Glial Density Research Articles

Dlx1/2 mice have abnormal enteric nervous system function

Decades ago, investigators reported that mice lacking DLX1 and DLX2, transcription factors expressed in the enteric nervous system (ENS), die with possible bowel motility problems. These problems were never fully elucidated. We found that mice lacking DLX1 and DLX2 (Dlx1/2-/- mice) had slower small bowel transit and reduced or absent neurally mediated contraction complexes. In contrast, small bowel motility seemed normal in adult mice lacking DLX1 (Dlx1-/-). Even with detailed anatomic studies, we found no defects in ENS precursor migration, or neuronal and glial density in Dlx1/2-/- or Dlx1-/- mice. However, RNA sequencing of Dlx1/2-/- ENS revealed dysregulation of many genes, including vasoactive intestinal peptide (Vip). Using immunohistochemistry and reporter mice, we then found that Dlx1/2-/- mice have reduced VIP expression and fewer VIP-lineage neurons in their ENS. Our study reveals what we believe is a novel connection between Dlx genes and Vip and highlights the observation that dangerous bowel motility problems can occur in the absence of easily identifiable ENS structural defects. These findings may be relevant for disorders like chronic intestinal pseudo-obstruction (CIPO) syndrome.

Chronic maternal interleukin-17 and autism-related cortical gene expression, neurobiology, and behavior.

Chronic inflammation during pregnancy (e.g., preeclampsia, diabetes) is linked to increased risk for offspring neurodevelopmental disorders such as autism spectrum disorder (ASD). However, mediators of such exposures that could be targeted with maternal intervention are unclear, as few chronic gestational inflammation models have been tested. One potential mediator is interleukin-17 (IL-17), a pro-inflammatory cytokine implicated in neurodevelopmental disorders and gestational disease. To test chronic maternal IL-17 impacts on offspring, C57BL/6J dams were administered IL-17A continuously throughout pregnancy. Offspring were assessed for body weight; cortical volume, gene expression, and cellular composition; and adult behavior. IL-17A-condition offspring exhibited decreased somatic and cortical size at embryonic day 18 (E18) and as adults. mRNA sequencing of E18 cortex revealed 320 differentially expressed genes in males, but none in females. These were significantly enriched for ASD (Simons Foundation Autism Research Initiative), synaptic, and cell cycle genes. By adulthood, neocortical glial cell density and gene expression were decreased, while GABAergic synaptic gene expression was increased in males. Furthermore, IL-17A-condition male but not female offspring exhibited reduced anxiety-like behavior. Social approach deficits in males were negatively correlated with neocortical GABAergic synaptic gene expression. Chronic gestational IL-17A was sufficient to cause ASD-like phenotypes early and persistently in male offspring. This echoes the male bias, altered cortical development, and behavioral findings in ASD, suggesting that chronic maternal IL-17 contributes to offspring ASD pathogenesis. Furthermore, the trajectory from embryonically dysregulated synaptic and cell cycle genes to disrupted adult glia, inhibitory synapses, and behavior suggests a mechanism for chronic maternal IL-17 effects on offspring.

Antiamnesic effects of tofisopam against scopolamine-induced cognitive impairments in rats

In this study, we investigated the potential therapeutic effects of tofisopam, a 2,3-benzodiazepine derivative anxiolytic, on cognitive deficits in rats with scopolamine-induced amnesia. Cognitive performance of the rats was investigated by using the Morris water maze and passive avoidance tests. Changes in motor activity were assessed by using the activity cage and Rota-rod tests and then morphological changes in the hippocampus were assessed via immunohistochemical stainings. The results indicated that scopolamine impaired learning and memory parameters in rats. Worsened cognitive performance, neuronal loss, and decreased hippocampal synaptophysin, Ki-67, and glial fibrillary acidic protein density were observed. Tofisopam administration at a dose of 50 mg/kg for seven days improved the impaired cognitive performance, enhanced the attenuated synaptic transmission in the hippocampus, increased proliferation in subgranular zones, and improved the decrease in astrocytes in amnesic rats. These findings point out the anti-amnesic effects of tofisopam with concomitant improvements in the hippocampal synaptogenesis, neurogenesis, and glial plasticity, for the first time. Presented beneficial effects of tofisopam on cognitive dysfunctions may have a notable clinical value considering the fact that one of the most important side effects of 1,4-benzodiazepines, which are classical anxiolytic drugs, is amnesia. However, these preclinical results need to be confirmed with further clinical studies, first.

