Konopaske GT, Lange N, Coyle JT, Benes FM. Prefrontal cortical dendritic spine pathology in schizophrenia and bipolar disorder. JAMA Psychiatry 2014;71(12):1323-1331. doi: 10.1001/jamapsychiatry.2014.1582.

 

Background: Previous studies have shown reduced dendritic spine density in the dorsolateral prefrontal cortex (DLPFC) of individuals with schizophrenia, but it was unclear whether this finding is generalizable or also present in bipolar disorder. Both disorders share overlapping features, including psychosis, cognitive deficits and similar neuroanatomical and genetic abnormalities, suggesting potential common neurobiological mechanisms.

 

Hypothesis: This study hypothesized that dendritic spine loss is present in the DLPFC of individuals with schizophrenia and possibly to an intermediate extent in those with bipolar disorder, reflecting shared but potentially differing pathophysiological processes.

 

Methods: The authors analyzed post mortem DLPFC tissue (Brodmann area 46) from individuals with schizophrenia (n=14), bipolar disorder (n=9) and controls (n=19). Golgi-stained pyramidal neurons in the deep half of cortical layer III were reconstructed using Neurolucida. Dendritic spine density, number of spines per dendrite and dendrite length were quantified, and potential confounding clinical factors were statistically controlled.

 

Results: Spine density was significantly reduced by 10.5% in bipolar disorder (p=0.02) and decreased by 6.5% in schizophrenia (p=0.06). The number of spines per dendrite was reduced in both schizophrenia (21.6%, p=0.003) and bipolar disorder (25.8%, p=0.005) compared with controls. Dendrite length was shorter in both schizophrenia (18.3%, p=0.005) and bipolar disorder (18.6%, p=0.005). Other dendritic parameters and somal area did not differ among groups.

 

Conclusions: This study demonstrated significant dendritic spine loss and reduced dendrite length in the DLPFC of individuals with both schizophrenia and bipolar disorder, suggesting that these conditions share underlying synaptic pathophysiological features.

Avior Y, Ron S, Kroitorou D, Albeldas C, Lerner V, Corneo B, Nitzan E, Laifenfeld D, Cohen Solal T. Depression patient-derived cortical neurons reveal potential biomarkers for antidepressant response. Transl Psychiatry 2021;11(1):201. doi: 10.1038/s41398-021-01319-5.

 

Background: Major depressive disorder (MDD) affects hundreds of millions globally, yet only about one-third of patients achieve remission after first-line antidepressant treatment. The lack of predictive biomarkers forces clinicians to rely on trial-and-error prescribing. Advances in patient-derived induced pluripotent stem cell (iPSC) technology offer a means to model neuronal characteristics linked to drug response in vitro, potentially enabling individualized antidepressant selection.

 

Hypothesis: This study hypothesized that neurons derived from depression patients’ lymphoblastoid cell lines (LCLs) would display cellular and molecular biomarkers predictive of clinical response to the antidepressant bupropion.

 

Methods: The authors reprogrammed LCLs from ten MDD patients in the STAR*D cohort into iPSCs, differentiated them into cortical neurons, and treated them with bupropion or vehicle. Synaptic morphology and dendritic spine characteristics were quantified using confocal microscopy, and dendritic and spine structures were analyzed with Neurolucida. Gene expression changes were examined through RNA sequencing.

 

Results: Neurons from bupropion responders exhibited significantly more synapsin puncta and colocalized pre- and postsynaptic markers than nonresponders, both before and after treatment. Responders’ neurons showed longer dendritic spines and distinct shifts in spine-type distributions following drug exposure. RNA sequencing revealed nine genes – such as MT1E, NPPB, NGF and ITGA2 – upregulated exclusively in responder-derived neurons after treatment.

 

Conclusions: Patient-derived cortical neurons recapitulated clinical antidepressant responses, identifying synaptic and transcriptional biomarkers that may predict bupropion efficacy. These findings support the feasibility of using in vitro neuronal assays for personalized antidepressant selection.

Földy C, Malenka RC, Südhof TC. Autism-associated neuroligin-3 mutations commonly disrupt tonic endocannabinoid signaling. Neuron 2013;78(3):498-509. doi: 10.1016/j.neuron.2013.02.036.

 

Background: Neuroligins are postsynaptic adhesion molecules that organize synaptic structure and function by interacting with presynaptic neurexins. Mutations in the neuroligin-3 (NL3) gene, including the R451C substitution and NL3 deletion, have been linked to autism spectrum disorders. Previous studies found robust synaptic alterations in R451C knockin mice but minimal effects in NL3 knockouts, raising uncertainty about a shared mechanism underlying autism-associated NL3 mutations.

 

Hypothesis: This study hypothesized that both NL3 R451C and NL3 knockout mutations produce a common synaptic defect that could reveal a shared molecular mechanism relevant to autism pathogenesis.

