Astrocytes are relatively resistant to injury compared to neurons and oligodendrocytes. Here, we report transient region-specific loss of astrocytes in mice early after pilocarpine-induced status epilepticus (SE). In the dentate hilus, immunoreactivity for glial acidic fibrillary protein (GFAP) was decreased, and the number of healthy appearing GFAP- or S100β-positive cells was significantly reduced (≥ 65%) 1 and 3 days after pilocarpine-induced SE. Many remaining GFAP-positive cells were shrunken, and 1 day after SE electron microscopy revealed numerous electron-dense degenerating astrocyte processes and degenerating glial somata in the hilus. Degeneration of GFAP-expressing cells may be linked to hilar neuronal death, because we did not observe loss of astrocytes after kainate-induced SE, after which hilar neurons remained intact. Ten days after SE, hilar GFAP immunoreactivity had returned, partially from GFAP-positive cells in the hilus. Unlike control mice, many GFAP-positive hilar processes originated from cell bodies located in the subgranular zone (SGZ). To investigate whether proliferation contributes to hilar repopulation, we injected 5-bromo-2′-deoxyuridine (BrdU) 3 days after SE. Five hours later and up to 31 days after SE, many BrdU/GFAP colabeled cells were found in the hilus and the SGZ, some with hilar processes, indicating that proliferation in both areas contributes to generation of hilar astrocytes and astrocyte processes. In contrast to pilocarpine-induced SE in mice, astrocyte degeneration was not found after pilocarpine-induced SE in rats. These findings demonstrate astrocyte degeneration in the mouse dentate hilus specifically in the mouse pilocarpine epilepsy model, followed by astrogenesis leading to hilar repopulation.
Stem cell; Seizure; Hilus; Kainate; Glial fibrillary acidic protein; Adult progenitor cell; Mouse strain
In vitro exposure of neural progenitor cell (NPC) populations to reduced O2 (e.g. 3% versus 20%) can increase their proliferation, survival and neuronal differentiation. Our objective was to determine if an acute (<1 hr), in vivo exposure to intermittent hypoxia (AIH) alters expansion and/or differentiation of subsequent in vitro cultures of NPC from the subventricular zone (SVZ). Neonatal C57BL/6 mice (postnatal day 4) were exposed to an AIH paradigm (20×1 minute; alternating 21% and 10% O2). Immediately after AIH, SVZ tissue was isolated and NPC populations were cultured and assayed either as neurospheres (NS) or as adherent monolayer cells (MASC). AIH markedly increased the capacity for expansion of cultured NS and MASC, and this was accompanied by increases in a proliferation maker (Ki67), MTT activity and hypoxia-inducible factor-1α (HIF-1α) signaling in NS cultures. Peptide blockade experiments confirmed that proteins downstream of HIF-1α are important for both proliferation and morphological changes associated with terminal differentiation in NS cultures. Finally, immunocytochemistry and Western blotting experiments demonstrated that AIH increased expression of the neuronal fate determination transcription factor Pax6 in SVZ tissue, and this was associated with increased neuronal differentiation in cultured NS and MASC. We conclude that in vivo AIH exposure can enhance the viability of subsequent in vitro SVZ-derived NPC cultures. AIH protocols may therefore provide a means to “prime” NPC prior to transplantation into the injured central nervous system.
