Conditional microglial depletion in rats leads to reversible anorexia and weight loss by disrupting gustatory circuitry.

Microglia are highly sensitive to dietary influence, becoming activated acutely and long-term by high fat diet. However, their role in regulating satiety and feeding in healthy individuals remains unclear. Here we show that microglia are essential for the normal regulation of satiety and metabolism in rats. Short-term microglial depletion in a Cx3cr1-Dtr rat led to a dramatic weight loss that was largely accounted for by an acute reduction in food intake. This weight loss and anorexia were not likely due to a sickness response since the rats did not display peripheral or central inflammation, withdrawal, anxiety-like behavior, or nausea-associated pica. Hormonal and hypothalamic anatomical changes were largely compensatory to the suppressed food intake, which occurred in association with disruption of the gustatory circuitry at the paraventricular nucleus of the thalamus. Thus, microglia are important in supporting normal feeding behaviors and weight, and regulating preference for palatable food. Inhibiting this circuitry is able to over-ride strong compensatory drives to eat, providing a potential target for satiety control.

Effects Of treadmill training on hindlimb muscles of spinal cord-injured mice.

INTRODUCTION: Treadmill training is known to prevent muscle atrophy after spinal cord injury (SCI), but the training duration required to optimize recovery has not been investigated. METHODS: Hemisected mice were randomized to 3, 6, or 9 weeks of training or no training. Muscle fiber type composition and fiber cross-sectional area (CSA) of medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) were assessed using ATPase histochemistry. RESULTS: Muscle fiber type composition of SCI animals did not change with training. However, 9 weeks of training increased the CSA of type IIB and IIX fibers in TA and MG muscles. CONCLUSIONS: Nine weeks of training after incomplete SCI was effective in preventing atrophy of fast-twitch muscles, but there were limited effects on slow-twitch muscles and muscle fiber type composition. These data provide important evidence of the benefits of exercising paralyzed limbs after SCI. Muscle Nerve, 2016 Muscle Nerve 55: 232-242, 2017.

Acute inhibition of acid sensing ion channel 1a after spinal cord injury selectively affects excitatory synaptic transmission, but not intrinsic membrane properties, in deep dorsal horn interneurons.

Following a spinal cord injury (SCI), secondary damage mechanisms are triggered that cause inflammation and cell death. A key component of this secondary damage is a reduction in local blood flow that initiates a well-characterised ischemic cascade. Downstream hypoxia and acidosis activate acid sensing ion channel 1a (ASIC1a) to trigger cell death. We recently showed that administration of a potent venom-derived inhibitor of ASIC1a, Hi1a, leads to tissue sparing and improved functional recovery when delivered up to 8 h after ischemic stroke. Here, we use whole-cell patch-clamp electrophysiology in a spinal cord slice preparation to assess the effect of acute ASIC1a inhibition, via a single dose of Hi1a, on intrinsic membrane properties and excitatory synaptic transmission long-term after a spinal cord hemisection injury. We focus on a population of interneurons (INs) in the deep dorsal horn (DDH) that play a key role in relaying sensory information to downstream motoneurons. DDH INs in mice treated with Hi1a 1 h after a spinal cord hemisection showed no change in active or passive intrinsic membrane properties measured 4 weeks after SCI. DDH INs, however, exhibit significant changes in the kinetics of spontaneous excitatory postsynaptic currents after a single dose of Hi1a, when compared to naive animals (unlike SCI mice). Our data suggest that acute ASIC1a inhibition exerts selective effects on excitatory synaptic transmission in DDH INs after SCI via specific ligand-gated receptor channels, and has no effect on other voltage-activated channels long-term after SCI.

Polysynaptic excitatory postsynaptic potentials that trigger spasms after spinal cord injury in rats are inhibited by 5-HT1B and 5-HT1F receptors.

