Efficacy of a novel prewarming system in the prevention of perioperative hypothermia. A prospective, randomized, multicenter study.

BACKGROUND: Perioperative hypothermia is a common complication during general anesthesia. Although rewarming of patients before surgery has been used as a preventive measure and some guidelines recommend it, the implementation of prewarming for every surgical patient is cumbersome. Therefore, we sought to determine the efficacy of two novel prewarming methods that could facilitate prewarming in daily practice. METHODS: This was a prospective, randomized, multi-center, controlled study. After IRB approval and informed consent, 90 patients undergoing surgery of 30-120 min duration with general anesthesia were randomly assigned to three groups: 1) standard preoperative insulation (Group A); 2) passive preoperative insulation with a commercial prewarming suit (Group B); 3) active preoperative prewarming with a forced-air warmer connected to a prewarming suit (Group C). All patients received warmed IV fluids and intraoperative forced air warming after induction of anesthesia. Oral temperatures were recorded in the preoperative and postoperative periods. Intraoperative core temperatures were measured with an esophageal probe. RESULTS: Repeated-measures analysis of variance (ANOVA) and post hoc Scheffé's test identified a significantly higher core temperature in the actively prewarmed group (Group C) compared to both passive groups (A, B) at 15, 30, 45, 60, and 75 min (P<0.05) after induction of anesthesia and at the end of surgery. During the first 30 min after admission at PACU, also higher oral temperatures were measured in Group C, compared with both passive insulation groups. CONCLUSION: In our study active prewarming with a forced-air warmer and an insulating prewarming suit achieves significantly higher core temperatures during anesthesia and at the end of surgery and avoids hypothermia at the end of surgery compared to commercial or conventional insulation techniques.

For whales and seals the ocean is not blue: a visual pigment loss in marine mammals.

Most terrestrial mammals have colour vision based on two spectrally different visual pigments located in two types of retinal cone photoreceptors, i.e. they are cone dichromats with long-to-middle-wave-sensitive (commonly green) L-cones and short-wave-sensitive (commonly blue) S-cones. With visual pigment-specific antibodies, we here demonstrate an absence of S-cones in the retinae of all whales and seals studied. The sample includes seven species of toothed whales (Odontoceti) and five species of marine carnivores (eared and earless seals). These marine mammals have only L-cones (cone monochromacy) and hence are essentially colour-blind. For comparison, the study also includes the wolf, ferret and European river otter (Carnivora) as well as the mouflon and pygmy hippopotamus (Artiodactyla), close terrestrial relatives of the seals and whales, respectively. These have a normal complement of S-cones and L-cones. The S-cone loss in marine species from two distant mammalian orders strongly argues for convergent evolution and an adaptive advantage of that trait in the marine visual environment. To us this suggests that the S-cones may have been lost in all whales and seals. However, as the spectral composition of light in clear ocean waters is increasingly blue-shifted with depth, an S-cone loss would seem particularly disadvantageous. We discuss some hypotheses to explain this paradox.

Heterogeneous distribution of AMPA glutamate receptor subunits at the photoreceptor synapses of rodent retina.

In the retina the segregation of different aspects of visual information starts at the first synapse in signal transfer from the photoreceptors to the second-order neurons, via the neurotransmitter glutamate. We examined the distribution of the four AMPA glutamate receptor subunits GluR1-GluR4 at the photoreceptor synapses in mouse and rat retinae by light and immunoelectron microscopy and serial section reconstructions. On the dendrites of OFF-cone bipolar cells, which make flat, noninvaginating contacts postsynaptic at cone synaptic terminals, the subunits GluR1 and GluR2 were predominantly found. Horizontal cell processes postsynaptic at both rod and cone synaptic terminals preferentially expressed the subunits GluR2, GluR2/3 and GluR4. An intriguing finding was the presence of GluR2/3 and GluR4 subunits on dendrites of putative rod bipolar cells, which are thought to signal through the sign-inverting metabotropic glutamate receptor 6, mGluR6. Furthermore, at the rod terminals, horizontal cell processes and rod bipolar cell dendrites showed labelling for the AMPA receptor subunits at the ribbon synaptic site or perisynaptically at their site of invagination into the rod terminal. The wide distribution of AMPA receptor subunits at the photoreceptor synapses suggests that AMPA receptors play an important role in visual signal transfer from the photoreceptors to their postsynaptic partners.