neural stem cell; neurosphere; intermittent hypoxia; population expansion; differentiation; Ki67; Pax6; HIF-1α
corticospinal tract; gp130 cytokines; interleukin-6; intrinsic growth capacity; Janus kinase; leukemia inhibitory factor; mTOR; spinal cord injury; STAT3; suppressor of cytokine signaling 3
Alzheimer's disease (AD) causes brain degeneration, primarily depleting cholinergic cells, and leading to cognitive and learning dysfunction. Logically, to augment the cholinergic cell loss, a viable treatment for AD has been via drugs boosting brain acetylcholine production. However, this is not a curative measure. To this end, nerve growth factor (NGF) has been examined as a possible preventative treatment against cholinergic neuronal death while enhancing memory capabilities; however, NGF brain bioavailability is challenging as it does not cross the blood–brain barrier. Investigations into stem cell- and gene-based therapy have been explored in order to enhance NGF potency in the brain. Along this line of research, a genetically modified cell line, called HB1.F3 transfected with the cholinergic acetyltransferase or HB1.F3.ChAT cells, has shown safety and efficacy profiles in AD models. This stem cell transplant therapy for AD is an extension of the neural stem cells' use in other neurological treatments, such as Parkinson's disease and stroke, and recently extended to cancer. The HB1 parent cell and its associated cell lines have been used as a vehicle to deliver genes of interest in various neurological models, and are highly effective as they can differentiate into neurons and glial cells. A focus of this mini-review is the recent demonstration that the transplantation of HB1.F3.ChAT cells in an AD animal model increases cognitive function coinciding with upregulation of acetylcholine levels in the cerebrospinal fluid. In addition, there is a large dispersion throughout the brain of the transplanted stem cells which is important to repair the widespread cholinergic cell loss in AD. Some translational caveats that need to be satisfied prior to initiating clinical trials of HB1.F3.ChAT cells in AD include regulating the host immune response and the possible tumorigenesis arising from the transplantation of this genetically modified cell line. Further studies are warranted to test the safety and effectiveness of these cells in AD transgenic animal models. This review highlights the recent progress of stem cell therapy in AD, not only emphasizing the significant basic science strides made in this field, but also providing caution on remaining translational issues necessary to advance this novel treatment to the clinic.
Alzheimer's disease; Neural stem cell; Neural growth factor; ChAT cells; Gene therapy
Neocortical neurons can be classified in four major electrophysiological types according to their pattern of discharge: Regular-Spiking (RS), Intrinsically-Bursting (IB), Fast-Rhythmic-Bursting (FRB), and Fast-Spiking (FS). Previously, we have shown that these firing patterns are not fixed and can change as a function of membrane potential and states of vigilance. Other studies have reported that extracellular calcium concentration ([Ca2+]o) fluctuates as a function of the phase of the cortical slow oscillation. In the present study we investigated how spontaneous and induced changes in [Ca2+]o affect the properties of action potentials (APs) and firing patterns in cortical neurons in vivo. Intracellular recordings were performed in cats anesthetized with ketamine-xylazine during spontaneous [Ca2+]o fluctuation and while changing [Ca2+]o with reverse microdialysis. When [Ca2+]o fluctuated spontaneously according to the phase of the slow oscillation, we found an increase of the firing threshold and a decrease of the afterhyperpolarization (AHP) amplitude during the depolarizing (active, up) phase of the slow oscillation and some neurons also changed their firing pattern as compared with the hyperpolarizing (silent, down) phase. Induced changes in [Ca2+]o significantly affected the AP properties in all neurons. The AHP amplitude was increased in high calcium conditions and decreased in low calcium conditions, in particular the earliest components. Modulation of spike AHP resulted in notable modulation of intrinsic firing pattern and some RS neurons revealed burst firing when [Ca2+]o was decreased. We also found an increase in AHP amplitude in high [Ca2+]o with in vitro preparation. We suggest that during spontaneous network oscillations in vivo, the dynamic changes of firing patterns depend partially on fluctuations of the [Ca2+]o.
The aim of this work was to evaluate the role of Ubiquitin-Proteasome System (UPS) on mitochondrial-driven alpha-synuclein (aSN) clearance in in vitro, ex vivo and in vivo Parkinson disease (PD) cellular models.
We used SH-SY5Y ndufa2 knock-down (KD) cells, PD cybrids and peripheral blood mononuclear cells (PBMC) from patients meeting the diagnostic criteria for PD. We quantified aSN aggregation, proteasome activity and protein ubiquitination levels. In PBMC of PD patients population we evaluated aSN levels in plasma and the influence of several demographic characteristics in the above mentioned determinations.
We found that ubiquitin-independent proteasome activity was up-regulated in SH-SY5Y ndufa2 KD cells while a down regulation was observed in PD cybrids and PBMC. Moreover, we observed an increase in protein ubiquitination that correlates with a decrease in ubiquitin-dependent proteasome activity. Accordingly, proteasome inhibition prevented ubiquitin-dependent aSN clearance. Ubiquitin-independent proteasome activity was positively correlated with ubiquitination in PBMC.
We also report a negative correlation of chymotrypsin-like activity with age in control and late-onset PD groups. Total ubiquitin content is positively correlated with aSN oligomers levels, which leads to an age-dependent increase of aSN ubiquitination in LOPD. Moreover, aSN levels are increased in the plasma of PD patients.
aSN oligomers are ubiquitinated and we identified an ubiquitin-dependent clearance insufficiency with accumulation of both aSN and ubiquitin. However, SH-SY5Y ndufa2 KD cells showed a significant up-regulation of ubiquitin-independent proteasomal enzymatic activity that could mean a cell rescue attempt. Moreover, we identified that UPS function is age-dependent in PBMC.
