Susceptibility of subregions of prefrontal cortex and corpus callosum to damage by high-dose oxytocin-induced labor in male neonatal mice

Induction and augmentation of labor is one of the most common obstetrical interventions. However, this intervention is not free of risks and could cause adverse events, such as hyperactive uterine contraction, uterine rupture, and amniotic-fluid embolism. Our previous study using a new animal model showed that labor induced with high-dose oxytocin (OXT) in pregnant mice resulted in massive cell death in selective brain regions, specifically in male offspring. The affected brain regions included the prefrontal cortex (PFC), but a detailed study in the PFC subregions has not been performed. In this study, we induced labor in mice using high-dose OXT and investigated neonatal brain damage in detail in the PFC using light and electron microscopy. We found that TUNEL-positive or pyknotic nuclei and Iba-1-positive microglial cells were detected more abundantly in infralimbic (IL) and prelimbic (PL) cortex of the ventromedial PFC (vmPFC) in male pups delivered by OXT-induced labor than in the control male pups. These Iba-1-positive microglial cells were engulfing dying cells. Additionally, we also noticed that in the forceps minor (FMI) of the corpus callosum (CC), the number of TUNEL-positive or pyknotic nuclei and Iba-1-positive microglial cells were largely increased and Iba-1-positive microglial cells phagocytosed massive dying cells in male pups delivered by high-dose OXT-induced labor. In conclusion, IL and PL of the vmPFC and FMI of the CC, were susceptible to brain damage in male neonates after high-dose OXT-induced labor.

Elevated protein synthesis in microglia causes autism-like synaptic and behavioral aberrations

Mutations that inactivate negative translation regulators cause autism spectrum disorders (ASD), which predominantly affect males and exhibit social interaction and communication deficits and repetitive behaviors. However, the cells that cause ASD through elevated protein synthesis resulting from these mutations remain unknown. Here we employ conditional overexpression of translation initiation factor eIF4E to increase protein synthesis in specific brain cells. We show that exaggerated translation in microglia, but not neurons or astrocytes, leads to autism-like behaviors in male mice. Although microglial eIF4E overexpression elevates translation in both sexes, it only increases microglial density and size in males, accompanied by microglial shift from homeostatic to a functional state with enhanced phagocytic capacity but reduced motility and synapse engulfment. Consequently, cortical neurons in the mice have higher synapse density, neuroligins, and excitation-to-inhibition ratio compared to control mice. We propose that functional perturbation of male microglia is an important cause for sex-biased ASD.

Classical complement cascade initiating C1q protein within neurons in the aged rhesus macaque dorsolateral prefrontal cortex

BACKGROUND

Cognitive impairment in schizophrenia, aging, and Alzheimer's disease is associated with spine and synapse loss from the dorsolateral prefrontal cortex (dlPFC) layer III. Complement cascade signaling is critical in driving spine loss and disease pathogenesis. Complement signaling is initiated by C1q, which tags synapses for elimination. C1q is thought to be expressed predominately by microglia, but its expression in primate dlPFC has never been examined. The current study assayed C1q levels in aging primate dlPFC and rat medial PFC (mPFC) and used immunoelectron microscopy (immunoEM), immunoblotting, and co-immunoprecipitation (co-IP) to reveal the precise anatomical distribution and interactions of C1q.

METHODS

Age-related changes in C1q levels in rhesus macaque dlPFC and rat mPFC were examined using immunoblotting. High-spatial resolution immunoEM was used to interrogate the subcellular localization of C1q in aged macaque layer III dlPFC and aged rat layer III mPFC. co-IP techniques quantified protein-protein interactions for C1q and proteins associated with excitatory and inhibitory synapses in macaque dlPFC.

RESULTS

C1q levels were markedly increased in the aged macaque dlPFC. Ultrastructural localization found the expected C1q localization in glia, including those ensheathing synapses, but also revealed extensive localization within neurons. C1q was found near synapses, within terminals and in spines, but was also observed in dendrites, often near abnormal mitochondria. Similar analyses in aging rat mPFC corroborated the findings in rhesus macaques. C1q protein increasingly associated with PSD95 with age in macaque, consistent with its synaptic localization as evidenced by EM.

CONCLUSIONS

These findings reveal novel, intra-neuronal distribution patterns for C1q in the aging primate cortex, including evidence of C1q in dendrites. They suggest that age-related changes in the dlPFC may increase C1q expression and synaptic tagging for glial phagocytosis, a possible mechanism for age-related degeneration.

Chronic adolescent exposure to ∆9-tetrahydrocannabinol decreases NMDA current and extrasynaptic plasmalemmal density of NMDA GluN1 subunits in the prelimbic cortex of adult male mice

Adolescence is a vulnerable period of development when limbic connection of the prefrontal cortex (PFC) involved in emotional processing may be rendered dysfunctional by chronic exposure to delta-9-tetrahydrocannabinol (∆9-THC), the major psychoactive compound in marijuana. Cannabinoid-1 receptors (CB1Rs) largely mediate the central neural effects of ∆9-THC and endocannabinoids that regulate NMDA receptor-dependent synaptic plasticity of glutamatergic synapses in the prelimbic prefrontal cortex (PL-PFC). Thus, chronic occupancy of CB1Rs by ∆9-THC during adolescence may competitively decrease the functional expression and activity of NMDA receptors in the mature PL-PFC. We used a multidisciplinary approach to test this hypothesis in adult C57BL/6J male mice that received vehicle or ∆9-THC in escalating doses (2.5-10 mg/kg/ip) through adolescence (postnatal day 29-43). In comparison with vehicle, the mice receiving ∆9-THC showed a hyperpolarized resting membrane potential, decreased spontaneous firing rate, increased current-induced firing threshold, and decreased depolarizing response to NMDA in deep-layer PL-PFC neurons analyzed by current-clamp recordings. Electron microscopic immunolabeling in the PL-PFC of adult mice that had received Δ9-THC only during adolescence showed a significant (1) decrease in the extrasynaptic plasmalemmal density of obligatory GluN1-NMDA subunits in dendrites of all sizes and (2) a shift from cytoplasmic to plasmalemmal distribution of GluN1 in large dendrites receiving mainly inhibitory-type synapses from CB1R-labeled terminals. From these results and concomitant behavioral studies, we conclude that social dysfunctions resulting from excessive intake of ∆9-THC in the increasingly available marijuana products used by male teens may largely reflect circuit defects in PL-PFC networks communicating through endocannabinoid-regulated NMDA receptors.

Factors Affecting Ultrastructural Quality in the Prefrontal Cortex of the Postmortem Human Brain

Electron microscopy (EM) studies of the postmortem human brain provide a level of resolution essential for understanding brain function in both normal and disease states. However, processes associated with death can impair the cellular and organelle ultrastructural preservation required for quantitative EM studies. Although postmortem interval (PMI), the time between death and preservation of tissue, is thought to be the most influential factor of ultrastructural quality, numerous other factors may also influence tissue preservation. The goal of the present study was to assess the effects of pre- and postmortem factors on multiple components of ultrastructure in the postmortem human prefrontal cortex. Tissue samples from 30 subjects were processed using standard EM histochemistry. The primary dependent measure was number of identifiable neuronal profiles, and secondary measures included presence and/or integrity of synapses, mitochondria, and myelinated axonal fibers. Number of identifiable neuronal profiles was most strongly affected by the interaction of PMI and pH, such that short PMIs and neutral pH values predicted the best preservation. Secondary measures were largely unaffected by pre- and postmortem factors. Together, these data indicate that distinct components of the neuropil are differentially affected by PMI and pH in postmortem human brain.

The orbitofrontal cortex projects to the parvafox nucleus of the ventrolateral hypothalamus and to its targets in the ventromedial periaqueductal grey matter

Although connections between the orbitofrontal cortex (OFC)-the seat of high cognitive functions-the lateral hypothalamus and the periaqueductal grey (PAG) have been recognized in the past, the precise targets of the descending fibres have not been identified. In the present study, viral tracer-transport experiments revealed neurons of the lateral (LO) and the ventrolateral (VLO) OFC (homologous to part of Area 13 in primates) to project to a circumscribed region in the ventrolateral hypothalamus, namely, the horizontally oriented, cylindrical parvalbumin- and Foxb1-expressing (parvafox) nucleus. The fine collaterals stem from coarse axons in the internal capsule and form excitatory synapses specifically with neurons of the parvafox nucleus, avoiding the rest of the hypothalamus. In its further caudal course, this contingent of LO/VLO-axons projects collaterals to the Su3- and the PV2 nuclei, which lie ventral to the aqueduct in the (PAG), where the terminals fields overlap those deriving from the parvafox nucleus itself. The targeting of the parvafox nucleus by the LO/VLO-projections, and the overlapping of their terminal fields within the PAG, suggest that the two cerebral sites interact closely. An involvement of this LO/VLO-driven circuit in the somatic manifestation of behavioural events is conceivable.

