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[3H]MK-801 binding asymmetry in the IMHV region of dark-reared chicks is reversed by imprinting.

Glutamate NMDA-type receptor binding in the intermediate medial hyperstriatum ventrale (IMHV) of dark-hatched chicks is lateralized. This lateralization was found to be markedly influenced by imprinting. In dark-reared chicks the binding of the selective ligand [3H]MK-801 was two-fold higher in the right IMHV than in the left IMHV. In contrast, imprinted chicks have significantly higher levels of [3H]MK-801 binding in the left IMHV region than in the right IMHV. Imprinting results in 2a learning-related increase in NMDA-type receptor binding levels in the left IMHV, whereas [3H]MK-801 binding levels in the right IMHV remain unchanged by imprinting. Thus, the plasticity present in the NMDA-type receptor system and associated with imprinting appears to occur in the left hemisphere only.

Animals↗

Slice cultures of the imprinting-relevant forebrain area medio-rostral neostriatum/hyperstriatum ventrale of the domestic chick: immunocytochemical characterization of neurons containing Ca(2+)-binding proteins.

The forebrain area medio-rostral neostriatum/hyperstriatum ventrale, a presumed analogue to the mammalian prefrontal cortex, displays a variety of synaptic changes during auditory filial imprinting. In order to study the underlying basic mechanisms of this synaptic plasticity we developed slice cultures of the medio-rostral neostriatum/hyperstriatum ventrale from newly hatched chicks. As a prerequisite for these investigations and in order to test the suitability of this system for future studies, we performed a thorough characterization of the in vitro tissue, of its cellular components and some of their biochemical features in comparison with in situ tissue. Since in situ the medio-rostral neostriatum/hyperstriatum ventrale has been previously shown to contain three distinct neuron populations characterized by the activity-regulated Ca(2+)-binding proteins parvalbumin, calbindin D28K and calretinin, we used these proteins as neuronal markers to study the survival and preservation of the morphological features of medio-rostral neostriatum/hyperstriatum ventrale neurons in vitro. In agreement with in vivo studies the three Ca(2+)-binding proteins are confined to neuronal cells and they are not colocalized, i.e. they appear to characterize three different neuron populations. The immunoreactive neurons in medio-rostral neostriatum/hyperstriatum ventrale cultures to a certain extent appear to form synaptic contacts with each other, shown by the double immuncytochemical experiments. One difference between cells in vivo and in vitro is their soma size, which is much larger in vitro than in vivo. This and our previous study on neuronal morphology demonstrates that morphologically and biochemically intact neurons can be maintained in medio-rostral neostriatum/hyperstriatum ventrale slice cultures, which may thus provide a suitable in vitro system for further studies of neuronal and synaptic plasticity in vitro.

Animals↗

Olfactory imprinting.

The term imprinting is used to refer to biologically relevant learning during a sensitive period defined by a particular developmental stage or physiological state. Although olfactory imprinting may occur at any age, and some of the best-studied paradigms involve adult animals, recent reports of long-term memory for odorants experienced during prenatal life present a particular challenge to our understanding of olfactory learning. Firstly, it is possible that these paradigms represent a form of exposure learning based on mechanisms different to the more familiar associative paradigms. Secondly, given the substantial addition of neural elements occurring during the perinatal period, these paradigms raise the question as to how the olfactory system, and eventually the brain, is able to acquire and retain information under conditions of major neural growth and change.

Aging↗

Monocular sleep in male domestic chicks.

Behavioural sleep during the first 2 weeks after hatching was studied in male chicks reared with an imprinting object (I-chicks) and in social isolation (NI-chicks). Time spent in sleeping with both eyes closed (binocular sleep) decreased gradually with age in both I-chicks and in NI-chicks whilst the number of episodes of binocular sleep decreased with age in NI-chicks but not in I-chicks. The pattern of monocular sleep (only one eye closed) of both I-chicks and NI-chicks showed no significant bias towards predominant left- or right-eye closure during the first week. During the second week, I-chicks showed a tendency towards more pronounced left-eye closure with a peak on day 10, whilst NI-chicks showed a tendency for more pronounced right-eye closure with peaks on days 9 and 11. In a different group of chicks, changing the colour of the imprinting object on day 8 produced a shift towards right-eye closure. In contrast, the removal of the imprinting object on day 8 did not cause any change in the pattern of monocular sleep. Differences with respect to sleeping patterns previously observed in females chicks are discussed.

Age Factors↗

Light experience and the development of behavioural lateralisation in chicks. II. Choice of familiar versus unfamiliar model social partner.