Parkinson’s disease; Ubiquitin-proteasome system; Mitochondria; Alpha-synuclein; Ubiquitin
Oxidative stress is commonly implicated in the pathogenesis of motor neuron disease. However, the cause and effect relationship between oxidative stress and motor neuron degeneration is poorly defined. We recently identified denervation at the neuromuscular junction in mice lacking the antioxidant enzyme, Cu, Zn-superoxide dismutase (SOD1) (Fischer et al., 2011). These mice show a phenotype of progressive muscle atrophy and weakness in the setting of chronic oxidative stress. Here, we investigated further the extent of motor neuron pathology in this model, and the relationship between motor pathology and oxidative stress. We report preferential denervation of fast-twitch muscles beginning between 1 and 4 months of age, with relative sparing of slow-twitch muscle. Motor axon terminals in affected muscles show widespread sprouting and formation of large axonal swellings. We confirmed, as was previously reported, that spinal motor neurons and motor and sensory nerve roots in these mice are preserved, even out to 18 months of age. We also found preservation of distal sensory fibers in the epidermis, illustrating the specificity of pathology in this model for distal motor axons. Using HPLC measurement of the glutathione redox potential, we quantified oxidative stress in peripheral nerve and muscle at the onset of denervation. SOD1 knockout tibial nerve, but not gastrocnemius muscle, showed significant oxidation of the glutathione pool, suggesting that axonal degeneration is a consequence of impaired redox homeostasis in peripheral nerve. We conclude that the SOD1 knockout mouse is a model of oxidative stress-mediated motor axonopathy. Pathology in this model primarily affects motor axon terminals at the neuromuscular junction, demonstrating the vulnerability of this synapse to oxidative injury.
SOD1; axon; neuromuscular junction; oxidative stress; motor neuron; ALS
After inflammation-induced demyelination, such as in the disease multiple
sclerosis, endogenous remyelination often fails. However, in animal models of
demyelination induced with toxins, remyelination can be quite robust. A
significant difference between inflammation-induced and toxin-induced
demyelination is the response of local cells within the lesion, including
astrocytes, oligodendrocytes, microglia/macrophages, and NG2+ cells, which
respond to inflammatory stimuli with increased extracellular matrix (ECM)
protein and chondroitin sulfate proteoglycan (CSPG) production and deposition.
Here, we summarize current knowledge of ECM changes in demyelinating lesions, as
well as oligodendrocyte responses to aberrant ECM proteins and CSPGs after
various types of demyelinating insults. The discovery that CSPGs act through the
receptor protein tyrosine phosphatase sigma (PTPσ) and the Rho-ROCK
pathway to inhibit oligodendrocyte process extension and myelination, but not
oligodendrocyte differentiation (Pendleton et
al., Experimental Neurology (2013) vol. 247, pp. 113-121), highlights
the need to better understand the ECM changes that accompany demyelination and
their influence on oligodendrocytes and effective remyelination.
Preclinical behavioral pharmacological and neuropharmacological evidence indicates that the NMDA receptor plays an important role in opioid dependence, however, the neural substrates subserving these actions are poorly understood. The central nucleus of the amygdala (CeA) is a critical coordinator of autonomic, behavioral, and emotional systems impacted by opioids, however there is no evidence that the essential NMDA-NR1 (NR1) subunit gene in the amygdala plays a role in opioid dependence. To determine the role of the NR1 subunit gene in the amygdala with respect to physical and psychological opioid withdrawal, a spatial-temporal deletion of this gene was produced by microinjecting a recombinant adeno-associated virus (rAAV) expressing the GFP reporter and Cre recombinase (rAAV-GFP-Cre) into the CeA of adult “floxed” NR1 mice (fNR1). Amygdala microinjection of rAAV-GFP-Cre produced a decrease in NR1 gene expression and protein immunolabeling in postsynaptic sites of neurons without signs of compromised ultrastructural neuronal morphology. Amygdala NR1 gene deletion also did not affect locomotor, somatosensory, or sensory-motor behaviors. In addition, bilateral local NR1 gene deletion did not impact somatic or visceral withdrawal symptoms precipitated by naloxone in morphine-dependent mice. However, there was a significant deficit in the expression of an opioid withdrawal-induced conditioned place aversion in mice with amygdala NR1 deletion. These results indicate that functional amygdala NMDA receptors are involved in aversive psychological processes associated with opioid withdrawal. More generally, spatial-temporal deletion of the NR1 subunit by Cre-loxP technology is an effective means to elucidate the neurogenetic substrates of complex phenotypes associated with drug abuse.
