Major Feedforward Thalamic Input Into Layer 4C of Primary Visual Cortex in Primate

One of the underlying principles of how mammalian circuits are constructed is the relative influence of feedforward to recurrent synaptic drive. It has been dogma in sensory systems that the thalamic feedforward input is relatively weak and that there is a large amplification of the input signal by recurrent feedback. Here we show that in trichromatic primates there is a major feedforward input to layer 4C of primary visual cortex. Using a combination of 3D-electron-microscopy and 3D-confocal imaging of thalamic boutons we found that the average feedforward contribution was about 20% of the total excitatory input in the parvocellular (P) pathway, about 3 times the currently accepted values for primates. In the magnocellular (M) pathway it was around 15%, nearly twice the currently accepted values. New methods showed the total synaptic and cell densities were as much as 150% of currently accepted values. The new estimates of contributions of feedforward synaptic inputs into visual cortex call for a major revision of the design of the canonical cortical circuit.

Benzodiazepines and the potential trophic effect of antidepressants on dentate gyrus cells in mood disorders

Modest antidepressant response rates of mood disorders (MD) encourage benzodiazepine (BZD) co-medication with debatable benefit. Adult hippocampal neurogenesis may underlie antidepressant responses, but diazepam co-administration impairs murine neuron maturation and survival in response to fluoxetine. We counted neural progenitor cells (NPCs), mitotic cells, and mature granule neurons post-mortem in dentate gyrus (DG) from subjects with: untreated Diagnostic and Statistical Manual of Mental Disorders (DSM) IV MD (n = 17); antidepressant-treated MD (MD*ADT, n = 10); benzodiazepine-antidepressant-treated MD (MD*ADT*BZD, n = 7); no psychopathology or treatment (controls, n = 18). MD*ADT*BZD had fewer granule neurons vs. MD*ADT in anterior DG and vs. controls in mid DG, and did not differ from untreated-MD in any DG subregion. MD*ADT had more granule neurons than untreated-MD in anterior and mid DG and comparable granule neuron number to controls in all dentate subregions. Untreated-MD had fewer granule neurons than controls in anterior and mid DG, and did not differ from any other group in posterior DG. MD*ADT*BZD had fewer NPCs vs. MD*ADT in mid DG. MD*ADT had more NPCs vs. untreated-MD and controls in anterior and mid DG. MD*ADT*BZD and MD*ADT had more mitotic cells in anterior DG vs. controls and untreated-MD. There were no between-group differences in mid DG in mitotic cells or in posterior DG for any cell type. Our results in mid-dentate, and to some degree anterior dentate, gyrus are consistent with murine findings that benzodiazepines counteract antidepressant-induced increases in neurogenesis by interfering with progenitor proliferation. We also confirmed, in this expanded sample, our previous finding of granule neuron deficit in untreated MD.

Transcranial low-level laser therapy enhances learning, memory, and neuroprogenitor cells after traumatic brain injury in mice

The use of transcranial low-level laser (light) therapy (tLLLT) to treat stroke and traumatic brain injury (TBI) is attracting increasing attention. We previously showed that LLLT using an 810-nm laser 4 h after controlled cortical impact (CCI)-TBI in mice could significantly improve the neurological severity score, decrease lesion volume, and reduce Fluoro-Jade staining for degenerating neurons. We obtained some evidence for neurogenesis in the region of the lesion. We now tested the hypothesis that tLLLT can improve performance on the Morris water maze (MWM, learning, and memory) and increase neurogenesis in the hippocampus and subventricular zone (SVZ) after CCI-TBI in mice. One and (to a greater extent) three daily laser treatments commencing 4-h post-TBI improved neurological performance as measured by wire grip and motion test especially at 3 and 4 weeks post-TBI. Improvements in visible and hidden platform latency and probe tests in MWM were seen at 4 weeks. Caspase-3 expression was lower in the lesion region at 4 days post-TBI. Double-stained BrdU-NeuN (neuroprogenitor cells) was increased in the dentate gyrus and SVZ. Increases in double-cortin (DCX) and TUJ-1 were also seen. Our study results suggest that tLLLT may improve TBI both by reducing cell death in the lesion and by stimulating neurogenesis.

