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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

Light exposure of the chick embryo influences monocular sleep.

Together with some aquatic mammals, several species of birds, such as the domestic fowl, exhibit a particular behavioural and electrophysiological state called 'unihemispheric sleep', in which one cerebral hemisphere is awake and the other is sleeping. Slow-wave sleep in one hemisphere is associated with closure of the contralateral eye, whilst the eye contralateral to the awake hemisphere is open; closure of both eyes, in contrast, is associated with bihemispheric slow-wave sleep or with REM sleep. During the last few days of incubation the chick embryo is turned in the egg so that it occludes its left eye, whereas light entering through the shell can stimulate the right eye. We found that in the first 2 days after hatching chicks coming from eggs incubated in the light and reared with an imprinting object slept mostly with their right-eye open, whereas those coming from eggs incubated in the dark slept mostly with their left-eye open. In chicks reared without an imprinting object, in contrast, the effect of incubation extended over the first 2 weeks in females, with dark-incubated chicks showing more pronounced left-eye closure than light-incubated chicks, whereas the effect of incubation was similar to that observed in chicks reared with the imprinting object during the first 2 days post-hatch in males and more variable from day to day thereafter. Asymmetric light stimulation of embryos can thus modulate, though it does not generate, the left-right direction of eye opening during post-hatching monocular sleep; apparently, such a modulation depends on the emotional/motivational state of the animal associated with the outcomes of a naturally occurring visual imprinting.

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↗
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↗
PubMed1991

The development of hemispheric asymmetries in neuronal activity in the domestic chick after visual experience.

Previous experiments have shown that a restricted part of the forebrain, the intermediate and medial part of the hyperstriatum ventrale (IMHV), is involved in the learning process of imprinting. Through this process chicks selectively approach, and so recognise, a visually conspicuous object to which they have been exposed. Previous work has also demonstrated that the left and right IMHV regions play different roles in the recognition memory of imprinting, and that exposure to an object results in changes in synaptic organisation in the left, but not in the right IMHV. We have enquired whether training has a differential effect on spontaneous multiple-unit impulse activity in the two regions. Thirty-two chicks were reared in darkness. Sixteen were trained by exposing them to a flashing, rotating box; the remaining chicks serving as dark-reared controls. The trained chicks were anaesthetised either immediately after training (0-h trained chicks) or returned to the dark incubator and anaesthetised 6 h after the end of training (6-h trained chicks). A single microelectrode penetration was made through the left IMHV simultaneously with a single penetration through the right IMHV; a single penetration was also made through a visual projection area, the left hyperstriatum accessorium. Recordings were made from between 3 and 7 sites in each penetration, and the mean multiple-unit firing rate for these sites was calculated. Spontaneous activity in the right IMHV changed in respect of activity in the left IMHV with time after training; no such effects were found in the left hyperstriatum accessorium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

The dorsocaudal neostriatum of the domestic chick: a structure serving higher associative functions.

The dorsocaudal neostriatal (dNC) complex consists of at least three functionally distinct subregions and is part of an 'imprinting' pathway, which interconnects several forebrain regions that are known to be involved in juvenile learning. Based on its anatomical features, at least one subregion of the dNC complex, the neostriatum dorsocaudale (Ndc) may be considered as the equivalent of the mammalian polysensory association cortices. Several lines of evidence point to a role for this forebrain region in learning and memory formation. After auditory or visual imprinting changes of stimulus-evoked metabolic activities and of synaptic densities have been measured in the Ndc. Pharmacological behavioral studies revealed that the activation of NMDA receptors plays a critical role during this learning process and that NMDA receptor activation is required for the associated metabolic and synaptic changes. In addition to glutamatergic afferents, anatomical studies revealed a massive input from monoaminergic and peptidergic pathways into the dNC complex, suggesting a modulatory role for these systems during imprinting. The results presented here together with data from other avian species support the view that the dNc complex, and in particular the Ndc, plays an important role in juvenile and adult learning.

Animals↗
PubMed1999

Early learning and the development of filial preferences in the chick.

Newly hatched domestic chicks (Gallus gallus domesticus) rapidly form a social preference for a conspicuous stimulus to which they are exposed. The learning process involved is known as filial imprinting. When chicks are exposed to an audio-visual compound stimulus, both auditory and visual learning are enhanced. The enhancement of visual imprinting is virtually abolished when chicks are exposed separately to the auditory element, either before or after training with the audio-visual compound. Simultaneous exposure to the two elements of the compound is superior to sequential exposure in achieving the enhancement of visual learning. These results are unlike Pavlovian conditioning, but are consistent with an interpretation of imprinting as a form of within-event learning, where links are formed between the representations of the elements of the compound, that can be weakened by separate exposure to an element. Apart from imprinting, chicks may show a developing predisposition to approach stimuli resembling conspecifics. The predisposition emerges in dark-reared chicks given some non-specific experience during a sensitive period, and is expressed as a relatively general preference for stimuli with a head and neck region. In the natural situation, the animal's response may be biased by the predisposition, and through imprinting it then learns the characteristics of individuals.