Addiction; Cre recombinase; Glutamate; Opioids; Synaptic Plasticity
To achieve a long lifespan, animals must be resistant to various injuries as well as be able to avoid or delay lethality from age-dependent diseases. Here we show that long-lived Mclk1+/− mutants have enhanced resistance to neurological damage following global cerebral ischemia/reperfusion (I/R) injury induced by transient bilateral common carotid artery occlusion (BCCAO). Both young (~100 days old) and relatively aged (~450 days old) mutants display increased resistance as indicated by a significant decrease in the amount of degenerating cells observed in forebrain cortex and in hippocampal areas after ischemia and reperfusion. Furthermore, less oxidative damage resulting from the procedure was measured in the brain of young Mclk1+/− animals. The finding that both young and old mutants are protected indicates that this is a basic phenotype of these mutants and not a secondary consequence of their slow rate of aging. Thus, the partial resistance to I/R injury by enhancing recovery from age-dependent vascular accidents is likely part of what allows for the increased lifespan of Mclk1+/− mutants. By relating this neuroprotective effect to previously reported characteristics of the Mclk1+/− phenotype, including altered mitochondrial metabolism and increased HIF-1α expression, this study establishes these mutants as useful models to analyze the mechanisms underlying tolerance to ischemia, particularly those associated with ischemic preconditioning, as well as to clarify the relation between aging and age-dependent diseases.
PMID: 20170652 CAMSID: cams4458
Mclk1; Ischemia; Reperfusion; Aging; Age-related diseases; Ischemic tolerance; BCCAO; Oxidative stress
Aging alters the ability of the brain to respond to injury. One of the major differences between the adult and aged brain is that comparable injuries lead to greater blood brain barrier disruption in the aged brain. The goals of these studies were to quantify the effects of age on BBB permeability using high field strength MRI T1 mapping and to determine whether activation of matrix metalloproteases, their inhibitors, or expression of blood brain barrier structural proteins, occludin, zonnula occludins-1 (ZO-1) and claudin-5 were altered following injury to the aged C57/Bl6 mouse brain. T1 mapping studies revealed greater blood brain barrier permeability in the aged (21–15 months old) brain than in the adult (4–6 months old) following controlled cortical impact. The increased blood brain barrier permeability in the pericontusional region was confirmed with IgG immunohistochemistry. MMP-9 activity was increased following controlled cortical impact in the aged brain, and this was accompanied by increased MMP-9 gene expression. MMP-2 activity was higher in the uninjured aged brain than in the adult brain. Occludin and ZO-1 mRNA levels were unchanged following injury in either age group, but claudin-5 mRNA levels were lower in the aged than the adult brain following injury. These results demonstrate quantitative increases in blood brain barrier permeability in the aged brain following injury that are accompanied by increased MMP-9 activation and decreased blood brain barrier repair responses.
Controlled cortical impact; Traumatic brain injury; Aging; T1 mapping; Blood brain barrier; MMP-9; MMP-2; Occludin; ZO-1; Claudin-5
Spinal lamina II, where nociceptive C-fibers terminate, expresses high amounts of the polysialylated form of neural cell adhesion molecule (PSA-NCAM). While enzymatic removal of the PSA moiety from NCAM did not affect normal sensitivity to thermal stimuli, it exacerbated nerve injury-induced neuropathic hyperalgesia. The genetic removal of the NCAM core protein also did not alter thermal sensitivity. However in the presence of a peripheral nerve injury, NCAM null-mutants exhibited a complete suppression of thermal hyperalgesia. This strong NCAM mutant phenotype appears to involve the long form of NCAM’s cytoplasmic domain, in that it is duplicated by selective genetic deletion of the NCAM-180 isoform. PSA appears therefore to provide a mechanism for modulation of chronic sensory overload, by means of attenuation of the activity of the NCAM-180 isoform, which reduces nociceptive transmission.