Treatment with CCR2 antagonist is neuroprotective but does not alter epileptogenesis in the pilocarpine rat model of epilepsy

Neuroinflammation role on epileptogenesis has been the subject of increasing interest. Many studies showed elevation in cytokines and chemokines expression following seizures, such as, CCL2 protein (C-C motif ligand 2 chemokine) and its specific receptor, CCR2. In addition, recent studies manipulating the CCL2/CCR2 complex verified improved seizure outcome in different seizure models. In the present study, the effects of CCR2 antagonist was investigated using the pilocarpine rat model of epilepsy. Status epilepticus (SE) was induced by pilocarpine i.p. injection in adult rats. Daily oral treatment with CCR2 antagonist or vehicle was initiated 5 h following SE and lasted 5 or 10 days. Rats were euthanized 5 days after SE to evaluate neuronal damage and glial density or 30 days after SE to investigate spontaneous seizures development and seizure susceptibility to a second hit pentylenetetrazol (PTZ) test. Rats that received CCR2 antagonist presented less degenerating cells at hippocampal CA1 region. There was also a significant decrease in CA1 volume after SE that was not observed in treated rats. On the other hand, microglia cell density increased after SE regardless of CCR2 antagonist use. Treatment with CCR2 antagonist did not alter spontaneous seizure occurrence or later seizure susceptibility to PTZ in chronic rats. Additional rats were pretreated with CCR2 antagonist prior to SE induction, but this did not change SE progression. The data show that oral treatment with CCR2 antagonist is neuroprotective, but does not alter other epileptogenic factors, such as, neuroinflammation, or seizure development, after pilocarpine-induced SE in rats.

Astrocytic plasticity at the dorsal dentate gyrus on an animal model of recurrent depression

Astrocytes are now known to play crucial roles in the central nervous system, supporting and closely interacting with neurons and therefore able to modulate brain function. Both human postmortem studies in brain samples from patients diagnosed with Major Depressive Disorder and from animal models of depression reported numerical and morphological astrocytic changes specifically in the hippocampus. In particular, these studies revealed significant reductions in glial cell density denoted by a decreased number of S100B-positive cells and a decrease in GFAP expression in several brain regions including the hippocampus. To reveal plastic astrocytic changes in the context of recurrent depression, we longitudinally assessed dynamic astrocytic alterations (gene expression, cell densities and morphologic variations) in the hippocampal dentate gyrus under repeated exposure to unpredictable chronic mild stress (uCMS) and upon treatment with two antidepressants, fluoxetine and imipramine. Both antidepressants decreased astrocytic complexity immediately after stress exposure. Moreover, we show that astrocytic alterations, particularly an increased number of S100B-positive cells, are observed after recurrent stress exposure. Interestingly, these alterations were prevented at the long-term by either fluoxetine or imipramine treatment.

Sex-specific effects of prenatal valproic acid exposure on sociability and neuroinflammation: Relevance for susceptibility and resilience in autism

