Biomedical subjects

G Rehkämper

Publications and source records attributed to G Rehkämper.

At least 19 recordsLinked to original sources

PubMed2006

[Intracranial fat bodies and their potential effect on brain composition and behaviour in domestic ducks with feather crests (3 case studies)].

Intracranial fat tissue was found in the brains of three crested ducks. The three ducks differed in the size of their crest and in the volume and the location of the fat body within their brains. The duck with the large crest showed a fat body which counts for 19 % of its brain volume. Due to this fat accumulation, brain structures, mainly the cerebellum, were moved laterally. This duck had serious problems in motor coordination. Fat body of the second duck with a middle sized crest was situated in neostriatum and constituted 0,6 % of total brain volume. Additionally this duck displayed an encephalocele. The last duck did show a small crest. Its fat body was found in the area of the tentorium cerebelli and made up 17 % of its brain volume. The later two ducks were not hampered behaviourally.

Animals↗

PubMed2004

Brain size, brain composition and intracranial fat bodies in a population of free-living crested ducks ('Hochbrutflugenten').

(1) Brain sizes and brain structure volumes of crested specimens from a population of 'Hochbrutflugenten' ducks (HBTcr), living under seminatural conditions, were compared with those of other duck breeds, among them the breed 'Landente' with the same morphological trait, the crest (LEcr). (2) Brains of both HBTcr and LEcr were larger than expected from an allometric comparison with uncrested breeds. (3) Fat bodies invading the skull were observed in both breeds. (4) In LEcr they could be voluminous; after subtraction of their volume from the brain volume, most brain structures measured were allometrically of the same size as in uncrested breeds. (5) In contrast, HBTcr had small fat bodies, and most of their brain structures were allometrically larger than those of the other breeds. (6) A small fat body in the skull does not appear to influence the survival of HBTcr under seminatural conditions.

Animals↗

PubMed2001

Brain alterations in crested versus non-crested breeds of domestic ducks (Anas platyrhynchos f.d.).

A comparison of brain size and brain composition was made between two uncrested duck breeds and Crested Ducks (CR) and between CR individuals that do possess crests and those that do not have the crest. Domestic ducks of the breed CR have allometrically larger brains than uncrested duck breeds. The crest inserts on a cushion of fat and connective tissue that is partly nourished by brain vessels via small holes in the skull. Through these holes, fat tissue may invade the brain cavity. Because the fat accumulations are sometimes hidden deep between the telencephalon, tectum, and cerebellum, they may be invisible macroscopically and, thus, give the impression of a large brain. The size of the crest, however, is not strictly correlated with fat accumulations in the brain, because 2 among 10 specimens of CR showed no fat body at all, and the investigation of 10 uncrested CR (ducks from the same genetic stock, but without the crests) also revealed fat accumulations in 6 specimens. After subtraction of the volume of the fat body, the brain volume of CR (crested and uncrested) was of equal size to that of "Hochbrutflugenten" and Pommeranian ducks, as was the volumes of most brain structures measured. Significantly smaller in CR were the olfactory bulbs, the prepiriform area, and the cerebellum, which was always situated in close proximity to the fat body in CR.

Adipose Tissue↗

PubMed2000

Visual perception and stimulus orientation in cattle.

The pupil in the eye of adult cattle is oval under contraction with the long axis nearly horizontal. Based on simple optophysical facts it is hypothesised that visual perception in such eyes is different for stimuli with vertically-separated details rather than stimuli with horizontally-separated details. This hypothesis was tested with three adult dairy bulls using an operant conditioning technique. The bulls had to discriminate a solid white line from broken white lines with decreasing interspaces. They solved this task better when the stimuli were presented vertically rather than horizontally. This result is discussed in terms of visual acuity and related to the topographical anatomy of the eye, particularly the pupil.

Animals↗

PubMed1999

Eye muscle nerves nuclear size in a breed of domestic rabbits with floppy ears.