In late-stage embryos of domestic fowl, exposure of the right eye to light entering through the shell induces asymmetry of the thalamofugal visual pathway, together with differences in performance according to whether the right or left eye (RE, LE) is in use (Behav. Brain Res. 38 (1990) 211). Nevertheless, at least some of the main specialisations of the right and left eye systems (RES, LES) are not dependent on such exposure. Higher ability of LES to assess and respond to novelty is present in dark-incubated (Da) chicks. This is probably also true of RES ability to control response, and specifically to inhibit shift to an alternative response (i.e. to a novel stimulus). We imprinted chicks on red table-tennis balls with a horizontal, white strip on their equator. At test, they chose between this and a ball with a vertical, white strip. Da chicks showed clear choice with the LE, but not with the RE. Unexpectedly, light-incubated (Li) chicks failed to show LE/RE differences in choice. Exploratory pecks at a novel feature were greatly reduced in Li. Two effects of light exposure on RES are likely. The first is greater use of RES in the home-cage, affecting what is learned about the companion ball. This may make RES more competent in assessing ball properties, and so explain the enhanced choice by RE, that abolished the RE/LE difference in Li. Secondly, the ability of RES to inhibit shift to an alternative response is enhanced. Light exposure and being female similarly opposed shift to the novel feature, but probably via different mechanisms. The effects of exposure are discussed as an example of the generation of a range of behavioural phenotypes, which are sustained within a single population by varying or frequency-dependent selection.

Age Factors↗

The effects of early post-hatching changes of imprinting object on the pattern of monocular/unihemispheric sleep of domestic chicks.

The pattern of monocular/unihemispheric sleep (Mo-Un sleep) was studied behaviourally in male and female chicks after early post-hatching changes of the imprinting object. Chicks were reared with an imprinting object on day 1 post-hatching which was removed or changed on day 2. On day 1, time spent in binocular sleep (both eyes closed) was similar in male and female chicks, though the number of episodes was lower in females than in males. There was no eye-closure bias in the pattern of Mo-Un sleep (one eye shut and the other open) in chicks of both sexes. On day 2, chicks subjected to the removal of imprinting object showed less time and number of episodes of binocular sleep than control chicks and chicks subjected to changes of imprinting object. There was no eye-closure bias in control chicks whilst a significant bias for more right Mo-Un sleep was recorded in chicks after removal and changes of imprinting object of both sexes. It is suggested that the removal or changes of imprinting object would cause a decrease of binocular sleep and trigger processes associated to secondary imprinting involving the left hemisphere. The bias for more right Mo-Un sleep (right eye-closure) could be the by-product of consolidation processes of secondary imprinting memories in the left hemisphere and/or of more left eye-opening as a result of periodical awakening of right hemisphere to control the environment after a stressful condition such as the removal or change of imprinting object.

Animals↗

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↗

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↗

Effects of social interaction on monocular/unihemispheric sleep in male and female domestic chicks.

The monocular/unihemispheric sleep was studied in male and female domestic chicks reared socially. In first week post-hatching, chicks were reared in couples whilst during the second week, for half of the chicks the cospecific was maintained (Conspec-chicks) and for the other half the conspecific was removed (No-Conspec-chicks). During the first week, female chicks showed a bias for more left-eye closure/right unihemipheric sleep, whilst male chicks did not show any eye-closure bias. In the second week, both female and male Conspec-chicks showed a bias for right eye-closure/left unihemispheric sleep. Female No-Conspec-chicks did not show any eye-closure bias whilst male No-Conspec-chicks showed a bias for more left eye-closure/right unihemispheric sleep. Based on the role of the avian brain lateralization, a bias for more right or left eye-closure could be associated with a prevalent activation of left or right hemisphere during wakefulness. Eye-opening during sleep might be connected with the hemisphere that was not or was less activated during wakefulness or with lateralization of the environment monitoring against predation.

Age Factors↗

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↗

Sexual imprinting can induce sexual preferences for exaggerated parental traits.

Sexual preferences in animals are often skewed toward mates with exaggerated traits. In many vertebrates, parents provide, through the learning process of "sexual imprinting," the model for the later sexual preference. How imprinting can result in sexual preferences for mates having exaggerated traits rather than resembling the parental appearance is not clear. We test the hypothesis that a by-product of the learning process, "peak shift", may induce skewed sexual preferences for exaggerated parental phenotypes. To this end, zebra finch (Taeniopygia guttata) males were raised by white parents, with beak color as the most prominent sexual dimorphism. We manipulated this feature with nail varnish. At adult age, each male was given a preference test in which he could choose among eight females with beak colors ranging from more extreme on the paternal to more extreme on the maternal side. The males preferred females with a beak of a more extreme color than that of their mothers, i.e., they showed a peak shift. Sexual imprinting can thus generate skewed sexual preferences for exaggerated maternal phenotypes, phenotypes that have not been present at the time of the learning. We suggest that such preferences can drive the evolution of sexual dimorphism and exaggerated sexual traits.

