Cells In Brain Regions Research Articles

Olfactory bulbectomy induces nociceptive alterations associated with gliosis in male rats

Major depressive disorder (MDD) is a major health concern worldwide with a wide array of symptoms. Emerging evidence suggests a high comorbidity between MDD and chronic pain, however, the relationship between these two diseases is not completely understood. Growing evidence suggests that glial cells play a key role in both disorders. Hence, we examined the effect of olfactory bulbectomy (OBX), a well-known model of depression-related behavior, on nociceptive behaviors and the number and morphology of astrocytes and glial cells in brain regions involved in the control of nociceptive processes in male rats. The brain regions analyzed included the basolateral amygdala (BLA), central amygdala (CeA), prefrontal cortex (PFC), and CA1 subregion of the hippocampus. A battery of behavioral tests, mechanical allodynia, thermal cold allodynia and mechanical hyperalgesia, was evaluated before and four weeks after OBX. Quantitative morphological analysis, as well as assessment of the number of glial fibrillary acidic protein (GFAP) and ionizing calcium-binding adaptor molecule 1 (Iba1) positive astrocytes and microglia were carried out to characterize glial remodeling and density, respectively. OBX caused mechanical and cold allodynia in an asynchronous pattern. The cold allodynia was noticeable one week following surgery, while mechanical allodynia became apparent two weeks after surgery. In the BLA, CeA and CA1, OBX caused significant changes in glial cells, such as hypertrophy and hypotrophy in GFAP-positive astrocytes and Iba1-positive microglia, respectively. Iba1-positive microglia in the PFC underwent selective hypotrophy due to OBX and OBX enhanced both GFAP-positive astrocytes and Iba1-positive microglia in the BLA. In addition, OBX increased the number of GFAP-positive astrocytes in the CeA and CA1. The amount of Iba1-positive microglia in the PFC also increased as a result of OBX. Furthermore, we found that there was a strong link between the observed behaviors and glial activation in OBX rats. Overall, our work supports the neuroinflammatory hypothesis of MDD and the comorbidity between pain and depression by demonstrating nociceptive impairment and significant microglial and astrocytic activation in the brain.

Astrocytes in the PVN are involved in corticotropin-releasing factor-induced sympathetic activation in rats

Corticotropin-releasing factor (CRF) plays a key role in stress responses in the brain. CRF activates not only the hypothalamic-pituitary-adrenal axis but also the sympathetic nervous system. We previously reported that both central administration of CRF and exposure to acute restraint stress (RS) increase plasma catecholamine levels and activate presympathetic neurons in the paraventricular hypothalamic nucleus (PVN). However, it is unclear whether glial cells in brain regions including the PVN are involved in CRF- or stress-induced sympathetic activation. In this study, we examined roles of astrocytes in the CRF-induced elevation of plasmas catecholamine levels (noradrenaline and adrenaline) using fluorocitrate which blocks glial metabolic function. Intracerebroventricular pretreatment of fluorocitrate suppressed the CRF-induced elevation of plasma levels of noradrenaline and adrenaline. On the other hand, microinjection of fluorocitrate into the PVN suppressed the CRF-induced elevation of adrenaline, but not of noradrenaline. Furthermore, we tried to examine effects of inhibition of astrocytes on RS-induced sympathetic activation. Our results suggest that astrocytic function in the brain is important for the CRF-induced sympathetic activation and the effects might be brain region-dependent.