Clinical neuropathology practice guide 5-2013: markers of neuronal maturation

This review surveys immunocytochemical and histochemical markers of neuronal lineage for application to tissue sections of fetal and neonatal brain. They determine maturation of individual nerve cells as the tissue progresses to mature architecture. From a developmental perspective, neuronal markers are all about timing. These diverse cellular labels may be classified in two ways: 1) time of onset of expression (early; intermediate; late); 2) labeling of subcellular structures or metabolic functions (nucleoproteins; synaptic vesicle proteins; enolases; cytoskeletal elements; calcium-binding; nucleic acids; mitochondria). Apart from these positive markers of maturation, other negative markers are expressed in primitive neuroepithelial cells and early stages of neuroblast maturation, but no longer are demonstrated after initial stages of maturation. These examinations are relevant for studies of normal neuroembryology at the cellular level. In fetal and perinatal neuropathology they provide control criteria for application to malformations of the brain, inborn metabolic disorders and acquired fetal insults in which neuroblastic maturation may be altered. Disorders, in which cells differentiate abnormally, as in tuberous sclerosis and hemimegalencephaly, pose another yet aspect of mixed cellular lineage. The measurement in living patients, especially neonates, of serum and CSF levels of enolases, chromogranins and S-100 proteins as biomarkers of brain damage may potentially be correlated with their corresponding tissue markers at autopsy in infants who do not survive. The neuropathological markers here described can be performed in ordinary hospital laboratories, not just research facilities, and offer another dimension of diagnostic precision in interpreting abnormally developed fetal and postnatal brains.

Hippocampal granule neuron number and dentate gyrus volume in antidepressant-treated and untreated major depression

Smaller hippocampal volume is reported in major depressive disorder (MDD). We hypothesize that it may be related to fewer granule neurons (GN) in the dentate gyrus (DG), a defect possibly reversible with antidepressants. We studied age-, sex-, and postmortem interval-matched groups: no major psychopathology (controls); unmedicated-MDD; and MDD treated with serotonin reuptake inhibitors (MDD*SSRI) or tricyclics (MDD*TCA). Frozen right hippocampi were fixed, sectioned (50 μm), immunostained with neuronal nuclear marker (NeuN), and counterstained with hematoxylin. GN and glial number, and DG and granule cell layer (GCL) volumes were stereologically estimated. Fewer GNs in the anterior DG were present in unmedicated-MDDs compared with controls (p=0.013). Younger age of MDD onset correlated with fewer GNs (p=0.021). Unmedicated-MDDs had fewer mid-DG GNs than MDD*SSRIs (p=0.028) and controls (p=0.032). Anterior GCL glial number did not differ between groups. Anterior/mid GCL volume was smaller in unmedicated-MDDs vs controls (p=0.008) and larger in MDD*SSRIs vs unmedicated-MDDs (p<0.001), MDD*TCAs (p<0.001), and controls (p<0.001). Anterior GCL volume and GN number (r=0.594, p=0.001), and mid DG volume and GN number (r=0.398, p=0.044) were correlated. Anterior DG capillary density correlated with GN number (p=0.027), and with GCL (p=0.024) and DG (r=0.400, p=0.047) volumes. Posterior DG volume and GN number did not differ between groups. Fewer GNs in unmedicated-MDD without fewer neuronal progenitor cells, as previously reported, suggests a cell maturation or survival defect, perhaps related to MDD duration. This may contribute to a smaller hippocampus and is potentially reversed by SSRIs. Postmortem studies are correlative and animal studies are needed to test implied causal relationships.