Nociception; thermal hyperalgesia; polysialic acid; NCAM; chronic pain
Focal cortical dysplasia (FCD) and other localized malformations of cortical development represent common causes of intractable pediatric epilepsy. Insights into the cellular and molecular pathogenesis of focal cortical malformations may reveal information about associated mechanisms of epileptogenesis and suggest new therapies for seizures caused by these developmental lesions. In animal models and human studies of FCD and the related disease of Tuberous Sclerosis Complex (TSC), the mammalian target of rapamycin (mTOR) pathway has been implicated in mediating cellular and molecular changes leading to the formation of the cortical malformations and the expression of epilepsy. The use of mTOR inhibitors may represent a rational therapeutic strategy for treating or even preventing epilepsy due to FCD and TSC.
Epilepsy; seizure; malformation of cortical development; tuberous sclerosis complex
This review addresses the state of gene therapy research for the treatment of epilepsy. Preclinical studies have demonstrated the anti-seizure efficacy of viral vector-based gene transfer through the use of a variety of strategies – from modulating classic neurotransmitter systems to targeting or overexpressing of neuropeptide receptors in seizure-specific brain regions. While these studies provide substantive proof of principle for viral vector gene therapy, future studies must address the challenges of vector immunity, cellular specificity and effective global delivery. As these issues are resolved, viral vector gene therapy should significantly impact the treatment of intractable epilepsy.
Modification of GABAergic inhibition is an intensely investigated hypothesis guiding research into mechanisms underlying temporal lobe epilepsy (TLE). Seizures can be initiated by blocking γ amino butyric acid type A (GABAA receptors, GABARs), which mediate fast synaptic inhibition in the brain, and controlled by drugs that enhance their function. Derivatives of steroid hormones called neurosteroids are natural substances that physiologically enhance GABAR function and suppress seizures. GABAR structure, function, expression, assembly, and pharmacological properties are changed in the hippocampus of epileptic animals. These alterations render GABARs less sensitive to neurosteroid modulation, which may contribute to seizure susceptibility. Plasticity of GABARs could play a role in periodic exacerbation of seizures experienced by women with epilepsy, commonly referred to as catamenial epilepsy.
Phytocannabinoids isolated from the cannabis plant have broad potential in medicine that has been well recognized for many centuries. It is presumed that these lipid soluble signaling molecules exert their effects in both the central and peripheral nervous system in large part through direct interaction with metabotropic cannabinoid receptors. These same receptors are also targeted by a variety of endogenous cannabinoids including 2-arachidonoyl glycerol and anandamide. Significant effort over the last decade has produced an enormous advance in our understanding of both the cellular and the synaptic physiology of endogenous lipid signaling systems. This increase in knowledge has left us better prepared to carefully evaluate the potential for both natural and synthetic cannabinoids in the treatment of a variety of neurological disorders. In the case of epilepsy, long standing interest in therapeutic approaches that target endogenous cannabinoid signaling systems are, for the most part, not well justified by available clinical data from human epileptics. Nevertheless, basic science experiments have clearly indicated a key role for endogenous cannabinoid signaling systems in moment to moment regulation of neuronal excitability. Further it has become clear that these systems can both alter and be altered by epileptiform activity in a wide range of in vitro and in vivo models of epilepsy. Collectively these observations suggest clear potential for effective therapeutic modulation of endogenous cannabinoid signaling systems in the treatment of human epilepsy, and in fact, further highlight key obstacles that would need to be addressed to reach that goal.
The focus of the review is on the behavioral and physiological manifestations of stress versus depression. The purpose of the review is to evaluate the conceptual approach of using stress models as surrogates for depression. Social stress and depression have many characteristics in common and promote each other. Both have adverse effects on social relationships and the quality of life, and increase risk of other diseases. However, they are not the same constructs. In human and nonhuman primates, the behavior and neurobiology of stressed individuals differ from that of depressed individuals. Some similarities in stress physiology in socially stressed and depressed individuals have been used to support the use of stressed animals as models of depression, and much has been learned from stress models of depression. However, the studies reviewed here also suggest that the depressed state also has different characteristics than the stressed state, and studying the differences may be important to furthering our understanding of each of these constructs as well as their mutual relationship.
