Relationship between feather pecking and ground pecking in laying hens and the effect of group size

The aim of this experiment was to study the relationship between feather pecking and ground pecking in laying hens and the effect of group size on feather pecking behaviour. Hisex White hens were kept in floor pens in group sizes of 15, 30, 60 and 120 birds, each with four replicates. Behavioural observations were performed at four different ages and focused on the number of feather pecks and aggressive pecks, both given and received. The part of the body pecked and the location of the bird was recorded as well as the number of pecks made to the floor, feeder and drinker.The results showed that most feather pecking activity occurred in the largest group size (120 birds) and there was some evidence of an increasing frequency of aggressive pecks with increasing group size. The parts of the body which were targets for feather pecking varied depending on the location of the bird giving the peck and the bird receiving it. When looking at the behaviour of individuals, birds doing a lot of feather pecking also showed more ground pecking.     

Anatomical specializations for nocturnality in a critically endangered parrot, the Kakapo (Strigops habroptilus)

The shift from a diurnal to nocturnal lifestyle in vertebrates is generally associated with either enhanced visual sensitivity or a decreased reliance on vision. Within birds, most studies have focused on differences in the visual system across all birds with respect to nocturnality-diurnality. The critically endangered Kakapo (Strigops habroptilus), a parrot endemic to New Zealand, is an example of a species that has evolved a nocturnal lifestyle in an otherwise diurnal lineage, but nothing is known about its' visual system. Here, we provide a detailed morphological analysis of the orbits, brain, eye, and retina of the Kakapo and comparisons with other birds. Morphometric analyses revealed that the Kakapo's orbits are significantly more convergent than other parrots, suggesting an increased binocular overlap in the visual field. The Kakapo exhibits an eye shape that is consistent with other nocturnal birds, including owls and nightjars, but is also within the range of the diurnal parrots. With respect to the brain, the Kakapo has a significantly smaller optic nerve and tectofugal visual pathway. Specifically, the optic tectum, nucleus rotundus and entopallium were significantly reduced in relative size compared to other parrots. There was no apparent reduction to the thalamofugal visual pathway. Finally, the retinal morphology of the Kakapo is similar to that of both diurnal and nocturnal birds, suggesting a retina that is specialised for a crepuscular niche. Overall, this suggests that the Kakapo has enhanced light sensitivity, poor visual acuity and a larger binocular field than other parrots. We conclude that the Kakapo possesses a visual system unlike that of either strictly nocturnal or diurnal birds and therefore does not adhere to the traditional view of the evolution of nocturnality in birds.     

Retinal projections in a snake, Thamnophis sirtalis

The retinofugal projections of the snake Thamnophis sirtalis were studied by the method of experimentally induced Wallerian degeneration stained by the Fink-Heimer method. The retinal ganglion cells project to all parts of the contralateral lateral geniculate complex, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterodorsalis, basal optic nucleus and superficial layers of the optic tectum. In addition, the retinofugal projections were observed terminating in portions of the ipsilateral lateral geniculate complex and nucleus posterodorsalis. Examination of the morphology of the retinal terminal areas stained for Nissl substance with cresyl violet led to the conclusion that these regions are well differentiated and should not be considered poorly developed when compared with other reptilian forms such as turtles.     

Regulation of human eye growth by the energy density of the radiation in the retina--a biophysical theory in ophthalmology

A number of theoretical and experimental models analyze regulation of eye growth in humans and animals. In this article we introduce a biophysical theory to explain human eye growth from an energetic point of view. We find different energy densities of the electromagnetic radiation in the retina for hyperopic, emmetropic and myopic eyes. We postulate a relation between the different energy densities of the radiation in the retina and growth regulation by the retina. Based on this relation between physics and biology we are modeling emmetropization, missing emmetropization in severe hyperopia and development and progression of myopia in correspondence with a number of clinical and experimental results.     

