Biomedical subjects

Hans-Joachim Bischof

Publications and source records attributed to Hans-Joachim Bischof.

13 recordsLinked to original sources

PubMed2006

Behavioural responses to video playbacks by zebra finch males.

A major problem for communication research is to provide standardized stimuli and to disentangle the relative contribution of different sensory channels to the compound signal and its effectiveness. Video techniques have frequently been used for this purpose. Fifty Hertz cathode ray tube (CRT) screens cannot be used for birds because their flicker frequency is lower than the time resolution of at least songbirds. Thin film transistor (TFT) screens have successfully been used to present video clips of behaving conspecifics. We show here that they are indeed transmitting video images in a way that enables zebra finches to react appropriately to live video images of conspecifics and that the test birds are able to detect small differences in the behaviour of the stimulus animals. Adding acoustic information strongly enhanced the reaction to the video clips.

Animal Communication↗

PubMed2006

C-fos induction in forebrain areas of two different visual pathways during consolidation of sexual imprinting in the zebra finch (Taeniopygia guttata).

Two forebrain areas in the hyperpallium apicale and in the lateral nidopallium of isolated male zebra finches are highly active (2-deoxyglucose technique) on exposure to females for the first time, that is first courtship. These areas also demonstrate enhanced neuronal plasticity when screened with c-fos immunocytochemistry. Both are areas involved in the processing of visual information conveyed by the two major visual pathways in birds, strengthening our hypothesis that courtship in the zebra finch is a visually guided behaviour. First courtship and chased birds show enhanced c-fos induction in the hyperpallial area, which could represent neuronal activity reflecting changes in the immediate environment. The enhanced expression of fos in first courtship birds in lateral nidopallial neurons indicates imminent long-lasting changes at the synaptic level that form the substrate for imprinting, a stable form of learning in birds.

Animals↗

PubMed2006

Afferentation of the lateral nidopallium: A tracing study of a brain area involved in sexual imprinting in the zebra finch (Taeniopygia guttata).

The lateral forebrain of zebra finches that comprises parts of the lateral nidopallium and parts of the lateral mesopallium is supposed to be involved in the storage and processing of visual information acquired by an early learning process called sexual imprinting. This information is later used to select an appropriate sexual partner for courtship behavior. Being involved in such a complicated behavioral task, the lateral nidopallium should be an integrative area receiving input from many other regions of the brain. Our experiments indeed show that the lateral nidopallium receives input from a variety of telencephalic regions including the primary and secondary areas of both visual pathways, the globus pallidus, the caudolateral nidopallium functionally comparable to the prefrontal cortex, the caudomedial nidopallium involved in song perception and storage of song-related memories, and some parts of the arcopallium. There are also a number of thalamic, mesencephalic, and brainstem efferents including the catecholaminergic locus coeruleus and the unspecific activating reticular formation. The spatial distribution of afferents suggests a compartmentalization of the lateral nidopallium into several subdivisions. Based on its connections, the lateral nidopallium should be considered as an area of higher order processing of visual information coming from the tectofugal and the thalamofugal visual pathways. Other sensory modalities and also motivational factors from a variety of brain areas are also integrated here. These findings support the idea of an involvement of the lateral nidopallium in imprinting and the control of courtship behavior.

Afferent Pathways↗

PubMed2006

ZENK expression in a restricted forebrain area correlates negatively with preference for an imprinted stimulus.

Sexual imprinting is an early learning process by which young birds acquire the characteristics of a potential sexual partner. The physiological basis of this learning process is an irreversible reduction of dendritic spines in two forebrain areas, the LNM (lateral nido-mesopallium) and the MNM (medial nido-mesopallium). The aim of the present study was to investigate whether these two brain areas are activated if the imprinted stimulus is presented to the adult bird after the end of the sensitive period. One group of zebra finch males was reared by their own parents. These birds, as adults, showed an exclusive preference for their own species in choice tests between a zebra finch and a Bengalese finch female. If exposed as adults to a zebra finch female, LNM and MNM showed lower activation, as measured by ZENK expression, compared to males exposed to a Bengalese finch female. A second group was reared by Bengalese finches and was exposed at day 100 to a zebra finch female for 1 week. As shown earlier, this regime leads to mixed choices, the birds are courting Bengalese and zebra finch females with a fixed ratio (preference score). If these birds were exposed to a zebra finch female as adults, the ZENK expression within LNM was much higher compared to group 1, and it showed a strong tendency to correlate negatively with the preference score: Birds with higher zebra finch preference showed lower activation compared to those with a low zebra finch and a high Bengalese finch preference. We propose that higher ZENK activation in group 2 is due to the rearing by a foster species which may result in a more complex neuronal network. The negative relation between activation and preference score may be explained by special properties of the LNM and MNM networks.