Dio2-CreErt2 Knockin Model to Identify T3-Generating Cells That Express Type 2 Deiodinase in Tissues

Background: Thyroid hormone promotes many developmental and homeostatic functions. Apart from adequate circulating levels, the concentration of the active hormone T3 within tissues may be amplified by type 2 deiodinase (Dio2) by conversion from the precursor T4. Dio2 is critical in auditory development, bone maturation, brain function and control of the hypothalamic-pituitary-thyroid axis. Despite its crucial role, an obstacle to studying Dio2 is that the protein has a short half-life, is at low levels and is often transiently expressed, making it difficult to identify Dio2 in tissues at cellular resolution. Methods: We derived a Dio2-CreERt2 knockin mouse that expresses tamoxifen-dependent Cre recombinase from the endogenous Dio2 gene. When crossed onto Ai6 reporter mice, following tamoxifen treatment, Dio2-CreERt2 expression is detected as fluorescent signal in specific cells in brain regions, pituitary, and other tissues. We showed previously that Dio2 is essential for hearing with rising expression levels in the cochlea prior to onset of hearing. The Dio2-CreERt2 model identified positive cell types in the cochlear spiral ligament, septal divisions and modiolus around the sensory epithelium. Dio2-positive fibrocytes were adjacent to and extended projections around blood capillary networks, the source of T4 supply. Transcriptome analysis of isolated positive cells revealed bone lineage-related origins for many of these cells. Conclusion: The Dio2-CreERt2 model detects Dio2 expression sensitively at cellular resolution. In the cochlea, Dio2-positive cell types reside in vascularized support tissues, suggesting combined endocrine and paracrine-like control of the T3 supply. Analysis of cell origins suggests novel interactions between endocrine and skeletal systems in promoting T3 action required for hearing.

Differences in the number of oxytocin, vasopressin, and tyrosine hydroxylase cells in brain regions associated with mating among great, midday, and Mongolian gerbils

Neurotransmitters, such as oxytocin (OT), vasopressin (AVP), and dopamine (DA), within the mesolimbic system have deeply conserved roles in regulating mating-related behaviors. However, comparative studies among monogamous and polygamous animals focus mainly on Microtus; very little research has been done in gerbils. Here, we measured body weight, body length, tail length, serum hormone concentrations, and the immunoreactive (ir)-cells of OT, AVP, and tyrosine hydroxylase (TH) in the brain of the polygamous great gerbil (Rhombomys opimus), midday gerbil (Meriones meridianus), and monogamous Mongolian gerbil (Meriones unguiculatus). Body weight, body length, tail length, and serum AVP concentrations were greater in the great gerbil than in the midday gerbil and Mongolian gerbil. The number of OT and AVP cells in the para ventricular nucleus (PVN) and supra optic nucleus (SON) of the hypothalamus were greater in the Mongolian gerbil than in the great gerbil and midday gerbil. Similarly, the number of TH cells in the PVN, medial preoptic area (MPOA), and ventral tegmental area (VTA) was greater in the Mongolian gerbil than in the great gerbil and midday gerbil. To summarize, the number of OT and AVP cells in the PVN and SON and TH cells in the PVN, MPOA, and VTA in the monogamous Mongolian gerbil are greater than those in the great gerbil and midday gerbil.

Glioma brain tumor detection and segmentation using weighting random forest classifier with optimized ant colony features

AbstractThe uncontrolled growth of cells in brain regions leads to the tumor regions and these abnormal tumor regions are scanned by magnetic resonance imaging (MRI) technique as an image. This paper proposes random forest classifier based Glioma brain tumor detection and segmentation methodology using feature optimization technique. The texture features are derived from brain MRI image and these derived feature set are now optimized by ant colony optimization algorithm. These optimized set of features are trained and classified using random forest classification method. This classifier classifies the brain MRI image into Glioma or non‐Glioma image based on the optimized set of features. Furthermore, energy‐based segmentation method is applied on the classified Glioma image for segmenting the tumor regions. The proposed methodology for Glioma brain tumor stated in this paper achieves 97.7% of sensitivity, 96.5% of specificity, and 98.01% of accuracy.

Hypomyelination and Oligodendroglial Alterations in a Mouse Model of Autism Spectrum Disorder.

