A comparison of plasma vitamin C and E levels in two Antarctic and two temperate water fish species

Antarctic fish have a high polyunsaturated lipid content and their muscle cells have a high mitochondria density suggesting that Antarctic fish are under greater oxidative stress than temperate water fish. To test this hypothesis, the plasma concentrations of the antioxidant vitamins E and C were measured in two Antarctic fish species, Pagothenia borchgrevinki and Trematomus bernacchii, and compared with the plasma concentrations of these vitamins in two New Zealand temperate water fish species, blue cod (Parapercis colias) and banded wrasse (Notolabrus fucicola). Neither vitamin is known to be synthesised in fish and so must be obtained from the diet. The plasma from both Antarctic fish species had vitamin E concentrations five to six times higher than those found in the two temperate water fish species. However, significantly higher levels of vitamin C were only found in the plasma of T. bernacchii, a benthic Antarctic fish. The average level of vitamin C in the plasma of the cryopelagic P. borchgrevinki was approximately one-third that of T. bernacchii. The T. bernacchii plasma yielded a high range of vitamin C values, possibly reflecting differences in nutritional status among the animals captured. No beta-carotene was found in any of the fish plasma samples studied. The data suggest that even though Antarctic fish live at -1.5 degrees C they may be exposed to greater metabolic stress from free radical mediated oxidation than temperate water species.     

Immunocytochemical observations on pineal organ and retina of the Antarctic teleosts Pagothenia borchgrevinki and Trematomus bernacchii

In spite of the unique conditions they have to operate under, the pineal organs of Antarctic fishes have not previously been examined. We determined immunohistochemically that in the end-vesicles and the pineal stalks of Pagothenia borchgrevinki (a species found directly beneath the sea-ice) as well as Trematomus bernacchii (a species preferring somewhat deeper water than the former) at least two populations of physiologically-different cells occurred that displayed reactions indicative of typical vertebrate photoreceptors. Comparisons with immunocytochemically treated retinal sections from the eyes of the same two species showed that anti-opsin reactivity, characteristic of rods, was particularly strong in the lumina of the pineal stalks of both species. Anti-visinin reactions stained cones in the retinal sections of both fishes and occurred throughout the pineal organs, but in particular in the end vesicles of the pineals of both species. The difference in preferred habitat depth between the two species appears to have had very little influence on both retinal and pineal immunocytochemistry. It is concluded that the pineal organs of both species, at least during the austral summer, exhibit signs of being directly photo-sensitive.     

Retinal Anatomy of hatchling sea turtles: Anatomical specializations and behavioral correlates

The eyes of three species of sea turtle hatchlings (loggerheads, green turtles, and leatherbacks) possess visual streaks, areas of densely packed ganglion cells running along the antero‐posterior retinal axis. These probably function to provide heightened visual acuity along the horizon. The vertical extent and absolute concentration of cells within the streak, compared to the rest of the retina, differ among the species. Leatherbacks have an additional specialized region (area temporalis) that might enhance their ability to detect prey below them in the water column. Green turtles and loggerheads, but not leatherbacks, show compensatory eye reflexes that keep the visual streak horizontal. Species differences in retinal structure and eye reflexes probably reflect their unique specializations in visual ecology and behaviour.     

The position of the retinal area centralis changes with age in Champsocephalus gunnari (Channichthyidae), a predatory fish from coastal Antarctic waters

Histological examinations of the topographical distribution and the area of highest density (the area centralis: AC) of presumed retinal ganglion cells found in the retina in 0- to 6-year-old Champsocephalus gunnari revealed differences between younger and older fish. Individuals of up to 2 years of age had the AC in the temporal retina, whereas in 3-, 4-, 5- and 6-year-old fish it was positioned in the ventro-temporal region of the retina. The main visual axis in the pitch plane of C. gunnari was shown to shift from facing forward to an upward-forward direction during growth, corresponding to the habitat change in this species from pelagic to benthic. Moreover, the AC in 0- to 3-year-old fish was near the retinal periphery, but displaced towards the inner retina in 4- to 6-year-old fish. This means that the visual axis in the horizontal plane of the younger fish was directed towards the frontal sector of vision, while in the older fish a slightly more lateral position was favoured. Therefore, younger fish can be expected to possess superior binocular vision when it comes to prey closely in front of them, but in older fish it seems more important to have a wider visual field to detect prey (and possibly predators) within a greater volume of water.     

