It is generally accepted that memory formation involves an irreversible passage via labile phases to the stable form of 'long-term memory' impervious to amnestic agents such as protein synthesis inhibitors. However, recent experiments demonstrate that reactivation of memory by way of a reminder renders it labile to such inhibitors, suggesting that such retrieval is followed by a so-called reconsolidation process similar or identical in its cellular and molecular correlates to that occurring during the initial consolidation. We compared the effects of the protein synthesis inhibitor anisomycin and the glycoprotein synthesis inhibitor 2-deoxygalactose on the temporal dynamics and pharmacological sensitivity of initial consolidation and memory expression following a reminder in a one-trial passive-avoidance task in day-old chicks. This comparison revealed three differences between the action of the inhibitors on newly formed compared with reactivated memory. First, the recall deficit after the reminder was temporary, whilst the amnesia following inhibitor treatment during training was stable. Second, the sensitive period for the effect of anisomycin was shorter in the reminder than in the training situation. Third, the effective dose for either inhibitor for reminder-associated amnesia was several times lower than for amnesia developing after training. Thus though like initial consolidation, memory expression at delayed periods following reminder depends on protein and glycoprotein synthesis, the differences between the temporal and pharmacological dynamics in the two situations point to the distinct character of the molecular processes involved in postreminder effects.

A protein synthesis inhibitor, anisomycin (ANI), and an inhibitor of glycoprotein synthesis, 2-deoxygalactose (2-D-gal), were used to investigate memory consolidation following visual categorization training in 2-day-old chicks. ANI (0.6 pmole/chick) and 2-D-gal (40 lamoles/chick) were injected intracerebrally at different time intervals from 1 hr before to 23 hr after the training. Retention was tested 24 hr post-training. Both ANI and 2-D-gal injections revealed two periods of memory sensitivity to pharmacological intervention. ANI impaired retention when injected from 5 min before to 30 min after the training or from 4 hr to 5 hr post-training, thus demonstrating that consolidation of long-term memory in this task requires two periods of protein synthesis. 2-D-Gal first produced an amnesia when it was injected in the interval from 5 min before to 5 min after the training. Injections made between 5 min and 5 hr post-training were without effect on the retention. The second period of memory impairment by 2-D-gal started at 5 hr post-training and lasted until 21 hr after the training. Administration of 2-D-gal made 23 hr after the training did not influence retention in the test at either 24 hr or 26 hr. These results are consistent 3Corresponding author.with the hypothesis that two waves of protein and glycoprotein synthesis are necessary for the formation of long-term memory. The prolonged duration of performance impairment by 2-D-gal in the present task might reflect an extended memory consolidation period for a categorization form of learning.

BackgroundSpecialized neural pathways, the song system, are required for acquiring, producing, and perceiving learned avian vocalizations. Birds that do not learn to produce their vocalizations lack telencephalic song system components. It is not known whether the song system forebrain regions are exclusively evolved for song or whether they also process information not related to song that might reflect their ‘evolutionary history’.Methodology/Principal FindingsTo address this question we monitored the induction of two immediate-early genes (IEGs) c-Fos and ZENK in various regions of the song system in zebra finches (Taeniopygia guttata) in response to an aversive food learning paradigm; this involves the association of a food item with a noxious stimulus that affects the oropharyngeal-esophageal cavity and tongue, causing subsequent avoidance of that food item. The motor response results in beak and head movements but not vocalizations. IEGs have been extensively used to map neuro-molecular correlates of song motor production and auditory processing. As previously reported, neurons in two pallial vocal motor regions, HVC and RA, expressed IEGs after singing. Surprisingly, c-Fos was induced equivalently also after food aversion learning in the absence of singing. The density of c-Fos positive neurons was significantly higher than that of birds in control conditions. This was not the case in two other pallial song nuclei important for vocal plasticity, LMAN and Area X, although singing did induce IEGs in these structures, as reported previously.Conclusions/SignificanceOur results are consistent with the possibility that some of the song nuclei may participate in non-vocal learning and the populations of neurons involved in the two tasks show partial overlap. These findings underscore the previously advanced notion that the specialized forebrain pre-motor nuclei controlling song evolved from circuits involved in behaviors related to feeding.

Synucleins comprise a family of small intracellular proteins that have recently attracted considerable attention because of their involvement in human diseases. Mutations of alpha-synuclein has been found in several families with hereditary early-onset Parkinson's disease and accumulation of this protein in characteristic cytoplasmic inclusions is a pathohistological hallmark of several neurodegenerative diseases that have been recently classified as 'alpha;-synucleinopathies' (reviewed in Brain Res. Bull. 50 (1999) 465; J. Neurosci. Res. 58 (1999) 120; Philos. Trans. R. Soc. Lond. Biol. Sci. 354 (1999) 1101; Brain Pathol. 9 (1999) 733). Aggregates of beta-synuclein and persyn (gamma-synuclein) also have been found in dystrophic neurites associated with Parkinson's and other neurodegenerative diseases (Proc. Natl. Acad. Sci. USA 96 (1999) 13450; and our unpublished observations). Moreover, persyn has been implicated in malignization of breast tumours (Cancer Res. 57 (1997) 759; Cancer Res. 59 (1999) 742; Hum. Mol. Genet. 7 (1998) 1417). All synucleins have distinct, although overlapping, patterns of expression in the embryonic, postnatal and adult mammalian nervous systems, suggesting important, although still not clear, biological functions in neuronal developing. Chicken embryo is a unique object for developmental studies that allows in vivo manipulations not always possible for mammalian embryos. Studies of synucleins expression in this model system could shed light on their functions in the developing nervous system. We cloned three chicken synucleins from the embryonic neural cDNA libraries and studied their expression in normal chicken embryonic tissues by Northern and in situ hybridization with specific probes. Our results demonstrate that primary structures and expression patterns of synucleins are similar in birds and mammals, suggesting that conserved function of synucleins is important for embryonic development of vertebrates.

The L1/NgCAM cell adhesion molecule is involved in neurite outgrowth, axonal fasciculation and cell migration in the nervous system. We studied the effects of antibodies against L1 injected intracranially at various times before and after training 2-day-old chicks in a visual categorization task. Memory retention was tested 24 h post-training. Anti-L1 antibodies impaired task retention only when administered in three restricted time windows: immediately before training, at about 5.5 h after training and from 15 to 18 h after training. No amnesia was produced by injections before, between or after these sensitive periods (from -1 to +21 h relative to training). These results indicate that there are multiple post-training periods during which L1 is involved in the formation of long-term memory.