AMPA-receptor trafficking and injury-induced cell death

AMPA receptor mediated behavioral plasticity in the isolated rat spinal cord

Previous research has demonstrated that the spinal cord is capable of a simple form of instrumental learning. Spinally transected rats that receive shock to a hind leg in an extended position quickly learn to maintain the leg in a flexed position, reducing net shock exposure whenever that leg is flexed. Subjects that receive shock independent of leg position (uncontrollable shock) do not exhibit an increase in flexion duration and later fail to learn when tested with controllable shock (learning deficit). The present study examined the role of the ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in spinal learning. Intrathecal application of the AMPA receptor antagonist CNQX disrupted performance of a spinal instrumental learning in a dose dependent fashion (Experiment 1). CNQX also disrupted the maintenance of the instrumental response (Experiment 2) and blocked the induction of the learning deficit (Experiment 3). Intrathecal application of the agonist AMPA had a non-monotonic effect, producing a slight facilitation of performance at a low dose and disrupting learning at a high concentration (Experiment 4). Within the dose range tested, intrathecal application of AMPA did not have a long-term effect (Experiment 5). The results suggest that AMPA-mediated transmission plays an essential role in both instrumental learning and the induction of the learning deficit.

Acute neuroimmune modulation attenuates the development of anxiety-like freezing behavior in an animal model of traumatic brain injury

Chronic anxiety is a common and debilitating result of traumatic brain injury (TBI) in humans. While little is known about the neural mechanisms of this disorder, inflammation resulting from activation of the brain's immune response to insult has been implicated in both human post-traumatic anxiety and in recently developed animal models. In this study, we used a lateral fluid percussion injury (LFPI) model of TBI in the rat and examined freezing behavior as a measure of post-traumatic anxiety. We found that LFPI produced anxiety-like freezing behavior accompanied by increased reactive gliosis (reflecting neuroimmune inflammatory responses) in key brain structures associated with anxiety: the amygdala, insula, and hippocampus. Acute peri-injury administration of ibudilast (MN166), a glial cell activation inhibitor, suppressed both reactive gliosis and freezing behavior, and continued neuroprotective effects were apparent several months post-injury. These results support the conclusion that inflammation produced by neuroimmune responses to TBI play a role in post-traumatic anxiety, and that acute suppression of injury-induced glial cell activation may have promise for the prevention of post-traumatic anxiety in humans.

Parasynaptic NMDA receptor signaling couples neuronal glutamate transporter function to AMPA receptor synaptic distribution and stability

At synapses, two major processes occur concomitantly after the release of glutamate: activation of AMPA receptors (AMPARs) to conduct synaptic transmission and activation of excitatory amino acid transporters (EAATs) for transmitter removal. Although crosstalk between the receptors and EAATs is conceivable, whether and how the transporter activity affects AMPAR synaptic localization remain unknown. Using cultured hippocampal and cortical rat neurons, we show that inhibition of glutamate transporters leads to rapid reduction in AMPAR synaptic accumulation and total AMPAR abundance. EAAT inactivity also results in elevated internalization and reduced surface expression of AMPARs. The reduction in AMPAR amount is accompanied by receptor ubiquitination and can be blocked by suppression of proteasome activity, indicating the involvement of proteasome-mediated receptor degradation. Consistent with glutamate spillover, effect of EAAT inhibition on AMPAR distribution and stability is dependent on the activation of parasynaptically localized NR2B-containing NMDA receptors (NMDARs). Moreover, we show that neuronal glutamate transporters, especially those localized at the postsynaptic sites, are responsible for the observed effect during EAAT suppression. These results indicate a role for neuron-specific glutamate transporters in AMPAR synaptic localization and stability.

Cytokines and brain excitability

Cytokines are molecules secreted by peripheral immune cells, microglia, astrocytes and neurons in the central nervous system. Peripheral or central inflammation is characterized by an upregulation of cytokines and their receptors in the brain. Emerging evidence indicates that pro-inflammatory cytokines modulate brain excitability. Findings from both the clinical literature and from in vivo and in vitro laboratory studies suggest that cytokines can increase seizure susceptibility and may be involved in epileptogenesis. Cellular mechanisms that underlie these effects include upregulation of excitatory glutamatergic transmission and downregulation of inhibitory GABAergic transmission.