Mapping pathologic circuitry in schizophrenia

Schizophrenia is a complex disorder lacking an effective treatment option for the pervasive and debilitating cognitive impairments experienced by patients. Working memory is a core cognitive function impaired in schizophrenia that depends upon activation of distributed neural network, including the circuitry of the dorsolateral prefrontal cortex (DLPFC). Accordingly, individuals diagnosed with schizophrenia show reduced DLPFC activation while performing working-memory tasks. This lower DLPFC activation appears to be an integral part of the disease pathophysiology, and not simply a reflection of poor performance. Thus, the cellular and circuitry alterations that underlie lower DLPFC neuronal activity in schizophrenia must be determined in order to identify appropriate therapeutic targets. Studies using human postmortem brain tissue provide a robust way to investigate and characterize these cellular and circuitry alterations at multiple levels of resolution, and such studies provide essential information that cannot be obtained either through in vivo studies in humans or through experimental animal models. Studies examining neuronal morphology, protein expression and localization, and transcript levels indicate that a microcircuit composed of excitatory pyramidal cells and inhibitory interneurons containing the calcium-binding protein parvalbumin is altered in the DLPFC of subjects with schizophrenia and likely contributes to DLPFC dysfunction.

Loss of M1 Receptor Dependent Cholinergic Excitation Contributes to mPFC Deactivation in Neuropathic Pain

In chronic pain, the medial prefrontal cortex (mPFC) is deactivated and mPFC-dependent tasks such as attention and working memory are impaired. We investigated the mechanisms of mPFC deactivation in the rat spared nerve injury (SNI) model of neuropathic pain. Patch-clamp recordings in acute slices showed that, 1 week after the nerve injury, cholinergic modulation of layer 5 (L5) pyramidal neurons was severely impaired. In cells from sham-operated animals, focal application of acetylcholine induced a left shift of the input/output curve and persistent firing. Both of these effects were almost completely abolished in cells from SNI-operated rats. The cause of this impairment was an ∼60% reduction of an M1-coupled, pirenzepine-sensitive depolarizing current, which appeared to be, at least in part, the consequence of M1 receptor internalization. Although no changes were detected in total M1 protein or transcript, both the fraction of the M1 receptor in the synaptic plasma membrane and the biotinylated M1 protein associated with the total plasma membrane were decreased in L5 mPFC of SNI rats. The loss of excitatory cholinergic modulation may play a critical role in mPFC deactivation in neuropathic pain and underlie the mPFC-specific cognitive deficits that are comorbid with neuropathic pain.SIGNIFICANCE STATEMENT The medial prefrontal cortex (mPFC) undergoes major reorganization in chronic pain. Deactivation of mPFC output is causally correlated with both the cognitive and the sensory component of neuropathic pain. Here, we show that cholinergic excitation of commissural layer 5 mPFC pyramidal neurons is abolished in neuropathic pain rats due to a severe reduction of a muscarinic depolarizing current and M1 receptor internalization. Therefore, in neuropathic pain rats, the acetylcholine (ACh)-dependent increase in neuronal excitability is reduced dramatically and the ACh-induced persisting firing, which is critical for working memory, is abolished. We propose that the blunted cholinergic excitability contributes to the functional mPFC deactivation that is causal for the pain phenotype and represents a cellular mechanism for the attention and memory impairments comorbid with chronic pain.

Ultrastructural evidence for impaired mitochondrial fission in the aged rhesus monkey dorsolateral prefrontal cortex

Dorsolateral prefrontal cortex mediates high-order cognitive functions that are impaired early in the aging process in monkeys and humans. Here, we report pronounced changes in mitochondrial morphology in dendrites of dorsolateral prefrontal cortex neurons from aged rhesus macaques. Electron microscopy paired with 3D reconstruction from serial sections revealed an age-related increase in mitochondria with thin segments that intermingled with enlarged ones, the 'mitochondria-on-a-string' phenotype, similar to those recently reported in patients with Alzheimer's disease. The thin mitochondrial segments were associated with endoplasmic reticulum cisterns, and the mitochondrial proteins Fis1 and Drp1, all of which initiate mitochondrial fission. These data suggest that the 'mitochondria-on-a-string' phenotype may reflect malfunction in mitochondrial dynamics, whereby fission is initiated, but the process is incomplete due to malfunction of subsequent step(s). Thus, aged rhesus monkeys may be particularly helpful in exploring the age-related changes that render higher cortical circuits so vulnerable to degeneration.

Prefrontal white matter pathology in air pollution exposed Mexico City young urbanites and their potential impact on neurovascular unit dysfunction and the development of Alzheimer's disease

Millions of urban children are chronically exposed to high concentrations of air pollutants, i.e., fine particulate matter (PM2.5) and ozone, associated with increased risk for Alzheimer's disease. Compared with children living with clear air those in Mexico City (MC) exhibit systemic, brain and intrathecal inflammation, low CSF Aβ42, breakdown of the BBB, attention and short-term memory deficits, prefrontal white matter hyperintensities, damage to epithelial and endothelial barriers, tight junction and neural autoantibodies, and Alzheimer and Parkinson's hallmarks. The prefrontal white matter is a target of air pollution. We examined by light and electron microscopy the prefrontal white matter of MC dogs (n: 15, age 3.17±0.74 years), children and teens (n: 34, age: 12.64±4.2 years) versus controls. Major findings in MC residents included leaking capillaries and small arterioles with extravascular lipids and erythrocytes, lipofuscin in pericytes, smooth muscle and endothelial cells (EC), thickening of cerebrovascular basement membranes with small deposits of amyloid, patchy absence of the perivascular glial sheet, enlarged Virchow-Robin spaces and nanosize particles (20-48nm) in EC, basement membranes, axons and dendrites. Tight junctions, a key component of the neurovascular unit (NVU) were abnormal in MC versus control dogs (χ(2)<0.0001), and white matter perivascular damage was significantly worse in MC dogs (p=0.002). The integrity of the NVU, an interactive network of vascular, glial and neuronal cells is compromised in MC young residents. Characterizing the early NVU damage and identifying biomarkers of neurovascular dysfunction may provide a fresh insight into Alzheimer pathogenesis and open opportunities for pediatric neuroprotection.

Characterization of prefrontal cortex microstructure and antioxidant status in a rat model of neurodegeneration induced by aluminium chloride and multiple low-dose streptozotocin

Diabetes mellitus (DM) is a risk factor for Alzheimer's disease (AD), and several individuals with AD are diabetic. Most non-transgenic animal models of AD make use of oral treatment with aluminium chloride (AlCl(3)) to induce brain lesions pathognomonic of the disease. Moreover, streptozotocin (STZ) can induce pathological features of either AD or DM depending on the mode of treatment. In the present study, we characterised prefrontal microanatomy and antioxidant defence system in a rat model of AD confounded by DM, with the objective of assessing the suitability of this model in the study of sporadic AD with DM co-morbidity. Adult Wistar rats were randomly assigned to receive either intraperitoneal STZ (30 mg/kg/day for 3 days; to induce DM), oral AlCl(3) (500 mg/kg/day for 4 weeks; to induce some brain lesions characteristic of AD); or both STZ and AlCl(3) (to induce AD with DM co-morbidity). Untreated rats served as controls. During treatment, blood glucose levels and body weights were evaluated repeatedly in all rats. At euthanasia, prefrontal cortex was homogenized in phosphate buffer solution and the supernatants assayed for some antioxidant enzymes (catalase, CAT; superoxide dismutase, SOD; and reduced glutathione, GSH). Moreover, following perfusion-fixation of the brain, frontal lobes were processed by the haematoxylin and eosin (H&E) or Congo red technique. Our findings showed that in rats co-administered AlCl(3) and STZ (AD + DM rats), prefrontal levels of GSH reduced significantly (p < 0.05), while reductions in SOD and CAT were not significant (p > 0.05) compared with the controls. Moreover, in this model of AD with DM co-morbidity, extensive neuronal cell loss was observed in the prefrontal cortex, but Congophilic deposits were not present. The neurodegenerative lesions and antioxidant deficits characteristic of this AlCl(3) + STZ (AD + DM) rat model were more pronounced than similar lesions associated with mono-treatment with either STZ (DM) or AlCl(3) (AD) alone; and this makes the AlCl(3) + STZ model a suitable option for the study of neurodegenerative diseases (such as AD) with DM co-morbidity.

