Postnatal development of retinal projections in the brushtailed possum, Trichosurus vulpecula

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.

Section: Introductionmentioning

confidence: 99%

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

Crewther

Sanderson

1984

“…There are also many similarities in the morphological and functional types of retinal ganglion cells giving origin to retinocollicular projections [Wässle and Illing, 1980;Rapaport and Wilson, 1983;Hofbauer and Dräger, 1985]. Thus, marsupials share many features with visually-specialized eutherians such as the occurrence of binocular segregation of retinocollicular terminals [Tigges and Tigges, 1970;Cavalcante et al, 1975;Graybiel, 1975;Hubel et al, 1975;Sanderson et al, 1982;Wie-Dvorak, 1984;Harman and Beazley, 1986;Dunlop, 1997].…”

Section: Introductionmentioning

confidence: 96%

“…The refined organization of the marsupial retinocollicular system has led to several studies of the normal and abnormal development of SC [Cavalcante and Rocha-Miranda, 1978a, b;Lent and Mendez-Otero, 1980;Sanderson et al, 1982;Cavalcante et al, 1984Cavalcante et al, , 1991Mendez-Otero et. al., 1985Harman and Beazley, 1986;Barradas et al, 1989Barradas et al, , 1995Harman, 1991;Mark et al, 1993;Dunlop, 1997].…”

Section: Introductionmentioning

confidence: 99%

Synaptogenesis in Retino-Receptive Layers of the Superior Colliculus of the Opossum Didelphis marsupialis

Correa-Gillieron

Cavalcante

1999

The maturation of the neuropil and synapse formation were examined in the retino-receptive layers of the superior colliculus (SCr-r) in the opossum from a period prior to the onset of arborization of retinocollicular fibers (postnatal day 22 – P22), at 44% of the coecal period (CP), to the end of the fast phase of optic fiber myelination and weaning time (P81 – 118% CP). Development of the SCr-r neuropil follows a protracted time course and can be divided into three broad stages, which are characterized by (I) Large extracellular spaces, numerous growth cones that participate rarely in synaptic junctions, vesicles-poor immature synapses (P22–P30), (II) Synapses of varied morphology with abundant synaptic vesicles, and small terminals with dark mitochondria and round synaptic vesicles (RSD terminals) synapsing mostly onto dendritic shafts, flat-vesicles (F) terminals (P40–P56), (III) Sequential appearance of retinal (R) and pleomorphic-vesicles (P) terminals and of RSD terminals synapsing onto spine or spine-like processes, appearance of glomerulus-like synaptic arrays (synaptic islets) (P61–P81). The advancement of synaptogenesis in SCr-r from stage I to II and from stage II to III correlates closely with the differentiation of astrocytes and oligodendrocytes, respectively.

“…In addition to the 3H-thymidine-labelled material, we had for examination a series of 24 brains of possums aged 9-83 days which had been prepared for a previous study [Sanderson et al, 1982]. This material provided for us a picture of the different brain re gions at various ages and some information about cell birth from observation of mitotic figures.…”

Section: Methodsmentioning

confidence: 99%

“…Since there was a long survival period following the injections, there has been time for the neurons to migrate to their final destinations, which are indicated in the drawings. [Sanderson et al, 1982], Note that the average adult brain weight of possums of 9.4 g [Haight and Neylon, 1978] is achieved by I year of age.…”

Section: Neurogenesis In Visual Centresmentioning

confidence: 99%

Neurogenesis in a Marsupial: The Brush-Tailed Possum <i>(Trichosurus vulpecula)</i>

Sanderson

Aitkin²

1990

Self Cite

The times of origin of neurons in the visual and auditory systems were studied in a marsupial, the brush-tailed possum, using tritiated thymidine autoradiography. Within the subcortical visual pathways, most neurons are generated between postnatal days 5 and 21, and the neurons of the primary visual cortex up to postnatal day 68. In the subcortical auditory pathways, most neurons are generated between postnatal days 5 and 28, and all auditory cortex neurons have appeared by postnatal day 46. Neurons in a single layer of cerebral cortex are generated during a period of about 2 weeks. Thus cortical neurogenesis in marsupials extends over a period similar to that seen in primates