Synaptic interactions between perifornical lateral hypothalamic area, locus coeruleus nucleus and the oral pontine reticular nucleus are implicated in the stage succession during sleep-wakefulness cycle

Effects of diet and ovariectomy on Toxoplasma gondii brain infection: functional alterations and neuronal loss in rats

Epidemiological evidence associates Toxoplasma gondii latent infection with the development of neuropsychiatric disorders, and various immunological and environmental factors play key pathophysiological roles through host immune response alterations. We investigated the cognitive and motor alterations occurring in the terminal stage of T. gondii infection in rats, and whether a low-protein diet, a high-fat diet or ovariectomy may accelerate their development, given the role of malnutrition and menopause on immunity and resistance to infection. In two sets of experiments, 2-month-old (157.5 ± 4.3 g, n = 42) male (n = 18) and female (n = 24) Wistar rats were infected with T. gondii (ATCC 40050). Open-field and elevated plus maze tests were performed in the terminal stage of infection first and then in the early stage in low-protein diet-fed, high-fat diet-fed and ovariectomized infected rats. Late-stage (90 days) infected and early-stage (17 days) low-protein diet-fed groups showed significant decreases in body weight (42.42%↓, P = 0.016 and 57.14%↓, P < 0.001 versus non-infected, respectively), increases in body temperature (P = 0.001 and P < 0.001, respectively), decreases in blood glucose levels (P = 0.006 and P = 0.020, respectively), signs of cognitive and motor impairment and lower neuron counts. The alterations observed in high-fat diet-fed and ovariectomized infected animals were milder. Low-protein diet feeding to T. gondii-infected rats accelerated the occurrence of the infection terminal stage. Thus, a diet low in proteins could transform a slow early-stage T. gondii infection into an active neurotoxoplasmosis with neuropsychiatric manifestations and possible neurodegeneration in rats.

Therapeutic potential of Garcinia kola against experimental toxoplasmosis in rats

Cerebral toxoplasmosis, the most common opportunistic infection in immunocompromised individuals, is increasingly reported in immunocompetent individuals due to mutant strains of Toxoplasma gondii, which, furthermore, are reported to be resistant to available treatments. We assessed the therapeutic potential of Garcinia kola, a medicinal plant reported to have antiplasmodial and neuroprotective properties, against experimental toxoplasmosis in rats. Severe toxoplasmosis was induced in male Wistar rats (156.7 ± 4.1 g) by injecting them with 10 million tachyzoites in suspension in 500 µl of saline (intraperitoneal), and exclusive feeding with a low-protein diet [7% protein (weight by weight)]. Then, animals were treated with hexane, dichloromethane, and ethyl acetate fractions of Garcinia kola. Footprints were analysed and open-field and elevated plus maze ethological tests were performed when symptoms of severe disease were observed in the infected controls. After sacrifice, blood samples were processed for Giemsa staining, organs were processed for haematoxylin and eosin staining, and brains were processed for Nissl staining and cell counting. Compared with non-infected animals, the infected control animals had significantly lower body weights (30.27%↓, P = 0.001), higher body temperatures (P = 0.033) during the sacrifice, together with signs of cognitive impairment and neurologic deficits such as lower open-field arena centre entries (P < 0.001), elevated plus maze open-arm time (P = 0.029) and decreased stride lengths and step widths (P < 0.001), as well as neuronal loss in various brain areas. The ethyl acetate fraction of Garcinia kola prevented or mitigated most of these signs. Our data suggest that the ethyl acetate fraction of Garcinia kola has therapeutic potential against cerebral toxoplasmosis.

Recruitment of Corticotropin-Releasing Hormone (CRH) Neurons in Categorically Distinct Stress Reactions in the Mouse Brain

