Cyto- and Chemoarchitecture of the Cortex of the Tammar Wallaby <i>(Macropus</i><i>eugenii)</i>: Areal Organization

Abstract

We have examined the cyto- and chemoarchitecture of the isocortex of a diprotodontid marsupial, the tammar wallaby (Macropus eugenii), using Nissl staining in combination with enzyme histochemical (acetylcholinesterase – AChE, NADPH-diaphorase – NADPHd, cytochrome oxidase) and immunohistochemical (non-phosphorylated neurofilament – SMI-32) markers. The primary sensory cortex showed distinctive patterns of reactivity in cytochrome oxidase, acetylcholinesterase and NADPH diaphorase. For example, in AChE material, S1 showed a heterogeneous appearance, with regions exhibiting a double layer of AChE activity (layers II and IV) adjacent to poorly reactive regions. In NADPHd preparations, activity in S1 was strongest in layers I to IV although, as in AChE material, there were consistent patches of reduced NADPHd activity which corresponded to poorly reactive regions in the AChE sections. Each of the primary sensory areas of the isocortex showed a different pattern of distribution of SMI-32+ neurons. In V1, SMI-32+ neurons were distributed in two layers (III and V) throughout the tangential extent of that region. In S1, SMI-32+ neurons were concentrated in layer V, but large and discrete patches within S1 had additional SMI-32+ neurons in layer III. In primary auditory cortex there was a dense band of SMI-32+ neurons in layer V, with only occasional labeled pyramidal neurons in layer III. In the secondary sensory areas (V2 and S2) SMI-32+ neurons were either distributed in layers III and V (V2) or solely within layer V (S2). The tangential and laminar distribution of Type I reactive NADPH diaphorase neurons in the tammar wallaby cortex was more like that seen in eutheria than in polyprotodontid metatheria.

Neocortical neuron types in Xenarthra and Afrotheria: implications for brain evolution in mammals

“…Characters were coded based on direct observation for the specimens in the current study, supplemented by written description in the literature for other species Boire et al 2005;Desgent et al 2005;Glezer et al 1993Glezer et al , 1998Hassiotis et al 2005;Hof et al 1996aHof et al , 1999Van der Gucht et al 2001) and examination of our own collections which include various marsupials, primates, rodents, carnivores, and cetartiodactyls. Because the marsupials represent a critical outgroup in defining the polarity of character evolution among eutherians, it should be noted that our determination of character states in Marsupialia for NPNFP-ir neurons was based on relatively limited available data from descriptions of the macropodid tammar wallaby (Macropus eugenii) in Ashwell et al (2005), corroborated by our observations of NPNFP-stained sections from a parma wallaby (Macropus parma) in our own collection. To simplify the visualization of phylogenetic trees, whenever the same character state was consistently present in all members of a clade, the higherorder taxonomic designation is shown in the reconstruction of character state evolution.…”

Somatosensory Areas of Manatee Cerebral Cortex: Histochemical Characterization and Functional Implications

“…Due to its location and cytochrome oxidase reactivity in layer III, area DD2 of the manatee brain might be a candidate for SII. Supragranular cytochrome oxidase staining was also found in secondary sensory areas in other species such as the tammar wallaby [Ashwell et al, 2005], whereas the motor cortex exhibited broad, dense staining as shown here for the manatee. SI appears to occupy roughly 25% of total cortical area ( table 2 ), which is comparable to other somatosensory specialists such as the naked mole-rat in which SI comprises approximately 31% of neocortex [Catania and Remple, 2002].…”

Neuron Types in the Presumptive Primary Somatosensory Cortex of the Florida Manatee <b><i>(Trichechus manatus latirostris)</i></b>

“…This pattern differs from what is seen in primates, rodents and carnivores, where staining is more diffusely distributed throughout the cortex wherever there are pyramidal neurons [Campbell and Morrison, 1989;Chaudhuri et al, 1996;Hof et al, 1996;Nimchinsky et al, 1997;Preuss et al, 1997;Budinger et al, 2000;Tsang et al, 2000;Van der Gucht et al, 2001;Sherwood et al, 2004;Baldauf, 2005;Boire et al, 2005;Bourne et al, 2005;Hof and Sherwood, 2005;Bourne et al, 2007;Van der Gucht et al, 2007] but is similar to what is also observed in afrotherians, xenarthrans, monotremes and marsupials Hassiotis et al, 2005;Sherwood et al, 2009]. Primates, rodents and carnivores also have different patterns of NPNFP-ir neuron distribution in different cortical areas [Campbell and Morrison, 1989;Campbell et al, 1991;Hof and Nimchinsky, 1992;Budinger et al, 2000;Van der Gucht et al, 2001, which is not as clearly variable across the cortex in afrotherians, xenarthrans, monotremes and marsupials Ashwell et al, 2005;Hassiotis and Paxinos, 2004;Hassiotis et al, 2005;Sherwood et al, 2009]. Although only the manatee S1 has been investigated in this study, the restriction of NPNFP-ir neurons to specific layers in two different cortical regions is similar to that seen in the majority of mammalian taxa and differs from the more derived pattern of certain groups such as primates, rodents and carnivores.…”