Rapid eye movement sleep induction by vasoactive intestinal peptide infused into the oral pontine tegmentum of the rat may involve muscarinic receptors

Modification of brain waves and sleep parameters by Citrus reticulata Blanco. cv. Sai-Nam-Phueng essential oil

Background

Citrus essential oil (EO) has been used for mood elevation and sedative hypnotic purposes. However, scientific proofs of its central nervous system (CNS) action remained largely unexplored. This study investigated chemotypes, electrical brain waves and sleep-wake effects of the essential oil from Citrus reticulata in rat model.

Methods

Chemical contents of citrus EO were analyzed using gas chromatography-mass spectrometry (GC–MS). Male Wistar rats implanted with electrodes on the frontal and parietal skulls were used for electroencephalographic (EEG) recording while inhaling the citrus EO (200 μl on cotton wool). Diazepam (10 mg/kg, p.o.) was used as a standard anxiolytic drug. EEG frequency analyses were performed by using Fast Fourier transform. All data were statistical analyzed using One-way ANOVA followed by Tukey's test.

Results

GC–MS analysis revealed d-limonene (95.7%) as a major constituent of citrus EO. The EEG results showed that overall EEG patterns of citrus EO effects were relatively similar to that of diazepam. However, significant differences between treatments were seen from sleep-wake analyses. Diazepam significantly increased episode numbers of awake and non-rapid eye movement (REM) sleep and reduced averaged episode duration. On the other hand, the citrus EO significantly decreased REM sleep latency and increased total time and episode numbers of REM sleep.

Conclusion

These findings demonstrated unique CNS effects of C. reticulata EO with EEG fingerprints and sleep-wake profiles. The data might be useful for citrus essential oil sub-classification and clinical application.

Wakefulness/sleep architecture and electroencephalographic activity in mice lacking the translational repressor 4E-BP1 or 4E-BP2

Sleep and sleep loss are affecting protein synthesis in the brain, but the contribution of translational control to wakefulness and sleep regulation remains poorly understood. Here, we studied the role of two suppressors of protein synthesis, the eukaryotic translation initiation factor 4E-binding proteins 1 and 2 (4E-BP1 and 4E-BP2), in sleep architecture and electroencephalographic (EEG) activity as well as in the EEG and molecular responses to acute sleep loss. The EEG of mice mutant for the genes encoding 4E-BP1 or 4E-BP2 (Eif4ebp1 and Eif4ebp2 knockout [KO] mice) was recorded under undisturbed conditions and following a 6-hour sleep deprivation (SD). The effect of SD on the expression of genes known to respond to SD was also measured in the prefrontal cortex of Eif4ebp1 and Eif4ebp2 KO mice. Eif4ebp1 KO mice differed from wild-type mice in parameters of wakefulness and sleep quantity and quality, and more subtly in the gene expression response to SD. For instance, Eif4ebp1 KO mice spent more time in slow-wave sleep (SWS) and showed altered baseline 24-h time courses of SWS delta (1-4 Hz) activity and sigma (10-13 Hz) activity. Eif4ebp2 KO mice differed from wild-type mice only for wakefulness and sleep quality, expressing changes in EEG spectral activity generally revealed during and after SD. These findings suggest different roles of effectors of translational control in the regulation of wakefulness and sleep and of synchronized cortical activity.

Feasibility of deep brain stimulation for controlling the lower urinary tract functions: An animal study

OBJECTIVE

To evaluate the feasibility of deep brain stimulation (DBS) and compare the potential of four DBS targets in rats for regulating bladder activity: the periaqueductal gray (PAG), locus coeruleus (LC), rostral pontine reticular nucleus (PnO), and pedunculopontine tegmental nucleus (PPTg).

METHODS

A bipolar stimulating electrode was implanted. The effects of DBS on the inhibition and activation of micturition reflexes were investigated by using isovolumetric intravesical pressure recordings.

RESULTS

PAG DBS at 2-2.5 V, PnO DBS at 2-2.5 V, and PPTg DBS at 1.75-2.5 V nearly completely inhibited reflexive isovolumetric bladder contractions. By contrast, LC DBS at 1.75 and 2 V slightly augmented reflexive isovolumetric bladder contractions in rats. DBSs on PnO and PPTg at higher intensities (2.5-5 V) demonstrated a higher success rate and larger contraction area evocation in activating bladder contractions in a partially filled bladder. DBS targeting the PPTg was most efficient in suppressing reflexive isovolumetric bladder contractions.

