Alberto Antonio Rasia-Filho

Dendritic spines are postsynaptic specializations that mainly contact excitatory inputs and modulate a wide range of processes involving synaptic transmission and plasticity. Based on morphological features, they were classified into stubby, wide, thin, mushroom, ramified, and double spines. However, spines display other than these “classical” shapes, which are morphologically more convoluted and were initially called “atypical” spines. They have been much less studied and, then, worthy of investigation. Here, atypical (or, rather, multimorphic) spines, as well as complex dendritic protrusions, were examined using the Golgi method and after 2D and 3D image reconstructions in dendrites, cell bodies, and axon hillocks of several neuron types from both rats and humans. A variety of morphological features of complex dendritic protrusions and multimorphic spines were characterized in basket cells, Purkinje cells, brush neurons and granule cells of the cerebellum, in multipolar neurons of the inferior olivary nucleus, in multipolar neurons of the posterodorsal medial amygdaloid nucleus, in short‐shaft pyramidal neurons of the hippocampus, in layers V–VI pyramidal and polymorphic neurons of the prefrontal cortex, and layers II–VI neurons of the anterior cingulate, precuneus, temporal, and occipital cortex. We provide evidence for the usual occurrence of these multimorphic spines, characterized by their heterogeneity in shape and size, and discuss the likely functional implications for synaptic processing, intraspine microdomains, compartmentalization features, and plasticity. Given their presence in rodents and humans, we also discuss the possible implications of multimorphic spines for more complex synaptic transmission across evolved neural circuits, laying the groundwork for future research.

SUMMARY: Neuronal morphology governs how neurons connect, integrate, and process information, offering critical insights into the functional architecture of the brain. Characterizing the three-dimensional (3D) morphology of individual neurons is key not only for mapping circuit connectivity but also for understanding the cellular diversity that emerges during development. Neural organoids are valuable models of human brain development and disease, yet their morphological complexity remains poorly characterized despite advances in single-cell transcriptomics. Here, we use 3D confocal imaging and manual reconstruction of 735 neurons to analyze forebrain (dorsal and ventral) and thalamic (dorsal and ventral) organoids, as well as forebrain, thalamic, and corticothalamic assembloids. We find that organoids and assembloids exhibit distinct morphologies resembling fetal brain neurons, including immature pyramidal-like, double-bouquet, and bushy-like neurons. Interregional assembloids show greater neuronal morphological complexity than individual organoids, with more extensive dendritic branching, longer projections, and diverse soma shapes. Corticothalamic assembloids further display features of emerging connectivity. We observe dendritic spines with excitatory and inhibitory profiles and varicosities, indicative of maturing synaptic architecture. Together, our work makes an initial effort in describing the diversity of neuronal morphology in human neural organoids and assembloids. It further establishes structural phenotyping as a critical dimension for validating human neural models and underscores their value for modeling morphofunctional disorders.

This review presents a discussion on how to conceptualize or define human love, which areas of the central nervous system are involved with its organization, and what neuroanatomical and functional heterogeneity occurs when subjectively perceiveing and expressing this felling to other people or even expressing other manifestations of love.

The rat posterodorsal medial amygdala (MePD) is sexually dimorphic, has a high concentration of receptors for gonadal hormones and prolactin (PRL), and modulates reproduction. To unravel genetic and functional data for this relevant node of the social behavior network, we studied the expression of ERα, ERβ, GPER1, Kiss1, Kiss1R, PRGR, PRL, PRLR, EGR1, JAK2, STAT5A, and STAT5B in the MePD of males and females along the estrous cycle using the RT-qPCR technique. We also investigated whether PRL in the MePD would affect the sexual behavior display of proestrus females by microinjecting saline, the PRL receptor antagonist Del1-9-G129R-hPRL (1 µM and 10 µM), or PRL (1 nM) and Del1-9-G129R-hPRL (10 µM) 3h before the onset of the dark-cycle period. The estrogen-dependent lordosis behavior, indicative of sexual receptivity of proestrus females, was recorded and compared before (control) and after (test) microinjections in these groups. Sex differences were found in the right and left MePD gene expression. ERα and Kiss1R, as well as PRL, Short PRLR , and STAT5B expression, is higher in cycling females than males. Kiss1 expression is higher in males than females, and GPER1 is higher during diestrus than proestrus. Furthermore, Del1-9-G129R-hPRL in the MePD significantly reduced the full display and quotient of lordosis in proestrus females, an effect restored by the co-microinjection of PRL. In conjunction, the expression of studied genes showed specific sex and estrous cycle phase features while, in proestrus, PRL action in the MePD plays an essential role in the display of lordosis during the ovulatory period. Highlights: The MePD expression of Kiss1 is higher in males than females. ERα and Kiss1R expression is higher in cycling females than males. PRL, Short PRLR, and STAT5B expression is higher in cycling females than males. GPER1 expression is higher during diestrus than in proestrus. Del1-9-G129R-hPRL action in the MePD reduced lordosis quotient during proestrus.

The central amygdaloid nucleus (CeA) has an ancient phylogenetic development and functions relevant for animal survival. Local cells receive intrinsic amygdaloidal information that codes emotional stimuli of fear, integrate them, and send cortical and subcortical output projections that prompt rapid visceral and social behavior responses. We aimed to describe the morphology of the neurons that compose the human CeA (N = 8 adult men). Cells within CeA coronal borders were identified using the thionine staining and were further analyzed using the “single‐section” Golgi method followed by open‐source software procedures for two‐dimensional and three‐dimensional image reconstructions. Our results evidenced varied neuronal cell body features, number and thickness of primary shafts, dendritic branching patterns, and density and shape of dendritic spines. Based on these criteria, we propose the existence of 12 morphologically different spiny neurons in the human CeA and discuss the variability in the dendritic architecture within cellular types, including likely interneurons. Some dendritic shafts were long and straight, displayed few collaterals, and had planar radiation within the coronal neuropil volume. Most of the sampled neurons showed a few to moderate density of small stubby/wide spines. Long spines (thin and mushroom) were observed occasionally. These novel data address the synaptic processing and plasticity in the human CeA. Our morphological description can be combined with further transcriptomic, immunohistochemical, and electrophysiological/connectional approaches. It serves also to investigate how neurons are altered in neurological and psychiatric disorders with hindered emotional perception, in anxiety, following atrophy in schizophrenia, and along different stages of Alzheimer's disease.

Visualizing nerve cells has been fundamental for the systematic description of brain structure and function in humans and other species. Different approaches aimed to unravel the morphological features of neuron types and diversity. The inherent complexity of the human nervous tissue and the need for proper histological processing have made studying human dendrites and spines challenging in postmortem samples. In this study, we used Golgi data and open-source software for 3D image reconstruction of human neurons from the cortical amygdaloid nucleus to show different dendrites and pleomorphic spines at different angles. Procedures required minimal equipment and generated high-quality images for differently shaped cells. We used the "single-section" Golgi method adapted for the human brain to engender 3D reconstructed images of the neuronal cell body and the dendritic ramification by adopting a neuronal tracing procedure. In addition, we elaborated 3D reconstructions to visualize heterogeneous dendritic spines using a supervised machine learning-based algorithm for image segmentation. These tools provided an additional upgrade and enhanced visual display of information related to the spatial orientation of dendritic branches and for dendritic spines of varied sizes and shapes in these human subcortical neurons. This same approach can be adapted for other techniques, areas of the central or peripheral nervous system, and comparative analysis between species.