Fruit size in wild olives: implications for avian seed dispersal

1. The response of frugivorous birds to an enlargement of fruit size, and the consequences for both birds and plants, are analysed for the interaction between avian seed dispersers and olives ( Olea europaea) .
2. The enlargement of fruit size promotes a shift in frugivorous birds' feeding behaviour, from swallowing fruits whole to pecking pieces of pulp. The relative frequency of olive consumption using each feeding behaviour was assessed by combining field data on frequency of appearance of olive pulp and seeds with data from laboratory trials.
3. Sardinian Warblers ( Sylvia melanocephala ) and European Robins ( Erithacus rubecula ) were mainly peckers both on cultivated and wild olives. Blackcaps ( Sylvia atricapilla ) consumed wild olives mainly by swallowing but consumed cultivated olives (larger than the wild ones) primarily by pecking. Song Thrushes ( Turdus philomelos ) were primarily swallowers of both types of fruits.
4. Laboratory trials with Song Thrushes, Blackcaps and European Robins showed that: (a) all were able to peck fruits; (b) fruit size determined a shift from swallowing to pecking, as pecking frequency increased with the enlargement of the fruit size; (c) all the species had an increased fruit handling failure rate when trying to swallow increasingly large fruits; and (d) from the birds' perspective, small shifts in fruit size may have important consequences on fruit profitability.
5. Pecking on olives turns the mutualistic fruit–frugivore interaction into a fruit-pulp predator interaction, thus arising a conflict between the plant and frugivorous birds.
6. This study shows that heavy dependence on fruit is not always simply related to seed dispersal. The same frugivorous bird species can act as a seed disperser or a pulp predator for the same plant species. The threshold between these roles is highly influenced by the ratio gape size/fruit size.     

Glaucoma-Induced Optic Disc Morphometric Changes and Glaucoma Diagnostic Ability of Heidelberg Retina Tomograph II in Highly Myopic Eyes

Purpose

This study was performed to first investigate the morphological differences in the optic nerve head between highly myopic non-glaucomatous controls and highly myopic glaucomatous eyes in comparison with the differences between emmetropic non-glaucomatous controls and emmetropic glaucomatous eyes using confocal scanning laser ophthalmoscopy. Further, the ability of the apparatus in glaucoma diagnosis in highly myopic eyes was compared with that in emmetropic eyes.

Methods

Healthy subjects and age-matched patients with early-stage open-angle glaucoma were divided into two groups: emmetropic eyes (−1.0 to +1.0 diopters) and highly myopic eyes (−12.0 to −5.0 diopters).The participants were comprised of 65 emmetropic normal eyes, 59 emmetropic glaucomatous eyes, 62 highly myopic normal eyes, and 68 highly myopic glaucomatous eyes and eyes with pathologic myopia were carefully excluded. Confocal scanning laser tomographic parameters were compared among all subjects after adjustment for age and disc area. The ROC curves and sensitivity and specificity for glaucoma detection using several clinical methods were then compared between the emmetropic and highly myopic eyes.

Results

Rim area, cup/disc area ratio, mean cup depth, and cup shape measure of glaucoma eyes are significantly different from those of normal eyes in both highly myopic eyes and emmetropic eyes. Methodological overestimation of retinal nerve fiber layer cross sectional area due to optic disc tilting was suggested in the highly myopic eyes. The diagnostic performance of glaucoma using several discriminant methods significantly deteriorated in the highly myopic eyes.

Conclusions

In the highly myopic glaucomatous eyes, confocal scanning laser tomographic parameters were significantly different from that of non-glaucomatous highly myopic eyes but diagnostic performance of glaucoma was deteriorated than that in emmetropic eyes. These findings demonstrate the utility and limitations of the apparatus in diagnosing glaucoma in highly myopic patients.     

Species‐specific differences in relative eye size are related to patterns of edge avoidance in an Amazonian rainforest bird community

Eye size shows a large degree of variation among species, even after correcting for body size. In birds, relatively larger eyes have been linked to predation risk, capture of mobile prey, and nocturnal habits. Relatively larger eyes enhance visual acuity and also allow birds to forage and communicate in low‐light situations. Complex habitats such as tropical rain forests provide a mosaic of diverse lighting conditions, including differences among forest strata and at different distances from the forest edge. We examined in an Amazonian forest bird community whether microhabitat occupancy (defined by edge avoidance and forest stratum) was a predictor of relative eye size. We found that relative eye size increased with edge avoidance, but did not differ according to forest stratum. Nevertheless, the relationship between edge avoidance and relative eye size showed a nonsignificant positive trend for species that inhabit lower forest strata. Our analysis shows that birds that avoid forest edges have larger eyes than those living in lighter parts. We expect that this adaptation may allow birds to increase their active daily period in dim areas of the forest. The pattern that we found raises the question of what factors may limit the evolution of large eyes.     