Autism spectrum disorders (ASDs) are neuropsychiatric diseases characterized by impaired social interaction, communication deficits, and repetitive and stereotyped behaviors. ASD etiology is unknown, and both genetic and environmental causes have been proposed. Different brain structures are believed to play a role in ASD-related behaviors, including medial prefrontal cortex (mPFC), hippocampus, piriform cortex (Pir), basolateral amygdala (BLA) and Cerebellum. Compelling evidence suggests a link between white matter modifications and ASD symptoms in patients. Besides, an hypomyelination of the mPFC has been associated in rodents to social behavior impairment, one of the main symptoms of ASD. However, a comparative analysis of myelination as well as oligodendroglial (OL)-lineage cells in brain regions associated to social behaviors in animal models of ASD has not been performed so far. Here, we investigated whether OL-lineage cells and myelination are altered in a murine model of ASD induced by the prenatal exposure to valproic acid (VPA). We showed an hypomyelination in the BLA and Pir of adult VPA-exposed mice. These results were accompanied by a decrease in the number of OL-lineage cells and of mature OLs in the Pir, in addition to the mPFC, where myelination presented no alterations. In these regions the number of oligodendrocyte progenitors (OPCs) remained unaltered. Likewise, activation of histone deacetylases (HDACs) on OL-lineage cells in adulthood showed no differences. Overall, our results reveal OL-lineage cell alterations and hypomyelination as neuropathological hallmarks of ASD that have been overlooked so far.

Developmental Exposure of Mice to T-2 Toxin Increases Astrocytes and Hippocampal Neural Stem Cells Expressing Metallothionein.

We previously reported that developmental exposure to T-2 toxin caused transient disruption of the hippocampal neurogenesis targeting neural stem cells (NSCs) and early-stage progenitor cells involving oxidative stress on weaning in mouse offspring. The present study examined metallothionein (MT) expression changes and their cellular identity in brain regions of these animals. T-2 toxin at 0, 1, 3, and 9mg/kg was given in the diet of maternal mice from gestational day 6 to postnatal day (PND) 21 on weaning. Offspring were maintained through PND 77 without T-2 toxin exposure. Male offspring were analyzed. Immunohistochemically, MT-I/II+ cells increased in the subgranular zone (SGZ) of the dentate gyrus and cerebral cortex at ≥ 3mg/kg and in the hilus of the dentate gyrus, corpus callosum, and cerebellum at 9mg/kg on PND 21, suggestive of operation of cytoprotective function against oxidative stress throughout the brain. Double immunohistochemistry analysis revealed MT-I/II+ SGZ cells to be NSCs and MT-I/II+ cells in other brain regions to be astrocytes as toxicity targets of T-2 toxin. Phosphorylated STAT3+ cell numbers increased only in the cerebellum in parallel with the increase of GFAP+ astrocytes at 9mg/kg, suggesting a STAT3-mediated transcriptional GFAP upregulation in cerebellar astrocytes. In the dentate gyrus, Il1a, Il1r1, and Mt2 increased transcripts at 9mg/kg, suggesting activation of the IL-1 signaling cascade, possibly causing MT-II upregulation. The increase of MT-I/II+ cells in all brain regions disappeared or was suppressed below the control level on PND 77, suggesting a recovery from the T-2 toxin-induced oxidative stress.

Myeloperoxidase-immunoreactive cells are significantly increased in brain areas affected by neurodegeneration in Parkinson\u2019s and Alzheimer\u2019s disease

