Bilateral projections from rat MI whisker cortex to the neostriatum, thalamus, and claustrum: Forebrain circuits for modulating whisking behavior

Abstract

In rats, whisking behavior is characterized by high-frequency synchronous movements and other stereotyped patterns of bilateral coordination that are rarely seen in the bilateral movements of the limbs. This suggests that the motor systems controlling whisker and limb movements must have qualitative or quantitative differences in their interhemispheric connections. To test this hypothesis, anterograde tracing methods were used to characterize the bilateral distribution of projections from the whisker and forepaw regions in the primary motor (MI) cortex. Unilateral tracer injections in the MI whisker or forepaw regions revealed robust projections to the corresponding MI cortical area in the contralateral hemisphere. Both MI regions project bilaterally to the neostriatum, but the corticostriatal projections from the whisker region are denser and more evenly distributed across both hemispheres than those from the MI forepaw region. The MI whisker region projects bilaterally to several nuclei in the thalamus, whereas the MI forepaw region projects almost exclusively to the ipsilateral thalamus. The MI whisker region sends dense projections to the contralateral claustrum, but those to the ipsilateral claustrum are less numerous. By contrast, the MI forepaw region sends few projections to the claustrum of either hemisphere. Bilateral deposits of different tracers in MI revealed overlapping projections to the neostriatum, thalamus, and claustrum when the whisker regions were injected, but not when the forepaw regions were injected. These results suggest that the bilateral coordination of the whiskers depends, in part, on MI projections to the contralateral neostriatum, thalamus, and claustrum.

Differential topography of the bilateral cortical projections to the whisker and forepaw regions in rat motor cortex

“…4, this shift in CS labeling with respect to the Rf was confirmed in coronal sections from a case in which FG was injected into the MI whisker region. Consistent with other findings in our lab (Alloway et al 2009), we observed a continuous and gradual decline in the density of CS labeling at more caudal sections. Our tangential reconstructions also confirm previous reports indicating that CS labeling is greater in the ipsilateral than in the contralateral hemisphere (Li et al 1986;Sloniewski et al 1986;Sadowski et al 1997).…”

“…Furthermore, differences in the amount of bilateral coordination of these body parts should be matched by corresponding differences in the interhemispheric connections of the whisker and forelimb regions in MI. In support of this view, we recently found that the MI whisker region projects more extensively to both sides of the thalamus, neostriatum, and other subcortical brain regions when compared to projections from the MI forepaw region (Alloway et al , 2009.…”

Type 1 cannabinoid receptor mapping with [18F]MK-9470 PET in the rat brain after quinolinic acid lesion: a comparison to dopamine receptors and glucose metabolism

“…Notably, studies with unilateral intranigral 6-hydroxydopamine (6-OHDA) application to model Parkinson's disease (PD) found similar findings of increased D 2 receptor densities in the contralateral caudate-putamen [49,50]. There is also histologic evidence for interhemispheric projections from the striatum to the motor cortex [51], and upon lesioning, evidence of increased sprouting from intact to damaged hemispheres [52]. From our observations, it also appears as if reactive compensation is not limited to striatal structures only.…”

All Rodents Are Not the Same: A Modern Synthesis of Cortical Organization

“…Several studies have examined the architecture and connectivity of motor cortex in rats and mice [Donoghue and Parham, 1983;Porter and White, 1983;Cicirata et al, 1986;Alloway et al, 2009;Colechio and Alloway, 2009] (see above for studies of cortical architecture). In some studies, cortex immediately rostral to S1 is reported to contain a small transitional zone with a reduced layer 4 compared to S1 and moderate myelination [Chapin and Lin, 1984;Campi and Krubitzer, 2010;Cooke et al, 2011].…”