Animals↗

Imprinting: seeing food and eating it.

A recent study has found that although, ordinarily, cuttlefish hatchlings prefer shrimp-like prey, when visually exposed to crabs in the first hours of day one, they later prefer crabs to shrimps. As the development of this preference occurs during a short sensitive phase, does not depend on food ingestion and is long lasting, it fulfils all the criteria for imprinting, a phenomenon more usually associated with vertebrates and social learning.

Animals↗

Effect of treatment at weaning with the serotonin antagonist mianserin on the brain serotonin and cerebrospinal fluid nocistatin level of adult female rats: a case of late imprinting.

Four weeks old (weanling) female rats were treated with the tricyclic antidepressant and histamine/serotonin receptor blocker mianserin for studying its faulty hormonal imprinting effect. Measurements were done four months later. Brain serotonin levels significantly decreased in four regions (hippocampus, hypothalamus, striatum and brainstem), without any change in the cortex. Sexual activity of the treated and control rats was similar. Cerebrospinal fluid nocistatin level was one magnitude higher in the treated rats, than in the controls. The density of uterine estrogen receptors was significantly reduced, while binding capacity of glucocorticoid receptors of liver and thymus remained at control level. The results call attention to the possibility of 1. a broad spectrum imprinting at the time of weaning by a receptor level acting non-hormone molecule 2. imprinting of the brain in a non-neonatal period of life and 3. a very durable (lifelong?) effect of the late imprinting with an antidepressant.

Animals↗

Amino acid neurotransmitter release and learning: a study of visual imprinting.

The intermediate and medial part of the hyperstriatum ventrale (IMHV) is an area of the domestic chick forebrain that stores information acquired through the learning process of imprinting. The effects of visual imprinting on the release of the amino acids aspartate, arginine, citrulline, gamma-aminobutyric acid (GABA), glutamate, glycine and taurine from the left and right IMHVs in vitro were measured at 3.5, 10 and 24 h after training. Chicks were exposed to an imprinting stimulus for 1 h, their preferences measured 10 min afterward and a preference score calculated as a measure of the strength of learning. Potassium stimulation was used to evoke amino acid release from the IMHVs of trained and untrained chicks in the presence and absence of extracellular Ca2+. Ca2+-dependent, K+-evoked release of glutamate was significantly (34.4%) higher in trained than in untrained chicks. This effect was not influenced by time after training or by side (left or right IMHV). Training influenced the evoked release of GABA and taurine from the left IMHV at both 3.5 and 10 h. The training effects at the two times were statistically homogeneous so data (< or = 10 h group) were combined for each amino acid respectively. For this < or = 10 h group, evoked release increased significantly with preference score. In contrast, for the 24 h group, evoked release of GABA and taurine was not significantly correlated with preference score. There were no significant correlations between preference score and GABA or taurine release in the right IMHV at any time, nor in the absence of extracellular calcium. No significant effects of training condition, time or side were observed for any other amino acid in the study. The present findings suggest that soon after chicks have been exposed to an imprinting stimulus glutamatergic excitatory transmission in IMHV is enhanced, and remains enhanced for at least 24 h. In contrast, the learning-related elevations in taurine and GABA release are not sustained over this period. The change in GABA release may reflect a transient increase in inhibitory transmission in the left IMHV.

Amino Acids↗

The chicken immediate-early gene ZENK is expressed in the medio-rostral neostriatum/hyperstriatum ventrale, a brain region involved in acoustic imprinting, and is up-regulated after exposure to an auditory stimulus.

