Effect of hippocampectomy on sleep patterns in cats

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.

What the cerveau isolé preparation tells us nowadays about sleep-wake mechanisms?

The intercollicular transected preparation opened a rich field for investigations of sleep-wake mechanisms. Initial results showed that brain stem ascending influences are essential for maintaining an activated cortex. It was subsequently shown that the forebrain also develops activating influences, since EEG desynchronization of the cortex reappears in the chronic cerveau isolé preparation, and continuous or almost continuous theta rhythm is able to occur in the acute cerveau isolé preparation. A brief "intermediate stage" of sleep occurs during natural sleep just prior to and after paradoxical sleep. It is characterized by cortical spindle bursts, hippocampal low frequency theta activity (two patterns of the acute cerveau isolé preparation) and is accompanied by a very low thalamic transmission level, suggesting a cerveau isolé-like state. The chronic cerveau isolé preparation also demonstrates that the executive processes of paradoxical sleep are located in the lower brain stem, while the occurrence of this sleep stage seems to be modulated by forebrain structures.

Sleep induced by drugs injected into the inferior horn of the lateral cerebral ventricle in dogs

1 In unanaesthetized dogs, cholinomimetic drugs and their antagonists were injected into the inferior horn of the left lateral cerebral ventricle. Injection volumes of 5 mul were used to limit spread of the drugs beyond the inferior horn. The effects on EEG and behaviour were recorded and compared with the effects of the same doses given into the body of the right lateral ventricle a little behind the foramen on Monro. 2 injections of cholinomimetic drugs into the inferior horn (acetylcholine 1-2 mug, physostigmine 1.0 mug, pilocarpine 100 mug and nicotine 10 mug) induced sleep during the following hour. The same doses injected into the body of the lateral ventricle did not produce sleep. 3 Cholinolytic drugs (atropine 10-20 mug, hyoscine 0.4-1.6 mug (+/-)-tubocuraine 10-20 ng and hexamethonium 40 mug) injected into the inferior horn also produced sleep, but the same doses injected into the body of the lateral ventricle were without effect. The EEG recorded after tubocurarine showed high voltage slow waves during sleep and desynchronized activation during rapid eye movement sleep. 4 Noradrenaline (10 mug) injected into the inferior horn produced sleep whereas the same dose given into the body of lateral ventricle did not produce sleep. The results with 5-hydroxytryptamine were equivocal. 5 It is suggested that the site for induction of sleep lies in structures lining the inferior horn of the lateral cerebral ventricle and that the cholinomimetic drugs probably act by a depolarizing block and the acetlycholine antagonists by a competitive block.

Monoamine changes in the brain of cats during slow-wave sleep

We have found that the metabolism of 5-hydroxytryptamine increases in the hippocampus and that the metabolism of dopamine decreases in the striatum and thalamus during slow-wave sleep, and we suggest that these changes are related to this stage of sleep. We have also found that the concentration of dopamine increases in the hippocampus during slow-wave sleep, and suggest that this may be related to the subsequent appearance of paradoxical sleep. These data raise new questions on the hippocampal role in the sleep-wakefulness cycle.