Fine structure of the retino-optic nerve junction in the chicken

The aim of this study is to investigate a fine structure of the retino-optic nerve junction in the chicken. We especially focused on the myelin sheaths and astrocytes in the intraocular optic nerve (ION) and its adjoining parts. A part of the axons of retinal nerve fiber layer (NFL) were myelinated. Ganglion cell axons were ensheathed by loose myelin in the NFL and by a compact one in the ION and optic nerve (ON). Myelin structure changed from loose type to a compact one within the very narrow NFL-ION junction. Loose myelin forming cells are dark type of oligodendrocytes in the retina. From the most peripheral ON to the choroidal part of ION, astrocytes contained abundant microtubules. The optic nerve around the lamina cribrosa is exposed to mechanical force during eye movement. It is suggested that these microtubules may perform the cytoskeletal function. Astrocytes in the retinal part of ION had longer processes filled with abundant gliofilaments. They may provide the mechanical support for the ganglion cell axons, which are exposed directly to intraocular pressure. Although astrocytes in the retinal level of ION extended their processes into the retina, their soma was never found in the retina.     

Differential effects of the trophic factors BDNF, NT-4, GDNF, and IGF-I on the isthmo-optic nucleus in chick embryos

The isthmo-optic nucleus (ION) of chick embryos is a model system for the study of retrograde trophic signaling in developing CNS neurons. The role of brain-derived neurotrophic factor (BDNF) is well established in this system. Recent work has implicated neurotrophin-4 (NT-4), glial cell line-derived neurotrophic factor (GDNF), and insulin-like growth factor I (IGF-I) as additional trophic factors for ION neurons. Here it was examined in vitro and in vivo whether these factors are target-derived trophic factors for the ION in 13- to 16-day-old chick embryos. Unlike BDNF, neither GDNF, NT-4, nor IGF-I increased the survival of ION neurons in dissociated cultures identified by retrograde labeling with the fluorescent tracer DiI. BDNF and IGF-I promoted neurite outgrowth from ION explants, whereas GDNF and NT-4 had no effect. Injections of NT-4, but not GDNF, in the retina decreased the survival of ION neurons and accelerated cell death in the ION. NT-4-like immunoreactivity was present in the retina and the ION. Exogenous, radiolabeled NT-4, but not GDNF or IGF-I, was retrogradely transported from the retina to the ION. NT-4 transport was significantly reduced by coinjection of excess cold nerve growth factor (NGF), indicating that the majority of NT-4 bound to p75 neurotrophin receptors during axonal transport. Binding of NT-4 to chick p75 receptors was confirmed in L-cells, which express chick p75 receptors. These data indicate that GDNF has no direct trophic effects on ION neurons. IGF-I may be an afferent trophic factor for the ION, and NT-4 may act as an antagonist to BDNF, either by competing with BDNF for p75 and/or trkB binding or by signaling cell death via p75.     

Corneal endothelial cell density decreases with age in emmetropic eyes

PURPOSE: To analyze the corneal endothelial cell density in healthy adult emmetropic subjects. METHODS: We analyzed the corneal endothelial cell density of a group made up of 225 emmetropic subjects (n=225). As age-matched control groups we analyzed two other groups, one made up of myopic subjects (n=209) and the other made up of hyperopic subjects (n=203). We recorded the mean of three consecutive measurements of the corneal endothelial cell density using the Topcon SP-2000P non-contact specular microscope (Topcon Corp., Tokyo, Japan). RESULTS: The mean age was 38.6+/-11.8 years, 40.7+/-12.2 years, and 39.2+/-10.5 years for emmetropic, myopic and hyperopic subjects respectively (p=0.994). No significant differences (p=0.920) in endothelial cell density values were found between emmetropic (2985+/-245 cells/mm2), myopic (2936+/-258 cells/mm2) and hyperopic eyes (2946+/-253 cells/mm2). Lower corneal endothelial cell density values were found in older emmetropic (p<0.001), myopic (p<0.001), and hyperopic subjects (p<0.001). A significant correlation between endothelial cell density and age was found in emmetropic (r=-0.958; p<0.001), myopic (r= -0.954; p<0.001) and hyperopic subjects (r= -0.948; p<0.001). CONCLUSIONS: In healthy emmetropic subjects there is a reduction in corneal endothelial cell density with age although there are no differences in corneal endothelial cell density values between emmetropic, myopic and hyperopic subjects.     

