Light exposure of chick embryo influences lateralized recall of imprinting memory

Environmental cues, such as light during the later part of incubation, are known to establish lateralization of some forms of visually guided behaviors in birds. The authors investigated the effect of light on lateralized recall of imprinting memory in chicks. On Day E19 of incubation, one eye was occluded for 24 hr. The other eye received stimulation by light. Chicks were imprinted and then tested for their imprinting preferences after administration of a low dose (500 ng) of glutamate into either hemisphere. Chicks that had the right eye exposed to light during incubation showed recall of the imprinting stimulus after injection of the left hemisphere but not after injection into the right hemisphere. The reverse was found for chicks that had the left eye exposed to light. Hence, the hemisphere ipsilateral to the eye exposed to light before hatching became essential for recall of imprinting memory. The hemisphere used in recall of imprinting memory received indirect visual inputs and was determined by environmental stimulation (asymmetrical light input)

Isolation-stress-induced facilitation of passive avoidance memory in the day-old chick

This study showed that facilitation of recall of a weak version of the 1-trial passive avoidance learning task could be achieved by behavioral "stressing" of day-old chicks after training. Recall, usually retained for less than 9 hr, was extended by socially isolating the chicks for 1 hr immediately after training. There was a brief 3-fold increase in plasma corticosterone levels 10 min after isolation. Facilitated recall was not evident when chicks were isolated 2 hr after training, and it was blocked by intracerebral administration of 2-ng RU 38486, a specific glucocorticoid receptor antagonist, per chick. Male chicks responded more to isolation than did female chicks, presumably a consequence of the additional stress of the injection procedure

Memory consolidation in day-old chicks requires BDNF but not NGF or NT-3; an antisense study

Neurotrophins have been implicated in memory consolidation and recall as well as in other forms of neural plasticity. This study examined the effects of Brain-Derived Neurotrophic Factor (BDNF), Nerve Growth Factor (NGF) and Neurotrophin-3 (NT-3) on consolidation of memory for a one-trial passive avoidance task in day-old chicks. In this task chicks, having pecked once at a bitter tasting bead, avoid a similar but dry bead subsequently. Intracerebral administration of antisense ODNs to BDNF 6-12 h prior to training induced amnesia for the avoidance response by 3 h after training. Administration of a 'control' scrambled sequence or saline had no effect on recall, chicks continued to avoid the bead. Treatment with BDNF-AS did not inhibit shorter-term recall; amnesia was not present 1 h after training, but prevented longer-term recall, as amnesia was still present 24 h after training. Treatment with BDNF-antisense reduced both BDNF mRNA and BDNF protein in the chick brain, but did not alter mRNA levels of glyceraldehyde-3-phosphate dehydrogenase. By contrast, no effect of antisense to NGF or NT-3 on behaviour was observed, even though administration reduced the mRNA for each. There were no significant effects of any antisense on other behavioural measures at the doses used. Thus we conclude that BDNF has a specific role in memory consolidation for the passive avoidance task. (C) 2001 Elsevier Science B.V. All rights reserved

Dehydroepiandosterone and its sulphate enhance memory retention in day-old chicks

We report the presence of dehydroepiandosterone (DHEA) and DHEA sulphate (DHEA-S) in the day-old-chick brain, and their possible role in memory formation. DHEA and DHEA-S were present in the brain at higher concentrations than in the plasma, Radioimmunoassay examination of the intermediate medial hyperstriatum ventrale 5 or 30 min after training or the lobus parolfactorius 60 or 120 min after training on the passive avoidance task did not show learning-related differences in absolute levels of DHEA or DHEA-S. However, bilateral intracerebral injections of DHEA or DHEA-S before or after training on the weak passive avoidance task enhanced recall 24 h after training. Memory retention was enhanced by administration of DHEA and DHEA-S 15 min before training or 30 and 60 but not 180 min after training

Light experience and the development of behavioural lateralization in chicks III: Learning to distinguish pebbles from grains