Social stress; Depression; Nonhuman primate; Animal models; Heart rate; Cortisol; Behavior; Coronary artery atherosclerosis; Body composition
Cancer results from dysregulation of growth and survival pathways in normal stem cells and progenitors. Identifying the cells from which a tumor arises can facilitate the development of animal models and point to novel targets for therapy. Medulloblastoma is an aggressive tumor of the cerebellum that occurs predominantly in children. Recent genomic studies suggest that medulloblastoma consists of 4 major subgroups, each with distinct mutations and signaling pathway deregulations, and each potentially arising from distinct populations of stem cells and progenitors. Here we review the major types of progenitor cells in the cerebellum and discuss their role in the genesis of medulloblastoma.
Medulloblastoma; Cell of origin; Mouse models
A better understanding of autonomic influence on motor reflex pathways in spinal cord injury is important to the clinical management of autonomic dysreflexia and spasticity in spinal cord injured patients. The purpose of this study was to examine the modulation of flexor reflex windup during episodes of induced sympathetic activity in chronic human spinal cord injury (SCI). We simultaneously measured peripheral vascular conductance and the windup of the flexor reflex in response to conditioning stimuli of electrocutaneous stimulation to the opposite leg and bladder percussion. Flexor reflexes were quantified using torque measurements of the response to a noxious electrical stimulus applied to the skin of the medial arch of the foot. Both bladder percussion and skin conditioning stimuli produced a reduction (43-67%) in the ankle and hip flexor torques (p<0.05) of the flexor reflex. This reduction was accompanied by a simultaneous reduction in vascular conductance, measured using venous plethysmography, with a time course that matched the flexor reflex depression. While there was an overall attenuation of the flexor reflex, windup of the flexor reflex to repeated stimuli was maintained during periods of increased sympathetic activity. This paradoxical depression of flexor reflexes and minimal effect on windup is consistent with inhibition of afferent feedback within the superficial dorsal horn. The results of this study bring attention to the possible interaction of motor and sympathetic reflexes in SCI above and below the T5 spinal level, and have implications for clinicians in spasticity management and for researchers investigating motor reflexes post SCI.
autonomic dysreflexia; windup; spasticity
Paraquat (PQ) is a potential human neurotoxicant and is used in models of oxidative stress. We determined the toxicokinetics (TK) and toxicodynamics (TD) of PQ in adult mouse brain following repeated or prolonged PQ exposure. PQ accumulated in different brain regions and reached a plateau after ~18 i.p. (10 mg/kg) doses and resulted in modest morbidity and mortality unpredictably associated with dose interval and number. PQ had divergent effects on horizontal locomotor behavior depending on the number of doses. PQ decreased striatal dopamine levels after the 18th to 36th i.p. dose (10 mg/kg) and reduced the striatal level of tyrosine hydroxylase. Drinking water exposure to PQ (0.03– 0.05 mg/ml) did not result in any mortality and resulted in concentration and time dependent levels in the brain. The brain half-life of PQ varied with mouse strain. PQ accumulates and may saturate a site in mouse brain resulting in complex PQ level and duration-related consequences. These findings should alter our risk assessment of this compound and demonstrate a useful, but complex dynamic model for understanding the consequences of PQ in the brain.
Parkinson’s disease; Dopamine system; Paraquat; Oxidative stress; Toxicokinetics; Toxicodynamics
The suprachiasmatic nucleus (SCN), site of the primary clock in the circadian rhythm system, has three major afferent connections. The most important consists of a retinohypothalamic projection through which photic information, received by classical rod/cone photoreceptors and intrinsically photoreceptive retinal ganglion cells, gains access to the clock. This information influences phase and period of circadian rhythms. The two other robust afferent projections are the median raphe serotonergic pathway and the geniculohypothalamic (GHT), NPY-containing pathway from the thalamic intergeniculate leaflet (IGL). Beyond this simple framework, the number of anatomical routes that could theoretically be involved in rhythm regulation is enormous, with the SCN projecting to 15 regions and being directly innervated by about 35. If multisynaptic afferents to the SCN are included, the number expands to approximately brain 85 areas providing input to the SCN. The IGL, a known contributor to circadian rhythm regulation, has a still greater level of complexity. This nucleus connects abundantly throughout the brain (to approximately 100 regions) by pathways that are largely bilateral and reciprocal. Few of these sites have been evaluated for their contributions to circadian rhythm regulation, although most have a theoretical possibility of doing so via the GHT. The anatomy of IGL connections suggests that one of its functions may be regulation of eye movements during sleep. Together, neural circuits of the SCN and IGL are complex and interconnected. As yet, few have been tested with respect to their involvement in rhythm regulation.
