Regulation of Na+/H+ exchange in opossum kidney cells by parathyroid hormone, cyclic AMP and phorbol esters

Parathyroid hormone (PTH) controls two proximal tubular brush border membrane transport systems, Na+/phosphate co-transport and Na+/H+ exchange. In OK cells, a cell line with proximal tubular transport characteristics, PTH acts via kinase C and kinase A activation to inhibit Na+/phosphate co-transport [6, 8, 9, 19, 22]. In the present study, we show that PTH inhibits Na+/H+ exchange and that this effect can be mimicked by pharmacological activation of kinase A and kinase C. Ionomycin-dependent increases in cytoplasmic Ca2+ concentration do not induce inhibition of Na+/H+ exchange; PTH-dependent inhibition of Na+/H+ exchange is not prevented by ionomycin or by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (Ca2+ clamping). Detailed dose-response curves for the different agonists, given either alone or in combination, suggest that the two regulatory cascades (kinase A and kinase C) are operating independent of each other and reach a common final target, resulting in 40-50% inhibition of Na+/H+ exchange. An analysis of intracellular pH sensitivity of Na+/H+ exchange suggests that inhibition is not related to a shift in set point, but is rather explained by a reduced Vmax of Na+/H+ exchange and/or reduced affinity for protons at the internal membrane surface. It is suggested that kinase A as well as kinase C can mediate PTH inhibition of renal proximal tubular Na+/H+ exchange and that the relative importance of a particular regulatory cascade is determined by the PTH-concentration-dependent rates in the liberation of diacylglycerol (phospholipase C/kinase C) and cAMP (adenylate cyclase/kinase A).

Studies on the energy metabolism of opossum (Didelphis virginiana) erythrocytes--VI. De novo purine nucleotide biosynthesis is limited to the final steps of the pathway in vitro

1. High pressure liquid radiochromatography was used to show the incorporation of [14C] formate with Z-compounds into ATP and GTP in opossum erythrocytes. 2. The use of Z-riboside with [14C] formate resulted in more extensive labeling of ATP than the Z-base/[14C] formate combination as substrates for nucleotide biosynthesis. 3. Substantial accumulation of ZMP and ZTP, but no ZDP was detected in the chromatograms. 4. ATP was unstable in red cells metabolizing in the presence of Z-compounds under an atmosphere of air as gas phase in these experiments.

Ion channels in opossum kidney cells

This review discusses the activation of ion transport pathways during regulatory volume decrease in opossum kidney (OK) cells. OK cells regulate their volume when exposed to a hypotonic medium. The changes in cell volume are caused by activation of ion transport pathways and the accompanying osmotically driven water movement so that the increased cell volume returns toward physiological levels. The reshrinking of hypotonically swollen cells is termed regulatory volume decrease. In OK cells separate K+ and Cl- conductances are activated. The Na+/H+ cotransport system seems not to be involved. The potassium pathway is mediated by a K+ channel with a slope conductance of about 12 pS. The occasionally observed widely distributed Ca2(+)- and voltage-dependent K+ channel of large unit conductance (120 pS) seems not to be involved. The volume regulatory decrease is accompanied by a cell depolarization from a resting potential of about -60 mV to about -20 mV followed by a repolarization. It will be discussed whether the depolarization is caused by the observed activation of stretch-sensitive ion channels of about 30 and 40 pS, respectively. The transient behavior of the cell volume parallels the time-dependent change of the total membrane current. For both recording techniques the volume regulatory decrease can be blocked by quinine. In addition an inward rectifying K+ channel of about 80 pS has been observed in high KCl solution.

Ontogeny of estrogen binding sites in the brain of gray short-tailed opossums (Monodelphis domestica)

This study evaluated the binding of [3H]estradiol to brain cytosols from gray short-tailed opossums ranging in age from newborn to 63 days postnatal. Estrogen binding was undetectable in whole-brain cytosol of newborn opossums. By postnatal day 4, high affinity (Kd = 0.2 nM), saturable (Bmax = 3 fmol/mg protein) estrogen binding sites were present, and estrogen binding in whole-brain remained low but detectable (2-5 fmol/mg) through day 63. In contrast, estrogen binding sites in the hypothalamus-preoptic area increased substantially from 3.4 fmol/mg on day 16 to 14 fmol/mg by day 63.

Ontogenesis of enkephalinergic afferent systems in the opossum cerebellum

Enkephalin (ENK) immunoreactive climbing fibers, mossy fibers and a beaded plexus of axons are present in the adult opossum's cerebellar cortex. We have used the indirect antibody peroxidase-antiperoxidase technique to study the ontogeny of enkephalinergic axons in the cerebellum of pouch young opossums from postnatal day (PD) 1 to PD 83. On PD 1, ENK axons are present in the intermediate layer of the cerebellar anlage. At PD 18, after a period of 'waiting', ENK fibers form clusters throughout the cerebellar cortex primarily within the nascent Purkinje cell layer. By PD 40, axon terminals with a climbing fiber phenotype circumscribe Purkinje cells; immature mossy fiber rosettes are present within the internal granule cell layer. A third axon phenotype, beaded ENK fibers can be distinguished on PD 68. Between PD 40 and PD 68, the distributions of ENK climbing and mossy fibers overlap in vermal lobules II-VIII and X, whereas in the hemispheres climbing fibers predominate. However, by PD 83, ENK positive climbing fibers are no longer evident in lateral folia. These results indicate that early arriving ENK axons are present before the differentiation of their cellular targets. Further, a transient appearance of ENK in discrete populations of developing climbing fibers suggests several developmental events: (1) cell death in the inferior olive, (2) collateral regression, or (3) a transient expression of this peptide, that may be characteristic of this chemically defined system of axons.

Distribution of immunoreactive substance P in opossum esophagus

We localized immunoreactive substance P and measured its content throughout the opossum esophagus. Substance P-like immunoreactive nerve fibers were more abundant in muscularis mucosae than in the longitudinal smooth muscle layer and more abundant in the latter than in the circular smooth muscle layer. The distribution of substance P-like immunoreactive nerve fibers in the circular muscle layer of the esophagogastric junction was comparable to that of the esophageal body. Immunoreactive fibers were also found on and in arteries, submucosal glands, and epithelium, but none were seen in striated muscle. Both the myenteric and submucous plexuses contained substance P-like immunoreactive nerve cell bodies and processes. In the muscularis propria, the content of substance P-like immunoreactive peptide (pg/mg protein, means +/- 1 SE) in the smooth muscle region of the esophageal body (5.9 +/- 0.6) exceeded that in the striated muscle region (2.5 +/- 0.2) and at the esophagogastric junction (1.8 +/- 0.5), but the latter two values were similar (P less than 0.05). Mucosal content of substance P in the region of the esophagogastric junction (1.2 +/- 0.1) differed from that of the smooth muscle region of the esophageal body (9.2 +/- 2.6) but not (P greater than 0.05) from that of the striated-muscle region (5.9 +/- 1.0). The broad distribution and diversity of immunoreactive structures suggest that substance P may have both sensory and motor functions in the esophagus.

