Efferent fibers from the motor cortex terminate bilaterally in the thalamus of rats and cats

Abstract

The anterograde transport of lectin-conjugated horseradish peroxidase (WGA-HRP) was here employed in order to visualize crossed corticothalamic efferents of the motor cortex in rats and cats. After WGA-HRP cortical injections in the rat retrogradely labeled cells were observed in the ipsilateral thalamus, and heavy anterograde labeling was observed both in the ipsi- and contralateral thalamus. The contralateral anterograde labeling was less intense than the ipsilateral one and it was distributed in the anterior intralaminar structures, in the parafascicular nucleus, in the ventromedial, ventrolateral and ventrobasal nuclei and in the posterior complex, symmetrically to the labeling observed on the ipsilateral side. Further experiments were made in the rat in order to ascertain that the bilateral anterograde labeling in the thalamus derived unilaterally from the cortex. To this purpose, kainic acid was injected unilaterally either into the frontal cortex or into the thalamus, and WGA-HRP was later injected on the same side in the frontal cortex. Moreover, WGA-HRP was injected into the frontal cortex after splitting of the corpus callosum. The results obtained in these experiments confirmed that cortical neurons projected bilaterally upon the thalamus. Further, these experiments indicated that at least the majority of the contralateral fronto-thalamic fibers crossed the midline in the thalamic massa intermedia. WGA-HRP injections into the pericruciate cortex in the cat confirmed the presence of anterogradely labeled terminals in the contralateral anterior and posterior intralaminar, ventral anterior, ventromedial and ventrolateral nuclei. The labeling was in all cases heavier in the intralaminar nuclei than in the other structures, but it was less intense than that observed in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Thalamic terminal morphology and distribution of single corticothalamic axons originating from layers 5 and 6 of the cat motor cortex

“…All of the single CT axons reconstructed showed only ipsilateral projection in our material. This finding is consistent with the weak contralateral CT projection reported by Molinari et al (1985).…”

“…In a previous study, Molinari et al (1985) reported contralateral CT projection from the cat Mx. In the present study, as a result of the bilateral injections of BDA in each animal, it was necessary to reconstruct single CT axons to distinguish contralateral and ipsilateral projections.…”

Functional Development of Large-Scale Sensorimotor Cortical Networks in the Brain

“…Activation of the M1 cortex begins with a current sink in infragranular layers that should reflect feedforward activation from S1 projections to the motor cortex, since these were shown to activate predominantly its deeper layers (Hoffer et al, 2005;Chakrabarti et al, 2008). Several routes interconnecting S1 to the other hemisphere were demonstrated in rodents: direct projections between homotopic regions in parietal (Olavarria et al, 1984;Welker et al, 1988;Koralek et al, 1990) and frontal (Mitchell and Macklis, 2005) cortices, as well as polysynaptic paths between cortical areas including transcallosal corticothalamic projections (Molinari et al, 1985;Alloway et al, 2008). The infragranular sinks recorded in the ipsilateral hemisphere at P21 should reflect activation from callosal projections.…”

Altered Contralateral Sensorimotor System Organization after Experimental Hemispherectomy: A Structural and Functional Connectivity Study

“…Support for this hypothesis (i.e., an inborn structural capacity for bilateral innervation) is given by a study that demonstrated that cortical neuronal projections reach the bilateral thalamus in developing rat and cat brain. 40 Our functional network analysis revealed an increase in clustering of the contralateral thalamus with other network nodes ( Figure 7). This increase, already present at 7 days after hemispherectomy, could well be indicative of the thalamus' role in ipsi and contralateral (sensori)motor control.…”