Photoreceptor types and distributions in the retinae of insectivores.

The retinae of insectivores have been rarely studied, and their photoreceptor arrangements and expression patterns of visual pigments are largely unknown. We have determined the presence and distribution of cones in three species of shrews (common shrew Sorex araneus, greater white-toothed shrew Crocidura russula, dark forest shrew Crocidura poensis; Soricidae) and in the lesser hedgehog tenrec Echinops telfairi (Tenrecidae). Special cone types were identified and quantified in flattened whole retinae by antisera/antibodies recognizing the middle-to-long-wavelength-sensitive (M/L-)cone opsin and the short-wavelength-sensitive (S-)cone opsin, respectively. A combination of immunocytochemistry with conventional histology was used to assess rod densities and cone/rod ratios. In all four species the rods dominate at densities of about 230,000-260,000/mm2. M/L- and S-cones are present, comprising between 2% of the photoreceptors in the nocturnal Echinops telfairi and 13% in Sorex araneus that has equal diurnal and nocturnal activity phases. This suggests dichromatic color vision like in many other mammals. A striking feature in all four species are dramatically higher S-cone proportions in ventral than in dorsal retina (0.5% vs. 2.5-12% in Sorex, 5-15% vs. 30-45% in Crocidura poensis, 3-12% vs. 20-50% in Crocidura russula, 10-30% vs. 40-70% in Echinops). The functional and comparative aspects of these structural findings are discussed.

An alternative pathway for rod signals in the rodent retina: rod photoreceptors, cone bipolar cells, and the localization of glutamate receptors.

In the mammalian retina, extensive processing of spatiotemporal and chromatic information occurs. One key principle in signal transfer through the retina is parallel processing. Two of these parallel pathways are the ON- and OFF-channels transmitting light and dark signals. This dual system is created in the outer plexiform layer, the first relay station in retinal signal transfer. Photoreceptors release glutamate onto ON- and OFF-type bipolar cells, which are functionally distinguished by their postsynaptic expression of different types of glutamate receptors, namely ionotropic and metabotropic glutamate receptors. In the current concept, rod photoreceptors connect only to rod bipolar cells (ON-type) and cone photoreceptors connect only to cone bipolar cells (ON- and OFF-type). We have studied the distribution of (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunits at the synapses in the outer plexiform layer of the rodent retina by immunoelectron microscopy and serial section reconstruction. We report a non-classical synaptic contact and an alternative pathway for rod signals in the retina. Rod photoreceptors made synaptic contact with putative OFF-cone bipolar cells that expressed the AMPA glutamate receptor subunits GluR1 and GluR2 on their dendrites. Thus, in the retina of mouse and rat, an alternative pathway for rod signals exists, where rod photoreceptors bypass the rod bipolar cell and directly excite OFF-cone bipolar cells through an ionotropic sign-conserving AMPA glutamate receptor.

Horizontal cells of the rabbit retina are non-selectively connected to the cones.

