Induction of rapid eye movement sleep by neurotrophin-3 and its co-localization with choline acetyltransferase in mesopontine neurons

Hypocretin (orexin) immunoreactivity in the feline midbrain: Relevance for the generation of wakefulness

Hypocretins (Hcrt) 1 and 2 are two neuropeptides synthesized from neurons that are located in the perifornical area of the lateral hypothalamus. These neurons project diffusely throughout the central nervous system, and have been implicated in the generation and maintenance of wakefulness, as well as in critical physiological processes that occur during this behavioral state, such as motivation. The hypocretinergic projections towards the feline midbrain have not been studied before. Therefore, the aim of the present study was to analyze their relationship to the midbrain neurons, that are critically involved in the control of sleep and wakefulness. With this purpose, we examined the distribution of Hcrt1-positive fibers in the midbrain and pontomesencephalic area of the domestic cat (Felis catus), and their relationship with catecholaminergic and cholinergic neurons by means of single and double immunohistochemistry. Hcrtergic axons with distinctive varicosities and buttons were heterogeneously distributed, exhibiting different densities in distinct regions of the midbrain. High Hcrtergic fiber densities were observed in the periaqueductal gray, interpeduncular nucleus, locus coeruleus and cholinergic mesopontine regions. In addition, we studied in detail the Hcrtergic projection towards the dopaminergic nuclei of the midbrain. While very few Hcrt + fibers were observed in the substantia nigra pars compacta, the highest density of Hcrtergic fibers was found in the dopaminergic ventral periaqueductal gray area (also called A10dc area); appositions between Hcrtergic terminals and dopaminergic somata and dendrites were observed within this area. Because this dopaminergic area has been involved in the control of wakefulness, the present anatomical data provides relevant support about the role of the Hcrtergic system in the generation of this behavioral state.

Decreased cpg15 augments oxidative stress in sleep deprived mouse brain

Sleep deprivation (SD) has detrimental effects on the physiological function of the brain. However, the underlying mechanism remains elusive. In the present study, we investigated the expression of candidate plasticity-related gene 15 (cpg15), a neurotrophic gene, and its potential role in SD using a REM-SD mouse model. Immunofluorescent and Western blot analysis revealed that the expression of cpg15 protein decreased in the hippocampus, ventral group of the dorsal thalamus (VENT), and somatosensory area of cerebral cortex (SSP) after 24-72 h of REM-SD, and the oxidative stress in these brain regions was increased in parallel, as indicated by the ratio of glutathione (GSH) to its oxidative product (GSSG). Over-expression of cpg15 in thalamus, hippocampus, and cerebral cortex mediated by AAV reduced the oxidative stress in these regions, indicating that the decrease of cpg15 might be a cause that augments oxidative stress in the sleep deprived mouse brain. Collectively, the results imply that cpg15 may play a protective function in the SD-subjected mouse brain via an anti-oxidative function. To our knowledge, this is the first time to provide evidences in the role of cpg15 against SD-induced oxidative stress in the brain.

Distribution of MCH-containing fibers in the feline brainstem: Relevance for REM sleep regulation

Neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator are localized in the postero-lateral hypothalamus and incerto-hypothalamic area. These neurons project diffusely throughout the central nervous system and have been implicated in critical physiological processes, such as sleep. Unlike rodents, in the order carnivora as well as in humans, MCH exerts its biological functions through two receptors: MCHR-1 and MCHR-2. Hence, the cat is an optimal animal to model MCHergic functions in humans. In the present study, we examined the distribution of MCH-positive fibers in the brainstem of the cat. MCHergic axons with distinctive varicosities and boutons were heterogeneously distributed, exhibiting different densities in distinct regions of the brainstem. High density of MCHergic fibers was found in the dorsal raphe nucleus, the laterodorsal tegmental nucleus, the periaqueductal gray, the pendunculopontine tegmental nucleus, the locus coeruleus and the prepositus hypoglossi. Because these areas are involved in the control of REM sleep, the present anatomical data support the role of this neuropeptidergic system in the control of this behavioral state.

The truncated TrkB receptor influences mammalian sleep

Brain-derived neurotrophic factor (BDNF) is a neurotrophin hypothesized to play an important role in mammalian sleep expression and regulation. In order to investigate the role of the truncated receptor for BDNF, TrkB.T1, in mammalian sleep, we examined sleep architecture and sleep regulation in adult mice constitutively lacking this receptor. We find that TrkB.T1 knockout mice have increased REM sleep time, reduced REM sleep latency, and reduced sleep continuity. These results demonstrate a novel role for the TrkB.T1 receptor in sleep expression and provide new insights into the relationship between BDNF, psychiatric illness, and sleep.