Flow cytometric analysis of intracellular pH in cultured opossum kidney (OK) cells

Suspensions of OK cells (a continuous renal epithelial cell line originating from the opossum kidney) were examined by flow cytometry. Three parameters were evaluated simultaneously; cell integrity as assayed by propidium iodide fluorescence, cell size as measured by time-of-flight, and intracellular pH as measured by fluorescence of 2',7'-bis-(2-carboxyethyl)-5,6 carboxyfluorescein (BCECF). The suspension was shown to be composed of both intact singlets and doublets of cells, and no difference was noted in the behavior of these two populations with respect to the resting intracellular pH, or of the response of intracellular BCECF to changes in pH. Evidence suggests that using NH4 prepulses to create an acid load broadens the intracellular pH distribution. The population of OK cells demonstrates a recovery from this acid load which is very homogeneous with respect to its sensitivity to Na+ removal of EIPA (ethylisopropyl-amiloride), suggesting that virtually all cells utilize Na+/H+ exchange for this recovery. The data also suggest heterogeneity in the cellular pH recovery from an acid load with respect to the observed rates of Na+/H+ exchange. Despite this heterogeneity, the Na+/H+ exchanger is observed to focus the resting intracellular pH of the population to approximately pH 7.4-7.5. The response of the population to PTH suggests that the majority of cells respond to the hormone, and that the total Na+/H+ exchange in individual cells is only partially inhibited even in the presence of saturating PTH concentrations.

Reciprocal effects of Ca2+ and Mg-ATP on the 'run-down' of the K+ channels in opossum kidney cells

Using the patch clamp technique, we identified an inwardly rectifying K+ channel in the membrane of opossum kidney cells. The single channel conductance was about 90 pS for inward currents and 30 pS for outward currents under a symmetrical high-K+ condition. The activity of the channel was found to decrease with time during recording from inside-out patches. In the solution with submicromolar Ca2+, the activity disappeared within 4-20 min. Intracellular Ca2+ promoted the run-down of the channel activity at 0.1-1 mM, whereas millimolar Mg-ATP restored the activity after run-down. The run-down channels could never be reactivated by ATP in the absence of Mg2+, or by a nonhydrolyzable ATP analog, AMPPNP, even in the presence of Mg2+.

Opossum kidney contains a functional receptor for the Escherichia coli heat-stable enterotoxin

The Escherichia coli heat-stable enterotoxin (ST1 or STa) binds to specific receptors on mammalian intestinal brush border membranes, and stimulates guanylate cyclase in those membranes. We have found a similar signal transduction system in brush border membranes prepared from kidney cortex of the American opossum (Didelphis virginiana, and in a cell line (OK cell) derived from that tissue. Activation of guanylate cyclase by ST1 is therefore not limited to intestinal cells. Furthermore, since it is unlikely that ST1 which is produced in the intestinal lumen, would have access to kidney receptors, this suggests the existence of an endogenous peptide resembling ST1, at least in marsupials.

Distribution of corticotropin-releasing factor in the cerebellum and precerebellar nuclei of the opossum: a study utilizing immunohistochemistry, in situ hybridization histochemistry, and receptor autoradiography

This study reports 1) a nonhomogeneous distribution of three morphologically distinct, corticotropin-releasing factor (CRF)-immunoreactive axonal phenotypes within the cerebellum of the opossum: climbing fibers, mossy fibers, and beaded fibers within the ganglionic plexus; 2) the existence of CRF binding sites within the cerebellar cortex; and 3) the distribution of CRF-containing neurons in brainstem precerebellar nuclei identified with immunohistochemistry and in situ hybridization histochemistry. CRF-immunoreactive climbing and/or mossy fibers were identified within all cerebellar lobules. The density of CRF-immunoreactive fibers was greatest in the vermis, where longitudinal bands of intensely immunoreactive climbing and mossy fibers were interspersed with regions containing fibers demonstrating lower levels of immunolabeling. CRF-immunoreactive fibers were present within all deep cerebellar nuclei. The topography of CRF-containing cerebellar fibers is discussed with respect to possible sites of origin within the brainstem. CRF-immunoreactive neurons were identified in all nuclei of the inferior olivary complex, although the number and intensity of immunostaining of CRF-containing cells varied within and among individual nuclei. CRF-immunoreactive somata were also present in brainstem nuclei known to give rise to cerebellar mossy fibers. In situ hybridization histochemistry utilizing an 35S-labeled synthetic 48-base oligodeoxynucleotide complementary to amino acids 22-37 of rat CRF proper revealed that CRF mRNA is transcribed in precerebellar nuclei. Variation in the level of CRF mRNA was detected among inferior olivary nuclei, in correspondence with variations detected in the levels of immunostaining. Data from this study suggest that variation in the level of CRF immunoreactivity detected within cerebellar afferent fibers may correlate with the level of CRF mRNA within cell bodies of origin of the projections. In vitro receptor autoradiography, utilizing 125I-Tyro-ovine CRF, revealed correspondence between CRF binding sites and CRF-immunoreactive fibers in the cerebellar cortex. Results of this study support suggestions for CRF-mediated circuitry in the cerebellum.

Immunohistochemical study of the developing endocrine pancreas of the opossum (Didelphis virginiana)

Cells immunoreactive for insulin, glucagon, somatostatin, bovine pancreatic polypeptide and 5-hydroxytryptamine are found in the pancreas of the newborn opossum and of all later stages examined. All immunoreactive cell types are present in primary and secondary islets and within elements of the exocrine pancreas. Cells immunoreactive for glucagon, bovine pancreatic polypeptide, somatostatin and 5-hydroxytryptamine generally are confined to the periphery of secondary (intralobular) islets, whereas insulin-immunoreactive cells occupy the central region. Endocrine cells within primary (interlobular) islets are randomly scattered. A small number of pancreatic-polypeptide-immunoreactive cells are reactive for the amine 5-hydroxytryptamine also, but the reverse is not observed. The endocrine pancreas continues to differentiate and develop throughout postnatal life and into adulthood. Little difference was observed between the head and tail regions of the opossum pancreas for the measurements made.

Comparative biochemistry of hepatic arylsulfatases from north and south American opossums

1. The Virginia opossum (Didelphis virginiana) possessed an arylsulfatase which had a relative molecular weight of 130 +/- 12 kDa, displayed anomalous kinetics, hydrolysed AA2S, and exhibited other properties of arylsulfatase A. No arylsulfatase B was found. 2. The arylsulfatase present in the gray short-tailed opossum (Monodelphis domestica) had a relative molecular weight of 56 +/- 4 kDa, exhibited linear kinetics, was inhibited by chloride, and possessed other characteristics of arylsulfatase B. No arylsulfatase A was found. 3. Arylsulfatases from both species occurred as multiple isozymes which were unaffected by neuraminidase or alkaline phosphatase treatment.

