Isabel de Andrés

Location and anatomical connections of a paradoxical sleep induction site in the cat ventral pontine tegmentum.

The brainstem mechanisms for the generation of paradoxical sleep are under considerable debate. Previous experiments in cats have demonstrated that injections of the cholinergic agonist carbachol into the oral pontine tegmentum elicit paradoxical sleep behaviour and its polygraphic correlates. The different results on the pontine structures that mediate this effect do not agree. We report here that limited microinjections of a carbachol solution into the ventral part of the oral pontine reticular nucleus in the cat induce, with a short latency, a dramatic, long‐lasting increase in paradoxical sleep. Moreover, neuronal tracing experiments show that this pontine site is connected with brain structures responsible for the different bioelectric events of paradoxical sleep. These two facts suggest that the ventral part of the oral pontine reticular nucleus is a nodal link in the neuronal network underlying paradoxical sleep mechanisms.

Neocortical and hippocampal electrical activities are similar in spontaneous and cholinergic-induced REM sleep.

Neocortical and hippocampal EEG power spectra obtained during REM-like sleep induced by unilateral carbachol microinjections (0.01 M, 0.02 M and 0.2 M; volume 20 nl) into the ventral part of the nucleus reticularis pontis oralis have been compared with EEG power spectra obtained during spontaneous REM sleep. Our findings indicate that neocortical and hippocampal electrical activities during the REM-like state generated by carbachol delivery in this pontine region mimic those present in spontaneous REM sleep.

Sleep-wakefulness effects after microinjections of hypocretin 1 (orexin A) in cholinoceptive areas of the cat oral pontine tegmentum

Hypocretinergic/orexinergic neurons, which are known to be implicated in narcolepsy, project to the pontine tegmentum areas involved in the control of rapid eye movement (REM) sleep. Here, we report the effects on sleep‐wakefulness produced by low‐volume microinjections of hypocretin (Hcrt)1 (20–30 nL, 100, 500 and 1000 μm) and carbachol (20–30 nL, 0.1 m) delivered in two areas of the oral pontine tegmentum of free‐moving cats with electrodes for chronic sleep recordings: in the dorsal oral pontine tegmentum (DOPT) and in the ventral part of the oral pontine reticular nucleus (vRPO). Carbachol in the DOPT produced dissociate polygraphic states, with some but not all REM sleep signs. In contrast, carbachol in the vRPO produced a shift with short latency from wakefulness (W) to REM sleep with all of its polygraphic and behavioral signs. Hcrt‐1 in the DOPT increased W and decreased both slow‐wave sleep (SWS) and REM sleep during the first 3 h post‐drug. The same doses of Hcr‐1 in the vRPO produced a significant suppression of REM sleep without a definitive trend for changes in the other states. Both groups showed significant decreases in the number of transitions from SWS to REM sleep. Thus, Hcrt‐1 produced distinct effects in cholinoceptive areas of the oral pontine tegmentum; in the DOPT it promoted W, suppressed SWS and probably defacilitated REM sleep, and in the vRPO it directly inhibited REM sleep. Hypocretinergic/orexinergic signaling is lost in narcoleptics and this absence would mean that pontine defacilitation/inhibition of REM sleep would also be absent, explaining why these patients can fall directly into REM sleep from W.

Functional anatomy of non-REM sleep

The state of non-REM sleep (NREM), or slow wave sleep, is associated with a synchronized EEG pattern in which sleep spindles and/or K complexes and high-voltage slow wave activity (SWA) can be recorded over the entire cortical surface. In humans, NREM is subdivided into stages 2 and 3–4 (presently named N3) depending on the proportions of each of these polygraphic events. NREM is necessary for normal physical and intellectual performance and behavior. An overview of the brain structures involved in NREM generation shows that the thalamus and the cerebral cortex are absolutely necessary for the most significant bioelectric and behavioral events of NREM to be expressed; other structures like the basal forebrain, anterior hypothalamus, cerebellum, caudal brain stem, spinal cord and peripheral nerves contribute to NREM regulation and modulation. In NREM stage 2, sustained hyperpolarized membrane potential levels resulting from interaction between thalamic reticular and projection neurons gives rise to spindle oscillations in the membrane potential; the initiation and termination of individual spindle sequences depends on corticothalamic activities. Cortical and thalamic mechanisms are also involved in the generation of EEG delta SWA that appears in deep stage 3–4 (N3) NREM; the cortex has classically been considered to be the structure that generates this activity, but delta oscillations can also be generated in thalamocortical neurons. NREM is probably necessary to normalize synapses to a sustainable basal condition that can ensure cellular homeostasis. Sleep homeostasis depends not only on the duration of prior wakefulness but also on its intensity, and sleep need increases when wakefulness is associated with learning. NREM seems to ensure cell homeostasis by reducing the number of synaptic connections to a basic level; based on simple energy demands, cerebral energy economizing during NREM sleep is one of the prevalent hypotheses to explain NREM homeostasis.