Termination of retinofugal fibers and lamination pattern in the lateral geniculate nucleus of the gibbon

The lateral geniculate nucleus (LGN) of the gibbon (Hylobates sp.) consists of four principal layers, i.e., layers 1 and 2 containing large somata and layers 3 and 4 comprising medium-sized neurons. In addition, there are intercalated layers S, imm and imp, each consisting of small cells. Tracing of retinofugal fibers with the autoradiographic method revealed that the retina projects to the ipsilateral layers 2, 3 and imp and to the contralateral layers 1, 4, S and imm. No 'hidden' layers have been found. This type of lamination pattern sets the LGN of the gibbon apart from that of all Old World monkeys, chimpanzee and man. Retinal projections to other subcortical regions are also described.     

Reaction to frustration in high and low feather pecking lines of laying hens from commercial or semi-natural rearing conditions

The effect of rearing conditions on feather pecking and reaction to frustration was studied in two lines of laying hens. From commercial rearing conditions (large group, no mother hen), seven birds from a high feather pecking line (HC birds) and eight birds from a low feather pecking line (LC birds) were used. From semi-natural rearing conditions (small group, mother hen present) seven birds from the high feather pecking line (HN birds) were used. Feather pecking behaviour of HC, LC, and HN groups was recorded for 30 min. After that, each bird was food deprived and trained to peck a key for a food reward in a Skinnerbox. After training, each bird was subjected to a frustration session in a Skinnerbox, where the feeder was covered with Perspex. Three HC birds showed severe feather pecking, compared with one HN bird and zero LC birds. Differences in reaction to frustration were found between birds from different lines, but not in birds from different rearing conditions. LC birds tended to put their head in the feeder more frequently than HC birds over all sessions. Although limited, this study indicates that rearing conditions influence feather pecking, but not reaction to frustration.     

The presence of extreme feather peckers in groups of laying hens

Feather pecking is a serious economic and welfare problem in laying hens. Feather damage occurs mainly through severe feather pecking (SFP). Selection experiments have proved that this behavior is heritable and lines have been divergently selected for high (HFP) and low feather pecking (LFP). The number of bouts of SFP per hen follows a Poisson distribution with a maximum nearby 0. A few studies indicate that the distribution within flocks is not homogenous but contains sub-groups of birds showing extremely high levels of feather pecking (EFP). It was the aim of the current study to re-analyze data on SFP of lines selected for HFP/LFP and their F2 cross so as to uncover hidden sub-populations of EFP birds. Data of seven selection generations of HFP and LFP selection lines as well as their F2 cross have been used. We fitted a two-component mixture of Poisson distributions in order to separate the sub-group of EFP from the remaining birds. HFP and LFP lines differed mainly in mean bouts per bird. The proportion of EFP was only marginal in the LFP as compared with the HFP and the F2 population. Selection for LFP did not result in total elimination of EFP. The presence of even small proportions of EFP may play an important role in initiating outbreaks of feather pecking in large flocks. Further studies on feather pecking should pay special attention to the occurrence of EFP sub-groups.     

Flying with diverse passengers: greater richness of parasitic nematodes in migratory birds

Environmental changes are simultaneously affecting parasitic diseases and animal migrations, making it important to understand the disease dynamics of migratory species, including their range of infections and investment into defences. There is an urgent need for such knowledge because migratory animals, especially birds, are important for pathogen transmission and also particularly sensitive to environmental changes. Here we compare the nematode species richness and relative immune investment (via relative spleen size) of almost 200 migratory and non‐migratory species within three diverse groups of birds (Anseriformes, Accipitriformes and Turdidae) with worldwide distributions and varied ecology. Our results provide the first large‐scale demonstration that migratory birds face greater challenge from macroparasites as they have significantly dissimilar nematode fauna and higher nematode species richness compared to non‐migratory species. Even though birds with relatively large spleens had more nematode species, there was no difference in relative spleen size between migratory and non‐migratory bird species. The physiological stress of migration can be exacerbated by the potential range of pathologies induced by their richer nematode communities, particularly in combination with environmental perturbations. Altered migration stemming from global changes can also have important consequences for nematode transmission. Synthesis Most studies on parasites of migratory birds versus non‐migratory birds focus upon blood parasites; here we compared the diversity of another important parasite group – nematodes (roundworms) in three orders of birds. We found for any given order, migratory species and species with proportionally larger spleens generally have a wider range of nematodes. It is unclear why migratory species harbour more nematode species. Global climate change is expected to influence both bird migration patterns and infectious diseases, which may increase host susceptibility to parasitism and also introduce diverse nematodes to new areas and potential hosts.     

