Hassiotis, MAshwell, Ken W SMarotte, LaurenLensing-Hohn, SMai, Jurgen K2015-12-130340-2061http://hdl.handle.net/1885/85700We have examined the distribution of immunoreactivity for GAP-43 in the developing and adult brain of a diprotodontid metatherian, the tammar wallaby (Macropus eugenii). The distribution of GAP-43 immunoreactivity in the neonatal wallaby brain was strikingly heterogeneous, in contrast to that reported for the newborn polyprotodontid opossum. Immunoreactivity for GAP-43 in the developing wallaby brain showed a caudal-to-rostral spatiotemporal gradient, with the brainstem well in advance of the telencephalon throughout the first 100 days of postnatal life. In many regions examined, GAP-43 immunoreactivity passed through the following phases: 1. intense immunoreactivity in developing fiber tracts and occasional somata; 2. diffuse homogeneous immunoreactivity; 3. selective loss of immunoreactivity in particular nuclei or cortical regions. In the isocortex, selective loss of GAP-43 immunoreactivity in the somatosensory and visual cortex (at postnatal day 115) coincided with the maturation of the laminar distribution of terminal thalamocortical axonal fields. Within adult cortical regions, GAP-43 immunoreactivity was highest in layer I of all regions, lower layers (V and VI) of primary somatosensory and visual cortices, layers II/III of motor and cingulate cortex, and layer IV of entorhinal cortex. Our findings suggest that, while patterning of GAP-43 immunoreactivity in the mature brain is similar across meta- and eutheria, there may be early developmental differences in the distribution of GAP-43 immunoreactivity between poly- and diprotodontid metatheria.Keywords: neuromodulin; animal experiment; animal tissue; article; brain development; brain maturation; brain stem; cingulate gyrus; controlled study; entorhinal cortex; immunoreactivity; marsupial; motor cortex; nerve fiber; newborn; nonhuman; olfactory cortex; op Cortex; Development; Marsupial; Metatherian; Synaptogenesis200210.1007/s00429-002-0278-12015-12-12