Increased expression of glial fibrillary acidic protein in prefrontal cortex in psychotic illness

Rat nucleus accumbens core astrocytes modulate reward and the motivation to self-administer ethanol after abstinence

Our understanding of the active role that astrocytes play in modulating neuronal function and behavior is rapidly expanding, but little is known about the role that astrocytes may play in drug-seeking behavior for commonly abused substances. Given that the nucleus accumbens is critically involved in substance abuse and motivation, we sought to determine whether nucleus accumbens astrocytes influence the motivation to self-administer ethanol following abstinence. We found that the packing density of astrocytes that were expressing glial fibrillary acidic protein increased in the nucleus accumbens core (NAcore) during abstinence from EtOH self-administration. No change was observed in the nucleus accumbens shell. This increased NAcore astrocyte density positively correlated with the motivation for ethanol. Astrocytes can communicate with one another and influence neuronal activity through gap-junction hemichannels. Because of this, the effect of blocking gap-junction hemichannels on the motivation for ethanol was examined. The motivation to self-administer ethanol after 3 weeks abstinence was increased following microinjection of gap-junction hemichannel blockers into the NAcore at doses that block both neuronal and astrocytic channels. In contrast, no effect was observed following microinjection of doses that are not thought to block astrocytic channels or following microinjection of either dose into the nucleus accumbens shell. Additionally, the motivation for sucrose after 3 weeks abstinence was unaffected by NAcore gap-junction hemichannel blockers. Next, Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) were selectively expressed in NAcore astrocytes to test the effect of astrocyte stimulation. DREADD activation increased cytosolic calcium in primary astrocytes, facilitated responding for rewarding brain stimulation, and reduced the motivation for ethanol after 3 weeks abstinence. This is the first work to modulate drug-seeking behavior with astrocyte-specific DREADDs. Taken together, our findings demonstrate that NAcore astrocytes can shape the motivation to self-administer ethanol; suggesting that the development of ligands which selectively stimulate astrocytes may be a successful strategy to abate ethanol-seeking behavior.

Evidence for morphological alterations in prefrontal white matter glia in schizophrenia and bipolar disorder

BACKGROUND

Brain imaging studies suggest that volume reductions and compromised white matter integrity occur in schizophrenia and bipolar disorder (BD). However, the cellular correlates have not yet been identified. To address this issue we assessed oligodendrocyte, astrocyte and microglial populations in postmortem white matter from schizophrenia, BD and nonpsychiatric control samples.

METHODS

The density, areal fraction and spatial distribution of glial fibrillary acidic protein (GFAP)-expressing astrocytes and ionized calcium-binding adaptor molecule-1 (IBA-1)-expressing microglia as well as the density, nuclear size and spatial distribution of Nissl-stained oligodendrocytes were quantified in postmortem white matter adjacent to the dorsolateral prefrontal cortex (Brodmann area 9) in schizophrenia, BD and control samples (n = 20). In addition, the oligodendrocyte-associated proteins myelin basic protein and 2,3-cyclic-nucleotide 3-phosphodiesterase (CNPase) were quantified in the same samples by enzyme-linked immunosorbent assay and immunoblotting.

RESULTS

Oligodendrocyte density (p = 0.012) and CNPase protein levels (p = 0.038) differed between groups, being increased in BD compared with control samples. The GFAP area fraction (p = 0.05) and astrocyte spatial distribution (p = 0.040) also differed between groups, reflecting decreased area fraction and increased cell clustering in both schizophrenia and BD samples.

LIMITATIONS

Oligodendrocytes were identified using morphological criteria.

CONCLUSION

This study provides evidence for glial pathology in prefrontal white matter in schizophrenia and BD. Changes in oligodendrocyte and astrocyte populations in white matter in the major psychiatric disorders may reflect disruptions in structural or metabolic support of axons.

