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Published on: November 14, 2013
Changes in metabolic activity in the hyperstriatum of the chick before and after hatching
1Department of Physiology, University of New England, Armidale, NSW, Australia.
Insights
Chick forebrain metabolic activity shifts before hatching. Early hyperstriatum accessorium (HA) activity is sensory-driven, not visual, while hyperstriatum dorsale (HD) develops later, impacting imprinting.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Behavior
Background:
- Understanding brain development and sensory processing in young animals is crucial for comprehending learning and imprinting.
- The chick forebrain, particularly the hyperstriatal regions, undergoes significant developmental changes around hatching.
Purpose of the Study:
- To investigate developmental changes in metabolic activity within chick forebrain hyperstriatal regions before and after hatching.
- To explore the role of sensory input and developmental stage on metabolic activity in specific brain regions related to imprinting.
Main Methods:
- Utilized [14C] 2-deoxyglucose (2-DG) autoradiography to measure metabolic activity in chick embryos (E19, E20) and post-hatchlings (D1).
- Manipulated sensory input by exposing subjects to light or darkness following 2-DG injection.
- Analyzed metabolic activity in the hyperstriatum accessorium (HA), hyperstriatum dorsale (HD), and intermediate medial hyperstriatum ventrale (IMHV).
Main Results:
- On E19, hyperstriatum accessorium (HA) showed higher metabolic activity than hyperstriatum dorsale (HD), regardless of light exposure, suggesting non-visual sensory processing.
- By E20, HA and HD activities were similar, and by D1 post-hatching, HD activity surpassed HA, indicating a developmental shift.
- Metabolic activity in the intermediate medial hyperstriatum ventrale (IMHV), crucial for imprinting, was higher on E19 and D1 than on E20, highlighting a quiescent period.
Conclusions:
- Hyperstriatum accessorium (HA) activity is not visually driven early in development and may process other sensory modalities.
- A developmental shift occurs in hyperstriatal metabolic activity, with HD becoming more active post-hatching.
- Reduced HA activity during the sensitive imprinting period may prioritize other sensory pathways, influencing imprinting mechanisms.
Abstract:
Changes in metabolic activity in the hyperstriatal regions of the chick forebrain have been assessed just prior to and after hatching using [14C] 2-deoxyglucose (2-DG) autoradiography. Embryos were injected on day E19, followed by either exposure to light for 30 min or being held in darkness. Other embryos were injected on day E20, after pipping of the egg shell had occurred, and chicks were injected on day 1 (D1) after hatching, followed by light exposure. In the E19 groups metabolic activity in visual regions of the hyperstriatum accessorium (HA) was significantly higher than that in the hyperstriatum dorsale (HD), the region which receives the thalamofugal visual projections. The result was the same in both the light and dark exposed embryos, indicating that the high level of activity in HA on day E19 is not visually driven and that HA may be processing inputs from other sensory modalities. At stage E20 the activities of HA and HD did not differ and by day 1 post-hatching HD activity exceeded that of HA. Activity in HA fell between E19 and E20, while in HD activity rose between E20 and D1. The developmental sequence of metabolic activity levels in the intermediate medial hyperstriatum ventrale (IMHV), a region involved with imprinting memory formation, was higher on E19 and D1 than on E20. E20 is thus a quiescent period of neural activity in the hyperstriatum prior to hatching. Although a small number of the embryos showed distinct hemispheric asymmetries in metabolic activity, overall there was no significant asymmetry in the embryo groups. The implications of these results for imprinting and early perceptual processing are discussed: it appears that HA activity may be inhibited or limited during the sensitive period for visual imprinting, thereby temporarily diminishing the importance of the thalamofugal visual pathway relative to the tectofugal pathway in the imprinting process.