In many wild species there is a correlation between the capacity for directional hearing and directional seeing, which is associated with the mobility of the eye balls. Among the breeds of domestic rabbits, there are some with pendulous, floppy external ears (e.g., Englische Widder, EW) that might limit directional hearing. The size of the brain stem nuclei in EWs has been determined and compared to rabbits with upright ears. In EW, the oculomotor nuclei are relatively larger than in the other breeds. Possibly, this indicates a compensation of a loss in directional hearing ability achieved through greater mobility of the eyes. At the same time, a variability of brain composition between the breeds, which is an intraspecific variability, is obvious.

Animals↗

PubMed1998

Allometric comparison of the brain and brain structures in the white crested polish chicken with uncrested domestic chicken breeds.

The feather crest on the head of the White Crested Polish Chicken covers a bony protuberance, a skull modification typical of crested chickens. The telencephalon is displaced into this protuberance, giving the brain the shape of an hour-glass. Allometric comparison (i.e., consideration of the influence of body weight on brain size) shows that the brain is relatively larger in crested chickens. This enlargement is partly due to enlarged ventricles, which are observed in some individuals. Among the brain structures measured, the tegmentum, cerebellum, tectum, paleostriatum, hippocampus, septum and olfactory bulb are not significantly larger in White Crested Polish chickens in comparison to those structures in seven uncrested chicken breeds; the optic tract, diencephalon, telencephalon, accessory hyperstriatum, dorsal and ventral hyperstriatum, and neostriatum, however, are significantly enlarged in this breed.

Animals↗

PubMed1998

Visual identification of small sizes by adult dairy bulls.

The objective of these trials was to measure the visual acuity of adult dairy bulls using a psychophysical approach. Three adult dairy bulls (2 Holstein Friesian and 1 Red Holstein) were trained to recognize a black disk and then to differentiate between that disk and a black annulus that had a white center. The diameter of the center of the annulus varied from 30 to 0.5 cm. Bulls could identify a white center as small as 1 cm. Because bulls had to discriminate between the black disk and the black annulus at a distance of at least 1.5 m, we calculated a visual angle of 23' (arc minutes) to describe the visual acuity of the bull. This acuity is much poorer than that of other ungulates, such as sheep, and even poorer than the acuity of younger cattle.

Animals↗

PubMed1998

Volumetric comparison of auditory brain nuclei in ear-tufted Araucanas with those in other chicken breeds.

Domestic chickens of the breed Araucana have ear-tufts, which affect the structure of the ear canal. Volumes of auditory brainstem nuclei were measured in three chicken breeds in order to evaluate whether the characteristics described for ear-tufted individuals of the Araucana chicken breed (alterations in the outer and middle ear anatomy) are associated with changes in the size of the relevant auditory nuclei. Allometric comparison reveals no size reductions of the angular, laminar and superior olivary nuclei in Araucanas, compared to Japanese Bantams and Brown Leghorns, but a slight increase in the size of the magnocellular nucleus.

Animals↗

PubMed1997

Visual discrimination in adult dairy bulls.

Adult Holstein-Friesian dairy bulls were trained to recognize a black disk and then to discriminate between that disk and smaller ones. The bulls learned these tasks, but much more slowly than did dairy calves. Achievement of a consistently high percentage of correct choices varied among bulls because of daily variation in the disposition of the bull, which seemed to affect willingness to concentrate on the experimental task. Nevertheless, all bulls demonstrated learning, and each bull remembered very well what he once had learned. A 36-cm disk was easily detected and discriminated from smaller disks. However, bulls were not able to discriminate between two disks that differed in area by less than a factor of 4. The ability to use visual cues, such as shapes and size of shapes, suggested that the visual system is important in the biology of bulls. The slow learning rate and the variability in the percentages of correct responses were not considered to be an indication of cognitive disabilities in general but rather a reflection of the daily disposition of the bull, which affected his willingness to cooperate.

Animals↗

PubMed1997

Size of somatosensory cortex and of somatosensory thalamic nuclei of the naturally blind mole rat, Spalax ehrenbergi.