CONCLUSION

PPTg DBS demonstrated stable results and high potency for controlling bladder contractions. PPTg might be a promising DBS target for developing new neuromodulatory approaches for the treatment of bladder dysfunctions.

SIGNIFICANCE

DBS could be a potential approach to manage bladder function under various conditions.

Decreased REM sleep and altered circadian sleep regulation in mice lacking vasoactive intestinal polypeptide

OBJECTIVES

Vasoactive intestinal polypeptide (VIP) has been implicated in sleep regulation as a promoter of rapid eye movement (REM) sleep. Previous work has shown that the amount of time spent in REM sleep is increased by intracerebroventricular administration of VIP, and reduced by treatment with VIP antagonists or antibodies against VIP. A variety of evidence suggests that VIP is critical for normal expression of circadian rhythmicity of diverse physiological and behavioral parameters. In the present study, we investigated the role of this peptide in sleep regulation using VIP-deficient (VIP-/-) mice.

METHODS

EEG/EMG sleep-wake patterns were recorded in VIP-/- mice and their wild-type littermate controls under normal light-dark (LD), constant darkness (DD) and sleep deprivation conditions.

RESULTS

VIP-/- mice exhibited reduced REM sleep time over the 24-h cycle while total daily amounts of NREM sleep and wakefulness were not altered significantly. The reduced REM sleep time in VIP-/- mice occurred entirely during the day due to a reduction in the duration, but not the frequency, of REM sleep bouts. In response to sleep deprivation, compensatory rebounds in NREM sleep and REM sleep were also attenuated in VIP-/- mice. Finally, the loss of VIP altered the temporal distribution of sleep in that the VIP -/- mice exhibited smaller amplitude rhythms in total sleep, NREM sleep, and REM sleep under both LD and DD.

CONCLUSIONS

These results indicate that VIP regulates the duration of REM sleep, sleep homeostatic mechanisms as well as the temporal patterning of sleep.

Pituitary adenylate cyclase-activating polypeptide and its receptors: 20 years after the discovery

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

A novel GABAergic afferent input to the pontine reticular formation: the mesopontine GABAergic column

Pharmacological manipulations of gamma-aminobutyric acid (GABA) neurotransmission in the nucleus pontis oralis (PnO) of the rat brainstem produce alterations in sleep/wake behavior. Local applications of GABA(A) receptor antagonists and agonists increase REM sleep and wake, respectively. These findings support a role for GABAergic mechanisms of the PnO in the control of arousal state. We have been investigating sources of GABA innervation of the PnO that may interact with local GABA(A) receptors in the control of state. Utilizing a retrograde tracer, cholera toxin-B subunit (CTb), injected into the PnO and dual-label immunohistochemistry with an antibody against glutamic acid decarboxalase-67 (GAD67), we report on a previously unidentified GABAergic neuronal population projecting to the contralateral PnO appearing as a column of cells, with long-axis in the sagittal plane, extending through the midbrain and pons. We refer to these neurons as the mesopontine GABAergic column (MPGC). The contiguous, columnar, anatomical distribution suggests operation as a functional neural system, which may influence expression of REM sleep, wake and other behaviors subserved by the PnO.

Blockade of GABA, type A, receptors in the rat pontine reticular formation induces rapid eye movement sleep that is dependent upon the cholinergic system

The brainstem reticular formation is an area important to the control of rapid eye movement (REM) sleep. The antagonist of GABA-type A (GABA(A)) receptors, bicuculline methiodide (BMI), injected into the rat nucleus pontis oralis (PnO) of the reticular formation resulted in a long-lasting increase in REM sleep. Thus, one factor controlling REM sleep appears to be the number of functional GABA(A) receptors in the PnO. The long-lasting effect produced by BMI may result from secondary influences on other neurotransmitter systems known to have long-lasting effects. To study this question, rats were surgically prepared for chronic sleep recording and additionally implanted with guide cannulas aimed at sites in the PnO. Multiple, 60 nl, unilateral injections were made either singly or in combination. GABA(A) receptor antagonists, BMI and gabazine (GBZ), produced dose-dependent increases in REM sleep with GBZ being approximately 35 times more potent than BMI. GBZ and the cholinergic agonist, carbachol, produced very similar results, both increasing REM sleep for about 8 h, mainly through increased period frequency, with little reduction in REM latency. Pre-injection of the muscarinic antagonist, atropine, completely blocked the REM sleep-increase by GBZ. GABAergic control of REM sleep in the PnO requires the cholinergic system and may be acting through presynaptic modulation of acetylcholine release.

