings indicate that "fullness" and pharmacological cues differentially impact the appetitive and consummatory behaviors reinforced by ethanol solutions, with intake being more sensitive to preload volume and seeking being more sensitive to preload pharmacology.