Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Genetics, Development and Cell Biology

First Advisor

Carol D. Jacobson


The anatomical localization and ontogeny of cholecystokinin (CCK), an abundant neuropeptide, and the estrogen receptor were examined in Monodelphis domestica, the Brazilian short-tailed opossum. An indirect immunohistochemical procedure was used to identify cholecystokinin-like immunoreactive (CCK LI) cell bodies and fibers. Somato containing CCK immunoreactivity were observed in the cerebral cortex, hippocampus, hypothalamus, thalamus, midbrain, and brainstem. CCK LI fibers had a wide distribution in the adult Monodelphis brain. The only region of the brain that did not contain CCK LI fibers was the cerebellum. Male opossums had a significantly higher density of CCK LI neuronal elements than that found in the females. The earliest expression of CCK immunoreactivity was in fibers in the dorsal brainstem of 5 day old opossum pups. This early expression of CCK LI in regions of the brain involved in feeding behavior correlates with the necessity of Monodelphis young to feed at a relatively early age. The wide distribution and varied patterns of onset of expression of CCK LI structures indicates CCK may have many functions in the opossum brain. A second series of studies examined the distribution of estrogen receptor-like immunoreactive (ER LI) cells in the brains of adult and developing male and female Brazilian opossums using Abbott H222 rat monoclonal estrogen receptor antibody. We believe specific regions of the Brazilian opossum brain may serve as substrata for the action of estrogen in the adult. Estrogen receptor immunoreactive cells were first observed in the dorsomedial and ventromedial hypothalamus of the opossum ten days after birth (10PN). The number of ER LI cells increased to the 60PN time point in all regions that contain ER LI cells in the adult opossum. Estrogen receptors are present in early development of the Monodelphis brain and may mark the beginning of a critical period for sexual differentiation of the opossum brain. No sex difference was noted for ER LI cells and ER LI was not colocalized with CCK LI. This data indicates that estrogen may not directly modulate CCK expression in Monodelphis domestica. (Abstract shortened with permission of author.)



Digital Repository @ Iowa State University,

Copyright Owner

Charles Allan Fox



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168 pages