Low circulating levels of bisphenol-A induce cognitive deficits and loss of asymmetric spine synapses in dorsolateral prefrontal cortex and hippocampus of adult male monkeys

Bisphenol-A (BPA) is widely used in the manufacture of plastics, epoxy resins, and certain paper products. A majority of the population in the developed world is routinely exposed to BPA from multiple sources and has significant circulating levels of BPA. Although BPA is categorized as an endocrine disruptor with a growing literature on adverse effects, it is uncertain whether cognitive dysfunction is induced in humans by exposure to BPA. The present study examined the impact of BPA in primate brain by exposing adult male vervet monkeys for 4 weeks continuously to circulating levels of BPA that were in the range measured in studies of humans environmentally exposed to BPA. This regimen of exposure to BPA decreased both working memory accuracy and the number of excitatory synaptic inputs on dendritic spines of pyramidal neurons in two brain regions that are necessary for working memory (prefrontal cortex and hippocampus). These observed behavioral and synaptic effects were ameliorated following withdrawal from BPA. As Old World monkeys (e.g., vervets) and humans share some uniquely primate morphological, endocrine, and cognitive traits, this study indicates the potential for significant cognitive disruption following exposure of humans to BPA.

A comparison between block and smooth modeling in finite element simulations of tDCS

Current density distributions in five selected structures, namely, anterior superior temporal gyrus (ASTG), hippocampus (HIP), inferior frontal gyrus (IFG), occipital lobe (OCC) and pre-central gyrus (PRC) were investigated as part of a comparison between electrostatic finite element models constructed directly from MRI-resolution data (block models), and smoothed tetrahedral finite element models (smooth models). Three electrode configurations were applied, mimicking different tDCS therapies. Smooth model simulations were found to require three times longer to complete. The percentage differences between mean and median current densities of each model type in arbitrarily chosen brain structures ranged from -33.33-48.08%. No clear relationship was found between structure volumes and current density differences between the two model types. Tissue regions nearby the electrodes demonstrated the least percentage differences between block and smooth models. Therefore, block models may be adequate to predict current density values in cortical regions presumed targeted by tDCS.

[ISOMETRIC RETRACTION AND THE INVISIBLE PROCESSES OF NERVE CELLS]

Recently, a large number of physiological studies on stress and hibernation had described an unusual morphological phenomenon of the rapid disappearance and reapperance of apical dendrites of pyramidal neurons of the hippocampus, prefrontal cortex and other parts of the brain. In this article an attempt is maid to explain this phenomenon on the basis of morphological analysis of natural elastic properties of neuroplasm and structural kinetics of partially preserved processes of the living isolated neurons. The neuroplasm displacement with its bidirectional flow was identified in the processes. A new physiological phenomenon is described--the isometric retraction of nerve cell processes, during which the neuroplasm fluxes were directed to the opposite sides, leading to abrupt thinning of middle parts of the processes and to a thickening of both ends. It is suggested that the extremely attenuated processes can reach the submicroscopic sizes, becoming invisible in the light microscope. The repeated reversible "disappearance" and "appearance" of the processes was demonstrated supravitally in the culture of neurons and of C-1300 neuroblastoma cells. Reduction of the diameter of the processes to a limit of their visibility was demonstrated by the example of their natural stretching. The same effect was observed in the areas between the reversible varicosities of the processes. These areas became extremely thin, and then invisible. Becoming thinner, the processes were capable of sharp extension. A review of the available literature and our own data allow to conclude that the phenomenon of the disappearance of the apical dendrites was due to their isometric retraction, which lead to the emergence of "invisible processes".

Medial prefrontal cortical estradiol rapidly alters memory system bias in female rats: ultrastructural analysis reveals membrane-associated estrogen receptors as potential mediators

High plasma levels of estradiol (E2) are associated with use of a place memory system over a response memory system. We examined whether infusing estradiol into the medial prefrontal cortex (mPFC) or anterior cingulate cortex (AC) could affect memory system bias in female rats. We also examined the ultrastructural distribution of estrogen receptor (ER)-α, ERβ, and G protein-coupled estrogen receptor 1 (GPER1) in the mPFC of female rats as a mechanism for the behavioral effects of E2 in the mPFC. Each rat was infused bilaterally with either E2 (0.13 μg) or vehicle into the mPFC or AC. The majority of E2 mPFC rats used place memory. In contrast, the majority of mPFC vehicle rats and AC E2 or vehicle rats used response memory. These data show that mPFC E2 rapidly biases females to use place memory. Electron microscopic analysis demonstrated that ERα, ERβ, and GPER1 are localized in the mPFC, almost exclusively at extranuclear sites. This is the first time that GPER1 has been localized to the mPFC of rats and the first time that ERα and ERβ have been described at extranuclear sites in the rat mPFC. The majority of receptors were observed on axons and axon terminals, suggesting that estrogens alter presynaptic transmission in the mPFC. This provides a mechanism via which ERs could rapidly alter transmission in the mPFC to alter PFC-dependent behaviors, such as memory system bias. The discrete nature of immunolabeling for these membrane-associated ERs may explain the discrepancy in previous light microscopy studies.

Cannabinoid modulation of alpha2 adrenergic receptor function in rodent medial prefrontal cortex

Endocannabinoids acting at the cannabinoid type 1 receptor (CB1R) are known to regulate attention, cognition and mood. Previous studies have shown that, in the rat medial prefrontal cortex (mPFC), CB1R agonists increase norepinephrine release, an effect that may be attributed, in part, to CB1Rs localised to noradrenergic axon terminals. The present study was aimed at further characterising functional interactions between CB1R and adrenergic receptor (AR) systems in the mPFC using in vitro intracellular electrophysiology and high-resolution neuroanatomical techniques. Whole-cell patch-clamp recordings of layer V/VI cortical pyramidal neurons in rats revealed that both acute and chronic treatment with the synthetic CB1R agonist WIN 55,212-2 blocked elevations in cortical pyramidal cell excitability and increases in input resistance evoked by the α2-adrenergic receptor (α2-AR) agonist clonidine, suggesting a desensitisation of α2-ARs. These CB1R-α2-AR interactions were further shown to be both action potential- and gamma-aminobutyric acid-independent. To better define sites of cannabinoid-AR interactions, we localised α2A-adrenergic receptors (α2A-ARs) in a genetically modified mouse that expressed a hemoagglutinin (HA) tag downstream of the α2A-AR promoter. Light and electron microscopy indicated that HA-α2A-AR was distributed in axon terminals and somatodendritic processes especially in layer V of the mPFC. Triple-labeling immunocytochemistry revealed that α2A-AR and CB1R were localised to processes that contained dopamine-β-hydroxylase, a marker of norepinephrine. Furthermore, HA-α2A-AR was localised to processes that were directly apposed to CB1R. These findings suggest multiple sites of interaction between cortical cannabinoid-adrenergic systems that may contribute to understanding the effect of cannabinoids on executive functions and mood.

Localization of excitatory amino acid transporters EAAT1 and EAAT2 in human postmortem cortex: a light and electron microscopic study

The process of glutamate release, activity, and reuptake involves the astrocyte, the presynaptic and postsynaptic neurons. Glutamate is released into the synapse and may occupy and activate receptors on both neurons and astrocytes. Glutamate is rapidly removed from the synapse by a family of plasma membrane excitatory amino acid transporters (EAATs), also localized to neurons and astrocytes. The purpose of the present study was to examine EAAT labeling in the postmortem human cortex at the light and electron microscopic (EM) levels. The postmortem prefrontal cortex was processed for EAAT1 and EAAT2 immunohistochemistry. At the light microscopic level, EAAT1 and EAAT2 labeling was found in both gray and white matter. Most cellular labeling was in small cells which were morphologically similar to glia. In addition, EAAT1-labeled neurons were scattered throughout, some of which were pyramidal in shape. At the EM level, EAAT1 and EAAT2 labeling was found in astrocytic soma and processes surrounding capillaries. EAAT labeling was also found in small astrocytic processes adjacent to axon terminals forming asymmetric (glutamatergic) synapses. While EAAT2 labeling was most prevalent in astrocytic processes, EAAT1 labeling was also present in neuronal processes including the soma, axons, and dendritic spines. Expression of EAAT1 protein on neurons may be due to the hypoxia associated with the postmortem interval, and requires further confirmation. The localization of EAATs on the astrocytic plasma membrane and adjacent to excitatory synapses is consistent with the function of facilitating glutamate reuptake and limiting glutamate spillover. Establishment that EAAT1 and EAAT2 can be measured at the EM level in human postmortem tissues will permit testing of hypotheses related to these molecules in diseases lacking analogous animal models.