Myeloperoxidase (MPO) is a key enzyme in inflammatory and degenerative processes, although conflicting reports have been presented concerning its expression in the brain. We studied the cellular localization of MPO and compared numbers of MPO cells in various brain regions between neurologically healthy individuals and patients with Parkinson’s disease (PD) or Alzheimer’s disease (AD; n = 10–25). We also investigated two rodent PD models. MPO immunoreactivity (ir) was detected in monocytes, perivascular macrophages and amoeboid microglia in the human brain parenchyma, whereas no co-localization with glial fibrillary acidic protein (GFAP) ir was observed. In the midbrain, caudate and putamen, we found a significant increase of MPO-immunoreactive cells in PD compared with control brains, whereas in the cerebellum, no difference was apparent. MPO ir was detected neither in neurons nor in occasional small beta-amyloid-immunoreactive plaques in PD or control cases. In the frontal cortex of AD patients, we found significantly more MPO-immunoreactive cells compared with control cases, together with intense MPO ir in extracellular plaques. In the hippocampus of several AD cases, MPO-like ir was observed in some pyramidal neurons. Neither rapid dopamine depletion in the rat PD model, nor slow degeneration of dopamine neurons in MitoPark mice induced the expression of MPO ir in any brain region. MPO mRNA was not detectable with radioactive in situ hybridization in any human or rodent brain area, although myeloid cells from bone marrow displayed clear MPO signals. Our results indicate significant increases of MPO-immunoreactive cells in brain regions affected by neurodegeneration in PD and AD, supporting investigations of MPO inhibitors in novel treatment strategies.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels.

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H2 S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H2 S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H2 S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H2 S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H2 S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H2 S were restored in HHcy animals administered H2 S. Exogenous H2 S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H2 S. These results clearly demonstrate that the protective effect of H2 S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H2 S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Protective Effect of Alpha Lipoic Acid against Phenytoin Induced Behavioral Abnormalities in Rats

Background: Long term administration of antiepileptic drug phenytoin is reported to cause behavioral abnormalities mediated via oxidative stress. The effect of an antioxidant alpha lipoic acid (ALA) against phenytoin induced behavioral abnormalities was investigated. Methods: The study was carried out in albino wistar rats. The rats were divided into five groups of six animals each. Group 1 received 0.2% carboxy methyl cellulose (CMC, p.o), group 2 received 20 mg/kg phenytoin (p.o), groups 3,4 and 5 received 50, 100 and 200 mg/kg (p.o) of ALA in 0.2% CMC, respectively 1 h prior to phenytoin for 45 days. Motor coordination, exploratory behavior, memory and spontaneous motor activity were evaluated by Rota rod, Hole board, Elevated plus maze and Actophotometer respectively. On day 45, regional brain lipid peroxidation and acetylcholinesterase (ACh E) activity along with brain histopathological investigation were performed after euthanasia. In addition, pharmacokinetic and pharmacodynamic drug interactions between phenytoin and ALA were also studied. Results: Long term administration of phenytoin showed behavioral abnormalities, increased regional brain malondialdehyde (MDA) and ACh E activity. The histopathological investigation showed congested and damaged cells in brain regions. ALA substantially reversed phenytoin induced behavioral abnormalities, oxidative stress and alleviated the histopathological abnormalities. There were no significant differences in the serum levels of phenytoin and the degree of protection offered by phenytoin in ALA supplemented groups revealing that there were no pharmacokinetic and pharmacodynamic interactions between phenytoin and ALA. Conclusion: This study reports the effectiveness of ALA against phenytoin induced behavioral abnormalities and oxidative stress in rats without altering the bioavailability of phenytoin and its therapeutic effect.

Androgen receptor distribution in the social decision-making network of eusocial naked mole-rats

Naked mole-rats are highly social rodents that live in large groups and exhibit a strict reproductive and social hierarchy. Only a few animals in each colony breed; the remainder are non-reproductive and are socially subordinate to breeders. We have examined androgen receptor immunoreactive (AR+) cells in brain regions comprising the recently described social decision-making network in subordinate and breeder naked mole-rats of both sexes. We find that subordinates have a significantly higher percentage of AR+ cells in all brain regions expressing this protein. By contrast, there were no significant effects of sex and no sex-by-status interactions on the percentage of AR+ cells. Taken together with previous findings, the present data complete a systematic assessment of the distribution of AR protein in the social decision-making network of the eusocial mammalian brain and demonstrate a significant role for social status in the regulation of this protein throughout many nodes of this network.