Sensory afferent transmission and associated spinal reflexes are normally inhibited by serotonin (5-HT) derived from the brain stem. Spinal cord injury (SCI) that eliminates this 5-HT innervation leads to a disinhibition of sensory transmission and a consequent emergence of unusually long polysynaptic excitatory postsynaptic potentials (EPSPs) in motoneurons. These EPSPs play a critical role in triggering long polysynaptic reflexes (LPRs) that initiate muscles spasms. In the present study we examined which 5-HT receptors modulate the EPSPs and whether these receptors adapt to a loss of 5-HT after chronic spinal transection in rats. The EPSPs and associated LPRs recorded in vitro in spinal cords from chronic spinal rats were consistently inhibited by 5-HT(1B) or 5-HT(1F) receptor agonists, including zolmitriptan (5-HT(1B/1D/1F)) and LY344864 (5-HT(1F)), with a sigmoidal dose-response relation, from which we computed the 50% inhibition (EC(50)) and potency (-log EC(50)). The potencies of 5-HT receptor agonists were highly correlated with their binding affinity to 5-HT(1B) and 5-HT(1F) receptors, and not to other 5-HT receptors. Zolmitriptan also inhibited the LPRs and general muscle spasms recorded in vivo in the awake chronic spinal rat. The 5-HT(1B) receptor antagonists SB216641 and GR127935 and the inverse agonist SB224289 reduced the inhibition of LPRs by 5-HT(1B) agonists (zolmitriptan). However, when applied alone, SB224289, SB216641, and GR127935 had no effect on the LPRs, indicating that 5-HT(1B) receptors do not adapt to chronic injury, remaining silent, without constitutive activity. The reduction in EPSPs with zolmitriptan unmasked a large glycine-mediated inhibitory postsynaptic current (IPSC) after SCI. This IPSC and associated chloride current reversed at -73 mV, slightly below the resting membrane potential. Zolmitriptan did not change motoneuron properties. Our results demonstrate that 5-HT(1B/1F) agonists, such as zolmitriptan, can restore inhibition of sensory transmission after SCI without affecting general motoneuron function and thus may serve as a novel class of antispastic drugs.

Acid-Sensing Ion Channels: Expression and Function in Resident and Infiltrating Immune Cells in the Central Nervous System.

Peripheral and central immune cells are critical for fighting disease, but they can also play a pivotal role in the onset and/or progression of a variety of neurological conditions that affect the central nervous system (CNS). Tissue acidosis is often present in CNS pathologies such as multiple sclerosis, epileptic seizures, and depression, and local pH is also reduced during periods of ischemia following stroke, traumatic brain injury, and spinal cord injury. These pathological increases in extracellular acidity can activate a class of proton-gated channels known as acid-sensing ion channels (ASICs). ASICs have been primarily studied due to their ubiquitous expression throughout the nervous system, but it is less well recognized that they are also found in various types of immune cells. In this review, we explore what is currently known about the expression of ASICs in both peripheral and CNS-resident immune cells, and how channel activation during pathological tissue acidosis may lead to altered immune cell function that in turn modulates inflammatory pathology in the CNS. We identify gaps in the literature where ASICs and immune cell function has not been characterized, such as neurotrauma. Knowledge of the contribution of ASICs to immune cell function in neuropathology will be critical for determining whether the therapeutic benefits of ASIC inhibition might be due in part to an effect on immune cells.

Stroke Severity, and Not Cerebral Infarct Location, Increases the Risk of Infection.