 

Methods: The authors performed paired whole-cell recordings between identified hippocampal interneurons and pyramidal neurons in mouse brain slices to assess GABAergic synaptic transmission. They compared synapses formed by parvalbumin (PV) and cholecystokinin (CCK) basket cells in wild-type, NL3 R451C knockin, and NL3 knockout mice. Morphological reconstructions of biocytin-filled neurons were performed using Neurolucida to assess axonal and dendritic organization.

 

Results: The R451C mutation markedly reduced synaptic strength at PV basket cell synapses but enhanced transmission at CCK basket cell synapses. The NL3 knockout produced no change at PV synapses but mimicked the R451C enhancement at CCK synapses. Both mutations abolished tonic, but not phasic, endocannabinoid signaling that normally suppresses GABA release from CCK basket cells. Modeling and simulation confirmed altered presynaptic release probabilities without structural changes.

 

Conclusions: The study concludes that NL3 is essential for tonic endocannabinoid signaling but not for phasic signaling. Both NL3 R451C and knockout mutations disrupt this mechanism, suggesting that impaired tonic endocannabinoid modulation of inhibition may contribute to autism pathophysiology.

Lázaro J, Hertel M, Sherwood CC, Muturi M, Dechmann DKN. Profound seasonal changes in brain size and architecture in the common shrew. Brain Struct Funct 2018;223(6):2823-2840. doi: 10.1007/s00429-018-1666-5.

 

Background: The common shrew (Sorex araneus) exhibits one of the most extreme reversible reductions in brain size among mammals, shrinking its brain mass by up to 26% from summer to winter and regrowing it in spring. This phenomenon, known as Dehnel’s phenomenon, has been linked to adaptations for energy conservation during periods of resource scarcity. However, the structural and cellular mechanisms underlying these seasonal brain size fluctuations remained unclear before this study.

 

Hypothesis: This study hypothesized that the seasonal changes in overall brain size of the common shrew are accompanied by differential volumetric and cellular alterations across brain regions, driven by adaptive functional and energetic demands rather than changes in cell number.

 

Methods: The authors trapped shrews across three seasonal age groups in southern Germany, processed their brains histologically and reconstructed the volumes of multiple brain regions using Neurolucida and quantified them with Neurolucida Explorer. Golgi-stained neurons were traced to assess soma and dendritic morphology in the anterior cingulate and somatosensory cortices and the caudoputamen. Statistical analyses compared volumetric and neuronal parameters across seasons and sexes.

 

Results: Total hemisphere volume decreased by 16.1% from summer to winter and regrew by 9.8% in spring. The hypothalamus and thalamus showed the largest reversible changes, while the neocortex and striatum shrank without regrowth. The hippocampus and olfactory bulb exhibited partial recovery, and several regions showed sex-specific differences. Neuronal analyses revealed reduced soma size and dendritic volume, particularly in the caudoputamen and anterior cingulate cortex, consistent with neuronal retraction.

 

Conclusions: The study concluded that profound and region-specific seasonal brain plasticity in shrews is linked to structural remodeling of neurons rather than changes in cell number. These reversible changes likely reflect adaptive responses to seasonal energy constraints and shifting ecological demands.

Kusnoor SV, Parris J, Muly EC, Morgan JI, Deutch AY. Extracerebellar role for Cerebellin1: modulation of dendritic spine density and synapses in striatal medium spiny neurons. J Comp Neurol 2010;518(13):2525-2537. doi: 10.1002/cne.22350.

 

Background: Cerebellin1 (Cbln1) is a secreted glycoprotein originally identified in the cerebellum, where it regulates granule cell–Purkinje cell synapses. Although widely distributed in the brain, its extracerebellar functions remain unclear. The parafascicular (PF) nucleus of the thalamus, a major source of glutamatergic input to striatal medium spiny neurons (MSNs), expresses high levels of Cbln1, suggesting that it may modulate thalamostriatal connectivity.

 

Hypothesis: This study hypothesized that Cbln1 expressed in PF neurons influences the synaptic organization and dendritic structure of striatal MSNs.

 

Methods: The authors used immunohistochemistry, tract tracing, electron microscopy and Golgi impregnation in wildtype and cbln1 knockout mice to determine Cbln1 localization and its effects on MSN morphology. Golgi-stained MSNs were reconstructed using Neurolucida to measure dendritic length and spine density.

 

Results: Virtually all PF neurons expressed Cbln1-immunoreactivity, whereas central medial nuclei rarely did. Cbln1-positive PF axons formed axodendritic synapses with MSNs. In cbln1-null mice, MSN dendritic spine density increased by approximately 22% compared with wildtype, while total dendritic length, spine shape and spine length distributions were unchanged. Ultrastructural analysis confirmed an increased density of axospinous asymmetric synapses without alteration in postsynaptic density length or perforation frequency.