36. Immune adaptation in the central nervous system in response to systemic infection

Introduction: Acute systemic inflammation leads to production of inflammatory mediators and transient metabolic and behavioural changes. In models of chronic neurodegeneration this acute inflammation can cause neuronal damage through activation of ‘primed’ microglia. Here, we investigated innate immune activation in the healthy and diseased CNS in response to chronic systemic bacterial infection. Methods: Mice received a sublethal dose (10 × 6 pfu) of life Salmonella typhimurium. Serum, spleen and brain cytokines were measured at various time points and microglia and endothelial cell phenotypes studied by immunohistochemistry. The ME7 prion model was used to study the effect of systemic inflammation on ongoing neurodegeneration. Results: Peripheral cytokines (IFNg, IL-1b, IL-12) peaked at day 7 while brain cytokine levels (IL-1b, IL-12) continued to increase in S. typhimurium infected mice up to 21 days. Transient changes in CD11b and CD68 expression on microglial cells were observed but persistent MHCII expression on cerebral endothelial cells was detected up to 8 weeks after infection. Mice with ME7 prion disease showed exaggerated activation of microglia following systemic infection and a significant increase in CD3+ cells in brain regions with ongoing neurodegeneration. Conclusion: These studies reveal significant phenotype changes in microglia and cerebral blood vessels of naı¨ve mice in response to systemic infection, suggesting ‘priming’ of microglial and/or endothelial cells. These changes may have a profound effect on pre-existing neurodegenerative disease.

Aberrant NF-KappaB Expression in Autism Spectrum Condition: A Mechanism for Neuroinflammation

Autism spectrum condition (ASC) is recognized as having an inflammatory component. Post-mortem brain samples from patients with ASC display neuroglial activation and inflammatory markers in cerebrospinal fluid, although little is known about the underlying molecular mechanisms. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a protein found in almost all cell types and mediates regulation of immune response by inducing the expression of inflammatory cytokines and chemokines, establishing a feedback mechanism that can produce chronic or excessive inflammation. This article describes immunodetection and immunofluorescence measurements of NF-κB in human post-mortem samples of orbitofrontal cortex tissue donated to two independent centers: London Brain Bank, Kings College London, UK (ASC: n = 3, controls: n = 4) and Autism Tissue Program, Harvard Brain Bank, USA (ASC: n = 6, controls: n = 5). The hypothesis was that concentrations of NF-κB would be elevated, especially in activated microglia in ASC, and pH would be concomitantly reduced (i.e., acidification). Neurons, astrocytes, and microglia all demonstrated increased extranuclear and nuclear translocated NF-κB p65 expression in brain tissue from ASC donors relative to samples from matched controls. These between-groups differences were increased in astrocytes and microglia relative to neurons, but particularly pronounced for highly mature microglia. Measurement of pH in homogenized samples demonstrated a 0.98-unit difference in means and a strong (F = 98.3; p = 0.00018) linear relationship to the expression of nuclear translocated NF-κB in mature microglia. Acridine orange staining localized pH reductions to lysosomal compartments. In summary, NF-κB is aberrantly expressed in orbitofrontal cortex in patients with ASC, as part of a putative molecular cascade leading to inflammation, especially of resident immune cells in brain regions associated with the behavioral and clinical symptoms of ASC.

Invariance in visual object recognition requires training: a computational argument

Visual object recognition is remarkably accurate and robust, yet its neurophysiological underpinnings are poorly understood. Single cells in brain regions thought to underlie object recognition code for many stimulus aspects, which poses a limit on their invariance. Combining the responses of multiple non-invariant neurons via weighted linear summation offers an optimal decoding strategy, which may be able to achieve invariant object recognition. However, because object identification is essentially parameter optimization in this model, the characteristics of the identification task trained to perform are critically important. If this task does not require invariance, a neural population-code is inherently more selective but less tolerant than the single-neurons constituting the population. Nevertheless, tolerance can be learned – provided that it is trained for – at the cost of selectivity. We argue that this model is an interesting null-hypothesis to compare behavioral results with and conclude that it may explain several experimental findings.

