RESUMO
The highly complex structure of the brain requires an approach that can unravel its connectivity. Using volume electron microscopy and a dedicated software we can trace and measure all nerve fibers present within different samples of brain tissue. With this software tool, individual dendrites and axons are traced, obtaining a simplified "skeleton" of each fiber, which is linked to its corresponding synaptic contacts. The result is an intricate meshwork of axons and dendrites interconnected by a cloud of synaptic junctions. To test this methodology, we apply it to the stratum radiatum of the hippocampus and layers 1 and 3 of the somatosensory cortex of the mouse. We find that nerve fibers are densely packed in the neuropil, reaching up to 9 kilometers per cubic mm. We obtain the number of synapses, the number and lengths of dendrites and axons, the linear densities of synapses established by dendrites and axons, and their location on dendritic spines and shafts. The quantitative data obtained through this method enable us to identify subtle traits and differences in the synaptic organization of the samples, which might have been overlooked in a qualitative analysis.
Assuntos
Microscopia Eletrônica , Fibras Nervosas , Sinapses , Animais , Camundongos , Microscopia Eletrônica/métodos , Fibras Nervosas/ultraestrutura , Sinapses/ultraestrutura , Axônios/ultraestrutura , Dendritos/ultraestrutura , Encéfalo/ultraestrutura , Córtex Somatossensorial/ultraestrutura , Camundongos Endogâmicos C57BL , Masculino , Software , Hipocampo/ultraestrutura , Hipocampo/citologia , Microscopia Eletrônica de VolumeRESUMO
Nasal chemosensation is considered the evolutionarily oldest mammalian sense and, together with somatosensation, is crucial for neonatal well-being before auditory and visual pathways start engaging the brain. Using anatomical and functional approaches in mice, we reveal that odor-driven activity propagates to a large part of the cortex during the first postnatal week and enhances whisker-evoked activation of primary whisker somatosensory cortex (wS1). This effect disappears in adult animals, in line with the loss of excitatory connectivity from olfactory cortex to wS1. By performing neonatal odor deprivation, followed by electrophysiological and behavioral work in adult animals, we identify a key transient regulation of nasal chemosensory information necessary for the development of wS1 sensory-driven dynamics and somatosensation. Our work uncovers a cross-modal critical window for nasal chemosensation-dependent somatosensory functional maturation.
Assuntos
Nariz , Córtex Olfatório , Córtex Somatossensorial , Animais , Camundongos , Animais Recém-Nascidos , Camundongos Endogâmicos C57BL , Nariz/fisiologia , Nariz/anatomia & histologia , Odorantes , Córtex Olfatório/crescimento & desenvolvimento , Córtex Olfatório/fisiologia , Córtex Olfatório/ultraestrutura , Privação Sensorial/fisiologia , Olfato/fisiologia , Córtex Somatossensorial/crescimento & desenvolvimento , Córtex Somatossensorial/fisiologia , Córtex Somatossensorial/ultraestrutura , Vibrissas/fisiologiaRESUMO
En el presente trabajo se describen algunos aspectos morfológicos de la evolución de la corteza cerebral, determinada por la expresión de la proteína asociada a microtúbulos 2 (MAP-2) en diferentes etapas del desarrollo postnatal (3,5,7 y 10 días). Se describe la organización de los procesos dendríticos y se discuten los resultados a la luz de las implicaciones anatomofuncionales