Age-related changes in rostral basal forebrain cholinergic and GABAergic projection neurons: relationship with spatial impairment

Both cholinergic and GABAergic projections from the rostral basal forebrain contribute to hippocampal function and mnemonic abilities. While dysfunction of cholinergic neurons has been heavily implicated in age-related memory decline, significantly less is known regarding how age-related changes in codistributed GABAergic projection neurons contribute to a decline in hippocampal-dependent spatial learning. In the current study, confocal stereology was used to quantify cholinergic (choline acetyltransferase [ChAT] immunopositive) neurons, GABAergic projection (glutamic decarboxylase 67 [GAD67] immunopositive) neurons, and total (neuronal nuclei [NeuN] immunopositive) neurons in the rostral basal forebrain of young and aged rats that were first characterized on a spatial learning task. ChAT immunopositive neurons were significantly but modestly reduced in aged rats. Although ChAT immunopositive neuron number was strongly correlated with spatial learning abilities among young rats, the reduction of ChAT immunopositive neurons was not associated with impaired spatial learning in aged rats. In contrast, the number of GAD67 immunopositive neurons was robustly and selectively elevated in aged rats that exhibited impaired spatial learning. Interestingly, the total number of rostral basal forebrain neurons was comparable in young and aged rats, regardless of their cognitive status. These data demonstrate differential effects of age on phenotypically distinct rostral basal forebrain projection neurons, and implicate dysregulated cholinergic and GABAergic septohippocampal circuitry in age-related mnemonic decline.

PPARγ activation prevents impairments in spatial memory and neurogenesis following transient illness

The detrimental effects of illness on cognition are familiar to virtually everyone. Some effects resolve quickly while others may linger after the illness resolves. We found that a transient immune response stimulated by lipopolysaccharide (LPS) compromised hippocampal neurogenesis and impaired hippocampus-dependent spatial memory. The immune event caused an ∼50% reduction in the number of neurons generated during the illness and the onset of the memory impairment was delayed and coincided with the time when neurons generated during the illness would have become functional within the hippocampus. Broad spectrum non-steroidal anti-inflammatory drugs attenuated these effects but selective Cox-2 inhibition was ineffective while PPARγ activation was surprisingly effective at protecting both neurogenesis and memory from the effects of LPS-produced transient illness. These data may highlight novel mechanisms behind chronic inflammatory and neuroinflammatory episodes that are known to compromise hippocampus-dependent forms of learning and memory.

Social isolation impairs adult neurogenesis in the limbic system and alters behaviors in female prairie voles

Disruptions in the social environment, such as social isolation, are distressing and can induce various behavioral and neural changes in the distressed animal. We conducted a series of experiments to test the hypothesis that long-term social isolation affects brain plasticity and alters behavior in the highly social prairie vole (Microtus ochrogaster). In Experiment 1, adult female prairie voles were injected with a cell division marker, 5-bromo-2'-deoxyuridine (BrdU), and then same-sex pair-housed (control) or single-housed (isolation) for 6 weeks. Social isolation reduced cell proliferation, survival, and neuronal differentiation and altered cell death in the dentate gyrus of the hippocampus and the amygdala. In addition, social isolation reduced cell proliferation in the medial preoptic area and cell survival in the ventromedial hypothalamus. These data suggest that long-term social isolation affects distinct stages of adult neurogenesis in specific limbic brain regions. In Experiment 2, isolated females displayed higher levels of anxiety-like behaviors in both the open field and elevated plus maze tests and higher levels of depression-like behavior in the forced swim test than controls. Further, isolated females showed a higher level of affiliative behavior than controls, but the two groups did not differ in social recognition memory. Together, our data suggest that social isolation not only impairs cell proliferation, survival, and neuronal differentiation in limbic brain areas, but also alters anxiety-like, depression-like, and affiliative behaviors in adult female prairie voles. These data warrant further investigation of a possible link between altered neurogenesis within the limbic system and behavioral changes.

Increased interstitial white matter neuron density in the dorsolateral prefrontal cortex of people with schizophrenia

BACKGROUND

Interstitial white matter neurons (IWMNs) may reflect immature neurons that migrate tangentially to the neocortex from the ganglionic eminence to form cortical interneurons. Alterations of interneuron markers have been detected in gray matter of dorsolateral prefrontal cortex in schizophrenia, and IWMNs are also reported to be altered in schizophrenia. In this study, we considered whether a potential link exists between these two pathological findings.