The role of mesopontine NGF in sleep and wakefulness

The microinjection of nerve growth factor (NGF) into the cat pontine tegmentum rapidly induces rapid eye movement (REM) sleep. To determine if NGF is involved in naturally-occurring REM sleep, we examined whether it is present in mesopontine cholinergic structures that promote the initiation of REM sleep, and whether the blockade of NGF production in these structures suppresses REM sleep. We found that cholinergic neurons in the cat dorso-lateral mesopontine tegmentum exhibited NGF-like immunoreactivity. In addition, the microinjection of an oligodeoxyribonucleotide (OD) directed against cat NGF mRNA into this region resulted in a reduction in the time spent in REM sleep in conjunction with an increase in the time spent in wakefulness. Sleep and wakefulness returned to baseline conditions 2 to 5 days after antisense OD administration. The preceding antisense OD-induced effects occurred in conjunction with the suppression of NGF-like immunoreactivity within the site of antisense OD injection. These data support the hypothesis that NGF is involved in the modulation of naturally-occurring sleep and wakefulness.

MCHergic projections to the nucleus pontis oralis participate in the control of active (REM) sleep

Neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator are located in the lateral hypothalamus and incerto-hypothalamic area and project diffusely throughout the central nervous system, including areas that participate in the generation and maintenance of sleep and wakefulness. Recent studies have shown that hypothalamic MCHergic neurons are active during active sleep (AS), and that intraventricular microinjections of MCH induce AS sleep; however, there are no data available regarding the manner in which MCHergic neurons participate in the control of this behavioral state. Utilizing immunohistochemical and retrograde tracing techniques, we examined, in the cat, projections from MCHergic neurons to the nucleus pontis oralis (NPO), which is considered to be the executive area that is responsible for the generation and maintenance of AS. In addition, we explored the effects on sleep and waking states produced by the microinjection of MCH into the NPO. We first determined that MCHergic fibers and terminals are present in the NPO. We also found that when a retrograde tracer (cholera toxin subunit B) was placed in the NPO MCHergic neurons of the hypothalamus were labeled. When MCH was microinjected into the NPO, there was a significant increase in the amount of AS (19.8+/-1.4% versus 11.9+/-0.2%, P<0.05) and a significant decrease in the latency to AS (10.4+/-4.2 versus 26.6+/-2.3 min, P<0.05). The preceding anatomical and functional data support our hypothesis that the MCHergic system participates in the regulation of AS by modulating neuronal activity in the NPO.

Effects of electrical stimulation of the posterior part of the hypothalamus on the spike activity of neurons in the oral nucleus of the pons

Chronic experiments were performed on four cats to study evoked spike activity in neurons in the oral nucleus of the pons to electrical stimulation of the posterior hypothalamus in the waking, slow-wave sleep, and paradoxical sleep states. A total of 42% of study neurons were found to respond to stimulation during waking. PS-on and PS-off neurons were identified in the oral nucleus of the pons, along with phasic cells showing bursts of activity during the physical manifestations of paradoxical sleep. Stimulation induced inhibitory responses in PS-on neurons, excitatory responses in PS-off neurons, and excitatory and inhibitory responses in 68% and 32% respectively of phasic neurons. The magnitudes of evoked responses in these neurons changed during the sleep-waking cycle. These data demonstrate the involvement of the posterior hypothalamus in controlling the mechanisms of paradoxical sleep, these mechanisms being located in the oral nucleus of the pons.

The role of tropomyosin-related kinase receptors in neurotrophin-induced rapid eye movement sleep in the cat

The microinjection of nerve growth factor and neurotrophin-3 into the rostro-dorsal pontine tegmentum of the cat evokes a state that is comparable to naturally-occurring rapid eye movement sleep. Using two experimental paradigms, we tested the hypothesis that neurotrophin high-affinity receptors (trkA and trkC, tropomyosin-related kinase A and C, respectively) mediate this effect. First, trk and fos immunohistochemistry were combined to determine whether tyrosine kinase receptor-containing neurons in the dorsal pontine tegmentum are active in cats that exhibit long-lasting periods of rapid eye movement sleep following the local microinjection of nerve growth factor. During approximately two hours of recording, nerve growth factor-treated cats spent 59.8% of the time in a rapid eye movement sleep-like state; vehicle-injected (control) animals remained in quiet wakefulness and non-rapid eye movement sleep. Whereas control and nerve growth factor-treated cats exhibited a similar mean number of trkA- and trkC-immunoreactive neurons in the dorsal pontine tegmentum, the number of trkA- and trkC-immunoreactive neurons that expressed Fos, i.e. double-labeled cells that are presumably activated, was significantly larger in cats that were injected with nerve growth factor. Axon terminals contained tyrosine kinase receptor immunoreactivity in this region; many were apposed to Fos-immunoreactive neurons. In addition, patterns of tyrosine kinase receptor and Fos immunoreactivity similar to those observed in nerve growth factor-injected cats were present, in conjunction with long-lasting rapid eye movement sleep, following the microinjection of carbachol into the dorsal pons. In a second series of studies, nerve growth factor or neurotrophin-3 was injected alone or after K-252a, a blocker of tyrosine kinase receptors, into the rostro-dorsal pontine tegmentum. Nerve growth factor or neurotrophin-3 alone produced, with a mean latency of 4 min, a rapid eye movement sleep-like state. However, neurotrophin injections preceded by K-252a were not effective in inducing rapid eye movement sleep. These results indicate that the activation of trkA and trkC receptors in neurons in the pontine tegmentum is responsible, at least in part, for the rapid eye movement sleep-inducing effect of nerve growth factor and neurotrophin-3. Furthermore, the data suggest that these neurotrophins are capable of acting both pre- and postsynaptically to activate pontine neurons that are involved in the generation of rapid eye movement sleep.