Animals↗

PubMed2006

Reduction of GABAergic neurons within the tectofugal visual system of white zebra finches.

The central visual system of white zebra finches is physiologically and anatomically different from normally coloured (wild type) animals. The main difference to normal birds is an enhanced response to ipsilateral stimulation in all areas of the tectofugal visual pathway. Previous experiments indicated that besides an enhancement of recrossing fibers, it might be a lack of inhibition which causes this effect. We show here that such an explanation can only be true for a part of the entopallium, the telencephalic station of this projection. Only within the so-called perientopallium, the number of GABAergic neurons is strongly reduced, while there is no significant difference between white and wild type birds in the other visual areas. It is speculated that these neurons in normal birds inhibit ipsilateral input conveyed by the second visual projection in birds, the thalamofugal pathway.

Animals↗

PubMed2006

Spatial memory and hippocampal function in a non-foodstoring songbird, the zebra finch (Taeniopygia guttata).

Spatial memory and hippocampal function have as yet been investigated mainly in pigeons and food storing songbirds. We show here that the zebra finch, a songbird not specialized in food storing and caching, is also able to learn a spatial memory task and uses a spatial map for finding food in a 'dry water maze'. Hippocampal lesions prevent learning and retention of this spatial task. The immediate early gene (IEG) products Zenk and Fos are expressed within the hippocampus when the bird is learning the task. Spatial learning cannot be assigned to any hippocampal subregion; IEG expression within the hippocampus is patchy and seems almost arbitrarily located. The IEG activation pattern in spatial memory experiments is compared with those in other learning experiments with zebra finches.

Animals↗

PubMed2004

Effects of hippocampal lesions on acquisition and retention of spatial learning in zebra finches.

We tested the role of the hippocampus in spatial memory of zebra finches. The birds were trained to find the location of a food site among four identical feeders arranged on the aviary floor. Extra-maze cues were present. The birds had to perform the task from four different starting points. Successful visits and the time to find the food were recorded. Hippocampal lesions made before acquisition led to a decrease in correct choices. Hippocampal lesions following training disrupted the retention of the spatial memory. Surprisingly, birds with hippocampal damage reached the food as quickly as intact birds, but they needed more visits to find the correct feeder. Therefore, the birds with hippocampal damage used an alternative, nonspatial memory-based strategy to find the food.

Analysis of Variance↗

PubMed2004

Sexual imprinting leads to lateralized and non-lateralized expression of the immediate early gene zenk in the zebra finch brain.

Sexual imprinting is an early learning process by which young birds acquire the features of a potential sexual partner. The physiological basis of this learning process is an irreversible reduction of spine densities in two forebrain areas, the lateral neo- and hyperstriatum (LNH) and the medial neo- and hyperstriatum (MNH). The aim of the present study was to investigate whether the immediate early gene zenk, which has been shown frequently to play a role in plastic processes in the song system of zebra finches, may also be involved in the structural changes observed in these areas. The first exposure to a female after an isolation period enhances zenk expression in a variety of brain areas including LNH, MNH, and optic tectum. In contrast to earlier results, it was only the neostriatal part of LNH which showed an enhancement on first courtship, while exposure to a nestbox enhanced the label within the entire LNH area. Unexpectedly, the IEG expression was clearly lateralized in some layers of the optic tectum. Because lateralization occurred independent of the experimental condition, our study adds to recent results which also support the idea of a lateralized organization of the avian visual system.

Animals↗

PubMed2004

c-fos is induced in the hippocampus during consolidation of sexual imprinting in the zebra finch (Taeniopygia guttata).

c-fos was used to mark regions of enhanced neuronal activity during sexual imprinting, an early learning process by which information about the prospective sexual partner is acquired and consolidated. In the present study, we demonstrate that the hippocampus, already known for its specialized spatial memory capacities in navigating pigeons and in food-storing birds, depicts a selective differential c-fos induction in a situation shown to lead to sexual imprinting, that is, exposing previously isolated male birds to a female for 1 h. c-fos induction is lateralized, the left hippocampus showing more c-fos activity than the right. Our results would indicate a role for the hippocampus in the consolidation process of imprinting, probably in the transfer of information to the other telencephalic areas that show alterations in synaptic connectivity as a result of consolidation of sexual imprinting.

Animals↗

PubMed2003

Unusual postnatal development of visually evoked potentials in four brain areas of white zebra finches.

The central visual system of white zebra finches is physiologically different from normally coloured (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in the white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. The present study shows that the enhancement of ipsilateral responses in white zebra finches is detectable in all areas of the tectofugal pathway, and also in the visual wulst, the only station of the thalamofugal pathway examined so far in white zebra finches. In all investigated areas, the enhancement is already obvious at 20 days after hatching, the earliest age that allows reliable recordings. A deficit in inhibition of ipsilateral stimuli, probably combined with a general increase in the number of ipsilateral projections, may cause the observed enhancements of ipsilateral responses in white birds.