Mammalian horizontal cells have generally been assumed to be spectrally non-selective in their cone contacts until recently, when specific contacts have been found for some species. The rabbit retina is frequently studied as a representative of dichromatic mammalian retinae. These are the reasons for elucidating the connections of the two types of horizontal cells (A-HCs and B-HCs) with the green-sensitive and blue-sensitive cones of the rabbit retina. Individual A-HCs and B-HCs were revealed by Lucifer Yellow injections, the total cone population overlying them was stained using peanut agglutinin, and the blue cones among these were identified by the antiserum JH 455 against blue cone opsin. Both A-HCs and B-HCs indiscriminately contact the two cone types available. This holds for the green cone-dominated dorsal retina and the blue cone-dominated ventral retina. No evidence was found for a third, potentially blue cone-selective, horizontal cell type [postulated by Famiglietti, E. V. (1990) Brain Res., 535, 174-179].

Absence of short-wavelength sensitive cones in the retinae of seals (Carnivora) and African giant rats (Rodentia).

Most non-primate mammals have two types of cone: short-wavelength sensitive (S) and middle-to-long-wavelength sensitive (M/L) cones. In two species of African giant rats, Cricetomys gambianus and C. emini, and in two species of earless seals, Phoca hispida and P. vitulina, the retinal cone types and cone distributions were assessed with antibodies specific for the M/L-cone opsin and the S-cone opsin, respectively. All four species were found to completely lack S-cones, while M/L-cones were present in low densities. M/L-cone densities, rod densities and cone/rod ratios were determined across the retina. Cone proportions are about 0.3-0. 5% in C. gambianus, 0.5-0.8% in C. emini, and 1.5-1.8% in P. hispida. An absence of S-cones has previously been reported in a few nocturnal mammals. As earless seals are visually active during night and day, we conclude that an absence of S-cones is not exclusively associated with nocturnality. The functional and comparative aspects are discussed.

Calcium-binding proteins in the retina of a calbindin-null mutant mouse.

Calcium-binding proteins are abundantly expressed in many neurons of mammalian retinae. Their physiological roles are, however, largely unknown. This is particularly true for calcium-modulating proteins ("calcium buffers") such as calbindin D28k. Here, we have studied retinae of wildtype (+/+) and calbindin-null mutant (-/-) mice by using immunocytochemical methods. Although calbindin immunoreactivity was completely absent in the calbindin (-/-) retinae, those cells that express the protein in wildtype retinae, such as horizontal cells, were still present and appeared normal. This was verified by immunostaining horizontal cells for various neurofilament proteins. In order to assess whether other calcium-binding proteins are upregulated in the mutant mouse and may thus compensate for the loss of calbindin, mouse retinae were also immunolabeled for parvalbumin, calretinin, and a calmodulin-like protein (CALP). In no instance could a change in the expression pattern of these proteins be detected by immunocytochemical methods. Thus, our results show that calbindin is not required for the maintenance of the light-microscopic structure of the differentiated retina and suggest roles for this protein in retinal function.

Starburst cholinergic amacrine cells in the tree shrew retina.

In all mammalian retinae studied to date, starburst cholinergic amacrine cells are a consistently occurring cell type. Here, we show that the cone-dominated retina of the tree shrew also has starburst cells with the characteristic radially symmetric branching pattern known from other species. Dendritic field sizes increase from 150 microm in the central retina to 300 microm in the retinal periphery. The characteristic morphology is established early during postnatal development. Labelling the starburst cholinergic cells with an antibody against choline acetyltransferase (ChAT) reveals two dendritic strata in the inner plexiform layer and two corresponding soma populations in the inner nuclear layer (orthotopic) and ganglion cell layer (displaced). These features are present in the adult and in early postnatal stages. In the adult, the density of the orthotopic population as well as the displaced population peaks in the central retina at about 2,200 cells/mm2 and has a peripheral minimum of 400 cells/mm2. These properties are qualitatively similar to those of starburst cells in rod-dominated retinae. In contrast to findings in other mammals, we did not see gamma-aminobutyric acid (GABA) or glutamic acid decarboxylase 65 kDa (GAD65) immunoreactivity in tree shrew starburst cells. These cells also appear to lack synaptophysin, a ubiquitous synaptic vesicle protein detected in the starburst cells of some other mammals. However, synaptoporin, a homologous synaptic vesicle protein, appears to be present in tree shrew starburst cells.

