Acute ketamine induces neuronal hyperexcitability and deficits in prepulse inhibition by upregulating IL-6

Acute ketamine administration results in psychotic symptoms similar to those observed in schizophrenia and is regarded as a pharmacological model of schizophrenia. Accumulating evidence suggests that patients with schizophrenia show increased IL-6 levels in the blood and cerebrospinal fluid and that IL-6 levels are associated with the severity of psychotic symptoms. In the present study, we found that a single ketamine exposure led to increased expression of IL-6 and IL-6Rα, decreased dendritic spine density, increased expression and currents of T-type calcium channels, and increased neuron excitability in the hippocampal CA1 area 12 h after exposure. Acute ketamine administration also led to impaired prepulse inhibition (PPI) 12 h after administration. Additionally, we found that the expression of signaling molecules IKKα/β, NF-κB, JAK2, and STAT3 was upregulated 12 h after a single ketamine injection. The decreases in dendritic spine density, the increases in calcium currents and neuron excitability, and the impairments in PPI were ameliorated by blocking IL-6 or IL-6Rα. Our findings show that blocking IL-6 or its receptor may protect hippocampal neurons from hyperexcitability, thereby ameliorating ketamine-induced psychotic effects. Our study provides additional evidence that targeting IL-6 and its receptor is a potential strategy for treating psychotic symptoms in acute ketamine-induced psychosis and schizophrenia.

Plasmalogens regulate the AKT-ULK1 signaling pathway to control the position of the axon initial segment

The axon initial segment (AIS) is a specialized region in neurons that encompasses two essential functions, the generation of action potentials and the regulation of the axodendritic polarity. The mechanism controlling the position of the axon initial segment to allow plasticity and regulation of neuron excitability is unclear. Here we demonstrate that plasmalogens, the most abundant ether-phospholipid, are essential for the homeostatic positioning of the AIS. Plasmalogen deficiency is a hallmark of Rhizomelic Chondrodysplasia Punctata (RCDP) and Zellweger spectrum disorders, but Alzheimer's and Parkinson's disease, are also characterized by plasmalogen defects. Neurons lacking plasmalogens displaced the AIS to more distal positions and were characterized by reduced excitability. Treatment with a short-chain alkyl glycerol was able to rescue AIS positioning. Plasmalogen deficiency impaired AKT activation, and we show that inhibition of AKT phosphorylation at Ser473 and Thr308 is sufficient to induce a distal relocation of the AIS. Pathway analysis revealed that downstream of AKT, overtly active ULK1 mediates AIS repositioning. Rescuing the impaired AKT signaling pathway was able to normalize AIS position independently of the biochemical defect. These results unveil a previously unknown mechanism that couples the phospholipid composition of the neuronal membrane to the positional assembly of the AIS.

Alkaloids from Corydalis decumbens suppress neuronal excitability in primary cultures of mouse neocortical neurons

Eight previously undescribed alkaloids, named corydemine, dihydrocorydemine, corydedine, 8,13-dioxo-14-hydroxytetrahydropalmatine, egenine-α-N-oxide, egenine-β-N-oxide, 7'-O-ethylegenine-α-N-oxide, and 7'-O-ethylegenine-β-N-oxide, together with three known ones, muramine, l-tetrahydropalmatine, and (+)-egenine, were isolated from the bulbs of Corydalis decumbens. Their structures were elucidated by comprehensive spectroscopic analysis and chemical correlation. The isolated compounds were tested for their ability to modulate neuronal excitability in primary cultured neocortical neurons. Four of the compounds, corydemine, dihydrocorydemine, muramine, and l-tetrahydropalmatine, inhibited neuronal excitability with IC₅₀ values of 3.6, 16.7, 13.5 and 14.0 μM, respectively.

Hippocampal Endothelin-1 decreases excitability of pyramidal neurons and produces anxiolytic effects

Anxiety disorders contribute to the pathophysiology of psychiatric diseases, including major depression, substance abuse, and schizophrenia. The hippocampus is important for anxiety modulation. However, the mechanisms that control the neuronal activity of the hippocampus in anxiety are still not clear. We found that Endothelin-1 (ET1) mRNA in the hippocampus was down-regulated in high-anxiety mice. Neutralizing endogenous ET1 in the hippocampal CA1 enhanced anxiety-like behaviors. We next revealed that most expression of ET1 and its receptors in the CA1 takes place in pyramidal neurons, and the ET1 signaling pathway directly regulated the excitability of CA1 pyramidal neurons and glutamatergic synaptic neurotransmission. Finally, we proved that neutralizing endogenous CA1 ET1 produces anxiogenic effects on low-anxiety mice, whereas infusing exogenous ET1 into the CA1 alleviates the anxiety susceptibility of high-anxiety mice. Together, these results indicate that ET1 signaling is critical in maintaining the excitability of glutamatergic neurons in the hippocampus and, thus, in modulating anxiety-like behaviors. Because ET1 is a risk factor for ischemic stroke, our findings might also help to explain the potential mechanism of emotional abnormality in stroke.

Functional Effects of Schizophrenia-Linked Genetic Variants on Intrinsic Single-Neuron Excitability: A Modeling Study

BACKGROUND

Recent genome-wide association studies have identified a large number of genetic risk factors for schizophrenia (SCZ) featuring ion channels and calcium transporters. For some of these risk factors, independent prior investigations have examined the effects of genetic alterations on the cellular electrical excitability and calcium homeostasis. In the present proof-of-concept study, we harnessed these experimental results for modeling of computational properties on layer V cortical pyramidal cells and identified possible common alterations in behavior across SCZ-related genes.

METHODS

We applied a biophysically detailed multicompartmental model to study the excitability of a layer V pyramidal cell. We reviewed the literature on functional genomics for variants of genes associated with SCZ and used changes in neuron model parameters to represent the effects of these variants.

RESULTS

We present and apply a framework for examining the effects of subtle single nucleotide polymorphisms in ion channel and calcium transporter-encoding genes on neuron excitability. Our analysis indicates that most of the considered SCZ-related genetic variants affect the spiking behavior and intracellular calcium dynamics resulting from summation of inputs across the dendritic tree.

CONCLUSIONS

Our results suggest that alteration in the ability of a single neuron to integrate the inputs and scale its excitability may constitute a fundamental mechanistic contributor to mental disease, alongside the previously proposed deficits in synaptic communication and network behavior.

Docosahexaenoic acid inhibits mechanical allodynia and thermal hyperalgesia in diabetic rats by decreasing the excitability of DRG neurons

Diabetes mellitus is a common metabolic disease in human beings with characteristic symptoms of hyperglycemia, chronic inflammation and insulin resistance. One of the most common complications of early-onset diabetes mellitus is peripheral diabetic neuropathy, which is manifested either by loss of nociception or by allodynia and hyperalgesia. Dietary fatty acids, especially polyunsaturated fatty acids, have been shown the potential of anti-inflammation and modulating neuron excitability. The present study investigated the effects of docosahexaenoic acid (DHA) on the excitability of dorsal root ganglion (DRG) neurons in streptozotocin (STZ)-induced diabetes rats. The effects of DHA on the allodynia and hyperalgesia of diabetic rats were also evaluated. Dietary DHA supplementation effectively attenuated both allodynia and hyperalgesia induced by STZ injection. DHA supplementation decreased the excitability of DRG neurons by decreasing the sodium currents and increasing potassium currents, which may contribute to the effect of alleviating allodynia and hyperalgesia in diabetic rats. The results suggested that DHA might be useful as an adjuvant therapy for the prevention and treatment of painful diabetic neuropathy.