Isolation, partial sequence and asynchronous appearance during lactation of lysozyme and alpha-lactalbumin in the milk of a marsupial, the common ringtail possum (Pseudocheirus peregrinus)

1. Lysozyme and alpha-lactalbumin from the milk of the common ringtail possum have been purified and partially sequenced. 2. The lysozyme had similar enzymic activity to the c-type lysozyme of the domestic hen and 43% homology over the N-terminal 49 residues. 3. alpha-Lactalbumin was present in the milk in two biologically active forms; the more acidic form had 66% sequence homology with the N-terminal 35 residues of red-necked wallaby, 54% with human and 43% with bovine alpha-lactalbumin. 4. SDS polyacrylamide-gel electrophoresis of milk samples showed that alpha-lactalbumin was present in the milk throughout lactation but that lysozyme first appeared only in mid-lactation. The implications of this functional adaptation are discussed.

Proteins in cerebrospinal fluid and plasma of postnatal Monodelphis domestica (grey short-tailed opossum)

1. The protein composition and concentrations of total protein in cerebrospinal fluid (CSF) and plasma of opossum (Monodelphis domestica) from birth until adulthood have been estimated. 2. Total protein in CSF increased from birth to a peak concentration between 5 and 10 days (500 mg/100 ml) after which it declined rapidly. 3. Total protein in plasma started at a low level at birth (below 400 mg/100 ml) and increased progressively to the adult value (8500 mg/100 ml). 4. Proteins identified in CSF and plasma were: albumin, alpha 1 antitrypsin, transferrin, alpha 2 macroglobulin, lipoproteins and immunoglobulin G. A fetal protein, probably alpha-fetoprotein, has been identified. 5. The only plasma proteins found within the brain, even in the very immature newborn of this species, appeared to have an intracellular rather than an extracellular distribution. This indicates that the blood-brain barrier is present very early in development and that there is also a CSF-brain barrier that appears to exclude CSF protein from brain extracellular space.

Control of parathyroid hormone-degrading activity in the opossum kidney cell: possible involvement of protein kinase C

To clarify the possible role of protein kinase C in the control of parathyroid hormone (PTH)-degrading activity (PTHDA) in a PTH-responsive opossum kidney (OK) cell line, we investigated the effects of protein kinase C activators, 12-O-tetradecanoyl phorbol 13-acetate (TPA), 1-oleoyl-2-acetyl-glycerol (OAG), and 4 beta-phorbol 12, 13-didecanoate (4 beta-PDD). TPA, OAG, and 4 beta-PDD enhanced PTHDA in a dose-dependent fashion (10-50 ng/ml, 10-100 microgram/ml, and 10-50 nM, respectively), whereas 4 alpha-PDD, a non-activator of protein kinase C, did not affect it. HPLC analysis of TPA-treated samples revealed increase of all immunoreactive PTH fragments produced by OK cells. These findings suggested that activation of protein kinase C in OK cells would augment PTHDA in the cells.

High performance liquid chromatographic analysis of insulin degradation products from a cultured kidney cell line

The kidney is a major site for insulin removal and degradation, but the subcellular processes and enzymes involved have not been established. We have examined this process by analyzing insulin degradation products by HPLC. Monoiodoinsulin specifically labeled on either the A14 or B26 tyrosine residue was incubated with a cultured kidney epithelial cell line, and both intracellular and extracellular products were examined on HPLC. The products were then compared with products of known structure generated by hepatocytes and the enzyme insulin protease. Intracellular and extracellular products were different, suggesting two different degradative pathways, as previously shown in liver. The extracellular degradation products eluted from HPLC both before and after sulfitolysis similarly with hepatocyte products and products generated by insulin protease. The intracellular products also eluted identically with hepatocyte products. Based on comparisons with identified products, the kidney cell generates two fragments from the A chain of intact insulin, one with a cleavage at A13-A14 and the other at A14-A15. The B chain of intact insulin is cleaved in a number of different sites, resulting in peptides that elute identically with B chain peptides cleaved at B9-B10, B13-B14, B16-B17, B24-B25, and B25-B26. These similarities with hepatocytes and insulin protease suggest that liver and kidney have similar mechanisms for insulin degradation and that insulin protease or a very similar enzyme is involved in both tissues.

Parathyroid hormone degradation by chymotrypsin-like endopeptidase in the opossum kidney cell

Cathepsin-D has been previously reported to cleave intact PTH into PTH-(1-34) and -(35-84) in membranous fractions of rat and bovine kidney. Whether PTH degradation occurs by intact kidney cells, however, has not been examined in detail. We have, therefore, examined this possibility using an opossum kidney (OK) cell line which possesses the characteristics of proximal renal tubules and responds to PTH. PTH radioimmunoreactivity recovered in trichloroacetic acid-soluble products and in fractions eluted from reverse phase HPLC was measured using an antibody directed to the midregion and C-terminus of PTH. In this study, intact OK cells, but not extracellular enzymes, cleaved human (h) PTH-(1-84) into three discrete fragments which were released into the medium in a time- and temperature-dependent fashion. Half-maximal velocity of PTH-degrading activity (PTHDA) was observed at 9 nM hPTH-(1-84). A 1000-fold molar excess of PTH antagonists [hPTH-(3-34) and [Tyr34]hPTH-(7-34)amide] markedly inhibited PTHDA, whereas ACTH, glucagon, or big gastrin did not suppress it, suggesting an involvement of the PTH receptor in PTHDA. This PTHDA was strongly inhibited by phenylmethylsulfonylfluoride and chymostatin, but not by trypsin inhibitor, elastatinal, or inhibitors of aspartic, cysteine, or metalloproteinases, suggesting that it is due to a seryl chymotrypsin-like endopeptidase. Analysis of chymotrypsin-digested products of hPTH-(1-84) eluted from HPLC exhibited five fragments detected by UV absorbance (210 nm), three of which were measurable by PTH RIA, and each corresponded to the three PTH fragments produced by OK cells. All three fragments were predominantly suppressed in the presence of chymostatin, suggesting that chymotrypsin-like activity is solely responsible for PTHDA in intact OK cells. To further explore the cleavage sites of PTH by chymotrypsin, amino acid analysis of chymotrypsin-cleaved products was performed. The results strongly support the conclusion that a chymotrypsin-like enzyme in OK cells cleaved the hormone between residues 23-24, and 34-35 to produce, at least, hPTH-(24-84) and -(35-84). Lysosomal blockers (chloroquine, ammonium chloride, or monensin) did not affect this PTHDA. Our present study indicates that chymotrypsin-like endopeptidase, but not other endopeptidase or lysosomal enzymes, is responsible for the limited hydrolysis of PTH by intact OK cells.