Retinal topography of ganglion cells in immature ocean sunfish, <Emphasis Type="Italic">Mola mola</Emphasis>

The ocean sunfish, Mola mola, is the largest known bony fish. Based on prior studies of diet composition, it is considered to be a pelagic zooplanktivore. However, a recent study using acoustic telemetry revealed that they repeatedly dive to depths of >50 m during the day. We examined the distribution of cells within the retinal ganglion cell layer in the immature ocean sunfish (c.a. 50 cm total length) and estimated their visual acuity with respect to the main visual axis and visual fields. Visual acuity was between 3.37 and 4.41 cycles/degree. The region of highest cell density was located in the dorso-temporal retina, indicating that the main visual axis of ocean sunfish is directed towards the lower frontal portion of the visual field. This axis is considered beneficial for detecting prey items when the sunfish are migrating vertically through the water column, and in foraging behavior near the sea bottom.     

Heart rate and ventilation in Antarctic fishes are largely determined by ecotype

Extrinsic neural and humoral influences on heart rate ( f H) and ventilation frequency ( f V) were examined following varying periods of post-surgical recovery in eight related Antarctic fish species inhabiting an array of inshore niches. Resting f H after recovery from handling was lower than previous reports, and the novel measurement of routine f H in free-swimming Dissostichus mawsoni (6·14 beats min⁻¹, bpm) is the lowest recorded for any fish. The extent of cardio-depressive cholinergic (vagal) tonus explained the large range of f H among species and varied with behavioural repertoire, being lower in the more active species, apart from Notothenia coriiceps . Adrenergic tonus was low compared with cholinergic tonus, with the exception of Trematomus newnesi . Hence, high cardiac cholinergic tonus may be a genotypic trait of the notothenioids that diverged with ecotype. Power spectral analysis showed that the vagal influence produced comparable spectra among species of similar morphology and ecotype. Removal of autonomic tonus resulted in a remarkably similar intrinsic f H between species. Simultaneous measurements of cardio-respiratory variables and oxygen consumption (     ) were made in the benthic Trematomus bernacchii and cryopelagic Pagothenia borchgrevinki . The slopes of the relationship between f H and     were similar. Trematomus bernacchii , however, had a higher     for a given f H than P. borchgrevinki , and P. borchgrevinki required a two-fold larger range in f H to reach a similar maximum     , suggesting that there is a difference in cardiovascular fitness between the two species. Overall, the data suggest that cardio-respiratory control in Antarctic nototheniids is largely determined by activity levels associated with a given ecotype.     

Plasma osmolarity, glucose concentration and erythrocyte responses of two Antarctic nototheniid fishes to acute and chronic thermal change

Haematocrit, haemoglobin concentration, plasma osmolarity and plasma glucose concentration of the Antarctic nototheniid fishes Pagothenia borchgrevinki and Trematomus bernacchii were monitored during 24 h periods of exposure to 3 and 6° C. The same haematological variables were also measured in P. borchgrevinki following a 5–6 week period of 4° C acclimation. The first plasma glucose measurements in acutely thermally‐stressed Antarctic nototheniids revealed a delayed hyperglycaemia which related well to the relatively slow stress‐related elevation of plasma cortisol in these species. Plasma osmolarity of both species was unchanged by acute 3° C exposure, but exhibited a delayed and transient increase during acute exposure to 6° C. Haematocrit was unaltered in T. bernacchii during the acute temperature increases but was elevated in the relatively active P. borchgrevinki . Following 5–6 weeks of warm‐acclimation (4° C) the plasma glucose concentration, haematocrit and haemoglobin concentration of P. borchgrevinki were not significantly different from fish at −1° C, but plasma osmolarity decreased toward the level found in temperate‐water teleosts.     