Acute Administration of 3,4‐Methylenedioxymethamphetamine Induces Profound Hyperthermia, Blood–Brain Barrier Disruption, Brain Edema Formation, and Cell Injury

The psychostimulant 3,4-,ethylenedioxymethamphetamine (MDMA, "ecstasy") is known to induce hyperthermia and alterations in neurochemical metabolism in the CNS. However, the detailed cellular or molecular mechanisms behind MDMA-induced neurotoxicity are still not well known. Since MDMA induces profound hyperthermia that could lead to intense cellular stress and cause disruption of the blood-brain barrier (BBB), this investigation examined the effects of acute MDMA on BBB dysfunction, brain edema, and cell injury in rats and mice. When MDMA (40 mg/kg, i.p.) was administered to rats or mice, these animals exhibited profound behavioral disturbances (hyperactivity and hyperlocomotion) and hyperthermia (>40 to 41 degrees C) at 4 h. At this time, the leakage of Evans blue dye was evident, particularly in the cerebellum, hippocampus, cortex, thalamus, and hypothalamus. This effect was most pronounced in mice compared to rats. Marked increase in brain water along with Na(+), K(+), and Cl(-) content was also seen in the aforementioned brain regions. Presence of distorted neuronal and glial cells in brain regions associated with leakage of Evans blue is quite common in MDMA-treated animals. Increased albumin immunoreactivity, indicating breakdown of the BBB, and upregulation of glial fibrillary acidic protein (GFAP), suggesting activation of astrocytes, were seen in most brain regions showing edematous changes. Upregulation of heat-shock protein (HSP72) immunoreactivity in the nuclei and cell cytoplasm of the neurons located in the edematous brain regions are quite common. Taken together, these observations are the first to show that MDMA has the capacity to disrupt BBB permeability to proteins and to induce the formation of edema, probably by inducing hyperthermia and cellular stress, as evident with HSP overexpression leading to cell injury.