Corticotropin-releasing hormone (CRH) neurons in the paraventricular hypothalamic nucleus (PVH) are in the position to integrate stress-related information and initiate adaptive neuroendocrine-, autonomic-, metabolic- and behavioral responses. In addition to hypophyseotropic cells, CRH is widely expressed in the CNS, however its involvement in the organization of the stress response is not fully understood. In these experiments, we took advantage of recently available Crh-IRES-Cre;Ai9 mouse line to study the recruitment of hypothalamic and extrahypothalamic CRH neurons in categorically distinct, acute stress reactions. A total of 95 brain regions in the adult male mouse brain have been identified as containing putative CRH neurons with significant expression of tdTomato marker gene. With comparison of CRH mRNA and tdTomato distribution, we found match and mismatch areas. Reporter mice were then exposed to restraint, ether, high salt, lipopolysaccharide and predator odor stress and neuronal activation was revealed by FOS immunocytochemistry. In addition to a core stress system, stressor-specific areas have been revealed to display activity marker FOS. Finally, activation of CRH neurons was detected by colocalization of FOS in tdTomato expressing cells. All stressors resulted in profound activation of CRH neurons in the hypothalamic paraventricular nucleus; however, a differential activation of pattern was observed in CRH neurons in extrahypothalamic regions. This comprehensive description of stress-related CRH neurons in the mouse brain provides a starting point for a systematic functional analysis of the brain stress system and its relation to stress-induced psychopathologies.

Insulin-like growth factor I sensitization rejuvenates sleep patterns in old mice

Sleep disturbances are common during aging. Compared to young animals, old mice show altered sleep structure, with changes in both slow and fast electrocorticographic (ECoG) activity and fewer transitions between sleep and wake stages. Insulin-like growth factor I (IGF-I), which is involved in adaptive changes during aging, was previously shown to increase ECoG activity in young mice and monkeys. Furthermore, IGF-I shapes sleep architecture by modulating the activity of mouse orexin neurons in the lateral hypothalamus (LH). We now report that both ECoG activation and excitation of orexin neurons by systemic IGF-I are abrogated in old mice. Moreover, orthodromical responses of LH neurons are facilitated by either systemic or local IGF-I in young mice, but not in old ones. As orexin neurons of old mice show dysregulated IGF-I receptor (IGF-IR) expression, suggesting disturbed IGF-I sensitivity, we treated old mice with AIK3a305, a novel IGF-IR sensitizer, and observed restored responses to IGF-I and rejuvenation of sleep patterns. Thus, disturbed sleep structure in aging mice may be related to impaired IGF-I signaling onto orexin neurons, reflecting a broader loss of IGF-I activity in the aged mouse brain.

The connections of Locus Coeruleus with hypothalamus: potential involvement in Alzheimer's disease

The hypothalamus and Locus Coeruleus (LC) share a variety of functions, as both of them take part in the regulation of the sleep/wake cycle and in the modulation of autonomic and homeostatic activities. Such a functional interplay takes place due to the dense and complex anatomical connections linking the two brain structures. In Alzheimer's disease (AD), the occurrence of endocrine, autonomic and sleep disturbances have been associated with the disruption of the hypothalamic network; at the same time, in this disease, the occurrence of LC degeneration is receiving growing attention for the potential roles it may have both from a pathophysiological and pathogenetic point of view. In this review, we summarize the current knowledge on the anatomical and functional connections between the LC and hypothalamus, to better understand whether the impairment of the former may be responsible for the pathological involvement of the latter, and whether the disruption of their interplay may concur to the pathophysiology of AD. Although only a few papers specifically explored this topic, intriguingly, some pre-clinical and post-mortem human studies showed that aberrant protein spreading and neuroinflammation may cause hypothalamus degeneration and that these pathological features may be linked to LC impairment. Moreover, experimental studies in rodents showed that LC plays a relevant role in modulating the hypothalamic sleep/wake cycle regulation or neuroendocrine and systemic hormones; in line with this, the degeneration of LC itself may partly explain the occurrence of hypothalamic-related symptoms in AD.