 

Conclusions: The findings demonstrate an extracerebellar role for Cbln1 in shaping striatal synaptic architecture. Loss of Cbln1 increases MSN spine and synapse density, indicating that Cbln1 normally constrains excitatory connectivity within the striatum.

 

 

Wei L, Simen A, Mane S, Kaffman A. Early life stress inhibits expression of a novel innate immune pathway in the developing hippocampus. Neuropsychopharmacology 2012;37(2):567-580. doi: 10.1038/npp.2011.239.

 

Background: Early life stress has been shown to cause enduring changes in emotional and cognitive behavior. The authors examined how brief daily separation (BDS) of mouse pups from their dams affects hippocampal development. Using a genome-wide screen, they identified lipopolysaccharide-binding protein (LBP), traditionally known for immune function, as a gene markedly affected by BDS during a critical developmental period.

 

Hypothesis: This study hypothesized that early life stress inhibits hippocampal LBP expression during development, thereby disrupting synaptic maturation and leading to anxiety-like and cognitive deficits in adulthood.

 

Methods: The authors subjected BALB/cByj mouse pups to BDS from postnatal day (PND) 1–21 and conducted behavioral, molecular and anatomical analyses. They also tested LBP knockout (k.o.) mice. Dendritic morphology in hippocampal CA1 neurons was quantified using Golgi staining analyzed with Neurolucida, and LBP expression was examined by quantitative PCR, in situ hybridization and immunohistochemistry.

 

Results: BDS impaired adult performance in hippocampal-dependent learning and increased anxiety-like behavior. BDS and acute maternal separation reduced LBP mRNA and protein in the hippocampus but not plasma. LBP colocalized with PSD95 and contacted microglia processes. LBP k.o. mice displayed increased dendritic spine density without changes in dendritic length, abnormal spine morphology, impaired object recognition and elevated anxiety-like behaviors resembling BDS effects.

 

Conclusions: The study demonstrates that LBP is required for normal hippocampal synaptic development. Early life stress reduces hippocampal LBP expression, potentially impairing microglia-mediated synaptic pruning and leading to persistent behavioral abnormalities in adulthood.

Papp T, Ferenczi Z, Szilagyi B, Petro M, Varga A, Kókai E, Berenyi E, Olah G, Halmos G, Szucs P, Meszar Z. Ultrasound used for diagnostic imaging facilitates dendritic branching of developing neurons in the mouse cortex. Front Neurosci 2022;16:803356. doi: 10.3389/fnins.2022.803356.

 

Background: Ultrasound is widely used for fetal imaging, and although considered safe, its potential subtle effects on brain development remain unclear. Neuronal differentiation and dendritic arborization are influenced by both intrinsic and extrinsic mechanical factors, suggesting that exposure to diagnostic ultrasound could modulate neuronal morphology. This study examined whether short-term, high-frequency ultrasound (HFU) exposure affects developing cortical neurons in mice.

 

Hypothesis: This study hypothesized that a single brief exposure to diagnostic-level HFU alters neuronal morphology in the developing mouse cortex by promoting dendritic branching through mechanosensitive receptor-mediated pathways.

 

Methods: The authors used in utero electroporation at embryonic day 14.5 to label layer V pyramidal neurons in the mouse retrosplenial cortex with fluorescent proteins. Embryos were then exposed at E18.5 to a 10-minute, 3 MHz HFU stimulus using clinical imaging parameters. Neurons were reconstructed in three dimensions using Neurolucida from confocal image stacks, and morphometric analyses were performed. Immunohistochemistry assessed c-Fos, BDNF and TRPC4 expression, and quantitative RT-PCR examined BDNF mRNA levels.

 

Results: Ultrasound-treated neurons displayed a significant increase in the number of basal dendrites compared to controls, while dendrite length, branching complexity and soma size were unchanged. HFU exposure transiently elevated c-Fos immunoreactivity without altering BDNF expression, although repeated HFU stimulation increased both c-Fos and BDNF levels. GFP-positive pyramidal neurons expressed TRPC4, suggesting mechanosensitive involvement.

 

Conclusions: A single diagnostic-level ultrasound exposure modestly enhanced dendritic branching of developing cortical neurons, potentially via TRPC4-mediated signaling. Repeated exposure amplified molecular markers of neuronal activation, implying that even clinically relevant ultrasound intensities can subtly modulate neuronal maturation.

Glaser JR, Glaser EM. Neuron imaging with Neurolucida – a PC-based system for image combining microscopy. Comput Med Imaging Graph 1990;14(5):307-317. doi: 10.1016/0895-6111(90)90105-k.

 

Background: Three-dimensional (3D) morphometry and imaging have become essential tools for studying neuronal structures, enabling quantitative analyses of morphology in relation to development, pathology and physiology. Previous systems demonstrated the potential of combining computer graphics with microscopy, but these required costly computers and lacked flexibility for widespread use.

