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PubMed1993

Intrinsic factor-cobalamin receptor activity in a marsupial, the American opossum (Didelphis virginiana).

1. Significant and specific binding of intrinsic factor-cobalamin occurred in proximal but not in the distal half of the intestine in an adult marsupial, the American opossum. 2. The purified opossum kidney receptor, like rat and canine kidney receptors, revealed a single band of M(r) approximately 230 on SDS-PAGE. However, unlike the rat and canine receptors, the opossum receptor was sensitive to both Endoglycosidase H and peptide-N-glycosidase F. 3. The opossum intrinsic factor-cobalamin receptor demonstrated a ten-fold higher affinity for intrinsic factor-cobalamin complex when the source of IF was from the opossum pancreas, rather than rat stomach. 4. The opossum kidney receptor had low immune-crossreactivity with anti-serum raised to rat and canine kidney receptor. 5. These studies suggest that intrinsic factor-cobalamin receptor expressed in the American opossum, though conserved, appears to be structurally different from the rat and canine receptors.

Animals↗

PubMed2003

Conspecific odor investigation by gray short-tailed opossums (Monodelphis domestica).

Gray short-tailed opossums (Monodelphis domestica) are small marsupials, which have recently become the subjects of numerous laboratory investigations. While these opossums have well-developed olfactory systems and complex scent-marking behaviors, the significance of their use of odors in conspecific communication is still poorly understood. Investigation of body odors by male and female opossums was examined in the present study. Males investigated flank and urine odors of nonestrous adult females significantly more than controls, but not urine from sexually inexperienced juvenile females or urine of females at cytological estrus. Since in this species females have an induced estrus, it would be advantageous for males to investigate and follow the odors of urine of diestrous females, which become receptive in proximity to males. Female opossums investigated odors of male mandibles and suprasternal glands significantly more than controls but not odors of male urine. We suggest that the use of glandular secretions is more common and more effective than urine for intraspecific communication between gray short-tailed opossums: In the semiarid conditions inhabited by the opossums, glandular secretions are less volatile and are effective for longer periods than urine and would be of greater value in intraspecific communication if, as suggested in the literature, these opossums are nomadic and meet one another infrequently.

Analysis of Variance↗

PubMed1999

Patterns of infestation by adult Dermacentor variabilis (Acari: Ixodidae) in a mark-recapture study of raccoons (Mammalia: Carnivora) and Virginia opossums (Mammalia: Didelphimorphia) in Tennessee.

A mark-recapture study of raccoons (Procyon lotor L.) and Virginia opossums (Didelphis virginiana Kerr) was conducted from February 1991 through April 1994 to determine host interactions with adult Dermacentor variabilis Say. We captured 1,293 raccoons and Virginia opossums during the 3-yr study (140 individual raccoons and 160 individual Virginia opossums) with 1,895 adult D. variabilis collected. Raccoons had a significantly higher mean intensity and higher prevalence of adult ticks than Virginia opossums (Mann-Whitney Z = 6.15, chi 2 = 51.9, P < 0.001). Mean intensity follows Margolis et al. (1982) as being the mean number of parasite species per infected host. Prevalence follows Margolis et al. (1982) as being the number of individuals of the host species infected with a parasite species divided by the number of hosts examined. The time required for a higher prevalence and mean intensity of ticks to occur on raccoons than Virginia opossums was < 7 d. No significant differences occurred between the mean intensity or prevalence of D. variabilis between sexes or among age classes of raccoons. Significant differences in prevalence and mean intensity of ticks occurred between sexes and among age classes of Virginia opposums. Infestation increased by 0.64 ticks per day on Virginia opossums and 1.77/d on raccoons during the first 7 d. The base host finding rate (ticks per host per day) of adult D. variabilis on Virginia opossums was 0.064 and 0.053 on raccoons. Tick interactions with hosts are quantified and may reflect behavioral differences between sexes and among age groups intraspecifically, and host preferences of adult D. variabilis interspecifically.