Role of astrocytes in memory and psychiatric disorders

Over the past decade, the traditional description of astrocytes as being merely accessories to brain function has shifted to one in which their role has been pushed into the forefront of importance. Current views suggest that astrocytes:(1) are excitable through calcium fluctuations and respond to neurotransmitters released at synapses; (2) communicate with each other via calcium waves and release their own gliotransmitters which are essential for synaptic plasticity; (3) activate hundreds of synapses at once, thereby synchronizing neuronal activity and activating or inhibiting complete neuronal networks; (4) release vasoactive substances to the smooth muscle surrounding blood vessels enabling the coupling of circulation (blood flow) to local brain activity; and (5) release lactate in an activity-dependent manner in order to supply neuronal metabolic demand. In consequence, the role of astrocytes and astrocytic gliotransmitters is now believed to be critical for higher brain function and recently, evidence begins to gather suggesting that astrocytes are pivotal for learning and memory. All of the above are reviewed here while focusing on the role of astrocytes in memory and psychiatric disorders.

Increased expression of astrocyte markers in schizophrenia: Association with neuroinflammation

OBJECTIVE

While schizophrenia may have a progressive component, the evidence for neurodegenerative processes as indicated by reactive astrocytes is inconclusive. We recently identified a subgroup of individuals with schizophrenia with increased expression of inflammatory markers in prefrontal cortex, and hypothesized that this subgroup would also have reactive astrocytes.

METHOD

We measured glial fibrillary acidic protein (GFAP) mRNA by quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR) and protein levels by immunoblotting in grey matter homogenate from 37 individuals with schizophrenia and 37 unaffected controls. We examined the morphology of GFAP-positive astrocytes in immunostained sections of middle frontal gyrus. We tested if GFAP expression or astrocyte morphology were altered in people with schizophrenia with increased expression of inflammatory markers. We used RNA-Seq data on a subset of patients and controls (n=20/group) to ascertain whether mRNA transcripts associated with astrogliosis were elevated in the individuals with active neuroinflammation.

RESULTS

GFAP (mRNA and protein) levels and astrocyte morphology were not significantly different between people with schizophrenia and controls overall. However, individuals with schizophrenia with neuroinflammation had increased expression of GFAP mRNA (t(33)=2.978, p=0.005), hypertrophic astrocyte morphology (χ(2)(2)=6.281, p=0.043), and statistically significant elevated expression of three mRNA transcripts previously associated with astrogliosis.

CONCLUSIONS

We found clear evidence of astrogliosis in a subset of people with schizophrenia. We suggest that the lack of astrogliosis reported in previous studies may be due to cohort differences in aetiopathology, illness stage, treatment exposure, or a failure to examine subsets of people with schizophrenia.

Hemichannels: new roles in astroglial function

The role of astrocytes in brain function has evolved over the last decade, from support cells to active participants in the neuronal synapse through the release of "gliotransmitters."Astrocytes express receptors for most neurotransmitters and respond to them through Ca(2+) intracellular oscillations and propagation of intercellular Ca(2+) waves. While such waves are able to propagate among neighboring astrocytes through gap junctions, thereby activating several astrocytes simultaneously, they can also trigger the release of gliotransmitters, including glutamate, d-serine, glycine, ATP, adenosine, or GABA. There are several mechanisms by which gliotransmitter release occurs, including functional hemichannels. These gliotransmitters can activate neighboring astrocytes and participate in the propagation of intercellular Ca(2+) waves, or activate pre- and post-synaptic receptors, including NMDA, AMPA, and purinergic receptors. In consequence, hemichannels could play a pivotal role in astrocyte-to-astrocyte communication and astrocyte-to-neuron cross-talk. Recent evidence suggests that astroglial hemichannels are involved in higher brain functions including memory and glucose sensing. The present review will focus on the role of hemichannels in astrocyte-to-astrocyte and astrocyte-to neuron communication and in brain physiology.