The evolution of stereopsis and the Wulst in caprimulgiform birds: a comparative analysis

Owls possess stereopsis (i.e., the ability to perceive depth from retinal disparity cues), but its distribution amongst other birds has remained largely unexplored. Here, we present data on species variation in brain and telencephalon size and features of the Wulst, the neuroanatomical substrate that subserves stereopsis, in a putative sister-group to owls, the order Caprimulgiformes. The caprimulgiforms we examined included nightjars (Caprimulgidae), owlet-nightjars (Aegothelidae), potoos (Nyctibiidae), frogmouths (Podargidae) and the Oilbird (Steatornithidae). The owlet-nightjars and frogmouths shared almost identical relative brain, telencephalic and Wulst volumes as well as overall brain morphology and Wulst morphology with owls. Specifically, the owls, frogmouths and owlet-nightjars possess relatively large brains and telencephalic and Wulst volumes, had a characteristic brain shape and displayed prominent laminae in the Wulst. In contrast, potoos and nightjars both had relatively small brains and telencephala, and Wulst volumes that are typical for similarly sized birds from other orders. The Oilbird had a large brain, telencephalon and Wulst, although these measures were not quite as large as those of the owls. This gradation of owl-like versus nightjar-like brains within caprimulgiforms has significant implications for understanding the evolution of stereopsis and the Wulst both within the order and birds in general.     

Evolutionary shifts in the melanin‐based color system of birds

Melanin pigments contained in organelles (melanosomes) impart earthy colors to feathers. Such melanin‐based colors are distributed across birds and thought to be the ancestral color‐producing mechanism in birds. However, we have had limited data on melanin‐based color and melanosome diversity in Palaeognathae, which includes the flighted tinamous and large‐bodied, flightless ratites and is the sister taxon to all other extant birds. Here, we use scanning electron microscopy and spectrophotometry to assess melanosome morphology and quantify reflected color for 19 species within this clade. We find that brown colors in ratites are uniquely associated with elongated melanosomes nearly identical in shape to those associated with black colors. Melanosome and color diversity in large‐bodied ratites is limited relative to other birds (including flightless penguins) and smaller bodied basal maniraptoran dinosaur outgroups of Aves, whereas tinamous show a wider range of melanosome forms similar to neognaths. The repeated occurrence of novel melanosome forms in the nonmonophyletic ratites suggests that melanin‐based color tracks changes in body size, physiology, or other life history traits associated with flight loss, but not feather morphology. We further anticipate these findings will be useful for future color reconstructions in extinct species, as variation in melanosome shape may potentially be linked to a more nuanced palette of melanin‐based colors.     

The evolution of body size in birds. I. Evidence for non-random diversification

The hypothesis that evolution of body size in birds was a random process coupled with an absolute lower boundary on body mass was tested using data on 6217 species of extant birds. The test was based on the fact that subclades within birds that have body masses much larger than this minimum should not have skewed log body mass distributions, while clades close to this boundary should. Bird species were classified into 23 orders suggested by Sibley and Monroe (1988). Thirteen orders that had average log body masses greater than the average for all birds had significantly skewed log body mass distributions. This is inconsistent with the hypothesis that evolution of body size in birds is random, but is constrained only at the smallest body masses. Most orders of birds cannot be considered random samples from the parental distribution of all birds. When the pattern of body mass evolution in birds is reconstructed using an estimate of the phylogenetic relationships among orders, there are many more instances where a large taxon putatively originated from a smaller one than vice versa. The non-random nature of body mass evolution in birds is consistent with models that postulate that evolution is constrained by the ability of individuals to turn resources into offspring.     