Receptors and cGMP signalling mechanism for E. coli enterotoxin in opossum kidney

Receptors for the heat-stable enterotoxin produced by Escherichia coli were found in the kidney and intestine of the North American opossum and in cultured renal cell lines. The enterotoxin markedly increased guanosine 3',5'-cyclic monophosphate (cGMP) production in slices of kidney cortex and medulla, in suspensions of intestinal mucosa, and in the opossum kidney (OK) and rat kangaroo kidney (PtK-2) cell lines. In contrast, atrial natriuretic factor elicited much smaller increases in cGMP levels of kidney, intestine, or cultured kidney cell lines. The enterotoxin receptors in OK cells had a molecular mass of approximately 120 kDa when measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of receptors crosslinked with 125I-enterotoxin. The occurrence of receptors for the E. coli peptide in OK implies that these receptors may be involved in the regulation of renal tubular function in the opossum. E. coli enterotoxin caused a much larger increase in urine cGMP excretion (10- to 50-fold over control) than did atrial natriuretic factor when these peptides were injected intravenously into opossums. However, atrial natriuretic factor elicited a marked diuresis, natriuresis, and increased urinary excretion of calcium, phosphate, potassium, and magnesium. In contrast, the enterotoxin did not acutely influence OK fluid and electrolyte excretion. Thus the substantial increase in cGMP synthesis produced by the bacterial peptide in OK cortex and medulla in vitro and the increased renal excretion of cGMP in vivo were not associated with changes in electrolyte or water excretion. Whether cGMP represents a second messenger molecule in the kidney is an interesting question that was raised but not answered in this series of experiments.

Brainstem origin of serotonin- and enkephalin-immunoreactive afferents to the opossum's cerebellum

Previous studies have described the distribution of serotonin- and enkephalin-immunoreactive elements in the posterior lobe vermis of the opossum's cerebellum. In the present study we have used a double labeling paradigm which combines the retrograde transport of horseradish peroxidase (HRP) with serotonin and enkephalin immunohistochemistry to determine the brainstem origin of serotoninergic and enkephalinergic neurons that project to the opossum's cerebellar cortex. Subsequent to HRP injections into the posterior lobe vermis, widespread areas of the medulla and pons were found to contain retrogradely labeled neurons. Serotonin-immunoreactive somata are present primarily in the raphe nuclei and the adjacent reticular formation. Enkephalinergic neurons were numerous in the raphe nuclei, medial accessory olive, gigantocellular reticular formation, locus coeruleus, and the nucleus of the trapezoid body. However, serotoninergic neurons that project to the cerebellum were located only in the medullary pyramids and the reticular formation adjacent to the raphe. Double-labeled enkephalinergic neurons were located 1) within the medullary pyramids, 2) throughout the extent of the caudal medial accessory olive, 3) in the rostral subnucleus a of the medial accessory olive, 4) in the nucleus reticularis gigantocellularis pars ventralis, 5) in the nucleus reticularis lateralis, and 6) in the nucleus reticularis ventralis lateral to the inferior olivary complex. These results indicate that although neurons containing serotonin and enkephalin immunoreactivity may be present in some of the same pontine and medullary nuclei, those serotoninergic and enkephalinergic neurons that project to the cerebellum are present primarily in restricted and spatially separate regions of the caudal medulla.

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) in the brain and nervus terminalis of the adult and early neonatal gray short-tailed opossum (Monodelphis domestica)

Luteinizing hormone-releasing hormone (LHRH) was detected by immunocytochemical procedures in cells and fibers in the brain and in the nervus terminalis of the adult and neonatal gray, short-tailed opossum (Monodelphis domestica). As in several species of eutherian mammals, LHRH-immunoreactive cells and fibers were seen in the medial septal nuclei, nucleus, and tract of the diagonal band and olfactory tubercle. Surprisingly, few LHRH-immunoreactive cells were found in the hypothalamus or in the preoptic area in either the adult or neonate. LHRH-immunoreactive fibers were seen in these regions and were numerous in the median eminence. The nervus terminalis in the gray opossum showed several distinctive characteristics. Immunoreactive and nonreactive cells, in ganglia along the peripheral and intracranial course of this nerve, were accompanied by thick fascicles of LHRH fibers and frequently lay adjacent to blood vessels. No LHRH-immunoreactive branches of the nervus terminalis were found in contact with the vomeronasal nerves as they traversed the medial surfaces of the main olfactory bulbs en route to the accessory olfactory bulbs. The LHRH-immunoreactive fibers in the central roots of the nervus terminalis formed a compact bundle on either side of midline, which coursed obliquely from clusters of ganglion cells on the ventromedial surface of the olfactory bulbs into the septum. Traced through serial sagittal sections, LHRH-immunoreactive fibers, in continuity with those in the triangular nucleus of the septum, ran down and around the rostral face of the anterior commissure and fanned out into the medial preoptic area. As previously observed in the fetal guinea pig and rat, LHRH was detected in ganglion cells of the nervus terminalis of the newborn gray opossum preceding its detection in any other area of the brain.

Regulation of sodium-dependent phosphate transport by parathyroid hormone in opossum kidney cells: adenosine 3',5'-monophosphate-dependent and -independent mechanisms

The hormonal regulation of Na+-dependent phosphate transport was studied in opossum kidney (OK) cells. PTH caused time- and concentration-dependent decreases in Na+-dependent phosphate transport, with 10 pM PTH-(1-34) producing a 19% decline in phosphate transport. The EC50 for PTH inhibition of phosphate transport was 50 pM. Kinetic analyses of phosphate transport indicated that PTH decreased the maximum velocity without affecting the Km for phosphate. PTH increased cAMP formation with an EC50 of 10 nM. 8-Bromo-cAMP and (Bu)2cAMP also inhibited phosphate transport. Forskolin increased cAMP formation and decreased phosphate transport, whereas the cyclase-inactive forskolin analog 1,9-dideoxyforskolin also inhibited phosphate transport. The PTH analog [8,18-norleucine,34-tyrosinamide]PTH-(3-34) reduced phosphate transport at concentrations from 10 nM to 30 microM, but did not increase cAMP formation at concentrations up to 10 microM. The adenylate cyclase inhibitor 2',5'-dideoxyadenosine produced concentration-dependent decreases in PTH-stimulated cAMP formation, but did not influence PTH inhibition of Na+-dependent phosphate transport. Vasoactive intestinal polypeptide and prostaglandin E1 increased cAMP formation in OK cells, but were weak inhibitors of phosphate transport. This study suggests that cAMP may not be the only transmembrane signaling mechanism involved in the regulation of Na+-dependent phosphate transport by PTH-(1-34) in OK cells.

Factors influencing prostatic 5 alpha-reductase activity in possum (Trichosurus vulpecula)

1. There were marked differences in prostatic wts among individual possums, but no evidence of a seasonally related change in wt could be established. It was concluded that the wt differences are mainly due to the changes in secretory activities. After castration the prostate wts fell while after administration of testosterone or oestradiol partially reversed this process. 2. Seven steroid conversion products were isolated from prostatic homogenates incubated with [3H] testosterone; 5 alpha-androstane-3 beta,17 beta-diol forming the highest yield. 3. While the 5 alpha-reductase activity of prostates from intact possums was very low (approx. 8% of the total yield), it increased to over 50% after castration. 4. Administration of testosterone or oestradiol partially reversed the post-castration rise in 5 alpha-reductase, while 17 beta-hydroxy-5 alpha-androstane-3-one (DHT) was ineffective. Administration of porcine FSH-NIH-P2 to both intact or castrated possums caused a marked rise in prostatic 5 alpha-reductase activity. 5. It was concluded that in possum, FSH may have a direct stimulatory effect on prostatic 5 alpha-reductase activity. The results are discussed in relation to placental mammals.