Effects of caudate nuclei or frontal cortical ablations in kittens: responsiveness to auditory stimuli and comparisons with adult-operated littermates.

Abstract These experiments assess the behavioral responsiveness of adult cats with extensive caudate nuclei or frontal cortical ablations, sustained either neonatally or in adulthood, to presentations of cat vocalizations or of tones. Each subject received 27 presentations, at 1-min intervals, of a 12 s sequence of taped vocalization (calls) on 2 successive days and, 1 week later, a similar series of 2-kHz tones of the same duration and intensity. The behavioral responses were scored using a six-point rating scale and the data were analyzed to compare responsiveness of the groups within each testing day, decrement of responsiveness across the trials of each session (habituation), and retention of habituation across successive days. We found that (a) all acaudate and afrontal cats persisted in responding at higher levels than intact animals in all three testing sessions; (b) the cats with caudate ablations were more responsive than those with frontal ablations to both calls and tones; (c) the hyperresponsiveness was more marked for adult-operated in relation to kitten-operated preparations; (d) in general, the responsiveness of all kitten groups decreased progressively across the three testings; and (e) for the adult-operated cats, there was a decrement between the two call sessions and an increase between the call and the tone sessions. These findings suggest that both the caudate nucleus and the frontal cortex participate in processes controlling the organisms responsiveness to external stimuli with the caudate removal producing the largest defect; they also indicate that, with some qualifications, the lesions sustained by the kitten result in less marked later effects than those sustained by the adult. Furthermore, they may help to explain some of the behavioral changes which we described previously for cats with caudate ablations.

Reassessing morphine effects in cats: II. Protracted effects on sleep-wakefulness and the EEG

Adult cats were implanted with standard electrodes to record EEG, EOG, and EMG. After 15 days, morphine sulphate or saline placebo was given IP at 0.5, 1.0, 2.0, 3.0 mg/kg, at least 15 days apart. Cats were continuously recorded for 72 hr postinjection. Wakefulness, drowsiness, NREM and REM sleep percentages were scored from polygraphic features and statistically analysed. There was a dose-dependent suppression of NREM and REM sleep for at least 6 hours postmorphine, with a progressive sleep recovery thereafter. During the insomnia period there was an EEG/behavioral dissociation where bursts of high-voltage waves were seen over a background of desynchrony; meanwhile the animal was first aroused although quiet and later showed stereotypic behavior. There was a prolonged NREM sleep rebound which started later at the higher doses. A significant, relatively brief REM sleep rebound was seen only at the lowest dose. The latency for NREM and REM sleep onset was also dose-dependent. Possible brain sites of morphine actions and similarities with effects in other species are discussed.

Chronic morphine administration in cats: Effects on sleep and EEG

Sleep-wakefulness and EEG responses to a chronic morphine treatment (2 mg/kg/day, IP, during 15 days) were studied in 8 cats provided with electrodes for EEG, EMG and EOG records. Results indicated that, in contrast to a resistance of the cats to exhibit overt signs of tolerance in the immediate behavioral and EEG responses to morphine, tolerance developed in sleep since: 1) there was a reduction in its onset latency after the initial insomnia period; 2) despite that the initial insomnia period was present throughout the treatment, compared to the effects of the first MS day, the total amount of both NREM sleep and REM sleep significantly increased in subsequent drug days, the total amount of REM sleep reached similar placebo values from day 5; 3) the restoration in the total amount of both sleep states was due to significant increases that occurred from day 5 after the first 6 hours of the MS injection. During the 19-24 hours after MS injections, increases of NREM and REM also resulted statistically significant compared to placebo values. A biphasic depressed and aroused response occurred during early withdrawal. REM sleep rebound was present after MS discontinuation and in the following week. Similarities with effects of opiate chronic administration in other species are discussed. These results support the potential use of the cat for the study of neural mechanisms involved in sleep chronic effects of opiates.