Muscle fine structure reflects ecotype in two nototheniids

The fine structure of swimming (pectoral) and myotomal (axial) skeletal muscle and myocardium of two species of Antarctic nototheniid fishes were studied by electron microscopy, comparing the cryopelagic Pagothenia borchgrevinki and the benthic Trematomus bernacchii . Mean fibre size varied by a factor of four among muscles within each species and may have reflected the locomotory power available, being larger in pectoral oxidative (red) and axial glycolytic (white) muscle of P. borchgrevinki . Both species use labriform locomotion, and the more active P. borchgrevinki had a greater capillary supply, expressed as a capillary to fibre ratio, than T. bernacchii to both red (3·48 ± 0·36 v . 1·63 ± 0·14, mean ±  s . e .; P  < 0·01) and white (2·70 ± 0·20 v . 1·53 ± 0·18, mean ±  s . e .; P  < 0·01) regions of the pectoral musculature. The greater aerobic scope of P. borchgrevinki was strikingly demonstrated in the higher mitochondrial content of all skeletal muscle types sampled, and the ventricular myocardium (0·269 ± 0·011 v . 0·255 ± 0·012 mean ±  s . e .; P  < 0·05). Minor differences were found in other elements of fibre composition, with the exception of a five‐fold greater lipid content in pectoral red fibres of P. borchgrevinki (0·074 ± 0·014 mean ±  s . e .) v . T. bernacchii (0·010 ± 0·003; P  < 0·05). Differences in muscle fine structure among species clearly reflected differences in their ecotype.     

Stenotherms at sub-zero temperatures: thermal dependence of swimming performance in Antarctic fish

We examined the burst swimming performance of two Antarctic fishes, Trematomus bernacchii and T. centronotus, at five temperatures between -1 degrees C and 10 degrees C. As Antarctic fishes are considered one of the most cold specialised and stenothermal of all ectotherms, we predicted they would possess a narrow thermal performance breadth for burst swimming and a correlative decrease in performance at high temperatures. Burst swimming was assessed by videotaping swimming sequences with a 50-Hz video camera and analysing the sequences frame-by-frame to determine maximum velocity, the distance moved throughout the initial 200 ms, and the time taken to reach maximum velocity. In contrast to our prediction, we found both species possessed a wide thermal performance breadth for burst swimming. Although maximum swimming velocity for both T. bernacchii and T. centronotus was significantly highest at 6 degrees C, maximum velocity at all other test temperatures was less than 20% lower. Thus, it appears that specialisation to a highly stable and cold environment is not necessarily associated with a narrow thermal performance breadth for burst swimming in Antarctic fish. We also examined the ability of the Antarctic fish Pagothenia borchgrevinki to acclimate their burst-swimming performance to different temperatures. We exposed P. borchgrevinki to either -1 degrees C or 4 degrees C for 4 weeks and tested their burst-swimming performance at four temperatures between -1 degrees C and 10 degrees C. Burst-swimming performance of Pagothenia borchgrevinki was unaffected by exposure to either -1 degrees C or 4 degrees C for 4 weeks. Maximum swimming velocity of both acclimation groups was thermally independent over the total temperature range of 1 degrees C to 10 degrees C. Therefore, the loss of any capacity to restructure the phenotype and an inability to thermally acclimate swimming performance appears to be associated with inhabiting a highly stable thermal environment.     

Planktivory in benthic nototheniid fish in McMurdo Sound,Antarctica

Synopsis Four species of nototheniid fish were sampled from below the sea ice near Cape Armitage, McMurdo Sound:Pagothenia borchgrevinki from just below the ice 1.5 km offshore,Trematomus bernacchii, Trematomus hansoni andTrematomus centronotus from off the bottom in about 20 m of water near the shore. Scale worms and isopods were conspicuous non-planktonic prey, and present in the three benthic fish species. The planktonic pteropod molluscLimacina helicina was numerically common in all four species of fish. The planktonic hyperiid amphipodHyperiella dilatata was also found in all fish species. WhereasP. borchgrevinki is planktivorous in accord with its pelagic habit, theTrematomus spp. clearly also feed on plankton from the water column.T. hansoni is particularly planktivorous, taking smaller copepods thanP. borchgrevinki.     

