Immunocytochemical study of the CLIP/ACTH-immunoreactive nerve fibres in the dorsal raphe nucleus of the rat

Neuroendocrine and Peptidergic Regulation of Stress-Induced REM Sleep Rebound

Sleep homeostasis depends on the length and quality (occurrence of stressful events, for instance) of the preceding waking time. Forced wakefulness (sleep deprivation or sleep restriction) is one of the main tools used for the understanding of mechanisms that play a role in homeostatic processes involved in sleep regulation and their interrelations. Interestingly, forced wakefulness for periods longer than 24 h activates stress response systems, whereas stressful events impact on sleep pattern. Hypothalamic peptides (corticotropin-releasing hormone, prolactin, and the CLIP/ACTH18-39) play an important role in the expression of stress-induced sleep effects, essentially by modulating rapid eye movement sleep, which has been claimed to affect the organism resilience to the deleterious effects of stress. Some of the mechanisms involved in the generation and regulation of sleep and the main peptides/hypothalamic hormones involved in these responses will be discussed in this review.

Distribution of ACTH immunoreactivity in the diencephalon and the brainstem of the dog

The present work describes for the first time the anatomical distribution of adrenocorticotropic hormone (ACTH) in the diencephalon and the brainstem of the dog by means of the indirect immunoperoxidase technique. The distribution found in this species agrees well with the pattern found in other mammals and particularly confirms much of the findings reported in the cat. An exception to that concordance is the presence of ACTH perikarya in the nucleus of the solitary tract of the dog, a population that has been described in the rat but not in the cat, and in the ventral mesencephalon. This last population spread across the ventral tegmental area from the raphe to the cerebral peduncle and appeared to be a specific feature of the canine brain. On the other hand, we can not see ACTH fibers in the substantia nigra of the dog which could be a characteristic of the domestic carnivores, opposite to rodents, since these fibers appeared to be also lacking in the cat. Nevertheless, the widespread distribution of ACTH fibers in the brain of the dog included many other nuclei containing monoaminergic neurons which supported a possible role for ACTH in the regulation of these neurotransmitter systems.

Glutamatergic afferent projections to the dorsal raphe nucleus of the rat

Based on WGA-apo-HRP-gold (WG) retrograde tracing, the present study revealed that different subdivisions of the dorsal raphe (DR) such as dorsomedial, ventromedial, lateral wing, and caudal regions receive unique, topographically organized afferent inputs, that are more restricted than previously reported. Phaseolus vulgaris leucoagglutinin anterograde tracing studies confirmed that the medial prefrontal cortex provides the major afferent input to each subdivision of the DR. Double-labeling studies combining WG tracing and glutamate immunostaining indicated that the medial prefrontal cortex, various hypothalamic nuclei including perifornical, lateral, and arcuate nuclei, and several medullary regions such as lateral and medial parabrachial nuclei, and laterodorsal tegmental nucleus provide the major glutamatergic input to each subregion of the DR. It should be noted that the degree of glutamatergic input from these afferent sites was specific for each DR subdivision. The present findings indicated that dorsomedial, ventromedial, lateral wing, and caudal subdivisions of the DR receive excitatory inputs from both cortical and subcortical sites which might be involved in regulation or modulation of a broad range of systems, including sensory and motor functions, arousal and sleep-wake cycle, biorhythmic, cognitive, and affective behaviors.

Immunoelectron microscopic study of beta-endorphinergic synaptic innervation of GABAergic neurons in the dorsal raphe nucleus

Using a preembedding double immunoreactive technique by immunostaining with antirat beta-endorphin and antisynthetic glutamic acid decarboxylase antisera sequentially, the synaptic relationships between beta-endorphinergic neuronal fibers and GABAergic neurons in the dorsal raphe nucleus of the rat were examined at the ultrastructural level. Although both beta-endorphin-like immunoreactive fibers and glutamic acid decarboxylase-like immunoreactive neurons can be found in the mediodorsal and medioventral parts of the dorsal raphe nucleus, the synapses between them were found only in the mediodorsal part. Most of the beta-endorphin-like immunoreactive neuronal fibers contained many dense-cored vesicles. The synapses made by beta-endorphin-like immunoreactive neuronal axon terminals on glutamic acid decarboxylase-like immunoreactive neurons were both symmetrical and asymmetrical, with the latter predominant, especially in the axo-dendritic synapses. Perikarya with beta-endorphin-like immunoreactivity were found only in the ventrobasal hypothalamus. These findings suggest the possibility that the beta-endorphin-producing neurons in the ventrobasal hypothalamus could influence GABAergic neurons in the dorsal raphe nucleus directly by synaptic relationships.