Infection is a leading cause of death in patients with stroke; however, the impact of cerebral infarct size or location on infectious outcome is unclear. To examine the effect of infarct size on post-stroke infection, we utilised the intraluminal middle-cerebral artery occlusion (MCAO) mouse model of ischemic stroke and adjusted the duration of arterial occlusion. At 1 day following stroke onset, the proportion of mice with infection was significantly greater in mice that had larger infarct sizes. Additionally, the presence of lung infection in these mice with severe strokes extended past 2 days, suggestive of long-term immune impairment. At the acute phase, our data demonstrated an inverse relationship between infarct volume and the number of circulating leukocytes, indicating the elevated risk of infection in more severe stroke is associated with reduced cellularity in peripheral blood, owing predominately to markedly decreased lymphocyte numbers. In addition, the stroke-induced reduction of lymphocyte-to-neutrophil ratio was also evident in the lung of all post-stroke animals. To investigate the effect of infarct location on post-stroke infection, we additionally performed a photothrombotic (PT) model of stroke and using an innovative systematic approach of analysis, we found the location of cerebral infarct does not impact on the susceptibility of post-stroke infection, confirming the greater role of infarct volume over infarct location in the susceptibility to infection. Our experimental findings were validated in a clinical setting and reinforced that stroke severity, and not infarct location, influences the risk of infection after stroke.

The impact of junk foods on the adolescent brain.

Adolescence is a significant period of physical, social, and emotional development, and is characterized by prominent neurobiological changes in the brain. The maturational processes that occur in brain regions responsible for cognitive control and reward seeking may underpin excessive consumption of palatable high fat and high sugar "junk" foods during adolescence. Recent studies have highlighted the negative impact of these foods on brain function, resulting in cognitive impairments and altered reward processing. The increased neuroplasticity during adolescence may render the brain vulnerable to the negative effects of these foods on cognition and behavior. In this review, we describe the mechanisms by which junk food diets influence neurodevelopment during adolescence. Diet can lead to alterations in dopamine-mediated reward signaling, and inhibitory neurotransmission controlled by γ-aminobutyric acid (GABA), two major neurotransmitter systems that are under construction across adolescence. We propose that poor dietary choices may derail the normal adolescent maturation process and influence neurodevelopmental trajectories, which can predispose individuals to dysregulated eating and impulsive behaviors.

Evolution of thyroid hormone distributor proteins.

Thyroid hormones (THs) are evolutionarily old hormones, having effects on metabolism in bacteria, invertebrates and vertebrates. THs bind specific distributor proteins (THDPs) to ensure their efficient distribution through the blood and cerebrospinal fluid in vertebrates. Albumin is a THDP in the blood of all studied species of vertebrates, so may be the original vertebrate THDP. However, albumin has weak affinity for THs. Transthyretin (TTR) has been identified in the blood across different lineages in adults vs juveniles. TTR has intermediate affinity for THs. Thyroxine-binding globulin has only been identified in mammals and has high affinity for THs. Of these THDPs, TTR is the only one known to be synthesised in the brain and is involved in moving THs from the blood into the cerebrospinal fluid. We analysed the rates of evolution of these three THDPs: TTR has been most highly conserved and albumin has had the highest rate of divergence.

Gait recovery following spinal cord injury in mice: Limited effect of treadmill training.

BACKGROUND: Several studies in rodents with complete spinal cord transections have demonstrated that treadmill training improves stepping movements. However, results from studies in incomplete spinal cord injured animals have been conflicting and questions regarding the training dosage after injury remain unresolved. OBJECTIVES: To assess the effects of treadmill-training regimen (20 minutes daily, 5 days a week) for 3, 6 or 9 weeks on the recovery of locomotion in hemisected SCI mice. METHODS: A randomized and blinded controlled experimental trial used a mouse model of incomplete spinal cord injury (SCI). After a left hemisection at T10, adult male mice were randomized to trained or untrained groups. The trained group commenced treadmill training one week after surgery and continued for 3, 6 or 9 weeks. Quantitative kinematic gait analysis was used to assess the spatiotemporal characteristics of the left hindlimb prior to injury and at 1, 4, 7 and 10 weeks post-injury. RESULTS: One week after injury there was no movement of the left hindlimb and some animals dragged their foot. Treadmill training led to significant improvements in step duration, but had limited effect on the hindlimb movement pattern. Locomotor improvements in trained animals were most evident at the hip and knee joints whereas recovery of ankle movement was limited, even after 9 weeks of treadmill training. CONCLUSION: These results demonstrate that treadmill training may lead to only modest improvement in recovery of hindlimb movement after incomplete spinal cord injury in mice.