Endogenous kynurenic acid regulates extracellular GABA levels in the rat prefrontal cortex

The tryptophan metabolite kynurenic acid (KYNA) is an endogenous antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR) and, at higher concentrations, inhibits ionotropic glutamate receptors. Increases in KYNA levels are seen in brain and cerebrospinal fluid in individuals with schizophrenia (SZ) and may be causally related to cognitive deficits in SZ and other psychiatric diseases. As dysfunction of circuits involving GABAergic neurons in the prefrontal cortex (PFC) likely plays a role in the cognitive impairments seen in these disorders, we examined the effects of KYNA on extracellular GABA in this brain area. Applied to awake rats for 2 h by reverse dialysis, KYNA concentration-dependently and reversibly reduced extracellular GABA levels, with 300 nM KYNA causing a nadir of ∼45% of baseline concentrations. This effect was not duplicated by reverse dialysis of the selective glycineB receptor antagonist 7-Cl-KYNA (100 nM) or the AMPA/kainate receptor antagonist CNQX (100 μM), and was prevented by co-application of galantamine (5 μM), a positive allosteric modulator of the α7nAChR. Conversely, inhibition of endogenous KYNA formation by reverse dialysis of (S)-4-(ethylsulfonyl)benzoylalanine (ESBA; 5 mM) reversibly increased GABA levels in the PFC, reaching a peak of ∼160% of baseline concentrations. Co-infusion of 30 nM KYNA neutralized this effect. Taken together, these results demonstrate a role for endogenous KYNA in the bi-directional control of GABAergic neurotransmission in the PFC. Pharmacological manipulation of KYNA may therefore be useful in the treatment of GABAergic impairments in SZ and other brain disorders involving the PFC.

[Reactivity of perineuronal astrocytes in the prefrontal cortex in schizophrenia: an ultrastructural morphometric study]

OBJECTIVE

Previously the ultrastructural alterations of astrocytes have been reported in schizophrenia. Reduced dendritic arborization of the neurons in layer 5 of the prefrontal cortex has been found in schizophrenia. Authors hypothesized that the abnormalities in perineuronal astrocytes (PA) might contribute to these neuronal changes. It was aimed to study the ultrastructure of PA in the prefrontal cortex in schizophrenia.

MATERIAL AND METHODS

Postmortem electron microscopic morphometric study of PA was performed in layer 5, area 10 of the prefrontal cortex in 39 cases of schizophrenia and 37 controls.

RESULTS

No significant group differences were found in areas of cell, nucleus, cytoplasm, volume fraction (Vv) of lipofuscin granules and areal density of PA. However, in the subgroup of women with schizophrenia, the areal density of PA was significantly lower and the area of PA was significantly higher as compared to the subgroup of healthy women (-52%, p<0,01; +32%, p<0.05 respectively) and to the subgroup of men with schizophrenia (-56%, p<0,01; +23%, p<0,05 respectively). The area of PA nucleus was negatively correlated with the duration of disease (r= -0.37, p=0.02) and positively with the age of disease onset (ADO) (r=0,47, p<0,01). Areas of PA and of PA nucleus were significantly lower in early ADO (<21 y.o.) as compared to the adult ADO (>21 y.o.) (-24%, p<0.05). Vv of lypofuscin granules was correlated with the age in control group (r=0.52, p=0.001), but not in schizophrenia group (r=0.13, p=0.4).

CONCLUSION

Significant differences in PA reactivity in the prefrontal cortex in the schizophrenia are associated with gender and age at onset of the disease.

Neuron-glia interaction as a possible glue to translate the mind-brain gap: a novel multi-dimensional approach toward psychology and psychiatry

Neurons and synapses have long been the dominant focus of neuroscience, thus the pathophysiology of psychiatric disorders has come to be understood within the neuronal doctrine. However, the majority of cells in the brain are not neurons but glial cells including astrocytes, oligodendrocytes, and microglia. Traditionally, neuroscientists regarded glial functions as simply providing physical support and maintenance for neurons. Thus, in this limited role glia had been long ignored. Recently, glial functions have been gradually investigated, and increasing evidence has suggested that glial cells perform important roles in various brain functions. Digging up the glial functions and further understanding of these crucial cells, and the interaction between neurons and glia may shed new light on clarifying many unknown aspects including the mind-brain gap, and conscious-unconscious relationships. We briefly review the current situation of glial research in the field, and propose a novel translational research with a multi-dimensional model, combining various experimental approaches such as animal studies, in vitro & in vivo neuron-glia studies, a variety of human brain imaging investigations, and psychometric assessments.