Animals↗

PubMed1999

C-->U editing of apolipoprotein B mRNA in marsupials: identification and characterisation of APOBEC-1 from the American opossum Monodelphus domestica.

The C->U editing of RNA is widely found in plant and animal species. In mammals it is a discrete process confined to the editing of apolipoprotein B (apoB) mRNA in eutherians and the editing of the mitochondrial tRNA for glycine in marsupials. Here we have identified and characterised apoB mRNA editing in the American opossum Monodelphus domestica. The apoB mRNA editing site is highly conserved in the opossum and undergoes complete editing in the small intestine, but not in the liver or other tissues. Opossum APOBEC-1 cDNA was cloned, sequenced and expressed. The encoded protein is similar to APOBEC-1 of eutherians. Motifs previously identified as involved in zinc binding, RNA binding and catalysis, nuclear localisation and a C-terminal leucine-rich domain are all conserved. Opossum APOBEC-1 contains a seven amino acid C-terminal extension also found in humans and rabbits, but not present in rodents. The opossum APOBEC-1 gene has the same intron/exon organisation in the coding sequence as the eutherian gene. Northern blot and RT-PCR analyses and an editing assay indicate that no APOBEC-1 was expressed in the liver. Thus the far upstream promoter responsible for hepatic expression in rodents does not operate in the opossum. An APOBEC-1-like enzyme such as might be involved in C->U RNA editing of tRNA in marsupial mitochondria was not demonstrated. The activity of opossum APOBEC-1 in the presence of both chicken and rodent auxiliary editing proteins was comparable to that of other mammals. These studies extend the origins of APOBEC-1 back 170 000 000 years to marsupials and help bridge the gap in the origins of this RNA editing process between birds and eutherian mammals.

APOBEC-1 Deaminase↗

PubMed2000

Lumen-to-surface pH gradients in opossum and rabbit esophagi: role of submucosal glands.

The opossum esophagus, like that of humans, contains a network of submucosal glands with the capacity to secrete bicarbonate ions into the esophageal lumen. To evaluate the role of these glands in protecting the epithelial surface from acid insult, we measured the lumen-to-surface pH gradient in opossum esophagus at different luminal pH and compared it to that of rabbit esophagus, an organ devoid of submucosal glands. Sections of opossum and rabbit esophageal epithelium were mounted luminal side up in a modified Ussing chamber. pH-sensitive microelectrodes, positioned within 5 microm of the epithelial cell surface, were used to monitor surface pH during perfusion with solutions of different pH. At luminal pH 7. 5, the pH(s) of both opossum and rabbit were similar (pH(s) = 7.5). Lowering luminal pH from 7.5 to 3.5 in opossum decreased pH(s) to 4.2+/-0.16, a value significantly higher than pH of perfusate, whereas in rabbit this maneuver decreased pH(s) to 3.69+/-0.08, a value not significantly different from pH of perfusate. In opossum but not in rabbit, addition of carbachol to the serosal solution increased basal pH(s) to 7.8+/- 0.1 and significantly blunted the decline in pH(s) on perfusion with acidic Ringer solution (pH 3.5), with pH(s) falling to 5.6+/-0.45. The effect of carbachol on surface buffering was inhibited by prior treatment with atropine. Luminal acidification to pH 2.0 in opossum (as in rabbit) abolished the lumen-to-surface pH gradient even after addition of serosal carbachol. We conclude that the presence of submucosal glands in esophagus contributes through bicarbonate secretion to creation of a lumen-to-surface pH gradient. Although this gradient can be modulated by carbachol, its capacity to buffer (and therefore to protect) the epithelial surface against back-diffusing H(+) is limited and dissipated at pH 2.0.

Acids↗

PubMed1997

Autoradiographic localization of arginine vasopressin binding sites in the brain of adult and developing Brazilian opossums.