Immune function genes, genetics, and the neurobiology of addiction

The neuroimmune system (i.e., the immune system and those components of the nervous system that help regulate immune responses), and in particular the innate immune system, play a role in the development of addictions, including alcoholism, particularly in the context of stressful situations. Certain cells of the neuroimmune system are activated both by stress and by environmental factors such as alcohol, resulting in the induction of genes involved in innate immunity. One of the molecules mediating this gene induction is a regulatory protein called nuclear factor-κB, which activates many innate immune genes. Innate immune gene induction in certain brain regions (e.g., the frontal cortex), in turn, can disrupt decision making, which is a characteristic of addiction to alcohol and other drugs. Likewise, altered neuroimmune signaling processes are linked to alcohol-induced negative affect and depression-like behaviors and also regulate alcohol-drinking behavior. Moreover, the expression of several genes and proteins involved in innate immunity is enhanced in addicted people. Finally, specific variants of multiple innate immune genes are associated with the genetic risk for alcoholism in humans, further strengthening the connection between increased brain innate immune gene expression and alcohol addiction.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Glutamate signaling in the pathophysiology and therapy of prenatal insults

Birth asphyxia and hypoxia-ischemia (HI) are important factors affecting the normal development and maturation of the central nervous system (CNS). Depending on the maturity of the brain, HI-induced damage at different ages is region-selective, the white matter (WM) peripheral to the lateral ventricles being selectively vulnerable to damage in premature infants. As a squeal of primary or secondary HI in the preterm infant, the brain injury comprises periventricular leukomalasia (PVL), accompanied by neuronal and axonal damage, which affects several brain regions. Premature delivery and improved neonatal intensive care have led to a survival rate of about 75% to 90% of infants weighting under 1500g both in Europe and in the United States. However, about 5-10% of these survivors exhibit cerebral palsy (CP), and many have cognitive, behavioral, attentional or socialization deficits. In this review, we first shortly discuss developmental changes in the expression of the excitatory glutamate receptors (GluRs), and then in more detail elucidate the contribution of GluRs to oligodendrocyte (OL) damage both in experimental models and in preterm human infants. Finally, therapeutic interventions targeted at GluRs at the young age are discussed in the light of results obtained from recent experimental HI animal models and from humans.

Rapid improvement of chronic stroke deficits after perispinal etanercept: three consecutive cases

BACKGROUND

Thrombolytic therapy reduces stroke size and disability by reperfusion and salvage of ischaemic penumbra. Emerging evidence suggests that retrieved penumbra may be the site of ongoing inflammatory pathology that includes extensive microglial activation. Microglial activation may be associated with excessive levels of tumour necrosis factor (TNF) and resultant neurotoxicity. Etanercept, a potent biologic TNF antagonist, reduces microglial activation in experimental models and has been therapeutically effective in models of brain and neuronal injury. Perispinal administration of etanercept, previously reported to be beneficial for the treatment of Alzheimer's disease, may facilitate delivery of etanercept into the brain.

OBJECTIVE

The objective of this report is to document the initial clinical response to perispinal etanercept in the first chronic stroke cohort so treated.

METHODS

Three consecutive patients with stable and persistent chronic neurological deficits due to strokes that had failed to resolve despite previous treatment and rehabilitation were evaluated at an outpatient clinic. They were treated off-label with perispinal etanercept as part of the clinic's practice of medicine.

RESULTS

All three patients had chronic hemiparesis, in addition to other stroke deficits. Their stroke distributions were right middle cerebral artery (MCA), brainstem (medulla) and left MCA. The two patients with MCA strokes had both received acute thrombolytic therapy. Each of the three patients was treated with an initial dose of perispinal etanercept 13, 35 and 36 months following their acute stroke, respectively. Significant clinical improvement following perispinal etanercept administration was observed in all patients. Onset of clinical response was evident within 10 minutes of perispinal injection in all patients. Improvements in hemiparesis, gait, hand function, hemi-sensory deficits, spatial perception, speech, cognition and behaviour were noted among the patients treated. Each patient received a second perispinal etanercept dose at 22-26 days after the first dose that was followed by additional clinical improvement.

CONCLUSIONS

Open-label administration of perispinal etanercept resulted in rapid neurological improvement in three consecutive patients with chronic neurological dysfunction due to strokes occurring 13-36 months earlier. These results suggest that stroke may result in chronic TNF-mediated pathophysiology that may be amenable to therapeutic intervention long after the acute event. Randomized clinical trials of perispinal etanercept for selected patients with chronic neurological dysfunction following stroke are indicated.