Age-related changes in cholinergic neurons in the laterodorsal and the pedunculo-pontine tegmental nuclei of cats: a combined light and electron microscopic study

In aged cats, light microscopic studies revealed significant decrease in the soma size of choline acetyltransferase (ChAT)-positive neurons in the laterodorsal and pedunculo-pontine tegmental nuclei (LDT and PPT), compared with adult control animals. In addition, a significant reduction of the total dendritic length and total dendritic segment number of ChAT-positive neurons was detected in both the LDT and PPT of aged cats. However, in contrast to the changes of soma and dendrites, no significant changes in the number of ChAT-positive neurons in aged were found comparing to that in the control cats in both the LDT and PPT; nor were there differences in the staining intensity of the somata of neurons in the adult and aged cats. Electron microscopic analysis highlighted degenerative changes in cholinergic neurons in the LDT and PPT of aged cats which included somata with intracytoplasmic vacuoles, darkened mitochondria, depletion of dendritic microtubules and severe demyelination of axons. These data indicate that profound atrophic changes occur in cholinergic systems of the LDT and PPT as a consequence of the aging process. These alterations likely reflect the cellular bases for the age-related changes in REM sleep that occur in old animals.

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.

Hypercapnia-induced modifications of neuronal function in the cerebral cortex of newborn piglets

There is significant controversy over the effects of hypercapnia on the human newborn brain. Previous studies have shown that 1 h of an arterial CO2 pressure (Paco2) of 80 mm Hg alters brain cell membrane Na+K+-ATPase enzyme activity in the cerebral cortex of newborn piglets. The present study tests the hypothesis that hypercapnia (either a Paco2 of 65 or 80 mm Hg) results in decreased energy metabolism and alters neuronal nuclear enzyme activity and protein expression, specifically Ca++/calmodulin-dependent kinase (CaMK) IV activity, phosphorylation of cAMP response element binding protein (CREB), and expression of apoptotic proteins in cortical neuronal nuclei of newborn piglets. Studies were performed in 20 anesthetized normoxic piglets ventilated at either a Paco2 of 65 mm Hg, 80 mm Hg, or 40 mm Hg for 6 h. Energy metabolism was documented by ATP and phosphocreatine (PCr) levels. Results show ATP and PCr levels were significantly lower in the hypercapnic groups than the normocapnic. CaMK IV activity, phosphorylated CREB density, and Bax protein expression were all significantly higher in the hypercapnic groups than the normocapnic group. Bcl-2 protein was similar in all three groups, making the ratio of Bax/Bcl-2 significantly higher in the hypercapnic groups than in the normocapnic group. We conclude that hypercapnia alters neuronal energy metabolism, increases phosphorylation of transcription factors, and increases the expression of apoptotic proteins in the cerebral cortex of newborn piglets and therefore may be deleterious to the newborn brain.

Serotonergic reticular formation cells inRana pipiens: Categorization, development, and tectal projections

The reticular formation contributes serotonin to many brain regions, including the optic tectum. We examined the organization and development of its serotonergic neurons in the leopard frog. Serotonin-immunoreactive (5-HT-ir) cells in adult frogs were organized into 10 distinct populations that were identified on the basis of their location and cellular morphology. Populations ranged in size from 16 to 2,066 cells and sometimes spanned more than one previously identified nuclear region. Four of the ten populations were absent in tadpoles. The remaining populations, though present, had two contrasting patterns of development. Half of the populations were established early and showed little change in numbers during tadpole stages but increased in size in juvenile and adult frogs. The other half increased dramatically during tadpole stages but failed to add many more cells in juveniles and adults. Three populations provided 90% of the serotonergic projections from the reticular region to the adult optic tectum. These projections were established early in development and likely originated from the dorsal raphe, median raphe, raphe pontis, raphe magnus, and reticularis pontis oralis. Termination sites were located in midtectal layers and were not topographically organized. We conclude that serotonergic cells within the reticular formation of the leopard frog have an organization similar to that found in mammals, that the overall increase in numbers of these cells is attributable to growth in different cell populations at different stages, and that input from this region changes activity levels in the optic tectum in a global rather than a site-specific manner.

Neurotrophins 3 and 4 enhance non-rapid eye movement sleep in rabbits

We determined if neurotrophins 3 and 4 (NT-3, NT-4) would promote sleep in rabbits. Two doses of NT-3 (50 and 500 ng) and three doses of NT-4 (50, 500 and 2000 ng) were intracerebroventricularly injected at dark onset. Additionally, 500 ng of each NT were injected during the light period. The electroencephalogram (EEG), brain temperature, and motor activity were recorded for 23 h following NT injection. NT-3 (500 ng dose) and NT-4 (500 and 2000 ng doses) injected at dark onset increased the time spent in non-rapid eye movement sleep. After the 2000 ng dose of NT-4, EEG power was reduced.