Auditory cortex in the marsupial possum Trichosurus vulpecula

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.

Section: Identifi Cation Of Functional Cortical Areas In the Tammar Wmentioning

confidence: 79%

Section: Nissl Staining and Enzyme Histochemical Features Of Tammar Wmentioning

confidence: 93%

Cyto- and Chemoarchitecture of the Cortex of the Tammar Wallaby (Macropuseugenii): Areal Organization

Ashwell¹,

Ll²,

Marotte

2005

“…This species has a well-developed visual system: the laminated lateral geniculate nucleus has eight layers of retinal input [Hayhow, 1967;Sanderson et al, 1978] and at least three visual areas are found in the cortex . We undertook this study in order to extend the range of spe cies for which information on the visual cortex is available and also to complement other studies on this species: on develop ment of the brain [Sanderson et al, 1982], and on the organization of auditory cortex [Gates and Aitkin. 1982] and sensorimotor cortex [Haight and Neylon, 1979].…”

Section: Introductionmentioning

confidence: 99%

Primary Visual Cortex in the Brushtailed Possum: Receptive Field Properties and Corticocortical Connections

Crewther

Sanderson

1984

The corticocortical connections and receptive field properties of primary or striate visual cortex of the brushtailed possum, Trichosurus vulpecula, have been examined. In this Australian marsupial species primary visual cortex has connections with four other visual areas in the occipital lobe. In these adjacent visual areas fibers from striate cortex terminate mainly in layers 3 and 4 and in some cases also in layers 1 and 2. In all four areas return connections to striate cortex originate predominantly in layers 2 and 3, and to a much lesser extent in layers 5 and 6. Interhemispheric connections of striate cortex are limited to the boundary of striate and peristriate cortex. In addition to its cortical connections, striate cortex makes reciprocal connections with the claustrum. Most neurons in striate cortex are highly binocular. Of our sample of 113 visually responsive neurons, only 30% were orientation selective. On the basis of these observations we have compared striate cortex of the marsupial brushtailed possum with striate cortices of the American marsupial opossum and those of placental mammals.

“…This raises the possibility that layers III-IV became the main target of thalamic ascending projections, at least in the primary auditory cortex, before the appearance of the typical mammalian koniocortex. However, the fact that other mammals with primitive features such as marsupials and monotremes, possess a well-devel oped layer IV [Abbie, 1940, cited by Sanides, 1969Sanides, 1969;Gates and Aitkin, 1982;Aitkin et al, 1986a] raises the alternative possibility that the cortex of insectivores reflects a secondarily degenerated state rather than a primitive stage.…”

Section: Discussionmentioning

confidence: 99%

Auditory Cortex of the Long-Eared Hedgehog (Hemiechinus auritus)

Batzri-Izraeli

Kelly²,

Glendenning³

et al. 1990

The boundaries of the primary auditory cortex of the long-eared hedgehog, Hemiechinus auritus, were determined by single-cell recordings, myeloarchitecture and retrograde horseradish peroxidase labeling in the medial geniculate, using anesthetized animals. The auditory cortex is located on the lateral surface of the temporal cortex, medial to the rhinal fissure. Responses to pure tones revealed an orderly representation of best frequencies in the primary auditory cortex, with low frequencies represented rostrally and high frequencies caudally. A second auditory field caudal to the primary one was indicated.