SBNeC 2010
Resumo:C.025


Prêmio
C.025Individual callosal neurons link precisely matching modules across the barrel fields in the rat somatosensory (S1) cortex.
Autores:Carlomagno Pacheco Bahia (UFPA - Instituto de Ciencias da SaudeUFRJ - Instituto de Ciencias Biomedicas - PNBC - ICB) ; Antonio Pereira Jr (UFPA - Instituto de Ciencias Biologicas) ; Jean Christophe Houzel (UFRJ - Instituto de Ciencias Biomedicas - PNBC - ICB)

Resumo

Rats scan their surroundings through active, rhythmic and bilateral movements of the whiskers. Although the ascending trigemino-cortical pathway is fully crossed, stimulation of a single whisker can exert both excitatory and inhibitory, timely precise influences, not only onto the contralateral S1 cortex, but also onto the ipsilateral hemisphere, via commissural networks. Callosal connections were shown to be particularly dense between interbarrel septa and extragranular layers, but their degree of precision at the single neuron level is unknown. To assess this issue, we applied targeted injections of sensitive neuronal tracers to reconstruct and analyze the morphology of individual callosal cell bodies and axonal arbors in the rat barrel field. Under ketamine/xylazine anesthesia, extracellular recordings of neuronal responses to mechanical whisker stimulations were used to target specific barrel or septal sites, where biotinylated dextran amines (10%, 3 or 10kDa) were injected iontophoretically. After 2 weeks survival time, serial 150μm-thick sections were incubated in ABC complex and processed for nickel-intensified DAB reaction. Labeled bodies and processes were 3D-reconstructed using Neurolucida System (MBF Bioscience). Subsequently, sections were unmounted and counterstained for Nissl susbtance in order to define the boundaries of cytoarchitectonic modules, whose contours were then added to the neuronal reconstructions. Callosal neurons (4160 retrogradely labeled cells) were identified in septal columns (N=276±14 cells), as well as within barrels (N=138±12; P≤0,0002) and throughout all layers (supragranular: 850±18 cells, granular: 411±43, infragranular: 110±19; P≤0,001). Thirty callosal cells (10 from each laminar compartment) were reconstructed. Dendrites of supragranular cells were significantly longer, and covered a wider cortical area than in other layers (P≤0,001). In addition, infralaminar callosal neurons display more complex dendritic trees in septal columns than within barrels (total length: P≤0,001; arbor area: P≤0,001; dendritic spines: P≤0,0651). Ten anterogradely labeled neurons were fully reconstructed with their axonal arbor. Individual axons terminate into weakly ramified and narrow columns homotopic to the cell body, achieving precise connectivity between restricted, corresponding domains of the opposite hemisphere. Septal terminals were as spatially restricted in septa as within barrels (total length, P=0,76; area, P=0,33), but had more complex geometry (fractal analysis, P≤0,0001) and distributed about twice as many boutons than within barrels (P≤0,001). Thus, individual callosal neurons establish sets of discrete, point-to-point connections between homotopic domains of the rat PMBSF, corresponding to symmetrically located vibrissa or septa.


Palavras-chave:  Barrel Field, Callossal Connection, Axonal Morphometry, Single Neuron, 3D-reconstruction