circadian; neuroanatomy; suprachiasmatic; intergeniculate leaflet; efferent; afferent; retrograde; anterograde; serotonin; connectivity; transneuronal
Daily rhythms in neural activity underlie circadian rhythms in sleep-wake and other daily behaviors. The cells within the mammalian suprachiasmatic nucleus (SCN) are intrinsically capable of 24-h timekeeping. These cells synchronize to each other and to local environmental cycles to drive coherent rhythms in daily behaviors. Recent studies have identified a small number of neuropeptides critical for this ability to synchronize and sustain coordinated daily rhythms. This review highlights the roles of specific intracellular and intercellular signals within the SCN that underlie circadian synchrony.
pacemaker; period gene; vasoactive intestinal polypeptide; suprachiasmatic nucleus; neuropeptide
Although the sodium channel blocker mexiletine is considered the first-line drug in myotonia, some patients experiment adverse effects, while others do not gain any benefit. Other antimyotonic drugs are thus needed to offer mexiletine alternatives. In the present study, we used a previously-validated rat model of myotonia congenita to compare six marketed sodium channel blockers to mexiletine. Myotonia was induced in the rat by injection of anthracen-9-carboxylic acid, a muscle chloride channel blocker. The drugs were given orally and myotonia was evaluated by measuring the time of righting reflex. The drugs were also tested on sodium currents recorded in a cell line transfected with the human skeletal muscle sodium channel hNav1.4 using patch-clamp technique. In vivo, carbamazepine and propafenone showed antimyotonic activity at doses similar to mexiletine (ED50 close to 5 mg/kg); flecainide and orphenadrine showed greater potency (ED50 near 1 mg/kg); lubeluzole and riluzole were the more potent (ED50 near 0.1 mg/kg). The antimyotonic activity of drugs in vivo was linearly correlated with their potency in blocking hNav1.4 channels in vitro. Deviation was observed for propafenone and carbamazepine, likely due to pharmacokinetics and multiple targets. The comparison of the antimyotonic dose calculated in rats with the current clinical dose in humans strongly suggests that all the tested drugs may be used safely for the treatment of human myotonia. Considering the limits of mexiletine tolerability and the occurrence of non-responders, this study proposes an arsenal of alternative drugs, which may prove useful to increase the quality of life of individuals suffering from non-dystrophic myotonia. Further clinical trials are warranted to confirm these results.
•Seven sodium channel blockers show antimyotonic activity in a rat model of myotonia.•The ED50 value ranges from 0.1 (riluzole, lubeluzole) to 5 mg/kg (mexiletine, carbamazepine).•The drugs use-dependently block hNav1.4 channels in cells in myotonic-like conditions.•The IC50 values in vitro were well linearly correlated with the ED50 values in vivo.•The study discloses promising new therapeutic options for myotonic patients.
Non-dystrophic myotonia; Sodium channel blockers; Mexiletine; Rat model; Patch-clamp; Over-excitability
Sleep disorders are nearly ubiquitous among patients with Parkinson’s disease (PD), and they manifest early in the disease process. While there are a number of possible mechanisms underlying these sleep disturbances, a primary dysfunction of the circadian system should be considered as a contributing factor. Our laboratory’s behavioral phenotyping of a well-validated transgenic mouse model of PD reveals that the electrical activity of neurons within the master pacemaker of the circadian system, the suprachiasmatic nuclei (SCN), is already disrupted at the onset of motor symptoms, although the core features of the intrinsic molecular oscillations in the SCN remain functional. Our observations suggest that the fundamental circadian deficit in these mice lies in the signaling output from the SCN, which may be caused by known mechanisms in PD etiology: oxidative stress and mitochondrial disruption. Disruption of the circadian system is expected to have pervasive effects throughout the body and may itself lead to neurological and cardiovascular disorders. In fact, there is much overlap in the non-motor symptoms experienced by PD patients and in the consequences of circadian disruption. This raises the possibility that the sleep and circadian dysfunction experienced by PD patients may not merely be a subsidiary of the motor symptoms, but an integral part of the disease. Furthermore, we speculate that circadian dysfunction can even accelerate the pathology underlying PD. If these hypotheses are correct, more aggressive treatment of the circadian misalignment and sleep disruptions in PD patients early in the pathogenesis of the disease may be powerful positive modulators of disease progression and patient quality of life.
Circadian; dopamine; Parkinson’s disease; Non-motor symptoms of Parkinson’s disease; Sleep; Suprachiasmatic nucleus