Exercise training after spinal cord injury selectively alters synaptic properties in neurons in adult mouse spinal cord.

Following spinal cord injury (SCI), anatomical changes such as axonal sprouting occur within weeks in the vicinity of the injury. Exercise training enhances axon sprouting; however, the exact mechanisms that mediate exercised-induced plasticity are unknown. We studied the effects of exercise training after SCI on the intrinsic and synaptic properties of spinal neurons in the immediate vicinity (<2 segments) of the SCI. Male mice (C57BL/6, 9-10 weeks old) received a spinal hemisection (T10) and after 1 week of recovery, they were randomized to trained (treadmill exercise for 3 weeks) and untrained (no exercise) groups. After 3 weeks, mice were killed and horizontal spinal cord slices (T6-L1, 250 µm thick) were prepared for visually guided whole cell patch clamp recording. Intrinsic properties, including resting membrane potential, input resistance, rheobase current, action potential (AP) threshold and after-hyperpolarization (AHP) amplitude were similar in neurons from trained and untrained mice (n=67 and 70 neurons, respectively). Neurons could be grouped into four categories based on their AP discharge during depolarizing current injection; the proportions of tonic firing, initial bursting, single spiking, and delayed firing neurons were similar in trained and untrained mice. The properties of spontaneous excitatory synaptic currents (sEPSCs) did not differ in trained and untrained animals. In contrast, evoked excitatory synaptic currents recorded after dorsal column stimulation were markedly increased in trained animals (peak amplitude 78.9±17.5 vs. 42.2±6.8 pA; charge 1054±376 vs. 348±75 pA·ms). These data suggest that 3 weeks of treadmill exercise does not affect the intrinsic properties of spinal neurons after SCI; however, excitatory synaptic drive from dorsal column pathways, such as the corticospinal tract, is enhanced.

SISCOM in children with tuberous sclerosis complex-related epilepsy.

Identification of a single epileptogenic focus in patients with tuberous sclerosis complex is a challenge. Noninvasive imaging modalities, including subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging (SISCOM), have been used to determine the dominant epileptogenic focus for surgical resection. We assessed whether complete resection of SISCOM hyperperfusion abnormality correlates with seizure-free outcome in 6 children with tuberous sclerosis complex-related epilepsy. The median seizure onset age was 4 months (range 1 day to 16 months). The age at surgery ranged from 8 months to 13 years. A dominant SISCOM hyperperfusion focus was identified in 5 patients with multiple tubers. SISCOM provided additional localizing information for epilepsy surgery in 3 patients with nonlocalizing or discordant electrophysiologic and neuroimaging findings. At a minimum of 2 years' follow-up, 3 patients were free of seizures overall. Freedom from seizures was associated with complete resection of SISCOM abnormality in 2 patients. These findings demonstrate that SISCOM can be useful in identifying the epileptogenic zone and in guiding the location and extent of epilepsy surgery in children with tuberous sclerosis complex and multifocal abnormalities. In children with tuberous sclerosis complex and intractable epilepsy, complete resection of the SISCOM hyperperfusion abnormality is associated with freedom from seizures.

Recovery of motoneuron and locomotor function after spinal cord injury depends on constitutive activity in 5-HT2C receptors.

Muscle paralysis after spinal cord injury is partly caused by a loss of brainstem-derived serotonin (5-HT), which normally maintains motoneuron excitability by regulating crucial persistent calcium currents. Here we examine how over time motoneurons compensate for lost 5-HT to regain excitability. We find that, months after a spinal transection in rats, changes in post-transcriptional editing of 5-HT2C receptor mRNA lead to increased expression of 5-HT2C receptor isoforms that are spontaneously active (constitutively active) without 5-HT. Such constitutive receptor activity restores large persistent calcium currents in motoneurons in the absence of 5-HT. We show that this helps motoneurons recover their ability to produce sustained muscle contractions and ultimately enables recovery of motor functions such as locomotion. However, without regulation from the brain, these sustained contractions can also cause debilitating muscle spasms. Accordingly, blocking constitutively active 5-HT2C receptors with SB206553 or cyproheptadine, in both rats and humans, largely eliminates these calcium currents and muscle spasms, providing a new rationale for antispastic drug therapy.