Myosin II regulates actin rearrangement-related structural synaptic plasticity during conditioned taste aversion memory extinction

Similar to memory formation, memory extinction is also a new learning process that requires synaptic plasticity. Actin rearrangement is fundamental for synaptic plasticity, however, whether actin rearrangement in the infralimbic cortex (IL) plays a role in memory extinction, as well as the mechanisms underlying it, remains unclear. Here, using a conditioned taste aversion (CTA) paradigm, we demonstrated increased synaptic density and actin rearrangement in the IL during the extinction of CTA. Targeted infusion of an actin rearrangement inhibitor, cytochalasin D, into the IL impaired memory extinction and de novo synapse formation. Notably, we also found increased myosin II phosphorylation in the IL during the extinction of CTA. Microinfusion of a specific inhibitor of the myosin II ATPase, blebbistatin (Blebb), into the IL impaired memory extinction as well as the related actin rearrangement and changes in synaptic density. Moreover, the extinction deficit and the reduction of synaptic density induced by Blebb could be rescued by the actin polymerization stabilizer jasplakinolide (Jasp), suggesting that myosin II acts via actin filament polymerization to stabilize synaptic plasticity during the extinction of CTA. Taken together, we conclude that myosin II may regulate the plasticity of actin-related synaptic structure during memory extinction. Our studies provide a molecular mechanism for understanding the plasticity of actin rearrangement-associated synaptic structure during memory extinction.

Scopolamine rapidly increases mammalian target of rapamycin complex 1 signaling, synaptogenesis, and antidepressant behavioral responses

BACKGROUND

Clinical studies report that scopolamine, an acetylcholine muscarinic receptor antagonist, produces rapid antidepressant effects in depressed patients, but the mechanisms underlying the therapeutic response have not been determined. The present study examines the role of the mammalian target of rapamycin complex 1 (mTORC1) and synaptogenesis, which have been implicated in the rapid actions of N-methyl-D-aspartate receptor antagonists.

METHODS

The influence of scopolamine on mTORC1 signaling was determined by analysis of the phosphorylated and activated forms of mTORC1 signaling proteins in the prefrontal cortex (PFC). The numbers and function of spine synapses were analyzed by whole cell patch clamp recording and two-photon image analysis of PFC neurons. The actions of scopolamine were examined in the forced swim test in the absence or presence of selective mTORC1 and glutamate receptor inhibitors.

RESULTS

The results demonstrate that a single, low dose of scopolamine rapidly increases mTORC1 signaling and the number and function of spine synapses in layer V pyramidal neurons in the PFC. Scopolamine administration also produces an antidepressant response in the forced swim test that is blocked by pretreatment with the mTORC1 inhibitor or by a glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor antagonist.

CONCLUSIONS

Taken together, the results demonstrate that the antidepressant actions of scopolamine require mTORC1 signaling and are associated with increased glutamate transmission, and synaptogenesis, similar to N-methyl-D-aspartate receptor antagonists. These findings provide novel targets for safer and more efficacious rapid-acting antidepressant agents.

Glutamate receptor composition of the post-synaptic density is altered in genetic mouse models of NMDA receptor hypo- and hyperfunction

The N-methyl-d-aspartate receptor (NMDAR) and α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR) are ionotropic glutamate receptors responsible for excitatory neurotransmission in the brain. These excitatory synapses are found on dendritic spines, with the abundance of receptors concentrated at the postsynaptic density (PSD). We utilized two genetic mouse models, the serine racemase knockout (SR-/-) and the glycine transporter subtype 1 heterozygote mutant (GlyT1+/-), to determine how constitutive NMDAR hypo- and hyperfunction, respectively, affect the glutamate receptor composition of the PSD in the hippocampus and prefrontal cortex (PFC). Using cellular fractionation, we found that SR-/- mice had elevated protein levels of NR1 and NR2A NMDAR subunits specifically in the PSD-enriched fraction from the hippocampus, but not from the PFC. There were no changes in the amounts of AMPAR subunits (GluR1, GluR2), or PSD protein of 95 kDa (PSD95) in either brain region. GlyT1+/- mice also had elevated protein expression of NR1 and NR2A subunits in the PSD, as well as an increase in total protein. Moreover, GlyT1+/- mice had elevated amounts of GluR1 and GluR2 in the PSD, and higher total amounts of GluR1. Similar to SR-/- mice, there were no protein changes observed in the PFC. These findings illustrate the complexity of synaptic adaptation to altered NMDAR function.

Enhanced dendritic spine number of neurons of the prefrontal cortex, hippocampus, and nucleus accumbens in old rats after chronic donepezil administration

In Alzheimer's disease brains, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been observed. These changes are particularly reflected in the decrement of both the dendritic tree and spine number. Donepezil is a potent and selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease. We have studied the effect of oral administration of this drug on the morphology of neuronal cells from the brain of aged rats. We examined dendrites of pyramidal neurons of the PFC, dorsal or ventral hippocampus (VH), and medium spiny neurons of the nucleus accumbens (NAcc). Donepezil (1 mg/kg, vo) was administrated every day for 60 days to rats aged 10 and 18 months. Dendritic morphology was studied by the Golgi-Cox stain procedure followed by Sholl analysis at 12 and 20 months ages, respectively. In all Donepezil-treated rats, a significant increment of the dendritic spines number in pyramidal neurons of the PFC and dorsal hippocampus was observed. However, pyramidal neurons of the VH and medium spiny cells of the NAcc only showed an increase in the number of their spines in 12-month-old rats. Our results suggest that Donepezil prevents the alterations of the neuronal dendrite morphology caused by aging.

Evidence for abnormal forward trafficking of AMPA receptors in frontal cortex of elderly patients with schizophrenia

Several lines of evidence point to alterations of alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor trafficking in schizophrenia. Multiple proteins, including synapse-associated protein 97 (SAP97), glutamate receptor-interacting protein 1 (GRIP1), and N-ethylmaleimide sensitive factor (NSF), facilitate the forward trafficking of AMPA receptors toward the synapse. Once localized to the synapse, AMPA receptors are trafficked in a complex endosomal system. We hypothesized that alterations in the expression of these proteins and alterations in the subcellular localization of AMPA receptors in endosomes may contribute to the pathophysiology of schizophrenia. Accordingly, we measured protein expression of SAP97, GRIP1, and NSF in the dorsolateral prefrontal cortex and found an increase in the expression of SAP97 and GRIP1 in schizophrenia. To determine the subcellular localization of AMPA receptor subunits, we developed a technique to isolate early endosomes from post-mortem tissue. We found increased GluR1 receptor subunit protein in early endosomes in subjects with schizophrenia. Together, these data suggest that there is an alteration of forward trafficking of AMPA receptors as well as changes in the subcellular localization of an AMPA receptor subunit in schizophrenia.

Effects of age on axon terminals forming axosomatic and axodendritic inhibitory synapses in prefrontal cortex

Much of the cognitive decline shown by aging primates can be attributed to dysfunction of prefrontal cortex and, as shown previously, about 30% of asymmetric (excitatory) and symmetric (inhibitory) axodendritic synapses are lost from the neuropil of layer 2/3 in prefrontal area 46 with age [Peters A, Sethares C, Luebke JI (2008) Neuroscience 152:970-981]. Whether there is a similar loss of inhibitory axosomatic synapses from this cortex has not been determined, but a study in primate motor cortex suggests that axosomatic synapses are not lost with age [Tigges J, Herndon JG, Peters A (1992) Anat Rec 232:305-315]. The present study is focused upon whether the remaining axon terminals forming inhibitory synapses in old monkeys hypertrophy to compensate for any age-related loss. Analysis of electron micrographs show that in layer 2/3 of area 46 in both young and old monkeys, axon terminals forming axosomatic synapses are significantly larger and contain more mitochondria than those forming axodendritic synapses and both axodendritic and axosomatic terminals become larger with age. However, while mitochondria in axodendritic terminals do not change in either size or amount with age, the mitochondria in axosomatic terminals become larger. Similarly, in terminals forming axodendritic synapses, the mean numbers of synaptic vesicle profiles is the same in young and old monkeys, whereas in terminals forming axosomatic synapses there is an increase in the numbers of synaptic vesicles with age. We also show that among these age-related changes, only the numbers of synaptic vesicles in axosomatic synapses are significantly correlated with the cognitive impairment indices displayed by the same monkeys. In summary, the data provide original evidence that axosomatic axon terminals increase in size and in their content of mitochondria and synaptic vesicles. Furthermore, based on our and previously published results, we speculate that these changes are linked to age-related cognitive decline.

