Callosal axon arbors in the limb representations of the somatosensory cortex (SI) in the agouti (Dasyprocta primnolopha).
The present report compares the morphology of callosal axon arbors projecting from and to the hind- or forelimb representations in the primary somatosensory cortex (SI) of the agouti (Dasyprocta primnolopha), a large, lisencephlic Brazilian rodent that uses forelimb coordination for feeding. Callosal axons were labeled after single pressure (n = 6) or iontophoretic injections (n = 2) of the neuronal tracer biotinylated dextran amine (BDA, 10 kD), either into the hind- (n = 4) or forelimb (n = 4) representations of SI, as identified by electrophysiological recording. Sixty-nine labeled axon fragments located across all layers of contralateral SI representations of the hindlimb (n = 35) and forelimb (n = 34) were analyzed. Quantitative morphometric features such as densities of branching points and boutons, segments length, branching angles, and terminal field areas were measured. Cluster analysis of these values revealed the existence of two types of axon terminals: Type I (46.4%), less branched and more widespread, and Type II (53.6%), more branched and compact. Both axon types were asymmetrically distributed; Type I axonal fragments being more frequent in hindlimb (71.9%) vs. forelimb (28.13%) representation, while most of Type II axonal arbors were found in the forelimb representation (67.56%). We concluded that the sets of callosal axon connecting fore- and hindlimb regions in SI are morphometrically distinct from each other. As callosal projections in somatosensory and motor cortices seem to be essential for bimanual interaction, we suggest that the morphological specialization of callosal axons in SI of the agouti may be correlated with this particular function.
Rocha
E G
EG
Laboratório de Neuroanatomia Funcional, Departamento de Morfologia-Universidade Federal do Pará, 66075-900 Belém, PA, Brasil.
Santiago
L F
LF
Freire
M A M
MA
Gomes-Leal
W
W
Dias
I A
IA
Lent
R
R
Houzel
J C
JC
Franca
J G
JG
Pereira
A
A
Picanço-Diniz
C W
CW
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure*; D001710:Biotin / Q000031:analogs & derivatives; D003337:Corpus Callosum / Q000166:cytology* / Q000502:physiology; D003911:Dextrans; D005121:Extremities / Q000294:innervation* / Q000502:physiology; D005552:Forelimb / Q000294:innervation / Q000502:physiology; D008297:Male; D009048:Motor Skills / Q000502:physiology; D009068:Movement / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology* / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology; D012377:Rodentia / Q000033:anatomy & histology* / Q000502:physiology; D013003:Somatosensory Cortex / Q000166:cytology* / Q000502:physiology; D013045:Species Specificity; D014110:Touch / Q000502:physiology
D003911:Dextrans; C076397:biotinylated dextran amine; D001710:Biotin