The horizontal cells of artiodactyl retinae: a comparison with Cajal's descriptions.

The morphology of horizontal cells in ox, sheep, and pig retinae as observed after Lucifer Yellow injections are described and compared with the descriptions of Golgi-stained cells by Ramón y Cajal (1893). Horizontal cells in the retinae of less domesticated species, wild pig, fallow and sika deer, mouflon, and aurochs were also examined. All these retinae have two types of horizontal cell; their morphologies are in common, although with some familial differences. Their basic appearance is as Cajal described; except in one important respect, a single axon-like process could not be identified on the external horizontal cells. It is concluded that external horizontal cells of artiodactyls correspond to the axonless (A-type) cells of other mammals. Cajal's internal horizontal cells have a single axon which contacts rods. This type corresponds to the B-type cells of other mammalian retinae. Artiodactyl A- and B-type horizontal cells differ from those of many other mammals in that the B-type dendritic tree is robust and the A-type dendritic tree is delicate. Historically, this morphological difference between orders of mammals has led to some confusion. The comparisons presented here suggest that the morphological types of primate horizontal cells can be integrated into a general mammalian classification.

Blue-cone horizontal cells in the retinae of horses and other equidae.

The morphology of horizontal cells chiefly of the horse, but also of asses, mules, and a zebra, has been examined by Lucifer yellow injections into lightly fixed retinae and by immunocytochemistry. In common with other mammals, equids have a B-type horizontal cell, i.e., a cell with dendrites synapsing with cones and possessing a single axon synapsing with rods. Most mammalian retinae have a further type of horizontal cell, the A-type, also synapsing with cones but without an axon. The second type of horizontal cell in equids also has no axon; otherwise, it is most unusual. Compared with other mammalian A-type cells, it has a vary large dendritic field, both absolutely and relative to the dendritic fields of B-type cells. The dendrites are fine and sparsely branching. Their most striking feature is that they bear a low density of irregularly spaced synaptic terminal aggregates, suggesting their cone contacts are selective. Immunolabelling of S (blue)-cones in horse retina showed that they comprise, depending on retinal location, 10-25% of the cone population. For a single horse A-type cell, it is shown that 44 of its 45 terminal aggregates are congruent with the pedicles of S-cones. Immunostaining with a calbindin antibody demonstrated that each type of horizontal cell forms an independent regular mosaic. The density ratio of B- to A-type cells varied between 5 and 10. This is the first demonstration in a mammalian retina of a horizontal cell type with a direct input exclusively from S-cones.

Unique distribution of somatostatin-immunoreactive cells in the retina of the tree shrew (Tupaia belangeri).

Somatostatin-like immunoreactive cells in the tree shrew retina were studied with the monoclonal antibody S8 against the neuropeptide somatostatin 14. As in some other mammals, immunoreactive somata are exclusively found in the ganglion cell layer. Immunoreactive processes form a sparse main plexus in the inner plexiform layer near the border of the inner nuclear layer; fewer additional processes are found closer to the ganglion cell layer. With retrograde labelling of retinal ganglion cells by injections of the tracer Fast Blue into the superior colliculus and lateral geniculate body and counterstaining of the retinae with S8, approximately 5% of the immunoreactive somata were double-labelled at any retinal location. The vast majority of somatostatin-like immunoreactive cells are thus displaced amacrine cells. Their somata are distributed over the entire retina. Their population density is highest in the temporal retina, with peak densities of approximately 5000 cells/mm2 near the central area and a steep density gradient. In the remaining retina densities are 200-400 cells/mm2, falling to approximately 100 cells/mm2 at the retinal margins. This is in stark contrast to the somatostatin-like immunoreactive cells in other mammalian retinae which have densities of 10-40 cells/mm2 and are confined to restricted retinal regions (inferior retina and/or retinal margin).