Visual Stimuli Evoked Action Potentials Trigger Rapidly Propagating Dendritic Calcium Transients in the Frog Optic Tectum Layer 6 Neurons

The superior colliculus in mammals or the optic tectum in amphibians is a major visual information processing center responsible for generation of orientating responses such as saccades in monkeys or prey catching avoidance behavior in frogs. The conserved structure function of the superior colliculus the optic tectum across distant species such as frogs, birds monkeys permits to draw rather general conclusions after studying a single species. We chose the frog optic tectum because we are able to perform whole-cell voltage-clamp recordings fluorescence imaging of tectal neurons while they respond to a visual stimulus. In the optic tectum of amphibians most visual information is processed by pear-shaped neurons possessing long dendritic branches, which receive the majority of synapses originating from the retinal ganglion cells. Since the first step of the retinal input integration is performed on these dendrites, it is important to know whether this integration is enhanced by active dendritic properties. We demonstrate that rapid calcium transients coinciding with the visual stimulus evoked action potentials in the somatic recordings can be readily detected up to the fine branches of these dendrites. These transients were blocked by calcium channel blockers nifedipine CdCl₂ indicating that calcium entered dendrites via voltage-activated L-type calcium channels. The high speed of calcium transient propagation, >300 μm in <10 ms, is consistent with the notion that action potentials, actively propagating along dendrites, open voltage-gated L-type calcium channels causing rapid calcium concentration transients in the dendrites. We conclude that such activation by somatic action potentials of the dendritic voltage gated calcium channels in the close vicinity to the synapses formed by axons of the retinal ganglion cells may facilitate visual information processing in the principal neurons of the frog optic tectum.     

Ecomorphology of retinal structures in zooplanktivorous haplochromine cichlids (Pisces) from Lake Victoria

Synopsis Before the decline of the species flock of haplochromine cichlids of Lake Victoria due to the Nile perch upsurge, there were many co-existing haploehromine species such as the taxonomically and ecologically well-studied zooplanktivores of the Mwanza Gulf. In spite of the scarcely separated niches of some of these species, no sign of competition for space or food could be demonstrated. As is argued in this paper, optical differentiation could well be an aspect of adaptive radiation of these zooplanktivores, particularly among the highly sympatric species. Our hypothesis is based on the morphological modifications of retinal structures in nine zooplanktivorous species. Interspecific variation was observed in composition, size and density of the photoreceptors and ganglion cells. The analyses included the intraretinal variation and size dependency of some of the structural parameters. The optical functions deduced from retinal structure indicate distinct interspecific differences in sensitivity thresholds and a slight differentiation in visual resolution. These functions correlate poorly with the photic conditions of the species-specific habitats. The optical properties can, on the other hand, be connected with the more subtle differentiation in food items and feeding behaviour among these species. It is our concluding hypothesis, that the optical differentiation among the haplochromine zooplanktivores primarily served resource partitioning by different modes of visual prey detection rather than niche partitioning by habitat.     

视网膜神经节细胞的协同活动以及信息编码

在脊椎动物的视觉系统中,信息的初级处理发生在视网膜.随着多电极记录技术的发展,视网膜神经节细胞的协同活动在不同物种中被广泛地观察到.然而,协同活动在视觉信息处理中的作用还不清楚,并且存在一定的争议.本文回顾了近些年关于视网膜神经节细胞协同活动的相关研究,对协同活动的分类、检测以及生理功能进行讨论.     

Respiration of antarctic fish from McMurdo Sound

1. Resting rates of oxygen uptake were measured for nine species of unstressed fish living at -1.8 degree C in McMurdo Sound, Antarctica (77-78 degrees S). Interspecific differences in VO2 were correlated with the habits and activity of the fish. 2. The cryopelagic Pagothenia borchgrevinki regulated oxygen uptake down to a critical PO2 of approximately 60 mmHg. The inactive benthic species Trematomus centronotus extracted oxygen to lower PO2 and appeared to have a lesser degree of oxyregulation when the data were analysed using a quadratic model. 3. Cutaneous oxygen uptake in the nototheniids T. bernacchii and P. borchgrevinki amounted to 9 and 17% of total VO2 under normoxic conditions which is less than that reported for scaleless Antarctic fish. 4. The contentious concept of metabolic cold adaptation in polar fish has been reviewed, and the opinion expressed that the phenomenon cannot be dismissed on the grounds of technically incompetent measurement, or through inappropriate extrapolation of data from fish at lower latitudes.     

