Cortical connections of the lateral mediodorsal thalamus in cynomolgus monkeys

Abstract

The prefrontal cortex has been defined as that cortical territory that has "essential or sustaining" connections with the mediodorsal (MD) nucleus of the thalamus. However, recent studies in the monkey have documented projections from MD to the more caudal, agranular regions of the frontal cortex, suggesting that the connections of MD may be characterized by a breadth of distribution and diversity of functional roles too great to be useful as a unifying and defining feature for a specific cortical territory. In this study, we placed tracer injections in the lateral divisions of MD in cynomolgus monkeys (Macaca fascicularis) to assess the relative proportions of connections devoted to diverse regions of the frontal cortex (FC). Three different patterns of label were observed in the cortex, associated with different locations within lateral MD. We have designated these as the ventrolateral MD-arcuate FC circuit, having most label in areas 8 and 6; the caudoventral MD-dorsomedial FC circuit, having most label in areas 24 and presupplementary motor area (SMA); and the anterodorsal MD-anterior FC circuit, with the most label in areas 9, 46, 12, and 10. Only two of the nine cases injected in lateral MD were predominantly connected with the anterior FC. Thus, particular locales within lateral MD are connected with multiple, functionally diverse cortical regions, including several not classically recognized as "prefrontal" areas. This divergence may distinguish MD-frontocortical and reciprocal corticothalamic pathways from the largely segregated pathways arising from the other thalamic nuclei that are interconnected with the frontal cortex, such as those from the ventrolateral nuclear group.

Presynaptic D1Dopamine Receptors in Primate Prefrontal Cortex: Target-Specific Expression in the Glutamatergic Synapse

“…Recently, D 1 Rs have been localized in neurons expressing calbindin or PV, including those in the mediodorsal thalamus that furnish the main projections to the PFC (Rodriguez-Moral and Cavada, 2003), yet it is unclear whether their axons incorporate the receptor. Nonetheless, the latter terminate in layers deep III and IV, with only few nonvaricose fibers present below this zone (Giguere and Goldman-Rakic, 1988;Erickson and Lewis, 2004). Moreover, the midlayer projections express PV and establish type I axospinous synapses , in agreement with the classic descriptions on sensory cortices (DeFelipe and Jones, 1991).…”

Molecular mechanisms contributing to dendritic spine alterations in the prefrontal cortex of subjects with schizophrenia

“…For example, the excitatory inputs from the medial dorsal thalamic nucleus (MD) synapse primarily on dendritic spines 39 and densely arborize in DLPFC layers deep 3 and 4, but do not innervate the deep cortical layers. 40 Interestingly, functional imaging studies have reported altered activation of the MD during working memory tasks in subjects with schizophrenia. 41 In addition, initial post-mortem studies reported a decrement in the number of MD neurons in subjects with schizophrenia, [42][43][44][45] although more recent studies have failed to confirm this finding.…”

The Reward Circuit: Linking Primate Anatomy and Human Imaging

“…(Haber et al, 1993;Ray and Price, 1993). These connections, however, are bidirectional (Erickson and Lewis, 2004;McFarland and Haber, 2002;Zikopoulos and Barbas, 2007). Moreover, while cortico-thalamic projections of the specific thalamic relay nuclei follow a general rule of reciprocity, the cortical projections to these thalamic nuclei are more extensive than their projections back to cortex (as seen in other thalamocortical systems) (Darian-Smith et al, 1999;McFarland and Haber, 2002;Sherman and Guillery, 1996).…”