Cortico-cortical connectivity of the somatosensory cortex of the agouti: Topographical organization and evolutionary implications.

Understanding patterns of cortico-cortical connections in both frequently and infrequently studied species advances our knowledge of cortical organization and evolution. The agouti (Dasyprocta aguti, a medium-size South American rodent) offers a unique opportunity, because of its large lissencephalic brain and its natural behaviors, such as gnawing and hiding seeds, that require bimanual interaction while sitting on its hindlimbs and aligning its head to receive images of the horizon on the retinal visual streak. There have been no previous studies of the intrinsic and extrinsic ipsilateral projections of the agouti's primary somatosensory cortical area (S1).

Organization of Somatosensory Cortex in the South American Rodent Paca (Cuniculus paca).

Introduction: The study of non-laboratory species has been part of a broader effort to establish the basic organization of the mammalian neocortex, as these species may provide unique insights relevant to cortical organization, function, and evolution.

Methods: In the present study, the organization of three somatosensory cortical areas of the medium-sized (5-11 kg body mass) Amazonian rodent, the paca (Cuniculus paca), was determined using a combination of electrophysiological microelectrode mapping and histochemical techniques (cytochrome oxidase and NADPH diaphorase) in tangential sections.

Results: Electrophysiological mapping revealed a somatotopically organized primary somatosensory cortical area (S1) located in the rostral parietal cortex with a characteristic foot-medial/head-lateral contralateral body surface representation similar to that found in other species.

The Multiple Representations of Complex Digit Movements in Primary Motor Cortex Form the Building Blocks for Complex Grip Types in Capuchin Monkeys.

In the present study, we investigated motor cortex (M1) and a small portion of premotor and parietal cortex using intracortical microstimulation in anesthetized capuchin monkeys. Capuchins are the only New World monkeys that have evolved an opposable thumb and use tools in the wild. Like most Old World monkeys and humans, capuchin monkeys have highly dexterous hands.

Thalamic Inputs to Posterior Parietal Cortical Areas Involved in Skilled Forelimb Movement and Tool Use in the Capuchin Monkey.

The posterior parietal cortex (PPC) is a central hub for the primate forebrain networks that control skilled manual behavior, including tool use. Here, we quantified and compared the sources of thalamic input to electrophysiologically-identified hand/forearm-related regions of several PPC areas, namely areas 5v, AIP, PFG, and PF, of the capuchin monkey (Sapajus sp). We found that these areas receive most of their thalamic connections from the Anterior Pulvinar (PuA), Lateral Posterior (LP) and Medial Pulvinar (PuM) nuclei.

The Organization and Connections of Second Somatosensory Cortex in the Agouti.

In order to understand how the mammalian sensory cortex has been structured during evolution, it is necessary to compare data from different species across distinct mammalian lineages. Here, we investigated the organization of the secondary somatosensory area (S2) in the agouti (), a medium-sized Amazonian rodent, using microelectrode mapping techniques and neurotracer injections. The topographic map obtained from multiunit electrophysiological recordings were correlated with both cytochrome oxidase (CO) histochemistry and with patterns of corticocortical connections in tangential sections.

Partitioning of the primate intraparietal cortex based on connectivity pattern and immunohistochemistry for Cat-301 and SMI-32.

We propose a partitioning of the primate intraparietal sulcus (IPS) using immunoarchitectural and connectivity criteria. We studied the immunoarchitecture of the IPS areas in the capuchin monkey using Cat-301 and SMI-32 immunohistochemistry. In addition, we investigated the IPS projections to areas V4, TEO, PO, and MT using retrograde tracer injections in nine hemispheres of seven animals.

Chronic recordings reveal tactile stimuli can suppress spontaneous activity of neurons in somatosensory cortex of awake and anesthetized primates.

In somatosensory cortex, tactile stimulation within the neuronal receptive field (RF) typically evokes a transient excitatory response with or without postexcitatory inhibition. Here, we describe neuronal responses in which stimulation on the hand is followed by suppression of the ongoing discharge. With the use of 16-channel microelectrode arrays implanted in the hand representation of primary somatosensory cortex of New World monkeys and prosimian galagos, we recorded neuronal responses from single units and neuron clusters.

Architectonic mapping of somatosensory areas involved in skilled forelimb movements and tool use.

Cebus monkeys stand out from other New World monkeys by their ability to perform fine hand movements, and by their spontaneous use of tools in the wild. Those behaviors rely on the integration of somatosensory information, which occurs in different areas of the parietal cortex. Although a few studies have examined and parceled the somatosensory areas of the cebus monkey, mainly using electrophysiological criteria, very little is known about its anatomical organization.

