Opossum Brain Research Articles

Galanin-like immunoreactivity in the adult and developing Brazilian opossum brain

The distribution of galanin-like immunoreactivity has been characterized in the brain of the adult and developing Brazilian opossum ( Monodelphis domestica). Two commercially available antisera were used to examine the distribution of galanin-like immunoreactive (GAL-IR) cells and fibers. Nuclear groups containing GAL-IR cell bodies and fibers were seen throughout the adult opossum brain. The distribution of GAL-IR elements seen is similar to that reported for other mammals. Based on these findings, we believe that galanin may have similar physiological functions in the adult Brazilian opossum as has been reported for other mammals. In the developing brain, GAL-IR structures were seen as early as 1 day postnatal (PN) in the developing hypothalamus and brainstem. By days 5 and 10 PN, there was a robust expression of galanin-like immunoreactivity in specific regions of the brain. Since neurogenesis and brain morphogenesis are actively occuring postnatally in the opossum, galanin may be playing a role in the differentation of specific regions of the brain.

Evidence for high levels of androgen in peripheral plasma during postnatal development in a marsupial: the gray short-tailed opossum (Monodelphis domestica).

Plasma samples were assayed for androgen in gray short-tailed opossums (Monodelphis domestica) on the day of birth and at selected ages through adulthood. Levels of androgen in mixed-sex plasma pools of animals 4 and 8 days of age were higher than in either sex at all other ages examined. At postnatal Days 16, 30, and 60 (weaning), levels of androgen were equivalent in males and females and as high as in adult males. In both sexes, androgen levels were lower at postnatal Day 84 (juveniles) than at younger ages; after puberty, levels were significantly higher in males than in females. These findings are discussed with respect to similarities and differences between marsupials and eutherians in hormonal environment during the perinatal period and with respect to the possible role of androgens in sexual differentiation of the gray opossum brain.

Ontogeny of cholecystokinin-like immunoreactivity in the Brazilian opossum brain

We have studied the anatomical distribution of cholecystokinin-like immunoreactive (CCK-IR) somata and fibers in the brain of the adult and developing Brazilian short-tailed opossum, Monodelphis domestica. Animals ranged in age from the day of birth (1PN) to young adulthood (180PN). A nickel enhanced, avidin-biotin, indirect immunohistochemical technique was used to identify CCK-IR structures. Somata containing CCK immunoreactivity were observed in the cerebral cortex, hippocampus, hypothalamus, thalamus, midbrain, and brainstem in the adult. Cholecystokinin immunoreactive fibers had a wide distribution in the adult Monodelphis brain. The only major region of the brain that did not contain CCK-IR fibers was the cerebellum. The earliest expression of CCK immunoreactivity was found in fibers in the dorsal brainstem of 5-day-old opossum pups. It is possible that the CCK-IR fibers in the brainstem at 5PN are of vagal origin. Cholecystokinin immunoreactive somata were observed in the brainstem on 10PN. The CCK-IR cell bodies observed in the brainstem at 10PN may mark the first expression of CCK-IR elements intrinsic to the brain. A broad spectrum of patterns of onset of CCK expression was observed in the opossum brain. The early occurrence and varied ontogenesis of CCK-IR structures indicates CCK may be involved in the function of a variety of circuits from the brainstem to the cerebral cortex. The early expression of CCK-IR structures in the dorsal brainstem suggests that CCK may modulate feeding behavior in the Monodelphis neonate. Cholecystokinin immunoreactivity in forebrain structures such as the suprachiasmatic nucleus, medial preoptic area, thalamus and cortical structures indicates that CCK may also be involved in circadian rhythmicity, reproductive functions, as well as the state of arousal of the Brazilian opossum. The ontogenic timing of CCK immunoreactivity in specific circuitry also indicates that CCK expression does not occur simultaneously throughout the brain. This pattern of CCK onset may relate to the temporal need for CCK in specific circuits of the central nervous system (CNS) during development.

Ontogeny of cells containing estrogen receptor-like immunoreactivity in the Brazilian opossum brain

In this study, we have used the Brazilian short-tailed opossum ( Monodelphis domestica) as a model to study the ontogeny of estrogen receptors in the mammalian brain. Monodelphis is a small, pouchless marsupial which breeds well under laboratory conditions and whose young are born in an immature sexually undifferentiated state. The Abbott H222 monoclonal rat estrogen receptor antibody (gift of Abbott Laboratories) was utilized in an indirect immunohistochemical procedure to detect estrogen receptors in developing opossum brains. Estrogen receptors were first expressed in the dorsomedial and ventromedial hypothalamus of the opossum 10 days after birth (10PN). Most regions that contained estrogen receptor-like immunoreactivity (ER LI) in the adult opossum contained ER LI at 15 PN. These areas include the lateral septum, medial preoptic area, bed nucleus of the stria terminalis, periventricular preoptic area and hypothalamus, amygdala, dorsomedial and ventromedial hypothalamic nuclei, arcuate nucleus, ventral premammillary nucleus, and the midbrain central grey. The number of cells that contain ER LI increased through 60PN in all regions that will contain ER LI in the adult opossum. These results indicate that 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.