Chronic intermittent hypoxia exposure induces memory impairment in growing rats

The study was aimed to examine the effect of chronic intermittent hypoxia (CIH) on spatial memory of growing rats and to explore the possible underlying mechanisms. Sixty two rats were trained to perform the 8-arm radial maze task and were divided into four groups: 2-week-CIH (2IH) 2-week-control (2C) 4-week-CIH (4IH) and 4-week-control (4C). There were more reference memory errors, working memory errors and total memory errors in 2IH and 4IH groups compared to the controls. The levels of 8-iso-Prostaglandin F(2-alpha) [8-ISO-PGF(2-alpha)] an in vivo marker for oxidative stress, in serum, hippocampus and prefrontal cortex were higher in CIH groups than the control groups. There were significant correlations between the levels of 8-ISO-PGF(2-alpha) and numbers of memory errors. The ultrastructural changes were evident in the hippocampal and prefrontal cortical tissues from the CIH groups. These results indicate that CIH can induce oxidative stress in brain tissues involved in spatial memory function.

Spatial and intracellular relationships between the alpha7 nicotinic acetylcholine receptor and the vesicular acetylcholine transporter in the prefrontal cortex of rat and mouse

The alpha 7 subunit of the nicotinic acetylcholine receptor (alpha7nAChR) is expressed in the prefrontal cortex (PFC), a brain region where these receptors are implicated in cognitive function and in the pathophysiology of schizophrenia. Activation of this receptor is dependent on release of acetylcholine (ACh) from axon terminals that contain the vesicular acetylcholine transporter (VAChT). Since rat and mouse models are widely used for studies of specific abnormalities in schizophrenia, we sought to determine the subcellular location of the alpha7nAChR with respect to VAChT storage vesicles in axon terminals in the PFC in both species. For this, we used dual electron microscopic immunogold and immunoperoxidase labeling of antisera raised against the alpha7nAChR and VAChT. In both species, the alpha7nAChR-immunoreactivity ((-)ir) was principally identified within dendrites and dendritic spines, receptive to axon terminals forming asymmetric excitatory-type synapses, but lacking detectable alpha7nAChR or VAChT-ir. Quantitative analysis of the rat PFC revealed that of alpha7nAChR-labeled neuronal profiles, 65% (299/463) were postsynaptic structures (dendrites and dendritic spine) and only 22% (104/463) were axon terminals or small unmyelinated axons. In contrast, VAChT was principally localized to varicose vesicle-filled axonal profiles, without recognized synaptic specializations (n=240). Of the alpha7nAChR-labeled axons, 47% (37/79) also contained VAChT, suggesting that ACh release is autoregulated through the presynaptic alpha7nAChR. The VAChT-labeled terminals rarely formed synapses, but frequently apposed alpha7nAChR-containing neuronal profiles. These results suggest that in rodent PFC, the alpha7nAChR plays a major role in modulation of the postsynaptic excitation in spiny dendrites in contact with VAChT containing axons.

[Influence of acupuncture and moxibustion on conditional position preference and prefrontal cortical ultrastructure in heroin re-addicted rats]

OBJECTIVE

To observe the effect of acupuncture and moxibustion on the conditional position preference (CPP) and prefrontal cortical ultrastructure in heroin re-addicted rats.

METHODS

Thirty-two Wistar rats were randomly divided into normal, model, medication and acu-moxibustion (acu-moxi) groups, with 8 cases in each. Re-addiction model was established by repeated intramuscular injection of heroin into the hindlimbs. Rats of medication group were treated with intragastric administration of Methadone during detoxification. For rats in acu-moxi group, acupuncture needle was inserted into "Baihui" (GV 20) and moxibustion treatment was used to bilateral "Shenshu" (BL 23) for 30 min during detoxification. Rats in normal group were given with intramuscular injection of normal saline during addiction. CPP tests were conducted once daily in a spatial place preference box for 8 days. On the 39th day of the experiment, the rats under anesthesia were killed for sampling the prefrontal cortex (PFC) tissue on an ice plate, then, the ultrastructure of the neurons was observed by using a transmission electron microscope.

RESULTS

After modeling, the rats' staying duration in the dark-box was shortened obviously (P < 0. 1). After the treatment, the staying duration in dark-box in acu-moxi group was significantly longer than that in model and medication groups (P < 0.01). Compared with normal control group, electron-microscopic results indicated that in PFC tissues of model and medication groups, vacuoles and edema of cytoplasm at different degrees, enlargement of the rough endoplasmic reticulum (REPR), vacuoles or disappearance of mitochondria, reduction of ribosome in number, and widening of the nuclear intermembrance interstice were seen. While in acu-moxi group, the number of mitochondria and ribosome increased slightly, the mitochondrial cristae was clear, the number of REPR increased relatively but dilated slightly, and the intermembrance space was basically normal.

CONCLUSION

Acu-moxibustion can improve heroin re-addicted rats' conditional position preference and has a protection effect on the cerebral cortical neurons. disappearance of mitochondria, reduction of ribosome in number, and widening of the nuclear intermembrance interstice were seen. While in acu-moxi group, the number of mitochondria and ribosome increased slightly, the mitochondrial cristae was clear, the number of REPR increased relatively but dilated slightly, and the intermembrance space was basically normal.

CONCLUSION

Acu-moxibustion can improve heroin re-addicted rats' conditional position preference and has a protection effect on the cerebral cortical neurons.

Chronic duloxetine treatment induces specific changes in the expression of BDNF transcripts and in the subcellular localization of the neurotrophin protein

There is growing evidence that brain-derived neurotrophic factor (BDNF) can be relevant to mood disorders and that modulation of its biosynthesis following prolonged antidepressant treatment may contribute to neuroplastic changes required for clinical response. In the present study, we investigated the effects of the novel antidepressant duloxetine on BDNF in the rat brain. Duloxetine is a serotonin-norepinephrine reuptake inhibitor that differs from other antidepressants by virtue of its balanced potency on both neurotransmitter systems. We found that chronic, but not acute, treatment with duloxetine produces a robust increase of exon V BDNF mRNA levels in frontal cortex when the animals were killed 1 or 24 h after the last administration. The expression of the neurotrophin was also increased in other cortical subregions, but not in the hippocampus. We also found that the increased expression of BDNF in frontal cortex was mainly sustained by enhanced mRNA levels for exons I and III, whereas the expression of exon IV was reduced. Protein analysis in different subcellular fractions showed that chronic treatment with duloxetine, but not with the prototypical SSRI fluoxetine, reduced mature BDNF in the cytosol, but markedly increased its levels in the crude synaptosomal fraction. Our data suggest that chronic treatment with the novel antidepressant duloxetine not only produces a marked upregulation of BDNF mRNA and protein, but may also affect the subcellular redistribution of the neurotrophin. These changes might improve synaptic plasticity and cognitive function that are defective in depressed subjects.

Molecular components and functions of the endocannabinoid system in mouse prefrontal cortex

Background

Cannabinoids have deleterious effects on prefrontal cortex (PFC)-mediated functions and multiple evidences link the endogenous cannabinoid (endocannabinoid) system, cannabis use and schizophrenia, a disease in which PFC functions are altered. Nonetheless, the molecular composition and the physiological functions of the endocannabinoid system in the PFC are unknown.

Methodology/Principal Findings

Here, using electron microscopy we found that key proteins involved in endocannabinoid signaling are expressed in layers V/VI of the mouse prelimbic area of the PFC: presynaptic cannabinoid CB1 receptors (CB1R) faced postsynaptic mGluR5 while diacylglycerol lipase α (DGL-α), the enzyme generating the endocannabinoid 2-arachidonoyl-glycerol (2-AG) was expressed in the same dendritic processes as mGluR5. Activation of presynaptic CB1R strongly inhibited evoked excitatory post-synaptic currents. Prolonged synaptic stimulation at 10Hz induced a profound long-term depression (LTD) of layers V/VI excitatory inputs. The endocannabinoid -LTD was presynaptically expressed and depended on the activation of postsynaptic mGluR5, phospholipase C and a rise in postsynaptic Ca²⁺ as predicted from the localization of the different components of the endocannabinoid system. Blocking the degradation of 2-AG (with URB 602) but not of anandamide (with URB 597) converted subthreshold tetanus to LTD-inducing ones. Moreover, inhibiting the synthesis of 2-AG with Tetrahydrolipstatin, blocked endocannabinoid-mediated LTD. All together, our data show that 2-AG mediates LTD at these synapses.