 

Hypothesis: This study hypothesized that a personal computer–based system can perform accurate and efficient 3D neuronal mapping and morphometric analysis by integrating image combination, microscope control and interactive computer graphics within a single platform.

 

Methods: The authors developed and tested Neurolucida, a PC-based software system designed for 3D neuron tracing and mapping through either optical or video microscopy. The system integrated computer-controlled microscope stage movement in XYZ dimensions, and provided modules for lens calibration, tracing, mapping, morphometric measurements and dynamic 3-D rotation and reconstruction of data. Neurolucida was used to trace and reconstruct neurons and serial electron microscopic sections with 0.5 µm precision, generating quantitative and visual morphometric datasets.

 

Results: The system successfully combined image overlay with real-time data acquisition, allowing accurate tracing, mapping and reconstruction of neuronal structures. Neurolucida achieved precise 3D positioning, provided dynamic rotation displays, enabled morphometric analyses and produced high-quality visualizations of traced neurons and serial sections.

 

Conclusions: The study concluded that Neurolucida provides an accurate, versatile and efficient tool for 3D neuronal imaging and morphometry, making advanced computer microscopy accessible on standard personal computers.

Van der Loos H, Glaser EM. Autapses in neocortex cerebri: synapses between a pyramidal cell’s axon and its own dendrites. Brain Res 1972;48:355-360. doi: 10.1016/0006-8993(72)90189-8.

 

Background: This study describes a previously unrecognized synaptic phenomenon in the neocortex, in which a neuron forms a synapse with its own dendrite. The authors introduced the term “autapse” to denote such self-synaptic contacts. This work arose from a long-term analysis of cortical circuitry using Golgi preparations of rabbit occipital cortex, during which these surprising synaptic arrangements were observed between pyramidal cells’ axon collaterals and their own basal dendrites.

 

Hypothesis: This study hypothesized that autapses represent a biologically meaningful feedback mechanism, allowing neurons to regulate their own dendritic input through inhibitory self-synapses, thereby gating part of their excitatory input and modifying the neuron’s impulse generation.

 

Methods: The authors examined Golgi-impregnated pyramidal cells from rabbit occipital cortex using a computer-assisted neuron reconstruction method they had developed previously – a semi-automatic “computer microscope” capable of tracking neuronal processes in three dimensions with micrometer precision. Twelve neurons were fully reconstructed to map their synaptic connections.

 

Results: Six of the twelve analyzed neurons possessed autapses, totaling fourteen such contacts. These occurred mainly on second- to fourth-order basal dendrites, at mean axonal distances of 169 μm from the soma, forming loops averaging 272 μm in length. Autapses appeared as either punctiform or climbing fiber arrangements, involving boutons terminaux or de passage.

 

Conclusions: The authors concluded that autapses are genuine structural features of neocortical pyramidal neurons and may serve as self-regulatory inhibitory circuits. They proposed that autapses could function as local gating mechanisms and recommended ultrastructural verification by electron microscopy to elucidate their morphology and prevalence across species.

Glaser EM, Van der Loos H. A semi-automatic computer-microscope for the analysis of neuronal morphology. IEEE Trans Biomed Eng 1965;12:22-31.

 

Background: Before this work, quantitative microscopic analysis of individual neurons was virtually absent from neuroscience because it was technically almost unfeasible. Manual tracing and measurement techniques were prohibitively slow and imprecise, making it impossible to gather meaningful numerical data on neuronal morphology within a reasonable timeframe.

 

Hypothesis: This study hypothesized that a semi-automatic, computer-assisted microscope makes quantitative three-dimensional analysis of single neurons technically feasible by combining precise optical imaging with electronic computation.

 

Methods: The authors developed and used a computerized light microscopy system that integrated linear-motion transducers with the microscope stage to record X, Y and Z coordinates. The system employed analog computation to determine distances according to the Pythagorean theorem, while results were printed digitally and simultaneously plotted in two dimensions. Using Golgi-stained rabbit cortical neurons and a calibrated stage micrometer, the authors assessed the instrument’s measurement accuracy, repeatability and operational speed.

 

Results: The new system reduced the time required for the complete analysis of one neuron from approximately 24 hours to approximately 45 minutes. Measurement errors were around ±1 µm or 3 percent, with empirical accuracy tests showing deviations of approximately 9–12 percent across repeated micrometer-based measurements. The apparatus performed stably and maintained coordinate accuracy throughout extended use.

 

Conclusions: This study marked a paradigm shift in basic neuroscience by transforming neuronal morphology from a qualitative to a quantitative discipline. The semi-automatic computer-microscope made precise, reproducible measurement of individual neurons feasible for the first time, laying the foundation for modern computational neuroanatomy.