Animals↗
PubMed1999

The recognition memory of imprinting: biochemistry and electrophysiology.

A restricted part of the intermediate and medial part of the hyperstriatum ventrale (IMHV) of the domestic chick forebrain is pivotal to the learning process of imprinting and is probably the site at which information about an imprinting stimulus is stored. A range of learning-related changes occur in the IMHV between 1 and 24 h after training. The earliest change described is in Fos-like immunoreactivity. There follow changes in phosphorylation of the protein kinase C substrate MARCKS, morphological changes in axospinous synapses, an increase in NMDA receptor number and increases in amounts of the major isoforms of the neural cell adhesion molecule and clathrin heavy chain. All but the change in Fos-immunopositivity occurs in the left, but not the right, IMHV. Insufficient nitric oxide synthase is available in the IMHV to support the hypothesis that nitric oxide is a retrograde messenger contributing to the effect on Fos-like immunoreactivity. In chicks anaesthetised approximately 24 h after imprinting training, the spontaneous mean neuronal firing rate is related to a preference score (a measure of learning). In unanaesthetised chicks 24 h after training, the responsiveness of some IMHV neurons is biassed specifically towards the imprinting stimulus.The responses of other neurons in the IMHV generalise across some features of the training stimulus, such as form or colour. Some neurons in the IMHV of unanaesthetised chicks are responsive to the distance of an imprinting stimulus from the chick; distance-sensitive neurons can be distinguished from distance-insensitive neurones by the action potential shape.

Animals↗
PubMed1999

Behavioural and neurophysiological aspects of sexual imprinting in zebra finches.

Sexual imprinting has been defined as the process by which young animals learn the characteristics of their future sexual partners. It is a two stage process including an acquisition period where features of the social environment are learnt, and a stabilization process by which, under the guidance of the previously acquired social information, a preference for a sexual partner is established and stabilized, so that it cannot be altered again subsequently. The stabilization process is short (1 h) and can be controlled experimentally. This allows for the design of experiments to examine the physiological events accompanying the imprinting process. During the stabilization process, four areas of the forebrain are more activated than in any other behavioural context. These are the hyperstriatum accessorium/dorsale (HAD), the archi-neostriatum caudale (ANC), the medial neo/hyperstriatum (MNH) and the lateral neo/hyperstriatum (LNH). Isolation during development reduces the spine density of neurons in HAD and ANC and enhances it in MNH and LNH. Subsequent exposure to a female (which stabilizes the previously acquired preference in behavioural experiments) for 1 week leads to an enhancement of spine densities in HAD and ANC, and to a reduction in MNH and LNH. The enhancement in HAD and ANC is reversible by a second isolation period after the exposure to a female, the reduction within MNH and LNH is not. This irreversibility indicates that the reduction process within MNH and LNH may be the anatomical manifestation of the imprinting process. The examination of spine densities in the four brain areas after two experiments which have been shown previously to affect the stabilization process in behavioural experiments, confirms this idea.

Animals↗
PubMed1997

Loss of imprinting and overexpression of IGF2 gene in gastric adenocarcinoma.

Both insulin-like growth factor II (IGF2) and H19 gene are located on chromosome 11p15.5 in close vicinity to each other, and are imprinted on different parental alleles. Although the exact mechanism remains unclear, loss of imprinting (LOI) leading to the biallelic expression of IGF2 and H19 genes has recently been reported in a variety of tumors. To study the role of IGF2 and H19 genes in gastric carcinogenesis, the LOI and loss of heterozygosity (LOH) status of these two genes were determined in 70 patients with gastric cancer. Among them, 30 patients were heterozygous for IGF2, 28 patients were heterozygous for H19, and 42 patients were heterozygous for either IGF2 or H19 gene. Among the 30 patients who were heterozygous for IGF2, one exhibited LOH (1/30, 3.3%) and 10 exhibited LOI (10/29, 34.5%). None of the 28 patients heterozygous for H19 gene had either LOH or LOI. LOI of IGF2 was more frequently found in the diffuse type (8/15, 53.3%) than the intestinal type (2/14, 14.3%, P < 0.05) gastric cancer. Five out of the six tumors with LOI of IGF2 exhibited overexpression of mRNA, but no obvious alterations of expression of H19 were noted by Northern hybridization. These data suggest that LOI leading to overexpression of IGF2 plays an important role in carcinogenesis of diffuse type gastric cancer.