The hypothesis that the somatosensory system in the naturally blind subterranean rodent Spalax ehrenbergi (= mole rat) is enlarged was tested by measuring the volume of somatosensory cortex and somatosensory thalamic nuclei (Nuclei ventrales posteromedialis and posterolateralis). Electrophysiology and tracing were used to identify and delineate these areas. On average the somatosensory cortex is 1.7 times larger and the thalamic nuclei are 1.3 times larger in the blind mole rat than in the sighted laboratory rat if different body weights are taken into consideration. This confirms the demands of a life underground where it seems touch would replace vision. The data reveal a remarkable brain plasticity among mammals under natural conditions.

Adaptation, Physiological↗

PubMed1997

Brain structure volumes in the mole rat, Spalax ehrenbergi (Spalacidae, Rodentia) in comparison to the rat and subterrestrial insectivores.

Natural blindness and a subterranean, digging mode of life demand peculiar adaptations of the central nervous system in the mole rat Spalax ehrenbergi, which are the focus of this quantitative investigation. Volumes of 25 brain structures in Spalax were evaluated allometrically, using the least encephalized mammalian species, the Madagassian hedgehog-like tenrecs (Tenrecinae) as a reference base, and their sizes compared with those of the rat (as a more generalized representative of rodents) and of some subterranean Insectivora. The allometric approach reveals that Spalax has a larger brain than tenrecs and the rat. Within the brain, the neocortex and diencephalon are well developed, an observation also made in other mammalian species with a relatively high encephalization. An unique feature in Spalax is the enlargement of motor structures of the brain, such as the cerebellum (and cerebellar nuclei), and the striatum. Most conspicuous is the large size of the nucleus motorius nervi trigemini, reflecting the importance of masticatory muscles for the special digging technique, which demand an intense use of the teeth for loosening the soil.

Animals↗

PubMed1997

[Early reception of Darwin's selection theory and its sequelae for comparative morphology today].

It is argued that Darwin's concept of evolutionary change is primarily based on the idea of functional adaptation. Genealogical aspects are seen as a secondary consequence of this hypothesis. Unfortunately, the reception of Darwin's work was concentrated on the genealogical aspects from the very beginning (Huxley, Haeckel) and thus channeled future development of evolutionary morphology in a very one-sided way. This direction of development led to the adoption of cladism as a very sophisticated concept of comparative morphology. Though cladism claims to contribute to our understanding of evolution, it is demonstrated that it suffers in this regard because of the incompatibility of "pure morphology" with the demands of functional thinking as an integrative part of Darwin's proposition.

Anatomy, Comparative↗

PubMed1994

Functional anatomy of the thalamus in the blind mole rat Spalax ehrenbergi: an architectonic and electrophysiologically controlled tracing study.

The occipital cortex of the naturally blind mole rat, Spalax ehrenbergi, is occupied by an area of somatosensory representation. To date, no visual cortex has been identified electrophysiologically. In order to determine whether there are corresponding modifications in the thalamus, thalamocortical connections were studied with neuroanatomical tracing methods. Three different fluorescent tracers were injected under electrophysiological control into distinct cortical areas. Injections into the somatosensory head/face and hindlimb/trunk areas of representation revealed a posteromedial ventral nucleus and a posterolateral ventral nucleus, respectively. Additional somatotopic labeling was found in an area dorsomedial to the two ventral nuclei. This structure may be equivalent to the posterior nuclear complex in the laboratory rat. Injections into the auditory cortex of the mole rat resulted in labeling of the medial geniculate body. In contrast to the situation in the laboratory rat, in which a prominent dorsolateral geniculate body and a ventrolateral geniculate body assume dorsolateral positions, the somatosensory thalamus of the mole rat almost reaches the dorsolateral surface. This finding is corroborated by the results of the architectonic study, which failed to reveal a differentiated lateral geniculate body. Our observations suggest that the thalamocortical visual system in the mole rat is minute, whereas the somatosensory system is expanded. This situation fits the mode of life of this subterranean animal, for which touch is more important than vision.

Animals↗

PubMed1992

Forebrain specialization and the olfactory system in anseriform birds. An architectonic and tracing study.

In anseriform birds the mediodorsal part of the rostral forebrain is covered by a corticoid (= layered) structure, establishing a unique feature of this avian group since in other birds the non-cortical accessory or dorsal hyperstriatum occupies the corresponding surface area of the hemisphere. The efferents of the olfactory bulb are shown to reach this region, which thus can be identified as a heavily enlarged retrobulbar area. The large expansion of this olfactory representation may indicate an important biological function. In comparison to the mammalian olfactory system the three stratified olfactory projection centers of birds should be regarded as retrobulbar, prepiriform and periamygdalar regions.