Expression of neurofilament proteins by horizontal cells in the rabbit retina varies with retinal location.

Classical neurofibrillar staining methods and immunocytochemistry with antibodies to the light, medium and heavy chain subunits of the neurofilament triplet have been used for in situ and in vitro investigation of the organization of neurofilaments in A- and B-type horizontal cells of the adult rabbit retina. Surprisingly, their expression and organization within a cell is dependent on its location along the dorso-ventral axis of the retina. A-type horizontal cells in superior retina consistently stained with a wide variety of neurofibrillar methods to reveal neurofibrillar bundles, which immunocytochemistry showed to contain all three neurofilament subunits. A-type horizontal cells in inferior retina were uniformly refractory to neurofibrillar staining, although they expressed all three subunits. However, there was less of the light and medium subunits; the organization of the filaments into bundles (neurofibrils) is minimal. B-type horizontal cells could not be stained with any neurofibrillar method and were not recognizable by in situ immunocytochemistry. However, B-type cells could be seen to express all three subunits in vitro, but the expression of the light and medium subunits was weak. There was only a slight difference between B-type cells taken from superior and inferior retina. Combined with the results of recent transfection studies, these findings suggest that the amount of the light neurofilament subunit present in a horizontal cell determines its content of neurofibrillar bundles, and that rabbit horizontal cells may contain more neurofilament protein, particularly of the heavy subunit, than is used for neurofilament formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of dendritic trees of rabbit retinal alpha ganglion cells: relation to differential retinal growth.

To provide a quantitative description of the postnatal development of dendritic trees in alpha ganglion cells of the rabbit retina, these cells were stained either by intracellular injection of Lucifer yellow or by application of the lipophilic dye DiI. This was done at three developmental stages: postnatal day (P) 8/9, P 16/17, and in adults. For different retinal locations we quantified the alpha cell dendritic field area, the number of dendritic branch points, and the average dendritic length between branch points. According to the alpha cell location, the data were collected in three groups representing the retinal center, midperiphery, and far periphery, respectively. The data were then correlated with the postnatal retinal expansion which is known to differ among the above topographic regions of the retinae (Reichenbach et al., 1993). Our results show that the growth of alpha ganglion cell dendrites is not proportional to, but significantly exceeds, that of the local retinal tissue. Between P 8/9 and adulthood, the area of central alpha cells increases almost six-fold from 26,000 to 144,000 microns 2 (retinal expansion: 2.2-fold), and that of peripheral cells more than 15-fold from 35,000 to 556,000 microns 2 (retinal expansion: four-fold). During this period, the coverage factor of alpha cell dendritic fields increases about three-fold, and reaches adult levels of about 3 (retinal center) and 2.2 (periphery), respectively. The number of dendritic branch points remains nearly constant, and the distance between them increases by a factor close to the square root of the factor by which the dendritic field area grows. Thus, it appears that, from the second postnatal week on, dendritic trees of rabbit alpha ganglion cells increase by intense "interstitial growth," rather than by outgrowth of (new) dendritic branches. This growth pattern is different from that of some other rabbit retinal ganglion cell types, and of alpha ganglion cells of the cat retina, whose dendritic trees expand at a rate equal to or less than that of the surrounding retinal tissue. The consequences for synaptic contacts with bipolar and amacrine cells are discussed; they suggest a high degree of synaptic plasticity during normal postnatal retinal growth.

Morphological types of horizontal cell in rodent retinae: a comparison of rat, mouse, gerbil, and guinea pig.