Role of endogenous release of norepinephrine in muscle spasms after chronic spinal cord injury.

The recovery of persistent inward currents (PICs) and motoneuron excitability after chronic spinal cord transection is mediated, in part, by the development of supersensitivity to residual serotonin (5HT) below the lesion. The purpose of this paper is to investigate if, like 5HT, endogenous sources of norepinephrine (NE) facilitate motoneuron PICs after chronic spinal transection. Cutaneous-evoked reflex responses in tail muscles of awake chronic spinal rats were measured after increasing presynaptic release of NE by administration of amphetamine. An increase in long-lasting reflexes, known to be mediated by the calcium component of the PIC (CaPIC), was observed even at low doses (0.1-0.2 mg/kg) of amphetamine. These findings were repeated in a reduced S2 in vitro preparation, demonstrating that the increased long-lasting reflexes by amphetamine were neural. Under intracellular voltage clamp, amphetamine application led to a large facilitation of the motoneuron CaPIC. This indicates that the increases in long-lasting reflexes induced by amphetamine in the awake animal were, in part, due to actions directly on the motoneuron. Reflex responses in acutely spinal animals were facilitated by amphetamine similar to chronic animals but only at doses that were ten times greater than that required in chronic animals (0.2 mg/kg chronic vs. 2.0 mg/kg acute), pointing to a development of supersensitivity to endogenous NE in chronic animals. In summary, the increases in long-lasting reflexes and associated motoneuron CaPICs by amphetamine are likely due to an increased release of endogenous NE, which motoneurons become supersensitive to in the chronic stages of spinal cord injury.

Spastic tail muscles recover from myofiber atrophy and myosin heavy chain transformations in chronic spinal rats.

Without intervention after spinal cord injury (SCI), paralyzed skeletal muscles undergo myofiber atrophy and slow-to-fast myofiber type transformations. We hypothesized that chronic spasticity-associated neuromuscular activity after SCI would promote recovery from such deleterious changes. We examined segmental tail muscles of chronic spinal rats with long-standing tail spasticity (7 mo after sacral spinal cord transection; older chronic spinals), chronic spinal rats that experienced less spasticity early after injury (young chronic spinals), and rats without spasticity after transection and bilateral deafferentation (spinal isolated). These were compared with tail muscles of age-matched normal rats. Using immunohistochemistry, we observed myofiber distributions of 15.9 +/- 3.5% type I, 18.7 +/- 10.7% type IIA, 60.8 +/- 12.6% type IID(X), and 2.3 +/- 1.3% type IIB (means +/- SD) in young normals, which were not different in older normals. Young chronic spinals demonstrated transformations toward faster myofiber types with decreased type I and increased type IID(X) paralleled by atrophy of all myofiber types compared with young normals. Spinal isolated rats also demonstrated decreased type I myofiber proportions and increased type II myofiber proportions, and severe myofiber atrophy. After 4 mo of complete spasticity (older chronic spinals), myofiber type transformations were reversed, with no significant differences in type I, IIA, IID(X), or IIB proportions compared with age-matched normals. Moreover, after this prolonged spasticity, type I, IIA, and IIB myofibers recovered from atrophy, and type IID(X) myofibers partially recovered. Our results indicate that early after transection or after long-term spinal isolation, relatively inactive tail myofibers atrophy and transform toward faster myofiber types. However, long-term spasticity apparently produces neuromuscular activity that promotes recovery of myofiber types and myofiber sizes.