Conclusions/Significance

Our data show that the endocannabinoid -retrograde signaling plays a prominent role in long-term synaptic plasticity at the excitatory synapses of the PFC. Alterations of endocannabinoid -mediated synaptic plasticity may participate to the etiology of PFC-related pathologies.

The role of oligodendrocyte pathology in schizophrenia

Neuroimaging and microarray studies provide evidence for myelin and oligodendrocyte abnormalities in schizophrenia (SZ). Electron microscopy demonstrated dystrophy, necrosis and apoptosis of oligodendrocytes, the most severely affected cells in SZ. The proportion of myelinated fibres with atrophy of axon and swelling of periaxonal oligodendrocyte processes increased significantly in the prefrontal cortex (PFC), caudate nucleus and hippocampus in SZ compared to controls. Morphometry showed a deficit of oligodendrocytes in the PFC and in adjacent white matter, lower number of oligodendroglial satellites of pyramidal neurons and a loss of pericapillar oligodendrocytes in the PFC in SZ compared to normal controls. A lowered number of oligodendrocytes in the PFC was also found in mood disorders. These data provide evidence for altered oligodendrocyte-axon, oligodendrocyte-neuron and oligodendrocyte-capillar interactions in SZ brains suggesting a key role of damage and loss of oligodendrocytes in altered neuronal connectivity and in atrophy of neurons in SZ.

Glutamate synaptic inputs to ventral tegmental area neurons in the rat derive primarily from subcortical sources

Dopamine and GABA neurons in the ventral tegmental area project to the nucleus accumbens and prefrontal cortex and modulate locomotor and reward behaviors as well as cognitive and affective processes. Both midbrain cell types receive synapses from glutamate afferents that provide an essential control of behaviorally-linked activity patterns, although the sources of glutamate inputs have not yet been completely characterized. We used antibodies against the vesicular glutamate transporter subtypes 1 and 2 (VGlut1 and VGlut2) to investigate the morphology and synaptic organization of axons containing these proteins as putative markers of glutamate afferents from cortical versus subcortical sites, respectively, in rats. We also characterized the ventral tegmental area cell populations receiving VGlut1+ or VGlut2+ synapses according to their transmitter phenotype (dopamine or GABA) and major projection target (nucleus accumbens or prefrontal cortex). By light and electron microscopic examination, VGlut2+ as opposed to VGlut1+ axon terminals were more numerous, had a larger average size, synapsed more proximally, and were more likely to form convergent synapses onto the same target. Both axon types formed predominantly asymmetric synapses, although VGlut2+ terminals more often formed synapses with symmetric morphology. No absolute selectivity was observed for VGlut1+ or VGlut2+ axons to target any particular cell population. However, the synapses onto mesoaccumbens neurons more often involved VGlut2+ terminals, whereas mesoprefrontal neurons received relatively equal synaptic inputs from VGlut1+ and VGlut2+ profiles. The distinct morphological features of VGlut1 and VGlut2 positive axons suggest that glutamate inputs from presumed cortical and subcortical sources, respectively, differ in the nature and intensity of their physiological actions on midbrain neurons. More specifically, our findings imply that subcortical glutamate inputs to the ventral tegmental area expressing VGlut2 predominate over cortical sources of excitation expressing VGlut1 and are more likely to drive the behaviorally-linked bursts in dopamine cells that signal future expectancy or attentional shifting.

Early social isolation decreases the expression of calbindin D-28k and dendritic branching in the medial prefrontal cortex of the rat

Social isolation in rodents is the most well characterized animal model for early stressful experiences and their neurobehavioral consequences. The present study analyzed the effects of early social isolation on the expression of the calcium binding protein calbindin-D28k (CAD) and dendritic arborization in the medial prefrontal cortex (mPFC) of the rat. Sprague-Dawley male rats were reared either under isolation or social conditions from 21 to 51 postnatal days. At the end of this period the animals were behaviorally evaluated in the open-field test, sacrificed, and mPFC serial sections were processed either for immunocytochemical labeling against CAD or Golgi-Cox-Sholl staining. Isolated-reared rats exhibited a dramatic decrease in the number of CAD immunoreactive neurons and a significant dendritic atrophy of layer II/III pyramidal cells in association with a reduced exploratory behavior.

Impaired Recognition Memory and Decreased Prefrontal Cortex Spine Density in Aged Female Rats

Aged F344 female rats (21 months) showed decreased performance, as compared to young rats (4 months), on an object recognition memory task. Golgi impregnation measured dendritic spine density of pyramidal neurons in the prefrontal cortex (layer II-III), a brain area important for recognition memory. Densities of spines in aged rats were 16% lower in tertiary, apical dendrites, but not significantly different in secondary basal dendrites. Concurrent measures of memory and spine density in the young and aged subjects show that age-related declines in recognition memory are associated with decreased cortical spine density.

Phosphorylation of CREB and DARPP-32 during late LTP at hippocampal to prefrontal cortex synapses in vivo

Specific patterns of stimulation applied in the ventral hippocampus produce long-term potentiation (LTP) of postsynaptic synapses in the prefrontal cortex in vivo. The induction of LTP is dependent on NMDA receptors and cAMP-dependant kinase (PKA) activation. Yet little is known concerning the cellular mechanisms underlying the expression of this neocortical form of LTP. In the present study, we tested whether LTP at hippocampal to prefrontal cortex synapses leads to activation of DARPP-32 and CREB as well as defined the temporal regulation of the phosphorylation states of both proteins. Our data indicate a peak in CREB and DARPP-32 phosphorylation during the late phase of prefrontal LTP (2 h posttetanus). These findings support the hypothesis that prolonged expression of hippocampal-prefrontal cortex LTP depends on a synergistic mechanism involving phosphorylation of both CREB and DARPP-32 via activation of the cAMP/PKA-dependent pathway.

Nucleus reuniens of the midline thalamus: link between the medial prefrontal cortex and the hippocampus

The medial prefrontal cortex and the hippocampus serve well recognized roles in memory processing. The hippocampus projects densely to, and exerts strong excitatory actions on, the medial prefrontal cortex. Interestingly, the medial prefrontal cortex, in rats and other species, has no direct return projections to the hippocampus, and few projections to parahippocampal structures including the entorhinal cortex. It is well established that the nucleus reuniens of the midline thalamus is the major source of thalamic afferents to the hippocampus. Since the medial prefrontal cortex also distributes to nucleus reuniens, we examined medial prefrontal connections with populations of nucleus reuniens neurons projecting to hippocampus. We used a combined anterograde and retrograde tracing procedure at the light and electron microscopic levels. Specifically, we made Phaseolus vulgaris-leuccoagglutinin (PHA-L) injections into the medial prefrontal cortex and Fluorogold injections into the hippocampus (CA1/subiculum) and examined termination patterns of anterogradely PHA-L labeled fibers on retrogradely FG labeled cells of nucleus reuniens. At the light microscopic level, we showed that fibers from the medial prefrontal cortex form multiple putative synaptic contacts with dendrites of hippocampally projecting neurons throughout the extent of nucleus reuniens. At ultrastructural level, we showed that medial prefrontal cortical fibers form asymmetric contacts predominantly with dendritic shafts of hippocampally projecting reuniens cells. These findings indicate that nucleus reuniens represents a critical link between the medial prefrontal cortex and the hippocampus. We discuss the possibility that nucleus reuniens gates the flow of information between the medial prefrontal cortex and hippocampus dependent upon attentive/arousal states of the organism.

[Abnormal patterns of cortical synaptic connectivity in schizophrenia]

Electron microscopic morphometric study of postmortem prefrontal cortex (area 10) and visual cortex (area 17) was performed to estimate the numeric density (Nv) of synapses in layers I and II, neurons in layer II and the number of synapses per neuron in layer II in 20 cases of chronic schizophrenia and 16 healthy controls using stereological physical dissector method. In the prefrontal cortex the Nv of axospinous synapses was significantly lower in layer I (-20%, p < 0.05) in schizophrenia group and in the subgroup with predominantly positive symptoms as compared to controls (p < 0.05). On the contrary, a significantly higher Nv of synapses (+24%, p < 0.05) and the number of synapses per neuron were found in layer II (+42%, p < 0.05) in schizophrenia group and in the subgroups of cases with predominantly negative symptoms and a continuous course of schizophrenia (p < 0.001) as compared to the control group. The subgroup of cases with predominantly negative symptoms displayed a significantly lower number of neurons in layer II of the prefrontal cortex compared to controls (p < 0.05) and the subgroup of cases with predominantly positive symptoms (p < 0.01). In the visual cortex the number of axodendritic synapses per neuron in layer II was significantly higher in schizophrenia, but the other parameters did not differ from those in the control group. These prominent abnormalities of synaptic connectivity might be the structural basis for altered cognitive functions associated with changes in intracortical, cortico-cortical, and cortico-subcortical pathways, and could contribute to the formation of positive and negative symptoms and altered neuronal plasticity in patients with schizophrenia.