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with an incidence four times higher in boys than in girls. By analyzing the effect of sex in a mouse model of ASD, we were able to identify immune alterations that could underlie this sex bias.Pregnant mice were injected subcutaneously with 600 mg/kg of valproic acid (VPA) or saline at gestational day 12.5. Their male and female offspring were evaluated in a social interaction test at adulthood, and only male VPA mice showed reduced sociability levels and a lack of preference for the social stimulus over a novel object. We then analyzed the corticosterone (CORT) response to an inflammatory stimulus, as a measure of the hypothalamus-pituitary-adrenal (HPA) function, and the neuroinflammatory state in adult and young animals. Adult VPA males exhibited increased basal CORT levels, while VPA females showed levels comparable to controls. As male mice showed a blunted CORT response at PD21 when compared to female mice, we propose that this early dimorphism could explain the different effects of VPA on HPA function. In addition, prenatal VPA exposure resulted in altered astroglial and microglial cell density levels in the cerebellum and dentate gyrus of adult mice. These neuroinflammatory effects were more pronounced in females than males, and appeared at early developmental stages. Hence, these postnatal glial density differences could underlie the behavioral alterations observed in adulthood, when only males show a social deficit.Our work contributes to the understanding of biological mechanisms affected by VPA on male and female rodents and shed light on the study of possible resilience mechanisms in the female population and/or susceptibility to ASD in boys.

Selective brain neuronal and glial losses without changes in GFAP immunoreactivity: Young versus mature adult Wistar rats

Normal ageing results in brain selective neuronal and glial losses. In the present study we analyze neuronal and glial changes in Wistar rats at two different ages, 45 days (young) and 420 days (mature adult), using Nissl staining and glial fibrillary acidic protein (GFAP) immunohistochemistry associated to the Sholl analysis. Comparing mature adults with young rats we noted the former present a decrease in neuronal density in the cerebral cortex, corpus callosum, pyriform cortex, L.D.D.M., L.D.V.L., central medial thalamic nucleus and zona incerta. A decrease in glial density was found in the dorsomedial and ventromedial hypothalamic nuclei. Additionally, the neuron/glia ratio was reduced in the central medial thalamic nucleus and increased in the habenula. No changes were found in the neuronal and glial densities or neuron/glia ratio in the other studied regions. The number of astrocytic primary processes and the number of intersections counted in the Sholl analysis presented no significant difference in any of the studied regions. Overall, neither GFAP positive astrocytic density nor GFAP immunoreactivity showed alteration.

Parsing the Heterogeneity of Brain Metabolic Disturbances in Autism Spectrum Disorder

BackgroundDespite rising prevalence of autism spectrum disorder (ASD), its brain bases remain uncertain. Abnormal levels of N-acetyl compounds, glutamate+glutamine, creatine+phosphocreatine, or choline compounds measured by proton magnetic resonance spectroscopy suggest that neuron or glial density, mitochondrial energetic metabolism, and/or inflammation contribute to ASD neuropathology. The neuroanatomic distribution of these metabolites could help evaluate leading theories of ASD. However, most prior magnetic resonance spectroscopy studies had small samples (all <60, most <20), interrogated only a small fraction of the brain, and avoided assessing effects of age, sex, and IQ. MethodsWe acquired near-whole-brain magnetic resonance spectroscopy of N-acetyl compounds, glutamate+glutamine, creatine+phosphocreatine, and choline compounds in 78 children and adults with ASD and 96 typically developing children and adults, rigorously evaluating effects of diagnosis and severity on metabolites, as moderated by age, sex, and IQ. ResultsEffects of ASD and its severity included reduced levels of multiple metabolites in white matter and the perisylvian cortex and elevated levels in the posterior cingulate, consistent with white matter and social-brain theories of ASD. Regionally, both slower and faster decreases of metabolites with age were observed in ASD versus TD. Male-female metabolite differences were widely smaller in ASD than typically developing children and adults. ASD-specific decreases in metabolites with decreasing IQ occurred in several brain areas. ConclusionsResults support multifocal abnormal neuron or glial density, mitochondrial energetics, or neuroinflammation in ASD, alongside widespread starkly atypical moderating effects of age, sex, and IQ. These findings help parse the neurometabolic signature for ASD by phenotypic heterogeneity.

Astrocyte, a Promising Target for Mood Disorder Interventions.