Synaptic contacts between serotonergic and cholinergic neurons in the rat dorsal raphe nucleus and laterodorsal tegmental nucleus

We examined synaptic connectivity between cholinergic and serotonergic neurons in the dorsal raphe nucleus and the laterodorsal tegmental nucleus of the rat. To this purpose we employed two variations (the combination of pre-embedding immunogold-silver intensification with avidin-biotin-peroxidase complex technique and the combination of avidin-biotin-peroxidase/3, 3'-diaminobenzidine/silver-gold intensification with avidin-biotin-peroxidase/3,3'-diaminobenzidine reaction) of a double pre-embedding immunoelectron procedure, using primary antibodies against vesicular acetylcholine transporter and serotonin. At the light-microscopic level, serotonin-like immunoreactive neurons in the dorsal raphe nucleus appeared as reddish black and vesicular acetylcholine transporter-like immunoreactive axon terminals were brown colored using a combination of pre-embedding immunogold-silver technique and avidin-biotin-peroxidase complex technique. Serotonin-like immunoreactive fibers projected to the laterodorsal tegmental nucleus. At the electron microscopy level, with both methods we observed in the dorsal raphe nucleus vesicular acetylcholine transporter-immunopositive axon terminals in synaptic contact with serotonin-like immunoreactive dendrites and, to a lesser degree, with serotonin-like immunoreactive cell bodies. These synapses usually were of the symmetrical type. Occasionally we noted, next to vesicular acetylcholine transporter-immunopositive axon terminals, also immunonegative terminals synapsing with the serotonin-like immunoreactive dendrites. In the laterodorsal tegmental nucleus we found serotonin-like immunoreactive axon terminals and immunonegative terminals forming synapses with vesicular acetylcholine transporter-immunoreactive dendrites. Most synapses formed by the serotonin-like immunopositive terminals were of the asymmetrical type. Our results suggest that serotonergic neurons in the dorsal raphe nucleus and cholinergic neurons in the laterodorsal tegmental nucleus may reciprocally influence each other by means of synaptic connectivity. Such connectivity may serve to regulate pain sensation, or be involved in the regulation of the sleeping-waking cycle.

Influence of a 1-h immobilization stress on sleep and CLIP (ACTH(18-39)) brain contents in adrenalectomized rats

Basal sleep amounts in adrenalectomized rats (AdX), as compared to intact animals, exhibit a significant increase in slow-wave sleep (SWS), a tendency towards an increase in paradoxical sleep (PS), and circadian rhythms (SWS and PS) flattened in amplitude. An immobilization stress (IS) of 1 h, imposed on AdX rats at the beginning of the dark period, is accompanied by an intense polygraphic waking. Just after the IS, SWS amount become significantly higher than in control rats (+44%/11 h of darkness) whereas significant increases of PS occur only 5-10 h after the IS (+24%/11 h of darkness). A specific radioimmunoassay for CLIP (corticotropin-like intermediate lobe peptide or ACTH(18-39)) was performed in biopsies taken either from the nucleus raphe dorsalis (nRD) or the arcuate nucleus (AN). In the nRD, just after the IS, phosphorylated CLIP (Ph-CLIP) concentration exhibits a decreasing tendency, but 4 h later, it increases significantly (+22%, p<0.05). In the AN, Ph-CLIP concentration remains unchanged after the IS as well as 4 h later. These results differ from those previously reported in intact animals also submitted to a 1-h IS, that is, a SWS rebound less marked (+27%/11 h of darkness), a PS rebound more important starting immediately after the IS (+46%/11 h of darkness) and a significant increase in Ph-CLIP occurring just after the end of the restraint. In conclusion, data obtained after a restraint stress either in AdX or in control rats point out the dependence of the PS rebound on the nRD Ph-CLIP concentration.

Influence of a 1 h immobilization stress on sleep states and corticotropin-like intermediate lobe peptide (CLIP or ACTH18-39, Ph-ACTH18-39) brain contents in the rat

A 1 h immobilization stress (IS) was imposed to rats at the beginning of the dark period, i.e., when the animals start to be active. The IS was accompanied by an intense polygraphic waking and followed, over 12 h of the dark period, by a significant rebound of slow-wave sleep (SWS, +17%) and paradoxical sleep (PS, +57%). In order to estimate the IS-related changes in the endogenous concentrations of corticotropin-like intermediate lobe peptide (CLIP, ACTH18-39) and related compounds, a specific radioimmunoassay (RIA) was used. Assays performed in cerebral biopsies taken from arcuate (AN) and raphe dorsalis (nRD) nuclei led to the obtention of 2 main immunoreactive peaks, corresponding to CLIP and its phosphorylated form Ph-CLIP. Just after end of the IS and within the nRD. Ph-CLIP immunoreactivity increased by about 95%. Four hours later, i.e., when PS rebound was maximal, a 37% increase in Ph-CLIP immunoreactivity was measured in the AN. These observations have never been described before. In the blood, at the end of the restraint, CLIP/ACTH1-39 total immunoreactivity was increased by 330%. It returned to baseline level 4 h later. Blood concentration of corticosterone was also increased by 56% at the end of the IS and was close to baseline level 4 h later. Data reported here indicate that the IS first triggers an increase in Ph-CLIP within the nRD. Since the nRD contains sleep permissive components, this increase might be determinant for the SWS and PS rebound induction. The changes observed in the blood as regards CLIP/ACTH1-39 total immunoreactivity and corticosterone concentration testify to the efficacy of the IS and are part of the conventional picture accompanying such a situation. Finally, the increase in Ph-CLIP, occurring in the AN 4 h after the end of the restraint, might be part of the restorative processes necessary to compensate the stress overshoot.

