Morphological identification of on- and off-centre brisk transient (Y) cells in the cat retina

Brisk transient (Y) cells were recorded extracellularly in the cat retina. The position and shape of their receptive field centres were plotted on a tangent screen, together with retinal landmarks, such as blood vessels adjacent to the recording area. After recording the retina was processed as a whole mount and stained with a reduced-silver method (see appendix). This technique stains the entire alpha cell population including the dendritic trees. Alpha cells are the morphological correlate of the brisk transient cells (Boycott & W?ssle 1974; Cleland et al. 1975). Maps of the screen plot and the histological preparation could be accurately superimposed by means of the retinal landmarks and each recorded brisk transient unit could unequivocally be attributed to a particular alpha cell. Alpha cell dendritic trees are unistratified in either of two laminae within the inner plexiform layer: (1) close to the inner nuclear layer border, 'outer alpha cells', or (2) about 10 micrometers further towards the ganglion cell layer, 'inner alpha cells'. This stratification difference can be observed in whole mounts for large populations of cells (W?ssle et al. 1981). Of the recorded brisk transient cells, all on-centre units were inner alphas and all off-centre units outer alphas.     

Quantitative analysis of dendritic morphology of the alpha and delta retinal ganglion cells in the rat: A cell classification study

Type I retinal ganglion cells in the rat have been classified into several groups based on the cell body size and dendritic morphology. Considerable overlap and heterogeneity within groups have been reported, which is especially obvious for the morphology of the dendritic tree. For that purpose, we analysed quantitatively the dendritic morphology of the alpha and delta rat retinal ganglion cells, using parameters which provide information on the dendritic field size, shape of the dendritic tree and dendritic branching complexity. We show that the alpha and delta cells have significantly different dendritic field sizes. Taking into account the level of stratification of the dendritic tree, we found a difference in the properties of the dendritic morphology between alpha inner and alpha outer cells, while the opposite result was obtained for the delta inner and delta outer delta cells. In this study we also call attention to the relationship between morphological parameters and retinal eccentricity. The significance of our quantitative results in terms of present alpha and delta rat retinal ganglion cell classification is discussed.     

Asymmetrical dendritic fields of retinal ganglion cells

By use of Golgi chrome—silver impregnation, studies were made of the dendritic branchings of feline and frog ganglion cells. It was shown that besides the known varieties of ganglion cells there were asymmetrical neurones whose dendrites lay all to one side. Essential differences distinguished these ganglion cells in the cat from those in the frog, differences depending upon the architectonics of the inner plexiform layer, which is broad and subdivided into layers in the frog, and narrow in the cat. We discuss the possible role of neurones with a unilateral arrangement of dendrites in relation to know electrophysiological data on retinal detectors and the receptive fields of ganglion cells.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 301–307, May–June, 1971.     

Remodeling of retinal ganglion cell dendrites in the absence of action potential activity

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX-treated, non-TTX-treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.     

Why is there discordant diversity in sengi (Mammalia: Afrotheria: Macroscelidea) taxonomy and ecology?

The seventeen species of sengis or elephant-shrews form a well-defined clade of mammals endemic to Africa that occupy the extremes of terrestrial habitats, from coastal deserts to montane forests. Because of their isolation on Africa soon after the break-up of Gondwanaland, theoretically sengis initially evolved with little competition from other placental radiations. Their life history features include myrmecophagy, saltatorial gaits, no or limited use of nests, social monogamy, small litters of precocial young and absentee maternal care of neonates. These traits together are unique to the Macroscelidea and represent a wedding of features usually associated with either small antelopes or anteaters. Combined, these features define an adaptive syndrome that presumably has been relatively immune to competition from contemporary mammals, partially due to phylogenetic inertia. Yet paradoxically, the syndrome is well suited to a wide range of terrestrial habitats, resulting in low taxonomic diversity. Because of their unusual phylogeny and low species diversity, conservation interest is high for those sengis with relatively low densities in fragmented forests.     

Remodeling of retinal ganglion cell dendrites in the absence of action potential activity.

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX-treated, non-TTX-treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.     

Cell-type specific dendritic contacts between retinal ganglion cells during development.