Mood disorders have multiple phenotypes and complex underlying biological mechanisms and, as such, there are no effective therapeutic strategies. A review of recent work on the role of astrocytes in mood disorders is thus warranted, which we embark on here. We argue that there is tremendous potential for novel strategies for therapeutic interventions based on the role of astrocytes. Astrocytes are traditionally considered to have supporting roles within the brain, yet emerging evidence has shown that astrocytes have more direct roles in influencing brain function. Notably, evidence from postmortem human brain tissues has highlighted changes in glial cell morphology, density and astrocyte-related biomarkers and genes following mood disorders, indicating astrocyte involvement in mood disorders. Findings from animal models strongly imply that astrocytes not only change astrocyte morphology and physiological characteristics but also influence neural circuits via synapse structure and formation. This review pays particular attention to interactions between astrocytes and neurons and argues that astrocyte dysfunction affects the monoaminergic system, excitatory–inhibitory balance and neurotrophic states of local networks. Together, these studies provide a foundation of knowledge about the exact role of astrocytes in mood disorders. Importantly, we then change the focus from neurons to glial cells and the interactions between the two, so that we can understand newly proposed mechanisms underlying mood disorders, and to identify more diagnostic indicators or effective targets for treatment of these diseases.

Role of D3 dopamine receptors in modulating neuroanatomical changes in response to antipsychotic administration

Clinical research has shown that chronic antipsychotic drug (APD) treatment further decreases cortical gray matter and hippocampus volume, and increases striatal and ventricular volume in patients with schizophrenia. D2-like receptor blockade is necessary for clinical efficacy of the drugs, and may be responsible for inducing these volume changes. However, the role of other D2-like receptors, such as D3, remains unclear. Following our previous work, we undertook a longitudinal study to examine the effects of chronic (9-week) typical (haloperidol (HAL)) and atypical (clozapine (CLZ)) APDs on the neuroanatomy of wild-type (WT) and dopamine D3-knockout (D3KO) mice using magnetic resonance imaging (MRI) and histological assessments in a sub-region of the anterior cingulate cortex (the prelimbic [PL] area) and striatum. D3KO mice had larger striatal volume prior to APD administration, coupled with increased glial and neuronal cell density. Chronic HAL administration increased striatal volume in both WT and D3KO mice, and reduced PL area volume in D3KO mice both at trend level. CLZ increased volume of the PL area of WT mice at trend level, but decreased D3KO PL area glial cell density. Both typical and atypical APD administration induced neuroanatomical remodeling of regions rich in D3 receptor expression, and typically altered in schizophrenia. Our findings provide novel insights on the role of D3 receptors in structural changes observed following APD administration in clinical populations.

Early-Life Adversity, but Not Suicide, Is Associated With Less Prefrontal Cortex Gray Matter in Adulthood.

BackgroundSuicide and major depression are prevalent in individuals reporting early-life adversity. Prefrontal cortex volume is reduced by stress acutely and progressively, and changes in neuron and glia density are reported in depressed suicide decedents. We previously found reduced neurotrophic factor brain-derived neurotrophic factor in suicide decedents and with early-life adversity, and we sought to determine whether cortex thickness or neuron or glia density in the dorsolateral prefrontal and anterior cingulate cortex are associated with early-life adversity or suicide.MethodsA total of 52 brains, constituting 13 quadruplets of nonpsychiatric controls and major depressive disorder suicide decedents with and without early-life adversity, were matched for age, sex, race, and postmortem interval. Brains were collected at autopsy and frozen, and dorsolateral prefrontal cortex and anterior cingulate cortex were later dissected, postfixed, and sectioned. Sections were immunostained for neuron-specific nuclear protein (NeuN) to label neurons and counterstained with thionin to stain glial cell nuclei. Cortex thickness, neuron and glial density, and neuron volume were measured by stereology.ResultsCortical thickness was 6% less with early-life adversity in dorsolateral prefrontal cortex and 12% less in anterior cingulate cortex (P < .05), but not in depressed suicide decedents in either region. Neuron density was not different in early-life adversity or with suicide, but glial density was 17% greater with early-life adversity in dorsolateral prefrontal cortex and 15% greater in anterior cingulate cortex, but not in suicides. Neuron volume was not different with early-life adversity or suicide.ConclusionsReported early-life adversity, but not the stress associated with suicide, is associated with thinner prefrontal cortex and greater glia density in adulthood. Early-life adversity may alter normal neurodevelopment and contribute to suicide risk.

