Src and Memory: A Study of Filial Imprinting and Predispositions in the Domestic Chick

Abstract

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The available evidence indicates that the intermediate medial mesopallium (IMM) in the domestic chick forebrain is a site of memory formation during visual imprinting. We have studied the role of Src, an important non-receptor tyrosine kinase, in memory formation. Amounts of total Src (Total-Src) and its two phosphorylated forms, tyrosine-416 (activated, 416P-Src) and tyrosine-527 (inhibited, 527P-Src), were measured 1 and 24 h after training in the IMM and in a control brain region, the posterior pole of nidopallium (PPN). One hour after training, in the left IMM, we observed a positive correlation between the amount of 527P-Src and learning strength that was attributable to learning, and there was also a positive correlation between 416P-Src and learning strength that was attributable to a predisposition to learn readily. Twenty-four hours after training, the amount of Total-Src increased with learning strength in both the left and right IMM, and amount of 527P-Src increased with learning strength only in the left IMM; both correlations were attributable to learning. A further, negative, correlation between learning strength and 416P-Src/Total-Src in the left IMM reflected a predisposition to learn. No learning-related changes were found in the PPN control region. We suggest that there are two pools of Src; one of them in an active state and reflecting a predisposition to learn, and the second one in an inhibited condition, which increases as a result of learning. These two pools may represent two or more signaling pathways, namely, one pathway downstream of Src activated by tyrosine-416 phosphorylation and another upstream of Src, keeping the enzyme in an inactivated state via phosphorylation of tyrosine-527.

Filial imprinting in domestic chicks; cytoplasmic polyadenylation element binding protein 3, predispositions and learning

“…Possible candidate regions for S' have been suggested [11,25]. In the present case as well as in previous studies, the molecular changes 24 h after training were more strongly expressed in the left IMM than in the right IMM [5,[7][8][9][10]12,15,16].…”

“…The script used for statistical analysis was essentially that published by Margvelani et al [5]. Data from the IMM and posterior pole of nidopallium (PPN) were analyzed separately owing to the functional disparity of the IMM and PPN, namely that the IMM is essential for imprinting and the PPN is not [5][6][7][8][9][10][11][12][13][14][15][16]. The left and right sides were analyzed separately because there is a functional hemispheric asymmetry in IMM with respect to imprinting [9].…”

“…Criteria for identifying learning-related changes in a particular brain region have been formulated [5,8,10], allowing one to distinguish side-effects of training from effects that are specific to learning and/or memory. The present study, as previously, experimentally investigated the relationship between amount of protein and strength of learning.…”

“…A series of learning-related molecular changes has been, thus, identified in the IMM, changes that are involved in a progression from transient/labile to trophic synaptic modifications, culminating in stable recognition memory [7–16]. These changes occur in proteins involved in cell adhesion, neurotransmitter release, cytoskeletal organization, oxidative phosphorylation, mitochondrial dynamics, local protein synthesis, and others [7–16].…”

“…Such evidence indicates that, 24 h after the end of training, two significant negative correlations with preference score are attributable to a predisposition to learn readily. The molecules having this property were the microRNA gga-miR-130b-3p (both on the left and right IMM) and the 416-tyrosine phosphorylated form of the nonreceptor tyrosine kinase Src (in the left IMM), expressed as a fraction of the total amount of Src [5,10]. One hour after the end of training, the positive correlation of 416P-Src in the left IMM is also attributable to the same type of predisposition [10].…”