METHODS

From a cohort of 29 schizophrenia subjects and 37 control subjects, IWMN densities were determined in the dorsolateral prefrontal cortex by counting neuronal nuclear antigen (NeuN) and somatostatin (SST)-positive cells. Double-label immunofluorescence was carried out to determine the overlap between SST+/NeuN+ and SST+/neuropeptide Y + neurons.

RESULTS

We found that density of NeuN + IWMNs in superficial white matter is significantly increased in schizophrenia subjects compared with control subjects. There was a significant negative correlation between SST mRNA expression in gray matter and NeuN + IWMN density. In schizophrenic patients with increased NeuN IWMN density, the density of SST-expressing neurons in white matter was also higher compared with control subjects. A subpopulation of SST immunopositive cells also show coexpression of neuropeptide Y.

CONCLUSIONS

Our study confirmed previous results indicating that the density of NeuN + IWMNs is increased in superficial white matter in schizophrenia. We provide the first evidence that increased IWMN density correlates with a gray matter interneuron deficit, suggesting that migration of interneurons from white matter to the cortex may be deficient in some patients with schizophrenia, consistent with an interneuron deficit in schizophrenia.

Subventricular zone-derived, newly generated neurons populate several olfactory and limbic forebrain regions

Neurogenesis persists in several regions of the adult mammalian brain. Although the hippocampus and olfactory bulb are most commonly studied in the context of adult neurogenesis, there is an increasing body of evidence in support of neurogenesis occurring outside of these two regions. The current study expands on previous data by showing newborn neurons with a mature phenotype are located in several olfactory and limbic structures outside of the hippocampus and olfactory bulb, where we previously described doublecortin/bromodeoxyuridine immature neurons. Notably, newborn neurons with a mature neuronal phenotype are found in the olfactory tubercles, anterior olfactory nuclei, tenia tecta, islands of Calleja, amygdala, and lateral entorhinal cortex. The appearance of newborn neurons with a mature phenotype in these regions suggests that these structures are destinations, and that newborn neurons are not simply passing through these structures. In light of the increasing body of evidence for neurogenesis in these and other olfactory, limbic, and striatal structures, we hypothesize that brain regions displaying adult neurogenesis are functionally linked.

Increased neurogenesis in the dentate gyrus after transient global ischemia in gerbils

Neurogenesis in the dentate gyrus of adult rodents is regulated by NMDA receptors, adrenal steroids, environmental stimuli, and seizures. To determine whether ischemia affects neurogenesis, newly divided cells in the dentate gyrus were examined after transient global ischemia in adult gerbils. 5-Bromo-2'-deoxyuridine-5'-monophosphate (BrdU) immunohistochemistry demonstrated a 12-fold increase in cell birth in the dentate subgranular zone 1-2 weeks after 10 min bilateral common carotid artery occlusions. Two minutes of ischemia did not significantly increase BrdU incorporation. Confocal microscopy demonstrated that BrdU immunoreactive cells in the granule cell layer colocalized with neuron-specific markers for neuronal nuclear antigen, microtubule-associated protein-2, and calbindin D28k, indicating that the newly divided cells migrated from the subgranular zone into the granule cell layer and matured into neurons. Newborn cells with a neuronal phenotype were first seen 26 d after ischemia, survived for at least 7 months, were located only in the granule cell layer, and comprised approximately 60% of BrdU-labeled cells in the granule cell layer 6 weeks after ischemia. The increased neurogenesis was not attributable to entorhinal cortical lesions, because no cell loss was detected in this region. Ischemic preconditioning for 2 min, which protects CA1 neurons against subsequent ischemic damage, did not prevent increased neurogenesis in the granule cell layer after a subsequent severe ischemic challenge. Thus, ischemia-induced dentate neurogenesis is not attributable to CA1 neuronal loss. Enhanced neurogenesis in the dentate gyrus may be a compensatory adaptive response to ischemia-associated injury and could promote functional recovery after ischemic hippocampal injury.