Adenocarcinoma↗
PubMed2002

Post-hatch development of dendritic arborization in cerebellar Purkinje neurons of quail chicks: a morphometric study.

To study development of the cerebellum in precocial birds during the early post-hatch period, dendritic arborization of Purkinje neurons was analyzed by intracellular Lucifer-yellow filling in fixed slices. Purkinje neurons were sampled from parasagittal slices of the cerebellar vermis of quail chicks (from 1 day pre-hatch to 14 days post-hatch). Confocal images revealed that the dendritic arborization expanded two-fold during the initial 3 days post-hatch, whereas the growth of cell bodies was much smaller. The dendritic expansion was accompanied by significant elongation of distal dendritic segments (5th and more distal segments), while the length of proximal dendrites (1st-4th segments) and the number of dendritic branches remained unchanged. Active synaptogenesis may occur selectively in distal dendrites during the early post-hatch period.

Age Factors↗
PubMed2001

GABA, taurine and learning: release of amino acids from slices of chick brain following filial imprinting.

The intermediate and medial hyperstriatum ventrale (IMHV) is a forebrain region in the domestic chick that is a site of information storage for the learning process of imprinting. We enquired whether imprinting is associated with learning-related increases in calcium-dependent, potassium-stimulated release of neurotransmitter amino acids from the IMHV. Chicks were hatched and reared in darkness until 15-30 h after hatching. They then either remained in darkness or were trained for 2 h by exposure to an imprinting stimulus. One hour later, the chicks were given a preference test and a preference score was calculated from the results of this test, as a measure of imprinting. Chicks were killed 2 h after training. Slices from the left and right IMHV of trained and untrained chicks were superfused with Krebs' solution either with or without calcium and the superfusate assayed for arginine, aspartate, citrulline, GABA, glutamate, glycine and taurine using high-performance liquid chromatography. For calcium-containing superfusates from the left IMHV, preference score was significantly correlated with potassium-stimulated release of (i) GABA (r=0.51, 23 d.f., P=0.008) and (ii) taurine (r=0.77, 23 d.f., P<0.0001). There was no significant difference between the mean values of trained and untrained chicks for either compound. However, examination of the variance of the data indicated that release of both GABA and taurine increased as a result of learning. No significant correlation between preference score and release was found for any of the amino acids from the right IMHV, nor for control tissue from the left IMHV superfused with calcium-free solution. These results demonstrate that the learning process of imprinting is associated with increases in releasable pools of GABA and taurine and/or membrane excitability in the left IMHV.

Animals↗
PubMed2002

A quantitative immuno-electron microscopic study of dopamine terminals in forebrain regions of the domestic chick involved in filial imprinting.

The mediorostral neostriatum/hyperstriatum ventrale and neostriatum dorsocaudale of the domestic chick are crucially involved in filial imprinting and are major targets of mesotelencephalic dopaminergic projections. To better understand the functional role of dopamine in these forebrain regions, the ultrastructure of dopamine terminals was studied by serial section electron microscopy using immunohistochemical labeling with antibodies to tyrosine hydroxylase and dopamine. At light as well as electron microscopic level, dopamine and tyrosine hydroxylase-immunoreactive fibers were present at moderate densities in the mediorostral neostriatum/hyperstriatum ventrale and high densities in the neostriatum dorsocaudale. The frequency of tyrosine hydroxylase-immunoreactive profiles per unit area was significantly higher in the neostriatum dorsocaudale than in the mediorostral neostriatum/hyperstriatum ventrale. In both regions, tyrosine hydroxylase-immunoreactive terminals were relatively small, with mean areas of 0.55 microm(2) in the mediorostral neostriatum/hyperstriatum ventrale and 0.48 microm(2) in the neostriatum dorsocaudale. The majority of tyrosine hydroxylase-immunoreactive synapses were symmetrical (83% in the mediorostral neostriatum/hyperstriatum ventrale, 75% in the neostriatum dorsocaudale) as opposed to asymmetrical (17 and 25%, respectively), but there were also tyrosine hydroxylase-immunoreactive terminals which lacked clear synaptic specializations. The preferred targets of the synaptic tyrosine hydroxylase-immunoreactive terminals were dendritic shafts (64% in the mediorostral neostriatum/hyperstriatum ventrale, 63% in the neostriatum dorsocaudale) and less frequently dendritic spines (17 and 23%, respectively) or perikarya (19 and 14%, respectively). In both forebrain regions, immunoreactive terminals were often found in close apposition to unstained terminals making asymmetrical synapses. In conclusion, these results indicate that the ultrastructural features of dopamine terminals in the avian telencephalon are very similar to those described in mammals and that dopamine may exert its effects primarily by modulating excitatory inputs.

