Evaluation of tear production in juvenile opossum using three different methods / Avaliação da produção lacrimal em gambás filhotes por três diferentes métodos

The establishment of parameters for tear production in different species is important for better understanding eye´s health and is one of the components of the ophthalmic semiological technique. Particularities derived from the anatomophysiology of non-domestic species induce the search for more reliable methodologies. The aim was to evaluate and compare tear production of white-eared opossum (Didelphis albiventris) and Brazilian common opossum (Didelphis aurita) by three different methods. Fifteen individuals of each species, juveniles, healthy, of both sexes, with 60 to 90 days of life, were physically restrained. Phenol red thread test (PRTT), endodontic absorbent paper point tear test (EAPPTT) and modified -Schirmer tear test (mSTT) were performed. PRTT was the most difficult to perform because of the wire malleability, while EAPPTT was more feasible for both species. The median ± semi-quartile range for PRTT were 19.79±2.61mm/15 "and 5.22±2.92mm/15", for EAPPTT were 16.25±1.82mm/min and 10.9±3.04mm/min, and for STTm were 0±1.63mm/min and 0±1.63mm/min for white-eared opossum and Brazilian common opossum respectively. There was no difference between the right and left eye neither sex. A significant difference was obtained for the same test to different species. No significant correlation was found between the tests for both species. The description of tear production parameters for juvenile white-eared opossum and Brazilian common opossum may be used as a tool, which will allow the early diagnosis of ocular diseases.(AU)

O estabelecimento do parâmetro de produção lacrimal nas diferentes espécies é importante para o entendimento da saúde do olho e é um dos componentes da semiotécnica oftálmica. Particularidades derivadas da anatomofisiologia das espécies não domésticas induzem a busca de metodologias que sejam mais fidedignas aos parâmetros. Objetivou-se com este estudo avaliar e comparar a produção lacrimal de gambás-de-orelha-branca (Didelphis albiventris) e gambás-de-orelha-preta (Didelphis aurita) por três diferentes métodos. Quinze indivíduos de cada espécie, juvenis, hígidos, de ambos os sexos, com 60 a 90 dias de vida, foram contidos fisicamente para realização do teste lacrimal do vermelho de fenol (TLVF), da ponta de papel absorvente estéril e do teste lacrimal de Schirmer modificado (TLSm). O TLVF foi o mais difícil de ser executado devido à maleabilidade do fio, enquanto a TEPA se mostrou mais exequível para ambas as espécies. A mediana ± intervalo semi-interquartil para o TLVF foi de 19,79±2,61mm/15" e 5,22±2,92mm/15", para a TEPA foram de 16,25±1,82mm/min e 10,93±3,04mm/min, e para o TLSm foram de 0±1,63mm/min e 0±1,63mm/min, para gambás-de-orelha-branca e gambás-de-orelha-preta, respectivamente. Não houve diferença entre o olho direito e esquerdo e nem quanto ao sexo. Obteve-se diferença significativa para um mesmo teste entre as espécies. Não foi encontrada correlação significativa entre os testes para ambas as espécies. A quantificação da porção aquosa da lágrima poderá auxiliar no diagnóstico precoce de doenças oculares nas espécies estudadas.(AU)

Small mammal populations of an agroecosystem in the Atlantic Forest domain, southeastern Brazil

This study reports 2 years of the population dynamics and reproduction of a small mammal community using the removal method. The study was conducted in a rural area of the Atlantic Forest, in Sumidouro, Rio de Janeiro State, Brazil. The population sizes, age structure and reproduction were studied for the four most common species in the study area. The overall diversity was 1.67 and ranged between 0.8 to 1.67. The species richness was 13 considering the whole study. The most abundant species were the rodents Nectomys squamipes (n = 133), Akodon cursor (n = 74), Oligoryzomys nigripes (n = 25) and the marsupials Didelphis aurita (n = 58) and Philander frenatus (n = 50). Seven other rodents were captured once: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. There were higher peaks for diversity and species richness during the winter (dry) months, probably due to higher food availability. The marsupials had a seasonal reproduction with highest population sizes at the end of the rainy seasons. Nectomys squamipes reproduced mostly during rainy periods. Akodon cursor reproduced predominantly in the winter with the highest population peaks occurring during this season. The analysis of the population dynamics of the rodent species indicated that no species behaved as an agricultural pest, probably due to the heterogeneous landscape of high rotativity of vegetable cultivation. Rodent populations were more susceptible to the removal procedure than marsupial ones.