Evolution of mammalian sensorimotor cortex: thalamic projections to parietal cortical areas in Monodelphis domestica.

The current experiments build upon previous studies designed to reveal the network of parietal cortical areas present in the common mammalian ancestor. Understanding this ancestral network is essential for highlighting the basic somatosensory circuitry present in all mammals, and how this basic plan was modified to generate species specific behaviors. Our animal model, the short-tailed opossum (Monodelphis domestica), is a South American marsupial that has been proposed to have a similar ecological niche and morphology to the earliest common mammalian ancestor.

Enhancement of median nerve regeneration by mesenchymal stem cells engraftment in an absorbable conduit: improvement of peripheral nerve morphology with enlargement of somatosensory cortical representation.

We studied the morphology and the cortical representation of the median nerve (MN), 10 weeks after a transection immediately followed by treatment with tubulization using a polycaprolactone (PCL) conduit with or without bone marrow-derived mesenchymal stem cell (MSC) transplant. In order to characterize the cutaneous representation of MN inputs in primary somatosensory cortex (S1), electrophysiological cortical mapping of the somatosensory representation of the forepaw and adjacent body parts was performed after acute lesion of all brachial plexus nerves, except for the MN. This was performed in ten adult male Wistar rats randomly assigned in three groups: MN Intact (n = 4), PCL-Only (n = 3), and PCL+MSC (n = 3).

A connection to the past: Monodelphis domestica provides insight into the organization and connectivity of the brains of early mammals.

The current experiment is one of a series of comparative studies in our laboratory designed to determine the network of somatosensory areas that are present in the neocortex of the mammalian common ancestor. Such knowledge is critical for appreciating the basic functional circuitry that all mammals possess and how this circuitry was modified to generate species-specific, sensory-mediated behavior. Our animal model, the gray short-tailed opossum (Monodelphis domestica), is a marsupial that is proposed to represent this ancestral state more closely than most other marsupials and, to some extent, even monotremes.

Distribution and morphology of nitrergic neurons across functional domains of the rat primary somatosensory cortex.

The rat primary somatosensory cortex (S1) is remarkable for its conspicuous vertical compartmentalization in barrels and septal columns, which are additionally stratified in horizontal layers. Whereas excitatory neurons from each of these compartments perform different types of processing, the role of interneurons is much less clear. Among the numerous types of GABAergic interneurons, those producing nitric oxide (NO) are especially puzzling, since this gaseous messenger can modulate neural activity, synaptic plasticity, and neurovascular coupling.

Topographic Organization and Corticocortical Connections of the Forepaw Representation in Areas S1 and SC of the Opossum: Evidence for a Possible Role of Area SC in Multimodal Processing.

In small-brained mammals, such as opossums, the cortex is organized in fewer sensory and motor areas than in mammals endowed with larger cortical sheets. The presence of multimodal fields, involved in the integration of sensory inputs has not been clearly characterized in those mammals. In the present study, the corticocortical connections of the forepaw representation in the somatosensory caudal (SC) area of the Didelphis aurita opossum was studied with injections of fluorescent anatomical tracers in SC.

Parallel evolution of cortical areas involved in skilled hand use.

Dexterous hands, used to manipulate food, tools, and other objects, are one of the hallmarks of primate evolution. However, the neural substrate of fine manual control necessary for these behaviors remains unclear. Here, we describe the functional organization of parietal cortical areas 2 and 5 in the cebus monkey.

Neuropil reactivity, distribution and morphology of NADPH diaphorase type I neurons in the barrel cortex of the adult mouse.

The mouse, like a few other rodent and marsupial species, displays a striking modular architecture in its primary somatosensory cortex (SI). These modules, known as barrels, are mostly defined by the peculiar arrangement of granule cells and thalamic axons in layer IV. In the present work, we studied both the distribution and morphology of neurons stained for NADPH diaphorase (NADPH-d) and neuropil reactivity in the posteromedial barrel subfield (PMBSF), which represents the mystacial whiskers.

A morphometric study of the progressive changes on NADPH diaphorase activity in the developing rat's barrel field.

The distribution of NADPH diaphorase (NADPH-d)/nitric oxide synthase (NOS) neurons was evaluated during the postnatal development of the primary somatosensory cortex (SI) of the rat. Both cell counts and area measurements of barrel fields were carried out throughout cortical maturation. In addition, NADPH-d and cytochrome oxidase (CO) activities were also compared in both coronal and tangential sections of rat SI between postnatal days (P) 10 and 90.