We are utilizing the Brazilian short-tailed opossum, Monodelphis domestica, to study the development of the vasopressinergic system. Earlier studies demonstrated that arginine vasopressin-like immunoreactivity was present very early in the Brazilian opossum brain, suggesting a role for vasopressin in the developing central nervous system of mammals. In this study, we have utilized [3H]arginine vasopressin autoradiography to describe the distribution of arginine vasopressin binding sites in adult and developing Brazilian opossum brains. In general, arginine vasopressin binding patterns in adult opossum brains resembled those of other species. However, we found very few labelled areas in neonatal Brazilian opossum brains. At birth, only the ventral tegmental area and the nucleus of the solitary tract were labelled. Binding was not evident in the forebrain until 25 days of postnatal age. The anterior pituitary was heavily labelled from birth onward, but binding in the brain itself remained at low levels until 35 days postnatal. Heavy binding was observed in only a few areas of the brain in adults, including the dorsal part of the lateral septal nucleus, the suprachiasmatic nucleus, the dorsal and median raphe, the nucleus of the solitary tract, and the caudal part of the spinal trigeminal nucleus. Surprisingly, arginine vasopressin binding sites in the Brazilian opossum appeared much later than arginine vasopressin immunoreactivity and, in many cases, after neurogenesis was complete. These findings suggest that the arginine vasopressin binding sites are not playing a developmental role in opossums, although the peptide is present at an early age.

Age Factors↗

PubMed2006

Lack of Sarcocystis neurona antibody response in Virginia opossums (Didelphis virginiana) fed Sarcocystis neurona-infected muscle tissue.

Serum was collected from laboratory-reared Virginia opossums (Didelphis virginiana) to determine whether experimentally infected opossums shedding Sarcocystis neurona sporocysts develop serum antibodies to S. neurona merozoite antigens. Three opossums were fed muscles from nine-banded armadillos (Dasypus novemcinctus), and 5 were fed muscles from striped skunks (Mephitis mephitis). Serum was also collected from 26 automobile-killed opossums to determine whether antibodies to S. neurona were present in these opossums. Serum was analyzed using the S. neurona direct agglutination test (SAT). The SAT was modified for use with a filter paper collection system. Antibodies to S. neurona were not detected in any of the serum samples from opossums, indicating that infection in the opossum is localized in the small intestine. Antibodies to S. neurona were detected in filter-paper-processed serum samples from 2 armadillos naturally infected with S. neurona.

Agglutination Tests↗

PubMed2001

Probability of Trypanosoma cruzi transmission by Triatoma infestans (Hemiptera: Reduviidae) to the opossum Didelphis albiventris (Marsupialia: Didelphidae).

The probability of Trypanosoma cruzi transmission to opossums by independent events of predation and fecal contamination during feeding ("biting") with positive Triatoma infestans was estimated. Negative female opossums were challenged for 23 hr with 10 infected third and fourth instars of T. infestans, and tests for positivity for T. cruzi by xenodiagnosis were performed at 30, 60, and 90 days. From these data, seven probability parameters were estimated by maximum likelihood, and likelihood ratio statistics confidence intervals were calculated. Simultaneous estimation of p1 (probability that a "bite" will infect an opossum), p3 (probability that a bug that has been eaten by an opossum will infect it), and p6 (probability that the opossum will become infected if faced with an infected triatomine), resulted in p1 = 0.06, p3 = 0.075, and p6 = 0.059. On average, each opossum should be exposed to an average of 700 encounters with bugs during its life, resulting in about eight potentially infective contacts, to produce the 35% opossum prevalence found in the field.

Animals↗

PubMed2000

Spontaneous behavior of the gray short-tailed opossum (Monodelphis domestica) in the elevated plus-maze: comparison with Long-Evans rats.

