Search

With the emergence of interest in studying the claustrum, a recent special issue of the Journal of Comparative Neurology dedicated to the claustrum (Volume 525, Issue 6, pp. 1313–1513) brought to light questions concerning the relationship between the claustrum (CLA) and a region immediately ventral known as the endopiriform nucleus (En). These structures have been identified as separate entities in rodents but appear as a single continuous structure in primates. During the recent Society for Claustrum Research meeting, a panel of experts presented data pertaining to the relationship of these regions and held a discussion on whether the CLA and En should be considered (a) separate unrelated structures, (b) separate nuclei within the same formation, or (c) subregions of a continuous structure. This review article summarizes that discussion, presenting comparisons of the cytoarchitecture, neurochemical profiles, genetic markers, and anatomical connectivity of the CLA and En across several mammalian species. In rodents, we conclude that the CLA and the dorsal endopiriform nucleus (DEn) are subregions of a larger complex, which likely performs analogous computations and exert similar effects on their respective cortical targets (e.g., sensorimotor versus limbic). Moving forward, we recommend that the field retain the nomenclature currently employed for this region but should continue to examine the delineation of these structures across different species. Using thorough descriptions of a variety of anatomical features, this review offers a clear definition of the CLA and En in rodents, which provides a framework for identifying homologous structures in primates. Uncertainty exists regarding the relationship between the claustrum and endopiriform nucleus, with discrepancies in how these nuclei are delineated across mammalian species. In this review, Smith et al. summarize recent findings that have identified anatomical markers for these regions in rodents to guide a reappraisal of these boundaries in primates. [ABSTRACT FROM AUTHOR]

The superior colliculus activates the zona incerta (ZI), which sends GABAergic projections to the posteromedial (POm) thalamic nucleus. Consistent with this circuit, we previously showed that stimulation of the superior colliculus activates ZI and causes inhibition of neuronal activity in POm (Watson et al., J Neurosci 35:9463-9476, 2015). Other studies, however, have shown that collicular stimulation activates the intralaminar nuclei of the thalamus. The present study extends these reports by showing that unilateral collicular stimulation causes bilateral activation of Pf that is concomitant with bilateral inhibition of POm. The opposing influences of the superior colliculus on Pf and POm are significant, because both these thalamic nuclei innervate the striatum, which is involved in behavioral selection. In view of data indicating that thalamostriatal projections from Pf and other intralaminar nuclei increase the sensitivity of the indirect pathway to corticostriatal inputs (Ding et al., Neuron 67:294-307, 2010), we tested whether POm stimulation might exert an opposing influence on the basal ganglia circuitry. Consistent with POm projections to the dorsolateral striatum (DLS), which is necessary for the expression of sensorimotor habits, we found that POm stimulation activates DLS and causes inhibition of neuronal activity in the lateral part of the substantia nigra pars reticulata, which is a major target of DLS and the direct pathway. These findings are discussed with respect to clinical reports indicating that deep brain stimulation in ZI is effective in reducing the symptoms of Parkinson's disease. [ABSTRACT FROM AUTHOR]

ABSTRACT We have previously shown that the claustrum is part of an interhemispheric circuit that interconnects somesthetic-motor and visual-motor cortical regions. The role of the claustrum in processing limbic information, however, is poorly understood. Some evidence suggests that the dorsal endopiriform nucleus (DEn), which lies immediately ventral to the claustrum, has connections with limbic cortical areas and should be considered part of a claustrum-DEn complex. To determine whether DEn has similar patterns of cortical connections as the claustrum, we used anterograde and retrograde tracing techniques to elucidate the connectivity of DEn. Following injections of retrograde tracers into DEn, labeled neurons appeared bilaterally in the infralimbic (IL) cortex and ipsilaterally in the entorhinal and piriform cortices. Anterograde tracer injections in DEn revealed labeled terminals in the same cortical regions, but only in the ipsilateral hemisphere. These tracer injections also revealed extensive longitudinal projections throughout the rostrocaudal extent of the nucleus. Dual retrograde tracer injections into IL and lateral entorhinal cortex (LEnt) revealed intermingling of labeled neurons in ipsilateral DEn, including many double-labeled neurons. In other experiments, anterograde and retrograde tracers were separately injected into IL of each hemisphere of the same animal. This revealed an interhemispheric circuit in which IL projects bilaterally to DEn, with the densest terminal labeling appearing in the contralateral hemisphere around retrogradely labeled neurons that project to IL in that hemisphere. By showing that DEn and claustrum have parallel sets of connections, these results suggest that DEn and claustrum perform similar functions in processing limbic and sensorimotor information, respectively. J. Comp. Neurol. 525:1363-1380, 2017. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

There is uncertainty concerning the circuit connections by which the superior colliculus interacts with the basal ganglia. To address this issue, anterograde and retrograde tracers were placed, respectively, into the superior colliculus and globus pallidus of Sprague-Dawley rats. In this two-tracer experiment, the projections from the superior colliculus terminated densely in the ventral zona incerta (ZIv), but did not overlap the labeled neurons observed in the subthalamic nucleus. In cases in which anterograde and retrograde tracers were placed, respectively, in sensory-responsive sites in the superior colliculus and posteromedial (POm) thalamus, the labeled projections from superior colliculus innervated the ZIv regions that contained the labeled neurons that project to POm. We also confirmed this colliculo-incertal-POm pathway by depositing a mixture of retrograde and anterograde tracers at focal sites in ZIv to reveal retrogradely labeled neurons in superior colliculus and anterogradely labeled terminals in POm. When combined with retrograde tracer injections in POm, immunohistochemical processing proved that most ZIv projections to POm are GABAergic. Consistent with these findings, direct stimulation of superior colliculus evoked neuronal excitation in ZIv and caused inhibition of spontaneous activity in POm. Collectively, these results indicate that superior colliculus can activate the inhibitory projections from ZIv to the POm. This is significant because it suggests that the superior colliculus could suppress the interactions between POm and the dorsolateral striatum, presumably to halt ongoing behaviors so that more adaptive motor actions are selected in response to unexpected sensory events. [ABSTRACT FROM AUTHOR]