Altered sleep intensity upon DBS to hypothalamic sleep-wake centers in rats

Deep brain stimulation (DBS) has been scarcely investigated in the field of sleep research. We hypothesize that DBS onto hypothalamic sleep- and wake-promoting centers will produce significant neuromodulatory effects and potentially become a therapeutic strategy for patients suffering severe, drug-refractory sleep–wake disturbances. We aimed to investigate whether continuous electrical high-frequency DBS, such as that often implemented in clinical practice, in the ventrolateral preoptic nucleus (VLPO) or the perifornical area of the posterior lateral hypothalamus (PeFLH), significantly modulates sleep–wake characteristics and behavior. We implanted healthy rats with electroencephalographic/electromyographic electrodes and recorded vigilance states in parallel to bilateral bipolar stimulation of VLPO and PeFLH at 125 Hz and 90 µA over 24 h to test the modulating effects of DBS on sleep–wake proportions, stability and spectral power in relation to the baseline. We unexpectedly found that VLPO DBS at 125 Hz deepens slow-wave sleep (SWS) as measured by increased delta power, while sleep proportions and fragmentation remain unaffected. Thus, the intensity, but not the amount of sleep or its stability, is modulated. Similarly, the proportion and stability of vigilance states remained altogether unaltered upon PeFLH DBS but, in contrast to VLPO, 125 Hz stimulation unexpectedly weakened SWS, as evidenced by reduced delta power. This study provides novel insights into non-acute functional outputs of major sleep–wake centers in the rat brain in response to electrical high-frequency stimulation, a paradigm frequently used in human DBS. In the conditions assayed, while exerting no major effects on the sleep–wake architecture, hypothalamic high-frequency stimulation arises as a provocative sleep intensity-modulating approach.

Connection Input Mapping and 3D Reconstruction of the Brainstem and Spinal Cord Projections to the CSF-Contacting Nucleus

Objective

To investigate whether the CSF-contacting nucleus receives brainstem and spinal cord projections and to understand the functional significance of these connections.

Methods

The retrograde tracer cholera toxin B subunit (CB) was injected into the CSF-contacting nucleus in Sprague-Dawley rats according the previously reported stereotaxic coordinates. After 7–10 days, these rats were perfused and their brainstem and spinal cord were sliced (thickness, 40 μm) using a freezing microtome. All the sections were subjected to CB immunofluorescence staining. The distribution of CB-positive neuron in different brainstem and spinal cord areas was observed under fluorescence microscope.

Results

The retrograde labeled CB-positive neurons were found in the midbrain, pons, medulla oblongata, and spinal cord. Four functional areas including one hundred and twelve sub-regions have projections to the CSF-contacting nucleus. However, the density of CB-positive neuron distribution ranged from sparse to dense.

Conclusion

Based on the connectivity patterns of the CSF-contacting nucleus receives anatomical inputs from the brainstem and spinal cord, we preliminarily conclude and summarize that the CSF-contacting nucleus participates in pain, visceral activity, sleep and arousal, emotion, and drug addiction. The present study firstly illustrates the broad projections of the CSF-contacting nucleus from the brainstem and spinal cord, which implies the complicated functions of the nucleus especially for the unique roles of coordination in neural and body fluids regulation.

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.

Tetrandrine, an alkaloid from S. tetrandra exhibits anti-hypertensive and sleep-enhancing effects in SHR via different mechanisms

BACKGROUND

Sleep disorders have been found to be associated with hypertension in both cross-sectional and longitudinal epidemiological studies. Tetrandrine, a major component of Stephania tetrandra, is well known as an antihypertensive agent. The anti-hypertension mechanism mainly relies on its L-type calcium channel blocking property. In the previous study, tetrandrine revealed both anti-hypertension and hypnotic effects in spontaneously hypertensive rats (SHRs).

PURPOSE

This study aims to elucidate whether the antihypertensive mechanism of tetrandrine in SHRs is relevant to its hypnotic effect.

DESIGN/METHODS

Sleep-wake behavior of the SHRs was detected by electroencephalography (EEG) and electromyography (EMG) recordings. Blood pressure was measured by noninvasive blood pressure tail cuff test. Immunohistochemistry was performed to evaluate the noradrenergic neuronal activity. The level of norepinephrine (NE) was detected by HPLC-ECD.

RESULTS

Amlodipine (100mg/kg, i.g.), the well-known L-type Ca²⁺ channel blockers (CCBs) exhibited remarkable antihypertensive activities in SHRs, but did not show effects on sleep of SHRs. Tetrandrine (30 and 60mg/kg/day, i.g.) significantly suppressed blood pressure of SHRs. Meanwhile, tetrandrine (60mg/kg/day, i.g.) remarkably increased non-rapid eye movement sleep (NREMS) time, bouts and mean duration. The hypnotic effect of tetrandrine was potentiated by prazosin (0.5mg/kg, i.p.) but attenuated by yohimbine (2mg/kg, i.p.). Administration of tetrandrine (60mg/kg/day, i.g.) not only significantly decreased c-Fos positive ratio of noradrenergic neurons in the locus coeruleus (LC), but also significantly decrease NE in the endogenous sleep-wake regulating pathways including LC, hypothalamus and ventrolateral preoptic nucleus (VLPO).