Este estudo reporta dois anos da dinâmica populacional e reprodução de uma comunidade de pequenos mamíferos através de método de remoção. O estudo foi realizado numa área rural na Mata Atlântica, em Sumidouro, Rio de Janeiro, Brasil. Os tamanhos populacionais, a estrutura etária e a reprodução foram estudados para as quatro espécies mais comuns na área de estudo. A diversidade total foi de 1,67 e variou entre 0,8 e 1,67. A riqueza de espécies foi de 13, considerando-se o estudo todo. As espécies mais abundantes foram os roedores Nectomys squamipes (n = 133), Akodon cursor (n = 74) e Oligoryzomys nigripes (n = 25) e os marsupiais Didelphis aurita (n = 58) e Philander frenatus (n = 50). Sete outras espécies de roedores foram capturadas somente uma vez: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. Houve maiores picos de diversidade e riqueza de espécies durante os meses de inverno (secos), provavelmente devido ao aumento na disponibilidade de recursos. Os marsupiais apresentaram reprodução estacional com maiores tamanhos populacionais no final das estações chuvosas. Nectomys squamipes reproduziu-se predominantemente durante períodos chuvosos. Akodon cursor reproduziu-se predominantemente no inverno, com os maiores picos populacionais ocorrendo durante esta estação. A análise da dinâmica populacional das espécies de roedores indicou que nenhuma se comportou como praga agrícola, provavelmente devido ao ambiente heterogêneo de alta rotatividade de cultivos de legumes. As populações dos roedores foram mais suscetíveis ao procedimento de remoção do que as dos marsupiais.

The action of post-dispersal beetles (Coleoptera: Scarabaeidae) and ants (Hymenoptera: Formicidae) on scats of Didelphis spp. (Mammalia: Didelphidae)

A two year study of dung beetles and ants acting on scats of two species of opossum (Didelphis spp.) was carried out. Scats were left in the field in order to detect post-dispersal agents. A portion of each scat (30 %) was examined for seeds in the laboratory. Beetles were recovered from burrows (51% of 84 faecal samples left in the field) where they either buried scats of opossums or were attracted, together with ants, to pitfalls (N = 10) baited with opossum scats. Dung beetles were the main post-dispersal agents of seeds found in scats of opossums, rolling the scats away or burying then on the site of deposition. They buried faeces at 4 to 15 cm in depth (N = 22 tunnels). The main dung beetles identified (medium to large size) were Eurysternus (28.7 % in pitfalls) and Dichotomius (13.7 %), Coprophanaeus (seen only directly on faeces), besides small-bodied beetles (< 10 mm; 57.6 %). The ant Acromirmex sp. transported some seeds from scats. This species was present in 25.5 % of all Formicidae samples (pitfall). These post-dispersal agents contribute to avert scat seed predators such as rodents, and to accelerate seed bank formation.

Por dos años estudiamos los escarabajos coprófagos y las hormigas que actúan en las heces de zarigüellas (Didelphis). Se dejaron excrementos en el campo para descubrir los agentes secundarios de dispersión. Una parte de cada excremento (30 %) fue analizada en laboratorio para estimar el número de semillas. Se recolectaron escarabajos del suelo (51 % de 84 excrementos dejados en el campo). También capturamos escarabajos y hormigas con trampas (N= 10). Los escarabajos coprófagos son los principales agentes secundarios de dispersión. Ruedan los excrementos o los entierran a 4-15 cm de profundidad (N= 22 túneles). Los escarabajos coprófagos de mayor tamaño fueron Eurysternus cyanescens (28.7 % en trampas), Dichotomius assifer (13.7 %) y Coprophanaeus saphirinus (sólo visto en madrigueras y directamente sobre los excrementos). Los escarabajos de menos de 10 mm fueron el 57.6 %. La hormiga Acromirmex sp. fue 25.5 % del total de hormigas capturadas en trampas. Hallamos varias especies de semillas en los excrementos, muchos de ellos enterrados por los escarabajos, y algunas fueron extraídas por las hormigas. Estos agentes secundarios ayudan a evitar los depredadores de semillas (eg. roedores) y aceleran la formación del banco de semillas, pues no las comen.

Morfologia externa do fígado e principais ramificaçöes da veia porta intra hepática no gambá (Didelphis albiventris) / External morphology of the liver and the ramifications of the intahepatic portal vein in the opossum (Didelphis albiventris)

No presente estudo foi descrita a segmentaçäo hepática do gambá sulamericano (Didelphis albiventris), visando á compreensäo da morfologia externa do fígado e das variaçöes anatômicas na disposiçäo da veia porta intra-hepática neste marsupial. Foram estudados vinte e sete fígados de gambás de ambos os sexos, jovens e adultos, por meio de técnicas anatömicas macroscóicas de corrosäo vascular, dissecaçäo e radiografia das ramificaçöes intra-hepáticas da veia porta. Um fígado, intacto e formolizado, foi examinado para descriçäo da lobaçäo hepática e posterior correlaçäo com a ramificaçäo portal. Externamente, o fígado do gambá é composto por quatro lobos principais: lateral direito, medial direito, medial esquerdo e lateral esquerdo; o lobo caudado é considerado como uma extensäo da face inferior do lobo lateral direito do fígado. Há grande variabilidade anatômica na ramificaçäo intra- hepática da veia porta para cada um destes lobos