Evaluation of the Toxicity and Neurological Effects of Fulranumab in Adult Cynomolgus Monkeys.

Fulranumab, an anti-human nerve growth factor antibody, was evaluated in a series of nonclinical toxicology studies. No treatment effects were observed in adolescent cynomolgus monkeys in standard design, repeat-dose toxicology studies of up to 6 months. Adverse effects on the developing nervous system were observed in offspring of pregnant cynomolgus monkeys treated with fulranumab. Subsequent studies including detailed morphologic investigations of the nervous system did reveal fulranumab-related changes in adult cynomolgus monkeys; this article is focused on those findings. A single dose of ≥1 mg/kg fulranumab administered subcutaneously (SC) caused a decrease in neuron and sympathetic ganglion size (superior cervical ganglion), observed morphologically and stereologically, with a resulting appearance of increased glial cell density. Similar results were observed in repeat-dose (15 to 52 weeks) toxicity studies at ≤50 mg/kg/wk fulranumab SC. These effects recovered after a 3-month treatment-free period. Fulranumab did not cause any neuronal death, necrosis, apoptosis, or any apparent decrease in function of sympathetic neurons/ganglia at any time point examined. A no observed effect level (NOEL) was established at 0.25 mg/kg fulranumab SC every 4 weeks for 28 weeks.

Effects of tanezumab on satellite glial cells in the cervicothoracic ganglion of cynomolgus monkeys: A 26-week toxicity study followed by an 8-week recovery period.

Tanezumab, a humanized monoclonal anti-NGF antibody, has demonstrated efficacy and safety profiles in Phase III clinical trials of chronic pain. In a 24-week study in non-human primates, morphological observations of sympathetic ganglia showed decreased ganglia volume, decreased neuronal size, and increased glial cell density compared with controls after 3 tanezumab treatments. Using stereological techniques to quantify glial cells, the present 26-week study found no significant difference after weekly treatments in total cervicothoracic ganglia satellite glial cell number between placebo- or tanezumab-treated cynomolgus monkeys. These findings suggest that tanezumab treatment does not result in a true gliosis in sympathetic ganglia.

Diet-induced insulin resistance elevates hippocampal glutamate as well as VGLUT1 and GFAP expression in AβPP/PS1 mice.

The symptomologies of Alzheimer's disease (AD) develop over decades suggesting modifiable lifestyle factors may contribute to disease pathogenesis. In humans, hyperinsulinemia associated with type 2 diabetes mellitus increases the risk for developing AD and both diseases share similar age-related etiologies including amyloidogenesis. Since we have demonstrated that soluble Aβ42 elicits glutamate release, we wanted to understand how diet-induced insulin resistance alters hippocampal glutamate dynamics, which are important for memory formation and consolidation. Eight to twelve-week-old C57BL/6J and AβPP/PS1 mice were placed on either a low-fat diet or high-fat diet (HFD) for 8months. A HFD led to significant weight increases as well as impaired insulin sensitivity, glucose tolerance, and learning in both C57BL/6J and AβPP/PS1 mice. AβPP/PS1 low-fat diet mice had elevated hippocampal basal as well as stimulus-evoked glutamate release that was further increased with consumption of a HFD. Immunohistochemistry indicated an increase in vesicular glutamate transporter 1 and glial fibrillary acidic protein density in hippocampal subregions corresponding with this elevated extracellular glutamate. While no differences in hippocampal plaque load were observed, the elevated astrogliotic response surrounding the plaques in AβPP/PS1 HFD mice may have been a compensatory mechanism to control plaque accumulation. These data support that AβPP/PS1 mice have chronically elevated extracellular glutamate that is exacerbated by a HFD and that modifiable lifestyle factors such as obesity-induced insulin resistance can contribute to AD pathogenesis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and for *Open Data* because it made the data publicly available. The data can be accessed at https://osf.io/5whvu (figures for data) and https://osf.io/gd5vf (materials and methods). The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14490.

