Abstract
Imprinting behaviour in chicks can be induced exclusively during a short period after hatching. During this period, visual information on the imprinting stimulus is conveyed to the visual Wulst (VW) in the telencephalon, which corresponds to the visual cortex of mammals, and then to the memory-storing region known as the intermediate medial mesopallium. These two regions are indispensable for imprinting. We previously showed that imprinting training altered the response pattern of the VW to the imprinting stimulus; however, the precise distribution of cells and the mechanism involved with this altered response remains unclear. Here we showed that a specific population of rostral VW cells responded to the imprinting stimulus by analysing the subcellular localization of Arc/arg3.1 transcripts in VW cells. GABAergic parvalbumin (PV) cells are abundant in the dorsal region of this area, and imprinting training doubled the number of activated PV-positive neurons. An injection of bicuculline, a GABA(A) receptor antagonist, in the dorsal VW disturbed the rostral distribution of responsive cells and thus resulted in a lack of imprinting. These results suggest that activated PV cells restrict VW cells response to dorsal area to form a specific imprinting pathway.
Highlights
Imprinting behaviour in chicks can be induced exclusively during a short period after hatching
The number of cells observed was not significantly different among conditions (Fig. 1e bottom; × 103; untreated, 2.72 ± 0.08; 0 min, 2.68 ± 0.07; 10 min, 2.75 ± 0.11; 20 min, 2.70 ± 0.07; 60 min, 2.75 ± 0.07; 120 min, 2.84 ± 0.09; untreated vs. 0 min, p = 0.45; vs. 10 min, p = 0.78; vs. 20 min, p = 0.81; vs. 60 min, p = 0.72; vs. 120 min, p = 0.21; t-tests). These results indicate that a 5-min image presentation immediately induced Arc transcripts in the nucleus of visual Wulst (VW) cells in chicks, mRNA began translocation to the cytoplasm approximately 10 min later, and transcripts were predominantly located in the cytoplasm after 20 min
Our analysis of the subcellular localization of Arc transcripts can reveal the activation history of VW cells after two sessions of image presentation separated by 20–120 min (Fig. 1f)
Summary
Imprinting behaviour in chicks can be induced exclusively during a short period after hatching During this period, visual information on the imprinting stimulus is conveyed to the visual Wulst (VW) in the telencephalon, which corresponds to the visual cortex of mammals, and to the memory-storing region known as the intermediate medial mesopallium. We showed that a specific population of rostral VW cells responded to the imprinting stimulus by analysing the subcellular localization of Arc/arg3.1 transcripts in VW cells. Using in vivo imaging of neuronal activity, we demonstrated that the imprinting training altered regions of the VW that respond to visual stimuli[6], suggesting that information relevant to the imprinting stimulus is processed in the VW. Imprinting training activated a subset of PV cells that appear to facilitate the specification and enhancement of the rostral VW cells crucial for eliciting imprinting behaviour
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