We observed the spontaneous behavior of a laboratory marsupial--the gray short-tailed opossum (Monodelphis domestica)--in the elevated plus-maze (EPM) during six consecutive sessions and compared it with the behavior of Long-Evans rats. During the first exposure to the maze both species spent most of the time in the enclosed arms but opossums showed much higher frequency of entries into the open arms and stayed there longer. On the third and subsequent days opossums reduced their entries into the open arms and spent more time on the central square, where unlike rats they frequently groomed their lower belly and hind legs. During the last sessions they started spending more time in the enclosed arms. It is concluded that probably opossums, like rats show a stable anxiety evoked by open space. However, in the rat anxiety prevails over motivation to explore a new environment, while in the opossum it is initially at equilibrium with curiosity which habituates slower than in the rat. Results are discussed in the context of different ecology of the gray opossum that actively searches and hunts quickly moving insects. Thigmotaxic behavior, while strong in both species, dominates spontaneous behavior of the rat, but not opossum.

Animals↗

PubMed1992

Serologic response of the opossum Didelphis virginiana to a temperature-sensitive mutant (ts-4) of Toxoplasma gondii.

A study was designed to measure the Toxoplasma gondii-specific IgM and IgG antibody responses of opossums inoculated with tachyzoites of the temperature-sensitive mutant of T. gondii, ts-4, and to examine its persistence in the tissues. Four young opossums seronegative for anti-Toxoplasma gondii IgM and IgG antibodies immediately after capture and 4 wk later were injected subcutaneously with 1.8 x 10(6) ts-4 tachyzoites; a fifth opossum (also seronegative) received an injection of saline only. Serum was collected weekly and titered by modified direct agglutination for anti-Toxoplasma gondii IgM and IgG. IgM titers were detectable from week 1 to week 6 postinoculation (PI). IgG was measurable by week 3 and remained high for 30 wk PI when the opossums were killed and examined. The control opossum did not develop a specific antibody response. At necropsy major lesions were not found. No anti-Toxoplasma gondii IgG was detected in serum collected from mice injected with tissues prepared from the opossums at necropsy, and no T. gondii was found on impression smears made at necropsy from these mice. Modified direct agglutination performed with or without 0.2 M 2-mercaptoethanol worked well for measuring specific IgM and IgG antibodies in experimentally infected opossums.

Agglutination Tests↗

PubMed1991

The lesions and prevalence of Trypanosoma cruzi in opossums and armadillos from southern Louisiana.

The prevalence of Trypanosoma cruzi in 48 opossums and 98 armadillos from southern Louisiana was studied. Sixteen opossums (33.3%) and 1 armadillo (1.1%) were positive for T. cruzi by blood culture. Hearts from 45 opossums and the tissues from the 1 blood culture-positive armadillo were available for histopathological examination. Although histopathology revealed T. cruzi pseudocysts in 6 opossums, 2 were not positive on blood culture. Therefore, 18 opossums (37.5%) were positive for T. cruzi. Twenty-two of 45 opossums had histological evidence of myocarditis. No lesion typical of infection with T. cruzi was observed in the armadillo tissues. These results substantiate that the opossum is a current reservoir host of T. cruzi infection in southern Louisiana and that armadillos may be of relatively minor importance.

Animals↗

PubMed1978

The opossum (Didelphis virginiana) as a host for Sarcocystis debonei from cowbirds (Molothrus ater) and grackles (Cassidix mexicanus, Quiscalus quiscula).

Sarcocystis-infected muscles from ducks, cowbirds, and grackles were fed to cats, opossums, rats, and a dog. Only the opossum (Didelphis virginiana) was a suitable definitive host. All opossums that were fed Sarcocystis-infected cowbirds (Molothrus ater) and grackles (Cassidix mexicanus and Quiscalus quiscula) passed sporocysts in their feces. Opossums that ate the cowbirds had prepatent periods of 5 and 10 days and remained patent for at least 105 days. Opossums that ate the grackles became patent on day 10 after the infective meal and remained patent for over 90 (Quiscalus) and 105 (Cassidix) days. A single opossum fed infected muscle from a pintail duck (Anas acuta) passed sporocysts in the feces from days 13 through 18 after infection. No sporocysts were passed by opossums fed infected muscle from the green-winged teal (Anas carolinensis) and shoveller (Spatula clypeata). Sporocysts of duck, cowbird, and grackle origin were structurally similar. Mean dimensions of sporocysts were: duck-origin, 11.2 by 8.2 micron; cowbird-origin, 11.4 by 7.8 micron; Cassidix-origin, 11.2 by 7.8 micron; and Quiscalus-origin, 11.6 by 7.7 micron. We designate the sporocysts of cowbird and grackle origin as Sarcoycstis debonei Vogelsang, 1929 (Syn. Isospora boughtoni Volk, 1938).