CONCLUSION

In spite of a good potency in blocking L-type Ca²⁺ channel, the hypnotic effects of tetrandrine may be related to its suppressing effects on the noradrenergic system other than to block calcium channels. As a multi-targets drug, tetrandrine might be favorable to the hypertension patients who suffered poor sleep.

Role of the Orexin System on the Hypothalamus-Pituitary-Thyroid Axis

Hypocretin/orexin (ORX) are two hypothalamic neuropeptides discovered in 1998. Since their discovery, they have been one of the most studied neuropeptide systems because of their projecting fields innervating various brain areas. The orexinergic system is tied to sleep-wakefulness cycle, and narcolepsy is a consequence of their system hypofunction. Orexinergic system is also involved in many other autonomic functions such as feeding, thermoregulation, cardiovascular and neuroendocrine regulation. The main aim of this mini review article is to investigate the relationship between ORX and thyroid system regulation. Although knowledge about the ORX system is evolving, its putative effects on hypothalamic-pituitary-thyroid (HPT) axis still appear unclear. We analyzed some studies about ORX control of HPT axis to know better the relationship between them. The studies that were analyzed suggest Hypocretin/ORX to modulate the thyroid regulation, but the nature (excitatory or inhibitory) of this possible interaction remains actually unclear and needs to be confirmed.

Hypothalamic feedforward inhibition of thalamocortical network controls arousal and consciousness

During non-rapid eye movement (NREM) sleep, synchronous synaptic activity in the thalamocortical network generates predominantly low-frequency oscillations (<4 Hz) that are modulated by inhibitory inputs from the thalamic reticular nucleus (TRN). Whether TRN cells integrate sleep-wake signals from subcortical circuits remains unclear. We found that GABA neurons from the lateral hypothalamus (LHGABA) exert a strong inhibitory control over TRN GABA neurons (TRNGABA). We found that optogenetic activation of this circuit recapitulated state-dependent changes of TRN neuron activity in behaving mice and induced rapid arousal during NREM, but not REM, sleep. During deep anesthesia, activation of this circuit induced sustained cortical arousal. In contrast, optogenetic silencing of LHGABA-TRNGABA transmission increased the duration of NREM sleep and amplitude of delta (1-4 Hz) oscillations. Collectively, these results demonstrate that TRN cells integrate subcortical arousal inputs selectively during NREM sleep and may participate in sleep intensity.

Organization of the orexin/hypocretin system in the brain of two basal actinopterygian fishes, the cladistians Polypterus senegalus and Erpetoichthys calabaricus

Cladistians are primitive actinopterygian fishes mostly neglected in neuroanatomical studies. In the present study, the detailed neuroanatomical distribution of orexin (hypocretin)-like immunoreactive (OX-ir) cell bodies and fibers was analyzed in the brain of two species representative of the two extant genera of cladistians. Antibodies against mammalian orexin-A and orexin-B peptides were used. Simultaneous detection of orexins with neuropeptide Y (NPY), tyrosine hydroxylase (TH), and serotonin (5-HT) was used to establish accurately the topography of the orexin system and to evaluate the possible interactions with NPY and monoaminergic systems. A largely common pattern of OX-ir distribution in the two cladistian species was observed. Most OX-ir cells were located in the suprachiasmatic nucleus and tuberal hypothalamus, whereas scarce cells were observed in the posterior tubercle. In addition, a population of OX-ir cells was found in the preoptic area only in Polypterus and some cells also contained TH. The observed widespread distribution of OX-ir fibers was especially abundant in the retrobulbar area, subpallial areas, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic area, prethalamus, thalamus, pretectum, optic tectum, and tegmentum. Low innervation was found in relation to monoaminergic cell groups, whereas a high NPY innervation was observed in all OX-ir cell groups. These relationships would represent the anatomical substrate for the functional interdependence between these systems. The organization of the orexin system in cladistians revealed a pattern largely consistent with those reported for all studied groups of vertebrates, suggesting that the primitive organization of this peptidergic system occurred in the common ancestor of gnathostome vertebrates.