In Monarchs, Cry2 Is King of the Clock

Internal clocks govern the daily rhythms of the most basic functions of waking, eating, and sleeping. The molecular basis of such pacemakers is best understood in fruit flies, where the interactions of a small set of molecules drive the insects' behaviors just as they do our own. The precise inner workings of each species' clock differ, however, as do the range of functions that clocks serve in each. In a new study, Haisun Zhu, Steven Reppert, and colleagues reveal the details of the clockwork in the monarch butterfly and show that it has aspects of clocks from both the mouse and the fly, the only other clock types known in animals. They further show that in addition to controlling the insect's daily activities, the butterfly clock may also aid its navigation during cross-continent migration. In fruit flies, five proteins are central to the operation of the clock. Clock (Clk) and Cycle (Cyc) bind together to form a transcriptional complex, which drives production of Period (Per) and Timeless (Tim). Per and Tim then link up to repress the production of Clk and Cyc, thus creating a negative-feedback loop controlling the concentrations of Per and Tim—the essence of the clock mechanism. The fifth protein, Cryptochrome (Cry), is light sensitive, and when it absorbs blue light, it disrupts the Per–Tim complex, thereby resetting the periodic oscillations, which keeps the molecular clock and it output rhythms in tune with the ambient light-dark cycle. The mammalian clock uses Clk and a Cyc-like protein, but it has no Tim. Instead of a single cryptochrome, it has two, neither of which is light sensitive, but both of which are the major repressors of the mammalian clock feedback loop. Previous work in the monarch has shown that it expresses its own version of Per, Tim, Clk, and Cyc, along with two cryptochromes: a fly-like cryptochrome, Cry1, and a mammalian-like cryptochrome, Cry2. The authors began their investigation into the detailed workings of the clock by showing that, as in the fly, the concentrations of Per and Tim fluctuate diurnally in the brains of the monarch. In a monarch cell line, they showed that while Cry1 absorbed light and triggered Tim degradation, the critical role in repressing Clk-Cyc transcription fell to Cry2. Since the mammalian orthologs of this protein play the same role in the mouse, it appears that Cry2 is the central timekeeper in two of the three known clocks (comparative genetic studies indicate Cry2 was lost in the Drosophila line). Two cryptochrome proteins, which act as critical components in an ancestral circadian clock mechanism characterized in monarch butterflies, may also connect the clock to the sun compass for successful navigation Back in the brain, the authors showed that Cry2 was also found in a few dozen cells in brain regions previously linked to time-keeping in the butterfly, and this Cry2 underwent circadian oscillation in these cells, but not in many other cells that were not involved in time keeping. By taking samples periodically over many hours, they found that nuclear localization of Cry2 coincided with maximal transcriptional repression of the clockwork, in keeping with its central role of regulating the feedback cycle. This is a novel demonstration of nuclear translocation of a clock protein outside flies. Finally, the authors investigated Cry2's activity in the central complex, the brain structure that is believed to house the navigational compass of the monarch. Monarchs integrate information on the position of the sun and the direction of polarized light to find their way from all over North America to the Mexican highlands, where they spend the winter. Cry2, but not the other clock proteins, was detected in parts of the central complex where it undergoes strong circadian cycling. Some cells containing Cry2 linked up with the clock cells, while others projected toward the optic lobe and elsewhere in the brain. Along with highlighting the central importance of Cry2 in the inner workings of the monarch's clock, the results in this study suggest that part of the remarkable navigational ability of the butterfly relies on its ability to integrate temporal information from the clock with spatial information from its visual system. This allows the monarch to correct its course as light shifts across the sky over the course of the day. Other cues used for charting its path remain to be elucidated.

Structural plasticity associated with exposure to drugs of abuse

Persistent changes in behavior and psychological function that occur as a function of experience, such those associated with learning and memory, are thought to be due to the reorganization of synaptic connections (structural plasticity) in relevant brain circuits. Some of the most compelling examples of experience-dependent changes in behavior and psychological function, changes that can last a lifetime, are those that accrue with the development of addictions. However, until recently, there has been almost no research on whether potentially addictive drugs produce forms of structural plasticity similar to those associated with other forms of experience-dependent plasticity. In this paper we summarize evidence that, indeed, exposure to amphetamine, cocaine, nicotine or morphine produces persistent changes in the structure of dendrites and dendritic spines on cells in brain regions involved in incentive motivation and reward (such as the nucleus accumbens), and judgment and the inhibitory control of behavior (such as the prefrontal cortex). It is suggested that structural plasticity associated with exposure to drugs of abuse reflects a reorganization of patterns of synaptic connectivity in these neural systems, a reorganization that alters their operation, thus contributing to some of the persistent sequela associated with drug use—including addiction.

Bird brains and songs: neural mechanisms of birdsong perception and memory

Abstract The males of songbirds and parrots learn their songs from a tutor. Until recently it was thought that in songbirds, brain nuclei in the so-called 'song system' were involved in song learning, in addition to their role in song perception and production. Experiments involving measurement of the expression of immediate early genes (IEG) showed that exposure to song leads to activation of cells in brain regions outside the song system, notably the caudomedial neostriatum (NCM) and the caudomedial hyperstriatum ventrale (CMHV), suggesting that these regions are involved in auditory perception. In addition, neuronal activation in the NCM correlates with the number of song elements that a male has learned from its tutor, suggesting that NCM may be (part of) the neural substrate for stored tutor song. Songbird females do not usually sing, but nevertheless they can learn the characteristics of tutor song, and they can develop a perceptual preference for tutor song over novel song. When exposed to male song, female songbirds and parrots show increased IEG expression in NCM and CMHV that is related to song complexity. In addition, the IEG response in the NCM (and perhaps in the CMHV) of female songbirds may also be related to song learning.