Animals↗

PubMed1998

Isolation of a third species of Sarcocystis in immunodeficient mice fed feces from opossums (Didelphis virginiana) and its differentiation from Sarcocystis falcatula and Sarcocystis neurona.

Opossums (Didelphis virginiana) were found to be hosts for 3 species of Sarcocystis: Sarcocystis falcatula with an avian intermediate host, S. neurona with an undetermined intermediate host, and a third, unnamed, species. Sporocysts from the intestines of 2 opossums (nos. 26 and 47) were fed to budgerigars (Melopsittacus undulatus), nude mice, and gamma-interferon knockout (KO) mice. Sporocysts of S. falcatula were not infective to nude or KO mice. Sporocysts of S. neurona induced encephalitis in KO and nude mice; only schizonts and merozoites were found in tissues of mice, and they reacted with anti-S. neurona serum raised against the SN-2 isolate of S. neurona originally obtained from tissues of a paralyzed horse. All 3 species of Sarcocystis were present in opossum no. 47. Sarcocystis neurona was isolated in cell culture from this opossum. Sporocysts from opossum no. 47 were lethal to budgerigars, indicating S. falcatula infection. Only 1 species of Sarcocystis (the third species) was found in opossum no. 26; the sporocysts were infective to KO and nude mice. Schizonts and merozoites of this species were predominantly in the liver but were also found in other tissues; schizonts did not react with anti-S. neurona serum. Merozoites of the third species were ultrastructurally distinct from S. falcatula and S. neurona merozoites. Sarcocysts were found in leg muscles of 2 mice killed 50 and 54 days after they were fed sporocysts from opossum no. 26. These sarcocysts had steeple-shaped protrusions on the cyst wall and were distinct from sarcocysts of S. falcatula and any other species of Sarcocystis.

Animals↗

PubMed1984

The distribution of glutamic acid decarboxylase immunoreactivity in the diencephalon of the opossum and rabbit.

We have examined the distribution of neurons and terminals immunoreactive for glutamic acid decarboxylase (GAD) in the thalamus and adjacent structures of the opossum (Didelphis virginiana) and the rabbit and have compared this distribution with the distributions we described previously for the cat and bushbaby (Galago senegalensis). The significance of these experiments depends, first, on the fact that GAD is the synthetic enzyme for GABA, and therefore that GAD immunoreactivity is a marker for GABAergic inhibitory neurons, and second, on previous findings that suggest that GABAergic neurons in the dorsal thalamus are local circuit neurons. In both cat and Galago, GAD-immunoreactive neurons are distributed essentially throughout the entire thalamus. In the opossum, GAD neurons are chiefly confined to the dorsal lateral geniculate nucleus and the lateral extremity of the lateral posterior nucleus. The distribution of GAD neurons in the rabbit is intermediate between that found in the opossum on the one hand and cat and Galago on the other. Like opossum, about 25% of the neurons in the lateral geniculate nucleus of rabbit are GAD immunoreactive. Unlike opossum, however, as many as 18% of the cells in the ventral posterior nucleus of the rabbit are GAD immunoreactive, and scattered cells are also labeled in other thalamic areas, such as the medial geniculate and the lateral group. Aside from the findings in the dorsal thalamus, the chief observation is that GAD-immunoreactive neurons and/or terminals densely fill all principal targets of the optic tract, including the ventral lateral geniculate nucleus; the superficial gray layer of the superior colliculus; the anterior, posterior, and olivary pretectal nuclei; the nucleus of the optic tract; and the medial and lateral terminal nuclei of the accessory optic tract. These results support the idea first put forward by Cajal that local circuit neurons increase in number during the course of the evolution of complex mammalian brains. If we can assume that the conservative opossum retains characteristics reflecting an early stage of mammalian evolution, the results suggest that thalamic local circuit neurons arose first in the visual system and only later in evolution spread throughout the thalamus.