Seasonal energetics of opossums (Didelphis virginiana) in Ohio

1. Female opossums acclimatized to each of the four seasons were not significantly different (P greater than 0.05) in oxygen consumption at a Ta of 0 degrees C; the overall average was 0.66 +/- 0.1 ml O2/g-hr. 2. Body weight decreased by 27% from autumn to spring; pelage density increased in winter, but thermal conductance changed very little between seasons. 3. Respirometry revealed no evidence of thermoregulatory adjustments in opossums acclimatized to winter in Ohio.

Distribution and ultrastructure of neurons in opossum piriform cortex displaying immunoreactivity to GABA and GAD and high-affinity tritiated GABA uptake

GABAergic neurons have been identified in the piriform cortex of the opossum at light and electron microscopic levels by immunocytochemical localization of GABA and the GABA-synthesizing enzyme glutamic acid decarboxylase and by autoradiographic visualization of high-affinity 3H-GABA uptake. Four major neuron populations have been distinguished on the basis of soma size, shape, and segregation at specific depths and locations: large horizontal cells in layer Ia of the anterior piriform cortex, small globular cells with thin dendrites concentrated in layers Ib and II of the posterior piriform cortex, and multipolar and fusiform cells concentrated in the deep part of layer III in anterior and posterior parts of the piriform cortex and the subjacent endopiriform nucleus. All four populations were well visualized with both antisera, but the large layer Ia horizontal cells displayed only very light 3H-GABA uptake, thus suggesting a lack of local axon collaterals or lack of high-affinity GABA uptake sites. The large, ultrastructurally distinctive somata of layer Ia horizontal cells receive a very small number of symmetrical synapses; the thin, axonlike dendrites of small globular cells are exclusively postsynaptic and receive large numbers of both symmetrical and asymmetrical synapses, in contrast to somata which receive a small number of both types; and the deep multipolar and fusiform cells receive a highly variable number of symmetrical and asymmetrical synapses on somata and proximal dendrites. Labeled puncta of axon terminal dimensions were found in large numbers in the neuropil surrounding pyramidal cell somata in layer II and in the endopiriform nucleus. Moderately large numbers of labeled puncta were found in layer I at the depth of pyramidal cell apical dendrites with greater numbers in layer Ia at the depth of distal apical segments than in layer Ib. High-affinity GABA uptake was demonstrated in the termination zone of the projection from the anterior olfactory nucleus to the anterior piriform cortex. Cell bodies of origin of this projection displayed heavy retrograde labeling with 3H-GABA. Matching neuropil and cellular labeling was demonstrated with the GABA-BSA antiserum but not with the GAD antiserum, thus suggesting that GABA is normally present in these cells but is taken up from the neuropil rather than synthesized. No comparable high-affinity GABA uptake was demonstrated in the association fiber systems that originate in the piriform cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

DNA methylation stabilizes X chromosome inactivation in eutherians but not in marsupials: evidence for multistep maintenance of mammalian X dosage compensation

In marsupials and eutherian mammals, X chromosome dosage compensation is achieved by inactivating one X chromosome in female cells; however, in marsupials, the inactive X chromosomes is always paternal, and some genes on the chromosome are partially expressed. To define the role of DNA methylation in maintenance of X chromosome inactivity, we examined loci for glucose-6-phosphate dehydrogenase and hypoxanthine phosphoribosyltransferase in a North American marsupial, the opossum Didelphis virginiana, by using genomic hybridization probes cloned from this species. We find that these marsupial genes are like their eutherian counterparts, with respect to sex differences in methylation of nuclease-insensitive (nonregulatory) chromatin. However, with respect to methylation of the nuclease-hypersensitive (regulatory) chromatin of the glucose-6-phosphate dehydrogenase locus, the opossum gene differs from those of eutherians, as the 5' cluster of CpG dinucleotides is hypomethylated in the paternal as well as the maternal gene. Despite hypomethylation of the 5' CpG cluster, the paternal allele, identified by an enzyme variant, is at best partially expressed; therefore, factors other than methylation are responsible for repression. In light of these results, it seems that the role of DNA methylation in eutherian X dosage compensation is to "lock in" the process initiated by such factors. Because of similarities between dosage compensation in marsupials and trophectoderm derivatives of eutherians, we propose that differences in timing of developmental events--rather than differences in the basic mechanisms of X inactivation--account for features of dosage compensation that differ among mammals.

The effects of cycloheximide on Na+/H+ antiporter activity in cultured opossum kidney cells

These studies examined the effects of cycloheximide on the Na+/H+ antiporter in cultured opossum kidney cells. The effects of cycloheximide on antiporter activity depended on the basal level of activity. These data suggest that the Na+/H+ antiporter may be regulated by several processes which are sensitive to protein synthesis inhibition.

Distribution of vasoactive intestinal polypeptide-immunoreactive structures in the opossum esophagus

Physiologic evidence that vasoactive intestinal polypeptide (VIP) regulates esophageal smooth muscle in the opossum has been gathered without knowledge of the distribution of VIP in that organ. We examined planar sections stained for VIP by the avidin-biotin complex method, measured VIP content in mucosa and muscularis propria by radioimmunoassay, and compared neural structures reactive to VIP antiserum with those revealed by osmication in the presence of zinc iodide. Immunoreactive terminal nerves interlaced smooth muscle bundles in all layers in all smooth muscle regions, formed loose tangled knots about widely dispersed muscle cells in striated muscle, and supplied vessels and submucosal glands. Bipolar interstitial cells in the circular muscle layer stained by osmication were not VIP-immunoreactive. Perikarya in both submucous and myenteric plexuses were VIP-immunoreactive. Vasoactive intestinal polypeptide-immunoreactive oval cells with round unstained nuclei and a faintly granular cytoplasm were scattered in the muscle in all regions and were concentrated in the planes of the plexuses. Vasoactive intestinal polypeptide content of muscularis propria in the smooth muscle esophageal body exceeded (p less than or equal to 0.05) that in the striated muscle esophageal body and the sphincter region, but contents in the latter two regions did not differ (p greater than or equal to 0.05). Mucosal content exceeded that of muscularis propria. The broad distribution and diversity of immunoreactive structures suggest that VIP may have functions in this organ besides the regulation of smooth muscle.