Proliferation of differentiated glial cells in the brain stem

Classical studies of macroglial proliferation in muride rodents have provided conflicting evidence concerning the proliferating capabilities of oligodendrocytes and microglia. Furthermore, little information has been obtained in other mammalian orders and very little is known about glial cell proliferation and differentiation in the subclass Metatheria although valuable knowledge may be obtained from the protracted period of central nervous system maturation in these forms. Thus, we have studied the proliferative capacity of phenotypically identified brain stem oligodendrocytes by tritiated thymidine radioautography and have compared it with known features of oligodentroglial differentation as well as with proliferation of microglia in the opossum Didelphis marsupialis. We have detected a previously undescribed ephemeral, regionally heterogenous proliferation of oligodendrocytes expressing the actin-binding, ensheathment-related protein 2' 3'- cyclic nucleotide 3' -phosphodiesterase (CNPase), that is not necessarily related to the known regional and temporal heterogeneity of expression of CNPase in cell bodies. On the other hand, proliferation of microglia tagged by the binding of Griffonia simplicifolia B4 isolectin, which recognizes an alpha-D-galactosyl-bearing glycoprotein of the plasma membrane of macrophages/microglia, is known to be long lasting, showing no regional heterogeneity and being found amongst both ameboid and differentiated ramified cells, although at different rates. The functional significance of the proliferative behavior of these differentiated cells is unknown but may provide a lowgrade cell renewal in the normal brain and may be augmented under pathological conditions.

Characterization of nerve-induced relaxation of gastrointestinal sphincteric smooth muscle in a South American opossum (Didelphis albiventris)

The presence of inhibitory nonadrenergic noncholinergic (NANC) intrinsic innervation of the circular muscle of the gastrointestinal sphincters of the South American (SA) opossum was investigated in vitro. Isolated circular muscle strips from the esophagogastric and ileocolonic junctions but not from the gastroduodenal (pylorus) region developed spontaneous tension. Tetrodotoxin (TTX, 1 muM) augmented the spontaneous tension only in the ileocolonic junction strips. Electrical field stimulation of esophagogastric and ileocolonic junction strips caused frequency-dependent responses consisting of a relaxation at lower frequencies (<1 Hz) and a biphasic response or contraction at higher frequencies. In the strips from the pyloric region electrical field stimulation abolished the spontaneous activity at lower frequencies and induced contractions at higher frequencies. The responses elicited by electrical field stimulation in the three sphincters were abolished by TTX (1 muM). Electrical field-induced contractions were reduced while relaxations were enhanced by atropine (1 muM). In the presence of atropine (1 muM) and guanethidine (3 muM), electrical field stimulation, nicotine and ATP induced frequency-or concentration-dependent relaxations of the three sphincters that were abolished by TTX (1 muM). Isoproterenol and sodium nitroprusside caused concentration-dependent relaxations which were TTX-resistant. These findings indicate that the sphincteric circular muscle of the SA opossum gastrointestinal tract is relaxed by the activation of intrinsic NANC nerves and therefore can be used as a model for the study of the mechanisms involved in these responses.

Neurogenesis in septum, amygdala and hippocampus in the marsupial brushtailed possum (Trichosurus vulpecula)

The times of origin of neurons in the septum, amygdala and hippocampus of the marsupial brushtailed possum, Trichosurus vulpecula, were determined with 3H thymidine autoradiography. The long time period for neurogenesis in the brushtailed possum facilitated analysis of neurogenetic gradients in the brain. A series of 20 possums were injected with 3H thymidine from postnatal (P) days 5-95 and were allowed to survive until brain cytoarchitecture was mature. Our results indicate that septal neurogenesis was complete by P21 (38 days after conception) with a medial to lateral gradient of neurogenesis evident in the lateral septal division. Neurogenesis in the amygdala was complete in the basal, central and medial amygdaloid nuclei by P21, and in the lateral amygdaloid nucleus by P46, with a medial to lateral gradient of neurogenesis evident in basal, central and lateral amygdaloid nuclei. In the hippocampus, neurogenesis of pyramidal cells was complete in field CA3 by P50, and in field CA1 by P55. Early forming pyramidal cells (P5-12) were distributed adjacent to the stratum oriens in fields CA1 and CA3, with later forming pyramidal cells distributing in the middle of the stratum pyramidale (P21-32) and on the edge adjacent to the stratum radiatum (P46). Neurogenesis of dentate granule cells extended over a long period of time, from P5, at least until P82, with the earliest forming granule cells (P5-12) distributed adjacent to the stratum moleculare, and the latest forming granule cells (P82) adjacent to the hilus.