High-Fat Diet During the Perinatal Period Induces Loss of Myenteric Nitrergic Neurons and Increases Enteric Glial Density, Prior to the Development of Obesity

Diet-induced obesity induces peripheral inflammation accompanied by a loss of myenteric neurons. Few studies, however, have investigated the effects of a high-fat diet (HFD) on either the development of myenteric neurons or prior to the occurrence of obesity. The present study assessed the effects of maternal HFD on the density and neurochemical phenotype of myenteric ganglia in the upper gastrointestinal tract. Sprague–Dawley rats were fed either a control or HFD (14% or 60% kcal from fat, respectively) from embryonic day 13; the fundus, corpus and duodenum were fixed thereafter at postnatal 2, 4, 6 and 12 weeks of age for subsequent immunohistochemical studies. While myenteric ganglion size did not differ throughout the study, HFD exposure decreased the number of nitrergic neurons by 6 weeks of age in all regions. This decrease was accompanied by a loss of PGP-immunoreactive neurons, suggesting a decline in myenteric neuronal number. HFD also increased myenteric plexus glial cell density in all regions by 4 weeks of age. These changes occurred in the absence of an increase in serum or gastric inflammatory markers. The present study suggests that exposure to a HFD during the perinatal time period results in glial proliferation and loss of inhibitory nitrergic neurons prior to the onset of obesity, suggesting that dietary alterations may affect gastrointestinal functions independently of increased adiposity or glycemic dysregulation.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

The neuropathology of bipolar disorder: systematic review and meta-analysis

Various neuropathological findings have been reported in bipolar disorder (BD). However, it is unclear which findings are well established. To address this gap, we carried out a systematic review of the literature. We searched over 5000 publications, identifying 103 data papers, of which 81 were eligible for inclusion. Our main findings can be summarised as follows. First, most studies have relied on a limited number of brain collections, and have used relatively small sample sizes (averaging 12 BD cases and 15 controls). Second, surprisingly few studies have attempted to replicate closely a previous one, precluding substantial meta-analyses, such that the latter were all limited to two studies each, and comprising 16–36 BD cases and 16–74 controls. As such, no neuropathological findings can be considered to have been established beyond reasonable doubt. Nevertheless, there are several replicated positive findings in BD, including decreased cortical thickness and glial density in subgenual anterior cingulate cortex, reduced neuronal density in some amygdalar nuclei, and decreased calbindin-positive neuron density in prefrontal cortex. Many other positive findings have also been reported, but with limited or contradictory evidence. As an important negative result, it can be concluded that gliosis is not a feature of BD; neither is there neuropathological evidence for an inflammatory process.

Regional brain volume changes following chronic antipsychotic administration are mediated by the dopamine D2 receptor

BackgroundNeuroanatomical alterations are well established in patients suffering from schizophrenia, however the extent to which these changes are attributable to illness, antipsychotic drugs (APDs), or their interaction is unclear. APDs have been extremely effective for treatment of positive symptoms in major psychotic disorders. Their therapeutic effects are mediated, in part, through blockade of D2-like dopamine (DA) receptors, i.e. the D2, D3 and D4 dopamine receptors. Furthermore, the dependency of neuroanatomical change on DA system function and D2-like receptors has yet to be explored. MethodsWe undertook a preclinical longitudinal study to examine the effects of typical (haloperidol (HAL)) and atypical (clozapine (CLZ)) APDs in wild type (WT) and dopamine D2 knockout (D2KO) mice over 9-weeks using structural magnetic resonance imaging (MRI). ResultsChronic typical APD administration in WT mice was associated with reductions in total brain (p = 0.009) and prelimbic area (PL) (p = 0.02) volumes following 9-weeks, and an increase in striatal volume (p = 0.04) after six weeks. These APD-induced changes were not present in D2KOs, where, at baseline, we observed significantly smaller overall brain volume (p < 0.01), thinner cortices (q < 0.05), and enlarged striata (q < 0.05). Stereological assessment revealed increased glial density in PL area of HAL treated wild types. Interestingly, in WT and D2KO mice, chronic CLZ administration caused more limited changes in brain structure. ConclusionsOur results present evidence for the role of D2 DA receptors in structural alterations induced by the administration of the typical APD HAL and that chronic administration of CLZ has a limited influence on brain structure.