Neuropeptide interactions and REM sleep: a role for Urotensin II?

Urotensin II (UII) is a peptide with structural similarity to the somatostatin family with potent vasoconstrictor activity. UII receptor is expressed broadly in the periphery, and most notably in the heart and microvessels. In the brain, the UII receptor can be detected in the spinal cord and in cholinergic nuclei in the brainstem known to be involved in REM sleep regulation. Recent data suggest that, in addition to their vasoactive properties, UII receptor ligands may have excitatory activity on a selective group of neurons that modulate REM sleep. This review focuses on the implications of these findings for the neurobiology of REM sleep regulation and discusses the possible impact of UII and other neuropeptides on the balance of the alternation between sleep states.

Tetrodotoxin inactivation of pontine regions: Influence on sleep–wake states

Studies using various methodologies have implicated n. reticularis pontis oralis (RPO) and n. subcoeruleus (SubC) in the generation of rapid eye movement sleep (REM). In rats, electrolytic lesions in these regions may give rise to the phenomenon of REM without atonia (REM-A), in which the electrophysiological features of REM are normal except that atonia is absent and elaborate behaviors may be exhibited. However, electrolytic lesions damage both cell bodies and fibers of passage, and the neural reorganization and adaptation that can occur post-lesion can complicate interpretation. Tetrodotoxin (TTX) is a sodium channel blocker that temporarily inactivates both neurons and fibers of passage and thus may be functionally equivalent to an electrolytic lesion, but without allowing time for neural adaptation. In this study, we examined the influence of microinjections of TTX into RPO and SubC on sleep in freely behaving rats. Rats (90 day old male Sprague-Dawley) were implanted with electrodes for recording EEG and EMG. Guide cannulae were implanted aimed into RPO or SubC. Each animal received one unilateral microinjection (TTXUH: 5.0 ng/0.2 microl) and two bilateral microinjections (TTXBL: 2.5 ng/0.1 microl; TTXBH: 5.0 ng/0.2 microl) of TTX, and control microinjections of saline alone (SAL). The injections were made 2 h following lights on, and sleep was recorded for the subsequent 22 h. Sleep was scored from computerized records in 10 s epochs. Recordings from the 10-h light period and the 12-h dark period were examined separately. TTX inactivation of RPO could decrease REM and non-REM (NREM), whereas inactivation of SubC produced relatively more specific decreases in REM with smaller effects on NREM. The results complement studies that have implicated RPO and SubC in REM generation. REM-A was not observed, suggesting that REM-A is a complex phenomenon that requires time for reorganization of the nervous system after insult.

Microinjection of neostigmine into the pontine reticular formation of the mouse: further evaluation of a proposed REM sleep enhancement technique

Microinjections of cholinergic agonists into the pontine reticular formation (PRF) powerfully induce rapid eye movement sleep (REMS) in cats but have comparatively weaker effects in rats. Recently, the cholinomimetic neostigmine has been reported to strongly enhance REMS following microinjection into the PRF of the mouse. That study used behavioral assessments of locomotion in lieu of electrophysiological measures of muscle tone to identify REMS. We sought to confirm that the behavioral state induced in mice by PRF injections of neostigmine meets standard electroencephalogram (EEG) and electromyogram (EMG) criteria for defining REMS. Cortical EEG, nuchal muscle EMG, and PGO waves were recorded from male C57BL/6N mice with chronic indwelling cannulae for the delivery of neostigmine to the PRF. Recordings were made during midday following injections of neostigmine (8.8 mM, 50 nl), 2 h after lights on (LD 12:12). Neostigmine induced a behavioral state characterized by low amplitude, highly desynchronized cortical EEG with little theta, no PGO waves, and a sustained high muscle tone. Behavioral states meeting standard criteria for slow-wave sleep (SWS) and REMS were significantly suppressed compared to baseline recordings, and REMS onset was delayed by 3 h. Consistent with earlier reports, neostigmine did strongly suppress locomotor activity in open field tests and in the home cage. Due to the failure to meet criteria for defining REMS, we conclude that neostigmine microinjection into the PRF of the mouse induces an abnormal waking state rather than REMS.