The extent of a neuron's dendritic field defines the region within which information is processed. The dendritic fields of functionally distinct ON and OFF center retinal ganglion cells (RGCs) form separate mosaics across the retina. Within each mosaic, neighboring dendritic fields overlap by a constant amount, sampling the visual field with the appropriate coverage. Contact-mediated lateral inhibition between neighboring RGCs has long been thought to regulate both the extent and overlap of dendritic fields during development. Here we show that dendro-dendritic contact exists between developing RGCs and occurs in a manner that would regulate the formation of ON and OFF mosaics separately. Dye-filled neighboring ON and OFF ferret alpha RGCs were reconstructed using multiphoton microscopy. At all neonatal ages examined, we observed dendro-dendritic contacts between RGCs of the same sign (ON/ON; OFF/OFF), but never between cells of opposite signs (ON/OFF). Terminal dendrites of one cell often touched a dendrite of its neighbor as they intersected. In some instances, the distal dendrite of one cell formed a fascicle with the proximal process of its neighbor. Alpha cells did not form contacts with neighboring beta cells of the same sign. Together, these observations suggest that dendro-dendritic contact between RGCs is cell-type specific. Dendritic contacts were observed even before the alpha cell arbors were completely stratified, suggesting that cell-cell recognition may take place early in their development. For each cell type, the relative overlap of dendritic fields was constant with age, despite a two-fold increase in field area. We suggest that dendro-dendritic contacts may be sites of intercellular signaling that could regulate local extension of dendrites to maintain the relative overlap of RGCs within a mosaic during development.     

Freeliving nematodes from the Salton Sea

Thirteen species, or putative species, of freeliving nematodes are recorded from a variety of habitats in the hypersaline Salton Sea, the largest inland lake in California. This doubles the number of species of multicellular invertebrates known to occur in the lake. All species are referable to known marine genera, and are regarded as having a marine coastal origin. The range of taxa present is representative of the full taxonomic spread found in marine coastal habitats, suggesting that a wide range of marine nematode taxa are capable of adapting to the hypersaline conditions. The broad spectrum of feeding types present suggests that nematodes play a variety of ecological roles within the lake.     

Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely 'transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these-the dental morphology known as zalambdodonty-was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages-marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene.     

Acid Phosphatase as a Selective Marker for a Class of Small Sensory Ganglion Cells in Several Mammals: Spinal Cord Distribution,Histochemical Properties,and Relation to Fluoride-Resistant Acid Phosphatase (FRAP) of Rodents

Fluoride-resistant acid phosphatase (FRAP) activity as characterized in rat and mouse was studied in sensory ganglion and spinal cord of several mammals, using both the Gomori lead-ion capture and azo-dye coupling methods. FRAP was specifically localized to small- and medium-diameter primary afferent neurons and inner substantia gelatinosa of all nonrodent animals studied, including rabbit, cat, dog, monkey, cow, and human. In rabbit, sciatic nerve transection resulted in depletion of enzymatic activity in ipsilateral spinal cord dorsal horn in a pattern corresponding to the distribution of central terminals of the nerve. Further analysis of the substrate specificity and pH dependence of FRAP was carried out primarily in rat sensory ganglion and spinal cord; the enzyme was found to hydrolyze a wide variety of phosphomonoesters in a relatively nonselective manner at both pH 5 and pH 7, including 5′-nucleotides, phosphorylated amino acids, and several exogenous compounds.

The visualization of FRAP-like activity in several nonrodent species is discussed with reference to previous work indicating its presence only in mouse and rat. Technical factors are considered that limit the applicability of the lead-ion histochemical method in demonstration of FRAP and in efforts at functional characterization of the enzyme, especially in light of its ability to hydrolyze a broad spectrum of substrates over a wide pH range. Alternative interpretations of the expression of acid phosphatase activity in a select class of small sensory ganglion cells are suggested, including several possible nonsynaptic roles of FRAP in the peripheral nervous system.     

Morphology and mosaic of on- and off-beta cells in the cat retina and some functional considerations

The beta type of ganglion cell can be subdivided in Golgi-stained whole mounts of the cat retina according to the branching level of the dendritic tree in the inner plexiform layer. The dendritic branching level of on-beta cells is nearer to the cell body; that of off-beta cells is about 10 micrometers further outwards. After horseradish peroxidase (HRP) injection into the lateral geniculate nucleus all beta cells were labelled. In this way it is shown that about 55% of all ganglion cells, irrespective of retinal topography, are beta cells. The spatial distribution of on- and off-beta cells was studied from the HRP-labelled material. On-beta cells form a lattice with regular inter-cell spacings; off-beta cells are also regularly arrayed. The two lattices are superimposed independently of each other. Beta cells are commonly assumed to be associated with the resolution of fine detail in the cat vision system. The mosaic of beta cells imposes some constraints and permits some predictions to be made with respect to the cat's visual discrimination.     