Distribution of enteroglucagon- and polypeptide YY-immunoreactive cells in the gastrointestinal tract of the white-belly opossum (Didelphis albiventris)

Several segments of the gastrointestinal tract of the white-belly opossum Didelphis albiventris were investigated immunocytochemically for the occurrence of polypeptide YY (PYY) and enteroglucagon (GLU). PYY- and GLU-immunoreactive cells were observed in the lower part of the ileum, cecum and colon. These cells were seen to emit cytoplasmic basal processes to the neighbouring cells with a number of them reaching the glandular lumen via apical cytoplasmic process. GLU-immunoreactive cells were also present in the oxyntic mucosae and in the pancreatic duct. Staining of consecutive sections for the two polypeptides, respectively, revealed the coexistence of immunoreactivity for PYY and GLU in the same cell type.

Effects of oestradiol, the oestrous cycle and pregnancy on weight, metabolism and cytosol receptors in the oviduct and vaginal complex of the brushtail possum (Trichosurus vulpecula)

Weight, RNA, DNA and protein content of the oviduct, vaginal cul-de-sac, lateral vagina and urogenital sinus and oestradiol and progesterone cytosol receptor concentrations in vaginal cul-de-sac, lateral vagina and urogenital sinus were examined after administration of oestradiol to ovariectomized animals and on days 0, 5, 9 and 13 of the non-pregnant cycle and on day 13 of the pregnant cycle. In ovariectomized animals, oestradiol induced an increase in weight, RNA:DNA and protein:DNA ratios and a decrease in DNA:tissue weight ratio for each organ and in addition an increase in total DNA in vaginal cul-de-sac and urogenital sinus. There was no effect of oestradiol on oestradiol cytosol receptor concentration but there was a significant increase in progesterone cytosol receptor concentration in all organs that were examined. During the oestrous cycle, changes in the wet weight of each organ showed a common pattern with maximum weight at day 0 followed by variable rates of decline until day 13. In oviduct and vaginal cul-de-sac, the decrease in weight was paralleled by a decrease in RNA:DNA and protein:DNA ratios whereas the DNA: tissue weight ratio showed the opposite pattern and total DNA remained unchanged. The changes in the lateral vagina and urogenital sinus were similar except that a significant decline in total DNA was also seen after day 0 and the DNA:tissue weight and protein:DNA ratios in the urogenital sinus and the lateral vagina respectively showed no significant changes. Progesterone cytosol receptor concentration in the lateral vagina and urogenital sinus were high on day 0 and then declined until day 13. In contrast, there were no consistent effects on oestradiol receptor concentration.

Vulpecholic acid (1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic acid): a novel bile acid of a marsupial, Trichosurus vulpecula (Lesson)

A novel trihydroxylated C24 bile acid was isolated from the gallbladder bile of the Australian opossum, Trichosurus vulpecula (Lesson). This acid, for which the name vulpecholic acid is proposed, was identified as 1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic. The structure proof included mass spectral and 1H and 13C nuclear magnetic resonance characterization of all crucial derivatives obtained by: oxidation of the methyl ester to a triketone with the enolizable 1,3-diketone function; methylation of this triketone to two isomeric methyl enol ethers; and reductive removal of oxygen functions from this triketone to give 5 beta-cholan-24-oic and 7-oxo-5 beta-cholan-24-oic acids. Vulpecholic acid was found in the bile in the unconjugated form; it accounted for more than 60% of the solid bile material. The marsupial T. vulpecula is the first example of a mammal secreting a 1 alpha-hydroxylated bile acid as well as the first example of a mammal secreting the major bile acid in a free form.

Digestion and metabolism of high-tannin Eucalyptus foliage by the brushtail possum (Trichosurus vulpecula) (Marsupialia: Phalangeridae)

The digestion and metabolism of Eucalyptus melliodora foliage was studied in captive brushtail possums (Trichosurus vulpecula). The foliage was low in nitrogen and silica but high in lignified fibre and phenolics compared with diets consumed by most other herbivores. The high lignin content was suggested as the main cause of the low digestibility of E. melliodora cell walls (24%); microscopic observations of plant fragments in the caecum and faeces revealed few bacteria attached to lignified tissues. The conversion of digestible energy (0.34 MJ X kg-0.75 X d-1) to metabolizable energy (0.26 MJ X kg-0.75 X d-1) was low compared to most other herbivores, probably because of excretion of metabolites of leaf essential oils and phenolics in the urine. When the inhibitory effect of leaf tannins on fibre digestion was blocked by supplementing the animals with polyethylene glycol (PEG), intake of dry matter, metabolizable energy and digestible fibre increased. These effects were attributed to the reversal by PEG of tannin-microbial enzyme complexes. It was concluded that the gut-filling effect of a bulk of indigestible fibre is a major reason why the brushtail possum does not feed exclusively on Eucalyptus foliage in the wild.

Neuropeptide Y-like immunoreactivity is absent from most perivascular noradrenergic axons in a marsupial, the brush-tailed possum

Noradrenergic perivascular axons were demonstrated in all systemic arteries and veins of a marsupial, the brush-tailed possum (Trichosurus vulpecula), by a catecholamine fluorescence procedure and with antisera directed against the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (D beta H). Perivascular axons with neuropeptide Y-like immunoreactivity (NPY-LI) were not found in most systemic arteries and veins using antisera which recognize NPY and other members of the pancreatic polypeptide family in diverse vertebrate species. The exceptions were the renal, coeliac, main mesenteric and iliac arteries, where up to 50% of axons with TH-LI or D beta H-LI also showed NPY-LI with two of the 4 antisera used. No noradrenergic nerve cell bodies in thoracic sympathetic ganglia had NPY-LI, whilst 3% of noradrenergic nerve cell bodies in lumbar sympathetic chain ganglia had weak NPY-LI. This marsupial is the first vertebrate species found to date in which the majority of perivascular noradrenergic axons do not contain NPY-LI. If these axons contain an as yet unidentified neuropeptide, it is unlikely to be closely related to NPY.

Immunolocalization of insulin, glucagon, pancreatic polypeptide, and somatostatin in the pancreatic islets of the possum, Trichosurus vulpecula

Antibodies to insulin, glucagon, pancreatic polypeptide (PP), and somatostatin were used in the immunofluorescence procedure to demonstrate localization of the four hormones in cells of the pancreatic islets of the brushtailed possum, Trichosurus vulpecula. Most pancreatic islets revealed some differences in the topographical distribution and cell number of each endocrine cell type. Insulin immunoreactive cells were observed in most islets where they occurred as groups of cells peripherally and within the islet. In several islets glucagon cells were the predominant cell population and were distributed peripherally as well as centrally. Pancreatic polypeptide cells were fewer in number and usually occurred as single cells within the islet. Cells immunoreactive to antisomatostatin serum were observed in varying numbers in the peripheral and central regions of the islet. The present immunofluorescence study demonstrates differences in the topographical distribution of the four major pancreatic hormones between a marsupial species and several of the eutherian mammals.