Localization of cells containing estrogen receptor-like immunoreactivity in the Brazilian opossum brain

The Brazilian opossum ( Monodelphis domestica) is a small, pouchless marsupial whose young are born in an immature, sexually undifferentiated state. Etgen and Fadem 10, and Handa and coworkers 13 have biochemically detected and characterized estrogen receptors in the forebrain of the Brazilian opossum. In this study, we have examine the distribution of estrogen receptor-like immunoreactive (ER-LI) cells in the brains of gonadectomized male and female Brazilian opossums using Abbott H222 rat monoclonal estrogen receptor antibody (H222 is a gift of Abbott Labs). An indirect immunohistochemical procedure employing the Vectastain Elite system and a nickel-enhanced DAB chromogen was used. A large number of ER-LI cell nuclei were observed in the medial preoptic area, ventral septal nucleus, medial division of the bed nucleus of the stria terminalis, lateral part of the ventromedial hypothalamus, premammillary nucleus, arcuate nucleus, posterior amygdaloid nucleus, and the midbrain central grey. Lower numbers of ER-LI cell nuclei were observed in the intermediate subdivision of the lateral sepatal nucleus, and in the anterior, medial, and posterior cortical amygdloid nuclei. The anatomical distribution of ER-LI in the Brazilian opossum brain is similar to that which has been reported for estrogen binding sites following biochemical analysis. Based on these findings, we believe specific regions of the Brazilian opossum brain may serve as substrata for the action of estrogen in the adult. In addition, these results are supportive of the use of this animal model to investigate the organizational effects of estrogen on the developing central nervous system.

Coesxistence of corticotropin releasing factor and enkephalin in cerebellar afferent systems

In this study, we tested the hypothesis that corticotropin-releasing factor (CRF) and enkephalin (ENK) coexist within restricted brainstem-cerebellar circuits. Antisera for CRF and ENK were applied simultaneously or to serial sections of adult opossum brain and were processed for fluorescence or peroxidase, antiperoxidase immunohistochemistry, respectively. CRF and ENK were colocalized in 1) climbing fibers within the flocculus and in bilateral foci in the cerebellar vermis; 2) fibers with morphological characteristics of simple mossy fiber terminals or climbing fiber glomeruli that were located within the granule cell layer of the vermis underlying the foci of CRF/ENK-IR climbing fibers; 3) mossy fiber terminals within the flocculus; 4) neuronal perikarya in subnucleus A and C of the medial accessory olive and in the dorsal cap of Kooy, nuclei known to project as climbing fibers; and 5) cell bodies in nucleus prepositus, the subtrigeminal reticular nucleus, and the reticular formation, likely origins of CRF/ENK colocalized mossy fibers. The demonstration that single climbing and mossy fibers contain two peptides extends previous studies that have described chemical heterogeneity within cerebellar afferent pathways. Furthermore, these results support suggestions that this heterogeneity may provide a substrate for differential regulation of signal transduction by chemically coded cerebellar afferents.

External morphology of pouch young opossum brains: a profile of opossum neurogenesis.

AbstractAn outline of opossum brain development was prepared by studying the external morphology of 27 pouch young opossum brains which were from one to 81 postnatal days old. Opossum brain development goes through three morphologically defined periods. (1) An embryonic period extends from conception to the third postnatal day. The brain is not much more than a neural tube at birth, but by the third day it has undergone a longitudinal compression which gives it the shape of an adult brain. (2) A period of regional differentiation extends from the fourth day to about the sixtieth day. All of the grossly visible adult brain structures sequentially appear within each brain region during this period. For example, the rhinal and orbital fissures appear on the dorsolateral cerebral hemispheres at about day 30; the di‐telencephalic fissures appear on the ventral brain surface at about the fifth day; the olfactory tubercles begin to appear by the eighth day; the hypothalamus attains its adult proportions by about the fifth day, but does not differentiate into its adult components until after the thirtieth day; the cerebellum has all of its adult components by the fortieth day. (3) A period of maturation extends from about the sixtieth day to weaning. Minor finishing changes take place in some brain structures during this period. For example, the trapezoid body is more clearly demarcated and the parafloccular lobes of the cerebellum become more prominent.

ELECTRON MICROSCOPIC STUDY OF THE CEREBRAL BLOOD VESSELS OF THE OPOSSUM.

Blood vessels of the opossum brain are paired, artery and vein, and end in a closed loop. Both anatomically and physiologically they are true end-arteries. The two limbs are enclosed within a single basement membrane and are separated from each other by an intercapillary cell thought to be analogous to the usual capillary pericytes. The similarity of this vascular arrangement to that in the rabbit placenta and in the medulla of the kidney is discussed in relation to the counter-current multiplier system.

The unusual mode of development of the blood vessels of the opossum's brain

The unusual mode of development of the blood vessels of the opossum's brain

The regeneration of end‐arteries in the opossum brain

The regeneration of end‐arteries in the opossum brain