Animals↗

PubMed1985

Extent and organization of opossum prefrontal cortex defined by anterograde and retrograde transport methods.

Prefrontal cortex is commonly defined as cortex which receives afferents from the thalamic mediodorsal nucleus (MD). The extent of opossum prefrontal cortex was mapped with anterograde and retrograde axonal transport methods. The prefrontal field was found to include not only cortex on the lateral convexity of the frontal lobe as reported in earlier studies, but, in addition, cortex within the rhinal fissure and cortex on the rostral medial wall of the hemisphere. The organization of the thalamic input to the medial wall was analyzed in some detail and compared with that of the rat. The reason for this emphasis stemmed from earlier observations which suggested that a lateral, nonolfactory segment of MD, prominent in the rat and other species, may not be present in opossum MD. In the rat, the lateral segment, which constitutes approximately one-third of MD, projects to a relatively large expanse of rostral medial cortex which is also projected upon by the anteromedial nucleus. The main projection field of the lateral one-third of opossum MD is to cortex on the lateral convexity of the frontal lobe which has no input from the anteromedial nucleus and has no counterpart in the rat. Only the most lateral edge of opossum MD projects to medial cortex, to a very small field, which is also projected upon by the anteromedial nucleus. In other respects, the organization of the rostral medial cortex is similar in rat and opossum. These results suggest that, rather than being absent, an equivalent of a nonolfactory segment may be present in opossum MD but is markedly reduced in size, compared to that in rat and other species.

Animals↗

PubMed1985

Origin of interhemispheric fibers in acallosal opossum (with a comparison to callosal origins in rat).

The neocortical origins of the anterior commissure in the acallosal, marsupial opossum were studied with the horseradish peroxidase (HRP) method. Following complete surgical transection of the anterior commissure, HRP was applied directly to the cut fiber tips. This procedure resulted in very large numbers of vividly labeled cells within the neocortex. The labeled cells were plotted and counted for comparison among cytoarchitectonic areas and among cortical layers. For comparative purposes, the neocortical origins of the corpus callosum are studied with the same procedure in the rat. No cytoarchitectonic area was entirely devoid of labeled cells in either species. The concentration of labeled cells throughout the entire neocortex averaged 25.2 cells/0.05 mm3 in opossum and 31.2 cells/0.05 mm3 in rat. The concentrations of labeled cells were correlated for the eight cytoarchitectonic areas common to the two species, though they were different enough in number to be statistically reliable. The distribution of labeled cells both among and within cytoarchitectonic areas was often more homogeneous in opossum than in rat. Although cortical layer 1 had no labeled cells in either species, the distribution of labeled cells across the remaining cortical layers differed sharply between the two species. In opossum, layer 3 had the most labeled cells (averaging 55% of the total number) while layer 5 had considerably less (averaging 12%). In rat, layer 5 had as many labeled cells as layer 3--both layers averaging 43% of the total number of labeled cells. In both species, striate cortex deviated markedly from other cytoarchitectonic areas. Although both species had very few labeled cells in striate cortex, those that were labeled were invariably supragranular in opossum and infragranular in rat. The similarities and dissimilarities in the topographic distribution of the origins of the two types of interhemispheric fiber systems seem to parallel the degree of cortical (and thalamic) differentiation in the two animals. However, the differences in laminar distribution are much greater and in particular, the small contribution of layer 5 in opossum as opposed to rat may well be functionally significant.