Pseudorabies virus membrane proteins gI and gE facilitate anterograde spread of infection in projection-specific neurons in the rat

The membrane proteins gI and gE of Pseudorabies virus (PRV) are required for viral invasion and spread through some neural pathways of the rodent central nervous system. Following infection of the rat retina with wild-type PRV, virus replicates in retinal ganglion neurons and anterogradely spreads to infect all visual centers in the brain. By contrast, gI and gE null mutants do not infect a specific subset of the visual centers, e.g., the superior colliculus and the dorsal lateral geniculate nucleus. In previous experiments, we suggested that the defect was not due to inability to infect projection-specific retinal ganglion cells, because mixed infection of a gE deletion mutant and a gI deletion mutant restored the wild-type phenotype (i.e., genetic complementation occurred). In the present study, we provide direct evidence that gE and gI function to promote the spread of infection after entry into primary neurons. We used stereotaxic central nervous system injection of a fluorescent retrograde tracer into the superior colliculus and subsequent inoculation of a PRV gI-gE double null mutant into the eye of the same animal to demonstrate that viral antigen and fluorescent tracer colocalize in retinal ganglion cells. Furthermore, we demonstrate that direct injection of a PRV gI-gE double null mutant into the superior colliculus resulted in robust infection followed by retrograde transport to the eye and replication in retinal ganglion neuron cell bodies. These experiments provide additional proof that the retinal ganglion cells projecting to the superior colliculus are susceptible and permissive to gE and gI mutant viruses. Our studies confirm that gI and gE specifically facilitate anterograde spread of infection by affecting intracellular processes in the primary infected neuron such as anterograde transport in axons or egress from axon terminals.     

Visual Function and Cortical Organization in Carriers of Blue Cone Monochromacy

Carriers of blue cone monochromacy have fewer cone photoreceptors than normal. Here we examine how this disruption at the level of the retina affects visual function and cortical organization in these individuals. Visual resolution and contrast sensitivity was measured at the preferred retinal locus of fixation and visual resolution was tested at two eccentric locations (2.5° and 8°) with spectacle correction only. Adaptive optics corrected resolution acuity and cone spacing were simultaneously measured at several locations within the central fovea with adaptive optics scanning laser ophthalmoscopy (AOSLO). Fixation stability was assessed by extracting eye motion data from AOSLO videos. Retinotopic mapping using fMRI was carried out to estimate the area of early cortical regions, including that of the foveal confluence. Without adaptive optics correction, BCM carriers appeared to have normal visual function, with normal contrast sensitivity and visual resolution, but with AO-correction, visual resolution was significantly worse than normal. This resolution deficit is not explained by cone loss alone and is suggestive of an associated loss of retinal ganglion cells. However, despite evidence suggesting a reduction in the number of retinal ganglion cells, retinotopic mapping showed no reduction in the cortical area of the foveal confluence. These results suggest that ganglion cell density may not govern the foveal overrepresentation in the cortex. We propose that it is not the number of afferents, but rather the content of the information relayed to the cortex from the retina across the visual field that governs cortical magnification, as under normal viewing conditions this information is similar in both BCM carriers and normal controls.     