Neonatal caffeine administration causes a permanent increase in the dendritic length of prefrontal cortical neurons of rats

We studied the morphological changes of the dendritic length of the pyramidal neurons of the prefrontal cortex (PFC) induced by the effect of chronic administration of caffeine in the neonatal rat. The caffeine (50 mg/kg, s.c.) was injected from day 1 after birth (P1) to day 12 (P12). The morphology of the pyramidal neurons of layer 3 of the PFC was investigated in these animals at two different ages, before puberty (P35) and after puberty (P70). Before the animals were sacrificed by using overdoses of sodium pentobarbital and being perfused intracardially with 0.9% saline, the locomotor activity in a novel environment was measured. The brains were then removed, processed by the Golgi-Cox stain, and analyzed by the Sholl method. The dendritic morphology clearly showed that the neonatal animals administered caffeine showed an increase in the dendritic length of the pyramidal neurons of the PFC when compared with the control animals at both ages. The present results suggest that neonatal administration of caffeine may in part affect the dendritic morphology of the pyramidal cells of this limbic structure and this effect persists after puberty and may be implicated in several brain processes.

Chronic treatment with Delta-9-tetrahydrocannabinol alters the structure of neurons in the nucleus accumbens shell and medial prefrontal cortex of rats

The potential of repeated exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) to produce long-lasting changes in synaptic connections in a manner similar to other drugs of abuse was evaluated in Sprague-Dawley rats. For 12 days, rats received two i.p. injections per day (8 h apart) of vehicle, a low dose of Delta(9)-THC (0.5 mg/kg), or escalating doses of Delta(9)-THC (0.5-4.0 mg/kg). Thirty days later, they were evaluated for sensitized locomotor activity (during the night cycle) for 60 min on each of three trials. Using a within-groups design, rats were tested following an injection of vehicle, 0.5 mg/kg Delta(9)-THC or 2.0 mg/kg Delta(9)-THC. The rats showed no evidence of sensitized locomotor activity in any group. Twenty-four hours after the final sensitization test, their brains were removed and then processed for Golgi-Cox staining. Prior exposure to Delta(9)-THC (both the low dose and the escalating doses) increased the length of the dendrites as well as the number of dendritic branches in the shell of the nucleus accumbens and in the medial prefrontal cortex, but not in the hippocampus, striatum, orbital frontal cortex, parietal cortex, or occipital cortex. These results are similar to those evident in brains of rats sensitized to amphetamine, and support previous findings that cannabinoids promote DA activity in the mesolimbic DA system.

Subchronic phencyclidine treatment decreases the number of dendritic spine synapses in the rat prefrontal cortex

BACKGROUND

A growing body of evidence suggests the existence of synaptic pathology in schizophrenia. Here we used the phencyclidine schizophrenia model to directly investigate at the electron microscopic level whether structural synaptic alterations are present in these animals.

METHODS

Adult male rats were treated according to our subchronic phencyclidine paradigm (5 mg/kg twice daily for 7 days, intraperitoneally). Following a one-week withdrawal period, the number of prefrontal cortical spine synapses was calculated using an unbiased electron microscopic stereological approach. The number of astroglia cells and the density of their processes was also analyzed following glial-fibrillary acidic protein immunohistochemistry.

RESULTS

Subchronic phencyclidine treatment resulted in a 41.2% decrease in the number of prefrontal spine synapses when compared to controls. This was accompanied by a 58.8% increase in astroglia process density, without significant change in the number of astroglia cells.

CONCLUSIONS

Our results demonstrate a severe reduction in the number of prefrontal spine synapses in an animal model of schizophrenia. This phenomenon may contribute to phencyclidine-induced cognitive dysfunction and decreased prefrontal cellular activity observed in this model.

Changes of spine density and dendritic complexity in the prefrontal cortex in offspring of mothers exposed to stress during pregnancy

Both chronic stress in adulthood and episodes of stress in the early postnatal period have been shown to interfere with neuronal development in limbic prefrontal cortical regions. The present study in rats showed for the first time that the development of layer II/III pyramidal neurons in the dorsal anterior cingulate (ACd) and orbitofrontal cortex (OFC) is significantly affected in offspring of mothers exposed to stress during pregnancy. In prenatally stressed (PS) male rat pups the ACd and OFC showed significantly lower spine densities on the apical dendrite (ACd, -20%; OFC, -25%), on basal dendrites reduced spine densities where found only in the OFC (-20% in PS males). Moreover, in both cortical areas a significant reduction of dendritic length was observed in PS males compared to control offspring, which was confined to the apical dendrites (ACd, -30%, OFC, -26%). Sholl analysis revealed that these alterations were accompanied by a significantly reduced complexity of the dendritic trees in both cortical regions. PS females displayed reductions of dendritic spine densities in the ACd and OFC on both the basal (ACd, -21%; OFC, -20%) and apical dendrites (ACd, -21%; OFC, -21%), however, in contrast to the findings in PS males, no dendritic atrophy was detected in the PS females. These findings demonstrate that gestational stress leads to significant alterations of prefrontal neuronal structure in the offspring of the stressed mothers in a sex-specific manner.

Dietary phytoestrogens enhance spatial memory and spine density in the hippocampus and prefrontal cortex of ovariectomized rats

Long-term maintenance of ovariectomized rats (9 weeks) on chow containing high phytoestrogen levels (Purina LabDiet 5001) as compared to chow with minimal phytoestrogens (Harlan 2016 Teklad) was associated with better performance of the spatial memory task, object placement, increased dendritic spine density in CA1 and prefrontal cortex pyramidal neurons, and higher uterine weights. Object recognition memory, anxiety on an elevated plus maze and body weight were unaffected by phytoestrogen levels in the diet.

Protective effects of omega-3 essential fatty acids against formaldehyde-induced neuronal damage in prefrontal cortex of rats

The aim of this study was to examine the neurotoxicity of formaldehyde on prefrontal cortex and the protective effects of omega-3 essential fatty acids against these toxic effects. For this purpose, 21 male Wistar rats were divided into three groups. The rats in group I comprised the controls, while the rats in group II were injected every other day with formaldehyde (FA). The rats in group III received omega-3 fatty acids daily while exposed to formaldehyde. At the end of the 14-day experimental period, all rats were killed by decapitation. The brains of the rats were removed and the prefrontal cortex tissues were obtained from all brain specimens. Some of the prefrontal cortex tissue specimens were used for determination of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) levels. The remaining prefrontal cortex tissue specimens were used for light microscopic and immunohistochemical evaluation. The levels of SOD and GSH-Px were significantly decreased, and MDA levels were significantly increased in rats treated with formaldehyde compared with those of the controls. Furthermore, in the microscopic examination of this group, formation of apoptotic bodies, pycnotic cells, and apoptotic cells including nuclear fragmentation and membrane budding were observed. However, increased SOD and GSH-Px enzyme activities, and decreased MDA levels were detected in the rats administered omega-3 fatty acids while exposed to formaldehyde. Additionally, cellular damage caused by formaldehyde was decreased, and structural appearance was similar to that of the control rats in this group. The biochemical and histological findings observed in all groups were also confirmed by immunohistochemical evaluation. It was determined that formaldehyde-induced neuronal damage in prefrontal cortex was prevented by administration of omega-3 essential fatty acids.

Ultrastructural organization of medial prefrontal inputs to the rhinal cortices

Accumulating evidence suggests that the medial prefrontal cortex (mPFC) plays a critical role in the formation, retrieval and long-term storage of hippocampal-dependent memories. Consistent with this, there are direct hippocampal projections to the mPFC. Moreover, the mPFC sends robust projections to the perirhinal and entorhinal cortices, two interconnected cortical fields that funnel information into and out of the hippocampus. However, the significance of the latter projection remains unclear because no data are available regarding the rhinal targets of mPFC axons. This question was examined in the present study using a combination of anterograde tracing with Phaseolus vulgaris leucoagglutinin and pre-embedding gamma-aminobutyric acid (GABA) immunocytochemistry in guinea pigs. Following Phaseolus vulgaris leucoagglutinin injections in the mPFC, anterogradely labeled axons were seen in the perirhinal (mainly superficial layers) and lateral entorhinal (mainly deep layers) cortices. In the electron microscope, the synaptic articulation of anterogradely labeled mPFC axon terminals with perirhinal and entorhinal neurons was found to be nearly identical. In these two rhinal fields, mPFC axon terminals only formed asymmetric synapses, typically with GABA-immunonegative spines ( approximately 70%) but occasionally with dendritic profiles ( approximately 30%), half of which were GABA immunopositive. In the light of earlier observations, these findings indicate that mPFC inputs exert mainly excitatory effects in the rhinal cortices, prevalently on principal neurons. Thus, these results suggest that the mPFC may affect hippocampal-dependent memories by enhancing impulse traffic into and out of the hippocampus at the level of the rhinal cortices.