Animals↗

PubMed1995

Ligation-induced acute pancreatitis in opossums: acinar cell necrosis in the absence of colocalization.

Acute necrotizing pancreatitis in opossums after bile and pancreatic duct ligation (BPDL) is a useful experimental corollary of gallstone-induced acute pancreatitis in humans. In experimental and human acute pancreatitis, a loss of segregation of the lysosomal enzyme cathepsin B and the zymogen proenzyme trypsinogen (colocalization) is implicated as the triggering event of disease pathogenesis, as cathepsin B can activate trypsinogen. The object of this study was to quantitate acinar cell necrosis and to study subcellular distribution of cathepsin B in BPDL-induced acute necrotizing pancreatitis in opossums. Bile and pancreatic ducts were ligated separately (no bile reflux) in four opossums while ducts were dissected in four sham controls. Opossums were killed 24 hr after operation. Three equidistant cross-sectional portions of each opossum pancreas were submitted to histologic examination. In blinded fashion, each focus of acinar cell necrosis was photographed and quantitated with digitizing morphometry. Numerical density (foci/cm2) and areal density (x10(3) micron 2/cm2) of focal acinar cell necrosis were determined. Differentially centrifuged pancreatic homogenates were assayed for cathepsin B, the lysosomal marker enzyme N-acetylglucosaminidase, and amylase. Morphometric quantitation of acinar cell necrosis confirmed development of acute necrotizing pancreatitis after 24 hr of BPDL in opossums. However, colocalization was not observed after BPDL, as evidenced by an absence of subcellular shift of cathepsin B activity (and N-acetyl-glucosaminidase activity) from the lysosome-enriched to the zymogen-enriched subcellular fraction. Amylase activity was increased in subcellular fractions after BPDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗

PubMed1983

The formation and growth of the cortical layers in the cerebellum of the opossum.

The development of the cerebellar cortex in the opossum was analyzed in Nissl-stained sections using qualitative and quantitative methods. The young of the opossum are born 12-13 days after conception and mature for approximately 85 days in an external pouch providing an excellent model for embryological studies. Qualitative observations of cerebellar growth were made from birth to postnatal day (PN) 19. At birth the opossum cerebellar anlage can be divided into two layers, a ventricular layer and an intermediate layer; histologically his is comparable to the rat cerebellar anlage at embryonic day 13 (Altman and Bayer 1978) and the human cerebellar anlage prior to the seventh embryonic week (Rakic and Sidman 1970). By PN 3 the cerebellar anlage consists of five layers: the ventricular layer, the ventral intermediate layer, the acellular layer, the dorsal intermediate layer and the marginal layer. The external granular layer begins migrating over the dorsal surface of the cerebellum at PN 5. The immature Purkinje cell layer is first seen at PN 12 and is subsequently arranged as four clusters between PN 12 and PN 22. At PN 19 the opossum cerebellum is comparable to the rat cerebellum at birth (Korneliussen 1968c). A quantitative analysis of cerebellar growth was performed between PN 17 and PN 77 using vermal sections. The area and thickness of each of the cortical layers was determined from five vermal sagittal sections using two methods; a Zeiss Videoplan and a point counting system. The external granular layer increases in area from PN 17 to PN 75, however its maximal width is achieved between PN 19 and PN 33. The persistence of the EGL until after PN 105 suggests that synaptic contacts between granule cell axons and Purkinje cells may continue to form after PN 77 when the Purkinje cell is mature based on Golgi and fine structural features (Laxson and King 1983). Between PN 17 and PN 77 the area of the molecular layer and the area of the internal granular layer increase at a more rapid rate than the other cerebellar layers. The maturation of the cerebellum in the opossum is a lengthy process lasting approximately 77 days in comparison to rodent cerebellar growth which requires about 25 days (Korneliussen 1968c). Also, the entire process of cortical lamination occurs after birth while the opossum is maturing in an external pouch.

Animals↗