Distribution of Mammalian-Like Melanopsin in Cyclostome Retinas Exhibiting a Different Extent of Visual Functions

Mammals contain 1 melanopsin (Opn4) gene that is expressed in a subset of retinal ganglion cells to serve as a photopigment involved in non-image-forming vision such as photoentrainment of circadian rhythms. In contrast, most nonmammalian vertebrates possess multiple melanopsins that are distributed in various types of retinal cells; however, their functions remain unclear. We previously found that the lamprey has only 1 type of mammalian-like melanopsin gene, which is similar to that observed in mammals. Here we investigated the molecular properties and localization of melanopsin in the lamprey and other cyclostome hagfish retinas, which contribute to visual functions including image-forming vision and mainly to non-image-forming vision, respectively. We isolated 1 type of mammalian-like melanopsin cDNA from the eyes of each species. We showed that the recombinant lamprey melanopsin was a blue light-sensitive pigment and that both the lamprey and hagfish melanopsins caused light-dependent increases in calcium ion concentration in cultured cells in a manner that was similar to that observed for mammalian melanopsins. We observed that melanopsin was distributed in several types of retinal cells, including horizontal cells and ganglion cells, in the lamprey retina, despite the existence of only 1 melanopsin gene in the lamprey. In contrast, melanopsin was almost specifically distributed to retinal ganglion cells in the hagfish retina. Furthermore, we found that the melanopsin-expressing horizontal cells connected to the rhodopsin-containing short photoreceptor cells in the lamprey. Taken together, our findings suggest that in cyclostomes, the global distribution of melanopsin in retinal cells might not be related to the melanopsin gene number but to the extent of retinal contribution to visual function.     

Two alpha-herpesvirus strains are transported differentially in the rodent visual system.

Uptake and transneuronal passage of wild-type and attenuated strains of a swine alpha-herpesvirus (pseudorabies [PRV]) were examined in rat visual projections. Both strains of virus infected subpopulations of retinal ganglion cells and passed transneuronally to infect retino-recipient neurons in the forebrain. However, the location of infected forebrain neurons varied with the strain of virus. Intravitreal injection of wild-type virus produced two temporally separated waves of infection that eventually reached all known retino-recipient regions of the central neuraxis. By contrast, the attenuated strain of PRV selectively infected a functionally distinct subset of retinal ganglion cells with restricted central projections. The data indicate that projection-specific groups of ganglion cells are differentially susceptible to the two strains of virus and suggest that this sensitivity may be receptor mediated.     

Temporal and mosaic distribution of large ganglion cells in the retina of a daggertooth aulopiform deep-sea fish (Anotopterus pharao)

The daggertooth Anotopterus pharao (Aulopiformes: Anotopteridae) is a large, piscivorous predator that lives within the epipelagic zone at night. In this species, the distribution of retinal ganglion cells has been examined. An isodensity contour map of ganglion cells shows that the cells concentrate in a slightly ventral region of the temporal retina. The region of high ganglion cell density contains 4.07 x 10(3) cells mm(-2), and the resulting visual acuity is 3.5 cycles deg(-1). Outside the area centralis, conspicuously large ganglion cells (LGCs) are observed in the temporal margin of the retina. The LGCs are regularly arrayed, and displaced into the inner plexiform layer. Thick dendrites extend into the outer part (sublamina a) of the inner plexiform layer. In the retinal whole mount, the total number of LGCs is 1590 (90.7 cm specimen), and the mean size of the LGCs is about four times larger than that of the ordinary ganglion cells. The morphological appearance of the LGCs was similar to the off-type alpha cells of the cat retina. The function of these distinctive LGCs is discussed in relation to specific head-up feeding behaviour.     

Retinal ganglion cell topography and visual acuity of the sleepy lizard (<Emphasis Type="Italic">Tiliqua rugosa</Emphasis>)

The spatial distribution of retinal ganglion cells provides valuable insight into the importance species place on observing objects in specific regions of their visual field with higher spatial resolving power. We estimate the total number, distribution and peak density of ganglion cells in retinal wholemounts of the sleepy lizard, Tiliqua rugosa, a scincid lizard endemic to southern Australia. Ganglion cells were readily discernable from amacrine cells by their size and shape, prominent nuclei and the accumulation of Nissl-positive substances in their cytoplasm. A total of 1,654,200 (±59,400) presumed ganglion cells were estimated throughout the retina, distributed irregularly and forming a loose horizontal streak of high cell density peaking at 15,500 cells per mm². With a post nodal distance of 6.25 mm, we calculate an upper limit of visual acuity of 6.8 c/deg.