Morphine effects in brainstem-transected cats: II. Behavior and sleep of the decerebrate cat.

Previous studies have shown that opiates suppress both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Furthermore, during the induced insomnia period, characteristic species-specific behaviors occur which are associated with high voltage slow waves in the EEG. This paper investigates the lower brainstem mechanisms involved in the generation of these effects, and describes the action of single morphine doses (0.5, 2.0 or 3.0 mg/kg, i.p.) on the behavior and REM sleep of chronic decerebrate cats. The effects of morphine in the decerebrate cat followed a 3-stage time course similar to that seen in intact cats: (1) autonomic manifestations (3-8 min postdrug); (2) a quiet state (10-60 min postdrug) with behavioral signs of NREM; and (3) a state of activated behavior (1-6 h postdrug), including motor activity and variations in muscle tone. The decerebrate cats also showed a dose-dependent suppression of REM sleep. The present results indicate that: (1) the lower brainstem provides the basic mechanisms for the behavioral deactivation-activation and the autonomic effects of the drug; (2) hypnogenic and synchronizing influences arising from the brainstem might induce the high voltage, slow burst EEG produced by opiates; (3) REM sleep suppression originates only partially in the lower brainstem; (4) the subsidiary action of the prosencephalon seems to be required for the full expression of the drugs effect on behavior and the EEG.

Morphine effects in brainstem-transected cats: I. EEG and ‘sleep-wakefulness’ in the isolated forebrain

In order to examine the prosencephalic mechanisms that might sustain the effects of opiates on EEG and sleep-wakefulness, the actions of morphine sulfate on the EEG and the pupil size were examined in the chronically isolated forebrain of brainstem-transected cats. Single morphine doses (0.5, 2.0 or 3.0 mg/kg, i.p.) administered to these animals produced a long-lasting EEG desynchronization in the isolated forebrain which was associated with pupil mydriasis. The specificity of these morphine effects was shown by the fact that naloxone blocks both the EEG and pupillary effects of the drug. After morphine, spontaneous synchronized EEG with delta waves normally seen in the isolated forebrain preparation was suppressed for 6-18 h, followed by a strong rebound. Both the suppression and rebound in synchronization with delta waves occurred in a dose-dependent manner. The duration of these effects closely paralleled previously reported morphine effects on non-rapid eye movement (NREM) sleep in intact cats. Therefore, in relation to the effects of morphine on EEG and sleep-wakefulness in intact animals, this study suggests that: (1) Morphine suppression of NREM sleep and the subsequent arousal state of the animal are mediated by prosencephalic structures; (2) the generation of the typical neocortical EEG slow burst activity produced by opiates depends on lower brainstem structures.

Re‐examination of the effects of raphe lesions on the sleep/wakefulness cycle states in cats

SUMMARY  To study the specific effects of central superior raphe nucleus (CeSR) lesions on the different sleep/wakefulness cycle states of the cat, nine animals with implanted electrodes for EOG, EMG and EEG recordings were used. Seven cats received diathermocoagulation lesions that destroyed between 13 and 100 percent of the CeSR; the remaining two cats, which suffered lesions in the paramedial region of the oral pontine reticular nucleus (RPO), were used to determine the effects on sleep/wakefulness states caused by damage to adjacent CeSR structures and/or passage fibres. Three prelesion and five postlesion weekly 24h recordings were obtained from each cat. Recordings were scored according to the polygraphic criteria for wakefulness (W), drowsiness (D), slow wave sleep (SWS) and paradoxical sleep (PS). Results indicated that insomnia is not produced exclusively by CeSR lesions, since adjacent paramedial RPO lesions also decrease both SWS and PS; however, increased W occurred after the former while increased D occurred after the latter. Correlation coefficient analyses showed that W is the only state that correlates significantly with the volume of CeSR destroyed. The following correlations between different states of the sleep/wakefulness cycle were, however, significant: W‐D, W‐SWS and SWS‐PS. Disinhibition of W, therefore, and not sleep loss seems to be the primary effect of CeSR lesions. Thus, the CeSR nucleus appears to be involved in arousal mechanisms rather than in direct sleep promotion.