Animals↗

PubMed1992

Electrophysiological mapping of body representation in the cortex of the blind mole rat.

The cortex of the blind mole rat (Spalax ehrenbergi) was explored for somatosensory responses with special reference to an extension into the occipital cortex which serves vision in sighted mammals. Head and body representation was similar as in other rodents or mammals. However, the somatosensory area extended far into the occipital cortex. No responses to auditory or visual stimulation were found caudal to the somatosensory area. However, auditory responses were recorded in an area lateral to and slightly caudal to the head representation. It is concluded that in this naturally blind animal the area normally occupied by the visual cortex serves somatosensory function.

Animals↗

PubMed1992

Distribution of cortical neurons projecting to dorsal column nuclear complex and spinal cord in the hedgehog tenrec, Echinops telfairi.

Using retrograde axonal flow and wheatgerm agglutinin conjugated to horseradish peroxidase, we studied the distribution of cortical neurons giving rise to spinal and dorsal column nuclear projections, and correlated the regions involved in the projections with the cytoarchitectonic areas recently identified in the lesser hedgehog tenrec, Echinops telfairi (Insectivora). Labeled cortical neurons were most numerous following injections of tracer into higher cervical segments, whereas almost none were found following thoracic injections. The cortical labeling appeared more prominent ipsilaterally than contralaterally after spinal injections, although it was more prominent on the contralateral side after injection into the dorsal column nuclear complex. The majority of labeled neurons found in lamina V occupied the neocortex adjacent to the interhemispheric fissure along the rostrocaudal extent of the small corpus callosum. This location corresponded to an intermediate rostrocaudal portion of the hemisphere, and particularly to area 2 of Rehkämper. In some cases, adjacent portions of areas 1 and 3 were also involved, as well as neocortical regions of the lateral hemisphere. The present data did not suggest a somatotopic organization of the projections; likewise, evidence for the presence of more than one somatosensorimotor representation was sparse.

Animals↗

PubMed1991

Parallel evolution in mammalian and avian brains: comparative cytoarchitectonic and cytochemical analysis.

Comparative morphology, which is based on the selection theory of evolution, analyses the impact of function upon structure and, therefore, emphasizes the adaptive events and biological advantage during the evolution of organs. A comparison based on analogies is described here as an adequate method. The hypothesis is proposed that the evolution of the brain follows the same trends in birds as in mammals. This hypothesis is proved by (1) allometric studies of brain weight and brain structure volume in relation to body weight in mammals and birds; (2) architectonic studies using image analysis on cell and fibre stains as well as on histochemical preparations and receptor autoradiography; and (3) hodological studies with injections of [3H]leucin, HRP and WGA-HRP. The results reveal a vast amount of structural and functional similarities in avian and mammalian brain organization, especially an expansion of structures that permit multimodal integration capacity in the telencephalon. Thus, a parallel evolution occurred in these two groups of vertebrates. It is argued that this may be a general phenomenon in evolution. A cladistic approach, which is based on the concept of homologies (plesio-, apomorphies), pushes aside the existence of analogies. For this reason, cladism does not seem to be a method to answer questions of evolutionary morphology adequately.

Animals↗

PubMed1991

Encephalization in hummingbirds (Trochilidae).

The brain mass in 23 hummingbird species was compared to that in galliform birds taking body mass into consideration. Hummingbird brain masses were determined by endocranial volumes, and their body masses were calculated from skeletal measurements. Galliform data were taken from a recent publication. Hummingbirds have brains that are approximately 2.5 times larger than those of galliform birds. Such encephalization may be due to (1) an enlargement of the telencephalon, or (2) an enlargement of functionally well-defined extratelencephalic brain parts. Based on the extremely specialized feeding behavior of the nectarivorous hummingbirds and the neurological demands associated with sucking nectar during hovering, the second hypothesis is better supported, but further studies are needed.

Animals↗