Dynamics of neuron spike activity in the oral nucleus of the pons during the sleep-waking cycle in cats

Chronic experiments on five cats were performed to study the spike activity of neurons in the oral nucleus of the pons during waking, slow-wave sleep, and paradoxical sleep. Groups of neurons with different dynamics of spike frequency were identified. Cells with rare discharges during waking and slow-wave sleep and maximum spike frequencies in the phasic stage of paradoxical sleep were regarded as PS-on neurons. Cells discharging at maximum frequency during waking, with decreases in frequency during slow-wave sleep and further decreases in paradoxical sleep, were regarded as PS-off neurons. Cells showing decreases in discharge frequency on the transition from waking to slow-wave sleep and increases in discharge frequency in paradoxical sleep, with grouped spikes during oculomotor activity, appeared to be responsible for generating the phasic phenomena of paradoxical sleep. The question of the involvement of neurons of different populations in the mechanisms of paradoxical sleep is discussed.

GABAergic regulation of REM sleep in reticularis pontis oralis and caudalis in rats

The nucleus reticularis pontis oralis (RPO) and nucleus reticularis pontis caudalis (RPC) are implicated in the generation of rapid eye movement sleep (REM). Work in cats has indicated that GABA in RPO plays a role in the regulation of REM. We assessed REM after local microinjections into RPO and RPC of the gamma-aminobutyric acid-A (GABA(A)) agonist, muscimol (MUS), and the GABA(A) antagonist, bicuculline (BIC). Rats (90-day-old male Sprague-Dawley) were implanted with electrodes for recording electroencephalographs (EEG) and electromyographs (EMG). Guide cannulae were aimed into RPO (n = 9) and RPC (n = 8) for microinjecting MUS (200, 1,000.0 microM) and BIC (0.056, 0.333, 1.0, 1,000.0, and 10,000.0 microM). Animals received bilateral microinjections of saline, MUS, and BIC (0.2 microl microinjected at 0.1 microl/min) into each region followed by 6-h sleep recordings. In RPO, MUS (1,000.0 microM) suppressed REM and BIC (1,000.0 microM) enhanced REM. In RPC, MUS (200, 1,000.0 microM) suppressed REM, but BIC (1,000.0 microM and less) did not significantly affect REM. Higher concentrations of BIC (10,000.0 microM) injected into RPO (n = 9) and RPC (n = 4) produced wakefulness and escape behavior. The results indicate that GABA in RPO/RPC is involved in the regulation of REM and suggest site-specific differences in this regulation.

Enhancement of rapid eye movement sleep in the rat by actions at A1 and A2a adenosine receptor subtypes with a differential sensitivity to atropine

The adenosine agonist cyclohexaladenosine injected into the medial pontine reticular formation of the rat induces a long-lasting increase in rapid eye movement sleep. To investigate the adenosine receptor-subtype(s) mediating this effect, the dose-response relationships for increasing rapid eye movement sleep by two highly selective adenosine receptor agonists were compared. Rats were surgically prepared for chronic sleep recording and bilateral guide cannulae were aimed at medial sites in the caudal, oral pontine reticular formation. Injections were made unilaterally in 60 nl volumes within 1 h after lights-on. The adenosine agonists used were A1-selective cyclohexaladenosine (10(-6)-10(-4) M) and A2a-selective CGS 21680 (10(-7)-10(-3) M). Each animal also received a series of three, paired-consecutive injections of the muscarinic receptor antagonist atropine (4x10(-3) M) followed by the lowest effective dose of each agonist or saline as control. The A2a receptor agonist, CGS 21680, was one order of magnitude more potent than the A1 receptor agonist, cyclohexaladenosine, in inducing rapid eye movement sleep increases. Preinjection of atropine at a dose that did not itself affect rapid eye movement sleep resulted in antagonism of CGS 21680, but not cyclohexaladenosine-induced rapid eye movement sleep. The differential sensitivity of these ligands to antagonism by atropine supports the conclusion that both A1 and A2a adenosine receptor subtypes in the reticular formation subserve agonist-induced rapid eye movement sleep and that they do so by independent mechanisms. The A2a mechanism requires the cholinergic system and may act through the increased release of acetylcholine. The A1 mechanism operates at a different locus possibly through an inhibition of GABA neurotransmission.