Glia–Neuron Interactions in the Sensory-Motor Cortex of Warm-Blooded Animals (Guinea Pigs and Ground Squirrels) with Different Habitat Conditions and the M-Cholinergic Reaction of the Brain

The glia–neuron interactions were analyzed in the sensory-motor cortex of guinea pigs and ground squirrels (Spermophilus undulatus) during the active summer months. The glial cells were more concentrated in close proximity (15–25 μm) to neurons (38% in guinea pigs and 22.4% in ground squirrels). A more concentrated distribution of glial cells might be very necessary for spontaneous inactive nerve cells (37.2% in guinea pigs and 23% in ground squirrels), since these neurons are associated with the highest energy demand during their functioning and are most susceptible to disturbances of ion homeostasis. The network structure of glia and the close contact between glial cells and brain capillaries provide additional energy for neurons and stabilize the ion balance in the extracellular medium. Glial density in the sensory-motor cortex of ground squirrels is 3 times higher than that in the cortex of guinea pigs. The high content of glial cells in the ground-squirrel cortex is the most important protective factor for survival of animals during long-term hibernation, when the diffusion of K+ ions from nerve cells drastically increases due to the high temperature sensitivity of the M-cholinergic response.

Role of medullary astroglial glutamine synthesis in tooth pulp hypersensitivity associated with frequent masseter muscle contraction.

BackgroundThe mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle hyperalgesia remain largely underinvestigated. In the present study, we aimed to determine whether masseter muscle contraction induced by daily electrical stimulation influences the mechanical head-withdrawal threshold and genioglossus electromyography activity caused by the application of capsaicin to the upper first molar tooth pulp. We further investigated whether astroglial glutamine synthesis is involved in first molar tooth pulp hypersensitivity associated with masseter muscle contraction.MethodsThe first molar tooth pulp was treated with capsaicin or vehicle in masseter muscle contraction or sham rats, following which the astroglial glutamine synthetase inhibitor methionine sulfoximine or Phosphate buffered saline (PBS) was applied. Astroglial activation was assessed via immunohistochemistry.ResultsThe mechanical head-withdrawal threshold of the ipsilateral masseter muscle was significantly decreased in masseter muscle contraction rats than in sham rats. Genioglossus electromyography activity was significantly higher in masseter muscle contraction rats than sham rats. Glial fibrillary acidic protein-immunoreactive cell density was significantly higher in masseter muscle contraction rats than in sham rats. Administration of methionine sulfoximine induced no significant changes in the density of glial fibrillary acidic protein-immunoreactive cells relative to PBS treatment. However, mechanical head-withdrawal threshold was significantly higher in masseter muscle contraction rats than PBS-treated rats after methionine sulfoximine administration. Genioglossus electromyography activity following first molar tooth pulp capsaicin treatment was significantly lower in methionine sulfoximine-treated rats than in PBS-treated rats. In the ipsilateral region, the total number of phosphorylated extracellular signal-regulated protein kinase immunoreactive cells in the medullary dorsal horn was significantly smaller upon first molar tooth pulp capsaicin application in methionine sulfoximine-treated rats than in PBS-treated rats.ConclusionsOur results suggest that masseter muscle contraction induces astroglial activation, and that this activation spreads from caudal to the obex in the medullary dorsal horn, resulting in enhanced neuronal excitability associated with astroglial glutamine synthesis in medullary dorsal horn neurons receiving inputs from the tooth pulp. These findings provide significant insight into the mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle contraction.