Retinal horizontal cells of four rodent species, rat, mouse, gerbil, and guinea pig were examined to determine whether they conform to the basic pattern of two horizontal cell types found in other mammalian orders. Intracellular injections of Lucifer-Yellow were made to reveal the morphologies of individual cells. Immunocytochemistry with antisera against the calcium-binding proteins calbindin D-28k and parvalbumin was used to assess population densities and mosaics. Lucifer-Yellow injections showed axonless A-type and axon-bearing B-type horizontal cells in guinea pig, but revealed only B-type cells in rat and gerbil retinae. Calbindin immunocytochemistry labeled the A- and B-type populations in guinea pig, but only a homogeneous regular mosaic of cells with B-type features in rat, mouse, and gerbil. All calbindin-immunoreactive horizontal cells in the latter species were also parvalbumin-immunoreactive; comparison with Nissl-stained retinae showed that both antisera label all of the horizontal cells. Taken together, the data from cell injections and the population studies provide strong evidence that rat, mouse, and gerbil retinae have only one type of horizontal cell, the axon-bearing B-type, whereas the guinea pig has both A- and B-type cells. Thus, at least three members of the family Muridae differ from other rodents and deviate from the proposed mammalian scheme of horizontal cell types. The absence of A-type cells is apparently not linked to any peculiarities in the photoreceptor populations, and there is no consistent match between the topographic distributions of the horizontal cells and those of the cone photoreceptors or ganglion cells across the four rodent species. However, the cone to horizontal cell ratio is rather similar in the species with and without A-type cells.

Unexpected presence of neurofilaments in axon-bearing horizontal cells of the mammalian retina.

In several mammals only one of the two types of retinal horizontal cell, the axonless A-type, appears to express neurofilaments. Neurofilament immunostaining of rodent retinas reveals a horizontal cell plexus that has previously been interpreted as belonging to A-type cells. Our intracellular Lucifer yellow injections strongly suggest that there are no A-type horizontal cells in rat and gerbil. Counterstaining of dye-injected cellular structures with a neurofilament antibody directly shows that the axon terminal systems of the axon-bearing B-type horizontal cells contain neurofilaments. These unexpected findings explain and reinterpret the neurofilament plexus in rodent retinas. In contrast, Lucifer yellow injections in guinea pig retina reveal both A- and B-type horizontal cells, showing that horizontal cell types are not uniform among rodents. In the guinea pig retina both A-type cells and B-type axon terminal systems contain neurofilaments.

Horizontal cells in the cone-dominated tree shrew retina: morphology, photoreceptor contacts, and topographical distribution.

While most mammalian retinas are rod dominated, in the tree shrew retina 95% of the photoreceptors are cones. We studied three shrew horizontal cells to look for features associated with this unusual photoreceptor arrangement. The morphology of horizontal cells was revealed by intracellular injections of Lucifer yellow, and their photoreceptor contacts were assessed by light and electron microscopy. Horizontal cell topography was studied in material stained with a neurofilament antibody and with toluidine blue. The tree shrew has two types of horizontal cell that are basically the same as A- and B-type horizontal cells of other mammals. All the photoreceptor contacts of the larger, axonless, A-type cell and the dendritic contacts of the smaller, axon-bearing, B-type cell are with cones. Both types contact nearly all the cones in their dendritic field and both types synapse with both red and blue cones. There is no anatomical evidence for chromatic selectivity. The sparsely branched B-type horizontal cell axon probably contacts rods as in other mammals. The unusual features of the A-type cell are the profuse dendritic terminal arborizations and the large dendritic field size. These features may be related to the abundance of cones but do not justify the conclusion for a special type of horizontal cell as has previously been supposed. Both types of horizontal cell have a central-peripheral density gradient; at any location B-type cells are up to three times as numerous as A-type cells. There are detailed features of the distributions that differ from those of other mammalian horizontal cells. The density maximum of B-type cells is in inferior retina and roughly coincides with that of the cones; the A-type maximum is located more superiorly. Neither maximum is colocalized with the ganglion cell peak in the central area. The mosaic of B-type cells is much more regular than that of A-type cells.

Dye-induced photolesion in the mammalian retina: glial and neuronal reactions.