Ultrastructural relationships of the pro-opiomelanocortin axons with the serotoninergic neurons in the dorsal raphe nucleus of the rat

The relationships of the corticotropin-like intermediate lobe peptide (CLIP)/ACTH-immunoreactive axons with the serotoninergic and non-serotoninergic neurons in the dorsal raphe nucleus of the rat were examined by means of a double label immunocytochemical method. It is suggested that the rare contacts established by the CLIP/ACTH-immunoreactive fibers with serotoninergic neurons (cell bodies and dendrites) are not under a synaptic from. In contrast, the contacts with non-serotoninergic neurons were predominantly formed with dendrites and showed a substantial number of synapses.

Sleep permissive components within the dorsal raphe nucleus in the rat

Two peptides known for their hypnogenic properties, CLIP (corticotropin-like intermediate lobe peptide or ACTH 18-39) or VIP (vasoactive intestinal polypeptide), were injected locally into the nucleus raphe dorsalis (nRD) of rats pretreated with p-chlorophenylalanine (PCPA). During the dark period, the PCPA insomnia was primarily associated with a reduction in paradoxical sleep (PS), whereas both slow wave sleep (SWS) and PS were decreased during the light period. Immunohistochemistry of serotonin in PCPA-pretreated animals indicated a clear disappearance of 5-HT fibers in the basal hypothalamus and the nRD as compared to control animals. Local injections of CLIP or VIP in the nRD restored PS and SWS. The positive injection sites corresponded to the anatomical distribution of either CLIP or VIP fibers, i.e., the entire nRD for VIP and the antero-dorsal part of this nucleus for CLIP. The sleep effects obtained in PCPA-pretreated rats involve a non-5-HT sleep permissive component within the nRD upon which these injected peptides act.

Immunoelectron microscopy of beta-endorphinergic synaptic innervation of nitric oxide synthase immunoreactive neurons in the dorsal raphe nucleus

On the basis of the comparing of the distribution of beta-endorphin-like immunoreactive neuronal fibres and nitric oxide synthase-like immunoreactive neurons in the dorsal raphe nucleus, the synapses between the two immunocytochemically identified neurons were studied with a modified DAB-silver-gold intensification double immunostaining technique at the electron microscopic level. Although both of them can be found in the mediodorsal and medioventral parts of the dorsal raphe nucleus, the synapses between them could only be found in the mediodorsal part. The majority of the beta-endorphin-like immunoreactive neuronal fibers contained many dense-cored vesicles. The synapses made by beta-endorphin-like immunoreactive neuronal axon terminals on nitric oxide synthase-like immunoreactive neurons were both symmetrical and asymmetrical with the former predominant, especially in the axo-dendritic ones. beta-Endorphin-like immunoreactive perikarya could only be found in the ventrobasal hypothalamus. These findings suggest the possibility that the beta-endorphin- producing neurons in the ventrobasal hypothalamus could influence nitric oxide synthase-containing neurons in the dorsal raphe nucleus by synaptic relations.

Evidence for a sleep-promoting influence of stress

In the present review the data supporting the existence at the central level of a stress-sleep relation are reported and discussed. An immobilization stress of 1 or 2 hour(s) is accompanied by a marked polygraphic waking and followed by a significant sleep rebound concerning mainly paradoxical sleep (PS). During the restraint, an important release of 5-hydroxyindoles [5-OHles, a good index of serotonin (5-HT) release] occurs in the basal hypothalamus (BH). This release, produced by the nerve endings originating from the nucleus raphe dorsalis (nRD), might secondarily influence the release and/or the synthesis of hypnogenic substances directly involved in the sleep rebound production. Corticotropin-like intermediate lobe peptide (CLIP, or ACTH18-39) is a peptide possessing hypnogenic properties and derived from proopiomelanocortin (POMC) whose perikarya are contained within the BH (arcuate nucleus). The POMC nerve endings impinge on the nucleus raphe dorsalis, a structure containing sleep permissive components upon which CLIP acts to trigger sleep. It remains to be defined how the activity of the neuronal loop described above is impaired under chronic stress conditions.