Differential effects of the trophic factors BDNF,NT‐4, GDNF,and IGF‐I on the isthmo‐optic nucleus in chick embryos

The isthmo‐optic nucleus (ION) of chick embryos is a model system for the study of retrograde trophic signaling in developing CNS neurons. The role of brain‐derived neurotrophic factor (BDNF) is well established in this system. Recent work has implicated neurotrophin‐4 (NT‐4), glial cell line–derived neurotrophic factor (GDNF), and insulin‐like growth factor I (IGF‐I) as additional trophic factors for ION neurons. Here it was examined in vitro and in vivo whether these factors are target‐derived trophic factors for the ION in 13‐ to 16‐day‐old chick embryos. Unlike BDNF, neither GDNF, NT‐4, nor IGF‐I increased the survival of ION neurons in dissociated cultures identified by retrograde labeling with the fluorescent tracer DiI. BDNF and IGF‐I promoted neurite outgrowth from ION explants, whereas GDNF and NT‐4 had no effect. Injections of NT‐4, but not GDNF, in the retina decreased the survival of ION neurons and accelerated cell death in the ION. NT‐4–like immunoreactivity was present in the retina and the ION. Exogenous, radiolabeled NT‐4, but not GDNF or IGF‐I, was retrogradely transported from the retina to the ION. NT‐4 transport was significantly reduced by coinjection of excess cold nerve growth factor (NGF), indicating that the majority of NT‐4 bound to p75 neurotrophin receptors during axonal transport. Binding of NT‐4 to chick p75 receptors was confirmed in L‐cells, which express chick p75 receptors. These data indicate that GDNF has no direct trophic effects on ION neurons. IGF‐I may be an afferent trophic factor for the ION, and NT‐4 may act as an antagonist to BDNF, either by competing with BDNF for p75 and/or trkB binding or by signaling cell death via p75. © 2000 John Wiley & Sons, Inc. J Neurobiol 43: 289–303, 2000     

Neuron death in the developing avian isthmo-optic nucleus, and its relation to the establishment of functional circuitry.

The present review covers all the published data on neuron death in the developing avian isthmo-optic nucleus (ION), which provides a particularly convenient situation for studying the causes and consequences of neuron death in the development of the vertebrate central nervous system. The main conclusions are as follows: The naturally occurring neuron death in the ION is related both temporally and causally to the ION's formation of afferent and efferent connections. The ION neurons need to obtain both anterograde and retrograde survival signals in order to survive during a critical period in embryogenesis. They may compete, at least for the retrograde signals, but the nature of the competition is still unclear. The retrograde signals are modified by action potentials. Neurons dying from a lack of anterograde survival signals can be distinguished morphologically from ones dying from a lack of retrograde signals. The neuron death refines circuitry by selectively eliminating neurons with "aberrant" axons projecting to the "wrong" (i.e., ipsilateral) retina or to the "wrong" (topographically inappropriate) part of the contralateral retina.     

Effects of neonatal axoplasmic transport attenuation on the response properties of vibrissae-sensitive neurons in the trigeminal principal sensory nucleus of the rat

We have previously shown that attenuation of axoplasmic transport by application of vinblastine to the developing infraorbital nerve (ION) results in a loss of central vibrissae-related patterns that is not accompanied by changes in the receptive field sizes for the V primary afferents innervating the whisker follicles. The present study examines the relationship between the loss of central vibrissae-related patterns and alterations in the response properties of neurons in the V principal sensory nucleus (PrV) of adult rats that sustained application of vinblastine to the ION at birth. Absence of histochemically demonstrable vibrissae-related patterns in PrV resulted in only modest changes in the receptive fields and response properties of vibrissae-sensitive neurons in this nucleus that projected to the contralateral thalamus. Response latencies to electrical activation of the V ganglion were similar in treated and untreated animals. The mean receptive field size was significantly increased from 1.3 +/- 0.7 vibrissae in controls to 1.7 +/- 0.9 vibrissae in vinblastine-treated animals, and the percentage of cells yielding a tonic response to vibrissae deflection was markedly reduced (p < 0.01 for both measures). Phasically responding cells recorded in vinblastine-treated animals showed a significant reduction in the mean number of spikes per stimulus following deflection of the vibrissae in either the preferred or non-preferred direction relative to cells recorded in normal animals (p < 0.05). The present results indicate that disruption of the normal vibrissae-related aggregates of neurons in PrV by application of vinblastine to the ION has limited effects on the functional representation of the vibrissae in this nucleus.