Substance P in the descending cholinergic projection to REM sleep-induction regions of the rat pontine reticular formation: anatomical and electrophysiological analyses

Release of acetylcholine within the pontine reticular formation (PRF) from the axon terminals of mesopontine cholinergic neurons has long been hypothesized to play an important role in rapid eye movement (REM) sleep generation. As some of these cholinergic neurons are known to contain substance P (SP), we used anatomical, electrophysiological and pharmacological techniques to characterize this projection in the rat. Double immunofluorescence demonstrated that 16% of all cholinergic neurons within the mesopontine tegmentum contained SP; this percentage increased to 27% in its caudal regions. When double immunofluorescence was combined with retrograde tracing techniques, it was observed that up to 11% of all SP-containing cholinergic neurons project to the PRF. Whole-cell patch-clamp recordings from in vitro brainstem slices revealed that SP administration depolarized or evoked an inward current in a dose-dependent manner in all PRF neurons examined, and that these effects were antagonized by a SP antagonist. The amplitude of the SP-induced inward current varied with changes in the Na+ concentration, did not reverse at the calculated K+ or Cl- equilibrium potentials, and was not attenuated in the presence of tetrodotoxin, low Ca2+ concentration or caesium ions. These data suggest that activation of a tetrodotoxin-insensitive cation channel(s) permeable to Na+ is responsible for a SP-induced inward current at resting membrane potentials. The depolarizing actions of SP appeared to be primarily due to activation of the adenylate cyclase pathway, and were additive with cholinergic receptor activation even at maximal concentrations. These data indicate that SP is colocalized in a subpopulation of mesopontine tegmental cholinergic neurons projecting to REM sleep-induction regions of the PRF, and that actions of these two neuroactive substances on PRF neurons are additive. If SP is coreleased with acetylcholine, the additive actions of the two neurotransmitters might heighten the excitability of postsynaptic PRF neurons and ensure the initiation and maintenance of REM sleep.

Interactions between cholinergic and GABAergic neurotransmitters in and around the locus coeruleus for the induction and maintenance of rapid eye movement sleep in rats

The noradrenergic "REM-off" neurons in the locus coeruleus cease firing, whereas some cholinergic and non-cholinergic "REM-on" neurons increase firing during rapid eye movement sleep. A reciprocal interaction between these neurons was proposed. However, acetylcholine did not inhibit neurons in the locus coeruleus. Nevertheless, since GABA levels increase during rapid eye movement sleep and picrotoxin injections into the locus coeruleus reduced rapid eye movement sleep, it was hypothesized that GABA in the locus coeruleus might play an intermediary inhibitory role for rapid eye movement sleep regulation. Therefore, the effects of GABA or carbachol (a mixed cholinergic agonist receptor) alone, as well as an agonist of one in presence of an antagonist of the other, in the locus coeruleus were investigated on sleep-wakefulness and rapid eye movement sleep. The cholinergic agonist carbachol increased, while the muscarinic antagonist receptor scopolamine decreased, the frequency of induction of rapid eye movement sleep per hour. In contrast, GABA and picrotoxin increased and decreased, respectively, the duration of rapid eye movement sleep per episode. However, when carbachol was injected in the presence of picrotoxin or GABA was injected in the presence of scopolamine, the effect of GABA or picrotoxin was dominant. Microinjection of both scopolamine and picrotoxin in combination reduced both the frequency of initiation as well as the duration per episode of rapid eye movement sleep. From these results we suggest that in the locus coeruleus cholinergic input modulates the frequency of induction of rapid eye movement sleep and this action is mediated through GABA interneurons, whereas the length of rapid eye movement sleep per episode is maintained by the presence of an optimum level of GABA. A model of neural connections for initiation and maintenance of rapid eye movement sleep is proposed and discussed.