The immediate-early gene zenk (an acronym for the avian orthologue of the mammalian genes zif-268, egr-1, ngfi-a and krox-24) has been extensively employed, in studies on oscine birds, as a marker of neuronal activity to reveal forebrain structures that are involved in the memory processes associated with the acquisition, perception and production of song. Audition-induced expression of this gene, in brain, has also recently been reported for the domestic chicken (Gallus gallus domesticus) and the Japanese quail (Coturnix coturnix japonica). Whilst the anatomical distribution of zenk expression was described for the quail, corresponding data for the chicken were not reported. We have, therefore, used in situ hybridisation to localise the mRNA that encodes the product of the zenk gene (which we call ZENK) within the brain of the 1-day-old chick. We demonstrate that this transcript is present in a number of forebrain structures including the medio-rostral neostriatum/hyperstriatum ventrale (MNH), a region that has been strongly implicated in auditory imprinting (which is a form of recognition memory), and Field L, the avian analog of the mammalian auditory cortex. Because of this pattern of gene expression, we have compared the level of the ZENK mRNA in chicks that have been subjected to a 30-min acoustic imprinting paradigm and in untrained controls. Our results reveal a significant increase (P< or =0.05) in the level of the ZENK mRNA in MNH and Field L, and in the two forebrain hemispheres; no increase was seen in the ectostriatum, which is a visual projection area. The data obtained implicate the immediate-early gene, zenk, in auditory imprinting, which is an established model of juvenile learning. In addition, our results indicate that the ZENK mRNA may be used as a molecular marker for MNH, a region that is difficult to anatomically and histochemically delineate.

Acoustic Stimulation↗

Early socio-emotional experience induces expression of the immediate-early gene Arc/arg3.1 (activity-regulated cytoskeleton-associated protein/activity-regulated gene) in learning-relevant brain regions of the newborn chick.

We have cloned a full-length complementary DNA from the chicken (Gallus gallus domesticus), which encodes a polypeptide that exhibits approximately 75% identity to the product of the mammalian gene Arc (activity-regulated cytoskeleton-associated protein), also known as arg3.1 (activity-regulated gene). Since this gene is an immediate-early gene that has been suggested to play a role in synaptic plasticity and learning and memory processes, its expression has been analyzed in a juvenile form of learning, namely, filial imprinting. Our results demonstrate that Arc/arg3.1 mRNA is detectable in the newborn chick brain, and that at this early age the level of this transcript can be altered by brief sensory/emotional experience. After postnatal exposure to a novel 30-min auditory imprinting stimulus, Arc/arg3.1 mRNA was found to be significantly increased in two higher associative areas, the mesopallium intermediomediale (P = 0.002) and the nidopallium dorso-caudale (P = 0.031), compared with naïve controls. The transcript level was also significantly elevated after imprinting in Area L pallii (P=0.045), which is analogous to the mammalian auditory cortex. In addition, increases were seen in the medio-rostral nidopallium/mesopallium (P = 0.054), which is presumed to be the analog of the mammalian prefrontal cortex, and the hyperpallium intercalatum (P = 0.054), but these did not quite reach significance. We discuss these data in the light of those obtained in an earlier study, in the same paradigm, for the avian immediate-early gene, zenk (an acronym for zif-268, egr-1, ngfi-a and krox-24, which are different names for the orthologous mammalian gene). We conclude that, although both the Arc/arg3.1 and zenk genes are induced by auditory imprinting, they are significantly up-regulated in different learning-relevant brain regions. It is, therefore, evident that they must be activated by different mechanisms.

Acoustic Stimulation↗

Regional and cellular distribution of the extracellular matrix protein tenascin-C in the chick forebrain and its role in neonatal learning.

The juvenile brain's pronounced synaptic plasticity in response to early experience and learning events is related to the fact that the genetically pre-programmed molecular machinery mediating neuronal development and synapse formation, is activated throughout postnatal brain development and thereby can be recruited for learning and long-term memory formation. In situ hybridization and immunocytochemistry experiments revealed that tenascin-C, one candidate molecule which we suspect to be involved in neonatal learning, is expressed in the forebrain of domestic chicks around the sensitive period during which auditory filial imprinting takes place. The involvement of tenascin-C in this juvenile learning task was tested by injections of monoclonal antibodies directed to distinct domains of the tenascin-C molecule into the avian prefrontal cortex analog, the medio-rostral nidopallium/mesopallium (formerly termed medio-rostral neostriatum/hyperstriatum ventrale), a forebrain area which has been shown to be critically involved in auditory filial imprinting. Injections of monoclonal antibody Tn 68, which is directed against a cell-binding domain of the tenascin-C molecule, strongly reduced the imprinting rate, as opposed to injections of the monoclonal antibody Tn 578, which binds to a domain involved in neurite outgrowth. Double labeling immunohistochemistry revealed that tenascin-C is associated with neurons which express the Ca(2+)-binding protein parvalbumin, and displays a staining pattern highly reminiscent of perineuronal nets of the extracellular matrix. These results indicate that a distinct domain of tenascin-C is functionally involved in the juvenile learning process of filial imprinting and further suggest a critical role of a specific neuronal subpopulation.

Age Factors↗