Aging↗

PubMed2003

The dynamics of spine density changes.

Numerous papers have been published describing the effects of learning and environmental changes on the wiring of brain areas in mammals and birds. The density of dendritic spines, which can be taken as a measure of the complexity of a given neuronal network, has been shown to increase or to decrease depending on the experiment and on the brain area involved. Almost no information is available concerning the speed with which a given network reacts to learning events or environmental changes. We therefore examined the time course of spine density changes in two areas of the zebra finch forebrain, which have been shown previously to be either involved in sexual imprinting (LNH, lateral part of the neo-hyperstriatum) or to react to environmental changes (ANC, archi-neostriatum caudale). The decrease of spine density in LNH of zebra finch males after sexual imprinting is very fast, the new level of spine density is reached after 2 days. In contrast, decrease of spine density within ANC as a consequence of transferring birds from a social condition into isolation is very slow, lasting about 3 weeks. The increase of spine density within ANC after transfer of the males from isolation to a social condition occurs within 3 days. The differences in adaptation times cannot be due to limitations in the growth speed of single spines, because this has been shown to be much faster (hours instead of days). Instead, the speed of adaptation may be dependent on the availability of information about the final wiring diagram and on functional aspects like the energy demands for maintenance or alteration of a given neuronal network, or the necessity of quick adaptation to enhance the fitness of the animal.

Animals↗

PubMed2002

Limitations of the sensitive period for sexual imprinting: neuroanatomical and behavioral experiments in the zebra finch (Taeniopygia guttata).

In the course of developmental sensitive periods, an animal receives input from the environment which shapes its behaviour and neuronal connectivity. While normally restricted to early development, it has been shown frequently that an extension of the sensitive period to later ages is possible by sensory deprivation or inadequate stimulation. This raises the question whether sensitive periods can be shifted to any age, or whether a time window exists within which sensitive period shifts are possible. We show here for sexual imprinting that such a time window exists, and we also show that the spine density changes during development in brain areas involved in imprinting predict the limits for sensitive period shifts. Based on these results, we speculate about the mechanisms which may underlay the regulation of spine density and thus the imprinting process.

Aging↗

PubMed2002

Enhanced fos expression in the zebra finch (Taeniopygia guttata) brain following first courtship.

Young zebra finch males that court a female for the first time develop a stable preference for the females of that species. On the neuronal level, consolidation of the imprinted information takes place. Here we demonstrate that first courtship or being chased around in the cage leads to enhanced fos expression in forebrain areas implicated in learning and imprinting in zebra finch males compared with birds reared in isolation or in the aviary. Two of the forebrain areas highly active during first courtship (as demonstrated by the 14C-2-deoxyglucose technique), the imprinting locus latral neo/hyperstriatum ventrale (LNH) and the secondary visual area hyperstriatum accessorium/dorsale (HAD), demonstrate enhanced fos expression. Two other imprinting-related areas, the medial neo/hyperstriatum ventrale (MNH) and archistriatum/neostriatum caudale (ANC), do show c-fos induction; however, the areas are not congruous with those demarcated by the 2-DG autoradiographic studies. Additional telencephalic areas include the olfactory lobe, the information storage site lobus parolfactorius (LPO), the memory site hippocampus, the auditory caudomedial neostriatum implicated in the strength of song learning, and the caudolateral neostriatum, which is comparable to the mammalian prefrontal cortex. In addition, c-fos is induced by first courtship and chasing in neurosecretory cell groups of the preoptic area and hypothalamus associated with the repertoire of sexual behavior and stress or enhanced arousal. Enhanced fos expression is also observed in brainstem sources of specific (noradrenergic, catecholaminergic) and nonspecific (reticular formation) activating pathways with inputs to higher brain areas implicated in the imprinting process. Birds reared in isolation or alternatively in the aviary with social and sexual contact to conspecifics showed attenuated or no fos expression in most of the above-mentioned areas. First courtship and chasing both lead to enhanced uptake of 2-DG in the four imprinting areas, as well as subsequent changes in spine density-an anatomical manifestation of the imprinting process. fos expression in the imprinting and other telencephalic, preoptic, hypothalamic, and mesencephalic brain regions indicates processing of stimuli originating from exposure (like chasing) and the analysis of stimuli in a behaviorally relevant, sexually explicit context (like first courtship). c-fos induction in these brain areas indicates its involvement in the triggering of neural changes that accompany the learning process of imprinting, leading eventually to alterations in dendritic spine density in the zebra finch.

Animals↗