The opossum photoreceptors: a model for evolutionary trends in early mammalian retina

The topography and spectral characteristics of mammalian photoreceptors correlate with both, the present ecological demands and the evolutionary history. The South American Opossum is a marsupial mammal with unspecialized habitus and crepuscular lifestyle. A sparse population of cones (max. = 3000/mm2) can be differentiated into four subtypes by morphological, topographical and immunocytochemical criteria. In spite of this unusual diversity the cone types can be split into two functional groups: The population of single cones labeled by antibody OS-2 for short wavelenght sensitive pigments was ubiquitous but at very low densities (200/mm2). The single cones labeled by antibody (COS-1) against long wavelength sensitive pigments constitute the dominant population in the area centralis (2300/mm2). These two single cone types correlate with the pair typically present in placental mammals. Discrimination of spatial and color contrast may be provided by this "modern" set. The COS-1 labeled double and single cones bearing an oil droplet, display a different pattern by being restricted to the inferior (non-tapetal) half of the retina (max = 800/mm2). This additional set of cones with oil droplets and long wavelength pigments is a conservative feature of the opossum retina and other marsupials. As an accessory cone system it is possibly providing enhanced sensitivity at mesopic conditions. During the early evolution of nocturnal mammals with its prominent expansion of rod vision these cone types were conserved but then were lost in placental mammals. Thus the unique features of mammalian are the result of two evolutionary steps: first a reduction of cone based vision, followed by a secondary differentiation of photopic vision and behaviour relying on the remaining set of cones.

The nucleus of the optic tract of the opossum

This paper reviews anatomical and electrophysiological data on the nucleus of the optic tract (NOT) of the opossum, a nucleus in the afferent branch of the horizontal optokinetic reflex. It is proposed that subcortical routes are essential for responses from the two eyes: a direct retinal projection from the contralateral eye and a commissural pathway between the two NOTs for the ipsolateral eye. In the latter case there's evidence that the commisural axons have a relay on inhibitory neurones. This circuit accounts for the differences in response pattern under monocular condition: temporo-nasal motion of the visual stimulus elicits excitation in the contralateral NOT, resulting in inhibition of the ipsolateral nucleus, while naso-temporal motion promotes inhibition in the contralateral nucleus, releasing the ipsolateral nucleus from the commissural input.

Developmental changes in synapses of the retino-recipient layers of the opossum superior colliculus

Changes in synaptic structure were examined in junctions of the retino-recipient layers of the opossum superior colliculus (SC) at critical developmental stages (30, 40 and 61 dai-old pouch young and adult controls). Criteria of classification were the presence and direction of curvature (smile, flat, frown and irregula) and the degree of aggregation of paramembranous components vis-a-vis curvature in the assessment of maturational changes

Patterns of cardiovascular and respiratory responses evoked by stimulation of the defense area in the white-belly opossum (Didelphis albiventris)

The present study describes, for the first time, the autonomic changes concomitant to the defense reaction in the opossum. Electrical stimulation of 2305 sites in the hypothalamus and brain stem evoked from 7% of them patterns of response including 40-240% muscle vasodilatation, characteristic of the defense reaction in anaesthetized animals. These responses also included a rise in arterial blood pressure, tachy- or bradycardia, and variable changes in ventilation ranging from apneusis to polypnea. It is suggested that the defense areas of the opossum are similar to those described for other species, but the defense responses resemble those of the rabbit

Biliary duct pressure and sphincter of Oddi resistance

A atividade eletromiográfica do esfíncter de Oddi e a pressäo biliar foram determinadas em sete opossums com vesícula biliar intacta e após a realizaçäo de colecistectomia. Morfina em dose de 0.2 mg/kg foi administrada endovenosamente após a obtençäo de registros de controle. O efeito de diferentes quantidades de infusäo de soluçäo salina sobre a pressäo biliar também foi estudado. Näo houve significantes alteraçöes na pressäo biliar entre os registros de controle (13.3 ñ 2.1 mmHg) e após a administraçäo de morfina (13.8 ñ 2.2 mmHg) nos opossums com vesícula biliar intacta. Entretanto, a pressäo biliar após a administraçäo de morfina (17.2 ñ 1.5 mmHg) foi significantemente mais elevada do que as pressöes de controle (13.2 ñ 2.3 mmHg) nos animais que tinham sido submetidos à colecistectomia (p < 0.01). Concluiu-se que a morfina näo aumenta a pressäo biliar em animais com vesícula biliar intacta, mas o faz em animais que foram submetidos à colecistectomia