Calcyon, a Novel Partner of Clathrin Light Chain, Stimulates Clathrin-mediated Endocytosis

In the central nervous system, clathrin-mediated endocytosis is crucial for efficient synaptic transmission. Clathrin-coated vesicle assembly and disassembly is regulated by some 30 adaptor and accessory proteins, most of which interact with clathrin heavy chain. Using the calcyon cytosolic domain as bait, we isolated clathrin light chain in a yeast two-hybrid screen. The interaction domain was mapped to the heavy chain binding domain and C-terminal regions of light chain. Further, the addition of the calcyon C terminus stimulated clathrin self-assembly in a dose-dependent fashion. Calcyon, which is a single transmembrane protein predominantly expressed in brain, localized to vesicular compartments within pre- and postsynaptic structures. There was a high degree of overlap in the distribution of LC and calcyon in neuronal dendrites, spines, and cell bodies. Co-immunoprecipitation studies further suggested an association of calcyon with the clathrin-mediated endocytic machinery. Compared with controls, HEK293 cells overexpressing calcyon exhibited significantly enhanced transferrin uptake but equivalent levels of recycling. Conversely, transferrin uptake was largely abolished in neocortical neurons obtained from mice homozygous for a calcyon null allele, whereas recycling proceeded at wild type levels. Collectively, these data indicate a role for calcyon in clathrin-mediated endocytosis in brain.

Evidence of white matter pathology in bipolar disorder adolescents experiencing their first episode of mania: a diffusion tensor imaging study

OBJECTIVE

Previous diffusion tensor imaging findings have supported suggestions that bipolar disorder is characterized by subtle white matter changes. The chronic nature of the study population, however, has limited interpretation of these findings. In this study the authors utilized diffusion tensor imaging to study white matter tracts of adolescents in their first episode of mania to address whether abnormalities are present in early bipolar disorder.

METHOD

Eleven medication-naive adolescents in their first episode of mania and 17 healthy subjects underwent diffusion tensor imaging scans. Fractional anisotropy and trace apparent diffusion coefficients of prefrontal and posterior regions of interest were compared between groups.

RESULTS

Bipolar adolescents showed significantly decreased fractional anisotropy only in superior-frontal white matter tracts. Trace apparent diffusion coefficients did not significantly differ in any regions examined.

CONCLUSIONS

These findings suggest that prefrontal white matter abnormalities are present early in bipolar disorder and may consist largely of axonal disorganization. The presence of changes in young first-episode patients also suggests that white matter pathology may represent an early marker of bipolar disorder.

Cortical white matter microstructural abnormalities in bipolar disorder

This article reports on preliminary findings describing microstructural abnormalities in the white matter of cortical areas thought to be associated with bipolar disorder. In all, 14 patients with bipolar disorder and 21 nonpsychiatrically ill control subjects underwent MR imaging including a diffusion tensor imaging (DTI) pulse sequence (six directions, b=1000 mm(2)/s). DTI data were analyzed on a workstation using a program that allowed calculation of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) within the following three white matter fiber tracts bilaterally: the orbital frontal cortex, and the superior and middle frontal gyri. These values were compared across patient groups. The left and right orbital frontal white matter exhibited significantly higher ADC values in bipolar subjects than control subjects on both the left (p=0.028) and right (p=0.011). Microstructural changes in the white matter of the orbital frontal areas as reflected by increased ADC values appear to be associated with bipolar disorder. Further research is needed to better understand the interaction of microstructural changes and bipolar symptoms and whether these changes are specific to bipolar disorder.

Subcellular localization of the dopamine D2 receptor and coexistence with the calcium-binding protein neuronal calcium sensor-1 in the primate prefrontal cortex

Structures of the cerebral cortex expressing the D2 dopamine receptor subtype (D2) are important sites of action of antipsychotic drugs. It has also been repeatedly suggested that the prefrontal cortex plays a significant role in neuropsychiatric disorders, including schizophrenia. Here, by using single and double immunohistochemical techniques with electron microscopy, we investigated in the primate prefrontal cortex the ultrastructural localization of D2 and we compared it with that of the neuronal calcium sensor-1 (NCS-1), a neuron-specific calcium-binding and D2-interacting protein. D2 immunoreactivity, revealed with preembedding immunoperoxidase in single labeling and with preembedding immunogold for double labeling, was localized in cell bodies with ultrastructural characteristics of both neurons and astroglia. D2 was localized in pre- and postsynaptic structures, including spines and dendrites, and in both excitatory- and inhibitory-like axon terminals. Immunogold labeling revealed peri- and extrasynaptic localization of D2 in postsynaptic structures, whereas extrasynaptic labeling was typically found in boutons. NSC-1 immunoreactivity was abundant in pre- and postsynaptic structures, in which it was also colocalized with D2. With the present strategy (that has high resolution but relatively limited sensitivity), NSC-1 was observed in about 10% of the D2-immunopositive spines and in a lower proportion of D2-immunopositive dendrites and boutons. The data demonstrate the localization of D2 in pre- and postsynaptic as well as extra- and perisynaptic structures of the primate prefrontal cortex. The data also show the coexistence of NCS-1 and D2 at the ultrastructural level. The latter finding suggests a role for NCS-1 in desensitization of D2 in the prefrontal cortex.

Neural and behavioral plasticity associated with the transition from controlled to escalated cocaine use

BACKGROUND

Rats given extended access to cocaine develop several symptoms of addiction, including a gradual escalation of drug intake, whereas rats given limited access do not. We asked here whether extended access to cocaine also produces drug-induced sensitization, a form of neurobehavioral plasticity implicated in addiction.

METHODS

Rats were given limited (1 hour/session) or extended access (6 hours/session) to self-administered cocaine. Following a period of abstinence, rats were selected at random for assessment of their psychomotor response to cocaine or drug-seeking during extinction or for anatomic studies.

RESULTS

When re-exposed to cocaine, rats allowed extended drug access showed greater drug-seeking behavior and were hypersensitive (sensitized) to the psychomotor activating effects of cocaine compared with rats given limited access. Extended access to cocaine was also associated with a greater increase in the density of dendritic spines on neurons specifically in the core of the nucleus accumbens (and not in the shell or medial or orbital frontal cortex).

CONCLUSIONS

The transition from stable to escalated cocaine use, a hallmark of addiction, is associated with especially robust behavioral sensitization and synaptic reorganization in the core of the nucleus accumbens.

Intermittent cortical stimulation evokes sensitization to cocaine and enduring changes in matrix and striosome neuron responsiveness

Both the behavioral sensitization syndrome and the changes in the responsiveness of striatal neurons evoked by chronic cocaine exposure may be linked to enhanced neocortical activity, yet a direct demonstration of the effects of cortical stimulation on these parameters is lacking. We have found that repeated stimulation of the rat prelimbic cortex with picrotoxin (0.25 microg/0.25 microl, five injections on alternate days followed by 7-day withdrawal) contributed to increase c-Fos protein expression in the striosomes of the dorsolateral striatum, while producing the opposite effect in the matrix compartment, after a single exposure to cocaine (25 mg/kg). Moreover, rats exposed to cortical stimulation showed decreased locomotor activation but enhanced stereotypy following acute cocaine treatment. Thus, pulsatile stimulation of the prelimbic cortex facilitated modifications in striatal activity typically produced by chronic cocaine treatment and sensitized drug-naive animals to acute cocaine challenge. These results suggest that enhanced activation of the prelimbic cortex may contribute to the long-term adaptations induced by cocaine on neural activity and behavior.

The brain-derived neurotrophic factor val66met polymorphism and variation in human cortical morphology

A variation in the BDNF gene (val66met) affects the function of BDNF in neurons, predicts variation in human memory, and is associated with several neurological and psychiatric disorders. Here, we show that, in magnetic resonance imaging scans of a large sample of normal individuals, this polymorphism affects the anatomy of the hippocampus and prefrontal cortex, identifying a genetic mechanism of variation in brain morphology related to learning and memory.