Localization of serotonin immunoreactivity in the opossum cerebellum

We have used the indirect antibody peroxidase-antiperoxidase technique to analyze the course of serotonin (5-hydroxytryptamine; 5HT) fibers to the deep cerebellar nuclei; the distribution of serotonin within the nuclei; the continued course of 5HT fibers to the cerebellar cortex; and the lobular and laminar distribution of this indoleamine in the cerebellar cortex. Only rarely are fibers found in either the restiform body or the brachium pontis. However, a distinct bundle of serotoninergic axons is present in the medial aspect of the brachium conjunctivum. Axons arise from this bundle and course dorsally into the neuropil of the deep cerebellar nuclei. The densest immunostaining is present in posterior and ventral regions of all four cerebellar nuclei. Within the nuclei large (24% of total) and small (76% of total) varicosities are present. The average distance between varicosities on individual axons is 3.85 micron (S.D. = 1.2). The innervation of the cerebellar cortex is derived primarily from fibers that course through the deep nuclei. At levels caudal to the deep nuclei a single midsagittal band courses into lobules VIII and IX. In the cerebellar cortex, serotoninergic axons and varicosities are present in all lobules; however, the fiber density is not uniform. The densest distribution is present in vermal lobule VIII and the dorsal folia of lobule IX. Within the granule cell layer of lobules VIII and IX, immunoreactive elements form a midsagittal band, and to a lesser degree, two parasagittal bands. Beaded serotoninergic fibers course through the deep and middle portion of the granule cell layer and give rise to a plexus at the border between the Purkinje cell and granule cell layers. Within this plexus axons extend long distances in the transverse and sagittal planes. Long beaded axons oriented in the transverse plane of the folia are also present in the deep molecular layer. A few radial serotoninergic fibers ascend to the pial surface and give rise to very short tangential branches. In all three cortical layers, both large (19% of total) and small (81% of total) varicosities are present. The average distance between varicosities on individual fibers is 5.3 micron (S.D. = 2.2).(ABSTRACT TRUNCATED AT 400 WORDS)

Photoreactivation of UV-induced pyrimidine dimers and erythema in the marsupial Monodelphis domestica

Post-UV treatment of the gray, short-tailed opossum Monodelphis domestica with photoreactivating light (320-400 nm) suppressed the appearance of UV-induced erythema as evidenced by an increase in the dose of UV required to elicit an erythemal response. The average erythema dose for animals held in the dark following UV exposure was 620 +/- 40 J/m2, whereas 2460 +/- 110 J/m2 were required for erythema induction with animals exposed to 90 min of photoreactivating light post-UV. Pre-UV exposure to photoreactivating light had no effect on the UV induction of erythema. The dose-response for the photoreversal of pyrimidine dimers in epidermal DNA of M. domestica was similar to that for the photoreactivation of erythema induction. These data not only support the notion that DNA is the primary chromophore involved in the induction of erythema but also identify pyrimidine dimers as the major DNA change responsible for its induction. These results also identify M. domestica as a useful whole-animal system with which to determine the role of pyrimidine dimers in other photobiological responses of mammalian skin.

The synthesis and metabolism of gonadal steroids in pouch young of the opossum, Didelphis virginiana

We have measured steroid hormone biosynthesis from pregnenolone in ovaries and testes, aromatization of testosterone in gonads and peripheral tissues, and 5 alpha-reduction of testosterone in peripheral tissues of developing opossum pouch young. Sex of the newborn opossums is discernible grossly with development of the pouch in females and the scrotum in males approximately 10 days after birth. Differentiated endocrine function of ovaries and testes was demonstrable as soon as development of the pouch or scrotum was apparent. The testes synthesized testosterone, and ovaries aromatized androgens to estrogens as assessed by the conversion of [1 beta-3H] testosterone to 3H2O. This endocrine differentiation of the gonads occurs days or weeks before differentiation of the male and female urogenital tracts. As in other species, 5 alpha-reduction of [1 beta-3H] testosterone was high in urogenital sinus and urogenital tubercle. However, 5 alpha-reductase activity was highest in mesonephros and structures derived from the mesonephros. In wolffian and mullerian ducts of pouch young less than 10 days old, 5 alpha-reductase activity was greater than 50 pmol/h . mg protein and decreased by 19 days of age to approximately 3 pmol/h . mg protein, a pattern different than in eutherian mammals in which testosterone itself appears to mediate virilization of the wolffian ducts. These studies provide the framework for studies of the endocrine control of phenotypic sexual differentiation in the opossum.

Neurohypophyseal hormones as evolutionary tracers: identification of oxytocin, lysine vasopressin, and arginine vasopressin in two South American opossums (Didelphis marsupialis and Philander opossum)

The neurohypophyseal hormones of two South American opossums (Didelphis marsupialis and Philander opossum) were isolated by molecular sieving and preparative high-pressure liquid chromatography (HPLC). One oxytocin-like and two vasopressin-like peptides were found in each species. These peptides have been identified by their amino acid composition and by their retention time in HPLC. Oxytocin, lysine vasopressin, and arginine vasopressin have been characterized in both species. Lysine vasopressin is roughly as abundant as arginine vasopressin. Comparison is made with Australian marsupials Macropodidae and Phalangeridae, and possible evolutionary mechanisms are discussed.

The sodium pump in opossum vascular smooth muscle

Ouabain-sensitive Rb+ uptake and [3H]ouabain binding were used to measure rates of Na+ pumping and the number of pump sites, respectively, in thoracic aortae from opossums. From the number of Rb+ ions pumped per site per minute, estimates of pump turnover have been made. Values obtained are comparable to those of other species (see Table 1).

Differences in steroidogenesis by the subcellular fractions of adrenocortical special zone and cortex proper of the female possum (Trichosurus vulpecula)

Steroidogenesis by subcellular fractions of adrenal cortex proper (C.P.) and special zone (S.Z.) of female possum (Trichosurus vulpecula) was studied. Mitochondrial, microsomal and cytosol cell fractions were incubated with appropriate substrates in the presence of an NADPH-generating system. The major products formed from [3H]progesterone and [3H]17 alpha-hydroxyprogesterone by the microsomal fraction of the C.P. were 11-deoxycortisol and 11-deoxycorticosterone and 3 alpha (beta)-hydroxy-5 alpha-androstan-17-one by the S.Z. The mitochondrial fraction converted [3H]11-deoxycortisol to cortisol in yields twenty times higher by the C.P. than by the S.Z. and to 17 alpha, 20 beta,21-trihydroxy-4-pregn-3-one thirty times higher by the S.Z. The conversion of [3H]androstenedione to 11 beta-hydroxyandrostenedione by the C.P. was approximately double that of the S.Z., while 18-hydroxyandrostenedione (tentatively identified) formed the highest yield in both zones. Incubation of the same substrates with cytosol formed two 5 beta-pregnane and two 5 beta-androstane derivatives in total yields less than 5% by C.P. and greater than 60% by S.Z. Aromatase activity, estimated by the release of [3H2O] from [1 beta 3H]testosterone, in the adrenals of 8 possums, was in each experiment negligibly low. Determination of total enzyme activities in the two zones revealed that 11 beta, 18 and 21-hydroxylases were higher in the C.P., while 17 alpha-hydroxylase was higher in the S.Z. Similar results were obtained when the rates of formation of hydroxylated products were estimated in the presence of saturating amounts of substrates. Active 5 alpha- and 5 beta-reductases, C17-20-lyase and 3 alpha (beta) and 20 beta-hydroxysteroid dehydrogenases were found almost exclusively in the S.Z. We conclude that the S.Z. at lower levels of activity than the C.P. could contribute to the basal secretion of corticosteroids. In addition, the S.Z. has a high capacity to form C19 steroids and 5 alpha- and 5 beta-reduced steroids. The possible role of the S.Z. in possum is discussed.