The ganglion cell layer of the retina of the rat: a Golgi study.

In whole-mounts of Golgi stained rat retinae four cell types are described in the ganglion cell layer. Three of these cell types are considered to be analogous to the alpha, delta and gamma cells described in the cat retina by Boycott & W?ssle (1974). The fourth cell type is thoughtt to be a displaced amacrine cell. All the cell types described are present in all parts of the retina. There is no evidence for an increase in dendritic field size with increasing distance from the optic disk.     

Dendritic field structure of the large ganglion cells in the retina of <Emphasis Type="Italic">Pholidapus dybowskii</Emphasis> Steindachner, 1880 (Pisces: Perciformes: Stichaeidae)

This paper deals with the dendritic field structure of three large ganglion cell types in the retina of a marine teleost, Pholidapus dybowskii. Cells were retrograde labeled with horseradish peroxidase applied to lesioned fibers of the optic nerve. Their morphology was studied in wholemounted retinae. Dendritic fields of α_ab cells were more complex. Their structural complexity measured using Kolmogorov and information fractal dimensions exceeded significantly those of α_a and biplexiform cells. The latter two types exhibited no significant differences in complexity and spatial heterogeneity of dendritic field. The cell types studied differed dramatically in the relationships between fractal and nonfractal parameters of their dendritic arbors. The functional and evolutionary implications of the dendritic field structure of retinal ganglion cells are discussed.     

Development of the mouse retina: emerging morphological diversity of the ganglion cells

The time course and regulatory mechanisms of dendritic development are subjects of intense interest. We approached these problems by investigating dendritic morphology of retinal ganglion cells (RGCs) at four early postnatal stages. The RGCs develop from a diffusely stratified and poorly differentiated group at birth (P0), to 16 distinct, morphologically well-defined subtypes before eye opening (P13). Even before bipolar cells make synaptic contacts with the RGCs (P8), most adultlike RGC subtypes are already present. Similar to previous studies in other mammalian species, our results indicate that the initiation of the RGC morphological maturation is independent of light stimulation and of formation of glutamatergic synapses. This study narrowed down the window of RGCs morphological maturation and highlighted a few early postnatal events as potential factors controlling the developmental process. Because mouse is the most popular mammalian model for genetic manipulation, this study provided a foundation for further exploring regulatory mechanisms of RGC dendritic development.     

Localisation of substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat: a light- and electron-microscopic study

The present study describes substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat. About 60% of neurons in the monkey ciliary ganglion and 40% in the cat ciliary ganglion were substance P-like immunoreactive, ranging from faint to moderate staining. Substance P-like immunoreactivity was located in cell bodies, dendritic profiles and axons. In the monkey, substance P-like immunoreactive pericellular arborisations were associated with about 0.5%–3% of the ganglion cells, which were either negatively, faintly or moderately stained. An electron-microscopic study demonstrated the presence of either substance P-like immunoreactive positive or negative axon terminals synapsing or closely associated with positive dendritic profiles in both the monkey and cat ciliary ganglia. The results suggest that substance P plays an important role in the ciliary ganglion, perhaps as a modulator or transmitter.     

Dynamics of behaviour during neuronal morphogenesis in culture

We report a developmental sequence in the type and frequency of behaviours of neurons differentiating in vitro. We characterised these changes with extensive analysis of time-lapse sequences from both the continuing cell line pheochromocytoma PC12 and primary mixed cell culture of cat and mouse central nervous system. PC12 cells activated by nerve growth factor (NGF) differentiate in a uniform and synchronous manner. This allowed the first quantification of changes in different neuron behaviours during morphogenesis. Shortly after NGF activation, PC12 cells are highly labile in morphology and exhibit a large variety of morphological behaviours. During the first week of differentiation, the frequency of these behaviours declines, and gross morphology becomes more stable. The frequency of neurite initiation after 1 week in NGF is one-seventh what it was after 2 days in NGF. Over the same period, neurite retraction declines to one-third, and somal migration ceases altogether. Growth-cone activity does not decline during development. These behaviour changes correlate with published data on the differentiation of the neurite cytoskeleton. A qualitatively similar ontogeny was noted in the differentiation of CNS neurons in mixed cell culture. Major differences occur in the relative timing of changes in behaviours. Mature, stable morphology is not detected in these cultures until 7 weeks in vitro.     