Neurodegeneration in the Niemann–Pick C mouse: glial involvement

A mouse model of Niemann–Pick type C disease has been found that exhibits neuropathology similar to the human condition. There is an age-related neurodegeneration in several brain regions and a lack of myelin in the corpus callosum in these mice. The purpose of the present study was to examine the Niemann–Pick mouse and determine whether: (1) microglia and astrocytes exhibit ultrastructural pathology similar to that found in neurons; (2) nerve fiber number is reduced when the myelin sheath is absent; and (3) the lysosomal hydrolase, cathepsin-D, is involved in the neurodegenerative process. Using light and electron microscopic methods, and immunocytochemistry, Niemann–Pick and control animals were examined at several ages. Cathepsin-D content was semi-quantitatively measured in neurons and glial cells in brain regions known to exhibit neurodegeneration, as was the density of glial fibrillary acidic protein-labeled astrocytes. The Niemann–Pick mouse exhibited: (1) an age-related increase in inclusion bodies in microglia and astrocytes, similar to that observed within neurons; (2) an almost complete absence of myelin in the corpus callosum by 7–8 weeks of age, along with a 30% reduction in the number of corpus callosum axons; (3) a mild age-related increase in cathepsin-D content within nerve cells in many brain regions. However, the cathepsin-D elevation was greatest in microglial cells; (4) an age-related increase in the number of microglial cells containing intense cathepsin-D immunoreactivity in both the thalamus and cerebellum. Both of these brain regions have been shown previously to exhibit an age-related loss of neurons; and (5) an increase in the number of reactive astrocytes immunostained for glial fibrillary acidic protein, especially in the thalamus and cerebellum. These data indicate that glial cells are a major target for pathology in the Niemann–Pick mouse. The lack of myelin within the corpus callosum may be related to the loss of nerve fibers in this structure. The increase in cathepsin-D-laden microglial cells, in brain regions previously shown to undergo neurodegeneration, is consistent with a role for microglia in the phagocytosis of dead neurons and in actively contributing to the neurodegenerative process. The activation of astrocytes in regions that undergo neurodegeneration is also consistent with a role for these glial cells in the neurodegenerative process.

Androgen and estrogen receptors coexist within individual neurons in the brain of the Syrian hamster.

Many aspects of reproductive neuroendocrine function and sexual behavior are responsive to both androgens and estrogens, suggesting that receptors for these steroid hormones may reside within single cells in brain regions that control reproductive function. We determined the distribution of estrogen receptor-containing neurons in 40-microns coronal brain sections in gonadectomized, DHT-treated male Syrian hamsters using immunocytochemistry with the H222 antibody (10 micrograms/ml; Abbott Laboratories). Subsequently, we colocalized estrogen receptors with androgen receptors using the PG-21 antibody (0.5 microgram/ml; G.S. Prins). In males, the distribution of estrogen receptor-containing neurons was similar to that reported previously for the female hamster. Colocalization of androgen and estrogen receptor immunoreactivity was observed in brain regions that contain numerous androgen and estrogen receptor-positive neurons, including subdivisions of the medial preoptic area, bed nucleus of the stria terminals, ventromedial nucleus of the hypothalamus, and the amygdalohippocampal area. Single-labelled estrogen receptor-containing neurons were most numerous in the amygdalohippocampal area and the rostral medial preoptic nucleus; androgen receptor-immunoreactive cells were most abundant in the ventral premammillary nucleus and the lateral septum. These data suggest the potential of androgens and estrogens to influence neuronal function within individual steroid receptor-containing neurons of the hamster limbic system.