Differences in cytochrome c oxidase capacity in smooth muscle of opossum esophagus and lower esophageal sphincter

The tonic contraction that defines the lower esophageal sphincter is exclusively aerobic, whereas the rhythmic contractions that characterize the smooth muscle of the esophageal body can be partially sustained anaerobically. Also, relative mitochondrial mass is greater in the sphincter than it is in the body of the esophagus. Full-thickness strips of the muscularis propria of the opossum esophagus were examined as to cytochrome c oxidase capacity to test the hypothesis that differences in oxidative metabolism exist among different levels of the smooth-muscled esophagus. Homogenates were examined as to rate of cytochrome c oxidation, deoxyribonucleic acid content, and protein content. The rate of cytochrome c oxidation was greatest at the top of the smooth muscle segment and declined distally to reach the lowest value in the lower esophageal sphincter. Deoxyribonucleic acid content did not differ among levels examined. Protein/deoxyribonucleic acid ratios were lower in the sphincter than at other levels of the smooth-muscled esophagus. The results indicate that the sphincter muscle has a lower capacity for oxidative metabolism than does the body, that a gradient exists along the esophageal body in oxidative capacity, and that smooth muscle cells in the sphincter are likely to be smaller than are those of the esophageal body. The gradient in oxidative capacity along the esophageal body may be related to other gradients that have been described in this region.

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.

The distribution and synaptic organization of serotoninergic elements in the inferior olivary complex of the opossum

Immunohistochemistry and high-resolution autoradiography were used to analyze the distribution and synaptic organization of serotonin (5HT) - containing elements in the inferior olivary complex of the opossum. Immunoreactive beaded varicosities are present throughout the olivary complex. The densest 5HT immunostaining is present in subnucleus b of the caudal medial accessory nucleus. The rostral principal olive is sparsely populated with immunoreactive elements. Fine beaded fibers arborize throughout the neuropil of all the olivary nuclei except in subnucleus b of the caudal medial accessory nucleus where they also circumscribe neuronal cell bodies. In addition, a distinct population of large beaded fibers are occasionally encountered in the neuropil of the medial accessory nucleus. Ultrastructurally, labeled profiles that correspond in size to the smaller beads (less than 1 micron) contain tubulovesicular elements, large dense-cored vesicles, and clear vesicles. In contrast, larger profiles (greater than 2 microns) are characterized by numerous clear synaptic vesicles. Synaptic junctions were encountered in only 2% of the labeled elements. The majority of the labeled profiles were in juxtaposition to small-diameter dendrites (less than 2 microns) except in the caudal medial accessory nucleus, where they also were found in apposition to olivary cell bodies. Our results, when compared with other accounts, indicate that rather than major differences in the nuclear distribution of serotonin between species, there are differences in the density of serotoninergic elements in specific nuclei of the mammalian inferior olive. Based on the size of the labeled profiles and the distinct vesicle populations, our data suggest there are at least two populations of 5HT varicosities that are in juxtaposition to olivary neurons. Further, boutons containing 5HT primarily interact with the distal dendrites of olivary neurons except in the caudal medial accessory nucleus where cell bodies are in apposition to 5HT varicosities.

Ascorbic acid turnover and excretion in two arboreal marsupials and in laboratory rabbits

Rates of turnover and routes of excretion of 1-14C-ascorbic acid were compared among laboratory rabbits and two species of arboreal marsupials. Ringtail possums (Pseudocheirus peregrinus) exhibited higher blood ascorbate levels than either brushtail possums (Trichosurus vulpecula) or rabbits, as well as greater pool sizes, shorter half-times and higher total entry rates of ascorbic acid. These differences were due partly to the high ascorbic acid content of Eucalyptus foliage, the ringtail's diet; when the dietary contribution of ascorbate was taken into account, endogenous entry rates (i.e. 'synthesis') were not significantly different among species. The main excretory route of 14C from 1-14C-ascorbate was expired CO2 in all three species. Estimates to total pool size of ascorbate by isotope dilution were higher than those by tissue analysis. This was considered to be due to excretion of 14C during equilibration of injected 1-14C-ascorbate with the body pool.

Isolation and convulsant effect of the 'insulin-like' proteins from the pancreas of the Brazilian opossum Didelphis albiventris

An opossum pancreatic insulin-like protein fraction was obtained at pH 5.2 which has high electrophoretic mobility. At pH 8.2, another pancreatic insulin-like protein fraction was obtained with low electrophoretic mobility. Isoelectric focusing studies showed that the high molecular weight protein has a pI value 8.35 and the low molecular weight protein has pI value of 3.9 when used at pH range between 3.5-10.0. The purified high and low molecular weight positive aldehyde-fuchsin proteins induced convulsions when administered subcutaneously to mice.

Acetylation of sulphanilamide in four marsupials and a monotreme

1. The urinary metabolites of sulphanilamide (100 mg/kg, i.p.) have been studied in four marsupials (the Tasmanian devil, brushtail possum, pademelon and barred bandicoot), a monotreme (the echidna) and a eutherian (the rat). 2. All species excreted some unchanged sulphanilamide (20-30% of dose in 24 h). The major urinary metabolite in the devil, possum and pademelon was N4-acetylsulphanilamide (6-17%). This was less than that excreted by the rat (40%). These three marsupials and the rat also excreted small amounts of N1-acetyl and N1, N4-diacetylsulphanilamide. 3. The bandicoot and echidna were virtually unable to acetylate sulphanilamide, unlike the 16 other species of animals and birds in which this has been studied. The reason for this metabolic defect is unknown.

Initial experiments with cyproterone acetate and 1-amino-3-chloro-2-propanol hydrochloride in the male Virginia opossum (Didelphis virginiana)

Cyproterone acetate (CA) was toxic for Didelphis virginiana at a dose range of 22-28 mg/kg IM. A loss of spermatozoal pairing int the cauda epididymidis did not occur until 2 wk after testicular degeneration caused by CA. The isomers of 1-amino-3-chloro-2-propanol hydrochloride (CL 88,236 and CL 88,237) were well tolerated by the opossum at doses up to 30 mg/kg IM. After 8 days of CL 88,236 and CL 88,237 treatment there was no effect on spermatozoal pairing in the cauda epididymidis or on the seminiferous epithelium.