Alterations in the morphology of ganglion cell dendrites in the adult rat retina after optic nerve transection and grafting of peripheral nerve segments

Summary Transected ganglion cell axons from the adult retina are capable of reinnervating their central targets by growing into transplanted peripheral nerve (PN) segments. Injury of the optic nerve causes various metabolic and morphological changes in the retinal ganglion cell (RGC) perikarya and in the dendrites. The present work examined the dendritic trees of those ganglion cells surviving axotomy and of those whose severed axons re-elongated in PN grafts to reach either the superior colliculus (SC), transplanted SC, or transplanted autologous thigh muscle. The elaboration of the dendritic trees was visualized by means of the strongly fluorescent carbocyanine dye DiI, which is taken up by axons and transported to the cell bodies and from there to the dendritic branches. Alternatively, retinofugal axons regrowing through PN grafts were anterogradely filled from the eye cup with rhodamine B-isothiocyanate. The transection of the optic nerve resulted in characteristic changes in the ganglion cell dendrites, particularly in the degeneration of most of the terminal and preterminal dendritic branches. This occurred within the first 1 to 2 weeks following axotomy. The different types of ganglion cells appear to vary in their sensitivity to axotomy, as reflected by a rapid degeneration of certain cell dendrites after severance of the optic nerve. The most vulnerable cells were those with small perikarya and small dendritic fields (type II), whereas larger cells with larger dendritic fields (type I and III) were slower to respond and less dramatically affected. Regrowth of the lesioned axons in peripheral nerve grafts and reconnection of the retina with various tissues did not result in a significant immediate recovery of ganglion cell dendrites, although it did prevent some axotomized cells from further progression toward posttraumatic cell death.     

Morphology and topography of on- and off-alpha cells in the cat retina

Neurofibrillar staining methods were found to stain all alpha cells of the cat retina completely, that is the perikaryon, the axon and the dendritic branches. The dendrites of the alpha cells in vertical sections were found to be unistratified and to occupy two narrow strata in the outer half of the inner plexiform layer. This difference in branching level could also be observed in whole-mount preparations and it has been demonstrated in the preceding paper (Peichl & W?ssle 1981) that it corresponds to the physiological on-off dichotomy. Thus the topographical distribution of on- and off-alpha cells could be studied. They are found to occur in about equal numbers. Both on- and off-alpha cell perikarya form a regular lattice and both lattices are superimposed independently. The dendritic branches of neighbouring alpha cells overlap and each retinal point is covered by the dendritic field of at least one on- and one off-alpha cell. The dendritic trees of on-alpha cells seem to have more small branches and are on the average smaller than those of off-alpha cells. The density of alpha cells was found to peak in the central area whence it continuously decreased towards the retinal periphery.     

A comparative and quantitative study of small intensely fluorescent (SIF) cells in the sympathetic ganglia of some small mammals

This comparative study of the number of SIF cells in the ganglions of the rat, cat, rabbit, mouse and hamster has confirmed that the mean number of SIF cells in the same ganglion of different species varies greatly, for instance in the superior cervical ganglion (SCG) of the rat and the cat, in the stellate ganglion of the cat and the mouse, or in the inferior mesenteric ganglion of the hamster and the other species. There is also considerable variability among individuals of the same animal species. In the SCG, the only ganglion for which there are data on the number of neurons, the ratio of SIF cells to neurons is around 1% in the rat, 0.2% in the rabbit, 0.3% in the mouse and 0.05% in the cat, i.e. a twenty-fold difference between the cat and the rat. Williams et al. (1975) distinguished type 1 SIF cells, corresponding to interneurons, from type 2, which are purely endocrine cells. Type 2 appears to be predominant in all ganglia, except the rabbit SCG where type 1 is highly predominant, and in all species, except the rat, in which this distinction is not applicable. The possible implications of these data on ganglionic functioning are discussed.