5 results
Small mammals and habitat structure in lowland rain forest of Peninsular Malaysia
- Catherine Kemper, David T. Bell
-
- Journal:
- Journal of Tropical Ecology / Volume 1 / Issue 1 / February 1985
- Published online by Cambridge University Press:
- 10 July 2009, pp. 5-22
-
- Article
- Export citation
-
A method of assessing rain forest structure by ranking relative abundance of 41 habitat variables was used to describe habitat differences among six trapping sites (324 subsites). Variables included aspects of all vegetation layers but concentrated on those considered to be important to small mammal distribution. Ordination and classification methods resulted in similar analyses of the data. Differences in habitat structure were primarily related to the moisture conditions of the trapping sites and secondarily to their successional age (regenerating versus primary forest). The most important habitat variables for differentiating between sites were LITTER, CLEARING, SOILS, PIG DAMAGE, FLOODING, FAN PALM, EMERGENTS, CANOPY SURFACE and SEEDLINGS. Habitat structure also varied within sites with some suggestion of small-scale patterning.
Small mammal captures were more likely in drier sites and subsites, but there was no difference in trap success between regenerating sites and primary forest sites. Greater numbers of species were captured in sites containing a variety of habitats, a discrete layering of vegetation and an extensive understorey. Small mammal captures were positively associated with five habitat variables (EMERGENTS, LITTER, ROTTING LOGS, SEEDLINGS, ROUGH BARK) and negatively associated with five others (LAYERS, BERTAM, SEDGES, PIG DAMAGE, FLOODING). The destruction caused by pigs is thought to be a major factor since it reduces litter and food availability over wide areas. Leopoldamys sabanus was the most abundant small mammal captured (40/68 individuals) and trap success differences among sites (0.4–1.9%) reflect its preference for higher, well-drained habitats.
The study demonstrates the usefulness of a simple method of ranking habitat features according to importance/abundance thus eliminating the all but impossible task of direct measurements in this complex system. This simple method of habitat description provides a basis for studying variables influencing faunal distribution patterns.
Laminar organization and ultrastructure of GABA-immunoreactive neurons and processes in the dorsal lateral geniculate nucleus of the tree shrew (Tupaia belangeri)
- Robert N. Holdefer, Thomas T. Norton, Ranney Mize R.
-
- Journal:
- Visual Neuroscience / Volume 1 / Issue 2 / March 1988
- Published online by Cambridge University Press:
- 02 June 2009, pp. 189-204
-
- Article
- Export citation
-
The distribution and ultrastructure of neurons and neuropil labeled by an antiserum to gamma-aminobutyric acid (GABA) were examined in the lateral geniculate nucleus (LGN) of the tree shrew (Tupaia belangeri). The LGN of this species segregates center type and cell class into three distinct pairs of laminae: a medial pair (laminae 1 and 2) containing ON-center cells, a more lateral pair (4, 5) containing OFF-center cells, and 2 laminae (3, 6) containing W-like cells. The relationship between this laminar segregation and the distribution of GABA immunoreactivity was investigated in the present study. GABA-immunoreactive neurons and neuropil were present in all six of the laminae. However, both the density of labeled cells (adjusted for neuronal density across laminae) and the density of labeled neuropil showed a medial-to-lateral gradient. The adjusted density of labeled cells was higher laterally than medially, and the density of labeled neuropil was significantly greater in the more lateral OFF-center laminae and W-like laminae than in the medial two ON-center laminae. Thus, inhibitory, GABAergic influences may modulate to different degrees the visual signals in the ON, OFF, and W pathways. Labeled cells had a mean cross-sectional area (107 μm2) approximately one-half that of unlabeled cells (216 μm2). They constitute 16–34% of the neurons in the LGN. At the electron microscope level, three different kinds of labeled profile were observed. Vesicle containing profiles like the F2 profiles of cat were postsynaptic to retinal terminals and presynaptic to conventional dendrites. Fl axon terminals with dense clusters of vesicles were also labeled as were some myelinated axons. Another labeled profile, which we suggest should be called an F3 process, was a large dendrite of irregular caliber with punctate groups of vesicles near the synapse. Our results suggest that GABAergic circuitry is an important part of the functional organization in the LGN of the tree shrew.
Lid-suture myopia in tree shrews with retinal ganglion cell blockade
- Thomas T. Norton, John A. Essinger, Neville A. McBrien
-
- Journal:
- Visual Neuroscience / Volume 11 / Issue 1 / January 1994
- Published online by Cambridge University Press:
- 02 June 2009, pp. 143-153
-
- Article
- Export citation
-
To determine whether central communication of retinal signals is necessary for the development of an experimentally induced myopia, tree shrews were exposed to monocular deprivation (MD) while the action potentials of retinal cells in the deprived eye were blocked with intravitreally injected tetrodotoxin (TTX-MD animals). TTX injections (0.6 μ 3 μL) and MD began about 15 days after eye opening, at the start of the susceptible period for the development of lid-suture myopia. Six injections were given, one every second day to produce 12 days of MD and TTX-blockade. Control TTX animals (TTX-open) received TTX in one eye, but not MD, on the same injection schedule and were always found to be behaviorally unresponsive to visual stimuli through the injected eye indicating that TTX blocked central communication of action potentials. Other control animals received intravitreally injected saline in either an open eye (saline-open), or an MD eye (saline-MD). A sham-injected group (sham-inj-MD) received MD and all anesthetic and surgical manipulations except for penetration of the sclera. In all groups, one eye in each animal was an untreated control.