Chicks searching for food grains against a background of unfamiliar pebbles usually peck pebbles less when using the right eye (RE), or both eyes, than when using the left eye (LE), provided that the embryo's RE has been exposed to light (Li), as is normal. When pecking is fast this right/left difference is mainly due to a heightened ability of RE chicks to inhibit premature pecks (and inappropriate responses in general). Dark incubation (Da) abolishes this ability in RE chicks, and RE and LE chicks show similar frequent pebble pecks. We show now that, under conditions that cause cautious pecking, both Li and Da chicks show a new effect: in both cases LE chicks peck pebbles more than RE chicks, probably because of the novelty of pebbles. Interest in novelty in LE chicks is known to be unaffected by light in incubation. Age-dependent effects are also important. RE and LE chicks, which had either the LE or RE exposed to light before hatching, were tested on days 3, 5, 8 or 12 post-hatching, under conditions giving normal fast pecking. Artificial exposure of the embryo's LE to light reversed the lateralization: in general, chicks using the light-exposed eye performed well at all ages. Irrespective of which eye system had heightened ability to inhibit pebble pecks, RE performance differed from usual on 2 days, whereas LE chicks showed no age-dependent changes. Changes confined to the RE system, therefore, affect behaviour independently of lateralization of the ability to inhibit inappropriate response

Observation learning in day-old chicks using a one-trial passive avoidance learning paradigm

We tested the hypothesis that day-old chicks, Gallus gallus domesticus, can learn to avoid an aversive stimulus if they observe the responses of another chick. In experiment 1, one of a pair of chicks (the actor) was allowed to peck at a bead coated in the bitter-tasting substance methylanthranilate (MeA), while we prevented the other chick (the observer) from pecking the bitter-tasting bead by separating the chicks with a piece of wire mesh. Both chicks avoided pecking at a similar but dry bead 0.5, 3 and 24 h after the observer chick saw the actor chick peck at an MeA-coated bead. By contrast, when the actor chick had pecked at a water-coated bead, both chicks continued to peck at a dry bead at 0.5, 3 and 24 h after training. Experiment 2 investigated whether observer chicks showed avoidance if they were prevented (by the insertion of an opaque barrier) from observing their companion pecking at the MeA-coated bead during either training or testing. Observer chicks that could not see their companion during training but could observe the actor chicks at test showed no subsequent avoidance whereas chicks that observed the actor chick at training, but not during testing, showed high levels of avoidance. Although the sensory cues (visual, auditory or olfactory) or types of behaviour (i.e. levels of pecking or head shaking) that the observer chick used to maintain avoidance remain unclear, the results show that chicks can learn about an aversive object by observing the responses of a conspecific. (C) 1998 The Association for the Study of Animal Behaviour

Sex differences in pregnenolone sulphate in the chick brain after training

Pregnenolone and pregnenolone sulphate are potent memory enhancers when administered to rodents prior to various learning and memory paradigms. Here, we show that training on a passive avoidance task results in the increased concentration of pregnenolone sulphate in the medial striatum, formerly known as lobus parolfactorius of female but not male chicks. In addition, we demonstrated potential for neuronal synthesis of pregnenolone in the day-old chick brain, including in the intermediate medial mesopallium, formerly known as intermediate medial hyperstriatum ventrale and the medial striatum. © 2005 Lippincott Williams & Wilkins

Role of brain-derived neurotrophic factor and presynaptic proteins in passive avoidance learning in day-old domestic chicks

The consolidation of a one-trial passive avoidance learning task in the day-old chick involves a number of transient and longer-term biochemical processes, including increased release of glutamate. This study demonstrated that brain-derived neurotrophic factor, a proposed modulator of synaptic transmission and neurotransmitter release, is involved in the cascade associated with memory consolidation in the chick and that its actions were linked to modulation of expression of SNAP-25, syntaxin and synaptophysin, required for exocytosis. Intracerebral injections of 5 mu l of antibodies to brain-derived neurotrophic factor into the left and right intermediate medial hyperstriatum ventrale resulted in a dose-dependent reduction in avoidance of an "aversive" bead by 3 h after training. Neurotrophin antibodies (0.5 mu g/chick) administered between Ih before, and up to 30 min after, training induced amnesia by 3 h which was sustained for at least 24 h. Injections of recombinant brain-derived neurotrophic factor (50 mu g/ml; 0.5 mu g/chick) just before training maintained avoidance in birds trained with a weaker aversant (10% methylanthranilate), such that chicks showed enhanced recall at times (24 h) beyond that when shorter-term forms of memory have decayed. In lysed synaptosomal membranes prepared from chicks injected with antibodies to brain-derived neurotrophic factor there was a decrease in expression of SNAP-25 and syntaxin in the left, but not the right, intermediate medial hyperstriatum ventrale, a region known to be associated with memory formation, which correlated with the decrease in neurotrophin concentration