Animals↗
PubMed1997

The genetics of Tourette syndrome.

Tourette syndrome has significant genetic determinants. The mode of transmission, while mildly controversial, generally is thought to be due to a single major locus inherited either as an autosomal dominant trait with reduced penetrance, or as a trait with intermediate inheritance in which some heterozygotes manifest the disorder. These is evidence for a Tourette syndrome spectrum of symptoms that includes obsessive-compulsive disorder. Systematic genome linkage studies of Tourette syndrome are progressing, but to date there are no significant linkage findings, although the search has included many neurologically relevant candidate genes.

Diseases in Twins↗
PubMed1997

Sensitization of olfactory guanylyl cyclase to a specific imprinted odorant in coho salmon.

The role of cGMP in olfactory signaling is not fully understood, but it is believed to play a modulatory role in intracellular signaling in vertebrate olfactory receptor neurons (ORNs). Here, we present evidence that cGMP in ORNs may play an important role in recognition of biologically relevant odors and olfactory learning. Specifically, we investigated the cellular mechanisms underlying olfactory imprinting in salmon. Salmon learn odors associated with their natal site as juveniles and later use these odors to guide their homing migration. This imprinting is believed to involve sensitization of the peripheral olfactory system to specific homestream odorants. We imprinted juvenile salmon to the odorant beta-phenylethyl alcohol (PEA) and examined the sensitivity of olfactory adenylyl and guanylyl cyclases to PEA during development. Stimulation of guanylyl cyclase activity by PEA was significantly greater in olfactory cilia isolated from PEA-imprinted salmon compared with PEA-naive fish only at the time of the homing migration, 2 years after PEA exposure. These results suggest that sensitization of olfactory guanylyl cyclase may play an important role in olfactory imprinting by salmon.

Animals↗
PubMed1999

Visual lateralization and monocular sleep in the domestic chick.

Behavioural sleep during the first 2 weeks of life was investigated in female chicks reared with an imprinting object or in social (visual) isolation. Binocular sleep tended to decrease and monocular sleep to increase with age in both rearing conditions. In chicks reared with an imprinted object. during the first week, monocular sleep with either right or left eye closure occurred with approximately the same frequency, except that on day 5 in which right eye closure dominated; during the second week, however, there was a clear bias towards more monocular sleep with left eye closure. During the second week, the pattern of monocular sleep was similar in both rearing conditions, but during the first week chicks reared with the imprinting object showed relatively more right eye closure compared to chicks reared without the imprinting object, an effect that might tentatively be associated with consolidation of imprinting memories in the left hemisphere. Binocular sleep occurred in all four body postures adopted by chicks during sleep: standing sleep, sleep with bill forward, sleep with bill on the ground, and sleep with head on the ground. Monocular sleep, in contrast, only occurred when chicks adopted the bill forward posture. When the colour of the imprinting object was suddenly changed on day 8, a striking shift towards predominant right eye closure during monocular sleep was observed. The same occurred when the imprinting object was suddenly removed from the home-cage on day 8, but not with other types of changes (i.e., when a novel different object was inserted into the home-cage or when a novel-coloured imprinting object was inserted into the home-cage together with the original one). It is argued that this phenomenon could be associated with right hemisphere involvement in response to novelty.

Aging↗
PubMed2003

Discriminative taste aversion learning: a learning task for older chickens.

The study of learning and memory using the chicken model has relied on three learning paradigms, passive avoidance learning, imprinting and the pebble floor task. Passive avoidance learning and imprinting have been used predominantly in very young chickens and cannot be used to access learning and memory in older chickens. We have established a new behavioural learning paradigm, Discriminative Taste Aversion Learning (DTAL), that can be used with both young and older animals. The task requires chickens to discriminate between food crumbs dyed either red or yellow with one colour being associated with the aversive tasting substance, methylanthranilate. Learning can be tested at various times after the training session by presenting chickens with the coloured food crumbs without an aversive taste. Both chickens tested at 5 and 15 days post-hatch learned to avoid the aversive crumbs. Furthermore, the protein synthesis inhibitor anisomycin (30 mM; 10 microl per hemisphere) injected into the intermediate medial hyperstriatum ventrale 15 min pre-training or 45 min post-training blocked long-term memory for the DTAL task when tested 24 h later. Memory for the task was unaffected by anisomycin injection 120 min post-training or in control animals injected with saline at similar times. The timing of the cellular processes of protein synthesis needed for consolidation of the DTAL appears to be similar to those described for the other behavioural paradigms in young chickens.

Age Factors↗