Muscarinic and PACAP receptor interactions at pontine level in the rat: significance for REM sleep regulation

Cholinergic and PACAPergic systems within the oral pontine reticular nucleus (PnO) play a critical role in REM sleep generation in rats. In this present work, we have investigated whether REM sleep enhancement induced by carbachol (a cholinergic agonist) or PACAP, depends on an interaction between muscarinic and PACAP receptors. This hypothesis was tested by recording sleep-wake cycles in freely moving rats injected into the PnO with PACAP in combination with the muscarinic receptor antagonist atropine, or with carbachol in combination with the PACAP receptor antagonist PACAP6-27. When administered alone, PACAP (3 pmol) or carbachol (110 pmol) induced an enhancement of REM sleep during 8 h (+61%, n = 8; +70%, n = 5), which was totally prevented by infusion of atropine (290 pmol) for PACAP, or of PACAP6-27 (3 pmol) for carbachol. Quantitative autoradiographic studies indicated that (i) PACAP (10-9-10-7 M) induced in the PnO an increase (+35%) of the specific binding of the muscarinic antagonist [3H]quinuclidinyl benzylate, which could be completely prevented by PACAP6-27 (IC50 = 8 x 10-8 M) and (ii) both carbachol and PACAP enhanced [35S]GTP-gamma-S binding in a concentration-dependent manner in the PnO. The maximal increase due to carbachol was significantly higher in the presence (+126%) than in the absence (+102%) of PACAP (0.1 microM). These data showed that interactions between muscarinic and PACAP receptors do exist within the PnO and play a role in the local mechanisms of REM sleep control in the rat.

Infusion of adenylyl cyclase inhibitor SQ22,536 into the medial pontine reticular formation of rats enhances rapid eye movement sleep

Microinjection of cholinergic and adenosinergic agonists into the medial pontine reticular formation of rats produces long lasting increases in the time spent in rapid eye movement sleep. Several G-protein-coupled muscarinic and adenosinergic receptors share a common action of inhibition of adenylyl cyclase and inhibition of cyclic adenosine monophosphate. Inhibition of cyclic adenosine monophosphate has been implicated in the mechanism of rapid eye movement sleep induction in the cat. We sought to determine whether a direct inhibitor of adenylyl cyclase microinjected into the rat reticular formation at sites where muscarinic and adenosinergic agonists are effective in producing long lasting elevations in rapid eye movement sleep also result in similar effects on the sleep/wake cycle. The caudal, oral pontine reticular formation was unilaterally infused with 60 nl volumes of carbachol (0.1-1.1mM) and N(6)-cyclohexyladenosine (0.1mM) each within 1h of lights on. Sites effective for significantly elevating rapid eye movement sleep for the 8h following microinjection of both receptor agonists were additionally injected with the adenylyl cyclase inhibitor, SQ22,536 (0.1M). Pontine injections of SQ22,536 resulted in significant mean increases in rapid eye movement sleep time and rapid eye movement sleep period frequency at all of these sites. As with the receptor agonists, SQ22,536 did not alter latency to rapid eye movement sleep onset. Rapid eye movement sleep amounts were observed to be significantly elevated by SQ22,536 at two days, but not at four days, following a single microinjection. These data implicate inhibition of cyclic adenosine monophosphate in the pons of the rat as a mechanism involved in the long-term modulation of rapid eye movement sleep. This mechanism may underlie the homeostatic regulation exhibited by this sleep-state.

Long-term enhancement of REM sleep by the pituitary adenylyl cyclase-activating polypeptide (PACAP) in the pontine reticular formation of the rat

In rats, rapid eye movement (REM) sleep can be elicited by microinjection of vasoactive intestinal polypeptide (VIP) into the oral pontine reticular nucleus (PnO). In the present study, we investigated whether this area could also be a REM-promoting target for a peptide closely related to VIP: the pituitary adenylyl cyclase-activating polypeptide (PACAP). When administered into the posterior part of the PnO, but not in nearby areas, of freely moving chronically implanted rats, PACAP-27 and PACAP-38 (0.3 and 3 pmol) induced a marked enhancement (60-85% over baseline) of REM sleep for 8 h that could be prevented by prior infusion of the antagonist PACAP-(6-27) (3 pmol) into the same site. Moreover, injections of PACAP into the centre of the posterior PnO resulted in REM sleep enhancement which could last for up to 11 consecutive days. Quantitative autoradiography using [125I]PACAP-27 revealed the presence in the PnO of specific binding sites with high affinity for PACAP-27 and PACAP-38 (IC50 = 2.4 and 3.2 nM, respectively), but very low affinity for VIP (IC50 > 1 microM). These data suggest that PACAP within the PnO may play a key role in REM sleep regulation, and provide evidence for long-term (several days) mechanisms involved in such a control. PAC1 receptors which have a much higher affinity for PACAP than for VIP might mediate this long-term action of PACAP on REM sleep.