Morphometric analysis of feedforward pathways from the primary somatosensory area (S1) of rats

In this report, we used biotinylated dextran amine to anterogradely label individual axons projecting from primary somatosensory cortex (S1) to four cortical areas in rats, namely the secondary somatosensory (S2), the parietal ventral (PV), the perirhinal (PR), and the contralateral S1 (S1c). A major goal was to determine whether axon terminals could be classified on the basis of morphological criteria, such as the shape and density of boutons, and the shape and size of individual terminal arbors. Evidence from reconstruction of isolated axon terminal fragments (n=111) supported a degree of morphological heterogeneity. In particular, morphological parameters associated with the complexity of terminal arbors and the proportion of beaded, en passant boutons (Bp) vs. stalked boutons terminaux (Bt) were found to differ significantly. Two broad groups could be established following a discriminant function analysis across axon fragments. Both groups occurred in all four target areas, possibly consistent with a commonality of presynaptic processing of tactile information in these areas. However, more work is needed to investigate synaptic function at the single bouton level and see how this might be associated with emerging properties in the postsynaptic targets.

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Morphometric analysis of feedforward pathways from the primary somatosensory area (S1) of rats

10.7287/peerj.preprints.480v1 ◽

2014 ◽

Author(s):

Andrea Lima de Sá ◽

Vânia Castro Corrêa ◽

Carlomagno Pacheco Bahia ◽

Ivanira Dias ◽

Walace Gomes Leal ◽

...

Keyword(s):

Function Analysis ◽

Synaptic Function ◽

Major Goal ◽

Biotinylated Dextran Amine ◽

Tactile Information ◽

Axon Terminals ◽

Cortical Areas ◽

Morphological Heterogeneity ◽

Morphological Criteria ◽

Biotinylated Dextran

In this report, we used biotinylated dextran amine to anterogradely label individual axons projecting from primary somatosensory cortex (S1) to four cortical areas in rats, namely the secondary somatosensory (S2), the parietal ventral (PV), the perirhinal (PR), and the contralateral S1 (S1c). A major goal was to determine whether axon terminals could be classified on the basis of morphological criteria, such as the shape and density of boutons, and the shape and size of individual terminal arbors. Evidence from reconstruction of isolated axon terminal fragments (n=111) supported a degree of morphological heterogeneity. In particular, morphological parameters associated with the complexity of terminal arbors and the proportion of beaded, en passant boutons (Bp) vs. stalked boutons terminaux (Bt) were found to differ significantly. Two broad groups could be established following a discriminant function analysis across axon fragments. Both groups occurred in all four target areas, possibly consistent with a commonality of presynaptic processing of tactile information in these areas. However, more work is needed to investigate synaptic function at the single bouton level and see how this might be associated with emerging properties in the postsynaptic targets.

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Serial and parallel processing of tactual information in somatosensory cortex of rhesus monkeys

Journal of Neurophysiology ◽

10.1152/jn.1992.68.2.518 ◽

1992 ◽

Vol 68 (2) ◽

pp. 518-527 ◽

Cited By ~ 124

Author(s):

T. P. Pons ◽

P. E. Garraghty ◽

M. Mishkin

Keyword(s):

Substantial Reduction ◽

Receptive Fields ◽

Somatosensory System ◽

Encounter Rate ◽

Specific Information ◽

Tactile Information ◽

Cortical Areas ◽

Area 3A ◽

Area 3B ◽

Made In

1. Selective ablations of the hand representations in postcentral cortical areas 3a, 3b, 1, and 2 were made in different combinations to determine each area's contribution to the responsivity and modality properties of neurons in the hand representation in SII. 2. Ablations that left intact only the postcentral areas that process predominantly cutaneous inputs (i.e., areas 3b and 1) yielded SII recording sites responsive to cutaneous stimulation and none driven exclusively by high-intensity or "deep" stimulation. Conversely, ablations that left intact only the postcentral areas that process predominantly deep receptor inputs (i.e., areas 3a and 2) yielded mostly SII recording sites that responded exclusively to deep stimulation. 3. Ablations that left intact only area 3a or only area 2 yielded substantial and roughly equal reductions in the number of deep receptive fields in SII. By contrast, ablations that left intact only area 3b or only area 1 yielded unequal reductions in the number of cutaneous receptive fields in SII: a small reduction when area 3b alone was intact but a somewhat larger one when only area 1 was intact. 4. Finally, when the hand representation in area 3b was ablated, leaving areas 3a, 1, and 2 fully intact, there was again a substantial reduction in the encounter rate of cutaneous receptive fields. 5. The partial ablations often led to unresponsive sites in the SII hand representation. In SII representations other than of the hand no such unresponsive sites were found and there were no substantial changes in the ratio of cutaneous to deep receptive fields, indicating that the foregoing results were not due to long-lasting postsurgical depression or effects of anesthesia. 6. The findings indicate that modality-specific information is relayed from postcentral cortical areas to SII along parallel channels, with cutaneous inputs transmitted via areas 3b and 1, and deep inputs via areas 3a and 2. Further, area 3b provides the major source of cutaneous input to SII, directly and perhaps also via area 1. 7. The results are in line with accumulating anatomic and electrophysiologic evidence pointing to an evolutionary shift in the organization of the somatosensory system from the general mammalian plan, in which tactile information is processed in parallel in SI and SII, to a new organization in higher primates in which the processing of tactile information proceeds serially from SI to SII. The presumed functional advantages of this evolutionary shift are unknown.

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ELECTRON MICROSCOPE HISTOCHEMICAL EVIDENCE FOR A PARTIAL OR TOTAL BLOCK OF THE TRICARBOXYLIC ACID CYCLE IN THE MITOCHONDRIA OF PRESYNAPTIC AXON TERMINALS

The Journal of Cell Biology ◽

10.1083/jcb.51.1.216 ◽

1971 ◽

Vol 51 (1) ◽

pp. 216-222 ◽

Cited By ~ 29

Author(s):

Ferenc Hajós ◽

Sándor Kerpel-Fronius

Keyword(s):

Tricarboxylic Acid Cycle ◽

Energy Coupling ◽

Tricarboxylic Acid ◽

Synaptic Function ◽

Coupling Mechanism ◽

Succinate Oxidation ◽

Acid Cycle ◽

Axon Terminals ◽

Massive Accumulation

Respiration-linked, massive accumulation of Sr2+ is used to reveal the coupled oxidation of pyruvate, α-oxoglutarate, succinate, and malate by in situ mitochondria. All of these substrates were actively oxidized in the dendritic and perikaryal mitochondria, but no α-oxoglutarate or succinate utilization could be demonstrated in the mitochondria of the presynaptic axon terminals. A block at an early step of α-oxoglutarate and succinate oxidation is proposed to account for the negative histochemical results, since the positive reaction with pyruvate and malate proves that these mitochondria possess an intact respiratory chain and energy-coupling mechanism essential for Sr2+ accumulation. This indicates that the mitochondria in the axon terminals would be able to generate energy for synaptic function with at least some of the respiratory substrates. With regard to the block in the tricarboxylic acid cycle, the oxaloacetate necessary for citrate formation is suggested to be provided by fixation of CO2 into some of the pyruvate.

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