Irradiation in the presence of a dye applied to the extracellular space is known to produce degenerative features in irradiated neurones and fibers. In the present study, we confirmed the potential use of this procedure as a lesion technique by showing the removal of degenerating elements as part of the glial reaction to the lesion. The dye Rose Bengal was applied to the vitreous body of a rat eye and a T-shaped irradiation pattern was projected onto the retina within the absorption band of the dye. Degenerative features were restricted to the irradiated area, which could be readily identified from its shape. Retinae examined after various survival times showed that macrophages invaded the damaged area within 1 day, and that mitotic activity of reactive glial cells subsequently occurred in the vicinity of the wound. Both cell types were identified by their structural features. Macrophages were also revealed by a staining technique using the dye Nile Red, whereas reactive glial cells were immunolabeled with an antibody directed against the glial fibrillary acidic protein. Reactive glial cells helped the macrophages to gradually remove injured cells and damaged processes. Their main task, however, appeared to be in scar formation, since their processes seemed to suture the lips of the wound together and restore the limiting membrane at the inner retina. After 2 months' survival time, the parent ganglion cells of most disrupted axon bundles had retrogradely degenerated, but regenerating ganglion cell axons were also observed. These results provide some new data about healing processes in the retina. They demonstrate that the dye-induced photolesion technique can be used to either remove or axotomize selected neurones in neural networks which have been made optically accessible.

Morphological types of ganglion cells in the dog and wolf retina.

The morphological types of ganglion cells in the dog and wolf retina were studied by intracellular staining with Lucifer Yellow. These retinae contain a range of ganglion cell types that closely correspond to those found in cat retina: alpha cells with large somata and large, relatively densely branched dendritic trees; beta cells with medium-sized somata and small, densely branched dendritic trees; and a variety of other types with smaller somata and varying dendritic branching patterns and dendritic field sizes. The correspondence of canine and cat ganglion cell types strengthens the view that there is a common set of ganglion cell types in carnivores. Alpha and beta cell dendritic trees of dog and wolf are monostratified in either the inner or the outer part of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Dendritic field sizes of dog alpha and beta cells increase from the central area to peripheral retina: alpha cell fields from 160-200 microns to about 1,100 microns diameter, and beta cell fields from 25 microns to about 360 microns diameter. These sizes are quantitatively very similar to those found in cat retina. The close qualitative and quantitative morphological correspondence of cat and dog ganglion cells suggests that they are also functionally very similar. It is likely that dog alpha cells have brisk-transient (Y), and dog beta cells brisk-sustained (X) concentric receptive fields. From the smallest beta cell sizes it is concluded that the visual acuity of the dog may be as good as that of the cat.

Topography of ganglion cells in the dog and wolf retina.

The topographical distribution of retinal ganglion cells in seven breeds of dog (Canis lupus f. familiaris) and in the wolf (Canis lupus) was studied in retinal wholemounts stained with cresyl violet or with a reduced silver method. A prominent feature of all wolf retinae was a pronounced "visual streak" of high ganglion cell density, extending from the central area far into both temporal and nasal retina. By contrast, either a pronounced or a moderate visual streak was found in dog retinae. It is hypothesized that a pronounced streak is an archetypal feature of Canis lupus, and that the moderate streak in some dogs is a corollary of breeding during domestication. Irrespective of the differences in streak form and retinal area, the estimated total number of ganglion cells was about 200,000 cells in the wolf and 115,000 in the dog. Ganglion cell density maxima in the central area of the wolf were about 12,000-14,000/mm2, and in the dog they ranged from 6,400/mm2 to 14,400/mm2. This implies individual differences in visual acuity. Alpha ganglion cells constituted 3-14% of all ganglion cells in the dog and 1-18% in the wolf, depending on retinal location. A distinct feature of all dogs and wolves was the absence of alpha cells in a substantial region of temporal peripheral retina. This has not been found in any other mammalian species and suggests corresponding functional deficits.