Two effects were found. All MD groups, including the TTX-MD animals, developed a significant vitreous chamber elongation in the deprived eye, indicating that an experimental myopia developed despite ganglion cell blockade. Thus, retinal mechanisms in tree shrew can detect the presence of a degraded visual image and produce an experimental myopia that does not depend on the receipt of visual messages by central neural structures. In addition, eyes in which the sclera was punctured had smaller vitreous chamber depths than comparable uninjected eyes, indicating that puncturing the sclera reduced the normal elongation. These data suggest that forces within the eye normally contribute to its expansion and may be resisted by the choroid and/or the sclera.
Retinal acetylcholine content in normal and myopic eyes: A role in ocular growth control?
- NEVILLE A. McBRIEN, CHARLES L. COTTRIALL, ROGER ANNIES
-
- Journal:
- Visual Neuroscience / Volume 18 / Issue 4 / July 2001
- Published online by Cambridge University Press:
- 11 January 2002, pp. 571-580
-
- Article
- Export citation
-
Retinal neurotransmitters are known to play a role in postnatal ocular development and eye growth. The success of muscarinic antagonists in blocking form-deprivation myopia has implicated retinal acetylcholine in the control of ocular growth. The present study investigated whether steady-state content of acetylcholine (ACh) and its metabolite choline (Ch) are altered in the retina of eyes developing axial myopia, in both tree shrews and chicks. Retinal ACh and Ch content were measured using reverse-phase high-performance liquid chromatography. Posterior and anterior retinal samples were analyzed from myopic (form deprived) and control eyes as well as age-matched normal eyes. Normative data on retinal neurotransmitter content demonstrated that chick retinas contained less than half the ACh and Ch neurotransmitter content of tree shrews when normalized to retinal protein (ACh: 61 ± 3 vs. 130 ± 6 ng, Ch: 131 ± 5 vs. 347 ± 25 ng). There was no significant difference in either ACh or Ch content between myopic and contralateral control eyes in either tree shrews or chicks, irrespective of the degree of myopia. This finding was consistent for both posterior, anterior, and consequently whole retinal samples. In contrast, dopamine and DOPAC contents were found to be reduced in myopic compared to control eyes of the same tree shrews (dopamine −6.9% and DOPAC −15.5%) and chicks (dopamine −12.3% and DOPAC −28.2%). These findings demonstrate that, contrary to dopamine and DOPAC content, steady-state retinal acetylcholine and choline content is not significantly altered during myopia development.
Localization of nitric oxide synthase in the tree shrew retina
- QI-LIN CAO, HEATHER A. MURPHY, HEYWOOD M. PETRY
-
- Journal:
- Visual Neuroscience / Volume 16 / Issue 3 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 399-409
-
- Article
- Export citation
-
Nitric oxide (NO) is a novel neuronal messenger that likely influences retinal function by activating retinal guanylyl cyclase to increase levels of cGMP. In the present study, the localization of neuronal nitric oxide synthase (nNOS, Type I NOS) in the cone-dominant tree shrew retina was studied using NADPH-d histochemistry and nNOS immunocytochemistry. Both NADPH-d and nNOS-immunoreactivity (IR) labeled the inner segments of rods and the myoids of a regular subpopulation of cones, with their corresponding nuclei outlined. The labeled cone myoids were co-localized with a marker for short-wave-sensitive (SWS) cones (S-antigen) and also displayed the regular triangular packing and density (7%) characteristic of SWS cones in tree shrew and other mammalian retinas. These measures confirmed the identity of the labeled cones as SWS cones. Photoreceptor ellipsoids of all cones were strongly labeled by NADPH-d reactivity, but lacked nNOS-IR. Another novel finding in tree shrew retina was that both NADPH-d and nNOS-IR labeled Müller cells, which have not been labeled by nNOS-IR in other mammalian retinas. Consistent with findings in rod-dominant retinas, two types of amacrine cells at the vitreal edge of the inner nuclear layer and a subpopulation of displaced amacrine cells at the scleral edge of the ganglion cell layer were labeled by both NADPH-d and nNOS-IR. Processes of these labeled cells were seen to extend into the inner plexiform layer, where dense punctate label was seen, especially in the central sublamina. These results show that localization of NOS in the cone-dominant tree shrew retina shares some common properties with rod-dominant mammalian retinas, but also shows some species-specific characteristics. The new finding of nNOS localization in tree shrew SWS cones and rods, but not in other cones, raises interesting questions about the roles of NO in the earliest level of visual processing.